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Application Frameworks & UI

Web and mobile frameworks, component libraries, API layers and product codebases.

1126 instructions from 43 repositories. Last updated 2026-05-03.

---

Consistent readable patterns

Apply consistent, type-safe idioms and keep logic/formatting easy to scan.

• Prefer the established guard/pattern style:

  // preferred if the surrounding code uses boolean guards
  theme && devtools.setTheme(theme)
  

• Remove redundant casts like as any when TypeScript can infer/narrow:

  const options = query.options // avoid unnecessary `as any`
  

• Extract and reuse common “value or function” handling instead of repeating typeof ... === 'function' checks; use shared helpers (e.g., a resolveValueOrFunction utility) across the codebase.
• Keep control flow structured: avoid duplicated assignments/notifications and hard-to-follow early returns. Split logic by the primary conditions (e.g., index change vs result change), then assign/notify accordingly.
• Enforce consistent formatting/import conventions (grouping, ordering, quote style) to reduce diff noise and improve readability.

Use these guidelines to guide refactors during reviews, not only new code.

---

Preserve and Map Errors

Standardize error handling so failures remain diagnosable and user-facing messages are complete.

Apply these rules: 1) Preserve diagnostic context when propagating/rethrowing

• If you rebuild or re-aggregate errors, do not unintentionally lose stack trace/throw location. Centralize error creation/throwing so the actual throw happens in a predictable place, and avoid patterns that always create a fresh error object without considering stack semantics.

2) Ensure every issue code is explicitly mapped

• When adding a new ZodIssueCode (or changing which codes are emitted), update defaultErrorMap and/or locale maps so users don’t see generic fallback messages.

3) Extract/format messages safely (no unsafe casts)

• Don’t assume catch (error) is an Error. Prefer instanceof Error or a shared helper that guarantees a string.

4) Don’t unintentionally suppress other validations

• If you use early returns in validation logic, verify you’re not preventing other expected errors from being added for the same input.

Example: safe message extraction

try {
  return JSON.parse(val);
} catch (e: unknown) {
  const message = e instanceof Error ? e.message : String(e);
  ctx.addIssue({
    code: ZodIssueCode.invalid_string,
    validation: "json",
    message,
  });
}

Example: stack-preserving handler shape

const zodErrorHandler = (messageOrObject: string | unknown) => {
  if (typeof messageOrObject === "string") {
    throw ZodError.fromString(messageOrObject);
  }
  throw messageOrObject; // keep original throw semantics where possible
};

Checklist for PRs in this area

• New/changed ZodIssueCode has explicit message mapping (default + locales if needed).
• Validation control flow (early returns) can’t hide required additional issues.
• No error as Error without instanceof or a safe conversion helper.
• Error propagation/rewrap logic reviewed for stack/throw-location implications.

---

Consistent dependency config

Maintain configuration consistency and compatibility by using a single, intentional strategy for dependency declarations, peer ranges, and script runtimes.

Apply these rules: 1) Pick a monorepo pattern per package type

• Internal packages: use workspace:* (so pnpm rewrites correctly) when the package is meant to work inside the workspace.
• Public/example packages: keep existing semver patterns; don’t introduce workspace:* in examples if the repo’s established convention is semver.

2) Prefer package-local dependency ownership

• If a package imports something at runtime, declare it in that package’s dependencies/peerDependencies (avoid relying on root devDependencies).

3) Use peerDependencies when you don’t bundle

• If your package primarily exposes types or relies on a host app to provide the dependency, declare it as a peerDependency (and match the repo’s compatibility range).

4) Make peer semver ranges explicit and future-proof

• Avoid awkward ranges that exclude supported majors.
• For platform integrations (e.g., Next), prefer “fail fast” ranges that reflect supported versions.

5) Don’t duplicate tooling already provided by shared configs

• If a shared config already supplies lint/typescript-eslint, avoid adding redundant devDependencies in each package.

6) Use the correct TS/script runner for the declared Node environment

• If Node doesn’t support TS natively, run TS scripts via tsx.

Example (peer range + script runner):

{
  "peerDependencies": {
    "next": "^13 || ^14",
    "typescript": "^5.0.0"
  },
  "scripts": {
    "verify-links": "pnpm tsx scripts/verify-links.ts"
  }
}

Example (workspace dep):

{
  "dependencies": {
    "@tanstack/query-core": "workspace:*"
  }
}

---

Minimize Hot-Path Work

When working on performance-sensitive code (query observers, hydration, render-triggering state, hot utilities), ensure you only do the necessary work and no redundant allocations/wrappers, while also preventing leaks.

Apply these rules:

• Avoid unnecessary network/UI work: don’t enable fetch/retry paths when data is already synchronously available—add/keep tests that assert loading-state transitions.
• Make change detection “minimal but correct”: compare the specific fields that can affect rendering; missing metadata/derived fields can silently block required recomputation, while incorrect comparisons can trigger extra recomputations.
• Eliminate repeated allocations in loops/hot paths: precompute data structures used by callbacks (e.g., create a Set once, not per filter iteration).
• Avoid redundant expensive computations: don’t call deep-compare/structural-sharing helpers twice when you can short-circuit.
• Wrap expensive logic once, not per-page/per-iteration.
• Always clean up long-lived resources (subscriptions, BroadcastChannels, event listeners) to prevent gradual performance degradation.

Example (single Set allocation in a hot utility):

function difference<T>(array1: T[], array2: T[]): T[] {
  const set2 = new Set(array2)
  return array1.filter((x) => !set2.has(x))
}

Example (wrap fetch once when a persister exists):

if (context.options.persister) {
  context.fetchFn = () =>
    context.options.persister!(fetchFn as any, {
      queryKey: context.queryKey,
      meta: context.options.meta,
      signal: context.signal,
    })
}

---

API typing parity

When evolving public API/TypeScript types, ensure the type surface exactly matches runtime behavior and intended layering, and reuse existing signature/overload patterns.

Practical rules: 1) Parity for accepted shapes: If the runtime supports multiple input forms (e.g. ref, computed, () => value), the exported types must accept the same set. 2) Mirror established method patterns: New methods should match the signature style of analogous APIs (e.g. fetchQuery/useQuery): same overload structure, same options interface, and consistent generic parameter order. 3) Correct abstraction layer: Don’t add an option to the wrong type (query vs observer). If behavior is observer-specific, it must live in observer-level options/types. 4) Migration via deprecated overloads: If v5 changes argument shape (object-only, etc.), provide a deprecated overload for old calling conventions rather than silently breaking. 5) Explicit precedence for conflicting inputs: When two options can interact (e.g. skipToken + enabled), define the precedence in both runtime and types so users can’t form contradictory combinations. 6) Avoid misleading widening: Don’t widen public event/action types in a way that implies users can subscribe/receive things that can’t actually occur through the supported mechanism.

Example (pattern for migration + deprecation):

// preferred v5 style
find(filters: QueryFilters): Query | undefined

/** @deprecated Use the single-object overload instead */
find(queryKey: QueryKey, filters?: OmitKeyof<QueryFilters, 'queryKey'>): Query | undefined

Example (precedence):

• If enabled: true must override queryFn: skipToken, encode that rule (and ideally prevent passing both in types via overloads/unions).

These checks prevent subtle regressions where developers rely on types to describe reality—especially for reactive/getter inputs, options placement, and overload/migration paths.

---

Consistent Unique Package Names

Use stable naming conventions that match repo/tooling expectations and avoid identifier collisions.

Rules

1. Keep script names consistent across packages: if CI/tooling expects specific npm/pnpm script keys, use the same keys in every package (don’t rename per-package).
2. Ensure package/example names are globally unique: every published/package identifier (e.g., package.json#name) must be unique across the repo to prevent collisions.
3. Name compatibility boundaries explicitly: when an experimental change affects behavior, reflect compatibility intent in naming (e.g., expose a *-core for the breaking surface and a separate * wrapper that preserves older behavior), instead of changing semantics under the same name.

Example (package.json)

{
  "name": "@tanstack/lit-query", 
  "type": "module",
  "scripts": {
    "test:types": "tsc --noEmit",
    "typecheck": "pnpm run test:types",
    "build": "pnpm run build:deps && pnpm run build:esm && pnpm run build:cjs"
  }
}

And if you need a compatibility wrapper vs breaking core:

• @scope/lib-core (breaking)
• @scope/lib (wrapper preserving old behavior)

This prevents CI from skipping packages, avoids naming collisions, and makes breaking/compatibility intent obvious from identifiers.

---

Standardize monorepo linting

Use shared root configuration for formatting and apply consistent ESLint rule severities across the monorepo, allowing only narrowly scoped exceptions.

• Formatting: avoid duplicating Prettier config in packages—inherit/extend the monorepo root Prettier settings.
• Linting: set intended rule severity (e.g., test-related rules) once in the root ESLint config so it applies across packages; if a package needs a deviation, disable the rule only for that package/files with an explicit override.

Example (root ESLint override pattern):

export default [
  {
    files: ['**/*.spec.ts*', '**/*.test.ts*', '**/*.test-d.ts*'],
    // apply Vitest expectations consistently across packages
    rules: {
      'vitest/expect-expect': 'error',
    },
  },
  {
    // narrowly scoped exception, only where needed
    files: ['packages/query-codemods/**'],
    rules: {
      '@typescript-eslint/require-await': 'off',
    },
  },
];

Result: fewer configuration drifts between packages, predictable CI failures, and minimal “special case” behavior that’s easy to audit.

---

Type-Safe, Scripted Tests

Ensure your testing approach covers both runtime behavior and public API types, and that the test scripts you expose are correct, documented, and preserve any packaging-specific smoke checks.

Apply this by: 1) Use the right Vitest commands for dev vs CI

• For watch mode, prefer the dedicated watch command.

{
  "scripts": {
    "test:lib": "vitest run",
    "test:lib:dev": "vitest watch"
  }
}

2) Make package verification steps explicit (and don’t remove needed checks)

• If a package publishes custom outputs/types (e.g., CJS with custom type shapes), keep a CJS/type smoke check and document what it protects.

3) Add compile-time assertions to type tests

• For hook/type APIs, use expect-type (commonly used by Vitest) or equivalent type-testing utilities to assert expected types in type-test files.

// example pattern for type tests
import { expectTypeOf } from 'expect-type'

expectTypeOf(useSuspenseQuery(/* ... */)).toMatchTypeOf<ExpectedReturnType>()

Result: consistent local/dev commands, reliable CI checks, and stronger guarantees that exported APIs behave correctly at both runtime and compile time.

---

Maintain Docs Integrity

Documentation should be kept correct and maintainable like code: ensure pages are registered, links are stable/valid, and shared doc sections follow the adapter conventions.

Apply these rules:

• Register docs pages: when adding a new reference/guide entry, add the corresponding id to docs/config.json so it appears in the site navigation.
• Use correct relative links: verify relative paths (including required .md extensions) so builds don’t break.
• Keep source links stable: if you link to GitHub source, point to the correct repository and use a commit-hash permalink (avoid main and fragile line-number URLs).
• Follow adapter overwrite conventions: use the established block markers so other framework adapters can safely overwrite sections (e.g., maintain React/Vue marker keyword conventions like Info vs Example).
• Avoid brittle, non-exhaustive explanations: when describing behavior triggers, link to the canonical guide (e.g., “important-defaults”) instead of listing a possibly incomplete set.

Example pattern for adapter-overwritable sections:

[//]: # 'Info2'

:::tip
React-specific note...
:::

[//]: # 'Info2'

Example pattern for canonical cross-linking:

• Don’t write “it happens on X/Y/Z triggers” unless X/Y/Z is guaranteed exhaustive; instead link to the canonical defaults doc that defines the trigger list.

---

Stable, lifecycle-correct hooks

Ensure React hooks and query integrations remain correct across renders, SSR/hydration, and subscriptions.

Rules: 1) Keep QueryClient stable in React components

• Create it once using one of: React.useState(() => new QueryClient()), React.useMemo(() => new QueryClient(), []), or a lazy useRef initializer.
• Avoid new QueryClient() directly in component render.
• In Server Components, creating a new QueryClient per request is fine.

2) Don’t break subscription/snapshot invariants

• Avoid reading refs (or mutating derived values) during render for SyncExternalStore/getSnapshot-style logic.
• If you need “latest filters/options”, update a ref in useEffect, and read the real source of truth inside the correct React lifecycle (e.g., getSnapshot) rather than during render.

3) Hydration-safe first render

• Make the initial/optimistic state that React renders match the server render.
• If stale data requires a refetch, trigger it after the first render/mount to prevent hydration mismatches.

4) Use supported disabling patterns

• If you want to disable conditionally, prefer skipToken over returning/defining a queryFn that will error while enabled: false patterns would otherwise spam logs.

Example (stable QueryClient + latest filters ref pattern):

import React from 'react'
import { QueryClient } from '@tanstack/react-query'

export function App() {
  const [queryClient] = React.useState(() => new QueryClient())

  // ...useQuery hooks using queryClient
  return null
}

And for “latest value” without render-time ref reads:

const [state, setState] = React.useState(() => client.isFetching(initialFilters))
const filtersRef = React.useRef(filters)
React.useEffect(() => {
  filtersRef.current = filters
}, [filters])
// Ensure the snapshot/getter reads in the right lifecycle, not during render-time ref reads.

---

Deterministic Concurrent State

When code runs with concurrent rendering and async workflows, ensure any async/derived value that can affect what gets rendered (or how consumers behave) is deterministic per concurrent “world”, and make promise behavior explicit.

Apply these rules: 1) Don’t use refs for render-visible concurrency state

• If a mutable value is read by render (directly or via context consumers) to decide which queries/results are active, store it in state (or another render-consistent mechanism), not a mutable ref.
• This avoids cross-tree leakage where concurrent renders expect different values.

2) Make enable/disable transitions deterministic

• Define what should happen to in-flight work when enabled toggles (e.g., reuse the same promise, or deterministically reject when disabled).
• Add tests that assert the exact expected promise/reuse behavior.

3) Be explicit about awaiting vs fire-and-forget

• In tests or code paths where you intentionally don’t wait for an async operation, explicitly discard the promise:

void queryClient.resumePausedMutations()

• If you need completion ordering, await it intentionally.

4) Treat CI-only failures as race-condition signals

• If tests intermittently fail, suspect async timing/races.
• Stabilize tests by awaiting the right signals (not arbitrary delays) and ensuring promise lifecycle/enablement semantics are exercised deterministically.

These practices prevent incorrect hydration/selection during concurrent rendering, clarify async semantics, and reduce flaky test outcomes caused by nondeterministic scheduling.

---

Precise API Contracts

When designing or documenting API options and callbacks, ensure the contract is exact, unambiguous, and type-safe.

• Specify true behavior and defaults: If an option affects multiple behaviors, document what it does exactly (including defaults). Prefer the control mechanism that precisely matches intent (e.g., stop polling by returning false from refetchInterval, not by disabling the query if that impacts more than polling).
• Make TypeScript reflect reality: Export/extract the correct public types, and ensure required/optional fields match current behavior (e.g., don’t claim mutationKey is required if it isn’t). Use narrower option types for wrappers (so unsupported options are rejected by TS rather than silently ignored).
• Avoid concept/name collisions: If different parts of the API use the same term (like multiple “context” meanings), either rename one concept or clearly distinguish them in docs and examples (optionally via a more explicit name like “scope”).
• Document cross-runtime input constraints: For SSR/server-action boundaries, ensure inputs are serializable; don’t pass function references as queryFn where only serializable values are allowed—call functions so arguments are safe.

Example (control-flow precision):

useQuery({
  queryKey: ['job', jobId],
  queryFn: () => fetchJobStatus(jobId),
  refetchInterval: (query) => {
    if (query.state.data?.status === 'complete') return false
    return 2000
  },
})

---

Explicit StaleTime Policy

For every query, define a clear staleness/refetch policy—especially for SSR/hydration—rather than relying on defaults or assumptions.

Standards

• Always choose staleTime deliberately (default is 0, which means cached data is treated as stale).
• Understand staleTime: Infinity vs staleTime: 'static':
  • With Infinity, “always” refetch triggers can still fire.
  • With 'static', those “always” triggers won’t revive the query; you must explicitly reset/clear via the query client.
• Hydration: HydrationBoundary prevents unnecessary refetching during hydration; hydrated queries will only refetch on mount if refetchOnMount: 'always' is explicitly set.
  • Ensure the UX/markup matches SSR first (render stale data), then refetch if it’s stale.
• Prefetching: don’t assume prefetchQuery uses the same freshness config as your useQuery observers. If you didn’t provide a staleTime/defaults, the call may treat cached data as stale (default 0).
• Error recovery: cached “not stale” data must not block refetch/retry when the query is in an error state—configure so error state still triggers recovery.
• SSR cache lifetime: avoid gcTime: 0 as it can cause hydration errors; be intentional about cache retention.

Example (SSR + explicit stale/refetch intent)

// query defaults (e.g., in your QueryClient)
const queryClient = new QueryClient({
  defaultOptions: {
    queries: {
      // pick one intentionally
      staleTime: 'static', // or Infinity, or a number
      // for hydration: only force mount refetch when truly needed
      refetchOnMount: 'always',
      // error recovery should still happen (ensure your retry policy allows it)
      retry: 2,
    },
  },
})

// SSR/CSR: render via HydrationBoundary to prevent unnecessary hydration refetch
return (
  <HydrationBoundary state={dehydratedState}>
    <App />
  </HydrationBoundary>
)

Practical checklist for PRs

• What is the intended staleTime (number / Infinity / 'static')?
• Should hydration refetch on mount (refetchOnMount), and why?
• If using prefetching, did you ensure the staleness policy matches expectations?
• If the query can error, what ensures refetch/retry still recovers users?

---

Contract-Accurate Testing

Tests should assert the behavior contract precisely, include the missing coverage for changed code, and stay isolated/noisy-control friendly.

Key rules:

• Assert the right semantics: if “no modification” includes referential identity, use toBe; if structure matters too, also use toStrictEqual.
• Add targeted tests for the actual change (ideally ones that would fail on main), including edge paths (e.g., false branches).
• For time/async behavior, assert intermediate states at meaningful time points (not only final success).
• When adding type-level guarantees, use Vitest expectTypeOf and write assertions that trigger the specific TypeScript checks you care about (e.g., excess properties).
• Keep tests isolated so any test can run independently; mock console when tests expect errors to be logged.

Example (identity + deep equality):

const options = mutationOptions({ mutationKey: ['key'], mutationFn: () => Promise.resolve(5) })
expect(options).toBe(options) // referential identity
expect(options).toStrictEqual({ mutationKey: ['key'], mutationFn: expect.any(Function) })

Example (time-based intermediate assertions):

render(BaseExample, { props: { options: { queries: [/* key1 resolves at 10ms, key2 at 20ms */] } } })
expect(getByText('Status 1: pending')).toBeInTheDocument()
await vi.advanceTimersByTimeAsync(11)
expect(getByText('Status 1: success')).toBeInTheDocument()
await vi.advanceTimersByTimeAsync(10)
expect(getByText('Status 2: success')).toBeInTheDocument()

Example (type-test style):

expectTypeOf(infiniteQueryOptions)
  .parameter(0)
  .not.toHaveProperty('stallTime')

---

Use Angular v19+ Strictness

When targeting Angular v19+ (or modernizing to it), align your package peer/dependency baselines and update tsconfig to the corresponding strict compiler settings—then apply the same policy across all Angular examples.

Apply:

• Compatibility baseline: prefer supporting the newer major where feasible (e.g., Angular 20+), and keep peerDependencies/dependency versions consistent across examples.
• tsconfig strictness (Angular v19+): ensure the Angular compiler strict options are enabled, including:
  • strictTemplates: true
  • strictStandalone: true (new in v19)
• Typecheck/build consistency: keep strict TS mode and recommended compile options used with Angular v19 (e.g., skipLibCheck: true and isolatedModules: true).

Example tsconfig (pattern):

{
  "compilerOptions": {
    "strict": true,
    "noImplicitOverride": true,
    "noPropertyAccessFromIndexSignature": true,
    "noImplicitReturns": true,
    "noFallthroughCasesInSwitch": true,
    "skipLibCheck": true,
    "isolatedModules": true,
    "target": "ES2022",
    "module": "ES2022",
    "lib": ["ES2022", "dom"]
  },
  "angularCompilerOptions": {
    "strictInjectionParameters": true,
    "strictInputAccessModifiers": true,
    "strictTemplates": true,
    "strictStandalone": true
  }
}

Also update example package.json dependencies together (Angular major/minor, zone.js, and TypeScript) so the toolchain is coherent.

---

Scoped cache reset rules

When code triggers cache reset/refetch or relies on cached freshness, make the behavior intentionally scoped and snapshot-correct:

• Scope reset-triggered refetches to the intended cache region:
  • Prefer predicates that limit refetch to relevant queries (e.g., only queries in error state, with active observers, and that are still effectively enabled).
  • Do not “global refetch” without guardrails, since cache resets can otherwise restart disabled work or cause unexpected churn.
• Don’t assert refetch-by-default semantics that conflict with freshness/floor rules:
  • If a mode enforces a minimum staleTime (e.g., Suspense), tests and calling code must expect the “freshness floor” behavior rather than immediate refetch on remount.
• Use stable, unique query keys in caching tests and reproduction:
  • Use the provided helpers/utilities for unique keys to avoid cross-test cache pollution.
• Snapshot per-operation metadata in cached records:
  • Ensure mutation/query records store the correct meta for each operation, even when meta changes after a re-render between mutations.

Example pattern for scoped reset refetch (adapted):

function createValue(client?: QueryClient) {
  let isReset = false
  return {
    clearReset: () => { isReset = false },
    reset: () => {
      isReset = true
      void client?.refetchQueries({
        predicate: (query) =>
          query.state.status === 'error' &&
          query.getObserversCount() > 0 &&
          query.observers.some(
            (observer) => resolveEnabled(observer.options.enabled, query) !== false,
          ),
      })
    },
  }
}

Practical checklist:

• If you add/modify reset/refetch logic: add/verify predicates for relevance + enabled/intent.
• If you modify caching freshness behavior: update tests to match the current staleTime/freshness contract.
• If you add caching-related tests: always use unique query keys (via helpers).
• If you change mutation meta handling: add a test that meta updated between mutations results in distinct cached meta snapshots for each mutation.

---

Resolve predicates, seed reducers

When building or extending algorithmic pipelines (streaming, reduction, conditional processing), ensure two correctness points:

1) Resolve dynamic conditions before acting

• If an option (e.g., “enabled”) can be a callback/function, resolve it to a concrete boolean using the library’s resolver (e.g., resolveEnabled) rather than treating it as a static flag.

2) Define the reducer’s initial accumulator/seed

• Ensure the first reducer invocation receives a predictable accumulator.
• Prefer matching native reduce semantics: either require/provide an explicit initial value, or implement the same “no initial value uses the first element as the seed” behavior.

Example (pattern):

// 1) Resolve a dynamic predicate before selecting work
const shouldProcess = (query: any) =>
  query.state.status === 'error' &&
  query.getObserversCount() > 0 &&
  query.observers.some((observer: any) =>
    resolveEnabled(observer.options.enabled, query), // resolve callback-based enabled
  )

// 2) Seed a reducer deterministically
function reduceChunks<TChunk, TAcc>(chunks: TChunk[], reducer: (acc: TAcc, c: TChunk) => TAcc, initial: TAcc) {
  let acc = initial
  for (const chunk of chunks) acc = reducer(acc, chunk)
  return acc
}

Apply this standard to prevent “first-step” surprises (wrong/empty accumulator) and to avoid silently skipping or incorrectly processing work due to unresolved callback-based conditions.

---

Configurable tooling rules

Specialized tooling (lint rules, dev-only packages, docs navigation) must be explicitly enabled and driven by configuration so it won’t misfire in the wrong project context.

Apply this standard:

• Lint rules: avoid broad directory/name heuristics. Make framework/server-specific checks opt-in, or allow configuration of the directories/files the rule applies to.
• Dev-only bundles: gate development tools with environment flags (e.g., only include devtools when NODE_ENV === 'development').
• Docs/UX surfaces: when adding new docs pages/features, update the relevant config sources (e.g., docs/config.json) so the change is actually discoverable.

Example (lint applicability via opt-in/config):

// eslint.config.js (example approach)
export default [
  {
    // Only run the SSR-specific rule for explicitly configured Next.js entrypoints
    rules: {
      '@tanstack/query/no-module-query-client': ['error', { enabled: true }],
    },
    files: [
      '**/pages/_app.{js,jsx,ts,tsx}',
      '**/pages/_document.{js,jsx,ts,tsx}',
      '**/app/_app.{js,jsx,ts,tsx}',
      '**/app/_document.{js,jsx,ts,tsx}',
    ],
  },
]

Example (env-gated devtools):

// Only include devtools in development bundles
if (process.env.NODE_ENV === 'development') {
  // import/load devtools
}

---

Deterministic CI Gates

Ensure CI/CD is deterministic and comprehensive: pin versions when dependencies/tooling have drifted, make the same checks run on PRs as on main, and test against the full supported toolchain/version range.

Apply it like this:

• Pin fixed versions for dependencies that already jumped majors and can’t be realigned (this restores predictable builds).
• Don’t let critical checks run only on main—add/enable equivalent tasks in PR workflows so failures are caught before merge.
• If you support multiple TypeScript versions, run a CI matrix (e.g., TS 4.7 + newer) and avoid using language/library features in code paths that won’t compile on older versions.

Example (dependency pinning in a changeset-style config):

{
  "fixed": [
    ["@some/package", "@some/other-package"],
    ["@some/devtools"],
    ["@some/svelte", "@some/svelte-devtools"]
  ]
}

Example (CI parity idea): if a quality check (e.g., sherif) isn’t running on PRs, add it to the PR workflow (or add equivalent tasks like formatting/lint scanning) so the same gates apply before merge.

Example (TypeScript compatibility): add a CI job per supported TS version (TS 4.7, TS 5.x) to prevent breaks when developers or tooling target different TypeScript releases.

---

Guard nullable inputs

When a value can be undefined/null, do not assume it exists—guard it before access and keep the type model consistent.

Rules

• Use optional chaining / nullish guards when reading fields from optional params:

  function f(params?: { message?: string | ((d: unknown[]) => string) }) {
    const message =
      typeof params?.message === "function"
        ? params.message
        : errorUtil.toString(params?.message);
  }
  

• Before using in, Object.keys, or nested properties, ensure the container object exists:

  if (refSeen.def && key in refSeen.def) {
    // safe
  }
  

• If a value is not actually optional, don’t add optional parameters/fallbacks—prefer required types (avoid “unnecessary undefined handling”).
• If you convert invalid data to undefined (e.g., coercion failures), make sure downstream code treats that undefined as the expected “invalid” state and update types accordingly.
• Be consistent in how you model “missing” vs “present but undefined” in types; adding : undefined can change runtime semantics ("prop" in obj). Prefer property absence when that’s the intended meaning.

Outcome: fewer runtime TypeErrors and clearer, more intentional null/undefined handling across the codebase.

---

Explicit undefined invariants

When handling query/mutation results, treat undefined (and null) as semantically distinct and enforce that distinction in both runtime checks and TypeScript types.

Coding standards

1. Never use truthy checks for cached/data presence.
   • Use explicit comparisons so valid falsy values (null, false, "") are not misclassified.
   • Prefer:
     • value !== undefined / value === undefined
2. Do not resolve/return undefined where the API contract says it can’t.
   • Avoid non-null assertions (!) that hide cancelled/empty states.
   • Add explicit branches for “cancelled/skip” paths.
3. For “skip”/sentinel control tokens, don’t treat them as normal data that returns undefined.
   • Prefer rejecting/throwing (or preventing execution) so that the invariant is preserved.
4. Align types with runtime: encode “undefined not allowed” in generics, and avoid type-widening fallbacks.
   • Prefer precise undefined/optional handling over {}-style fallbacks that widen unions.

Example

// 1) Presence checks: don’t use truthy
const data = query.state.data
const hasData = data !== undefined // null/false/"" are valid

// 2) Imperative fetch contract: never resolve undefined
async function fetchQueryImperative() {
  if (initialFetchCancelled) {
    throw new Error('Cancelled')
  }
  // safe: data is guaranteed by control flow
  return data
}

// 3) Skip token: don’t return undefined as “success data”
if (queryFn === skipToken) {
  return Promise.reject(
    new Error('Attempted to invoke queryFn when set to skipToken')
  )
}

Applying these rules prevents subtle SSR/hydration mismatches, avoids incorrect cache restore decisions, and keeps null/undefined behavior predictable across the codebase.

---

Hot-Path Performance Rules

Default to the cheapest behavior: gate expensive work behind explicit options or conditions, and keep the parsing “fast path” strictly minimal.

Practical rules:

• Don’t do expensive checks by default (e.g., uniqueness/duplicate detection); make it opt-in or only run when requested.
• Avoid exceptions in hot paths (prefer non-throwing validation branches; don’t rely on try/catch/throw for normal control flow).
• Minimize allocations on the hot path: only create parsing context/temporary structures when you’re actually going to report an issue.
• Reduce avoidable property access/copies in performance-critical code; avoid repeated computations inside tight loops.
• Use early-exit algorithms when they can reduce average work (and benchmark against alternatives—e.g., Set vs double-loop depends on duplicate rates).
• If environment checks are needed (feature detection), do them once via a toggle/initialization strategy—not on every call.

Example pattern (non-throwing, avoid eager ctx/allocation):

_parse(input: ParseInput) {
  const status = getStatus();

  // Fast path: keep ctx/allocations out unless needed
  if (/* invalid condition */) {
    const ctx = this._getOrReturnCtx(input); // create only now
    addIssueToContext(ctx, { code: '...' });
    status.dirty();
    return status;
  }

  // No try/catch/throw in normal flow
  return status;
}

Before/after any performance-sensitive change, run benchmarks or flamegraphs on realistic workloads (include the operations that trigger JIT/fast-pass warmup if relevant).

---

Centralize Stale Invalidation

When implementing or modifying caching/fetch decisions, treat “fresh vs stale” as a single source of truth derived from the query’s invalidation + stale-time logic. Avoid adding ad-hoc fetch conditions at the observer/queryClient level that bypass (or redefine) TTL semantics.

Concrete rules: 1) Model semantic events (e.g., “background error while data exists”) by updating invalidation state in the query/state layer (e.g., set isInvalidated: true).

• Fetch decision code should rely on isStale() / existing stale-time helpers, not on status === 'error' special-cases. 2) Preserve staleTime meaning.
• ensureQueryData/prefetchQuery should decide whether to return cached data now vs kick off a background fetch; they should not silently reinterpret the option (e.g., don’t turn “prefetch threshold” into “global query staleTime”). 3) If you implement TTL via timers:
• Recompute isInvalidated when staleTime changes.
• When staleTime === 0, mark as invalidated deterministically.
• After state/data updates (e.g., reducer runs), recompute and update/clear the stale timer accordingly. 4) Keep fetch orchestration scope-safe.
• If hydration/pending logic affects whether background fetches run, scope it per QueryClient and ensure SSR-derived state is sanitized so client hydration reuses the intended freshness state.

Example pattern (central invalidation drives fetch):

// In reducer/state update (when an error happens during a background refetch
// and existing data remains):
return {
  ...state,
  status: 'error',
  isInvalidated: true, // centralize semantic freshness change here
}

// In fetch decision logic (observer/queryObserver):
const shouldFetch = value === 'always' || (value !== false && query.isStale())

Applying these rules prevents subtle regressions like staleTime: 'static' data being refetched due to observer-level error checks, and avoids TTL drift when staleTime or data updates occur.

---

Deterministic CI Practices

When touching CI/CD workflows, keep execution deterministic and CI stable:

• Don’t duplicate steps: if a publish script already runs tests, avoid running test:ci again in the workflow.
• Remove redundant conditionals: if on: branch filters already restrict when a workflow/job runs, don’t keep extra if: checks that always evaluate the same way.
• No lockfile churn: if you didn’t change dependencies, don’t commit pnpm-lock.yaml. If it changed accidentally (wrong pnpm version, etc.), reset it back to the target branch.
• Configure required CI secrets: integrations like Codecov must use GitHub Actions secrets (e.g., CODECOV_TOKEN) and supported action versions.
• Verify vs autofix separation: “verify-only” checks that detect problems (but don’t automatically fix) belong in CI, while autofix should only handle tasks that can be auto-corrected.

Example (remove redundant if when triggers already constrain branches):

on:
  push:
    branches: ['main', 'alpha', 'beta', 'rc']

jobs:
  test-and-publish:
    # No extra `if:` needed here; branch filter already limits execution
    runs-on: ubuntu-latest
    steps:
      - run: pnpm run test:pr --parallel=3

---

Type-safe option consistency

Typed “options” objects (e.g. queryOptions, infiniteQueryOptions, mutationOptions) should round-trip cleanly across all API entrypoints that accept them (hooks, suspense/non-suspense hooks, and QueryClient methods).

Standard

1. Assignability invariant: Any object returned by a *Options factory must be assignable to every corresponding Use*Options / client/method parameter type without requiring userland type assertions.
2. Transformation propagation: If an option supports a transformation callback (e.g. select), the callback’s return type must be preserved identically across every entrypoint that consumes that option.
3. Ergonomic typing helpers: When advanced generic composition is needed (reusable wrappers), export Any* utility types (e.g. AnyUseQueryOptions) so consumers can write correct generic helpers without brittle casts or excessive type parameters.
4. Enforce with type tests: Add *.test-d.tsx coverage for (a) passing the same options object into each entrypoint, and (b) verifying select/transformed data types.

Example (what to ensure)

const options = infiniteQueryOptions({
  queryKey: ['key'],
  queryFn: () => Promise.resolve('string'),
  getNextPageParam: () => 1,
  initialPageParam: 1,
  select: (data) => data.pages, // transformed type
})

// Should compile with identical transformed output types:
const a = useSuspenseInfiniteQuery(options)
const b = await new QueryClient().infiniteQuery(options)

// Team rule: both should infer the same selected/transformed type.

Apply this when evolving API types: if a change fixes typing for one entrypoint (e.g. useInfiniteQuery) it must be validated for the client methods and suspense variants too.

---

Persist Only Settled Queries

When using async/concurrent flows (streaming, dehydration/rehydration, optimistic updates), ensure you never persist “in-flight” async state and you always return promises from async callbacks.

1) Don’t persist promises during streaming/dehydration

• If a query might still be pending, configuring persistence to store only settled/resolved outcomes prevents serialization issues when pending work is dehydrated and streamed.

<PersistQueryClientProvider
  client={queryClient}
  persistOptions={{
    persister,
    // Persist only queries that have resolved (not pending promises)
    dehydrateOptions: { shouldDehydrateQuery: defaultShouldDehydrateQuery },
  }}
>
  {children}
</PersistQueryClientProvider>

2) Don’t drop promise lifecycles in concurrency callbacks

• For concurrency-related callback hooks (e.g., mutation lifecycle handlers) that trigger async work, write them in a way that returns the promise (consistent concise arrow syntax is preferred).

useMutation({
  onSettled: () => queryClient.invalidateQueries({ queryKey: ['todos'] }),
});

Practical checklist:

• Any persistence/dehydration layer: allow only resolved/errored (settled) query results to be stored.
• Any callback that triggers async operations: return the promise so downstream orchestration/lifecycle expectations remain correct.

---

Test error propagation

When changing error handling, add/maintain tests that:

• Cover all supported configuration shapes (e.g., useErrorBoundary: true and useErrorBoundary: (err) => boolean).
• Assert the exact outcome of error handling logic (e.g., whether an error is redacted during dehydration/rehydration).
• Keep tests deterministic: don’t manipulate NODE_ENV or other globals unless the behavior truly differs.
• Ensure the test name/expectations match the real trigger (e.g., the hook that throws and causes the boundary to render).
• Use the correct async error pattern so the error is observed by the code path under test (prefer Promise.reject(err) / then(() => Promise.reject(err))).

Example (boundary + config variant):

it('lets errors fall through when useErrorBoundary is falsey', async () => {
  const key = queryKey()

  function Page() {
    useQueries({
      queries: [{
        queryKey: key,
        queryFn: () => Promise.reject(new Error('boom')),
        useErrorBoundary: (err) => err.message.includes('boom'),
      }],
    })

    return null
  }

  // assert: boundary behavior matches the function result
})

Example (redaction rule):

const queryClient = createQueryClient({
  defaultOptions: {
    dehydrate: {
      shouldDehydrateQuery: () => true,
      shouldRedactErrors: () => false,
    },
  },
})

await expect(
  dehydrate(queryClient).queries[0]!.promise,
).resolves.toBeInstanceOf(Promise) // and then assert the thrown error is the original

The goal is confidence that error propagation/redaction behaves exactly as intended across supported modes, without relying on brittle or misleading test setup.

---

Vue example correctness

When writing Vue (including Nuxt) code snippets or API docs, ensure the example is correct for the shapes the API truly supports and for the Nuxt/Vue environment.

• For reactive inputs, don’t restrict types to a single form (e.g., only Ref). If the API accepts reactive values and getters/computed, type it accordingly (e.g., MaybeRefOrGetter) and normalize when you need an actual value.
• For Nuxt 3 snippets, import composables/helpers from the correct alias used by Nuxt auto-imports (typically #imports), so the snippet works when copied.

Example (typing + normalization for reactive inputs):

import { computed, type MaybeRefOrGetter, type Ref } from 'vue'
import { toValue } from 'vue'

function useTodos(todoId: MaybeRefOrGetter<string>) {
  const normalizedId: Ref<string> = computed(() => toValue(todoId))
  // ...use normalizedId.value where a plain string is needed
}

Nuxt 3 import alias (plugin/snippet correctness):

import { defineNuxtPlugin, useState } from '#imports'

This keeps docs precise and copy-pastable rather than only “almost correct” for real-world reactive inputs or Nuxt runtime resolution.

---

Prefer inferred, clear async

When writing code and tests, optimize for clarity and idiomatic TypeScript:

1) Prefer async/await when the async function includes a side effect.

// Clear: side effect is explicit
queryFn: async () => {
  await sleep(10)
  fetched = true
  return 'fetched'
}

// Less explicit when side effects are involved
queryFn: () => sleep(10).then(() => {
  fetched = true
  return 'fetched'
})

2) Let TypeScript infer callback types; avoid explicit parameter annotations/imports when they’re redundant.

// Prefer inference
onMutate: async (newTodo, context) => {
  // ...
}
// If the types infer correctly, remove extra imports/annotations.

3) Simplify type-level assertions by removing unnecessary generics/wrappers; use direct indexed access or the minimal expression that captures the intended type.

// Prefer minimal type plumbing
expectTypeOf(queryKey[dataTagSymbol]).toEqualTypeOf<InfiniteData<string>>()

---

Assert meaningful outcomes

When writing tests, validate the actual user-visible behavior and structured error data, not just a substring or a indirectly implied result. Make failures unambiguous (no swallow-pass patterns) and keep tests easy to debug.

Apply this standard:

• Prefer full message assertions (especially for formatted/translated strings) and assert structured fields like error.path / error.details when those are part of the contract.
• Avoid patterns that can accidentally always pass (e.g., empty try/catch without assertions inside).
• For behavior with control-flow semantics (e.g., fatal), add tests that prove the flow stops/continues, not only that an error exists.
• Cover realistic inputs and edge cases; add additional cases when current regex/validation logic is suspected incomplete.
• Improve debugging and maintenance with table-driven tests (test.each / equivalent) instead of ad-hoc concatenation.
• Where type-level expectations matter, add type tests (e.g., with tsd) rather than relying solely on compile-time errors.

Example (meaningful runtime assertions):

const result = schema.safeParse(badInput);
expect(result.success).toBe(false);
if (!result.success) {
  expect(result.error.issues[0].message).toBe("full expected message");
  expect(result.error.issues[0].path).toEqual(['points']);
}

Example (prove fatal stops):

const schema = z
  .object({ test: z.literal(true) })
  .nullable()
  .refine(v => v !== null, { message: 'foo', fatal: true })
  .superRefine((v, ctx) => { if (v && (v as any).test) ctx.addIssue({ code: 'custom', message: 'bar' }); });

const out = schema.safeParse(null);
expect(out.success).toBe(false);
expect(out.error.issues.map(i => i.message)).toEqual(['foo']);

---

Dependency-Aware Changesets

When using CI/CD release automation based on Changesets, declare only the minimal packages that drive the release (so CI/CD doesn’t process redundant package updates), and ensure the release workflow is documented in an operationally explicit way.

1) Keep changeset package lists minimal (dependency-driven)

• In the changeset frontmatter, prefer listing the “root” package(s) that cause dependency packages to release automatically.

Example changeset frontmatter:

---
'@tanstack/query-core': patch
---

Avoid enumerating many packages unless they truly need independent version bumps.

2) Document the real CI/CD steps contributors must expect

• If your pipeline generates a preview PR (Changesets Action) and publishes only after that PR is merged, your contributing/release docs must clearly state:
  • you must create/add a changeset (or ensure one exists)
  • a preview PR will appear and needs review
  • you must merge the preview PR for publishing to NPM

This prevents maintainer surprises and reduces cycle-time confusion when switching release tooling.

---

Stable React Rendering

Write React components and tests so they don’t depend on React’s internal render/callback sequencing, and so Suspense boundaries capture the work that actually suspends.

Apply:

• Put the suspending query/resource inside the component that’s rendered within the Suspense boundary (move query hooks into a child component).
• Don’t use boolean “first/last render” assumptions or logic tied to how many times React calls callbacks; React 19 can change counts/order.
• Base tests on observable state/DOM output; if React 18 vs 19 truly differs, branch expectations by version.
• Prefer effects for client-only orchestration/updates; use lazy initializers for useState when constructing objects.

Example (Suspense + boundary correctness):

import { createQuery } from '@tanstack/solid-query' // or equivalent React Query patterns
import React, { Suspense } from 'react'

function Posts({ postId }: { postId: number }) {
  const query = createQuery(() => ({
    queryKey: ['posts', postId],
    queryFn: () => fetch('/api/posts/' + postId).then(r => r.json()),
  }))

  return <div>{String(query.data?.title ?? '')}</div>
}

export function Home() {
  const [postId, setPostId] = React.useState(1)

  return (
    <>
      <button onClick={() => setPostId(id => Math.max(1, id - 1))}>Prev</button>
      <button onClick={() => setPostId(id => id + 1)}>Next</button>

      <Suspense fallback={<div>Loading post...</div>}>
        <Posts postId={postId} />
      </Suspense>
    </>
  )
}

Example (avoid render-count assumptions):

// Instead of: if (!boundary) { ... }
// Use count/state-based expectations or version-conditional assertions.
let callCount = 0
const useErrorBoundary = () => (++callCount, callCount < 3)

---

Keep API Types Synced

Any runtime API you expect developers to use must be discoverable and accurate in the public contract: update README/API docs and ensure the method is declared in the shipped .d.ts. Avoid “hiding” APIs behind missing typings or relying on long-lived @ts-expect-error type suppressions; fix the types/integration so the typed contract matches runtime behavior.

Practical checks:

• If a method exists (e.g., cancel()), confirm it’s:
  • documented in the public API/README
  • exported/declared in .d.ts
  • consistent with the runtime semantics
• If you see a @ts-expect-error in a place that affects integration/public config, create a follow-up to remove it once types are corrected.

Example (prefer existing API + ensure it’s part of the public contract):

// Prefer the dedicated API if it exists.
query.clear = () => {
  // Use public, typed method instead of duplicating internals.
  if (query.cancel) query.cancel()
  else {
    clearTimeout(query.staleTimeout)
    clearTimeout(query.cacheTimeout)
  }
}

// Then ensure docs + .d.ts include `cancel(): void` (or the correct signature).

---

Configuration Version Isolation

When changing package/tooling configuration (peer deps, TS/ESLint parser versions, tsup/esbuild settings, or feature/behavior flags), make version and behavior control explicit and isolated so CI/build/tests don’t break unexpectedly.

Apply these rules: 1) Pin or resolve the exact toolchain versions needed per package (don’t rely on repo-root defaults). If a test/build requires a newer TS feature set, resolve the parser/tooling in the package config. 2) Isolate build config overrides: if parent-level build plugins/settings cause failures, import the config you need and re-apply only the safe settings locally. 3) Gate experimental runtime behavior behind a config/option (or provide an experimental hook) rather than enabling it unconditionally. 4) Centralize derived configuration: decisions like enabled/skipToken interactions should be handled in one config derivation function (e.g., defaultQueryOptions) rather than scattered condition checks. 5) Document the “why” (e.g., “TS 4.9+ required for satisfies”, “peer dep bump needed for $derived override support”) and verify tests after dependency/version changes.

Example (package-local tool resolution):

const ruleTester = new ESLintUtils.RuleTester({
  // Use the package-resolved parser so TS-feature tests are consistent
  parser: require.resolve('@typescript-eslint/parser') as any,
});

Example (experimental gating):

export function useBaseQuery(/*...*/){
  if (!isServer && experimental_autoprefetch) {
    // allow prefetch during render only when explicitly enabled
  }
}

---

validate before accessing

Always validate that values exist and have expected properties before accessing them, especially when removing non-null assertions or performing type casting. Avoid making assumptions about value presence or type safety without explicit checks.

Key practices:

• When removing non-null assertion operators (!), add explicit null/undefined checks
• Validate input types before casting, especially with schema validation libraries
• Use specific filtering logic instead of generic Boolean filtering that may exclude valid falsy values
• Consider whether to pass empty objects vs undefined parameters based on actual usage

Example from the discussions:

// Risky - assumes route exists after removing non-null assertion
const route = this.looseRoutesById[d.routeId]

// Better - validate before use
const route = this.looseRoutesById[d.routeId]
if (!route) return

// Risky - Boolean filter excludes valid falsy numbers like 0, -1
paths.filter(Boolean).join('/')

// Better - explicit check for meaningful values
paths.filter((val) => val !== undefined && val !== null).join('/')

This prevents runtime errors from null reference exceptions and ensures code behaves correctly with edge case values.

---

Test TanStack Query Properly

When writing Angular unit/SSR tests for TanStack Query, align with Angular’s task tracking and keep caches isolated:

• Prefer Angular injection helpers: test components/services should call injectQuery/injectMutation (not ad-hoc query execution) so Angular can track in-progress work via PendingTasks (Angular 19+).
• Await completion via stability: in unit tests, use ApplicationRef.whenStable() or fixture.whenStable() to wait until queries/mutations become idle.
• Isolate per spec: create a new QueryClient for every test and provide it with provideTanStackQuery(queryClient) / provideQueryClient(queryClient). Clear caches in afterEach if you reuse helpers.
• Keep test and production configs separate: do not include withDevtools (or other app dev configuration) in unit test providers—this can slow tests.
• Version note: TestBed.tick() exists in newer Angular versions (introduced in Angular 20). If you rely on ticking effects, ensure your project version supports it.

Example (unit test pattern):

import { injectQuery } from '@tanstack/angular-query-experimental'
import { QueryClient } from '@tanstack/query-core'
import { ApplicationRef, TestBed } from '@angular/core/testing'
import { provideTanStackQuery } from '@tanstack/angular-query-experimental'

let queryClient: QueryClient

beforeEach(() => {
  queryClient = new QueryClient({
    defaultOptions: {
      queries: { retry: false },
    },
  })

  TestBed.configureTestingModule({
    providers: [provideTanStackQuery(queryClient)],
  })
})

afterEach(() => {
  queryClient.clear()
})

it('loads initial data', async () => {
  const appRef = TestBed.inject(ApplicationRef)

  const query = TestBed.runInInjectionContext(() =>
    injectQuery(() => ({
      queryKey: ['greeting'],
      queryFn: () => 'Hello',
    })),
  )

  // If your Angular version supports it, you can trigger effects:
  // TestBed.tick()

  await appRef.whenStable()

  expect(query.status()).toBe('success')
  expect(query.data()).toBe('Hello')
})

---

Use meaningful names

Use descriptive, self-explanatory names for variables, methods, fields, and types. Avoid single-letter variables, abbreviations, and generic naming that obscures intent.

Key principles:

• Use descriptive variable names instead of single letters: id_value instead of v, customer instead of c
• Make method and field names self-explanatory: mandate_type instead of action_type, is_sdk_client_token_generation_enabled instead of is_sdk_session_token_generation_enabled
• Use domain-specific types instead of primitives: id_type::CustomerId instead of String for customer identifiers
• Use enums instead of string literals for categorical data: AuthenticationStatus::Y instead of "Y"
• Avoid redundant naming: use client instead of superposition_client when the struct name already indicates context
• Use constants for hardcoded values: const ITEM_TYPE: &str = "plan" instead of inline strings

Example:

// Poor naming
let c = &item.response.customer;
let n = c.name.as_ref().map(|n| n.clone().expose());
pub customer_id: String,
pub payment_method: String,

// Good naming  
let customer = &item.response.customer;
let customer_name = customer.name.as_ref().map(|name| name.clone().expose());
pub customer_id: id_type::CustomerId,
pub payment_method: PaymentMethodType,

Clear, meaningful names reduce cognitive load, improve code maintainability, and make the codebase more accessible to new developers.

---

Organize code structure

Maintain clean and well-organized code structure by following consistent organizational patterns. This improves readability, maintainability, and reduces cognitive load for developers.

Key practices to follow:

1. Import Organization: Place all imports at the top of files and avoid wildcard imports ```rust // Good use common_enums::enums; use hyperswitch_domain_models::payment_method_data::PaymentMethodData;

// Avoid use crate::hyperswitch_ai_interaction::*; use masking::ExposeOptionInterface; // Move to top

2. **Functional Organization**: Group related functionality together and place code in appropriate modules
```rust
// Move validation logic to validator.rs
// Keep type transformations in transformers.rs  
// Place constants in dedicated const files or appropriate modules

1. Eliminate Code Duplication: Extract common logic into shared functions rather than duplicating implementations

   // Instead of separate v1/v2 functions with identical logic
   pub fn common_method() -> Result<Self, Error> {
    // shared implementation
   }
   

2. Use Explicit Patterns: Avoid wildcard matching and imports for better code clarity ```rust // Good match token_data { storage::PaymentTokenData::TemporaryGeneric(token) => { /* … / } storage::PaymentTokenData::PermanentCard(card) => { / … */ } }

// Avoid match token_data { storage::PaymentTokenData::TemporaryGeneric(token) => { /* … / } _ => { / … */ } }

5. **Remove Unnecessary Code**: Clean up unused variables, commented code blocks, and unnecessary utility functions that duplicate existing functionality.

This organizational approach ensures code remains maintainable as the codebase grows and makes it easier for team members to locate and understand functionality.

---

## simplify control flow patterns

<!-- source: twentyhq/twenty | topic: Code Style | language: TypeScript | updated: 2025-09-17 -->

Improve code readability by simplifying control flow structures and avoiding unnecessary complexity. This involves three key practices:

**1. Use early returns instead of nested if/else blocks:**
```typescript
// Avoid nested structures
if (condition) {
  // logic
} else {
  // more logic
}

// Prefer early returns
if (!condition) {
  return earlyResult;
}
// main logic continues

2. Break complex logic into smaller, named functions:

// Instead of complex nested logic
const getFieldFromSchema = (fieldKey: string, schema: RecordFieldNodeValue) => {
  return isRecordOutputSchemaV2(schema)
    ? schema.fields[fieldKey]
    : schema[fieldKey];
};

3. Use appropriate language constructs:

// Use find() instead of manual loops
const contentType = Object.entries(headers)
  .find(([key]) => key.toLowerCase() === 'content-type')?.[1];

// Use simple comparisons instead of array includes for basic checks
if (depth > MAX_DEPTH) // instead of [0, 1, MAX_DEPTH].includes(depth)

These patterns make code easier to follow, reduce cognitive load, and minimize the chance of errors. Nested if/else structures are particularly hard to read and maintain, while early returns create a clear flow where exceptional cases are handled first, leaving the main logic unindented and easy to follow.

---

simplify code structure

Write code that is easy to read and understand by avoiding unnecessary complexity in structure and logic. This includes several key practices:

Avoid complex nesting and nested ternaries:

// ❌ Hard to read with nesting
const result = isStandardizedFormat ? (
  toolOutput && typeof toolOutput === 'object' && 'success' in toolOutput ? 
    Boolean(toolOutput.result) : 
    Boolean(toolResult?.result)
) : false;

// ✅ Split into clear, explicit steps
const isStandardizedFormat = toolOutput && typeof toolOutput === 'object' && 'success' in toolOutput;
const hasResult = isStandardizedFormat 
  ? Boolean(toolOutput.result)
  : Boolean(toolResult?.result);

Simplify boolean comparisons:

// ❌ Unnecessary explicit comparison
if (hasAnySoftDeleteFilter === true) {

// ✅ Direct boolean usage
if (hasAnySoftDeleteFilter) {

Prefer switch statements over if-else chains:

// ❌ Long if-else chain
if (activeTabId === ROLES_LIST_TABS.TABS_IDS.USER_ROLES) {
  matchesTab = role.canBeAssignedToUsers;
} else if (activeTabId === ROLES_LIST_TABS.TABS_IDS.AGENT_ROLES) {
  matchesTab = role.canBeAssignedToAgents;
} else if (activeTabId === ROLES_LIST_TABS.TABS_IDS.API_KEY_ROLES) {
  matchesTab = role.canBeAssignedToApiKeys;
}

// ✅ Clear switch statement
switch (activeTabId) {
  case ROLES_LIST_TABS.TABS_IDS.USER_ROLES:
    return role.canBeAssignedToUsers;
  case ROLES_LIST_TABS.TABS_IDS.AGENT_ROLES:
    return role.canBeAssignedToAgents;
  case ROLES_LIST_TABS.TABS_IDS.API_KEY_ROLES:
    return role.canBeAssignedToApiKeys;
  default:
    return role.canBeAssignedToUsers;
}

Use early returns to reduce nesting:

// ❌ Nested conditions
const rolesOptions = rolesData?.getRoles?.reduce((acc, role) => {
  if (role.canBeAssignedToAgents) {
    acc.push({ label: role.label, value: role.id });
  }
  return acc;
}, []);

// ✅ Early return pattern
const rolesOptions = rolesData?.getRoles?.reduce((acc, role) => {
  if (!role.canBeAssignedToAgents) return acc;
  
  acc.push({ label: role.label, value: role.id });
  return acc;
}, []);

Prefer functional methods for better readability:

// ❌ Nested forEach loops
data.forEach((dataPoint, dataIndex) => {
  keys.forEach((key, keyIndex) => {
    configs.push(createConfig(dataPoint, key, keyIndex));
  });
});

// ✅ Functional approach with flatMap
const configs = data.flatMap((dataPoint, dataIndex) =>
  keys.map((key, keyIndex) => createConfig(dataPoint, key, keyIndex))
);

The goal is to make code self-documenting and reduce cognitive load for other developers. When code structure is simple and clear, it’s easier to understand, debug, and maintain.

---

API type consistency

Use structured types instead of generic strings in API definitions to improve type safety and clarity. Prefer enums over string literals, specific ID types over generic strings, and maintain consistent data type usage across request/response models.

Key practices:

• Use enum types for status fields instead of strings: pub status: SubscriptionStatus not pub status: String
• Use specific ID types: merchant_id: impl Into<id_type::MerchantId> not merchant_id: String
• Use connector enums: connector: Connector not connector: String
• Maintain URL validation with proper types: base_url: Url not base_url: String
• Use consistent amount types (MinorUnit vs StringMajorUnit) based on context

Example:

// Good - structured types
#[derive(Debug, Clone, serde::Serialize)]
pub struct CreateSubscriptionResponse {
    pub status: SubscriptionStatus,  // enum instead of String
    pub merchant_id: id_type::MerchantId,  // specific ID type
    pub connector: Connector,  // enum instead of String
}

// Avoid - generic strings
pub struct CreateSubscriptionResponse {
    pub status: String,  // unclear what values are valid
    pub merchant_id: String,  // loses type safety
    pub connector: String,  // no validation
}

This approach prevents runtime errors, improves API documentation, enables better IDE support, and makes the codebase more maintainable.

---

Avoid hardcoded configuration values

Configuration values should not be hardcoded in the source code. Instead, they should be externalized to configuration files, environment variables, or made configurable through application settings. This improves maintainability, allows for environment-specific customization, and prevents deployment issues.

Common examples of values that should be configurable:

• Timeout durations and retry intervals
• Buffer times and scheduling delays
• Currency lists and supported payment methods
• URL endpoints and connection strings
• Feature-specific thresholds and limits

Example of problematic hardcoded values:

// Bad: Hardcoded timeout
tokio::time::sleep(tokio::time::Duration::from_secs(3)).await;

// Bad: Hardcoded buffer time  
schedule_time + time::Duration::minutes(15)

// Bad: Hardcoded currency check
if option.price.currency_code != common_enums::Currency::USD {

Example of proper configuration approach:

// Good: Configurable timeout
let timeout = config.superposition.initialization_timeout_secs;
tokio::time::sleep(tokio::time::Duration::from_secs(timeout)).await;

// Good: Configurable buffer time
let buffer_minutes = config.revenue_recovery.calculate_workflow_buffer_minutes;
schedule_time + time::Duration::minutes(buffer_minutes)

// Good: Configurable supported currencies
let supported_currencies = &config.amazon_pay.supported_currencies;
if !supported_currencies.contains(&option.price.currency_code) {

When reviewing code, look for magic numbers, hardcoded strings, and fixed values that could vary between environments or should be tunable by operators. Require these to be moved to appropriate configuration structures with sensible defaults.

---

Use semantically accurate names

Names should clearly and accurately reflect their actual purpose, functionality, and scope. Avoid misleading terminology that doesn’t match the component’s or variable’s true behavior.

Key principles:

• Component names should describe what they actually do, not what they seem to do
• Boolean variables should clearly indicate what condition they represent
• Follow established naming conventions (e.g., “Styled” prefix for styled components)
• Use descriptive constants instead of magic numbers
• Choose parameter names that allow for future extensibility

Examples of improvements:

// ❌ Misleading - not for "object options" but "select field options"
ObjectOptionsDropdownCreateNewOption

// ✅ Clear and accurate
AddSelectOptionMenuItem

// ❌ Unclear boolean with double negative
const isPlainString = !streamData.includes('\n') || !streamData.split('\n').some(...)

// ✅ Clear and positive
const hasStructuredStreamData = (data: string): boolean => {
  if (!data.includes('\n')) return false;
  return data.split('\n').some(line => { /* ... */ });
}

// ❌ Missing naming convention
const AddStyleContainer = { /* ... */ }

// ✅ Follows styled component convention  
const StyledAddContainer = { /* ... */ }

// ❌ Single parameter limits extensibility
uniqueNotEditableKey="content-type"

// ✅ Array allows multiple values
readonlyKeys={["content-type"]}

This ensures code is self-documenting and reduces cognitive load for developers trying to understand the codebase.

---

Avoid expensive repeated operations

Identify and eliminate expensive operations that are performed repeatedly, such as object creation in loops, redundant computations, or duplicate filtering operations. Cache expensive objects like RegExp instances, i18n instances, or computed results to improve performance and prevent memory leaks.

Examples of optimization:

• Cache RegExp objects outside loops instead of creating them repeatedly
• Use instance maps to reuse expensive objects like i18n instances
• Store intermediate results when filtering or processing the same data multiple times
• Optimize data structure initialization (e.g., use new Map(array.map()) instead of forEach loops)

// Bad: Creating RegExp in loop
for (const [accented, unaccented] of Object.entries(specialChars)) {
  result = result.replace(new RegExp(accented, 'g'), unaccented);
}

// Good: Single RegExp with callback
const specialCharsRegex = new RegExp(`[${Object.keys(specialChars).join('')}]`, 'g');
return text.replace(specialCharsRegex, (match) => specialChars[match]);

// Bad: Filtering same array twice
const filtered1 = enrichedSeries.filter(series => series.shouldEnableArea);
const filtered2 = enrichedSeries.filter(series => series.shouldEnableArea);

// Good: Store intermediate result
const areaEnabledSeries = enrichedSeries.filter(series => series.shouldEnableArea);

---

Use proper null utilities

Use dedicated null checking utilities like isDefined or isUndefinedOrNull instead of generic type coercion functions like Boolean(). Prefer undefined over empty strings or null as default values to maintain type safety and prevent runtime errors.

Avoid patterns like:

// Problematic
const isStreaming = Boolean(agentStreamingMessage) && streamData === agentStreamingMessage;
fieldName = '',  // empty string default
sourceHandle: null,  // explicit null

// Better
const isStreaming = isDefined(agentStreamingMessage) && streamData === agentStreamingMessage;
fieldName,  // undefined default
sourceHandle: DEFAULT_SOURCE_HANDLE_ID,  // meaningful default

This approach provides clearer intent, better type safety, and reduces the likelihood of runtime errors caused by unexpected falsy values.

---

Use proper PostgreSQL types

Leverage PostgreSQL’s native data types and features instead of generic alternatives to improve performance, type safety, and query capabilities. Use JSONB for structured data instead of storing raw text, implement PostgreSQL enums for constrained values rather than varchar columns, and establish proper foreign key relationships with meaningful column names.

Examples:

• Store structured data as JSONB: @Column({ type: 'jsonb' }) instead of raw text for better retrieval performance and query capabilities
• Use PostgreSQL enums: @Column({ type: 'enum', enum: PreferredCalendar }) with database-level enum creation instead of varchar
• Design proper relationships: Use recordId and objectMetadataId pointing to metadata tables instead of generic objectId/objectType pairs
• Apply appropriate constraints: Mark columns as non-nullable when they have defaults: @Column({ nullable: false, default: value })

This approach enables better query optimization, data integrity, and leverages PostgreSQL’s advanced features for improved application performance.

---

Use descriptive specific names

Names should be descriptive and specific enough to clearly communicate their purpose and avoid confusion. This includes using full words instead of abbreviations, being domain-specific when necessary, and ensuring names accurately reflect the function’s behavior or data’s purpose.

Key guidelines:

• Use full words instead of abbreviations: isRightToLeftLocale instead of isRtlLocale
• Be domain-specific to avoid naming conflicts: getSentFolderCandidatesByRegex could be getImapSentFolderCandidatesByRegex
• Avoid ambiguous names that could cause confusion: FlatEntityMapsCacheService vs WorkspaceFlatMapCacheService
• Use descriptive variable names: stepExecution.result instead of result.result
• Be specific about scope and context: useUpdateMultipleRecordsFromManyObjects instead of useUpdateManyRecordsFromManyObjects

Example:

// ❌ Ambiguous and abbreviated
const isRtlLocale = (locale: string) => { ... }
const mergeInProgressState = atom({ ... })

// ✅ Descriptive and specific  
const isRightToLeftLocale = (locale: string) => { ... }
const isMergeInProgress = atom({ ... })

This helps with IDE autocompletion, reduces naming conflicts, and makes code more self-documenting for better maintainability.

---

API identifier consistency

Maintain consistent naming conventions for API identifiers, configuration keys, and payment method types. Use snake_case for all API identifiers to ensure uniformity across the system. This includes payment method types, configuration field names, and connector specifications.

When defining payment method types in configuration files, use lowercase with underscores rather than PascalCase or mixed formats. For example:

# Correct
payment_method_type = "amazon_pay"
google_pay_pre_decrypt_flow = "network_tokenization"

# Incorrect  
payment_method_type = "AmazonPay"

This consistency improves API predictability, reduces integration errors, and maintains a professional interface standard. Consider centralizing configuration logic in appropriate traits or specifications to avoid scattered configuration management across the codebase.

---

Enforce restrictive security defaults

Always start with the most restrictive security settings and only grant additional permissions when absolutely necessary. This principle applies to user authorization, iframe sandboxing, API access, and any security-sensitive features.

For user permissions, implement proper hierarchy validation rather than simple boolean checks. Users should only be able to perform actions on resources at their permission level or below.

For iframe embedding, use minimal sandbox attributes and allow policies:

// Restrictive approach - only grant necessary permissions
<iframe
  sandbox="allow-scripts allow-forms allow-popups"
  allow="encrypted-media"
  allowFullScreen
/>

// Avoid overly permissive settings
<iframe
  sandbox="allow-scripts allow-same-origin allow-forms allow-popups"
  allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"
/>

This approach reduces attack surface, prevents privilege escalation, and follows security best practices by defaulting to deny rather than allow.

---

Single source of truth

Establish a single authoritative source for each piece of data in your API interfaces rather than maintaining duplicate or parallel state. Derive computed values from the authoritative source instead of storing them separately.

When designing component interfaces, identify what should be the canonical source of truth and derive other values from it. This prevents inconsistencies and reduces complexity.

For example, instead of storing both headers and bodyType separately:

// Avoid: Maintaining parallel state
type BodyInputProps = {
  headers: Record<string, string>;
  bodyType: BodyType; // Duplicate information
  onChange: (value?: string, isBodyType?: boolean) => void;
};

// Prefer: Single source of truth
type BodyInputProps = {
  headers: Record<string, string>; // Single source
  onChange: (value?: string) => void;
};

// Derive bodyType from headers when needed
const bodyType = deriveBodyTypeFromHeaders(headers);

Similarly, when accessing related data, prefer getting it from the authoritative source rather than relying on indirect indicators. Instead of checking sourceHandleId, get the actual source node to ensure type safety and accuracy.

---

Semantic naming consistency

Use names that match the value’s real meaning and align with established/public API conventions.

Practical rules:

• Name by semantics, not by adjacent intuition: if “context” is being reinterpreted, rename (and deprecate old names with clear JSDoc) rather than silently changing what the term means.
• Match existing public API / adapter conventions: if the library exposes setQueries(queries) and callers already use “queries”, keep internal variables consistent (even if “options” feels more precise).
• Use framework/runtime signaling in names: in Angular, functions that rely on an injection context should be clearly marked (e.g., prefer injectX when using inject(...)).
• Match prop/example naming: prefer client vs queryClient when it mirrors QueryClientProvider client={...} and the corresponding destructuring examples.
• Signal API stability explicitly: new experimental/unstable additions should include experimental_/unstable_ in the name when that’s the project’s convention.
• Avoid ambiguous plural/generic terms: if a field implies a specific contract (e.g., fetching multiple pages), choose names that help enforce/communicate the required pairing.

Examples:

// Semantic rename with deprecation
export interface MutationState<TData, TError, TVariables, TScope = unknown> {
  /** @deprecated Use `scope` instead. */
  context: TScope | undefined
  scope: TScope | undefined
}

// Keep naming consistent with public API
// useQueries({ queries }) ... setQueries(queries)
const defaultedQueries = /* keep `queries` naming */

// Angular injection-context signaling
export function injectIsFetching(filters?: QueryFilters, queryClient?: QueryClient) {
  // uses `inject(...)` internally; name reflects requirement
}

// Provider-aligned naming
useQuery({
  queryKey,
  queryFn: ({ client, signal }) => {/* ... */},
})

// Stability signaling
experimental_promise: Promise<TData>

---

Security-critical code review

Changes to security-sensitive areas like authentication, input validation, and business logic require extra scrutiny and thorough review. These modifications can introduce vulnerabilities if not properly validated.

Key areas requiring heightened security review:

• Authentication and authorization logic changes
• Input processing and data sanitization
• Business operations that could be financially abused
• API endpoints and service layer security controls

When reviewing such changes, verify that:

• Security implications are thoroughly understood and documented
• Input validation prevents injection attacks (SQL, CSV, XSS, etc.)
• Business logic prevents abuse scenarios (e.g., credit manipulation)
• Changes don’t weaken existing security controls

Example of proper input sanitization:

// Prevent CSV injection by prefixing dangerous formulas
const sanitizedValue = value.startsWith('=') || value.startsWith('+') 
  ? `${CSV_INJECTION_PREVENTION_ZWJ}${value}` 
  : value;

For authentication changes, consider reverting risky modifications if the security impact cannot be clearly demonstrated as safe. As one reviewer noted: “This change is risky. What you’re checking now is not the same as what was checked before.”

---

optimize data structure lookups

Choose data structures that provide optimal time complexity for your access patterns. When you need frequent lookups by key, use Map instead of Record with Array.find() operations to achieve O(1) instead of O(n) complexity.

The most common anti-pattern is building a Record and then using Array.find() to search through collections, which results in O(n) time complexity for each lookup. Instead, use Map for constant-time lookups.

Example of inefficient approach:

const dataMap: Record<string, LineChartSeries> = {};
for (const series of data) {
  dataMap[series.id] = series;
}

// Later, expensive O(n) lookup:
const enrichedSeriesItem = enrichedSeries.find(
  (item) => item.id === someId
);

Optimized approach:

const dataMap = new Map<string, LineChartSeries>(
  data.map((series) => [series.id, series])
);

// Later, efficient O(1) lookup:
const enrichedSeriesItem = dataMap.get(someId);

This optimization is particularly important in frequently called functions, loops, or when dealing with large datasets where the performance difference becomes significant.

---

Choose appropriate concurrency patterns

Select concurrency mechanisms that align with your system architecture and established codebase patterns. Avoid using database transactions and pessimistic locking when working with connection pooling, as they can cause unintended side effects where one connection commits on behalf of another. Instead, follow existing patterns in the codebase for handling race conditions and ensuring data consistency.

For workload distribution, prefer job-based parallelization over sequential processing. Rather than iterating through all workspaces in a single job, enqueue separate jobs for each workspace to enable parallel processing and better resource utilization.

When designing async operations, consider the proper sequencing of dependent tasks. For example, synchronization operations should be ordered appropriately - sync folders before processing messages to detect user changes.

Example of preferred job distribution pattern:

// Instead of processing all workspaces sequentially:
for (const activeWorkspace of activeWorkspaces) {
  await processWorkspace(activeWorkspace);
}

// Enqueue separate jobs for parallel processing:
for (const activeWorkspace of activeWorkspaces) {
  await this.messageQueue.add('process-workspace', { 
    workspaceId: activeWorkspace.id 
  });
}

This approach improves system performance, reduces blocking operations, and follows established concurrency patterns that work well with the existing infrastructure.

---

simplify API interfaces

Keep API interfaces simple and focused by avoiding unnecessary input wrapping, extracting context parameters appropriately, and limiting exposure of internal implementation details.

Key principles:

• Flatten input structures: Avoid wrapping single properties in input objects. Put properties directly at the root level instead of nesting them unnecessarily.
• Extract context parameters: Remove workspace/tenant identifiers from input objects and pass them as separate parameters to maintain clear separation of concerns.
• Use appropriate types: Choose specific input/output types over generic database entities. Prefer CreateViewFieldInput over Partial<Entity> and UpdateInput over QueryDeepPartialEntity.
• Limit API exposure: Don’t expose internal fields like workspaceId in public APIs when users don’t need that information.
• Provide specific operations: Instead of generic flexible APIs, offer specific operations like switchToYearly() or cancel() rather than exposing the entire data model.

Example:

// ❌ Avoid unnecessary input wrapping
async createPublicDomain(
  @Args('input') { domain }: PublicDomainInput,
) { ... }

// ✅ Put properties directly at root level
async createPublicDomain(
  @Args('domain') domain: string,
) { ... }

// ❌ Don't mix context with business data
async create(
  viewFieldData: Partial<ViewFieldEntity>, // contains workspaceId
) { ... }

// ✅ Extract context parameters
async create(
  viewFieldData: CreateViewFieldInput,
  workspaceId: string,
) { ... }

This approach reduces API complexity, improves type safety, and maintains clear boundaries between public interfaces and internal implementation details.

---

Protect sensitive data

Wrap all sensitive data fields in Secret<> types to prevent accidental exposure through logs, debug output, serialization, or error messages. This includes authentication tokens, API keys, PII data, payment information, and any credentials.

Fields that should be wrapped in Secret<>:

• Authentication tokens and API keys (access_token, client_secret, proxy_url)
• PII data (names, phone numbers, email addresses, social security numbers)
• Payment information (card numbers, bank account numbers, payment tokens)
• Internal identifiers that could be sensitive (vault IDs, processor tokens)

Example implementation:

// Instead of:
pub struct PaymentData {
    pub bank_number: Option<String>,
    pub client_secret: Option<String>,
    pub token: String,
}

// Use:
pub struct PaymentData {
    pub bank_number: Option<Secret<String>>,
    pub client_secret: Option<Secret<String>>,
    pub token: Secret<String>,
}

For highly sensitive data like KMS-encrypted tokens, consider additional encryption layers beyond the Secret<> wrapper. The Secret<> type prevents accidental logging and provides controlled access through methods like expose() or peek(), ensuring sensitive data is only accessed intentionally.

---

use Option combinators

Leverage Rust’s Option API methods like map, and_then, is_some(), and filter instead of manual pattern matching or nested conditional statements when working with optional values. This approach reduces code complexity, improves readability, and prevents common null-handling errors.

Avoid manual checks:

// Instead of this:
let is_there_an_active_payment_attempt_id = payment_intent.active_attempt_id.is_some();
if let Some(_customer_acceptance) = customer_acceptance {
    // nested logic
}

// Use Option combinators:
payment_intent.active_attempt_id.map(|attempt_id| {
    // handle the case when present
}).unwrap_or_else(|| {
    // handle the None case
});

// For simple existence checks:
if customer_acceptance.is_some() {
    // logic when present
}

Chain operations safely:

// Instead of nested match/if statements:
match connector_customer_id {
    Some(connector_customer_id) => {
        match update_token_expiry_based_on_schedule_time(state, &connector_customer_id, Some(s_time)).await {
            Ok(_) => {}
            Err(e) => { /* error handling */ }
        }
    }
    None => { /* log warning */ }
}

// Use Option methods:
connector_customer_id
    .map(|id| update_token_expiry_based_on_schedule_time(state, &id, Some(s_time)))
    .transpose()?
    .unwrap_or_else(|| logger::warn!("No connector customer id found"));

This pattern makes null safety explicit, reduces indentation levels, and leverages Rust’s type system to prevent null reference errors at compile time.

---

Validate configuration consistency

Ensure configuration values have consistent defaults across all systems and validate configuration structures using shared schemas. When introducing new configuration options, establish system-detected defaults that work intelligently based on browser or environment context, similar to existing patterns for date/time formats and timezone detection.

Use validation schemas (preferably Zod) that can be shared between frontend, backend, and CLI components to maintain consistency. Support flexible configuration sources through environment variables while maintaining a clear hierarchy of configuration precedence.

Example implementation:

// In twenty-shared
export const ConfigSchema = z.object({
  dateFormat: z.enum([DateFormat.MONTH_FIRST, DateFormat.DAY_FIRST]).default(DateFormat.MONTH_FIRST),
  timeFormat: z.enum([TimeFormat.HOUR_12, TimeFormat.HOUR_24]).default(TimeFormat.HOUR_24),
  numberFormat: z.enum([NumberFormat.COMMAS_AND_DOT, NumberFormat.DOTS_AND_COMMA]).default(NumberFormat.COMMAS_AND_DOT),
});

// Ensure consistent defaults across frontend and backend
export const defaultConfig = {
  dateFormat: detectDateFormat(), // System-detected default
  timeFormat: detectTimeFormat(), // System-detected default  
  numberFormat: detectNumberFormat(), // System-detected default
};

Always verify that default values match between different parts of the system (e.g., Recoil state defaults should match backend environment variable defaults) to prevent configuration conflicts.

---

avoid hard-coded test data

Hard-coded test data creates maintenance burdens and unrealistic test scenarios. Instead of manually defining static values or adding workarounds for dynamic fields, leverage existing test utilities and generation functions.

Use utility functions like RequestBodyUtils.js for generating test data dynamically rather than hard-coding values such as customer IDs, amounts, or other parameters. For fields that are inherently dynamic (like authentication data that changes between requests), design tests to either generate appropriate values or properly handle the variability rather than adding comments to “ignore” fields.

Example of improvement:

// Instead of:
customer_id: "Customer123_UCS",
amount: 0,

// Use:
customer_id: generateCustomerId(),
amount: generateTestAmount(),

This approach reduces test brittleness, improves maintainability, and creates more realistic test scenarios that better reflect production behavior.

---

explicit error handling

Avoid catch-all patterns and implicit error handling. Handle each error case explicitly, use the ? operator for error propagation instead of explicit returns, and never silently ignore errors.

Key practices:

• Replace wildcard patterns (_, unwrap_or_default()) with explicit case handling
• Use ? operator instead of return Err(...) for consistent error propagation
• Log errors even when continuing execution, don’t silently ignore failures
• Provide meaningful error context with attach_printable() or change_context()

Example of problematic patterns:

// Avoid catch-all wildcards
match capture_method {
    Some(CaptureMethod::Manual) => Status::Authorized,
    _ => Status::Charged,  // Too broad, handle each case explicitly
}

// Avoid explicit returns
if error.is_some() {
    return Err(SomeError);  // Use ? operator instead
}

// Avoid silent error handling
match result {
    Ok(value) => value,
    Err(_) => {} // Log the error at minimum
}

Better approach:

match capture_method {
    Some(CaptureMethod::Manual) => Status::Authorized,
    Some(CaptureMethod::Automatic) => Status::Charged,
    Some(unsupported) => return Err(UnsupportedCaptureMethod(unsupported)),
    None => return Err(MissingCaptureMethod),
}

// Use ? for error propagation
let result = operation().change_context(MyError::OperationFailed)?;

// Always handle errors meaningfully
match result {
    Ok(value) => value,
    Err(e) => {
        logger::error!("Operation failed: {:?}", e);
        return Err(e);
    }
}

---

Use domain-specific exceptions

Create custom exception classes for each domain/module instead of throwing generic errors or letting applications crash. Include both technical details for developers and user-friendly messages for end users. Handle exceptions at the appropriate service layer rather than at API boundaries.

Key principles:

• Define custom exception classes with specific error codes for each domain (e.g., DnsManagerException, BillingException, ViewException)
• Include userFriendlyMessage field for client-facing error communication
• Validate inputs early to prevent exceptions rather than catching them later
• Handle domain-specific exceptions at the service layer, not at GraphQL/controller layers
• Map technical exceptions to appropriate HTTP status codes when needed

Example:

// Good: Domain-specific exception with user-friendly message
throw new DnsManagerException(
  'Hostname already registered',
  DnsManagerExceptionCode.HOSTNAME_ALREADY_REGISTERED,
  { userFriendlyMessage: 'Domain is already registered' },
);

// Bad: Generic error that crashes the application
throw new Error('More than one custom hostname found in cloudflare');

// Good: Validate before processing
if (!isDefined(fieldToDelete)) {
  throw new ViewException(
    'Field not found',
    ViewExceptionCode.FIELD_NOT_FOUND,
    { userFriendlyMessage: 'The field you are trying to delete does not exist' }
  );
}

This approach prevents application crashes, provides better debugging information, and enables graceful error handling throughout the application stack.

---

Database schema consistency

Ensure database schema definitions are consistent with ORM annotations and include proper constraints for data integrity and security. This includes matching primary key definitions between migrations and ORM models, making foreign key relationships mandatory where appropriate, and requiring tenant identifiers in queries to prevent cross-tenant data access.

Key practices:

1. Primary key consistency: Verify that Diesel annotations match SQL migration primary key definitions
2. Mandatory relationships: Make foreign keys non-nullable when they represent required relationships
3. Tenant isolation: Always include merchant_id or similar tenant identifiers in queries for multi-tenant security

Example issues to avoid:

// ❌ Primary key mismatch
#[diesel(primary_key(id))]  // Only 'id' specified
// But SQL migration has: PRIMARY KEY (id, created_at)

// ❌ Nullable foreign key that should be mandatory
subscription_id -> Nullable<Varchar>,  // Should be required

// ❌ Query without tenant isolation
async fn find_by_id(id: String) -> Result<Entity> {
    // Missing merchant_id constraint - security risk
}

// ✅ Correct implementations
#[diesel(primary_key(id, created_at))]  // Matches migration

subscription_id -> Varchar,  // Mandatory relationship

async fn find_by_merchant_id_and_id(
    merchant_id: &MerchantId, 
    id: String
) -> Result<Entity> {
    // Proper tenant isolation
}

This ensures data integrity, prevents security vulnerabilities, and maintains consistency between database schema and application code.

---

Avoid repeated expensive operations

Replace repeated expensive operations like find(), filter(), or sort() with pre-computed maps or cached results to improve performance. When the same lookup or computation is performed multiple times, create a map or dictionary for O(1) access instead of O(n) searches.

Examples of optimization:

Instead of repeated find() calls:

// ❌ Inefficient - O(n) lookup each time
const handlePointClick = (point) => {
  const series = data.find((s) => s.id === point.seriesId);
  // ... later in code
  const anotherSeries = data.find((s) => s.id === otherId);
};

// ✅ Efficient - O(1) lookup with pre-computed map
const dataMap = useMemo(() => 
  data.reduce((map, item) => ({ ...map, [item.id]: item }), {}), 
  [data]
);

const handlePointClick = (point) => {
  const series = dataMap[point.seriesId];
  // ... later in code
  const anotherSeries = dataMap[otherId];
};

Instead of repeated sorting:

// ❌ Inefficient - sorting already sorted data
const actionsToRegister = Object.values(actionConfig ?? {})
  .filter((action) => action.availableOn?.includes(viewType))
  .sort((a, b) => a.position - b.position);

// ✅ Efficient - pre-sort the configuration
const sortedActionConfig = useMemo(() => 
  Object.values(actionConfig ?? {}).sort((a, b) => a.position - b.position),
  [actionConfig]
);

This optimization is particularly important in render loops, event handlers, and frequently called functions where the same expensive operations are performed repeatedly.

---

Explicit Error Narrowing

When using data/mutation libraries, treat error handling as a two-step process: (1) type errors conservatively at the boundary, and (2) implement recovery/UI logic that matches the library’s actual error-state semantics.

1) Use conservative global error typing

• Prefer a global error type of unknown (or keep the default) so call sites must explicitly narrow before reading properties.

2) Don’t assume placeholder/optimistic flows preserve error status

• If you migrate from keepPreviousData to placeholderData, update UI logic: placeholderData puts the query into success state, even though background refetches could fail.

3) Wire recovery callbacks to the correct inputs

• For optimistic rollback, use the value returned from onMutate (as provided to onError) rather than relying on older callback signatures.

4) Place try/catch only where the promise can throw

• Some helper calls (e.g., prefetch) return a Promise<void> that you can await but “will never throw”, so don’t wrap them in try/catch as if they were failing operations.

Example (TanStack Query placeholder + conservative error typing):

import { useQuery } from '@tanstack/react-query'

useQuery({
  queryKey: ['some-query'],
  queryFn: async () => {
    // ensure you narrow before using error details
    if (Math.random() > 0.5) throw new Error('some error')
    return 42
  },
  // placeholderData replaces keepPreviousData
  placeholderData: (previous) => previous,
})

// At call sites with global error = unknown, narrow explicitly before using properties.
// Example:
// if (error instanceof SomeError) { error.code ... }

Follow these rules to prevent accidental “error access” without narrowing, avoid UI bugs caused by changed status semantics, and ensure rollback and error handling occur in the right place.

---

prefer type guards

Use semantic type guards like isDefined() instead of basic type checks (typeof, simple null checks) or unsafe type assertions (as!, !). Type guards provide better readability, type safety, and null reference prevention.

Prefer this:

// Use semantic type guards
if (!isDefined(activeTabId)) return;
if (!isDefined(pageLayout)) {
  throw new PageLayoutException(/*...*/);
}

// Filter out null values
return objectNameSingulars
  .map(name => objectMetadataItems.find(item => item.nameSingular === name))
  .filter(isDefined);

Instead of:

// Avoid basic type checks and unsafe assertions
if (!activeTabId) return;  // unclear intent
if (typeof parsed === 'object') { /*...*/ }  // prefer specific type guards
return restoredPageLayout!;  // unsafe assertion
filteredFields[key] = { /*...*/ } as FieldOutputSchemaV2;  // forced typing

This approach eliminates null reference errors, makes code intent clearer, and leverages TypeScript’s type system for better compile-time safety.

---

Ensure documentation clarity

Documentation should be clear, accurate, and consistently structured to provide maximum value to developers. Avoid overly broad or inaccurate statements that may mislead users, and prefer explanatory content over warnings when possible.

Key practices:

• Rewrite or remove unclear sections rather than leaving confusing content
• Use specific, accurate language instead of broad generalizations (e.g., “For some validation libraries…” instead of “For validation libraries…”)
• Provide explanatory headings and examples instead of warnings when appropriate
• Maintain consistent formatting patterns across similar documentation sections
• Avoid duplicate headings when using frontmatter titles, as the website renders the frontmatter title as the main heading

Example of improvement:

<!-- Instead of unclear or overly broad statements -->
For validation libraries we recommend using adapters...

<!-- Use more specific, accurate language -->
For some validation libraries like Zod v3, we recommend using adapters...

When documenting API properties, maintain consistent patterns:

### `defaultOnCatch` property
- Type: `(error: Error, errorInfo: ErrorInfo) => void`
- Optional  
- Defaults to `routerOptions.defaultOnCatch`
- The default `onCatch` handler for errors caught by the Router ErrorBoundary

This approach ensures documentation serves as a reliable reference that developers can trust and easily understand.

---

Add tests for functionality

New functionality should include corresponding tests to ensure code quality and maintainability. When introducing new methods, utilities, or services, always add appropriate test coverage.

For new utility functions or services, consider starting with integration tests as they are often more maintainable and require less mocking. For complex logic that would benefit from isolated testing, extract the functionality into a separate utility that can be easily unit tested.

Example approach:

// When adding a new service method like toggleInterval()
async toggleInterval(workspace: Workspace) {
  const billingSubscription = await this.getCurrentBillingSubscriptionOrThrow(
    { workspaceId: workspace.id },
  );

  return billingSubscription.interval === SubscriptionInterval.Year
    ? this.switchToMonthlyInterval(billingSubscription)
    : this.switchToYearlyInterval(billingSubscription);
}

// Add corresponding integration test
describe('BillingSubscriptionService', () => {
  it('should toggle billing interval correctly', async () => {
    // Test implementation using makeGraphqlAPIRequest
  });
});

This practice helps catch regressions early, documents expected behavior, and makes the codebase more reliable for future development.

---

Synchronize environment configurations

When making configuration changes, ensure all relevant environment files are updated consistently to prevent environment-specific inconsistencies and deployment issues.

Configuration changes should be propagated across all applicable files including:

• Development, sandbox, and production environment files
• Docker compose configurations
• Example and template configuration files
• Environment-specific deployment configurations

Example of proper synchronization:

# If adding a new connector configuration in development.toml:
[newconnector]
base_url = "https://api-test.example.com/"

# Also update in:
# - sandbox.toml
# - production.toml (with production URL)
# - docker_compose.toml
# - config.example.toml (with documentation comments)

Always verify that configuration keys, formatting, and documentation comments remain consistent across all environment files. Pay special attention to URL formatting (trailing slashes), time unit specifications in comments, and naming conventions to maintain uniformity across environments.

---

explicit error type handling

Handle errors with explicit type checking and intentional decisions rather than generic catch-all approaches. This improves error handling precision and makes error recovery logic clearer.

Key practices:

• Check for specific error types and names rather than generic Error catching
• Use precise string matching (startsWith) instead of loose matching (includes) for error identification
• Be explicit about when errors should be silently handled vs when they should propagate
• Provide sensible defaults while allowing type flexibility when needed

Example of explicit error type checking:

// Good: Explicit check for specific error type
if (e instanceof DOMException && e.name === 'AbortError') {
  // Handle as normal control flow
  return handleAbortError()
}

// Good: Specific error detection
function isRecoverableError(error: unknown): boolean {
  if (error instanceof Error) {
    return error.message.startsWith(`${RECOVERABLE_ERROR}: `)
  }
  return false
}

// Good: Explicit about silent error handling with documentation
try {
  const context = defaultTransformer.parse(serializedContext)
  return { context, data: formData }
} catch (e) {
  // Intentionally return fallback when context parsing fails
  // to allow request processing to continue
  return { data: formData }
}

This approach prevents unexpected error swallowing, makes error handling intentions clear to other developers, and enables more precise error recovery strategies.

---

Minimize hook re-renders

Design React hooks to minimize unnecessary re-renders by avoiding common anti-patterns that cause performance issues.

Key principles:

1. Avoid umbrella hooks - Don’t create hooks that combine multiple responsibilities, especially mixing read and write operations. Split them into focused, single-purpose hooks.

2. Don’t return functions from hooks - Functions returned from hooks create new references on each render, triggering re-renders in consuming components. Instead, use utility functions defined outside React scope or stable callbacks with useRecoilCallback.

3. Minimize state dependencies - Use techniques like recoil callbacks with snapshot and set to avoid taking direct dependencies on state atoms, preventing re-renders when those states update.

4. Keep action hooks dependency-free - Hooks that perform actions (like create, update, delete) should typically not subscribe to state changes.

Example of problematic pattern:

// ❌ Bad: Umbrella hook with functions
export const useBillingPlan = () => {
  const plans = useRecoilValue(plansState);
  
  const getBaseLicensedPrice = (planKey) => {
    // Function creates new reference each render
    return plans.find(p => p.key === planKey);
  };
  
  return { plans, getBaseLicensedPrice };
};

Better approach:

// ✅ Good: Focused hooks with stable returns
export const usePlans = () => useRecoilValue(plansState);

export const useCreateWidget = () => {
  return useRecoilCallback(({ snapshot, set }) => async (widgetData) => {
    // No state dependencies, won't cause re-renders
    const currentWidgets = await snapshot.getPromise(widgetsState);
    set(widgetsState, [...currentWidgets, widgetData]);
  });
};

---

Use defensive SQL clauses

Always use defensive SQL clauses like IF NOT EXISTS and IF EXISTS in migration scripts to make them idempotent and prevent failures when run multiple times or in different environments. This ensures migrations can be safely re-executed without causing errors due to existing schema elements.

Example:

-- Good: Uses IF NOT EXISTS to prevent errors
ALTER TABLE payment_intent ADD COLUMN IF NOT EXISTS enable_overcapture BOOLEAN;

-- Good: Uses IF EXISTS for safe removal
ALTER TABLE subscription DROP COLUMN IF EXISTS profile_id;

When performing complex operations like column renaming or constraint modifications, understand that some operations require separate statements and cannot be nested within a single ALTER TABLE command.

---

Follow React component patterns

React components should be rendered as standard JSX elements, not called as functions, and should follow established architectural patterns. This ensures consistency with React conventions and maintainability.

When you see a component being called as a function like WorkflowActionMenuItems(props), refactor it to proper JSX syntax: <WorkflowActionMenuItems {...props} />. Additionally, ensure components have proper data backing and follow established patterns in the codebase.

Example of incorrect usage:

{WorkflowActionMenuItems(HUMAN_INPUT_ACTIONS, theme, handleCreateStep)}

Example of correct usage:

<WorkflowActionMenuItems 
  actions={HUMAN_INPUT_ACTIONS} 
  theme={theme} 
  onCreateStep={handleCreateStep} 
/>

This pattern maintains React’s declarative nature and ensures components integrate properly with React’s rendering system and developer tools.

---

Markdown formatting consistency

Ensure consistent markdown formatting in documentation by wrapping all technical terms, API names, property names, and code-related content in backticks. This improves readability and maintains visual consistency across documentation.

Examples of proper formatting:

• Property names: classNames, styles, href, variant
• API attributes: aria-*, shape="round"
• Technical terms: @layer antd

Common mistakes to avoid:

• Writing classNames instead of classNames
• Using plain text for property values like variant="filled" instead of variant="filled"
• Missing backticks around technical terms in changelog entries

This standard ensures that code-related content is visually distinguished from regular text, making documentation easier to scan and understand for developers.

---

Extract reusable components

Eliminate code duplication by extracting common functionality into shared utilities, constants, and base classes. When you notice repeated code patterns, logic, or constants across multiple files, consolidate them into reusable components.

Key practices:

• Extract common classes into separate files (like BaseHandler for shared method overrides)
• Replace hardcoded values with shared constants (use LAYOUT_PREVIEW_CONTENT_PLACEHOLDER instead of inline HTML strings)
• Centralize logic into single functions (consolidate variable extraction into one place)
• Move parsing and utility functions to dedicated utility files
• Create shared DTOs and validation schemas to avoid duplication

Example:

// Before: Duplicated HTML template
const contentPlaceholder = '<div style="border: 1px dashed #E1E4EA;">...</div>';

// After: Shared constant
import { LAYOUT_PREVIEW_CONTENT_PLACEHOLDER } from '@novu/shared';
return body?.replace(regex, LAYOUT_PREVIEW_CONTENT_PLACEHOLDER);

This approach improves maintainability, reduces bugs from inconsistent implementations, and makes future changes easier by having a single source of truth.

---

Use descriptive names

Names should clearly describe what they represent or do, rather than how they’re implemented or using generic terms. Avoid abbreviations and use full, descriptive words that accurately reflect the purpose and behavior of the code element.

Key principles:

• Choose names that describe the actual purpose: _scrollToFirstSelectableDate instead of _checkOnCustomDaysDisplay
• Use full words instead of abbreviations: lineHeightFactor instead of lineHeight, avoid “hsw” for half_stroke_width
• Reflect the actual data type or behavior: ExpectedFrameConstraints instead of ExpectedFrameSize when returning constraints
• Use semantic accuracy over implementation details: traversalOwner instead of overlayPortalParent to avoid widget-layer concepts
• Follow language style guidelines: use text_frame in C++, avoid anonymous parameter names like _
• Apply conventional prefixes: k for constants (kSystemToolbarToggleDebounceThreshold), handle for callbacks (handleSystemHideToolbar)

Example of good descriptive naming:

// Bad: Generic and unclear purpose
void _checkOnCustomDaysDisplay() { ... }

// Good: Clearly describes what the function does
void _scrollToFirstSelectableDate() { ... }

// Bad: Abbreviation
final double hsw = half_stroke_width;

// Good: Full descriptive name
final double halfStrokeWidth = half_stroke_width;

This approach improves code readability and maintainability by making the codebase self-documenting through clear, purposeful naming.

---

Use descriptive names

Choose names that clearly and unambiguously describe their purpose rather than being overly generic or technical. Names should be self-documenting and immediately convey what the entity does or represents.

Key principles:

• Prefer descriptive names over generic ones: MAX_ANIMATION_DURATION instead of ANIMATION_TIMEOUT
• Choose contextual names for user-facing types: IgnoreUnknownProps instead of DeepStripStringIndexUnknown
• Method names should clearly indicate behavior: trackClasses instead of addClasses (which implies DOM manipulation)
• Follow the philosophy: “choose the shortest name that unambiguously and meaningfully describes a thing”

Examples:

// ❌ Generic or misleading names
const ANIMATION_TIMEOUT = 4000;
export type DeepStripStringIndexUnknown<T> = ...;
addClasses(details: AnimationDetails, classes: string[]): void;

// ✅ Descriptive and clear names  
const MAX_ANIMATION_DURATION = 4000;
export type IgnoreUnknownProps<T> = ...;
trackClasses(details: AnimationDetails, classes: string[]): void;

Avoid names that could confuse developers about the actual functionality. When in doubt, err on the side of being more descriptive rather than more concise.

---

API evolution strategy

When evolving APIs, design for extensibility and provide clear migration paths to maintain backward compatibility while improving developer experience.

Key principles:

1. Design for future extensibility: Wrap parameters in objects rather than using simple types when future expansion is likely. For example, prefer (info: { props }) => Result over (props) => Result to allow adding additional context later without breaking changes.

2. Provide clear deprecation paths: When replacing APIs, mark old ones as deprecated with clear migration instructions and warnings. Use strikethrough formatting in documentation: ~~oldAPI~~ with replacement guidance.

3. Avoid temporary APIs: Don’t introduce new APIs that will be deprecated soon. If a better design is coming in the next major version, wait for it rather than creating intermediate APIs that add confusion.

4. Standardize naming across components: When introducing new patterns, apply them consistently. For example, unifying destroyTooltipOnHide, destroyPopupOnHide, and destroyOnClose to a single destroyOnHidden pattern across all components.

Example of good API evolution:

// Before: Simple parameter
filterOption: (inputValue, option): boolean

// After: Extensible object wrapper  
filterOption: (inputValue, option, direction: 'left' | 'right'): boolean

// Documentation shows both with clear migration path
| ~~vertical~~ | 排列方向，与 `orientation` 同时存在，以 `orientation` 优先 | boolean | `false` | 5.21.0 |
| orientation | 排列方向 | `horizontal` \| `vertical` | `horizontal` |  |

This approach ensures APIs can evolve gracefully while giving developers clear guidance on migration paths and preventing confusion from temporary or inconsistent naming patterns.

---

Prevent component re-mounting

Maintain stable component structure to prevent unnecessary re-mounting and unmounting of child components. Conditional rendering that changes component tree structure can cause child components to lose state and trigger mount/unmount cycles, breaking components with mount effects.

Use techniques like refs to track rendering state, stable Context providers, and consistent component tree structure. Avoid patterns that conditionally return different component types or structures based on state changes.

Example of problematic pattern:

const LazyComponent = ({ children, ...props }) => {
  const [lazy, setLazy] = React.useState(true);
  if (lazy) {
    return (
      <div onMouseEnter={() => setLazy(false)}>
        {children}
      </div>
    );
  }
  return <InternalTooltip {...props}>{children}</InternalTooltip>;
};

Better approach using refs to maintain structure:

const needWrapMotionProviderRef = React.useRef(false);
needWrapMotionProviderRef.current = needWrapMotionProviderRef.current || motion === false;

if (needWrapMotionProviderRef.current) {
  return <MotionProvider motion={motion}>{children}</MotionProvider>;
}

This ensures components don’t re-mount when conditions change, preserving component state and avoiding performance issues.

---

Use semantic descriptive names

Choose variable, function, and type names that clearly communicate their purpose, source, and context. Names should be self-documenting and avoid ambiguity or conflicts with existing identifiers.

Key principles:

• Use specific, descriptive names over generic ones (e.g., formItemName instead of defaultName, ButtonClassNamesType instead of generic Partial<Record<...>>)
• Avoid naming conflicts by using distinct aliases when necessary (e.g., cls for classnames utility vs classNames for semantic props)
• Maintain consistency across similar components (e.g., use iconPosition consistently rather than mixing iconPos and iconPosition)
• Prefer names that don’t require users to understand complex internal relationships

Example:

// ❌ Generic and potentially confusing
const defaultName = useId();
classNames?: Partial<Record<ButtonSemanticName, string>>;

// ✅ Semantic and descriptive  
const randomId = useId();
const defaultName = formItemName || randomId;
classNames?: ButtonClassNamesType;

// ❌ Naming conflict
import classNames from 'classnames';
// ... later in code
<div classNames={props.classNames} />

// ✅ Clear distinction
import cls from 'classnames';
// ... later in code  
<div className={cls(...)} classNames={props.classNames} />

---

Use reactive signal patterns

Prefer Angular’s reactive signal patterns over manual subscription management and imperative approaches. Use signals directly in templates without calling getters, convert observables to signals with toSignal(), and maintain reactive data flow throughout your application.

Key practices:

• In templates, reference signals directly: [(checked)]="mySignal" not [(checked)]="mySignal()"
• Convert observables to signals with toSignal() for reactive data that updates over time
• Use toSignal(router.events.pipe(map(() => !!router.getCurrentNavigation()))) instead of manual subscription management for navigation state
• Avoid creating unnecessary signals just to trigger effects - work directly with observables when appropriate

Example of preferred reactive pattern:

@Component({
  template: `
    @if (loading()) {
      <div>Loading...</div>
    }
    <div [class.admin]="isAdmin" [class.dense]="density() === 'high'">
  `
})
export class MyComponent {
  private route = inject(ActivatedRoute);
  private router = inject(Router);
  
  // Convert observable to signal for reactive updates
  private data = toSignal(this.route.data);
  user = computed(() => this.data()?.user as User);
  
  // Use toSignal for navigation state
  loading = toSignal(
    this.router.events.pipe(
      map(() => !!this.router.getCurrentNavigation())
    ),
    { initialValue: false }
  );
  
  // Direct signal usage in two-way binding
  isAdmin = signal(false);
  density = signal<'normal' | 'high'>('normal');
}

This approach provides better performance, cleaner code, and leverages Angular’s reactive primitives effectively.

---

Algorithm precision handling

Choose algorithms that handle edge cases and mathematical precision correctly to avoid subtle bugs and unexpected behavior.

When implementing algorithms, prioritize mathematical soundness and robust edge case handling over apparent simplicity. Use established mathematical formulas and precise operations rather than approximations that may fail in corner cases.

Key practices:

• Use substring() instead of split() for string processing when you need precise control: currentLabel.substring(baseLabel.length) avoids issues when the base pattern appears multiple times
• Apply proper unit conversions with mathematical constants: event.rotation = (double)state->rotation * (M_PI / 180) for degrees to radians
• Handle floating-point precision in division operations: use lerpValue.round() after render-level calculations rather than redundant division-based rounding
• Validate all edge cases in algorithms, especially zero values and boundary conditions: check for metrics.physical_width == 0 and constraint relationships
• Fix mathematical formulas to use correct operations: (math.max(first.bottom, second.bottom) - math.min(first.top, second.top)) for proper area calculations

The goal is to prevent runtime failures and visual glitches caused by algorithmic edge cases that surface only under specific conditions. Invest time in understanding the mathematical properties of your algorithms and test boundary conditions thoroughly.

---

Avoid reactive over-engineering

Choose the simplest React primitive that meets your requirements rather than reaching for complex reactive patterns. Avoid useEffect when useState, useMemo, or useCallback would suffice. If you find yourself using useEffect to copy data from one state to another state, it’s a sign you should restructure your component’s state management.

Prefer direct approaches over unnecessary reactive complexity:

• Use useState for simple state management
• Use useMemo for derived values instead of useEffect + useState
• Use useCallback for stable function references instead of useEffect dependencies
• Reserve useEffect for true side effects like API calls, DOM manipulation, or cleanup

Example of over-engineering:

// Avoid: Using useEffect to derive state
const [count, setCount] = useState(0);
const [doubledCount, setDoubledCount] = useState(0);

useEffect(() => {
  setDoubledCount(count * 2);
}, [count]);

// Prefer: Using useMemo for derived values
const [count, setCount] = useState(0);
const doubledCount = useMemo(() => count * 2, [count]);

This approach reduces complexity, improves performance, and makes component logic more predictable and easier to debug.

---

Handle optional values safely

Always provide safe defaults or fallbacks when working with optional or potentially undefined values. Avoid using non-null assertion operators (!) on optional parameters, and ensure proper handling in type checking and value merging scenarios.

Key practices:

• Use default objects instead of non-null assertions: val(info || { props: {} }) instead of val(info!)
• Order type checks to handle undefined cases first: check for object & not null, then boolean, then provide defaults
• Provide fallbacks for missing values: color: var(--ant-tooltip-color, ${tooltipColor}) instead of assuming the CSS variable exists
• Skip undefined values in object merging to preserve existing values rather than overwriting with undefined

Example:

// ❌ Dangerous - assumes info exists
return val(info!) as T;

// ✅ Safe - provides default
return val(info || { props: {} as Props }) as T;

// ❌ No fallback for missing CSS variable  
color: 'var(--ant-tooltip-color)',

// ✅ Provides fallback
color: `var(--ant-tooltip-color, ${tooltipColor})`,

This prevents runtime errors and ensures predictable behavior when dealing with optional or missing values.

---

Future-proof configuration defaults

When designing configuration options, avoid hardcoded values and ensure defaults can be changed in future versions without breaking existing code. Make boolean flags negatable so users can opt out when defaults change, avoid ambiguous null vs empty configuration states, and provide clear migration paths for deprecated options.

Key practices:

• Make boolean flags negatable even if currently only one direction is useful: addFlag('enable-feature', negatable: true) allows future default changes
• Avoid hardcoded opinionated values like min/max ranges - make them configurable properties instead
• Distinguish between null (not set) and empty (explicitly disabled) configuration states to avoid ambiguity
• When deprecating configuration options, provide clear messaging about alternatives and timeline for removal

Example of good configuration design:

// Good: Negatable flag allows future default changes
addFlag('enable-gradle-managed-install', negatable: true)

// Good: Configurable properties instead of hardcoded values  
class ProgressBarConfig {
  final double minValue;
  final double maxValue; 
  // Instead of hardcoded setAttribute('aria-valuemin', "0")
}

// Good: Clear distinction between states
if (config != null && config.enabled) {
  // Feature explicitly enabled
} else if (config != null && !config.enabled) {
  // Feature explicitly disabled  
} else {
  // Feature not configured, use default behavior
}

This approach ensures configuration systems remain flexible and maintainable as requirements evolve, while providing clear upgrade paths for users.

---

Enforce CI workflow gates

Establish and enforce proper CI/CD workflow gates to maintain code quality and release safety. This includes preventing direct commits to protected branches and validating CI status before releases.

Key practices:

1. Branch Protection: Avoid direct commits to master/main branches. Use feature branches and pull requests instead: git checkout -b feature-branch rather than committing directly to master.

2. Release Gating: Implement proper CI validation before releases. When CI is pending, either wait for completion or implement fallback validation (like running local CI checks) rather than bypassing all checks.

3. Risk Assessment: When considering CI bypasses, evaluate alternatives such as checking only critical CI jobs (e.g., artifact builds) or requiring local validation as a safety net.

Example from release script:

if (data.state === 'pending') {
  const shouldSkip = await confirm({
    message: '是否要跳过 CI 检查继续发布？',
    default: false,
  });
  
  if (!shouldSkip) {
    showMessage('已取消发布，请等待 CI 完成后再试', 'fail');
    process.exit(1);
  }
  // Consider running local CI as fallback validation
}

This approach balances development velocity with code quality by ensuring proper workflow gates are respected while providing escape hatches for legitimate edge cases.

---

Centralize shared configurations

Avoid duplicating configuration values across multiple files. Instead, define shared configurations in centralized locations and import them where needed. This prevents inconsistencies and makes configuration management more maintainable.

When the same configuration values are needed in multiple files, create a single source of truth rather than hardcoding values in each location. For example, instead of defining connector lists directly in test files:

// Avoid: Hardcoded in test file
const UCS_SUPPORTED_CONNECTORS = ["authorizedotnet"];

Use centralized configuration:

// Preferred: Import from centralized config
import { UCS_SUPPORTED_CONNECTORS } from "../../configs/Payment/Utils.js";

Similarly, for timeout values and other environment-specific settings, maintain consistency by using the same configuration source across related files. This approach reduces the risk of configuration drift and makes updates easier to manage.

---

explicit database constraints

Be explicit about database constraints and avoid relying on database-level defaults. Always specify NOT NULL constraints where appropriate and let the application layer handle default values rather than the database schema. Use appropriate primary key strategies like SERIAL for auto-incrementing IDs.

This approach gives the application more control over data validation and ensures schema intentions are clear to all developers.

Example:

-- Avoid this - implicit nullability and database defaults
CREATE TABLE user_session (
    id VARCHAR(64) PRIMARY KEY,
    created_at TIMESTAMP DEFAULT now()
);

-- Prefer this - explicit constraints and application-controlled defaults  
CREATE TABLE user_session (
    id SERIAL PRIMARY KEY,
    session_id VARCHAR(128) NOT NULL,
    created_at TIMESTAMP NOT NULL
);

---

validate disabled state accessibility

When UI components with interactive elements (like buttons with href attributes) are disabled, ensure they maintain proper accessibility standards and don’t create security vulnerabilities. Disabled states should properly prevent user interaction while maintaining clear visual and programmatic indication of their state.

Improperly handled disabled states can lead to security issues where users might interact with elements that should be non-functional, potentially bypassing intended security controls or creating confusing user experiences that could be exploited.

Example from the discussion:

- 🐞 Fix accessibility issue when Button `href` is disabled.

Always verify that disabled interactive components:

• Properly prevent click/navigation events
• Maintain appropriate ARIA attributes
• Provide clear visual indication of disabled state
• Don’t create accessibility barriers for screen readers

---

Control focus and suspense

When implementing React hooks around navigation focus or React Suspense:

1) Treat focus/mount as distinct

• If you use useFocusEffect to run data refetches, remember the callback also runs on initial mount. Skip the first run when appropriate.
• Effects clean up when the screen/component goes out of focus.

2) For Suspense + prefetch, don’t “prefetch with suspense”

• If the goal is to warm the cache without extending the current Suspense fallback, use dedicated prefetch hooks (e.g., usePrefetchQuery / usePrefetchInfiniteQuery) rather than forcing suspense queries just to prefetch.

3) Avoid re-renders for non-UI-affecting query observers

• When you mount a query only to trigger background fetching (and not to render its result), suppress observer-triggered updates (e.g., notifyOnChangeProps: []).

4) Don’t expect placeholderData to work with useSuspenseQuery

• With suspense, loading UI is handled by Suspense/ErrorBoundary; use startTransition when changing query keys to avoid unwanted fallback churn.

Example (focus refetch with correct skip, plus cache-warming prefetch without suspense):

import { useFocusEffect } from '@react-navigation/native'
import { useQueryClient } from '@tanstack/react-query'

function useRefreshOnFocus(refetch: () => Promise<unknown>) {
  const queryClient = useQueryClient()

  useFocusEffect(
    // If you keep local “first run” logic, ensure you skip the initial mount run.
    (callback) => {
      // callback pattern used by React Navigation; you can also use a ref.
      let isFirst = true

      const run = async () => {
        if (isFirst) {
          isFirst = false
          return
        }
        // Prefer explicit query behavior rather than always invoking refetch()
        queryClient.refetchQueries({ queryKey: ['posts'], stale: true, type: 'active' })
      }

      run()
      return callback()
    },
    [queryClient]
  )
}

Key checklist before approving PRs:

• Does useFocusEffect logic explicitly handle the initial mount run?
• Do you use prefetch-only hooks for Suspense prefetching (not suspense queries)?
• Are “background-only” queries preventing unnecessary re-renders (notifyOnChangeProps: [])?
• Are you using startTransition for query-key updates instead of relying on placeholderData with useSuspenseQuery?

---

Choose optimal algorithms

When implementing functionality, carefully evaluate and select the most efficient algorithmic approaches for data processing, pattern matching, and operations. Consider computational complexity and performance implications of different approaches.

Key principles:

• Use built-in optimized operations like flatten() instead of manual clone-and-map chains
• Prefer pattern matching over boolean flag checks for cleaner branching logic
• Select appropriate algorithms for specific use cases (e.g., ID generation, deserialization)
• Avoid unnecessary data cloning when more efficient alternatives exist

Example of applying pattern matching instead of boolean checks:

// Instead of:
let is_mca_connector_type_payout = matches!(mca.connector_type, enums::ConnectorType::PayoutProcessor);
if is_mca_connector_type_payout {
    // handle payout logic
} else {
    // handle payment logic  
}

// Use direct pattern matching:
match mca.connector_type {
    enums::ConnectorType::PayoutProcessor => {
        // handle payout logic
    }
    _ => {
        // handle payment logic
    }
}

This approach reduces intermediate variables, improves readability, and makes the algorithmic flow more explicit. Always consider the computational complexity and choose the approach that best balances performance, maintainability, and clarity.

---

Optimize database queries

Structure database queries and schemas for optimal performance by avoiding nullable fields when possible, organizing query conditions efficiently, and using targeted indexes.

Key practices:

1. Avoid nullable fields for performance: Use default values instead of nullable fields, especially in ClickHouse where non-null values perform better: ```typescript // Preferred severity: { type: CHLowCardinality(CHString(‘none’)) } critical: { type: CHBoolean(false) }

// Instead of severity: { type: CHNullable(CHString()) } critical: { type: CHNullable(CHBoolean()) }

2. **Structure conditions to minimize OR operations**: Group related conditions into arrays rather than chaining multiple OR statements:
```typescript
// Preferred - cleaner and more performant
const snoozedCondition: Array<MessageQuery> = [];
if (query.snoozed === false) {
  snoozedCondition.push({ snoozedUntil: { $exists: false } }, { snoozedUntil: null });
}

// Instead of multiple OR statements in the main query
requestQuery.$or = [{ snoozedUntil: { $exists: false } }, { snoozedUntil: null }];

1. Use partial indexes for filtered queries: Apply partial filter expressions to create more efficient indexes for specific use cases:

   // Targeted index with partial filtering
   messageSchema.index(
     {
    _subscriberId: 1,
    _environmentId: 1,
    read: 1,
    archived: 1,
    seen: 1,
    createdAt: -1,
     },
     {
    name: 'in_app_messages_count',
    partialFilterExpression: { channel: 'in_app' },
     }
   );
   

This approach improves query performance, reduces index size, and ensures better database resource utilization across different database systems.

---

Lockfile Change Hygiene

Lockfiles (e.g., pnpm-lock.yaml) are configuration artifacts and should only change when the dependency configuration (package.json / workspace manifests) changes. If there are no package.json changes, do not commit lockfile updates; treat any lockfile-only diffs as accidental/experimental output and revert them.

How to apply:

• Before creating a PR, check what changed:
  • If only pnpm-lock.yaml changed (or shows unrelated experiment sections) and no package.json/package workspace manifests changed, revert pnpm-lock.yaml.
• If you need to test dependency resolution, do it locally and ensure the working tree doesn’t introduce lockfile-only diffs into the PR.

Example rule of thumb:

• ✅ package.json changed → lockfile may update and should be committed.
• ❌ package.json did not change → revert pnpm-lock.yaml so the PR contains only intentional configuration changes.

---

Extract methods for clarity

Break down large methods and extract repeated code patterns into smaller, focused methods or getters to improve readability and maintainability.

When you encounter large conditional blocks, complex logic, or repeated patterns, consider extracting them into well-named private methods or getters. This makes the code easier to understand, test, and modify.

Examples of when to extract:

1. Large if/else blocks: Instead of having complex conditional logic inline, extract it into descriptive methods: ```dart // Before: Large conditional block if (hasNewline) { // 20+ lines of complex logic } else { // 15+ lines of different logic
   }

// After: Extract into focused methods final Path path = hasNewline ? _createMultilineIndicatorPath() : _createSingleLineIndicatorPath();

2. **Repeated patterns**: When the same logic appears multiple times, extract it into a reusable method:
```dart
// Before: Repeated pattern
auto data_host_buffer = HostBuffer::Create(
    GetContext()->GetResourceAllocator(), GetContext()->GetIdleWaiter(),
    GetContext()->GetCapabilities()->GetMinimumUniformAlignment());
auto indexes_host_buffer = 
    GetContext()->GetCapabilities()->NeedsPartitionedHostBuffer()
        ? HostBuffer::Create(/* same parameters */)
        : data_host_buffer;

// After: Extract into helper method
auto [data_host_buffer, indexes_host_buffer] = createHostBuffers();

1. Complex conditions: Extract boolean logic into descriptive getters: ```dart // Before: Complex inline condition if (widget.separatorBuilder != null && index.isOdd) { // logic }

// After: Extract into getter bool get hasSeparators => widget.separatorBuilder != null; bool get isSeparator => hasSeparators && index.isOdd;

This practice reduces cognitive load, makes code self-documenting through method names, and creates natural boundaries for testing individual pieces of functionality.

---

## Build configuration consistency

<!-- source: angular/angular | topic: CI/CD | language: Markdown | updated: 2025-08-29 -->

Maintain consistent build and release configurations across the project by following established patterns and ensuring documentation accuracy. When implementing new build configurations or modifying existing ones, reference how similar components handle the same requirements to maintain uniformity.

For package distribution, follow the same inclusion/exclusion patterns as other packages in the monorepo. For build tooling, use standardized configurations and document version-specific requirements clearly. For release processes, prefer simpler, more reliable commands over complex multi-step operations.

Example of consistent release packaging:
```shell
# Prefer this simple approach
git archive HEAD -o ~/angular-source.zip

# Over complex multi-command approaches
rm -rf dist/ **/node_modules/ && zip -r ~/angular-source.zip * -x ".git/*" -x "node_modules/*"

This approach reduces the likelihood of configuration drift, makes troubleshooting easier, and ensures that build processes remain reliable and maintainable across different environments and team members.

---

React hook dependencies

Carefully manage dependencies in React hooks to avoid stale closures and ensure correct behavior. When using useCallback, useMemo, or useEffect, include all reactive values that the hook depends on in the dependency array, even if it affects stability.

Common issues to watch for:

• Stale closures where hooks capture outdated values from their first render
• Trading hook stability for correctness by omitting dependencies
• Complex state management in custom hooks that can lead to race conditions

Example of problematic stale closure:

const matchIndex = useMatch({ select: (match) => match.index })

const navigate = React.useCallback((options) => {
  // matchIndex here is stale - captured from first render
  const from = router.state.matches[matchIndex]?.fullPath
  return router.navigate({ from, ...options })
}, [router]) // matchIndex missing from deps

// Better: obtain fresh values inside the callback
const navigate = React.useCallback((options) => {
  const currentMatches = router.state.matches
  const from = currentMatches[currentMatches.length - 1]?.fullPath
  return router.navigate({ from, ...options })
}, [router])

For custom hooks with async operations, avoid useState for promises that can become stale in development mode. Instead, create promises only when needed:

// Problematic: promise created on every render
const [promise, setPromise] = useState(createPromise)

// Better: create promise only when blocking occurs
const blockerFn = async () => {
  const promise = new Promise((resolve) => {
    setResolver({ proceed: () => resolve(true) })
  })
  return await promise
}

Always prioritize correctness over performance optimizations like callback stability.

---

Centralize configuration management

Extract configuration state, feature flags, and version-dependent settings into dedicated services rather than hardcoding values or prop drilling through component hierarchies. This approach improves maintainability, testability, and allows for easier updates without code changes.

For global settings, use a centralized service:

// Instead of prop drilling
[signalGraphEnabled]="signalGraphEnabled()"
(showSignalGraph)="showSignalGraph.emit($event)"

// Use a settings service
@Injectable()
export class SettingsService {
  signalGraphEnabled = signal(false);
  // Other configuration properties
}

For version-dependent features, avoid hardcoded version strings:

// Instead of hardcoded versions
"Angular applications using version 21 and greater"

// Use configurable version requirements
"Angular applications using version {{minVersion}} and greater"

This pattern prevents configuration from being scattered across components and makes it easier to manage environment-specific settings, feature toggles, and version requirements from a single source of truth.

---

Explain non-obvious code

Add explanatory comments for any code that isn’t immediately self-explanatory, including magic numbers, implementation decisions, parameter purposes, and edge cases. This improves code maintainability and helps future developers understand the reasoning behind specific choices.

Key areas requiring explanation:

• Magic numbers and constants: Document how values were derived and their significance
• Parameter relationships: Explain dependencies, constraints, and edge case behavior
• Implementation decisions: Clarify why specific approaches were chosen
• Non-obvious logic: Add context for complex conditional statements or calculations
• Platform-specific behavior: Document differences across platforms or versions

// Bad: No explanation for magic numbers or logic
class MaterialTextSelectionControls extends TextSelectionControls {
  @override
  Offset getHandleAnchor(TextSelectionHandleType type, double textLineHeight) {
    return switch (type) {
      TextSelectionHandleType.collapsed => const Offset(_kHandleSize / 2.18, -4.5),
      // ...
    };
  }
}

// Good: Clear explanations provided
class MaterialTextSelectionControls extends TextSelectionControls {
  @override
  Offset getHandleAnchor(TextSelectionHandleType type, double textLineHeight) {
    return switch (type) {
      // These values were eyeballed to match a physical Pixel 9 running Android 16,
      // which horizontally centers the anchor 1 pixel below the cursor.
      TextSelectionHandleType.collapsed => const Offset(_kHandleSize / 2.18, -4.5),
      // ...
    };
  }
}

// Bad: Unclear parameter purpose
void hideToolbar([bool hideHandles = true, Duration? toggleDebounceDuration]);

// Good: Parameter purpose documented
/// Hides the text selection toolbar.
///
/// By default, [hideHandles] is true, and the toolbar is hidden along with its
/// handles. If [hideHandles] is set to false, then the toolbar will be hidden
/// but the handles will remain.
///
/// When [toggleDebounceDuration] is non-null, a subsequent call to [toggleToolbar]
/// should not show the toolbar unless a duration threshold has been exceeded.
void hideToolbar([bool hideHandles = true, Duration? toggleDebounceDuration]);

This practice is especially important for Flutter framework code where implementation details affect developer experience and debugging.

---

Extract common patterns

When you encounter repeated code patterns, conditional logic within loops, or similar implementations across components, extract them into reusable utilities or common styles. This improves maintainability, reduces bundle size, and makes the codebase more consistent.

Key practices:

• Extract repeated styles into common utilities (e.g., blur effects, reset functions)
• Remove conditional checks from loops by handling special cases separately
• Flatten function parameters instead of using object destructuring to reduce bundle size
• Use direct comparisons instead of array methods like includes() for simple checks
• Choose implementation approaches that support future extensibility

Example:

// Instead of conditional logic in loop:
items.forEach(item => {
  if (item.type === 'special') {
    // special handling
  }
  // regular processing
});

// Extract special cases:
const specialItems = items.filter(item => item.type === 'special');
const regularItems = items.filter(item => item.type !== 'special');
specialItems.forEach(handleSpecialItem);
regularItems.forEach(handleRegularItem);

This approach makes code more readable, testable, and often results in better performance and smaller bundle sizes.

---

Make errors explicit

Always make error conditions explicit and visible rather than hiding them through silent failures, default return values, or unchecked operations. This includes validating results before use, using assertions for invalid states, and logging unexpected conditions.

Key practices:

• Check results of operations like find() before dereferencing to prevent crashes
• Use assertions instead of returning default values to hide errors: assert(scrollOffset.isFinite && itemExtent.isFinite) rather than return 0
• Add error logging for conditions that shouldn’t happen: FML_LOG(ERROR) << "Unexpected condition"
• Throw clear errors for unexpected duplicate events rather than silently ignoring them

Example of making errors explicit:

// Bad: Hides error by returning default value
if (itemExtent > 0.0) {
  final double actual = scrollOffset / itemExtent;
  if (!actual.isFinite) {
    return 0; // Silently hides the error
  }
}

// Good: Makes error explicit with assertion
assert(scrollOffset.isFinite && itemExtent.isFinite, 
       'scrollOffset and itemExtent must be finite');
if (itemExtent > 0.0) {
  final double actual = scrollOffset / itemExtent;
}

This approach helps developers identify issues during development and provides better debugging information when problems occur.

---

Avoid unnecessary memoization

Memoization (useMemo, useCallback, React.memo) should only be used when the performance benefits outweigh the overhead costs. Avoid memoization in these scenarios:

1. Simple computations: For basic logic like conditional assignments or simple object property access, the memoization overhead often exceeds the computation cost.

2. Incomplete dependency arrays: When you can’t reliably maintain all dependencies, memoization becomes error-prone and can cause stale closures or missed updates.

3. Object/array dependencies: When dependencies are objects or arrays that frequently change reference (like props), memoization is often ineffective.

Example of unnecessary memoization to avoid:

// ❌ Avoid - simple conditional logic doesn't need memoization
const closablePlacement = React.useMemo(() => {
  if (closable === false) return undefined;
  if (closable === undefined || closable === true) return 'start';
  return closable?.placement === 'end' ? 'end' : 'start';
}, [closable]);

// ✅ Better - direct computation is faster
const closablePlacement = closable === false ? undefined : 
  (closable === undefined || closable === true) ? 'start' :
  (closable?.placement === 'end' ? 'end' : 'start');

When to use memoization:

• Expensive computations (complex calculations, data transformations)
• Stable dependencies that rarely change
• Components that render frequently with the same props

Remember: “Sometimes memoization indeed causes negative optimization” - measure performance impact rather than assuming memoization always helps.

---

Add explanatory comments

Code should include explanatory comments when the purpose, behavior, or context is not immediately clear from reading the code itself. This is especially important for:

• Non-obvious implementation decisions: When code deviates from expected patterns or removes common safeguards, explain why.
• Complex data structures: Interface fields, especially those with specific usage patterns or constraints, should be documented.
• Important behavioral details: When functionality has side effects or specific requirements that affect how it should be used.
• Context-dependent logic: Code that requires understanding of broader system behavior or migration patterns.

Example:

// Before - unclear why early return was removed
if (ngDevMode) {
  // ... complex logic
}

// After - explains the reasoning
if (ngDevMode) {
  // Note: Early return removed to ensure proper cleanup in all code paths
  // ... complex logic
}

// Before - unclear field purpose
export interface ProjectedSignalNode {
  propertyNode: ReactiveNode | undefined;
  lastProperty: PropertyKey | undefined;
}

// After - explains field usage
export interface ProjectedSignalNode {
  // Only used when the projectedSignal key argument is reactive
  propertyNode: ReactiveNode | undefined;
  // Tracks the last accessed property for change detection
  lastProperty: PropertyKey | undefined;
}

Comments should focus on the “why” rather than the “what” - explaining the reasoning, constraints, or important context that future developers need to understand when modifying or using the code.

---

Eliminate redundant operations

Identify and remove unnecessary operations that impact performance, including redundant checks, duplicate calculations, unnecessary allocations, and redundant code paths. This is especially critical in hot paths like widget rebuilds, message handling, and frequently called methods.

Examples of redundant operations to avoid:

1. Redundant null/validation checks: Remove checks that are already handled by the called function: ```dart // Avoid - parseFloat already handles NaN if (parsed != null && !parsed.isNaN) { styleProperty = parsed; }

// Better - let parseFloat handle it styleProperty = parsed;

2. **Unnecessary allocations in hot paths**: Avoid creating new objects on every call, especially in message handlers or frequent operations:
```dart
// Avoid - allocates list on every message
final List<Handler> handlers = List<Handler>.from(_messageHandlers);

// Better - use debug assertions to prevent modification during iteration

1. Expensive operations during rebuilds: Move costly operations like ancestor chain walks out of build methods: ```dart // Avoid - walks ancestor chain every rebuild if (Navigator.maybeOf(context, rootNavigator: true) != this) {

// Better - move to didChangeDependencies

4. **Duplicate calculations**: Restructure code to avoid computing the same value multiple times:
```dart
// Avoid - computes lerpValue twice
double lerpValue = ui.lerpDouble(widget.min, widget.max, value)!;
if (widget.divisions != null) {
  lerpValue = (lerpValue * widget.divisions!).round() / widget.divisions!;
}

// Better - use if-else with single computation per path

1. Redundant code paths: Remove unnecessary processing when simpler approaches achieve the same result, especially when API changes make certain fallback logic obsolete.

---

Thread safety synchronization

Ensure proper synchronization when accessing shared data structures and coordinate operations across multiple threads to prevent race conditions.

Key practices:

1. Protect shared data with mutexes: When modifying shared data structures, use appropriate locking mechanisms: ```cpp // Before: Unprotected access expected_frame_constraints_.erase(view_id);

// After: Protected with mutex std::scoped_lock<std::mutex> lock(resize_mutex_); expected_frame_constraints_.erase(view_id);

2. **Clean up before destruction**: Unregister handlers and cleanup resources before destroying objects to avoid receiving callbacks during destruction:
```cpp
@override
void destroy() {
  if (_destroyed) return;
  
  // Unregister BEFORE destroying to avoid race conditions
  _owner.removeMessageHandler(this);
  _Win32PlatformInterface.destroyWindow(getWindowHandle());
  _destroyed = true;
  _delegate.onWindowDestroyed();
}

1. Consolidate multi-threaded operations: When operations span multiple threads, consider consolidating critical sections to a single thread or use proper coordination. As noted in platform view embedding: “We still do it in 2 different threads… Those 2 threads would be in a race condition.” Consider posting all related operations to the same thread:

   // Consolidate to platform thread
   task_runners_.GetPlatformTaskRunner()->PostTask([&, jni_facade = jni_facade_]() {
     HideOverlayLayerIfNeeded();
     jni_facade->applyTransaction();
   });
   

Race conditions between threads processing different frame states can lead to inconsistent UI state and are difficult to debug. Always consider the threading model when designing APIs that modify shared state.

---

Minimize API test data

Keep API test configurations lean by including only the fields necessary for the specific test scenario. Avoid bloated request/response objects that contain extraneous data, and resist creating duplicate API test patterns when existing ones can be reused.

This practice improves test maintainability, reduces confusion, and makes test intentions clearer. Before adding new API test configurations, evaluate whether existing patterns can be adapted or if all included fields are truly required for the test case.

Example of bloated vs. minimal API test data:

// Bloated - includes unnecessary fields
UCSConfirmMandate: {
  Request: {
    confirm: true,
    customer_id: "Customer123_UCS",
    payment_type: "setup_mandate",
    // ... many other fields that may not be needed for this specific test
    all_keys_required: true,
    metadata: {
      ucs_test: "recurring_payment",
      payment_sequence: "recurring",
    },
  }
}

// Minimal - only necessary fields
UCSConfirmMandate: {
  Request: {
    confirm: true,
    customer_id: "Customer123_UCS",
    payment_type: "setup_mandate",
  }
}

When creating new API test commands or configurations, first check if existing patterns can handle your use case to avoid maintenance overhead and confusion.

---

Centralize Complex Regex

When adding validation logic that uses complex literals (especially RegExp), keep it consistent and maintainable:

• Don’t scatter regex literals inline across files/branches—move them to a shared constant block near other related regexes.
• If the regex is too complex to be readable/reviewable, extract it into a named helper (e.g., isValidIpv6) so the parsing/intent is clear.
• Reuse the centralized constant/helper everywhere in the module; avoid creating unused helpers.
• If eslint/linter requires suppression for regex style, prefer refactoring to satisfy the linter, and only use eslint-disable when behavior is unchanged and the suppression is clearly justified.

Example (centralizing a slug regex):

// Regex constants near other regexes
const slugRegex = /^[a-z0-9]+(?:-[a-z0-9]+)*$/;

export function isSlug(value: string): boolean {
  return slugRegex.test(value);
}

// Reuse in validation instead of repeating the literal
// if (check.kind === "slug") { ... slugRegex ... }

This improves readability, reduces review/merge churn, and makes future tweaks to validation patterns less error-prone.

---

validate migration data comprehensively

Migration scripts must thoroughly validate data conditions and handle edge cases to ensure reliable data transformation. Always check for data existence before applying operations, properly handle duplicate records, and avoid migrating calculated or derived fields.

Key practices:

• Check data existence: Verify that related data exists before performing operations (e.g., “Should we update that site setting only when there are tag groups?”)
• Handle duplicates gracefully: Ensure migrations can continue when duplicates are found, returning existing records rather than failing
• Skip calculated fields: Exclude computed columns like first_unread_pm_at that should be recalculated rather than migrated
• Cover edge cases: Consider scenarios like missing seed data or schema evolution (e.g., custom palettes based on non-seeded built-in schemes)
• Manage schema changes: When fields are split or renamed, maintain backward compatibility and proper synchronization

Example of proper duplicate handling:

duplicate = DB.query_single(<<~SQL, name: name).first
  SELECT id from ai_personas where name = :name
SQL

if duplicate.present?
  duplicate  # Return existing record to continue migration
else
  # Create new record
end

This approach prevents migration failures and ensures data integrity across different migration scenarios and schema versions.

---

Avoid generic naming

Choose specific, descriptive names over generic ones for all identifiers including variables, functions, components, and test IDs. Generic names lack context and can cause confusion as the codebase grows. Names should clearly communicate their purpose and scope.

Examples of improvements:

• reference_id → trace_reference_id (adds context about what type of reference)
• ai → aiPhone or calAiPhone (specifies the AI functionality)
• 404-page → app-router-not-found-page (indicates the specific context)
• DeleteHistoryDialog → DeleteBookingDialog (clarifies what is being deleted)

When naming identifiers, ask yourself: “Will another developer understand the purpose and scope of this identifier without additional context?” If not, make the name more specific and descriptive.

---

Provide error feedback

Always provide clear user feedback when errors occur or operations fail, rather than allowing silent failures or showing disabled UI without explanation. This includes detecting existing error states, preventing validation errors through input sanitization, and displaying appropriate messages for failed operations.

Key practices:

• Replace silent failures with explicit error detection and user messaging
• Show warning messages instead of unexplained disabled UI elements
• Provide toast notifications for operations that can fail
• Sanitize inputs to prevent downstream validation errors
• Clear problematic form state proactively to avoid validation conflicts

Example from the discussions:

// Bad: Silent failure with disabled select
<Select isDisabled={isPending} />

// Good: Clear messaging about why functionality is unavailable  
{!userHasDefaultSchedule ? (
  <Alert severity="warning" title={t("view_only_edit_availability_not_onboarded")} />
) : (
  <Select isDisabled={isPending} />
)}

This prevents user confusion and ensures they understand why certain actions are unavailable or have failed.

---

Consistent null safety patterns

Apply null safety operators consistently throughout your code to prevent runtime errors and improve readability. Use the nullish coalescing operator (??) for default values, optional chaining (?.) for safe property access, and simplify null checks when semantically equivalent.

Key patterns to follow:

• Use ?? for default values: const crossAxis = options.crossAxisShift ?? true; instead of verbose if-statements
• Use ?. for safe navigation: topic?.tags || params?.tags and topic?.get?.("isPrivateMessage")
• Simplify falsy checks when appropriate: !userFields[siteField.id] instead of isEmpty(userFields[siteField.id]) when null/false are equivalent
• Apply these patterns consistently - if you use safe navigation in one place, consider if other similar accesses need it too

This prevents null reference exceptions while keeping code concise and readable. Be mindful that different null safety patterns serve different purposes - choose the right tool for each situation.

---

precise build targeting

Build targets should use specific file patterns rather than broad globs to improve build performance, clarity, and maintainability. Avoid capturing unnecessary files that can lead to build system constraints and complexity.

When defining build targets, be explicit about which files are actually needed rather than using overly broad patterns like glob(["**/*.ts"]). This prevents unintended dependencies, reduces build times, and makes the build configuration more understandable.

Example of improvement:

# Instead of broad globbing
srcs = glob(["**/*.ts"]),

# Use specific patterns
srcs = glob(["*.spec.ts"]),

Additionally, consider organizing BUILD files closer to the source files they target. If a build target primarily globs files from a specific subdirectory, it may be better to create a BUILD file in that subdirectory rather than managing it from a parent directory. This approach reduces complexity and makes the build structure more intuitive.

---

Safe configuration access

Always verify configuration properties exist before accessing them to prevent runtime errors. Configuration settings may not be available depending on installed plugins, enabled features, or user preferences.

Use appropriate safety patterns:

• For object properties: Use the in operator to check existence: "saml_enabled" in this.siteSettings
• For nested properties: Use optional chaining: this.site.default_dark_color_scheme?.id > 0
• For user preferences: Provide fallbacks: this.currentUser?.user_option?.timezone || moment.tz.guess()

This prevents crashes when accessing configuration that depends on optional plugins, feature flags, or user-specific settings that may not be present in all environments.

---

algorithm implementation trade-offs

When implementing algorithms, carefully evaluate trade-offs between built-in methods, custom implementations, and different algorithmic approaches. Consider factors like browser compatibility, performance characteristics, maintainability, and edge case handling.

Key considerations:

• Compatibility vs. Performance: Built-in methods may not be available in all target environments. For example, Array.findLast() requires Safari 15.4+, necessitating custom implementations for broader compatibility.
• Data Structure Handling: Choose appropriate data structures based on usage patterns. For FormData processing, always using arrays simplifies logic despite slight overhead, while conditional arrays add complexity but optimize common cases.
• String Processing Approaches: Consider regex vs. conditional logic based on complexity and performance needs. Regex may seem simpler but can introduce escaping issues and compilation overhead.

Example from the discussions:

// Custom implementation for compatibility
export function findLast<T>(
  array: ReadonlyArray<T>,
  predicate: (item: T) => boolean,
): T | undefined {
  for (let i = array.length - 1; i >= 0; i--) {
    const item = array[i]!
    if (predicate(item)) return item
  }
  return undefined
}

// vs. built-in (when available)
array.findLast(predicate)

Document the reasoning behind algorithmic choices to help future maintainers understand the trade-offs made.

---

Centralize workflow scheduling

Avoid scattering workflow scheduling logic across multiple handlers. Instead, create dedicated service methods for different workflow contexts to improve maintainability and reduce duplication.

When workflow scheduling logic becomes scattered across handlers, it leads to code duplication and makes the system harder to maintain. The solution is to centralize this logic in a dedicated WorkflowService with context-specific methods.

Problem: Multiple calls to scheduleWorkflowReminders scattered throughout handlers, with complex filtering logic duplicated across different files.

Solution: Create dedicated service methods for each workflow context:

// Instead of scattered calls across handlers
await scheduleWorkflowReminders({ evt, workflows: filteredWorkflows, ... });

// Use dedicated service methods
await WorkflowService.scheduleWorkflowsOnNewBooking({ 
  evt, 
  isFirstBooking, 
  isPaid, 
  ... 
});

await WorkflowService.scheduleWorkflowsOnConfirmation({ 
  evt, 
  isFirstBooking, 
  isPaid, 
  ... 
});

This approach encapsulates workflow orchestration logic, reduces duplication, and makes the codebase more maintainable by providing clear entry points for different workflow scenarios.

---

Use descriptive identifiers

Choose names that clearly communicate purpose and reduce cognitive load for future readers. Avoid generic, abbreviated, or ambiguous identifiers in favor of self-documenting ones.

Key principles:

• Variables: Use descriptive names that indicate content and purpose (@tags_with_synonyms instead of @synonym_target_tag_ids)
• Parameters: Make parameter names explicit about what they accept (post_or_post_id instead of post_id when accepting both Post objects and IDs)
• Methods: Include context when it aids clarity (update_category_read_restricted instead of update_read_restricted_flags)
• Constants: Use descriptive names over generic ones (NO_DESTINATION_COOKIE instead of NO_COOKIE)
• SQL aliases: Prefer readable aliases over cryptic abbreviations (mapped_categories instead of mc)

Example:

# Avoid: Generic parameter name that doesn't indicate flexibility
def reset_bumped_at(post_id = nil)
  post = post_id.is_a?(Post) ? post_id : Post.find(post_id)
end

# Prefer: Clear parameter name indicating it accepts both types
def reset_bumped_at(post_or_post_id = nil)
  post = post_or_post_id.is_a?(Post) ? post_or_post_id : Post.find(post_or_post_id)
end

The goal is to write code that reads like well-written prose, where the intent is immediately clear without requiring additional mental parsing or context switching.

---

contextual API parameters

Design APIs to provide contextual information and adapt behavior based on current usage context. Pass context objects to callbacks, compute derived attributes based on state, and generate appropriate options dynamically.

When designing component APIs, include context parameters that provide relevant state information to callback functions. This enables more intelligent behavior and better integration.

Example:

// Good: Provide context to callbacks
const notification = {
  context: { notification: props.notification } satisfies Parameters<AppearanceCallback['notification']>[0]
};

// Good: Compute derived attributes based on context
if (isEnhancedDigestEnabled && (isTextVariable || isUrlVariable)) {
  const aliasFor = resolveRepeatBlockAlias(
    isTextVariable ? (text ?? '') : (url ?? ''),
    editor,
    isEnhancedDigestEnabled
  );
  return commands.updateButton?.({ ...attrs, aliasFor: aliasFor ?? null });
}

// Good: Generate options based on variable context
const options = useMemo(() => {
  if (variableName.match(/^steps\..+\.events$/)) {
    return variables.filter((v) => v.name.startsWith('payload')).map((v) => ({ label: v.name, value: v.name }));
  }
  return [];
}, [variableName, variables]);

This approach makes APIs more intelligent and reduces the burden on API consumers to manually compute contextual information.

---

Choose appropriate algorithms

Select algorithms and data structures that match the problem domain and access patterns rather than using convenient but suboptimal approaches. For complex parsing tasks, use proper AST-based parsing instead of regex. Design data structures that align with how data will be accessed and modified.

For example, when parsing structured expressions:

// Avoid regex for complex parsing
const objectLiteralRegex = /^\s*\{\s*([^}]*)\s*\}\s*$/;

// Use AST-based parsing instead
const parsed = new HtmlParser().parse(template, '', {
  tokenizeExpansionForms: true,
  tokenizeBlocks: true,
  preserveLineEndings: true,
});

When designing data structures, consider access patterns:

// Instead of complex nested mappings
private _hostNodes = new Map<Node, Map<Node, Node[]>>();

// Consider simpler structures that match usage
private _hostNodes = new Map<Node, { insertionPoint: Node; styles: Node[] }>();

Create consistent interfaces for strategy patterns to eliminate conditional logic:

// Update strategies to share interface with consistent parameters
interface Strategy {
  supports(element: Element): boolean;
  build(element: Element, index?: number): ComponentTreeNode[];
}

This approach reduces complexity, improves maintainability, and ensures algorithms scale appropriately with data size and usage patterns.

---

Test observable behavior

Focus on testing what users see and experience rather than internal implementation details. Tests should verify the actual behavior that matters to users, not how the code achieves that behavior internally.

Why this matters:

• Tests remain valid when implementation changes
• Avoids the need for @visibleForTesting annotations
• Creates more maintainable and meaningful tests
• Catches real bugs that affect user experience

Instead of testing implementation details:

// Bad: Testing controller value directly
expect(controller.value, closeTo(0.5, 0.01));

// Bad: Adding @visibleForTesting just for tests
@visibleForTesting
Set<Color> distinctVisibleOuterColors() { ... }

Test observable behavior:

// Good: Test what the user sees - the actual progress indicator rendering
expect(
  find.byType(LinearProgressIndicator),
  paints
    ..rect(rect: expectedBackgroundRect)
    ..rect(rect: expectedProgressRect)
);

// Good: Test animation effects users can observe
expect(
  find.byType(FadeTransition),
  paints..opacity(0.5) // Test the actual fade effect
);

Key practices:

• Test visual output using paints matchers
• Verify user interactions and their effects
• Test accessibility announcements and semantic properties
• Use existing public APIs to access test state
• Mock platform channels to test system integrations

This approach creates tests that are both more robust and more meaningful, as they verify the actual user experience rather than internal code structure.

---

Optimize expensive operations

Minimize performance impact of costly operations through strategic ordering, batching, and avoiding unnecessary work. Place cheaper conditional checks before expensive operations to enable early exits, batch DOM manipulations using requestAnimationFrame to reduce repaints, and ensure optimizations don’t create additional computational overhead.

For conditional checks, evaluate lightweight operations first:

// Good: Check cheap operations first
if (ele.scrollWidth > ele.clientWidth || ele.scrollHeight > ele.clientHeight) {
  return true;
}
// Only execute expensive DOM operations if needed
const rect = ele.getBoundingClientRect();
const childRect = childDiv.getBoundingClientRect();

For DOM operations, use requestAnimationFrame to batch updates:

let isScheduled = false;

const adjustElementWidth = (width: number, wrapper: HTMLElement): void => {
  if (!isScheduled) {
    isScheduled = true;
    requestAnimationFrame(() => {
      wrapper.style.width = `${width + ELEMENT_GAP}px`;
      isScheduled = false;
    });
  }
};

Verify that optimizations actually reduce work rather than creating additional iterations or computations. Profile performance-critical code paths to ensure improvements deliver measurable benefits.

---

comprehensive security checks

Ensure that security checks for authorization, authentication, and information disclosure are comprehensive and consistently applied across all contexts, rather than being conditional on specific scenarios or implementation details.

Security measures should not be limited by contextual conditions. For example, don’t restrict admin/owner permission checks to only team event types - apply them universally. Similarly, ensure that redirects and URL handling don’t inadvertently expose sensitive information like private booking paths.

Example of comprehensive authorization:

// Instead of conditional checks:
if (eventType.teamId) {
  const hasTeamOrOrgPermissions = await checkTeamOrOrgPermissions(userId, eventType.teamId);
}

// Apply comprehensive checks regardless of context:
const hasTeamOrOrgPermissions = await checkTeamOrOrgPermissions(
  userId, 
  eventType.teamId, 
  eventType.team?.parent?.id
);

This approach prevents security gaps that can occur when authorization logic is incomplete or when sensitive information is exposed through inadequate URL handling or redirect mechanisms.

---

Cache expensive operations

Identify and eliminate duplicate computations by caching results of expensive operations. This includes memoizing method calls, avoiding redundant database queries, and caching computed values that are used multiple times.

Common patterns to watch for:

• The same method being called multiple times with identical parameters
• Database queries executed repeatedly with the same conditions
• String interpolations or computations performed for every iteration in loops

Use memoization for expensive operations:

def used_flag_ids(flag_ids)
  @used_flag_ids ||= Flag.used_flag_ids(flag_ids)
end

Cache intermediate results in loops:

# Instead of interpolating keys for every row
records.each { |record| process(interpolate_key(record)) }

# Cache the interpolated keys
cached_keys = records.map { |record| interpolate_key(record) }
cached_keys.each { |key| process(key) }

Avoid running the same detection logic multiple times by setting flags or headers to communicate state between components rather than re-computing the same conditions.

---

minimize unsafe reference lifetime

When working with methods that return potentially unsafe references or data that could become invalid, pass the results directly to safety/copy methods rather than storing them in intermediate variables. This minimizes the lifetime of unsafe references and reduces the risk of using invalidated data.

Intermediate variables that hold unsafe references extend their lifetime unnecessarily and create additional opportunities for null reference errors or use-after-free scenarios.

// Avoid - extends lifetime of unsafe reference
name := c.Cookies("name")  // unsafe reference stored
safe := c.CopyString(name) // used later

// Prefer - immediate safety conversion
safe := c.CopyString(c.Cookies("name"))

// Avoid - extends lifetime of unsafe reference  
body := c.Body()           // unsafe reference stored
safe := c.CopyBytes(body)  // used later

// Prefer - immediate safety conversion
safe := c.CopyBytes(c.Body())

This pattern is especially important when working with frameworks or APIs that explicitly warn about reference validity, such as Fiber’s context methods that are “only valid within the handler.”

---

Manage state dependencies properly

Ensure components establish explicit dependencies when they need to react to external changes, and avoid state updates during build phases to prevent rendering conflicts.

When components depend on external state (like context or inherited data), use dependency-establishing patterns rather than direct lookups that don’t trigger rebuilds:

// Problematic: Overlay.of doesn't establish dependency
final overlayState = Overlay.of(context);

// Better: Use InheritedWidget-based approach that establishes dependencies
// This ensures rebuilds when the overlay changes

When state changes occur during build phases (like in didChangeDependencies), defer state updates to avoid “setState during build” errors:

void handleCloseRequest() {
  if (widget.onCloseRequested != null) {
    if (SchedulerBinding.instance.schedulerPhase != SchedulerPhase.persistentCallbacks) {
      // Defer to avoid setState during build
      SchedulerBinding.instance.addPostFrameCallback((_) {
        widget.onCloseRequested!();
      });
    } else {
      widget.onCloseRequested!();
    }
  }
}

This prevents runtime errors and ensures predictable component behavior, similar to React’s rules about not calling setState during render and properly managing effect dependencies.

---

maintain consistent style

Ensure consistent application of coding style conventions throughout the codebase, including naming patterns, type usage, code organization, and formatting standards.

Key areas to maintain consistency:

Naming Conventions:

• Use consistent casing for constants (e.g., STACKOVERFLOW not StackOverflow)
• Remove underscore prefixes from private members as per current standards
• Apply readonly modifier consistently to input signals and computed values

Type Usage:

• Prefer unknown over any for better type safety
• Use consistent patterns for optional chaining and type assertions

Code Organization:

• Place documentation comments before decorators consistently
• Extract repeated constants to the top of files or shared utilities
• Use async/await syntax consistently instead of Promise.resolve()

Example of consistent readonly usage:

// Consistent - all inputs marked as readonly
readonly docContent = input<DocContent | undefined>();
readonly urlFragment = toSignal(this.route.fragment);
readonly hasClosed = linkedSignal(() => { ... });

// Inconsistent - missing readonly modifiers
docContent = input<DocContent | undefined>();
urlFragment = toSignal(this.route.fragment);

Example of consistent constant extraction:

// Good - constants extracted and consistently named
const MAX_DISPLAY_LENGTH = 200;
const COPY_FEEDBACK_TIMEOUT = 2000;
const STACKOVERFLOW = 'https://stackoverflow.com/questions/tagged/angular';

// Avoid - magic numbers and inconsistent naming
setTimeout(() => { ... }, 2000);
export const StackOverflow = 'https://stackoverflow.com/questions/tagged/angular';

Consistency in style reduces cognitive load, improves maintainability, and makes the codebase more professional. Establish team conventions and apply them uniformly across all files.

---

Use modern null handling

Leverage modern JavaScript operators and patterns for cleaner, more robust null and undefined handling. This improves code readability and reduces boilerplate while maintaining safety.

Key patterns to adopt:

1. Nullish coalescing (??) for default values when you specifically want to handle null and undefined:

   // Instead of
   return this.args.onChange ? this.args.onChange : () => {};
   // Use
   return this.args.onChange ?? (() => {});
   

2. Nullish coalescing assignment (??=) for lazy initialization:

   // Instead of
   if (!this.#pendingCleanup[phase]) {
     this.#pendingCleanup[phase] = [];
   }
   // Use
   this.#pendingCleanup[phase] ??= [];
   

3. Logical OR assignment (||=) for falsy value defaults:

   // Instead of
   value = value || "";
   // Use
   value ||= "";
   

4. Leverage truthy/falsy behavior to simplify boolean checks: ```javascript // Instead of return d.hours() !== 0 || d.minutes() !== 0 || d.seconds() !== 0; // Use return d.hours() || d.minutes() || d.seconds();

// Instead of .filter((e) => e) // Use .filter(Boolean)

5. **Avoid redundant null checks** when functions handle undefined gracefully:
```javascript
// Instead of
if (this.handleBlurTimer) {
  cancel(this.handleBlurTimer);
}
// Use (since cancel handles undefined)
cancel(this.handleBlurTimer);

These patterns reduce code verbosity while maintaining or improving null safety, and they clearly express intent about how null/undefined values should be handled.

---

API consistency patterns

Ensure that similar APIs follow consistent patterns and conventions across the codebase. When designing or modifying APIs, maintain the same expressivity, return type patterns, and usage conventions as existing similar APIs.

Key areas to check:

• Return type consistency: Use established patterns like OneOrMany<T> consistently across similar APIs rather than mixing single values and arrays arbitrarily
• Expressivity consistency: Ensure similar API handlers have the same capabilities (e.g., “animation event handlers should have the same expressivity/shape as normal event handlers”)
• Usage pattern consistency: Provide uniform ways to create and use similar constructs (e.g., always use static factory methods rather than mixing constructors and factories)
• Import consistency: Export related functionality from the same public API entry points
• Behavioral consistency: Apply the same logic across similar use cases rather than having different behaviors for equivalent scenarios

Example from the codebase:

// Inconsistent - mixing different return patterns
function someApi(): ValidationError | ValidationError[] // inconsistent with other APIs

// Consistent - following established OneOrMany pattern  
function someApi(): OneOrMany<ValidationError> // matches other similar APIs

// Inconsistent - different creation patterns
new ReactiveMetadataKey() vs MetadataKey.someFactory()

// Consistent - uniform factory pattern
MetadataKey.reduce() // always use static factories

This helps users build intuitive mental models and reduces cognitive load when working with related APIs.

---

API parameter clarity

Design API parameters with clear naming, structured formats, and intuitive interfaces that are easy for clients to use and maintain. Avoid complex string parsing, ambiguous parameter names, or structures that require clients to perform additional processing.

Key principles:

• Use descriptive, unambiguous parameter names that clearly indicate their purpose
• Prefer structured parameter formats (hashes, objects) over string-based query languages that require regex parsing
• Design plugin APIs with clear signatures that accept the expected parameters directly
• Consider client usability when designing parameter passing (e.g., pre-filling forms with passed data)

Example of good parameter design:

# Good: Clear parameter structure
plugin.register_modifier(:similar_topic_candidate_ids) do |existing_ids, args|
  # args contains structured data that's easy to access
  args[:candidates] # Clear what this contains
end

# Good: Structured options instead of string parsing
options_hash = {
  status: options[:status],
  category: options[:category]
}
TopicsFilter.new(scope: result, guardian: @guardian).filter(options_hash)

Example of problematic parameter design:

# Problematic: Unclear parameter names and string manipulation
plugin.register_modifier(:modifier_name) do |plugin_candidate_ids, title, raw, guardian|
  # Unclear what plugin_candidate_ids contains
end

# Problematic: String parsing instead of structured data
options[:q] ||= +""
options[:q] << " status:#{status}" # Requires regex parsing later

This approach makes APIs more maintainable, reduces parsing complexity, and improves the developer experience for API consumers.

---

Avoid hardcoded configuration values

Replace hardcoded values in configuration code with design tokens, parameters, or configurable constants to ensure consistency and maintainability across the codebase.

When writing configuration-related code, avoid embedding magic numbers or fixed values directly. Instead, use design tokens for spacing, colors, and sizes, or make values configurable through parameters.

Bad:

[`&-vertical`]: {
  display: 'flex',
  flexDirection: 'column',
  rowGap: 8,  // hardcoded value
  [`&${groupPrefixCls}-large`]: {
    rowGap: 12,  // hardcoded value
  },
}

// or
maxWidth: 'calc(100% - 4px)',  // hardcoded 4px

Good:

[`&-vertical`]: {
  display: 'flex',
  flexDirection: 'column',
  rowGap: token.marginXS,  // use design token
  [`&${groupPrefixCls}-large`]: {
    rowGap: token.marginSM,  // use design token
  },
}

// or make it configurable
const mergedConfig = {
  ...contextConfig,
  ...userConfig,  // proper configuration merging
};

This approach ensures that configuration values remain consistent across components, can be easily updated globally through design tokens, and reduces the risk of inconsistencies when modifications are needed.

---

Avoid hardcoded configuration values

Extract hardcoded configuration values into constants, environment variables, or function parameters to improve maintainability and flexibility. Magic numbers, provider names, file size limits, and other configuration values should not be embedded directly in business logic.

Examples of what to avoid:

// Bad: Hardcoded provider name
const newNumber = await prisma.calAiPhoneNumber.create({
  data: {
    provider: "retell", // Hardcoded provider
    // ...
  }
});

// Bad: Magic numbers
const creditMultiplier = team.isOrganization ? 0.2 : 0.5; // Magic numbers

// Bad: Hardcoded file size limit
if (file.size > MAX_IMAGE_FILE_SIZE) { // Hardcoded constant

Better approaches:

// Good: Get provider from service response
const provider = retellPhoneNumber.provider || "retell";

// Good: Use named constants or environment variables
const ORG_CREDIT_MULTIPLIER = 0.2;
const TEAM_CREDIT_MULTIPLIER = 0.5;
const creditMultiplier = team.isOrganization ? ORG_CREDIT_MULTIPLIER : TEAM_CREDIT_MULTIPLIER;

// Good: Make limits configurable
export const validateImageFile = async (
  file: File, 
  maxFileSize: number, // Accept as parameter
  t: (key: string) => string
): Promise<boolean> => {
  if (file.size > maxFileSize) {

This approach makes code more testable, allows for environment-specific configurations, and reduces the risk of inconsistencies when the same values are used in multiple places.

---

Favor component composition

Design components to be configurable through props rather than relying on external context like URL paths or modifying shared UI components directly. This approach improves reusability, maintainability, and reduces coupling between components and their usage contexts.

Key principles:

1. Use props for configuration: Instead of deriving component behavior from routes or global state, pass configuration explicitly through props
2. Compose rather than modify: When customizing existing components, use composition patterns (like passing custom components as props) rather than modifying the base component
3. Reuse existing components: Before creating new components, check if existing ones can be reused or extended

Example of good composition:

// Instead of modifying Select component directly
<Select 
  components={{ 
    Option: CustomOption 
  }} 
  // other props
/>

// Instead of path-based configuration
<BillingCredits 
  teamId={teamId}
  isOrgScoped={isOrgScoped}
/>

This pattern makes components more predictable, testable, and easier to refactor when requirements change.

---

Optimize configuration specificity

Ensure configuration files use precise patterns and avoid redundant dependencies. Configuration specifications should be as specific as necessary to match their intended purpose, and unnecessary or duplicate entries should be removed to maintain clean, efficient configurations.

When defining file patterns in build configurations, use specific glob patterns that match exactly what you need rather than overly broad selectors. For test configurations, explicitly target test files:

# Instead of capturing all TypeScript files
srcs = glob(["**/*.ts"]),

# Be specific about test files
srcs = glob(["**/*.spec.ts"]),

Similarly, avoid specifying redundant dependencies when they are already provided by existing toolchain versions. Review dependency declarations to ensure each entry serves a unique purpose and remove any that are automatically included by other dependencies.

---

Use safe navigation operator

Prefer Ruby’s safe navigation operator (&.) over explicit nil checks when calling methods on potentially nil objects. This approach makes code more readable, reduces boilerplate, and prevents NoMethodError exceptions in a clean, idiomatic way.

The safe navigation operator only calls the method if the object is not nil, returning nil otherwise. This eliminates the need for verbose conditional checks while maintaining null safety.

Example:

# Instead of explicit nil checking:
if row[:description]
  row[:description] = sanitize_field(row[:description])[0...MAX_DESCRIPTION_LENGTH]
end

# Use safe navigation:
row[:description] = sanitize_field(row[:description])&.slice(0, MAX_DESCRIPTION_LENGTH)

# Instead of:
if @options[:used_flag_ids]
  @options[:used_flag_ids].include?(object.id)
end

# Use:
@options[:used_flag_ids]&.include?(object.id)

This pattern is particularly valuable in serializers, service objects, and anywhere you’re working with optional parameters or potentially nil objects. It reduces cognitive load and makes the happy path more prominent in your code.

---

consistent null handling patterns

Use consistent and meaningful null/undefined handling patterns throughout your code. Prefer positive type guards over negated early returns, maintain consistency between null and undefined return types, and be careful with optional chaining semantics.

Key practices:

1. Use positive conditionals: Instead of if (!ts.isIdentifier(node.name)) return;, use if (ts.isIdentifier(node.name)) { ... } else if (ts.isObjectBindingPattern(node.name)) { ... }

2. Consistent return types: Choose either null or undefined consistently for similar functions. For example, prefer return null over return undefined when indicating “no result found”.

3. Careful optional chaining: Understand semantic differences between document?.documentElement?.getAnimations and explicit checks. Optional chaining can still throw if the base object is undefined in some contexts.

4. Derive state from data presence: Instead of manually managing loading states, derive them from whether data exists: const isLoading = computed(() => !this.transferStateData() && !this.error())

5. Meaningful null/undefined: Use null/undefined to represent meaningful states like “no constraint applies” or “validation skipped” rather than just absence of data.

Example of improved null handling:

// Before: Negated early return
if (!ts.isIdentifier(node.name)) {
  return;
}

// After: Positive conditionals with explicit handling
if (ts.isIdentifier(node.name)) {
  migrateIdentifierParameter(context);
} else if (ts.isObjectBindingPattern(node.name)) {
  migrateObjectBindingParameter(context);
} else {
  return;
}

---

verify authorization explicitly

Always perform explicit authorization checks rather than assuming existing security controls are sufficient. Security vulnerabilities often arise from bypassed or missing permission verification, especially in edge cases like impersonation windows, controller action bypasses, or privilege escalation scenarios.

Key practices:

• Add explicit permission checks even when controller-level security exists
• Verify user capabilities at the method level, not just at routing
• Handle edge cases like time windows where permissions might change
• Ensure anonymous users are properly restricted from authenticated features

Example from impersonation security:

def impersonated_user
  return if impersonated_user_id.blank?
  return if impersonation_expires_at.blank? || impersonation_expires_at.past?
  
  # Add explicit guardian check for edge cases
  return unless Guardian.new(user).can_impersonate?(target_user)
  
  User.find_by(id: impersonated_user_id).tap { |u| u.is_impersonating = true }
end

Example from permission methods:

def can_create_theme?(user)
  return false if !user.admin?  # Explicit check first
  # Additional restrictions can be applied via modifiers
  DiscoursePluginRegistry.apply_modifier(:user_guardian_can_create_theme, true, user, self)
end

This prevents security bypasses that occur when relying solely on higher-level controls that may not cover all code paths or edge cases.

---

Select specific database fields

Always explicitly select only the database fields you actually need instead of using broad includes or fetching entire objects. This practice significantly improves query performance, reduces memory usage, and minimizes data exposure.

Why this matters:

• Reduces database load and network transfer
• Improves application performance
• Prevents accidental exposure of sensitive data
• Makes code more maintainable by clearly showing data dependencies

How to apply:

Instead of fetching everything:

// ❌ Avoid - fetches all fields
const booking = await prisma.booking.findUnique({
  where: { uid: bookingUid },
  include: {
    attendees: true,
    user: true,
    eventType: {
      include: {
        owner: true,
      }
    }
  }
});

Be specific about what you need:

// ✅ Better - select only required fields
const booking = await prisma.booking.findUnique({
  where: { uid: bookingUid },
  include: {
    attendees: {
      select: {
        id: true,
        email: true,
        name: true
      }
    },
    user: {
      select: {
        id: true,
        name: true
      }
    },
    eventType: {
      select: {
        id: true,
        title: true
      }
    }
  }
});

Special considerations:

• For JSON columns, you cannot use select - use fields: true or omit entirely
• Avoid redundant queries when data is already available from previous fetches
• Consider conditional subqueries for performance-critical paths (e.g., only fetch attendees for seated events)

---

React component API clarity

Ensure React component APIs are well-designed with accurate TypeScript interfaces, clear documentation, and intuitive developer experience. This includes: (1) Using precise type definitions that match actual functionality, avoiding misleading exposed props from internal implementations, (2) Providing accurate property descriptions in documentation that match the component’s actual behavior, (3) Offering clean, intuitive import paths that improve developer experience, and (4) Maintaining consistency between TypeScript interfaces and documentation.

For example, when exposing component props, omit internal implementation details:

// Good: Clean public interface
export interface TreeProps<T extends BasicDataNode = DataNode>
  extends Omit<RcTreeProps<T>, 'prefixCls' | 'showLine' | 'dropIndicatorRender'> {
  // Only expose props that users should actually use
}

// Good: Accurate property descriptions
| size | Set the size of tag | `large` \| `middle` \| `small` | `small` |

// Good: Clean import paths
import { createCache, extractStyle, StyleProvider } from 'antd/cssinjs';

This approach prevents confusion when developers see auto-complete suggestions for props they shouldn’t use, ensures documentation accurately reflects component behavior, and provides a smoother development experience through cleaner APIs.

---

Extract duplicate code

When you notice repeated code patterns, logic blocks, or similar implementations across methods or classes, extract the common functionality into reusable methods or utilities. This improves maintainability, reduces bugs, and makes the codebase more consistent.

Look for these common duplication patterns:

• Similar conditional logic blocks that could be extracted into a shared method
• Repeated boilerplate code that could be centralized into a utility method
• Multiple instances of similar object creation that could use a factory method
• Repeated test setup code that could be moved into helper methods

Example of extracting duplicate conditional logic:

# Before: Duplicate logic in filter_users and filter_groups
def filter_users(values:)
  values.each do |value|
    if value.include?("+")
      usernames = value.split("+")
      require_all = true
      if value.include?(",")
        @scope = @scope.none
        next
      end
    else
      usernames = value.split(",")
      require_all = false
      if value.include?("+")
        @scope = @scope.none
        next
      end
    end
    # ... rest of logic
  end
end

# After: Extract common pattern
def filter_users(values:)
  values.each do |value|
    usernames, require_all = parse_filter_value(value)
    next if usernames.nil?
    # ... rest of user-specific logic
  end
end

private

def parse_filter_value(value)
  if value.include?("+") && value.include?(",")
    @scope = @scope.none
    return [nil, nil]
  end
  
  if value.include?("+")
    [value.split("+"), true]
  else
    [value.split(","), false]
  end
end

Before implementing new functionality, check if similar logic already exists that could be reused or if the new code could be designed to share common patterns with existing implementations.

---

optimize test fixtures

Use the fab! shorthand syntax for creating test fixtures and reuse fabricated objects across tests to improve performance and maintainability. The fab! method creates objects once per test context and reuses them, reducing database overhead compared to creating new objects for each test.

Preferred approach:

fab!(:theme_1, :theme)
fab!(:theme_2, :theme) 
fab!(:tag_1, :tag)
let(:tags) { [tag_1, tag_2, tag_3] }

Instead of:

fab!(:theme_1) { Fabricate(:theme) }
fab!(:theme_2) { Fabricate(:theme) }
let(:tags) { 3.times.collect { Fabricate(:tag) } }

When possible, reuse top-level fabricated objects in nested contexts rather than creating new ones. For example, use event = Fabricate(:event, post: admin_post) instead of post = Fabricate(:post, user: Fabricate(:admin)) when an admin_post fixture already exists at the top level. This approach reduces test setup time, improves readability, and makes test dependencies more explicit.

---

optimize iteration patterns

Minimize computational complexity by optimizing iteration patterns and data processing flows. Apply early filtering when possible, but preserve data integrity when order or indexing matters.

Key principles:

1. Filter early: Apply filters at the data source rather than after multiple transformations
2. Avoid nested loops: Replace nested iterations with more efficient single-pass algorithms when possible
3. Consider data integrity: Sometimes separate operations are necessary to maintain correct indexing or ordering

Examples:

❌ Avoid late filtering:

const allWorkflows = eventTypeWorkflows;
// ... multiple operations on allWorkflows
const workflows = allWorkflows.filter((workflow) => {
  if (triggerEvents && !triggerEvents.includes(workflow.trigger)) return false;
});

✅ Filter early:

const allWorkflows = eventTypeWorkflows.filter((workflow) => {
  return !triggerEvents || triggerEvents.includes(workflow.trigger);
});

❌ Avoid nested loops when possible:

for (let i = 0; i < bookingsWithRemainingSeats.length; i++) {
  for (let j = i; j < busyTimes.length; j++) {
    // processing logic
  }
}

✅ Single iteration approach:

bookings.forEach(booking => {
  if (booking.attendeesCount < eventType.seatsPerTimeSlot) {
    // process booking directly
  }
});

⚠️ Exception - preserve data integrity:

// When index position matters, separate filter + reduce is correct
.filter((attendee) => typeof attendee.name === "string" && typeof attendee.email === "string")
.reduce((acc, attendee, index) => {
  acc[`Attendee ${index + 1}`] = `${attendee.name} (${attendee.email})`;
  return acc;
}, {})

This approach reduces time complexity from O(n²) to O(n) in many cases while maintaining code correctness.

---

Contextual error responses

Choose error response strategies based on the error’s origin, caller context, and downstream impact rather than blindly propagating upstream errors. Consider whether throwing a 5xx error will cause harmful retries or mislead about the actual source of the problem.

For external webhooks and integrations, return 2xx responses with error details in the response body to prevent retry storms when the issue is internal misconfiguration:

// Instead of throwing 500 for internal config issues
if (!webhookToken) {
  throw new HttpError({ statusCode: 500, message: "Token not configured" });
}

// Return 200 with error details to prevent retries
if (!webhookToken) {
  return {
    message: "ok",
    processed: 0,
    failed: 0,
    skipped: payload.value.length,
    errors: ["MICROSOFT_WEBHOOK_TOKEN is not defined"],
  };
}

For user input validation errors, use 4xx status codes even when the error originates from a downstream service:

// If Twilio returns 400 for invalid phone number user entered
if (isTwilioError(cause) && cause.status === 400) {
  return new HttpError({ statusCode: 400, message: cause.message });
}

Log upstream errors appropriately while returning status codes that accurately reflect whether the issue is with the client request, server configuration, or external service availability.

---

Validate configuration dependencies

Configuration settings often depend on other settings or external resources to function correctly. Always implement validation to check these dependencies and provide clear error messages when requirements are not met.

When adding new configuration settings:

1. Identify all dependencies (other settings, external services, required credentials)
2. Implement validation that checks these dependencies are satisfied
3. Document interactions with other settings clearly
4. Use appropriate setting types (enums instead of free-form strings when possible)

Example validation pattern:

video_conversion_enabled:
  default: false
video_conversion_service:
  enum: "VideoConversionServiceSetting"
  default: "aws_mediaconvert"

With corresponding validation: “If video_conversion_enabled is true and video_conversion_service is aws_mediaconvert, then mediaconvert_role_arn and S3 credentials must be present.”

This prevents runtime failures and reduces user confusion by catching configuration errors early and providing actionable feedback.

---

Use named constants

Replace hardcoded string literals and magic values with named constants to improve code maintainability and readability. This practice prevents typos, makes the code self-documenting, and provides a single source of truth when the same value is used in multiple places.

Instead of using hardcoded strings directly in the code:

String prefix = "--aot-shared-library-name=";
Path pathWithoutSoFile = internalStorageDirAsPathObj.resolve(Paths.get("library.so"));

Extract them to meaningful constants:

private static final String AOT_SHARED_LIBRARY_NAME_PREFIX = "--aot-shared-library-name=";
private static final String DEFAULT_LIBRARY_NAME = "library.so";

String prefix = AOT_SHARED_LIBRARY_NAME_PREFIX;
Path pathWithoutSoFile = internalStorageDirAsPathObj.resolve(Paths.get(DEFAULT_LIBRARY_NAME));

This approach makes the code more maintainable, reduces duplication, and clearly communicates the purpose of each value through descriptive constant names.

---

Follow established naming conventions

Ensure all identifiers follow the established naming conventions for the codebase and framework being used. This includes using native JavaScript private method syntax with # instead of underscore prefixes, following camelCase for JavaScript methods and variables, matching existing naming patterns for consistency, and avoiding deprecated naming conventions.

Key guidelines:

• Use native private methods (#methodName) instead of underscore prefixes (_methodName)
• Follow camelCase for JavaScript identifiers (copyToClipboard not copy_to_clipboard)
• Match existing naming patterns in the codebase (e.g., plugin outlets should start with post-, translation components should use @key to match other i18n code)
• Avoid deprecated method names (use find() instead of findBy())
• Choose descriptive names that make code self-documenting (clearSelection() is clearer than inline -1)

Example of preferred private method syntax:

// ❌ Avoid underscore prefix
_buildGroupedEvents(detail) {
  // implementation
}

// ✅ Use native private syntax
#buildGroupedEvents(detail) {
  // implementation
}

Consistent naming reduces cognitive load, improves code maintainability, and ensures compatibility with modern JavaScript standards and framework conventions.

---

explicit null validation

Always validate null values explicitly rather than using silent fallbacks or implicit handling. When null values are unexpected or could cause issues, use assertions or explicit checks to fail fast and provide clear error messages.

Avoid silent fallbacks like DateTime.now() when a null value indicates a programming error. Instead, use explicit null checks and assertions to catch issues early in development.

Prefer explicit validation:

// Bad - silent fallback
selectableDayPredicate?.call(initialDateTime ?? DateTime.now())

// Good - explicit null handling  
assert(
  selectableDayPredicate == null || 
  initialDate == null || 
  selectableDayPredicate!(initialDate!),
  'Initial date must be selectable when predicate is provided'
);

Use assertions for unexpected nulls:

// Bad - silent failure
final VoidCallback? callback = callbacks[actionId];
if (callback != null) {
  callback();
}

// Good - explicit validation
final VoidCallback? callback = callbacks[actionId];
assert(callback != null, 'No callback registered for action: $actionId');
callback?.call();

Validate numeric values:

// Bad - silent failure on invalid values
if (itemExtent > 0.0) {
  // process...
}

// Good - explicit validation
if (itemExtent > 0.0 && scrollOffset.isFinite && itemExtent.isFinite) {
  // process...
} else {
  assert(false, 'Invalid numeric values: itemExtent=$itemExtent, scrollOffset=$scrollOffset');
}

This approach prevents crashes from unexpected null values, makes debugging easier by failing fast with clear messages, and ensures that null handling is intentional rather than accidental.

---

AI documentation clarity

Ensure AI-related documentation, comments, and explanations are clear, accurate, and well-structured. This includes fixing spelling errors, using precise terminology, adding necessary context about experimental features, and employing active voice for better readability.

Key practices:

• Fix spelling errors immediately (e.g., “asynchronous” not “asyncronous”) as they can block merges
• Use precise, professional language (“preferred” instead of “favorite”)
• Add context and links for technical concepts (e.g., link to MCP documentation when mentioning Model Context Protocol)
• Use active voice for clearer explanations (“You can configure LLM APIs” instead of “LLM APIs can be configured”)
• Simplify complex technical explanations while maintaining accuracy
• Mark experimental features clearly to set proper expectations

Example improvement:

// Before: "LLM APIs can be configured to return structured data"
// After: "You can configure LLM APIs to return structured data"

// Before: "The Angular CLI includes a Model Context Protocol (MCP) server"
// After: "The Angular CLI includes an experimental [Model Context Protocol (MCP) server](https://modelcontextprotocol.io/)"

Clear documentation is especially critical for AI features as they often involve complex concepts, experimental APIs, and emerging patterns that developers may be unfamiliar with.

---

Use descriptive identifiers

Choose specific, descriptive names for variables, functions, and parameters that clearly communicate their purpose and content. Avoid generic terms that could be ambiguous or misleading.

Key principles:

• Replace generic names with specific, contextual ones
• Ensure names accurately reflect the data or functionality they represent
• Avoid names that could be confused with other similar concepts
• Consider the broader context where the identifier will be used

Examples of improvements:

// ❌ Generic and potentially misleading
const userInfo = rawBookingData.user;
const users = await prisma.user.findMany({...});
const redirectTo = userId;

// ✅ Specific and descriptive  
const bookingSlug = rawBookingData.user;
const attendeesAvailability = await prisma.user.findMany({...});
const redirectToUserId = userId;

Avoid naming conflicts:

// ❌ Confusing - boolean vs string with same base name
customLabel: true,        // boolean property
customLabel: "My Label"   // string in options

// ✅ Clear distinction
supportsCustomLabel: true,    // boolean property  
customLabel: "My Label"       // string in options

This practice improves code readability, reduces cognitive load, and prevents misunderstandings about data types and purposes.

---

Use modern syntax

Adopt modern JavaScript and Ember syntax patterns instead of legacy approaches to improve code readability and maintainability.

Key modern patterns to use:

Native private methods - Use # prefix instead of underscore convention:

// ❌ Legacy
_buildEventObject(from, to) {
  // implementation
}

// ✅ Modern
#buildEventObject(from, to) {
  // implementation  
}

Boolean attributes - Use proper boolean syntax instead of explicit true/false:

<!-- ❌ Legacy -->
<input disabled={{true}} />

<!-- ✅ Modern -->
<input disabled />

Optional chaining - Use ?. for cleaner conditional calls:

// ❌ Legacy
if (this.onBlur) {
  this.onBlur(this.normalize(this.hexValue));
}

// ✅ Modern  
this.onBlur?.(this.normalize(this.hexValue));

Modern array methods - Use .at() for array access:

// ❌ Legacy
const lastWord = words[words.length - 1];

// ✅ Modern
const lastWord = words.at(-1);

These modern syntax patterns are now well-supported and provide cleaner, more expressive code that aligns with current JavaScript and Ember best practices.

---

Centralize configuration management

Avoid duplicate configuration processing and keep configuration data properly centralized. When configuration utilities or hooks already exist, use them instead of manually processing the same data. Keep translations in locale files rather than embedding them directly in data structures, and prefer design tokens over hardcoded values for styling configurations.

Example of avoiding duplicate processing:

// ❌ Don't manually process config when utilities exist
const { previewMask } = previewConfig && typeof previewConfig === 'object' ? previewConfig : {};

// ✅ Use existing configuration hooks
const [contextPreviewConfig, contextPreviewRootClassName, contextPreviewMaskClassName] = 
  usePreviewConfig(contextPreview);

Example of proper configuration separation:

// ❌ Don't embed translations in data
const colors = [
  {
    name: 'red',
    english: 'Dust Red',
    chineseDescription: '斗志、奔放',
  }
];

// ✅ Use locale keys and keep translations centralized
const colors = [
  {
    name: 'red',
    english: 'Dust Red',
    descriptionKey: 'colors.red.description',
  }
];
// Then use: locale[color.descriptionKey]

This approach improves maintainability, reduces duplication, and ensures configuration changes are centralized and consistent across the application.

---

prefer CSS custom properties

Use CSS custom properties (CSS variables) instead of hardcoded values for fonts, spacing, colors, and other design tokens. This improves maintainability, enables consistent theming, and makes design system changes easier to implement across the codebase.

Examples of preferred patterns:

/* Good - uses custom properties */
font-family: var(--font-family);
margin-bottom: var(--space-2);
border: 1px solid var(--content-border-color);

/* Avoid - hardcoded values */
font-family: system-ui, Arial, sans-serif;
margin-bottom: 10px;
border: 1px solid var(--primary-low);

When choosing custom properties, use semantic names that reflect the property’s purpose (like --content-border-color for content separation vs --input-border-color for form inputs) rather than generic color names.

---

optimize data structure choices

Choose data structures that optimize for your access patterns and computational complexity requirements. When you need frequent membership testing or existence checking, prefer Set over Array to achieve O(1) lookup complexity instead of O(n) linear scanning.

Key optimizations to consider:

• Replace Array with Set when doing frequent include? operations
• Use Set’s add? method to efficiently combine existence checking with insertion
• Consider the time complexity of your chosen data structure’s operations

Example transformation:

# Instead of O(n) array scanning:
HUMANIZED_ACRONYMS_HASH = HUMANIZED_ACRONYMS.map { |a| [a, true] }.to_h.freeze

# Use O(1) Set operations:
HUMANIZED_ACRONYMS_SET = HUMANIZED_ACRONYMS.to_set.freeze

For existence checking with conditional insertion:

# Instead of separate check and add:
next if existing_moderation_groups.include?([category_id, group_id])
existing_moderation_groups.add([category_id, group_id])

# Use Set's efficient add? method:
next unless existing_moderation_groups.add?([category_id, group_id])

This approach reduces algorithmic complexity and improves performance, especially as data sets grow larger.

---

Self-documenting identifiers

Choose names that are immediately understandable without requiring additional context, documentation lookup, or guessing. Identifiers should clearly communicate their purpose, units, and behavior to reduce cognitive load for developers.

For configuration settings and labels, prioritize descriptive language over technical jargon. When technical terms are necessary, pair them with plain language explanations. For time-based or measurement settings, include units directly in the name to eliminate ambiguity.

Examples:

• Prefer pending_users_reminder_delay_minutes over pending_users_reminder_delay
• Prefer “Allow editing options after posting (dynamic poll)” over “Enable dynamic mode (allow editing options after posting)”

This approach prevents developers from having to guess units, look up documentation, or decipher technical terminology, leading to more maintainable and accessible code.

---

Optimize React patterns

Prefer derived values over state and use appropriate React hooks for better performance and cleaner code. When a value can be computed from existing state, props, or context, derive it instead of storing it in separate state. This reduces unnecessary re-renders and simplifies state management.

For derived values, compute them directly in the component body or use useMemo for expensive calculations. When working with refs, prefer useImperativeHandle over useEffect for ref forwarding as it’s more semantically correct and can be optimized with proper dependency arrays.

Example of converting state to derived value:

// Before: Storing derived value in state
const [activeLocation, setActiveLocation] = useState<ParsedLocation>(
  location ?? state.location,
)

// After: Computing derived value
const activeLocation = location ?? state.location

Example of proper ref handling:

// Before: Using useEffect for ref forwarding
React.useEffect(() => {
  if (!ref) return
  if (typeof ref === 'function') {
    ref(innerRef.current)
  } else {
    ref.current = innerRef.current
  }
})

// After: Using useImperativeHandle
React.useImperativeHandle(ref, () => innerRef.current!, [])

---

enforce consistent SSO flows

When single sign-on (SSO) is enabled as the primary authentication mechanism, ensure all authentication entry points consistently redirect to the SSO endpoint without complex conditional logic. Avoid respecting secondary authentication parameters that could create inconsistent behavior or potential security gaps.

Complex conditionals around authentication flows can introduce vulnerabilities where users might bypass the intended SSO flow or encounter inconsistent authentication behavior across different routes.

Example of problematic code:

// Avoid complex conditionals when SSO is primary auth
if (auth_immediately && enable_discourse_connect) {
  // Only redirect in some cases
  window.location = getURL(`/session/sso?return_path=${returnPath}`);
}

Preferred approach:

// When SSO is enabled, always redirect regardless of other flags
if (enable_discourse_connect) {
  const returnPath = cookie("destination_url") 
    ? getURL("/") 
    : encodeURIComponent(url);
  window.location = getURL(`/session/sso?return_path=${returnPath}`);
}

This ensures that SSO remains the authoritative authentication method when enabled, preventing potential bypass scenarios and maintaining consistent security posture across all authentication flows.

---

API parameter design

Design API parameters thoughtfully by making them optional when appropriate, avoiding unnecessary required parameters, and maintaining backward compatibility when changing parameter signatures. Consider the actual usage patterns and avoid forcing users to provide parameters that have sensible defaults or aren’t always needed.

Key principles:

• Make parameters optional when they have reasonable defaults or aren’t always required
• Avoid breaking changes by preserving existing parameter signatures when possible
• Remove unnecessary parameters that add complexity without value
• Ensure all documented parameters actually work as intended

Example of good parameter design:

// Before: forcing unnecessary required parameter
interface MatchRoutesFn {
  (pathname: string, locationSearch: AnySchema) // always required
}

// After: making parameter optional when it has defaults
interface MatchRoutesFn {
  (pathname: string, locationSearch?: AnySchema) // optional when not needed
}

// Before: passing unnecessary parameters
navigate: (opts: any) => this.navigate({ ...opts, from: match.pathname })

// After: removing unnecessary complexity  
navigate: (opts: any) => this.navigate(opts)

This approach reduces API surface area, improves developer experience, and prevents breaking changes that force users to update working code unnecessarily.

---

Maintain comprehensive documentation

When making code changes, ensure all relevant documentation is updated comprehensively across different formats and locations. This includes:

1. JSDoc comments for functions, especially internal APIs that need usage context
2. Inline comments for complex logic sections to aid future maintainers
3. External markdown documentation when adding new API properties or references
4. Clear test expectations that explicitly show expected transformations

For example, when adding a new function:

/**
 * @internal
 * Handles hash-based scrolling during route transitions.
 * Should be setup in the `<Transitioner>` component.
 */
export function handleTransitionerHashScroll(router: AnyRouter) {
  // Actually fire off the `beforeLoad` callback
  const beforeLoadContext = await route.options.beforeLoad?.(beforeLoadFnContext)
}

And ensure corresponding updates to:

• API documentation files (e.g., RouterOptionsType.md, RouterType.md)
• External reference links (MDN, etc.) in markdown files
• Test cases with explicit expected values rather than computed ones

This comprehensive approach ensures that documentation remains synchronized with code changes and provides clear guidance for future developers.

---

async resource cleanup

Always ensure proper cleanup of asynchronous resources (subscriptions, timeouts, event listeners) to prevent memory leaks and race conditions. Use Angular’s DestroyRef or similar lifecycle management patterns instead of manual cleanup.

When working with subscriptions, timeouts, or event listeners, establish cleanup mechanisms at the point of creation. This prevents resources from outliving their intended lifecycle and causing unexpected behavior in concurrent scenarios.

Example of proper cleanup pattern:

// Good: Using DestroyRef for automatic cleanup
constructor(private destroyRef: DestroyRef) {
  const subscription = router.events.subscribe((s: Event) => {
    if (s instanceof NavigationEnd) {
      this.update();
    }
  });
  this.destroyRef.onDestroy(() => subscription.unsubscribe());
}

// Good: Timeout with cleanup consideration
const timeout = setTimeout(() => removeFn(), ANIMATION_TIMEOUT);
details.animateFn(() => {
  clearTimeout(timeout);
  removeFn();
});

For event listeners on elements that will be removed from the DOM, cleanup may be automatic, but for long-lived subscriptions and timers, explicit cleanup is essential to maintain application stability and prevent resource exhaustion.

---

Avoid N+1 queries

Prevent N+1 query performance issues by batching database operations instead of making individual queries within loops. This is critical for application performance as each individual query adds significant overhead.

Problem Pattern:

# BAD: N+1 queries - one query per iteration
field_ids.map do |fid|
  if UserField.find_by(id: fid).field_type == "confirm"  # Query per field!
    # process field
  end
end

# BAD: N+1 queries in user/group lookups
names.each do |name|
  if user_id = User.find_by_username(name)&.id  # Query per name!
    user_ids << user_id
  elsif group_id = Group.find_by(name: name)&.id  # Query per name!
    group_ids << group_id
  end
end

Solution Pattern:

# GOOD: Single batch query
confirm_field_ids = UserField.where(field_type: "confirm", id: field_ids).pluck(:id)
field_ids.map do |fid|
  if confirm_field_ids.include?(fid)
    # process field
  end
end

# GOOD: Batch queries for users and groups
found_users = User.where(username_lower: names.map(&:downcase)).pluck(:username, :id).to_h
user_ids.concat(found_users.values)
remaining_names = names - found_users.keys
group_ids.concat(Group.where(name: remaining_names).pluck(:id)) if remaining_names.present?

Always preload or batch-fetch related data before processing collections. Use where().pluck(), includes(), or joins() to minimize database round trips.

---

Include contextual log information

Log messages should include sufficient context to make them useful for debugging, monitoring, and audit trails. Include relevant entity IDs, operation details, and descriptive information that helps identify what was happening when the log entry was created.

Key practices:

• Include entity IDs (user ID, upload ID, job ID) in log messages
• Add operation context to describe what process was running
• Make error messages descriptive rather than generic
• Log important state changes for audit purposes
• Avoid silent failures - log warnings when operations can’t complete normally

Example of good contextual logging:

# Good - includes IDs and operation context
Rails.logger.info("Completed video conversion for upload ID #{upload.id} and job ID #{args[:job_id]}")
Rails.logger.error("Upload #{upload.id} URL remained blank after #{MAX_RETRIES} retries when optimizing video")

# Poor - lacks context
Rails.logger.info("Conversion completed")
Rails.logger.error("URL blank after retries")

This approach ensures log entries provide actionable information for troubleshooting and create comprehensive audit trails for critical operations like user impersonation or data processing workflows.

---

avoid underscore prefixes

Do not use underscore prefixes (_) for private or internal methods and properties. The team consensus is to avoid this naming convention. Instead, use one of these alternatives:

1. Remove the prefix entirely for methods that don’t need to be explicitly marked as private
2. Use proper private syntax with # prefix for truly private class members

Examples:

❌ Avoid:

_isInLightMode() {
  return this.interfaceColor.colorModeIsLight;
}

_getUserColorSchemeDifferences() {
  // implementation
}

✅ Prefer:

// Option 1: Remove prefix
isInLightMode() {
  return this.interfaceColor.colorModeIsLight;
}

// Option 2: Use proper private syntax
#getUserColorSchemeDifferences() {
  // implementation
}

// Option 3: Convert to getter when appropriate
get userColorSchemeDifferences() {
  // implementation
}

This convention improves code clarity and follows modern JavaScript standards while maintaining team consistency.

---

CI conditional job handling

When implementing CI workflows with path-based filtering, ensure that conditional jobs don’t inadvertently block PR merges when they don’t execute. Maintain proper path filtering to run jobs only when relevant files change, but account for scenarios where filtered jobs are listed as required dependencies.

For workflows with path filtering, use if conditions or separate the conditional jobs from required job lists to prevent blocking PRs that don’t trigger those specific workflows.

Example of problematic configuration:

# atoms-e2e.yml - runs only on specific paths
on:
  pull_request:
    paths:
      - 'packages/atoms/**'

# pr.yml - requires atoms job even when it doesn't run
jobs:
  required-checks:
    needs: [
      e2e-embed,
      e2e-atoms,  # This blocks PRs when atoms-e2e doesn't run
    ]

Instead, handle conditional dependencies appropriately by either using conditional requirements or separating path-specific jobs from universal requirements.

---

Control event propagation

Prevent unintended network requests and interface conflicts by properly controlling event propagation in interactive elements. Use event.stopImmediatePropagation() when multiple event listeners on the same element or its ancestors could trigger conflicting network operations.

This is particularly important when:

• Form submissions or network requests could be triggered by event bubbling
• Multiple components handle the same event type and could interfere with each other
• Autocomplete or similar features need to prevent default browser behavior

Example:

case "Enter":
case "Tab":
  event.preventDefault();
  event.stopImmediatePropagation(); // Prevents other listeners from triggering unwanted network calls

Consider binding events to the most appropriate element level rather than relying on event bubbling, especially for network-triggering operations like prefetching or form submissions. This reduces the risk of unintended network activity and improves code maintainability.

---

break complex expressions

Break down complex boolean expressions and conditions into well-named intermediate variables to improve code readability and maintainability. Instead of writing dense one-liners, use descriptive variable names that clearly communicate the intent of each condition.

For unused parameters in catch blocks or function signatures, prefix them with an underscore to maintain access for debugging while silencing linter warnings.

Example of improving a complex boolean expression:

// Instead of this complex one-liner:
return !(d.status !== 'error' && Date.now() - d.updatedAt < gcTime)

// Break it down into descriptive variables:
const isError = d.status === 'error'
const isElapsed = Date.now() - d.updatedAt >= gcTime
return isError && isElapsed

Example of proper unused parameter handling:

// Instead of empty catch:
} catch {

// Use underscore prefix for potential debugging access:
} catch (_err) {
  // Can still access _err for console.log during development
}

This approach makes code self-documenting and easier to understand, debug, and maintain.

---

comprehensive test coverage

Ensure test suites provide comprehensive coverage by including edge cases, different input scenarios, and all code paths. Tests should cover not just the happy path, but also boundary conditions, error cases, and various input combinations.

When writing tests, consider these coverage areas:

• Edge cases: Empty inputs, null/undefined values, boundary conditions
• Input variations: Different data types, formats, and combinations that the code might encounter
• Integration scenarios: How the code behaves with different dependencies or configurations
• Error conditions: Invalid inputs, network failures, or other error states
• State changes: All possible state transitions and their effects

For example, when testing ARIA property binding:

// Don't just test basic functionality
it('should bind ARIA properties', () => {
  // Basic test...
});

// Also test edge cases and variations
it('should bind interpolated ARIA attributes', () => {
  // Test interpolation: aria-label="{{label}} menu"
});

it('should bind ARIA attribute names with hyphens', () => {
  // Test: aria-errormessage, aria-haspopup
});

it('should handle component inputs vs attributes', () => {
  // Test component with ariaLabel input vs aria-label attribute
});

Missing test coverage often indicates incomplete understanding of the feature’s behavior and can lead to regressions. Comprehensive testing builds confidence in code changes and helps catch issues before they reach production.

---

Improve code readability

Structure code to match logical flow and extract intermediate variables to improve readability. When dealing with multiple discrete cases, prefer switch statements over if/else chains for better extensibility. Replace magic numbers with named constants for self-documentation.

Examples:

Restructure conditionals to match logical flow:

// Instead of complex nested logic, make structure follow the logic
if (isDark) {
  load(…, true);
} else {
  load(…, false);
  load(…, true);
}

Extract intermediate variables:

// Extract complex expressions into named variables
const paramsString = transformedParams.join(", ");
return `[quote="${paramsString}"]\n${contents.trim()}\n[/quote]\n\n`;

Use switch for multiple cases:

// Switch statements are more extensible than if/else chains
switch (this.typeFilter) {
  case "user_selectable":
    schemes = schemes.filter((scheme) => scheme.user_selectable);
    break;
  case "from_theme":
    schemes = schemes.filter((scheme) => scheme.theme_id);
    break;
}

Replace magic numbers:

// Use named constants instead of magic numbers
const MAX_RESULTS = 20;
const MIN_ITEMS_FOR_FILTER = 8;

---

Design contextual API interfaces

API interfaces should expose only relevant data and functionality based on context, configuration, and user requirements. This principle ensures efficient data transfer, cleaner interfaces, and appropriate user experiences.

Key practices:

• Pass only required fields instead of entire objects to minimize data transfer
• Filter available actions/responses based on entity configuration flags
• Adapt interface behavior for different contexts (e.g., different app types, user permissions)
• Remove unnecessary parameters from API calls
• Use generic, context-appropriate naming for API events and methods

Example from the discussions:

// Instead of passing the entire schedule object
const DeleteDialogButton = ({ schedule, ... }) => {
  // Only pass required fields
  const DeleteDialogButton = ({ scheduleId, scheduleName, ... }) => {

// Filter actions based on configuration
const isDisabledCancelling = booking.eventType.disableCancelling;
const isDisabledRescheduling = booking.eventType.disableRescheduling;

if (isDisabledCancelling) {
  bookedActions = bookedActions.filter((action) => action.id !== "cancel");
}

if (isDisabledRescheduling) {
  bookedActions.forEach((action) => {
    if (action.id === "edit_booking") {
      action.actions = action.actions?.filter(
        ({ id }) => id !== "reschedule" && id !== "reschedule_request"
      );
    }
  });
}

This approach reduces payload sizes, improves performance, and creates more maintainable API contracts that clearly communicate their requirements and capabilities.

---

Use semantic naming

Choose semantic, non-redundant names that clearly express intent and context. Remove unnecessary prefixes when the context is already clear, use semantic design tokens instead of hardcoded values, and prefer precise type definitions over generic ones.

Key practices:

• Remove redundant prefixes: Use quickJumperInputWidth instead of paginationQuickJumperInputWidth when the context (pagination) is already established
• Use semantic design tokens: Replace hardcoded values like 8px with semantic tokens like token.marginXS
• Avoid unnecessary type aliases: Export functions directly rather than maintaining separate type definitions when the function signature is self-explanatory
• Use precise union types: Specify exact values like 'timePicker' | 'datePicker' instead of generic string types

Example:

// ❌ Redundant prefix and hardcoded value
const paginationQuickJumperInputWidth = '8px';

// ✅ Semantic naming
const quickJumperInputWidth = token.marginXS;

// ❌ Unnecessary type alias
type UseOrientation = (orientation?: Orientation) => [Orientation, boolean];
const useOrientation: UseOrientation = (orientation) => { ... };

// ✅ Direct export with clear signature
export default function useOrientation(orientation?: Orientation): [Orientation, boolean] { ... }

---

Guard unsafe API calls

Always check the availability or state of data before accessing potentially unsafe API methods that can throw runtime errors. Many Angular APIs provide guard methods to safely check state before accessing values.

For example, when working with the resource API, always use hasValue() to guard calls to value(), as calling value() on a resource in an error state will throw an exception:

// ❌ Unsafe - can throw if resource is in error state
@if (imgResource.value() === '') {
  <div>Error state</div>
} @else {
  <img [src]="imgResource.value()" />
}

// ✅ Safe - guard with hasValue() first
@if (imgResource.isLoading()) {
  <div>Loading...</div>
} @else if (imgResource.hasValue()) {
  <img [src]="imgResource.value()" />
} @else {
  <div>Error state - retry available</div>
}

This pattern applies to other Angular APIs as well. Similarly, when handling errors in RxJS streams, ensure error handlers return the correct observable types expected by operators like catchError, which expects an ObservableInput rather than raw values.

The key principle is defensive programming: verify the state or availability of data before attempting to access it, preventing runtime errors and providing better user experience through proper error states.

---

avoid dynamic test generation

Avoid using loops (forEach, for, etc.) to dynamically generate tests from arrays or objects, as this pattern makes debugging significantly harder. When a test fails, it’s difficult to set breakpoints on specific cases or identify which iteration caused the failure.

Instead, use one of these approaches:

Option 1: Individual tests for each case

test("autocompletes black text", async function (assert) {
  await testHexCode(assert, "000", "000000");
});

test("autocompletes white text", async function (assert) {
  await testHexCode(assert, "fff", "ffffff");
});

Option 2: Single test with multiple assertions

test("autocompletes hex codes", async function (assert) {
  let result;
  const autocompleteHex = (color) => (result = color.replace("#", ""));

  await render(
    <template><ColorInput @onChangeColor={{autocompleteHex}} /></template>
  );

  await fillIn(".hex-input", "000");
  assert.strictEqual(result, "000000", "black text");
  
  await fillIn(".hex-input", "fff");
  assert.strictEqual(result, "ffffff", "white text");
  
  await fillIn(".hex-input", "f2f");
  assert.strictEqual(result, "f2f2f2", "2 digit sequence");
}

Both approaches allow developers to easily debug specific test cases, set targeted breakpoints, and understand test failures more quickly. Choose individual tests when cases are complex or unrelated, and single tests with multiple assertions when testing variations of the same behavior.

---

Avoid breaking changes

When modifying existing APIs, prioritize backward compatibility to prevent breaking changes that would force developers to maintain separate code paths for different SDK versions. Use deprecation with clear migration paths instead of direct breaking changes, make new parameters optional with sensible defaults, and avoid changing existing default values.

For new required parameters, add them as optional with defaults:

// Instead of breaking change:
void getHandleAnchor(TextSelectionHandleType type, double textLineHeight, {required double cursorWidth})

// Use optional with default:
void getHandleAnchor(TextSelectionHandleType type, double textLineHeight, {double cursorWidth = 2.0})

For API replacements, use proper deprecation:

@Deprecated(
  'Use sendAnnouncement instead. '
  'This API is incompatible with multiple windows. '
  'This feature was deprecated after 3.35.0-0.1.pre.'
)
static Future<void> announce(String message) { ... }

static Future<void> sendAnnouncement(int viewId, String message) { ... }

Avoid changing default values as this constitutes a breaking change. Instead, add new options while preserving existing defaults. When designing new APIs, make parameters explicit rather than implicit to prevent future breaking changes when assumptions need to be updated.

---

Choose appropriate presentation formats

Select the most effective format for presenting different types of information in documentation. Use tables for structured data with multiple attributes, step-by-step explanations for processes, and clear section organization to avoid duplication or confusion.

For structured data like command options, use tables instead of lists:

| Flag | Type | Default | Description |
|------|------|---------|-------------|
| `--read-only` | boolean | `false` | Only register tools that do not make changes |
| `--local-only` | boolean | `false` | Only register tools that do not require internet |

For complex processes, provide detailed step-by-step breakdowns:

## How SSG works

Here's what happens when SSG renders your application:

1. Angular analyzes your routes at build time
2. Static HTML files are generated for each specified route
3. The initial page loads from pre-rendered HTML
4. Once loaded, navigation works like a standard CSR application

Avoid duplicating content between sections (like API reference and guides) unless adding substantial value through examples or different perspectives. Organize sections with clear, non-overlapping headers that accurately reflect their content scope.

---

validate business logic constraints

Before adding database constraints or designing schema relationships, thoroughly understand the underlying business logic and data relationships. Constraints that seem logical at first glance may break existing functionality or prevent valid use cases.

Key practices:

• Research existing code to understand how data is actually used before adding unique constraints
• Consider future extensibility when designing schemas - use discriminator fields instead of separate optional columns
• Validate that proposed constraints align with actual business requirements, not just theoretical data integrity

Example from schema design:

// Instead of separate optional fields for different credit types:
model CreditExpenseLog {
  smsSegments     Int?
  callDuration    Int?
  // Consider a more extensible approach:
  creditFor       String  // "SMS", "CALL", etc.
  amount          Int
  metadata        Json?   // Store type-specific data
}

This approach prevents constraint conflicts like @@unique([outlookSubscriptionId, eventTypeId]) when the same subscription ID is legitimately reused across multiple event types, and makes the schema more maintainable as new credit types are added.

---

Clarify configuration option limitations

When documenting or designing configuration options, explicitly state both what the option does AND what it doesn’t do, including any limitations or side effects. Users often make incorrect assumptions about configuration behavior based on names alone.

For example, avoid ambiguous descriptions like “Only register tools that do not make changes” and instead be specific about scope and limitations: “Only register Angular MCP tools that don’t modify your code. Your editor or coding agent may still perform edits.”

Similarly, when explaining optional configuration properties, clarify the implications of omitting them:

// ❌ Unclear: "you need to provide a configuration object"
@Injectable({ providedIn: 'root' })

// ✅ Clear: explain what happens when omitted
// providedIn isn't required; if omitted, the service isn't automatically 
// provided and must be added to the providers array of bootstrapApplication 
// or a component/directive
@Injectable()

This prevents developers from misunderstanding configuration behavior and helps them make informed decisions about which options to use in different contexts.

---

explicit type checking

Always perform explicit type and existence checks before operations that could fail with null or undefined values. Instead of relying on truthiness checks, use specific type guards to prevent runtime errors.

For function calls, check the actual type before invocation:

// Instead of just checking truthiness
if (rootNode.onRender) {
    rootNode.onRender();
}

// Use explicit type checking
if (typeof rootNode.onRender === 'function') {
    rootNode.onRender();
}

For value operations, handle edge cases explicitly:

// Instead of assuming non-empty
const outputHeight = output.split('\n').length;

// Handle empty values explicitly
const outputHeight = output === '' ? 0 : output.split('\n').length;

This pattern prevents common runtime errors caused by attempting operations on null, undefined, or incorrectly typed values, and makes the code’s assumptions explicit and safer.

---

avoid unnecessary complexity

Remove code complexity that doesn’t provide clear value, particularly in type definitions, configuration options, and formatting constraints. This includes eliminating redundant type omissions, using descriptive names for configuration options, and avoiding formatting rules that conflict with user preferences.

Examples of unnecessary complexity to avoid:

• Omitting types that get overwritten anyway: Omit<ButtonProps, 'href'> when href is replaced by the framework
• Generic configuration names: use routeFileFormatter instead of just formatter
• Formatting constraints that assume specific code structure and conflict with user style preferences

The goal is to maintain clean, readable code without imposing arbitrary style restrictions or type gymnastics that don’t serve a functional purpose. When in doubt, prefer simpler approaches that give users more control over their code style.

---

Prevent async race conditions

When handling multiple concurrent async operations (like user input triggering API calls or messageBus updates), implement mechanisms to prevent race conditions where stale results could overwrite newer state.

Use request IDs to track and validate async operations:

async fetchSuggestions() {
  const input = this.currentInputValue || "";
  const requestId = ++this.suggestionRequestId;
  
  const results = await this.suggester.search(input);
  
  // Only process if this is still the latest request
  if (requestId === this.suggestionRequestId) {
    this.suggestions = results;
  }
}

Alternatively, use AbortController to cancel outdated requests:

async fetchSuggestions() {
  // Cancel previous request
  if (this.abortController) {
    this.abortController.abort();
  }
  
  this.abortController = new AbortController();
  const results = await this.suggester.search(input, { 
    signal: this.abortController.signal 
  });
  
  this.suggestions = results;
}

This prevents scenarios where fast user interactions or component state changes could result in displaying incorrect data from slower, outdated async operations.

---

Explicit null checks

Always use explicit null and undefined checks instead of relying solely on optional chaining, especially when you need predictable boolean results or want to prevent null/undefined values from propagating to APIs, URLs, or causing runtime errors.

Use explicit checks with logical operators to ensure clean boolean results:

// Preferred: explicit check ensures boolean result
const isPlatformUser = redirectUrl && redirectUrl.includes("platform") && redirectUrl.includes("new");

// Avoid: optional chaining can return undefined, making isPlatformUser potentially undefined
const isPlatformUser = redirectUrl?.includes("platform") && redirectUrl?.includes("new");

Provide defensive fallbacks for arrays and objects that might be null/undefined:

// Safe array access with fallback
const schedule = (atomSchedule.schedule || []).map(avail => ({
  startTime: new Date(avail.startTime),
  endTime: new Date(avail.endTime),
  days: avail.days,
}));

// Prevent undefined values in object spreads
query: {
  slug: ctx.query.user,
  ...(ctx.query.orgRedirection !== undefined && { orgRedirection: ctx.query.orgRedirection }),
}

Check for both null and undefined when the distinction matters:

// Comprehensive check for functions that don't accept null
if (value !== undefined && value !== null) {
  return decodeURIComponent(value);
}

This approach prevents runtime errors, ensures predictable data types, and makes your code’s null-handling behavior explicit and intentional.

---

Use specific descriptive names

Choose specific, meaningful names that clearly communicate purpose rather than generic or ambiguous alternatives. This applies to classes, methods, variables, and examples in documentation.

For component classes, follow established naming conventions by removing unnecessary suffixes when they don’t add semantic value. For method names, select terms that clearly indicate functionality without creating confusion about the underlying implementation or capabilities.

In examples and documentation, prefer descriptive names that reflect the actual use case rather than generic placeholders.

Examples:

// Prefer specific over generic
export class CharacterViewer { } // instead of AppComponent
export class UserDetail { }      // instead of UserDetailComponent

// Choose clear, unambiguous method names  
stream: ({userId}) => this.userData.load(userId),  // instead of fetch()

// Use semantically accurate variable names
request: ({value}) => `/api/check-username?${value()}`, // correct signal usage

This practice improves code readability, reduces cognitive load, and helps other developers quickly understand the purpose and scope of different code elements.

---

Test organization standards

Write tests that are well-organized, maintainable, and reflect real usage patterns. Test names should describe behavior and requirements rather than implementation details. Group related tests under appropriate describe blocks and avoid redundant test cases.

Key principles:

• Name tests based on expected behavior: “should prevent multiple clicks when loading” instead of “should update loading state correctly when using ref”
• Group related tests logically: Use one describe block per feature/component area rather than creating separate describes for single test cases
• Test through realistic component usage patterns rather than isolated utility functions to ensure proper coverage
• Remove or consolidate redundant tests when new test cases already cover the same scenarios
• Extract complex test scenarios into dedicated test files (e.g., semantic.test.tsx) for better organization

Example of good test organization:

describe('CheckableTag', () => {
  it('should render icon when provided', () => {
    // Test icon rendering behavior
  });
  
  it('should handle click events correctly', () => {
    // Test click behavior
  });
  
  it('should support custom classNames and styles', () => {
    // Test styling behavior
  });
});

This approach makes tests easier to navigate, maintain, and ensures they accurately reflect how components are actually used in applications.

---

Keep API handlers thin

API handlers should be lightweight and focused on request/response handling, not business logic. Extract specific parameters from requests and delegate complex operations to dedicated services rather than handling everything in the controller.

Key principles:

• Parse and extract only the specific data needed from requests
• Avoid passing entire request objects to service methods
• Delegate business logic to application services
• Keep handlers focused on HTTP concerns (parsing, validation, response formatting)

Example of what to avoid:

async reassignBooking(bookingUid: string, requestUser: UserWithProfile, request: Request) {
  // Handler doing too much work with entire request object
}

Better approach:

async reassignBooking(bookingUid: string, requestUser: UserWithProfile, teamMemberEmail?: string) {
  // Extract specific parameter in handler, pass only what's needed
  const teamMemberEmail = req.query.teamMemberEmail;
  return this.bookingService.reassignBooking(bookingUid, requestUser, teamMemberEmail);
}

This pattern improves testability, reduces coupling, and makes the API surface clearer by explicitly showing what data each operation requires.

---

Semantic naming consistency

Choose semantically clear and consistent names across related elements in your codebase. Names should convey their purpose without requiring additional context or explanation, and related elements should follow consistent naming patterns.

Key principles:

• Use descriptive names that clearly indicate functionality (e.g., folder vs directory where folder aligns with native behavior)
• Maintain consistency between related elements like filenames and display names (e.g., if changing “Icon Position” to “Icon Placement”, also update the corresponding filename from icon-position.tsx to icon-placement.tsx)
• Avoid ambiguous or auto-generated identifiers (e.g., prefer #inputsearch over #inputsearch-1)
• Follow consistent ordering patterns for API documentation (alphabetical for properties, then methods)

Example:

// Good: Semantic and consistent naming
<code src="./demo/icon-placement.tsx">Icon Placement</code>

// Bad: Inconsistent between filename and display
<code src="./demo/icon-position.tsx">Icon Placement</code>

This ensures code is self-documenting and maintainable, reducing confusion for developers who encounter the code without prior context.

---

MessageBus subscription practices

When using MessageBus for network communication, follow these essential practices to ensure reliable message handling and prevent memory leaks:

1. Use consistent channel names between subscribe and unsubscribe calls to avoid subscription leaks
2. Include the third argument when subscribing for better message bus practices
3. Always pair subscriptions with unsubscriptions in component lifecycle methods

Example of proper MessageBus usage:

constructor() {
  super(...arguments);
  const settingName = this.setting.setting;
  
  if (this.canSubscribeToSettingsJobs) {
    // Use third argument for better practice
    this.messageBus.subscribe(`/site_setting/${settingName}/process`, this.onMessage, this);
  }
}

willDestroy() {
  super.willDestroy(...arguments);
  const settingName = this.setting.setting;
  
  if (this.canSubscribeToSettingsJobs) {
    // Ensure channel name matches subscription exactly
    this.messageBus.unsubscribe(`/site_setting/${settingName}/process`, this.onMessage);
  }
}

This prevents subscription leaks, improves message handling reliability, and follows MessageBus best practices for network communication management.

---

avoid @Optional decorator

Avoid using the @Optional decorator in NestJS dependency injection as it disables runtime DI validation during bootstrap. This can cause missing provider dependencies to go undetected during compilation, leading to runtime failures without clear error messages.

Instead of using @Optional, prefer TypeScript optional properties with the ? syntax to maintain type safety while preserving NestJS’s ability to validate dependencies at startup.

Example:

// Avoid - disables DI validation
constructor(
  @Optional()
  private sendWebhookMessage: SendWebhookMessage
) {}

// Prefer - maintains DI validation
constructor(
  private sendWebhookMessage?: SendWebhookMessage
) {}

This approach ensures that dependency injection issues are caught early in the development cycle rather than surfacing as obscure runtime errors in production.

---

Intentional async usage

Be deliberate about when to use the async keyword and await expressions. Making a function async changes its behavior - it will always return a Promise, even for early returns. This can break conditional logic that checks for synchronous vs asynchronous behavior.

Consider these patterns:

• Use async only when you actually need to await something
• For functions with early returns that should be synchronous, return Promise.all() or similar constructs directly instead of using async/await
• Remove unnecessary await keywords that don’t add value

Example from the codebase:

// Avoid: Always returns Promise due to async, breaks early return logic
const executeHead = async () => {
  if (!match) {
    return // Still returns Promise<undefined>
  }
  // ... rest of function
}

// Prefer: Early returns are synchronous, later returns are Promise
const executeHead = () => {
  if (!match) {
    return // Returns undefined directly
  }
  return Promise.all([
    // async operations here
  ])
}

This approach preserves the ability to use patterns like if('then' in result) to detect whether a function returned a Promise or a synchronous value.

---

Use semantic naming patterns

Establish consistent naming conventions that preserve semantic meaning and follow established patterns. Use descriptive names that clearly indicate purpose and type.

Key guidelines:

• Suffix enums with “Enum” for consistency: SeverityLevelEnum instead of SeverityLevel
• Prefix boolean functions with semantic indicators: shouldLogAnalytics() instead of isLogAnalytics()
• Use semantic names in iterations: map((variable) => ...) instead of map((error) => ...)
• Avoid confusing terms in class names: WorkflowStepFetcher instead of StepTemplateFetcher
• Preserve original casing in user-facing suggestions: use searchText instead of searchLower for variable name suggestions
• Maintain consistent parameter naming across similar functions: stick to workflowId rather than mixing workflowIdOrInternalId

Example:

// Good
export enum SeverityLevelEnum { ... }
function shouldLogAnalytics(): boolean { ... }
invalidVariables.map((variable) => ({ message: variable.name }))

// Avoid  
export enum SeverityLevel { ... }
function isLogAnalytics(): boolean { ... }
invalidVariables.map((error) => ({ message: error.name }))

This ensures code is self-documenting and maintains consistency across the codebase.

---

Configuration documentation standards

Ensure configuration properties and settings are documented with consistent formatting and precise specifications. Configuration property names should be wrapped in backticks for proper formatting in documentation and changelogs. Version dependencies must specify exact version ranges rather than vague references like “latest version”. Documentation should clearly describe what each configuration controls and its impact.

Examples of proper formatting:

• ✅ Button 组件支持 shape 全局配置 (property name in backticks)
• ✅ 使用 @ant-design/icons@5.x 配合 antd@5.x (specific version ranges)
• ✅ Tooltip 的渲染节点，默认渲染到 body 上 (clear description of what the configuration controls)

This standard helps maintain consistency across documentation, prevents version compatibility issues, and ensures developers understand exactly what each configuration option does and how to use it properly.

---

Safe setting modifications

When modifying site settings during operations like imports, jobs, or plugin initialization, implement proper safeguards to prevent unintended permanent changes. Consider the impact on existing sites and provide mechanisms for restoration or warnings.

Key practices:

• Wrap temporary setting changes in restore logic or dedicated configuration steps
• Query actual data requirements before adjusting settings (e.g., check maximum tag length before setting max_tag_length)
• Set conditional defaults based on plugin availability rather than hardcoded values
• Use centralized default configuration patterns like USER_OPTION_DEFAULTS instead of inline hardcoded values
• Provide warnings when settings will be modified, especially during imports to existing sites

Example from tag import:

# Instead of hardcoding:
SiteSetting.max_tag_length = 100 if SiteSetting.max_tag_length < 100

# Query actual requirements:
max_tag_length_needed = source_db.query("SELECT MAX(LENGTH(name)) FROM tags").first
SiteSetting.max_tag_length = max_tag_length_needed if SiteSetting.max_tag_length < max_tag_length_needed

Example for conditional defaults:

# In base configuration:
USER_OPTION_DEFAULTS = {
  hide_profile: SiteSetting.default_hide_profile,
  assignable_level: Group::ALIAS_LEVELS[:nobody] # Set unconditionally with comment explaining why
}

This approach prevents configuration drift, reduces surprises for site administrators, and makes operations more predictable across different environments.

---

leverage existing Angular patterns

Before implementing new functionality, check if Angular already provides a suitable utility, service, or pattern that can be reused. This promotes consistency across the codebase, reduces duplication, and follows established Angular conventions.

Key areas to check:

• Services and utilities: Use existing services like Clipboard service instead of implementing custom clipboard functionality
• API patterns: Follow established patterns like using ng global APIs for devtools functionality rather than creating new approaches
• Injection tokens: Use factory functions in injection tokens with default implementations instead of separate providers
• Built-in functions: Reuse existing functions like retrieveTransferredState() instead of reimplementing similar logic

Example of good practice:

// Instead of custom clipboard implementation
async copyToClipboard(text: string) {
  await navigator.clipboard.writeText(text);
}

// Use Angular's Clipboard service
constructor(private clipboard = inject(Clipboard)) {}
copyToClipboard(text: string) {
  this.clipboard.copy(text);
}

// Instead of separate provider
export const WINDOW_PROVIDER: Provider = {
  provide: WINDOW,
  useValue: window,
};

// Use factory in token definition
export const WINDOW = new InjectionToken<Window>('WINDOW', {
  factory: () => window,
});

This approach ensures better maintainability, leverages Angular’s built-in optimizations, and provides a more consistent developer experience.

---

Consistent text formatting

Ensure text formatting follows established guidelines and maintains consistency within the same context. This applies to documentation strings, localization files, user interface text, and error messages.

When established formatting guidelines exist, follow them consistently. For example, prefer sentence case over title case in user-facing strings:

# Good - follows sentence case guidelines
associated_accounts_by_provider:
  title: "Associated accounts by login method"
  labels:
    provider: "Login provider"
    no_accounts: "No associated accounts"

# Avoid - inconsistent title case
associated_accounts_by_provider:
  title: "Associated Accounts by Login Method"
  labels:
    provider: "Login Provider"

Additionally, maintain internal consistency within the same file or related contexts. Ensure similar elements use the same formatting patterns:

# Good - consistent formatting across similar entries
theme_source: "Theme '%{name}'"
plugin_source: "Plugin '%{name}'"

# Avoid - inconsistent punctuation
theme_source: "Theme '%{name}'"
plugin_source: "Plugin: '%{name}'"

This practice improves user experience, maintains professional appearance, and reduces cognitive load for both users and developers.

---

Verify SSR documentation accuracy

Ensure that documentation about server-side rendering (SSR), static site generation (SSG), and related rendering strategies is technically accurate and complete. Avoid making misleading claims about performance characteristics or technical behavior, and include all relevant benefits and use cases.

Common issues to watch for:

• Inaccurate claims about how rendering strategies affect bundle size (bundle size is primarily affected by lazy loading, not rendering strategy)
• Imprecise descriptions of when SSR occurs (e.g., “each request” vs “initial request”)
• Missing important benefits like SSR’s role in data pre-fetching and server-side data availability

Example of problematic content:

## Performance considerations
### Bundle size optimization
Different strategies affect bundle size:
- **SSR**: Initial bundle can be smaller with code splitting
- **SSG**: Optimal with incremental hydration and `@defer`

This section makes unsupported claims about SSR/SSG affecting bundle size when the actual factor is lazy loading and code splitting techniques that are independent of rendering strategy.

When documenting rendering strategies, verify technical claims against actual framework behavior and ensure comprehensive coverage of all benefits and limitations.

---

consistent configuration naming

Configuration variable names should follow consistent patterns and be descriptive enough to clearly convey their purpose and scope. When naming similar configuration parameters, maintain uniform naming conventions throughout the codebase.

For time-based configuration parameters, explicitly indicate the time scope in the variable name. Use consistent patterns like max_retries_per_day and max_retries_last_30_days rather than mixing formats like max_daily_retry_count and retry_count_30_day.

Example of improved naming:

# Instead of:
max_daily_retry_count = 3
retry_count_30_day = 20

# Use:
max_retries_per_day = 3
max_retries_last_30_days = 20

This approach makes configuration files more readable and reduces confusion when developers need to understand or modify these settings. Consistent naming patterns also make it easier to search for and group related configuration parameters.

---

Simplify complex expressions

Extract repeated expressions and complex conditional logic into clear, readable variables to improve code maintainability and reduce cognitive load.

Key practices:

• Extract repeated expressions (like Date.now(), type === 'countdown') into descriptive variables
• Replace nested ternary operators with if-else statements wrapped in useMemo for complex logic
• Use destructuring instead of repeated optional chaining (?.)
• Simplify conditional expressions by extracting boolean conditions into named variables

Example:

// ❌ Avoid: Complex nested ternary and repeated expressions
const closePosition = props.closable === false 
  ? undefined 
  : props.closable === undefined || props.closable === true || props.closable?.position === undefined || props.closable?.position === 'start'
    ? 'start' 
    : 'end';

// ❌ Avoid: Repeated expressions and optional chaining
if (down && timestamp < Date.now()) {
  const timeDiff = !down ? Date.now() - timestamp : timestamp - Date.now();
  customCheckboxProps?.onChange?.(e);
}

// ✅ Prefer: Clear variables and structured logic
const closePosition = useMemo(() => {
  const { closable } = props;
  
  if (closable === false) return undefined;
  if (closable === true || closable === undefined) return 'start';
  if (typeof closable === 'object') {
    return closable.position === 'end' ? 'end' : 'start';
  }
  return 'start';
}, [props.closable]);

// ✅ Prefer: Extract repeated expressions and destructure
const now = Date.now();
const isCountdown = type === 'countdown';
const { onChange } = customCheckboxProps || {};

if (isCountdown && timestamp < now) {
  const timeDiff = !isCountdown ? now - timestamp : timestamp - now;
  onChange?.(e);
}

This approach makes code more readable, easier to debug, and reduces the likelihood of errors from repeated complex expressions.

---

Specify stable dependency versions

Always use specific semantic versions or caret ranges for stable releases in package.json and other dependency configuration files. Avoid using “latest” or development/pre-release versions as they can introduce unpredictable behavior and breaking changes that affect build reproducibility and team consistency.

Use specific versions like:

{
  "devDependencies": {
    "eslint-plugin-unused-imports": "^3.0.0",
    "@prisma/extension-optimize": "^1.0.1"
  }
}

Instead of:

{
  "devDependencies": {
    "eslint-plugin-unused-imports": "latest",
    "@prisma/extension-optimize": "0.0.0-dev.202407222340"
  }
}

This practice ensures that all team members and CI/CD environments use the same dependency versions, preventing unexpected failures and maintaining consistent behavior across different development environments.

---

Dependency version specification

Ensure proper dependency version specification and compatibility management in package.json files. Use explicit version ranges for peer dependencies to express compatibility constraints, avoid workspace references in examples and published packages, and properly classify dependencies based on usage patterns.

Key practices:

• Use version ranges for peer dependencies to support multiple major versions: "zod": "^3.25.0 || ^4.0.0"
• Explicitly declare peer dependencies required by strict dependency managers like pnpm
• Replace workspace references with absolute versions in examples: use "^1.46.3" instead of "workspace:^"
• Add version constraints for peer dependencies: "arktype": ">=2 <=3"
• Avoid adding dependencies that are inherited from monorepo root (like vitest)
• Remove unused dependencies after verification they’re not actually used
• Use absolute version numbers without workspace prefixes for external compatibility (codesandbox, etc.)

Example:

{
  "peerDependencies": {
    "@tanstack/router-core": "^1.120.5",
    "zod": "^3.25.0 || ^4.0.0"
  },
  "devDependencies": {
    "@tanstack/react-router": "^1.46.3"
  }
}

---

API terminology consistency

Maintain consistent, precise terminology throughout API documentation and interfaces. Avoid ambiguous or misleading terms that could confuse developers about the API’s behavior, and use professional language that clearly communicates the intended functionality.

Key practices:

• Use precise technical terms that accurately describe behavior (e.g., avoid “async signals” when signals are always synchronous)
• Maintain consistent capitalization for technical terms (e.g., always use “HTTP” when not part of an identifier)
• Avoid informal or subjective language like “battle-tested” in favor of objective descriptions
• Eliminate first-person pronouns (“we”, “us”) in API documentation

Example of improved terminology:

// Instead of: "Managing async signals with Resources API"
// Use: "Managing async data with Resources API"

// Instead of: "battle-tested libraries like Zod"  
// Use: "popular open-source libraries like Zod"

// Instead of: "You can define an http resource"
// Use: "You can define an HTTP resource"

This ensures developers have a clear, unambiguous understanding of API capabilities and constraints, reducing integration errors and improving the overall developer experience.

---

Consider accessibility in markup

When writing HTML markup, consider the accessibility implications of your formatting and structural choices. This includes avoiding text formatting that may negatively impact screen readers and ensuring proper semantic HTML usage.

Key considerations:

• Avoid ALL CAPS text in content as screen readers may spell out each letter individually (“E-V-E-N” instead of “even”)
• Use semantic HTML elements appropriately - for example, nav elements should contain navigation links, not standalone buttons
• Consider whether container elements serve a semantic purpose or if they can be simplified

Example of problematic markup:

<nav>
  <button type="button" (click)="toggle()">Toggle Element</button>
</nav>
<div class="indicator">
  EVEN
</div>

Better approach:

<button type="button" (click)="toggle()">Toggle Element</button>
<div class="indicator">
  Even
</div>

This ensures better screen reader compatibility and cleaner semantic structure while maintaining the same functionality.

---

Prefer early returns

Use early returns and guard clauses instead of nested if-else statements to improve code readability and reduce complexity. Apply the fail-fast principle by handling edge cases and invalid conditions first, then proceeding with the main logic.

Benefits:

• Reduces nesting levels making code easier to follow
• Makes the happy path more prominent and readable
• Eliminates unnecessary else clauses
• Improves maintainability by clearly separating error handling from business logic

Examples:

Instead of:

const isCancellationReasonRequired = () => {
  if (!props.teamCancellationSettings) {
    return props.isHost;
  }
  
  if (props.isHost) {
    return props.teamCancellationSettings.mandatoryCancellationReasonForHost;
  } else {
    return props.teamCancellationSettings.mandatoryCancellationReasonForAttendee;
  }
};

Prefer:

const isCancellationReasonRequired = () => {
  if (!props.teamCancellationSettings) {
    return props.isHost;
  }
  
  if (props.isHost) return props.teamCancellationSettings.mandatoryCancellationReasonForHost;
  
  return props.teamCancellationSettings.mandatoryCancellationReasonForAttendee;
};

For conditional rendering, handle the simpler/shorter condition first:

// Instead of lengthy if-else blocks
{!schedule?.timeBlocks?.length ? (
  <SimpleComponent />
) : (
  <ComplexComponent />
)}

---

Stable Index Mapping

Prefer stable data-structure lookups over recomputing indices in update paths—especially when the underlying collection can reorder.

Guideline

1. Avoid linear searches in hot paths: if you need an element’s position during frequent updates, don’t use patterns like array.indexOf(x) repeatedly. Use a map (e.g., WeakMap/Map) that gives the current index in O(1).
2. Preserve invariants under reordering: if you consider capturing an index in a subscription/callback, ensure that index remains valid after operations like setQueries() reorder the internal list. If not, don’t capture the position—compute it via the maintained map at update time.
3. Add regression tests for subtle ordering/shape issues:
   • Ordering: tests should cover reordering while subscriptions are active, and verify result placement after updates/invalidation.
   • Aggregation semantics: when appending streamed chunks, ensure you don’t accidentally change array dimensionality (e.g., avoid implicit flattening).

Example (index stability + O(1) lookup)

// Bad: recomputes position each update (and may be O(n))
function onUpdate(observer: Observer, result: Result) {
  const index = observers.indexOf(observer) // linear + fragile
  if (index !== -1) results[index] = result
}

// Good: keep a maintained index map and look up at update time
const indexMap = new WeakMap<Observer, number>()

function onUpdate(observer: Observer, result: Result) {
  const index = indexMap.get(observer)
  if (index !== undefined) results[index] = result
}

Example (stream aggregation shape correctness)

// If TQueryFnData could itself be an array, avoid implicit flattening:
// concat(chunk) may flatten a chunk when chunk is an array.
result = prev.concat([chunk]) // keeps 1-dimensional “array of chunks” shape

---

ensure test reliability

Write tests that are stable, independent, and non-flaky by following proper isolation and waiting practices. Tests should create their own data, clean up after themselves, and avoid dependencies on other tests or external state.

Key practices:

• Test Isolation: Each test should create its own test data and clean up afterward to avoid dependencies between tests
• Proper Waiting: Use waitForLoadState("networkidle") or wait for specific elements instead of arbitrary timeouts with waitForTimeout()
• Avoid Hardcoded Values: Use dynamic values (like randomString()) instead of hardcoded identifiers that might conflict
• Cleanup Resources: Always clean up created test data to prevent state leakage

Example of proper test isolation:

it("should create the membership of the org", async () => {
  // Create test user for this specific test
  const testUserForCreate = await userRepositoryFixture.create({
    email: `test-create-${randomString()}@api.com`,
    username: `test-create-${randomString()}`,
  });

  return request(app.getHttpServer())
    .post(`/v2/organizations/${org.id}/memberships`)
    .send({ userId: testUserForCreate.id, accepted: true, role: "MEMBER" })
    .expect(201)
    .then(async (response) => {
      const createdMembership = response.body.data;
      // ... assertions ...
      
      // Clean up
      await membershipRepositoryFixture.delete(createdMembership.id);
      await userRepositoryFixture.deleteByEmail(testUserForCreate.email);
    });
});

Reliable tests reduce CI failures, improve developer confidence, and prevent blocking of development workflows.

---

Avoid redundant operations

Identify and eliminate duplicate or inefficient operations that waste computational resources. Common patterns to watch for include:

1. Duplicate function calls: Multiple calls to expensive operations like database queries or API endpoints within the same request flow
2. Inefficient database queries: Fetching all records and filtering in memory instead of using proper WHERE clauses
3. Excessive API calls: Triggering API calls on frequent user interactions like keystrokes without debouncing

Example of problematic code:

// Bad: Duplicate expensive calls
await getAvailableSlots({...}); // calls getUserAvailability internally
await ensureAvailableUsers({...}); // also calls getUserAvailability internally

// Bad: Inefficient database query
const allSubscriptions = await prisma.calendarSubscription.findMany({
  select: { selectedCalendarId: true },
});
const excludeIds = allSubscriptions.map((sub) => sub.selectedCalendarId);

// Good: Single call or proper WHERE clause
await ensureAvailableUsers({users: [...users, ...guests]});

// Good: Efficient database query
const selectedCalendars = await prisma.selectedCalendar.findMany({
  where: { calendarSubscriptionId: null }
});

Before implementing functionality, analyze the call flow to identify potential redundant operations and consolidate them into single, efficient calls.

---

Provide specific error context

Error messages should be specific and contextual rather than generic, helping users understand exactly what went wrong and where. When handling errors, provide detailed information about the cause and set errors on the specific fields or components that triggered them.

For API errors, catch specific error conditions and set targeted error messages:

onError: (error) => {
  // Check if it's a conflict error (topic already exists)
  if (error instanceof NovuApiError && error.status === 409) {
    // Set error on the key field specifically
    form.setError('key', {
      type: 'manual',
      message: 'A topic with this key already exists',
    });
  }
}

Instead of generic messages like “Step was skipped”, provide context about why the action failed: “Step skipped due to missing credentials” or “Step skipped - email address required”. This helps users quickly understand what happened and what they might need to do to resolve the issue.

---

avoid redundant operations

Identify and eliminate redundant computations, function calls, and expensive operations that can be cached, memoized, or combined. This includes avoiding repeated function invocations with the same parameters, caching expensive calculations, and combining multiple operations that access the same data.

Examples of optimization opportunities:

• Cache expensive function results: Instead of calling getComponentDef(instance.constructor) multiple times, store the result in a variable
• Combine related operations: Merge isAnimationRunning and cancelAnimations functions to avoid duplicate animation lookups
• Extract static objects: Move objects and functions that don’t depend on method parameters outside the method to avoid recreation on each call
• Use memoization: For expensive logic functions that may be called repeatedly with the same inputs, consider using computed signals or manual caching

// Before: Redundant function calls
function componentUsesShadowDomEncapsulation(lView: LView): boolean {
  const instance = lView[CONTEXT];
  return instance?.constructor
    ? getComponentDef(instance.constructor)?.encapsulation === ViewEncapsulation.ShadowDom ||
        getComponentDef(instance.constructor)?.encapsulation === ViewEncapsulation.IsolatedShadowDom
    : false;
}

// After: Cache the result
function componentUsesShadowDomEncapsulation(lView: LView): boolean {
  const instance = lView[CONTEXT];
  if (!instance?.constructor) return false;
  
  const componentDef = getComponentDef(instance.constructor);
  return componentDef?.encapsulation === ViewEncapsulation.ShadowDom ||
         componentDef?.encapsulation === ViewEncapsulation.IsolatedShadowDom;
}

This optimization reduces computational overhead, improves runtime performance, and can significantly impact applications with frequent function calls or expensive operations.

---

limit error handling scope

When implementing error handling, carefully limit the scope of try-catch blocks to prevent cascading failures and ensure error handlers themselves cannot cause additional errors. Wrap only the specific operations that may throw, not the error handling logic itself.

The key principle is that error handlers should be resilient and not introduce new failure points. If an error handler throws, it can mask the original error and make debugging significantly more difficult.

Example of proper scope limiting:

// ❌ Bad: try-catch wraps both injection and error handler execution
try {
  const errorHandler = injector.get(INTERNAL_APPLICATION_ERROR_HANDLER, null);
  errorHandler?.(error);
} catch (err) {
  // This catches errors from both injection AND error handler execution
}

// ✅ Good: try-catch only wraps the injection call
try {
  const errorHandler = injector.get(INTERNAL_APPLICATION_ERROR_HANDLER, null);
} catch (err) {
  // Handle injection failure
  return;
}
// Error handler executes outside try-catch - if it throws, we want to know
errorHandler?.(error);

Additional considerations:

• For non-critical operations (like logging or debugging), consider ignoring errors entirely rather than propagating them
• Use conditional checks before processing to avoid unnecessary allocations and operations
• When errors are expected due to baseline API support, document why they’re being ignored

This approach ensures that error handling remains predictable and doesn’t introduce additional failure modes that could compromise system stability.

---

Use dynamic configuration access

Always access configuration values through proper service APIs rather than hardcoding them or using unreliable access patterns. This ensures configuration remains maintainable and behaves consistently across different contexts.

When accessing site settings or configuration values:

• Use established service patterns like site service for configuration lookup
• Avoid hardcoding configuration arrays or objects directly in code
• Prefer reliable configuration access methods over workarounds

Example of proper configuration access:

// Instead of hardcoding:
const response = await ajax("/hashtags", {
  data: { slugs, order: ["category", "channel", "tag"] },
});

// Use service-based lookup:
const response = await ajax("/hashtags", {
  data: { slugs, order: this.site.hashtag_configurations.order },
});

This approach prevents issues where “the value was always false even when the site setting was true” and eliminates the need for temporary hardcoded values that developers “forgot to go back and replace.”

---

Avoid repeated object creation

Prevent performance degradation by avoiding the creation of functions, objects, regular expressions, and other expensive operations inside loops or frequently executed code paths. Instead, hoist these creations outside the loop or to a higher scope where they can be reused.

This optimization is particularly important in performance-critical sections like routing logic, data processing loops, and render functions where the same operation may be executed hundreds or thousands of times.

Examples of what to avoid:

// Bad: Function created on every iteration
for (const [index, match] of matches.entries()) {
  function makeMaybe(value, error) {
    if (error) return { status: 'error', error }
    return { status: 'success', value }
  }
  // use makeMaybe...
}

// Bad: Regex created on every filter call
items.filter(d => !d.name.match(new RegExp(pattern, 'g')))

Better approach:

// Good: Function hoisted outside the loop
function makeMaybe(value, error) {
  if (error) return { status: 'error', error }
  return { status: 'success', value }
}

for (const [index, match] of matches.entries()) {
  // use makeMaybe...
}

// Good: Regex created once
const regex = new RegExp(pattern, 'g')
items.filter(d => !d.name.match(regex))

This practice reduces memory allocation overhead, garbage collection pressure, and improves execution speed in performance-sensitive code paths.

---

API consistency patterns

Ensure API design follows consistent patterns for naming, typing, and composition to improve developer experience and maintainability.

Key principles:

1. Use fully qualified names in deprecation messages - Include the full path like MetaArgs.loaderData instead of just loaderData to provide clear migration guidance.

2. Prefer type-only imports for types - Use import type { ServerBuild } instead of import { ServerBuild } when importing only for type annotations.

3. Use consistent generic parameter naming - Prefer descriptive names like Context over abbreviated forms like C for better readability:

   export interface LoaderFunction<Context = any> {
     (args: LoaderFunctionArgs<Context>): Promise<DataFunctionValue> | DataFunctionValue;
   }
   

4. Choose appropriate type definitions - Use export type for simple function signatures instead of interfaces when no extension is needed:

   export type HeadersFunction = (args: HeadersArgs) => Headers | HeadersInit;
   

5. Build composable APIs - Design new functions to leverage existing ones rather than duplicating logic:

   export const redirectWithReload: RedirectFunction = (url, init) => {
     let response = redirect(url, init);
     response.headers.set("X-Remix-Reload-Document", "true");
     return response;
   };
   

6. Preserve request context appropriately - When creating new request objects, copy relevant properties from the original rather than creating minimal requests:

   let loaderRequest = new Request(request.url, {
     body: null,
     headers: request.headers,
     method: request.method,
     redirect: request.redirect,
     signal: request.signal,
   });
   

These patterns improve API discoverability, reduce confusion during migrations, and create more predictable interfaces for developers.

---

Mock external dependencies only

When writing tests for Home Assistant integrations, mock external library dependencies rather than Home Assistant internals like coordinators, entities, or config entries. Test integration behavior through proper setup and service calls instead of directly manipulating internal objects.

What to mock:

• External API clients and libraries your integration depends on
• Network calls, file system operations, and other I/O
• Third-party services and hardware interfaces

What NOT to mock:

• Home Assistant coordinators, entities, or platforms
• Config entries, entity registry, or device registry
• Home Assistant’s internal service layer

How to test:

• Set up the integration normally using config_entry.add_to_hass(hass) and hass.config_entries.async_setup()
• Use hass.services.async_call() to simulate user interactions
• Verify behavior through entity states and service call effects
• Test error conditions by making your mocked external library raise exceptions

Example:

# ❌ Don't mock HA internals
@pytest.fixture
def mock_coordinator():
    coordinator = Mock(spec=MyDataUpdateCoordinator)
    coordinator.data = {"device_1": {"state": "on"}}
    return coordinator

# ✅ Mock external library instead
@pytest.fixture
def mock_api_client():
    with patch("my_integration.MyAPIClient") as mock:
        client = mock.return_value
        client.get_devices.return_value = [{"id": "device_1", "state": "on"}]
        client.set_device_state = AsyncMock()
        yield client

# ✅ Test through service calls
async def test_turn_on_device(hass, mock_api_client, config_entry):
    config_entry.add_to_hass(hass)
    await hass.config_entries.async_setup(config_entry.entry_id)
    
    await hass.services.async_call(
        "switch", "turn_on", {"entity_id": "switch.my_device"}, blocking=True
    )
    
    mock_api_client.set_device_state.assert_called_once_with("device_1", True)

This approach ensures tests verify actual integration behavior rather than implementation details, making them more robust and meaningful.

---

avoid code duplication

Create reusable components instead of duplicating similar code patterns. When you find yourself writing similar classes, functions, or logic blocks, extract the common functionality into base classes, helper functions, or generic components that can be parameterized.

Examples of duplication to avoid:

• Multiple entity classes with similar structure - create a base entity class
• Repeated device info logic across platforms - move to shared base entity or helper function
• Similar validation or processing logic - extract to utility functions in separate modules
• Multiple classes differing only in small details - create generic class with configurable descriptions

For instance, instead of creating separate button classes:

class SetSleepTimerButton(ButtonEntity):
    # implementation

class ClearSleepTimerButton(ButtonEntity):  
    # similar implementation

Create a generic class with descriptions:

class GenericButton(ButtonEntity):
    def __init__(self, description: ButtonEntityDescription):
        self.entity_description = description
        
    async def async_press(self) -> None:
        await self.entity_description.press_fn()

This approach improves maintainability, reduces bugs, and makes code more readable by eliminating repetitive patterns.

---

organize related code together

Keep related functionality grouped together to improve code discoverability and maintainability. This includes placing related functions in the same module, maintaining consistent test file placement, and avoiding unnecessary file fragmentation.

Key practices:

• Place related functions near each other (e.g., prependBasename should live in utils.ts next to stripBasename)
• Maintain consistent test file organization within the repository - either always use __tests__ directories or always place tests next to implementation
• Avoid creating single-line modules when the code could logically belong in an existing utility module
• Group related types and exports in appropriate directory structures (e.g., exports from internal-export.ts live in types/internal-export/ folder)
• Prefer direct imports from source files over barrel file re-exports to maintain clear dependency relationships

Example of good organization:

// utils.ts - related string manipulation functions together
export function stripBasename(pathname: string, basename: string) { ... }
export function prependBasename(pathname: string, basename: string) { ... }

// Avoid creating separate single-line modules when functionality fits logically elsewhere
// Instead of: types/register.ts with just "export interface Register {}"
// Consider: utils.ts or existing appropriate module

This approach reduces cognitive load when navigating the codebase and makes it easier to find related functionality.

---

Use shared string keys

Replace hardcoded strings in configuration files with shared string key references to maintain consistency and enable centralized management. This practice reduces duplication, ensures uniform messaging across components, and makes updates easier to maintain.

Instead of using hardcoded strings:

{
  "config": {
    "step": {
      "user": {
        "data": {
          "email": "Email",
          "password": "Password"
        }
      }
    },
    "abort": {
      "already_configured": "Device is already configured"
    }
  }
}

Use shared string key references:

{
  "config": {
    "step": {
      "user": {
        "data": {
          "email": "[%key:common::config_flow::data::email%]",
          "password": "[%key:common::config_flow::data::password%]"
        }
      }
    },
    "abort": {
      "already_configured": "[%key:common::config_flow::abort::already_configured_device%]"
    }
  }
}

This approach allows for centralized string management, consistent terminology across the application, and easier localization. Look for existing common keys before creating new hardcoded strings, and reuse error messages and standard configuration labels wherever possible.

---

API naming consistency

Ensure related APIs use consistent naming patterns, parameter structures, and calling conventions across the codebase. When introducing new APIs alongside existing ones, maintain naming consistency to provide clarity and reduce cognitive load for developers.

Key principles:

• Use consistent naming patterns for related functionality (e.g., loaderData and actionData instead of mixing data and actionData)
• Apply consistent calling conventions (e.g., if one configuration expects a function call like routes(), maintain that pattern)
• Use consistent formatting in documentation and changesets (e.g., backticks around API names: createWorkersKVSessionStorage)
• When deprecating APIs, provide clear migration paths with consistent naming in the replacement

Example of good consistency:

// Before: Inconsistent naming
interface RouteArgs {
  data: any;           // inconsistent with actionData
  actionData: any;
}

// After: Consistent naming  
interface RouteArgs {
  loaderData: any;     // consistent with actionData
  actionData: any;
}

This ensures developers can predict API patterns and reduces the learning curve when working with related functionality.

---

Guard nullable value access

Always use appropriate guards or type checks before accessing potentially null or undefined values. Prefer type-safe guard methods that provide both runtime protection and TypeScript type narrowing over manual null checks.

For Angular resource APIs, use hasValue() before accessing value() since it acts as both an error guard and type guard that narrows the type to remove undefined:

const firstName = computed(() => {
  if (userResource.hasValue()) {
    // hasValue() guards against errors and narrows type
    return userResource.value().firstName;
  }
  return undefined; // fallback for error/loading states
});

For optional component inputs or router data, prefer making inputs required when possible rather than handling undefined throughout your component:

// Prefer this - required input
settings = input.required<Settings>();

// Over this - optional input requiring null checks
settings = input<Settings>(); // Would need settings()?.theme

This pattern prevents runtime errors while leveraging TypeScript’s type system to catch potential null reference issues at compile time.

---

Configuration access patterns

Ensure configuration data is accessed through proper service layers with dependency injection rather than direct database calls in presentation components. Configuration settings should be retrieved via dedicated repository classes or service methods, not through direct Prisma interactions in getServerSideProps or component logic.

This pattern improves testability, maintainability, and follows proper separation of concerns. Configuration access should be abstracted behind service interfaces that can be easily mocked and tested.

Example of what to avoid:

// Bad: Direct Prisma call in getServerSideProps
const teamSettings = await prisma.team.findUnique({
  where: { id: teamId },
  select: {
    mandatoryCancellationReasonForHost: true,
    mandatoryCancellationReasonForAttendee: true,
  },
});

Example of proper approach:

// Good: Use service layer with dependency injection
const teamSettings = await teamConfigurationService.getTeamCancellationSettings(teamId);

Additionally, avoid hardcoded configuration values like !true and instead use proper boolean constants or configuration objects that clearly express intent and can be easily modified.

---

Batch operations efficiently

Collect and execute similar operations together rather than performing them individually to reduce overhead and improve performance. This applies to entity creation, API calls, and state updates.

Key optimization strategies:

1. Batch entity additions: Collect all entities during initialization and add them with a single async_add_entities() call instead of multiple calls
2. Combine executor jobs: Group related synchronous operations into a single executor job to minimize expensive context switching between the event loop and thread pool
3. Use selective updates: Choose appropriate update mechanisms - use async_update_listeners() when state is already updated locally, or async_request_refresh() for buffered updates instead of immediate full refreshes

Example of batching entity creation:

# Instead of multiple calls:
if param_sensors:
    async_add_entities(param_sensors)
if status_sensors:
    async_add_entities(status_sensors)
if alarm_sensors:
    async_add_entities(alarm_sensors)

# Collect all entities and add at once:
all_entities = []
all_entities.extend(param_sensors)
all_entities.extend(status_sensors) 
all_entities.extend(alarm_sensors)
if all_entities:
    async_add_entities(all_entities)

This approach reduces function call overhead, improves code clarity, and can significantly improve performance when dealing with large numbers of operations.

---

Use accessible terminology

Choose clear, understandable names and terminology that are appropriate for your intended audience, avoiding technical jargon or obscure references that may not be widely understood. This is especially important for user-facing strings, error messages, and interface labels.

When naming user-facing elements, prioritize clarity over brevity. For example, use “Internal Notes” or “Moderator Notes” instead of ambiguous terms, and explain concepts rather than referencing technical terms like “Scunthorpe Problem” that administrators may not recognize.

Additionally, consider internationalization implications when choosing names and variable patterns. Use proper pluralization forms even for constants, as translators need context and many languages have complex pluralization rules.

Example:

# Avoid technical jargon
comparison: Please be mindful of the Scunthorpe Problem when blocking partial matches

# Better - explain the concept clearly  
comparison: Be careful when blocking partial matches, as legitimate words may contain blocked terms

# Use proper pluralization even for constants
over_total_limit: You have exceeded the limit of %{limit} scheduled posts

# Better - supports all languages properly
over_total_limit:
  one: You have exceeded the limit of %{limit} scheduled post
  other: You have exceeded the limit of %{limit} scheduled posts

---

Environment-aware feature gating

Always check environment variables, deployment modes, subscription tiers, and feature flags before enabling functionality or changing application behavior. Combine multiple configuration checks when necessary to ensure features are only available in appropriate contexts.

Key practices:

• Check environment type before enabling development-only features
• Validate subscription tiers before allowing premium functionality
• Combine feature flags with environment checks for proper gating
• Use different behavior paths for self-hosted vs cloud deployments

Example implementation:

// Check environment type for dev-only features
{currentEnvironment?.type === EnvironmentTypeEnum.DEV ? (
  <DevelopmentEditor />
) : (
  <ProductionView />
)}

// Combine subscription tier with feature limits
if (tier === ApiServiceLevelEnum.FREE && data?.layouts?.length >= 1) {
  return <UpgradePrompt />;
}

// Combine feature flags with deployment mode
{isWebhooksManagementEnabled && !IS_SELF_HOSTED && (
  <WebhooksSection />
)}

// Different behavior for deployment modes
{IS_SELF_HOSTED ? 'Contact Sales' : 'Upgrade to Team Tier'}

This approach prevents features from being exposed in inappropriate environments and ensures consistent behavior across different deployment scenarios.

---

Use asyncio.gather concurrency

When performing multiple independent async operations, use asyncio.gather() to execute them concurrently instead of sequentially. This improves performance by allowing operations to run in parallel rather than waiting for each to complete before starting the next.

Apply this pattern when you have:

• Multiple API calls that don’t depend on each other
• Independent coordinator refreshes during setup
• Parallel data fetching operations

Avoid creating individual tasks for frequent operations that could be batched together, as this leads to task proliferation and overhead.

Example:

# Instead of sequential execution:
records_a = await client.list_dns_records(zone_id=zone_id, type="A")
records_aaaa = await client.list_dns_records(zone_id=zone_id, type="AAAA")

# Use concurrent execution:
records_a, records_aaaa = await asyncio.gather(
    client.list_dns_records(zone_id=zone_id, type="A"),
    client.list_dns_records(zone_id=zone_id, type="AAAA")
)

# For coordinator setup:
await asyncio.gather(
    *(coordinator.async_config_entry_first_refresh() for coordinator in coordinators)
)

This pattern significantly reduces total execution time when operations can run independently and improves overall system responsiveness.

---

Avoid optimization anti-patterns

Identify and eliminate code patterns that appear to be performance optimizations but actually hurt performance or negate their intended benefits. Common anti-patterns include:

1. Ineffective debouncing: Cancelling debounce timers immediately before setting new ones defeats the purpose of debouncing and can lead to excessive function calls.

2. Misused performance decorators: Using decorators like @cached when a native getter would suffice can introduce negative performance implications in modern frameworks.

3. Excessive component instantiation: Rendering patterns that create unnecessary component instances (e.g., rendering every placeholder in every position) waste resources and hurt performance.

Example of debouncing anti-pattern:

// Anti-pattern: Cancelling debounce immediately
if (this.searchTimer) {
  cancel(this.searchTimer); // This negates debouncing benefits
}
this.searchTimer = discourseDebounce(this, this._performSearch, 300);

// Better: Let debounce handle the timing
this.searchTimer = discourseDebounce(this, this._performSearch, 300);

Before implementing performance optimizations, verify they actually provide the intended benefit and don’t introduce overhead that outweighs their advantages. Profile and measure the impact of optimization patterns to ensure they deliver real performance improvements.

---

API response transformation

When integrating external APIs, implement a translation layer that transforms responses into a standardized, user-friendly format. This protects consumers from upstream API changes and ensures responses are self-documenting without requiring external documentation.

Key practices:

• Convert field names to snake_case for consistency
• Transform complex data structures into intuitive formats (e.g., duration arrays like [12, 0] into {“hours”: 12, “minutes”: 0})
• Maintain schema control to prevent breaking changes when external APIs evolve
• Ensure responses are consumable without referring to external API documentation

Example transformation:

# External API response
{
  "programId": 146,
  "duration": [12, 0]  # hours, minutes array
}

# Transformed response
{
  "program_id": 146,
  "duration": {
    "hours": 12,
    "minutes": 0
  }
}

This approach ensures automations and integrations remain stable even when external API providers make undocumented changes, while improving the developer experience through clear, self-explanatory data structures.

---

classify data sensitivity

Properly evaluate whether data contains sensitive information before applying security measures like redaction. Not all identifiers or structured data require protection - understand the nature and content of the data to make informed security decisions.

For example, group IDs that are random strings (like 66a810bbaa36cf27c75073afb71aeda4b6b1f9d4-422) don’t contain personal information and may not need redaction in test snapshots, while actual user credentials or personal identifiers would require protection.

# Good - Understanding data nature before redaction
'groups': dict({
  'test-groupid': dict({  # Random string, not sensitive
    'name': '**REDACTED**',  # Actual group name may be sensitive
  }),
})

Consider the actual content and purpose of data rather than applying blanket security policies to all structured information.

---

Consistent naming standards

Ensure all user-facing strings follow Home Assistant’s naming conventions for consistency and proper internationalization. This includes using sentence-case for translatable strings, proper spelling and capitalization of technical terms, and leveraging common string references where available.

Key requirements:

• Use sentence-case for all translatable strings: “Network role” not “Network Role”
• Capitalize abbreviations consistently: “API key”, “VIN”, “URL”, “ID”
• Use correct spelling: “IFTTT” not “IFTT”, “Unsynchronized” not “Unsynchronised”
• Prefer standard terminology: “Maximum/Minimum” over “Maximal/Minimal”
• Leverage common string references: "[%key:common::state::charging%]" instead of custom “Charging”
• Write out unclear abbreviations: “Trip manual average speed” instead of “TM avg. speed”

Example corrections:

// Before
"name": "Network Role"
"api_key": "API key"
"charging_system_charging": "Charging"

// After  
"name": "Network role"
"api_key": "[%key:common::config_flow::data::api_key%]"
"charging_system_charging": "[%key:common::state::charging%]"

This ensures consistent user experience across the platform and enables proper translation workflows.

---

Stable, Controllable API

When changing or adding public API in schema/validation libraries, prioritize a stable, user-controlled surface:

• Avoid “deprecated-from-day-1” APIs. If an equivalent non-deprecated API already exists, prefer removing/migrating rather than adding new deprecated entry points.
• Make behavioral toggles user-configurable via options (e.g., allow selectively disabling specific validation checks) instead of bundling all behaviors unconditionally.
• Preserve backward compatibility in type-level changes: when introducing new generic/type parameters (e.g., adding an options-driven strictness flag), provide non-breaking defaults.
• Keep user-facing helper typing tied to the schema contract (e.g., exemplify() should constrain the example to the schema’s output type so changes break at compile time).
• Ensure format/shorthand APIs are “feature-complete” for the migration story (missing refinement methods becomes a blocker when deprecated methods are removed).
• Export public types that users need to compose APIs (e.g., discriminated-union option types), matching how other package types are exposed.

Example (options-based control idea):

// Don’t hard-code all hostname checks; allow opt-out per consumer need.
const schema = z.string().hostname({
  allowIPv4: true,
  allowIPv6: false,
  allowPunycode: true,
});

---

Clear variable naming

Use descriptive, unambiguous variable and function names that clearly convey their purpose and avoid conflicts with Python built-ins or Home Assistant conventions.

Key Guidelines:

• Avoid overriding Python built-in names like id, list, type
• Use descriptive names that prevent confusion about functionality
• Follow Home Assistant naming conventions for entities and translation keys
• Avoid unnecessary prefixes in unique identifiers

Examples:

# Bad: Overrides Python built-in
@dataclass
class RedgtechDevice:
    id: str  # Conflicts with built-in id() function

# Good: Use descriptive alternative
@dataclass
class RedgtechDevice:
    unique_id: str

# Bad: Ambiguous function name
class VolvoSensorDescription:
    is_available: Callable[[Vehicle], bool] = lambda _: True

# Good: Clear, specific name
class VolvoSensorDescription:
    supported_fn: Callable[[Vehicle], bool] = lambda _: True

# Bad: Unnecessary prefix in unique ID
self._attr_unique_id = f"fluss_{device['deviceId']}"

# Good: Clean unique ID (domain provides namespace)
self._attr_unique_id = str(device["deviceId"])

# Bad: Confusing field duplication
class VolvoEntityDescription:
    key: str
    api_field: str  # Same as key but camelCase

# Good: Use key directly or choose one clear name
class VolvoEntityDescription:
    key: str  # Use this for both purposes

Translation Keys: Use lowercase, snake_case format consistently:

# Bad: Mixed case
translation_key="powerLevel"

# Good: Snake case
translation_key="power_level"

This prevents runtime errors, improves code readability, and ensures consistency with Home Assistant’s established patterns.

---

trust server-side validation

When integrating with external APIs or services that implement their own input validation, avoid duplicating that validation logic on the client side. Trust the authoritative server’s validation mechanisms rather than attempting to replicate them locally.

This principle prevents validation inconsistencies, reduces maintenance overhead, and avoids potential security gaps that could arise from imperfect client-side validation implementations. The external service is the authoritative source for what constitutes valid input, and attempting to second-guess or replicate their validation logic can lead to discrepancies.

For example, when working with a third-party API that accepts various input formats (addresses, coordinates, URLs), let the service handle the validation:

# Good: Let the external service validate
def share_to_vehicle(data):
    # Send data directly to external API
    # Let Tesla/external service validate the input format
    response = external_api.share(data)
    return response

# Avoid: Duplicating external validation logic
def share_to_vehicle(data):
    # Don't try to replicate Tesla's validation rules
    if not validate_address_format(data):  # Unnecessary
        raise ValidationError("Invalid format")
    response = external_api.share(data)
    return response

Focus your validation efforts on your own application’s business logic and data integrity requirements, not on replicating external service validation.

---

API documentation consistency

Ensure all API-related descriptions, field names, and documentation accurately reflect the terminology and specifications used by external service providers. Descriptions should be consistent between code comments, user-facing strings, and external documentation.

When referencing external APIs:

• Use the exact spelling and capitalization as specified in the official documentation (e.g., “API-Key” not “API-KEY” if that’s how the provider documents it)
• Ensure service descriptions match between code and external documentation
• Use precise language in templates and descriptions (e.g., “A template to compose” rather than “The template to render”)
• Handle URLs through proper description placeholders and support markdown formatting

Example from discussions:

{
  "data_description": {
    "api_key": "The tankerkoenig API-Key to be used.",
    "search_terms": "Terms to search for in all recipe properties."
  }
}

This prevents user confusion and ensures the integration accurately represents the external service’s interface and capabilities.

---

Consistent documentation language

Maintain consistency in wording, formatting, and specificity across all documentation strings to improve readability and translation quality.

Key practices:

• Use consistent phrasing patterns for similar concepts (e.g., “A [template]… to compose the payload to be published at the xyz topic”)
• Avoid unnecessary words like “Select” in descriptions - prefer direct statements (“The instance where…” vs “Select the instance where…”)
• Use proper capitalization and avoid ALL CAPS for better translatability
• Be specific in descriptions rather than generic (e.g., “to extract the current humidity value” vs “to extract the payload for the current humidity topic”)
• Proofread for typos that can confuse users and translators

Example of consistent template description:

{
  "fan_mode_command_template": "A [template](https://example.com) to compose the payload to be published at the fan mode command topic.",
  "power_command_template": "A [template](https://example.com) to compose the payload to be published at the power command topic."
}

This ensures documentation is professional, clear, and maintainable across the entire codebase while supporting internationalization efforts.

---

Handle async cancellation properly

When implementing async operations with cancellation support, ensure that cancelled operations do not continue to update application state and that all cleanup logic is properly consolidated. This prevents race conditions where cancelled requests might still modify data after cancellation.

Key practices:

1. Track cancellation state: Set a cancelled flag when abort controllers are triggered, both from internal clear() calls and external abort signals
2. Prevent state updates: Check cancellation status before updating data/status to avoid processing results from cancelled operations
3. Consolidate cleanup: Group related cleanup logic in existing disposal handlers rather than creating multiple separate listeners
4. Handle async cleanup limitations: Be aware that async cleanup hooks may not work reliably in all environments (e.g., Windows process termination)

Example implementation:

clear: () => {
  if (options.abortController) {
    options.abortController.abort(new DOMException('Request aborted as the async data was cleared.', 'AbortError'))
  }
  if (nuxtApp._asyncDataPromises[key.value]) {
    (nuxtApp._asyncDataPromises[key.value] as any).cancelled = true
  }
}

// Listen for external cancellation
options.abortController.signal.addEventListener('abort', () => {
  if (nuxtApp._asyncDataPromises[key.value]) {
    (nuxtApp._asyncDataPromises[key.value] as any).cancelled = true
  }
})

// Consolidate cleanup in existing disposal handler
if (hasScope) {
  onScopeDispose(() => {
    off()
    stopPolling() // Add to existing handler rather than creating new one
  })
}

---

Use descriptive specific names

Choose descriptive, specific names that clearly communicate intent and behavior rather than generic or ambiguous alternatives. Names should be self-documenting and reduce the need for additional context or comments.

Key principles:

• Be specific over generic: Use start_with?('_misskey') instead of broad start_with?('_') when the intent is specific to Misskey properties
• Clarify behavior in method names: Use by_language_length instead of by_language when sorting by length, or forwardable? instead of can_forward? to follow Ruby predicate conventions
• Make scope names unambiguous: Use category_account instead of account for scopes to avoid confusion with model attributes
• Use descriptive parameter names: Replace generic options = {} with explicit forward_to_domains = [] to clarify expected usage
• Extract complex logic with descriptive names: Instead of inline complex conditions, use helper methods like last_page? and paginating_down?

Example:

# Avoid generic/ambiguous names
scope :account, -> { where(category: 'account') }
def can_forward?

# Use descriptive, specific names  
scope :category_account, -> { where(category: 'account') }
def forwardable?

This approach improves code readability, reduces cognitive load, and makes the codebase more maintainable by ensuring names accurately reflect their purpose and behavior.

---

Use appropriate logging levels

Choose the correct logging level based on the nature and expected frequency of the event being logged. Follow these guidelines:

Use debug for application events: The info level is reserved for system-level messages. Use debug for application-specific information like successful authentication, data processing steps, or operational status updates.

Reserve exception for unexpected errors: Use _LOGGER.exception() only when you truly need the full stack trace to understand what went wrong - typically for unexpected errors where the system cannot continue normally. For expected errors like authentication failures or connection timeouts, use warning or error instead.

Avoid duplicate logging: Don’t log the same event with both exception and error. Choose one based on whether you need the stack trace.

Example of proper level usage:

try:
    client = HannaCloudClient()
    await client.authenticate(email, password, code)
    _LOGGER.debug("Authentication successful for user %s", email)
except (Timeout, RequestsConnectionError):
    _LOGGER.warning("Connection timeout during authentication")
    errors["base"] = "cannot_connect"
except AuthenticationError:
    _LOGGER.warning("Authentication failed for user %s", email)
    errors["base"] = "invalid_auth"
except Exception:
    _LOGGER.exception("Unexpected error during authentication")
    errors["base"] = "unknown"

This approach ensures logs are appropriately categorized, reduces noise in production logs, and provides meaningful stack traces only when needed for debugging unexpected issues.

---

prefer None over placeholders

When data is unavailable, unknown, or invalid, return None instead of placeholder strings like “Unknown”, “Unspecified”, or “???”. This makes the absence of data explicit and prevents downstream code from treating placeholder values as legitimate data.

Apply this pattern when:

• API responses contain unknown/invalid values that should be mapped to None
• Optional device attributes are missing and would otherwise get placeholder defaults
• Enum values are unrecognized and should be treated as missing rather than preserved as strings

Example:

# Avoid placeholder defaults
model=host_data.get("devmodel")  # Returns None if missing
# Instead of:
model=host_data.get("devmodel", "Unknown")

# Map invalid values to None
return {"???": None, "UNSPECIFIED": None}.get(raw_value, raw_value)
# Instead of:
return {"???": "unknown"}.get(raw_value, raw_value)

Always pair with null checks:

if self._device.data["_state"]["lastComms"] is not None:
    self._last_comms = dt_util.utc_from_timestamp(
        self._device.data["_state"]["lastComms"]
    )

This approach makes data availability explicit, prevents confusion between actual values and placeholders, and enables proper null safety patterns throughout the codebase.

---

early nil validation

Check for nil values early in methods and handle them gracefully before they can cause runtime errors or trigger expensive operations. This prevents NoMethodError exceptions and improves performance by avoiding unnecessary processing.

Key patterns to implement:

• Add nil checks at the beginning of methods before calling methods on potentially nil objects
• Use early returns to exit gracefully when required values are missing
• Place nil validations before expensive operations like database queries or Redis locks
• Use conditional access patterns when objects might be nil

Example of the problem:

def effective?
  published? && effective_date.past?  # NoMethodError if effective_date is nil
end

Example of the solution:

def accept_embedded_quote_request
  quoted_status_uri = value_or_id(@object['object'])
  quoting_status_uri = value_or_id(@object['instrument'])
  approval_uri = value_or_id(first_of_value(@json['result']))
  return if quoted_status_uri.nil? || quoting_status_uri.nil? || approval_uri.nil?
  
  # Continue with expensive operations only after nil validation
  with_redis_lock("announce:#{value_or_id(@object)}") do
    # ... rest of method
  end
end

For conditional access to potentially nil objects:

# Safe conditional access
cached[key] || (uncached[shortcode] if uncached)

# Safe method checking
params[scope].respond_to?(:[]) && params[scope][:password].present?

---

Use semantic naming

Choose names that clearly communicate purpose and align with established domain terminology. Prioritize semantic clarity over brevity, and ensure consistency with the codebase’s vocabulary.

Key principles:

• Use domain-consistent terminology (e.g., MAX_STATUS_CHARS instead of MAX_TOOT_CHARS when “status” is the established term in code)
• Name components based on their actual scope and purpose (e.g., moderation_notes instead of report_notes when used across multiple contexts)
• Extract complex logic into descriptively named methods that communicate their intent
• Choose user-appropriate terminology in UI contexts (e.g., “Filtered” instead of technical terms like “NOOP”)

Example of good semantic naming:

# Instead of inline complex logic:
if @report.account.local? && !@statuses.empty? && (@report.account.user.settings['web.expand_content_warnings'] || @report.account.user.settings['web.display_media'] == 'show_all')

# Extract to semantically named method:
if @report.account.local? && !@statuses.empty? && @report.account.user.all_content_visible?

# Method clearly communicates its purpose:
def all_content_visible?
  settings['web.expand_content_warnings'] || settings['web.display_media'] == 'show_all'
end

This approach reduces cognitive load, improves code maintainability, and makes the codebase more accessible to new developers.

---

documentation generation compatibility

When making code changes, ensure compatibility with documentation generation tools like JSDoc and TypeDoc. This includes: (1) Exporting types that should appear in generated documentation, (2) Avoiding duplicate exports across modules that can confuse documentation parsers, and (3) Formatting code examples appropriately for documentation rendering.

For exports, make sure types intended for public API documentation are properly exported:

export type {
  AwaitProps,
  IndexRouteProps,
  LayoutRouteProps,
  MemoryRouterOpts, // Export so typedoc picks it up
}

For code examples in JSDoc, handle existing markdown formatting to prevent double-wrapping:

markdown += example.includes("```")
  ? `${example}\n\n`
  : `\`\`\`tsx\n${example}\n\`\`\`\n\n`;

When creating nested modules, update documentation generation scripts to handle the new structure and prevent conflicts from duplicate component names across modules.

---

prefer simple code patterns

Choose straightforward, readable code patterns over complex or clever alternatives. This improves maintainability and reduces cognitive load for other developers.

Key principles:

• Use direct boolean methods instead of complex expressions: array.some(condition) instead of array.find(condition) !== null
• Prefer simple conditional operators: value && expression instead of value ? expression : null when appropriate
• Use explicit control structures over indirection: direct switch statements instead of mapping objects when the logic is clearer
• Choose appropriate data types: booleans for binary states instead of numeric flags, specific types when mutation isn’t needed
• Avoid unnecessary complexity: split complex expressions across lines rather than using comma operators or complex casting

Example:

// Complex/clever approach
const result = items.find(item => item.active) !== null ? processItems() : null;
const status = flags & DIRTY_FLAG !== 0 ? 1 : 0;

// Simple, readable approach  
const hasActiveItem = items.some(item => item.active);
if (hasActiveItem) {
  processItems();
}
const isDirty = (flags & DIRTY_FLAG) !== 0;

The goal is code that can be quickly understood by any team member, even when they’re unfamiliar with the specific context or under time pressure.

---

Optimize database queries

Write efficient database queries by leveraging proper indexes, using performance-optimized ActiveRecord methods, and avoiding unnecessary database operations. Key practices include:

1. Use indexes effectively: Structure queries to utilize existing indexes. For example, use Account.arel_table[:username].lower.in(usernames.map(&:downcase)) to leverage lowered username indexes instead of queries that cause sequential scans.

2. Prefer exists() over count(): Use exists? instead of count.zero? to avoid unnecessary COUNT operations: ```ruby

   Instead of

   Follow.where(conditions).count.zero?

Use

!Follow.where(conditions).exists?

3. **Remove redundant indexes**: Avoid creating single-column indexes when composite indexes already cover them. An index on `["account_id", "group_id"]` makes a separate `["account_id"]` index unnecessary.

4. **Simplify complex queries**: When Arel becomes overly complex, consider raw SQL for better readability and maintainability:
```ruby
# Instead of complex Arel constructions
scope :matches_partially, ->(str) { where("'%' || username || '%'") }

1. Handle query ordering conflicts: Use reorder(nil) to clear existing ORDER BY clauses when they conflict with new ordering requirements, preventing incorrect results from multiple conflicting sort orders.

---

migration data dependencies

Ensure that migrations properly handle data dependencies and sequencing to prevent deployment failures. When migrations depend on specific records existing (like default roles or seed data), create those records within the migration itself rather than relying on seeds or post-deployment processes.

Key considerations:

• Pre vs Post-deployment timing: Data deletions and dependency setup should occur in pre-deployment migrations, while column removals and cleanup happen in post-deployment migrations
• Avoid ActiveRecord models: Use direct SQL in migrations for better performance and to avoid dependency on model definitions that may change over time
• Handle missing dependencies: When adding foreign key constraints or default values that reference other records, ensure those records exist within the same migration

Example from the discussions:

class PopulateEveryoneRole < ActiveRecord::Migration[7.1]
  disable_ddl_transaction!
  
  class UserRole < ApplicationRecord
    EVERYONE_ROLE_ID = -99
    FLAGS = { invite_users: (1 << 16) }.freeze
  end
  
  def up
    # Ensure the required role exists before other migrations depend on it
    UserRole.create!(id: UserRole::EVERYONE_ROLE_ID, permissions: UserRole::FLAGS[:invite_users])
  end
end

For complex data transformations, consider splitting operations across multiple migrations with proper sequencing, and use disable_ddl_transaction! when necessary for large data operations.

---

API backward compatibility

When updating existing APIs, maintain backward compatibility by deprecating old options rather than introducing breaking changes. Add new properties while keeping old ones functional, marking them as deprecated to guide migration without forcing immediate updates.

Key principles:

• Never make previously optional parameters required without maintaining the old signature
• When renaming API properties, keep the old names working alongside new ones
• Mark deprecated options clearly in documentation but continue supporting them
• Provide migration paths that don’t require immediate code changes

Example approach for API updates:

// Instead of breaking change:
// OLD: { blockerFn?: Function }
// NEW: { shouldBlockFn: Function } // ❌ Breaking!

// Use backward-compatible approach:
type UseBlockerOpts = {
  shouldBlockFn: BlockerFn // New preferred option
  enableBeforeUnload?: boolean
} & {
  blockerFn?: LegacyBlockerFn // Keep old option, mark deprecated
  condition?: boolean // Keep old option, mark deprecated
}

This approach ensures existing code continues working while encouraging adoption of improved APIs. Keep public API surfaces minimal by avoiding exposure of internal types that change frequently, focusing documentation on stable, user-facing interfaces only.

---

precise null type checking

Use precise null and undefined type checking that matches the actual usage context. Distinguish between checking if a type contains undefined (undefined extends T) versus checking if a type is exactly undefined (Equal<T, undefined> extends true). For inferred return types, use the “contains undefined” check since the type may be a union. For direct values and top-level parameters, use exact equality checks.

Additionally, ensure optional modifiers in type definitions match actual implementation requirements. Remove optional modifiers (?) when parameters are required in the implementation, and use precise typing to distinguish required parameters (string) from optional ones (string | null | undefined).

Example of precise undefined checking:

// For inferred types - check if undefined is in the union
type IsDefined<T> = undefined extends T ? false : true;

// For exact values - check if type is exactly undefined  
type IsExactlyUndefined<T> = Equal<T, undefined> extends true ? false : true;

// Distinguish required vs optional parameters
type PathParams<Path> = {
  [key in RequiredPathParam<Path>]: string;
} & {
  [key in OptionalPathParam<Path>]?: string | null | undefined;
};

// Remove optional modifier when parameter is actually required
getFetcher<TData = any>(key: string): Fetcher<TData>; // not key?: string

This approach prevents type errors, ensures API contracts match implementations, and provides better developer experience through more accurate IntelliSense and compile-time checking.

---

Consistent null safety patterns

Maintain consistent approaches to null and undefined handling throughout the codebase. Use optional chaining (?.) for safe property access, but be mindful that it may not always be equivalent to explicit type and null checks. When accessing properties on values that could be objects, always include explicit null checks alongside type checks since typeof null === 'object'. Avoid non-null assertion operators (!) and instead provide explicit fallback values.

Examples:

// Good: Explicit null check with type check
onClose={typeof closable === 'object' && closable !== null ? closable.onClose : undefined}

// Good: Optional chaining for simple cases
if (selectable?.length > 0 && selectType) { ... }

// Good: Explicit fallback instead of non-null assertion
initExpandedKeys = props.expandedKeys || defaultExpandedKeys || [];

// Avoid: Non-null assertion without fallback
initExpandedKeys = (props.expandedKeys || defaultExpandedKeys)!;

Consider the semantic difference between optional chaining and explicit checks - optional chaining treats all falsy values the same way, while explicit checks allow for more nuanced handling of different null/undefined scenarios.

---

API flexibility balance

When designing APIs, carefully balance simplicity for common use cases with flexibility for advanced scenarios. Consider whether to expose simple interfaces (strings, direct exports) that make typical usage ergonomic, or more flexible interfaces (objects, options parameters) that enable customization.

For return values, prefer simple types when most users need straightforward access, but consider objects when users need to combine or manipulate the data. For example, returning htmlAttributes: "class=\"foo\" id=\"bar\"" makes simple insertion easy, while an object would better support merging with existing attributes.

For method parameters, design signatures that minimize boilerplate. Accept both single values and arrays rather than forcing callers to wrap single items: method(value) and method([value1, value2]) instead of always requiring method([value]).

For extensibility, use options objects for functions that may grow additional parameters over time:

// Instead of: migrate(source, filename)
// Use: migrate(source, { filename })

This allows future enhancements without breaking existing calls and keeps the API clean as requirements evolve.

---

consistent null checking

Ensure null checks follow consistent patterns and proper ordering for better readability and safety. Always place the variable being checked on the left side of null comparisons, use defensive programming with hasKey() checks before accessing map values, and maintain null-safe fallbacks when appropriate.

Key practices:

• Use variable != null instead of null != variable for better readability
• Implement defensive checks like action.hasKey("key") before accessing map values
• Consider null-safe fallbacks: action.hasKey("label") ? action.getString("label") : null
• Add explicit null checks for potentially nullable return values, even when parent objects are non-null

Example:

// Good: Consistent ordering and defensive programming
if (!action.hasKey("name") || !action.hasKey("label")) {
  throw new IllegalArgumentException("Unknown accessibility action.");
}
String actionLabel = action.hasKey("label") ? action.getString("label") : null;

// Good: Proper null check ordering
if (!mSendMomentumEvents || mPostSmoothScrollRunnable != null) {
  return;
}

// Avoid: Inconsistent null check ordering
if (!mSendMomentumEvents || null != mPostSmoothScrollRunnable) {
  return;
}

---

Prevent regression crashes

When implementing error handling or bug fixes, avoid introducing new crash conditions that would break previously working code. Focus on defensive programming that handles edge cases without creating new failure points.

Key principles:

1. Backward compatibility first: Don’t add new validation that crashes on previously accepted inputs
2. Complete error handling: Ensure all code paths have proper error responses (like calling onResponseReceived for all URI handlers)
3. Proper state management: Reset and initialize state variables in lifecycle methods to prevent recycling issues

Example from accessibility handling:

// DON'T: Add new crash conditions
if (!action.hasKey("name") || !action.hasKey("label")) {
  // This crashes apps that worked before without labels

// DO: Handle missing data gracefully  
if (!action.hasKey("name")) {
  continue; // Skip invalid actions without crashing
}
if (action.hasKey("label")) {
  // Use label when available, but don't require it
}

Before adding new error conditions, consider whether the change maintains backward compatibility while still providing proper error handling for new scenarios.

---

Maintain inline documentation

Ensure inline code comments are accurate, current, and provide meaningful explanations for complex or unclear code sections. Comments should be updated whenever the associated code changes to prevent misleading documentation.

Add explanatory comments for:

• Unclear device categories, constants, or identifiers
• Complex logic or business rules
• Non-obvious code sections that future developers might struggle to understand

Update existing comments when:

• Code behavior changes
• Function signatures are modified
• Logic flow is altered

Example of adding missing explanatory comment:

# Micro Storage Inverter
# Energy storage and solar PV inverter system with monitoring capabilities
"xnyjcn": (
    # device configuration...
)

Example of updating stale comment:

# The light supports both white (with or without adjustable color temperature)
# and HS, determine which mode the light is in. We consider it to be in HS color
# mode, when work mode is anything else than "white".
if (
    self.device.status.get(self._color_mode_dpcode) != WorkMode.WHITE
):
    return ColorMode.HS
return (
    self._white_color_mode if self._white_color_mode else ColorMode.COLOR_TEMP
)

Well-maintained inline documentation reduces cognitive load for code reviewers and future maintainers, making the codebase more accessible and reducing the likelihood of bugs introduced by misunderstanding existing code.

---

Complete accurate documentation

Documentation should provide complete, accurate guidance that doesn’t mislead developers about correct usage patterns. Avoid documentation structures that suggest incorrect import paths or API usage, and ensure that configuration examples are accompanied by practical usage demonstrations.

When documenting APIs or configurations, consider how the documentation structure itself might be interpreted by users. For example, avoid typedoc entry point configurations that create misleading nested structures suggesting incorrect import paths like react-router/index when the correct import is just react-router.

Additionally, when showing configuration setup (like TypeScript plugins), include concrete usage examples in the same context:

// tsconfig.json - Configuration
{
  "plugins": [{ "name": "@react-router/dev" }]
}

// app/routes/example.tsx - Usage demonstration  
export default function ExampleRoute() {
  // Show actual usage of the plugin's types/features here
}

This ensures developers understand both how to configure tools and how to actually use the features they enable, preventing incomplete or confusing documentation.

---

Validate environment variables

Always validate environment variables before use and implement proper fallback strategies. For required variables, fail fast with clear error messages. For optional variables with empty values, ensure they don’t short-circuit fallback chains.

// Bad: Empty value leads to malformed URL
$hostname = System::getEnv('_APP_CONSOLE_DOMAIN', System::getEnv('_APP_DOMAIN', ''));

// Good: Check for truthy value before fallback
$hostname = System::getEnv('_APP_CONSOLE_DOMAIN', null);
if (empty($hostname)) {
    $hostname = System::getEnv('_APP_DOMAIN', '');
    if (empty($hostname)) {
        throw new \RuntimeException('Required environment variable _APP_DOMAIN is not set');
    }
}

When implementing environment variable handling:

1. For required variables, throw an exception if missing or invalid
2. For optional variables with fallbacks, check for empty strings before using
3. Document all environment variables in .env.example with descriptions and default values
4. For configuration files that consume environment variables, add validation logic
5. Verify type correctness (e.g., using intval() for numeric settings, checking IP formats)
6. Add validation for variables containing URLs, file paths, or other structured data

---

Ensure database transactional integrity

When performing multiple related database operations, use transactions and proper error handling to maintain data consistency. Without proper safeguards, partial failures can leave your database in an inconsistent state with orphaned or mismatched records.

Here are specific practices to follow:

1. Wrap related operations in transactions when one operation depends on another:

// BAD: Operations can partially succeed, leaving orphaned metadata
$collection = $dbForProject->createDocument('collections', $metadata);
$dbForProject->createCollection('collection_' . $collection->getInternalId());

// GOOD: Use transaction to ensure atomicity
$dbForProject->withTransaction(function() use ($dbForProject, $metadata) {
    $collection = $dbForProject->createDocument('collections', $metadata);
    $dbForProject->createCollection('collection_' . $collection->getInternalId());
});

1. Add rollback logic when transactions aren’t available:

// GOOD: Explicit rollback when second operation fails
try {
    $collection = $dbForProject->createDocument('collections', $metadata);
    try {
        $dbForProject->createCollection('collection_' . $collection->getInternalId());
    } catch (Exception $e) {
        // Clean up partial state
        $dbForProject->deleteDocument('collections', $collection->getId());
        throw $e;
    }
} catch (Exception $e) {
    // Handle and rethrow
}

1. Return fresh data after mutations to prevent stale state:

// BAD: Returns stale data
$dbForProject->updateDocument('transactions', $id, ['operations' => $count + 1]);
return $response->dynamic($transaction); // Still has old count!

// GOOD: Return fresh data
$transaction = $dbForProject->updateDocument('transactions', $id, ['operations' => $count + 1]);
return $response->dynamic($transaction); // Has updated count

1. Validate all mutation paths for operations like bulk creates, updates, increments, and decrements to ensure they’re properly processed in transactions.

2. Use reference capture (&$variable) in database connection factories to properly reuse connections rather than creating new ones on each call.

Implementing these practices will help maintain database integrity, prevent orphaned records, and ensure your application data remains consistent even when operations fail.

---

Comprehensive migration planning

When changing identifier systems (e.g., from using getInternalId() to getSequence()), implement comprehensive migration strategies to preserve data integrity and backward compatibility. For each change:

1. Create explicit migration scripts to update or rename existing resources
2. Implement fallback mechanisms for transitional periods
3. Update all related queries, metrics, and references consistently
4. Test thoroughly with real data before deploying

// Example migration for collection renaming:
public function migrateCollections(): void
{
    $buckets = $this->dbForProject->find('buckets');
    
    foreach ($buckets as $bucket) {
        $oldName = 'bucket_' . $bucket->getInternalId();
        $newName = 'bucket_' . $bucket->getSequence();
        
        if ($this->dbForProject->hasCollection($oldName) && !$this->dbForProject->hasCollection($newName)) {
            // Rename collection to preserve existing data
            $this->dbForProject->renameCollection($oldName, $newName);
            Console::success("Migrated collection {$oldName} → {$newName}");
        }
    }
}

Without proper migration planning, changes to identifier systems often result in orphaned data, broken queries, and critical production issues.

---

Consistent placeholder conventions

Ensure all placeholders in localization files follow consistent naming conventions to prevent runtime errors and text leakage in the UI. This applies to both sprintf-style placeholders (%s) and template variables ({{name}}).

Common issues to watch for:

1. Correct sprintf order: Use %s not s%

   -"emails.invitation.subject": "Invitació a l'equip %s a s%",
   +"emails.invitation.subject": "Invitació a l'equip %s a %s",
   

Placeholder errors are particularly problematic because they can:

• Break runtime string substitution
• Cause literal placeholder text to appear in the UI
• Lead to crashes in formatting functions
• Create inconsistent user experiences across languages

---

centralize configuration management

Migrate configuration from direct environment variable access to Rails’ config_for mechanism for better organization, testability, and maintainability. Instead of accessing ENV variables directly throughout the codebase, consolidate them into YAML configuration files loaded at application startup.

Why this matters:

• Enables the Rails/EnvironmentVariableAccess cop to enforce “configure at load time” practices
• Centralizes configuration in one place for easier management
• Improves testability by allowing config reloading in specs
• Prevents load order issues with configuration dependencies
• Reduces duplication of configuration logic across controllers and models

How to apply:

1. Move ENV variable access from code to config/mastodon.yml or similar config_for files
2. Access configuration via Rails.configuration.x.namespace instead of ENV directly
3. Keep any string parsing/processing logic in the consuming classes, only move the raw ENV.fetch calls to config files
4. Maintain test coverage for environment variable effects using config reloading in specs

Example:

# Before - scattered ENV access
def mfa_force_enabled?
  ENV['MFA_FORCE'] == 'true'
end

def authorized_fetch_mode?
  %w(true all).include?(ENV.fetch('AUTHORIZED_FETCH', 'false'))
end

# After - centralized in config/mastodon.yml
# mfa_force: <%= ENV.fetch('MFA_FORCE', 'false') %>
# authorized_fetch: <%= ENV.fetch('AUTHORIZED_FETCH', 'false') %>

# Then access via:
def mfa_force_enabled?
  Rails.configuration.x.mastodon.mfa_force == 'true'
end

def authorized_fetch_mode?
  %w(true all).include?(Rails.configuration.x.mastodon.authorized_fetch)
end

This approach consolidates configuration management while preserving the ability to test environment variable behavior and avoiding configuration logic duplication across the application.

---

Minimize try block scope

Only include code that can actually raise exceptions within try blocks. Move variable assignments, logging statements, and other operations that cannot fail outside of the try block to avoid accidentally catching unintended exceptions and to improve code clarity.

This practice ensures that exception handling is precise and that you only catch the specific errors you intend to handle, rather than masking unexpected failures in seemingly safe operations.

Example of what to avoid:

try:
    session = async_get_clientsession(hass)
    api = RedgtechAPI()
    access_token = await api.login(email, password)
    if access_token:
        _LOGGER.debug("Login successful, token received.")
        # ... more processing
except Exception as e:
    _LOGGER.error("Login failed: %s", e)

Better approach:

session = async_get_clientsession(hass)
api = RedgtechAPI()
try:
    access_token = await api.login(email, password)
except Exception as e:
    _LOGGER.error("Login failed: %s", e)
    return

if access_token:
    _LOGGER.debug("Login successful, token received.")
    # ... more processing

By limiting the try block to only the await api.login() call, you ensure that any exceptions from session creation or API instantiation are not accidentally caught and mishandled as login failures.

---

Version migration dependencies carefully

When updating dependencies for migration-related components or making schema changes, verify compatibility and ensure backward compatibility:

1. For dependency updates:
   • Verify that version constraints point to valid, published versions
   • Check changelogs for breaking API or CLI changes
   • Update lockfiles to lock in the exact tested version

     # After updating a migration dependency in composer.json
     composer update utopia-php/migration && git add composer.lock
     

2. For schema changes:
   • Update all affected models, serializers, and tests
   • Ensure systems can handle both old and new schemas during migration periods
   • Test migrations with new dependencies before deployment

For example, when adding a new field like "expired": boolean to an API schema, update all client models while maintaining compatibility with targets that don’t include this field yet.

---

CSS modifier naming

Use consistent modifier patterns with -- prefixes for CSS classes and variables. Prefer semantic base names combined with modifiers over long descriptive names. This approach improves maintainability and creates predictable naming schemes.

For CSS classes, use BEM-like modifier syntax:

.filter-tip__button {
  &.--selected {  // Use -- prefix for modifiers
    background: var(--primary);
  }
}

For CSS variables, group related properties using modifier patterns:

:root {
  --title-color: var(--primary);
  --title-color--header: var(--header_primary);  // Related modifier
}

For component names, use concise base names with modifiers rather than long descriptive names:

// Prefer this:
.empty-state {
  &.--topic-filter { }
}

// Over this:
.empty-topic-filter-education { }

---

Environment variable descriptive naming

Environment variables should use descriptive, specific names that clearly indicate their purpose and scope to avoid conflicts and improve maintainability. Generic names can lead to confusion when multiple features need similar configuration options.

Use specific, self-documenting names that include the feature or component they control:

# Avoid generic names
MFA_FORCE=true
MAX_CHARS=500

# Use descriptive, specific names
REQUIRE_MULTI_FACTOR_AUTH=true
MAX_TOOT_CHARS=500

This practice prevents naming conflicts when different features need similar configuration (e.g., character limits for posts vs. bios) and makes the configuration’s intent immediately clear to developers. Additionally, avoid leaving test-specific environment variables in development configuration files to prevent confusion about which settings are actually required for the application to function.

---

Structure documentation interfaces

Organize interfaces and component props documentation to improve API clarity and maintainability. Extract reusable interfaces into separate declarations to generate dedicated documentation pages, and ensure prop documentation accurately represents the code structure, especially for rest/spread operators.

When documenting components with rest/spread props, clearly indicate they represent collections of properties rather than individual parameters. Avoid documenting every individual property when they map to standard web APIs - instead, reference the appropriate external documentation.

// Good: Extract interface for dedicated docs page
export interface MemoryRouterOpts {
  initialEntries?: string[];
  initialIndex?: number;
}

// Good: Clear rest/spread documentation
/**
 * @param props.dataLinkProps Additional props to pass to the
 * underlying link elements (collection of standard HTML attributes)
 */
function PrefetchPageLinks({ page, ...dataLinkProps }: Props) {
  // Implementation
}

This approach ensures documentation is well-organized, technically accurate, and provides appropriate level of detail without duplicating standard web API documentation.

---

minimize memory allocations

Prioritize reducing memory allocations and choosing efficient data structures to improve performance. Avoid unnecessary string/byte conversions, use maps for O(1) lookups instead of slices, and leverage compiler optimizations where possible.

Key strategies:

• Use utils.EqualFold instead of utils.ToLower for case-insensitive comparisons to avoid allocations
• Choose maps over slices for lookups: map[int]bool instead of []int for O(1) performance
• Preallocate slices with appropriate capacity to avoid runtime growth
• Combine string operations to reduce allocations: strings.ToLower(scheme + "://" + host) instead of separate calls
• Leverage Go compiler optimizations for []byte to string comparisons
• Use library-specific optimized functions like fasthttp.ParseFloat and UnsafeBytes when available

Example:

// Inefficient - multiple allocations
if utils.ToLower(cookie.SameSite) == CookieSameSiteNoneMode {
    // process
}

// Efficient - no allocations  
if utils.EqualFold(cookie.SameSite, CookieSameSiteNoneMode) {
    // process
}

// Inefficient - O(n) lookup
var cacheableStatusCodes = []int{200, 203, 300, 301}
if slices.Contains(cacheableStatusCodes, status) { /* ... */ }

// Efficient - O(1) lookup
var cacheableStatusCodes = map[int]bool{200: true, 203: true, 300: true, 301: true}
if cacheableStatusCodes[status] { /* ... */ }

---

Stable dependency version management

Always use stable, well-defined version constraints in configuration files to ensure reproducible builds and prevent unexpected behavior. Avoid using development branches for production dependencies.

Key practices:

1. Use semantic versioning constraints:
   • Use ^ for minor updates: "package": "^1.2.3"
   • Use ~ for patch updates: "package": "~1.2.3"
   • Pin exact versions when needed: "package": "1.2.3"
2. Never use dev branches in production unless absolutely necessary. If required:

   {
     "require": {
       "package": "1.2.*",
     },
     "minimum-stability": "dev",
     "prefer-stable": true
   }
   

3. Always commit lock files (e.g., composer.lock) to ensure consistent dependency versions across environments.

4. When updating versions, update all related configuration files and documentation to maintain consistency.

---

SSR documentation completeness

Ensure server-side rendering documentation provides complete implementation details with proper build configurations and explanatory context. SSR setup guides should include comprehensive Vite configurations that clearly separate client and server bundles, detailed explanations of script purposes, and complete file structures.

When documenting SSR setup:

1. Include complete Vite configurations with separate client/server build environments: ```ts // vite.config.ts const ssrBuildConfig: BuildEnvironmentOptions = { ssr: true, outDir: “dist/server”, rollupOptions: { input: path.resolve(__dirname, “src/entry-server.tsx”), output: { entryFileNames: “[name].js”, chunkFileNames: “assets/[name]-[hash].js”, }, }, };

const clientBuildConfig: BuildEnvironmentOptions = { outDir: “dist/client”, rollupOptions: { input: path.resolve(__dirname, “src/entry-client.tsx”), }, };

2. **Provide explanatory context** for build processes and script purposes:
```json
{
  "scripts": {
    "build:client": "vite build",
    "build:server": "vite build --ssr"
  }
}

Add descriptions explaining that separate build processes ensure client and server bundles are served from distinct directories (dist/client and dist/server).

1. Include complete file structures showing root route configurations, entry points, and server setup with proper HTML document rendering patterns.

This ensures developers understand not just what to configure, but why each piece is necessary for proper SSR implementation.

---

Assert response fully always

Always validate all relevant aspects of API responses in tests, including status codes, headers, and body content. Don’t partially validate responses or make assumptions about response structure.

Example of incomplete testing:

$response = $this->client->call(Method::POST, '/endpoint');
$this->assertNotEmpty($response['body']); // Too vague

Better approach with comprehensive validation:

$response = $this->client->call(Method::POST, '/endpoint');
// Validate HTTP status
$this->assertEquals(201, $response['headers']['status-code']);

// Validate response structure
$this->assertIsArray($response['body']);
$this->assertArrayHasKey('id', $response['body']);

// Validate specific content
$this->assertEquals('expected-value', $response['body']['field']);
$this->assertGreaterThan(0, $response['body']['count']);

Key points:

1. Always assert HTTP status codes
2. Validate response structure before checking content
3. Include both positive and negative assertions
4. Test edge cases and error conditions
5. Verify all relevant response fields, not just the “happy path”

---

Configuration option consistency

Ensure configuration options follow consistent naming conventions and are documented accurately. Use “default” prefix for options that can be overridden at more specific levels (e.g., defaultOutputPath instead of outputPath). Document only public APIs - avoid documenting internal or experimental configuration options that are not yet part of the public interface. Provide clear, grammatically correct descriptions for all configuration options, including proper property names and examples.

Example of consistent naming:

// Good - follows default + override pattern
export default defineConfig({
  codeSplittingOptions: {
    defaultBehavior: [['component'], ['errorComponent']], // Global default
    splitBehavior: ({ routeId }) => { /* per-route override */ }
  }
})

// Bad - unclear relationship between global and specific options  
export default defineConfig({
  codeSplittingOptions: {
    outputPath: (path) => path, // Should be defaultOutputPath
  }
})

This ensures developers can easily understand configuration hierarchies and reduces confusion about which options are available and how they interact.

---

test real user interactions

Write tests that simulate actual user behavior and verify real rendering outcomes rather than testing implementation details or internal state. Use data-testid attributes with getByTestId instead of getByRole for better maintainability, as it allows changing text and HTML structure without breaking tests. Focus on testing what users actually see and interact with on screen.

For user interactions, test real events like hover, focus, and click behaviors:

// Good: Test actual rendering and user interaction
test('when user hovers over link, it preloads route', async () => {
  const router = createRouter({ 
    routeTree, 
    defaultPreload: 'intent' 
  })
  
  render(<RouterProvider router={router} />)
  
  const link = screen.getByTestId('posts-link')
  
  // Test real user interaction
  fireEvent.focus(link)
  
  // Verify actual rendering outcome
  expect(await screen.findByRole('heading', { name: 'Posts' }))
    .toBeInTheDocument()
})

// Avoid: Testing only internal state
test('loader function gets called', () => {
  expect(mockLoader).toHaveBeenCalled() // Less valuable
})

Always verify that components actually render on screen using testing-library queries, and test edge cases like different router configurations (e.g., with basePath set) to ensure comprehensive real-world coverage.

---

Use object methods consistently

When working with Document objects, always use their accessor methods rather than array-style syntax. Use $object->getAttribute('property') and $object->setAttribute('property', $value) instead of $object['property']. This ensures proper encapsulation, maintains data integrity through validation, and creates more resilient code that won’t break if the underlying implementation changes.

-// Avoid direct array access on Document objects
-if (isset($session['clientName']) && empty($session['clientName'])) {
-    $session['clientName'] = !empty($session['userAgent']) ? $session['userAgent'] : 'UNKNOWN';
-}

+// Prefer method access for Document objects
+if ($session->getAttribute('clientName', null) === null || empty($session->getAttribute('clientName'))) {
+    $clientName = !empty($session->getAttribute('userAgent')) ? $session->getAttribute('userAgent') : 'UNKNOWN';
+    $session->setAttribute('clientName', $clientName);
+}

This pattern ensures your code leverages the Document object’s built-in validation and transformation features while providing better readability and maintainability.

---

Validate security configurations

Always verify that security middleware configurations use correct constant values, proper parameter specifications, and follow established security practices. Incorrect configuration values can create vulnerabilities or cause security features to fail silently.

Key areas to validate:

• Use framework-defined constants instead of string literals (e.g., fiber.CookieSameSiteLaxMode instead of "Lax")
• Specify encryption key lengths correctly with proper AES algorithm mapping (16, 24, or 32 bytes for AES-128, AES-192, AES-256-GCM respectively)
• Understand the security implications of advanced features before implementation
• Ensure proper middleware ordering, especially placing encryption middlewares before those that read cookies

Example of proper CSRF configuration:

app.Use(csrf.New(csrf.Config{
    CookieName:        "__Host-csrf_",
    CookieSecure:      true,
    CookieHTTPOnly:    true,
    CookieSameSite:    fiber.CookieSameSiteLaxMode, // Use constant, not "Lax"
    CookieSessionOnly: true,
    Extractor:         csrf.FromHeader("X-Csrf-Token"),
}))

Example of proper encryption key specification:

// Generate 32-byte key for AES-256-GCM
key := encryptcookie.GenerateKey(32)
app.Use(encryptcookie.New(encryptcookie.Config{
    Key: key, // 32 bytes for AES-256-GCM
}))

This validation prevents security misconfigurations that could compromise application security or cause middleware to behave unexpectedly.

---

Use descriptive names

Choose variable, function, and file names that clearly describe their purpose, behavior, and content. Names should be self-documenting and avoid ambiguity about what they represent or do.

Key principles:

• Reflect actual behavior: Use names that accurately describe what the code does, not just what it might do. For example, hasIntersected instead of isIntersecting when the value doesn’t toggle back to false.
• Be specific and clear: Prefer shared-imports.d.ts over shared.d.ts, or cookieStore over listenCookieChanges to identify the specific API being used.
• Use inclusive language: Replace terms like whitelist with allowlist to maintain inclusive terminology.
• Choose semantic function names: Use shouldPrefetch() instead of checkShouldPrefetch() when the function returns a boolean indicating whether an action should be performed.

Example of good descriptive naming:

// Before: unclear behavior
const isIntersecting = ref(false)
function checkShouldPrefetch() { /* ... */ }

// After: clear and descriptive  
const hasIntersected = ref(false)
function shouldPrefetch(): boolean { /* ... */ }

// Before: generic naming
whitelist: string[]

// After: descriptive and inclusive
allowlist: string[]

This approach makes code more maintainable and reduces the need for additional documentation or comments to explain what identifiers represent.

---

Limit plugin outlet APIs

When creating plugin outlets or extension points, avoid exposing entire component instances, controllers, or large objects. Instead, pass explicit, minimal arguments that represent only the data and actions that plugins actually need.

Exposing entire objects makes them part of the public API, making future refactoring difficult and creating tight coupling between internal implementation and external consumers.

Bad:

<PluginOutlet
  @name="sub-category-item"
  @outletArgs={{hash subCategoryItem=this}}
/>

<PluginOutlet
  @name="exception-wrapper"
  @outletArgs={{lazyHash controller=@controller}}
/>

Good:

<PluginOutlet
  @name="sub-category-item"
  @outletArgs={{lazyHash 
    category=this.category
    unreadCount=this.unreadTopicsCount
    newCount=this.newTopicsCount
    hideUnread=this.hideUnread
  }}
/>

<PluginOutlet
  @name="exception-wrapper"
  @outletArgs={{lazyHash
    errorHtml=@controller.errorHtml
    isForbidden=@controller.isForbidden
    reason=@controller.reason
    requestUrl=@controller.requestUrl
  }}
/>

This approach creates stable, documented interfaces that can evolve independently of internal implementation changes.

---

Validate documentation links

Always verify that URLs in documentation resolve correctly (return HTTP 200) before merging changes. Broken links create a poor user experience and reduce the credibility of documentation.

For important user-facing documents like README files, include a verification step in your review process:

#!/bin/bash
# Simple script to verify a documentation link
curl -I https://example.com/your/documentation/link | head -n 1
# Should return HTTP/1.1 200 OK

If a link points to content that’s not yet published (like upcoming blog posts), either:

1. Wait to merge until the content is live
2. Remove the link to avoid broken references
3. Update with a correct alternative URL

This verification is especially important for prominent links in README files or other entry-point documentation that will be immediately visible to users.

---

Authorization hierarchy verification

Always implement comprehensive authorization checks that verify user permissions at the appropriate hierarchy level (individual → team → organization) before allowing operations. Consider multiple permission levels and provide proper fallbacks when users have different roles across teams or organizations.

Key principles:

• Check individual ownership first (userId matches)
• Verify team-level permissions (admin/owner roles) for team resources
• Include organization-level permissions when applicable
• Use Permission-Based Access Control (PBAC) with role-based fallbacks
• Ensure permission dependencies are met (e.g., list permissions before modify permissions)

Example implementation:

// Check individual ownership first
const userReschedulingIsOwner = isUserReschedulingOwner(userId, originalRescheduledBooking?.userId);

// Check team-level permissions
let isTeamOwnerOrAdmin = false;
if (isTeamEventType && originalRescheduledBooking?.eventType?.teamId) {
  const membership = await prisma.membership.findFirst({
    where: {
      teamId: originalRescheduledBooking.eventType.teamId,
      userId: user?.id,
      role: { in: [MembershipRole.OWNER, MembershipRole.ADMIN] }
    }
  });
  isTeamOwnerOrAdmin = !!membership;
}

// Check organization-level permissions
const hasOrgPermission = await permissionCheckService.checkPermission({
  userId,
  teamId,
  permission: "organization.adminApi",
  fallbackRoles: [MembershipRole.OWNER, MembershipRole.ADMIN]
});

if (!userReschedulingIsOwner && !isTeamOwnerOrAdmin && !hasOrgPermission) {
  throw new TRPCError({ code: "FORBIDDEN", message: "Insufficient permissions" });
}

This prevents unauthorized access by ensuring users can only perform operations they have legitimate permissions for, whether through direct ownership, team membership, or organizational authority.

---

realistic documentation examples

Use practical, complete examples in documentation rather than oversimplified or contrived ones that cut corners. Documentation examples should reflect real-world usage patterns and include necessary context, edge cases, and limitations.

Avoid examples that:

• Cut corners for brevity (like localStorage without SSR checks)
• Are overly contrived or artificial
• Omit important details or error handling
• Don’t show realistic usage patterns

Instead, provide examples that:

• Include necessary context and setup
• Show proper error handling and edge cases
• Demonstrate realistic usage scenarios
• Explain limitations and considerations

For example, when documenting state management, instead of a simple localStorage example that ignores SSR concerns:

// Avoid: Oversimplified example
let data = $state([], {
  onchange() {
    localStorage.setItem('data', JSON.stringify(data));
  }
});

Provide a more complete example or choose a simpler concept:

// Better: Realistic validation example
let email = $state('', {
  onchange() {
    if (email && !email.includes('@')) {
      console.warn('Invalid email format');
    }
  }
});

This ensures developers can apply the concepts correctly in their own projects without encountering unexpected issues or missing critical implementation details.

---

document configuration hierarchies

When documenting configuration options, clearly explain all available configuration levels and their precedence order. Many configuration options can be set globally, per-component, or dynamically, and users need to understand these different approaches.

Structure configuration documentation by listing all available methods in order of precedence:

// Multiple ways to set configuration options:

// 1. Globally, via compilerOptions in svelte.config.js
export default {
  compilerOptions: {
    css: 'injected',
    a11y: {
      rules: {
        'label-has-associated-control': {
          labelComponents: ['CustomInputLabel'],
          controlComponents: ['CustomInput'],
          depth: 3
        }
      }
    }
  }
}

// 2. Dynamically, using build tool options
// (e.g., dynamicCompileOptions in vite-plugin-svelte)

// 3. Per-component, with svelte:options (overrides other methods)
<svelte:options css="injected" />

This approach helps developers understand their configuration choices and prevents confusion about which settings take precedence. Always include practical examples showing the actual syntax for each configuration level.

---

maintain naming consistency

Ensure consistent naming conventions across the entire codebase, including terminology, file names, directory structures, and API naming. Inconsistent naming creates confusion and poor developer experience.

Key areas to maintain consistency:

Terminology: Use the same terms consistently across code, documentation, and templates. For example, choose either “browser” or “client” and use it consistently throughout the codebase rather than mixing terms.

Directory/File Naming: Maintain consistent naming patterns across templates, examples, and documentation. If using app/routes/ in templates, use the same structure in tutorials and examples rather than switching to app/pages/.

API Documentation: Follow consistent naming patterns for documentation files, especially for unstable APIs. For example, consistently handle unstable API documentation naming to maintain stable URLs.

File Naming: Use descriptive, specific names rather than generic ones. Instead of file-storage.server.ts, use avatar-storage.server.ts to clearly indicate the file’s purpose.

Example of inconsistent naming to avoid:

// Documentation uses "browser" 
entry.browser.tsx

// But code comments refer to "client"
// This is the client entry point...

// Templates use different directory names
app/routes/contact.tsx  // in one template
app/pages/contact.tsx   // in another template

Before introducing new naming conventions, audit existing patterns and align with established conventions. When changes are necessary, update all related files, documentation, and examples simultaneously to maintain consistency.

---

documentation linking standards

Ensure proper linking and cross-referencing in documentation to improve navigation and discoverability. Use correct JSDoc syntax for type references and consistently link to related concepts where they are mentioned.

For TypeScript types in JSDoc comments, use {@link TypeName} syntax instead of markdown-style links:

/**
 * The {@link Blocker} object returned by the hook has the following properties:
 */

Cross-link to related concepts when they are mentioned in documentation text:

These are the requests that return the [`loader`][loader] and [`action`][action] data to the browser.

Link hooks and components where they are referenced rather than only in “See” sections:

You can use [`<Link state>`][link-component-state-prop] or [`useNavigate`][use-navigate] to change the location state.

This practice helps users discover related functionality and creates a more interconnected documentation experience that reduces the need to search for related concepts separately.

---

Review configuration constants regularly

Configuration constants and mappings require regular maintenance to stay aligned with evolving platform capabilities. Outdated configurations can introduce unnecessary complexity, while incomplete mappings can cause functionality loss.

Periodically audit configuration constants to:

1. Remove redundant manual conversions when automatic alternatives become available
2. Ensure mapping dictionaries are complete for all supported values
3. Update configurations when underlying platform capabilities change

Example of configuration constants that need review:

# Before: Manual unit conversion (now redundant)
DEVICE_CLASS_UNITS = {
    "current": "mA",  # Manual conversion from A to mA
}

# After: Let platform handle automatic conversions
DEVICE_CLASS_UNITS = {
    "current": "A",   # Use standard unit, let platform convert
}

# Ensure complete mappings to avoid losing device classes
DEVICE_CLASS_UNITS = {
    "current": "A",
    "duration": "min",  # Add missing mappings
    "voltage": "V",
}

This prevents bugs where valid configurations are incorrectly removed due to incomplete mappings, and eliminates maintenance overhead from obsolete manual conversions.

---

Document CI/CD changes

Always document changes to CI/CD configurations and scripts, and ensure pull requests remain focused on their intended purpose. When modifying build scripts, dependencies, or deployment processes:

1. Review all dependency changes to ensure they are necessary for the current work
2. Keep changes focused and avoid unintended modifications that may affect the build pipeline
3. If simplifying or removing build/deployment scripts, document the new procedure clearly

Example:

# When removing scripts from package.json
@@ -2,24 +2,13 @@
   "name": "nestjs",
   "version": "5.0.0",
   "description": "Modern, fast, powerful node.js web framework",
+  "private": true,
   "scripts": {
-    "publish": "./node_modules/.bin/lerna publish --exact -m \"chore(@nestjs) publish %s release\"",
+    // Scripts removed
   
   // Add a comment explaining the change
   // Example: "// Publish process simplified - run 'yarn run lerna publish' directly"

Adding a CONTRIBUTING.md or updating README.md with new procedures when removing or changing build scripts ensures that the team can maintain continuity in the CI/CD workflow.

---

Complete OpenAPI annotations

Ensure all API endpoints have complete and accurate OpenAPI annotations to support proper SDK generation and documentation. Use appropriate decorators, include all necessary metadata, and verify that generated SDKs work correctly.

Key requirements:

• Use @ApiPropertyOptional for optional fields instead of @ApiProperty with required: false
• Add additionalProperties: true for object types to enable proper SDK type generation
• Include nullable: true when fields can be null (different from optional)
• Use @ApiHideProperty conditionally when properties should not appear in public documentation
• Ensure response decorators properly override schemas rather than deleting them
• Add complete metadata including examples, descriptions, and type information

Example of proper annotations:

@ApiPropertyOptional({
  description: 'The data sent with the notification.',
  type: 'object',
  nullable: true,
  example: { key: 'value' },
  additionalProperties: true
})
data?: Record<string, unknown>;

// Conditional hiding for internal-only properties
@ApiHideProperty() // when IS_DOCKER_HOSTED !== 'true'
@IsOptional()
@IsNumber()
priority?: number;

This ensures accurate documentation generation, proper SDK type inference, and consistent API behavior across all client libraries.

---

Update deprecated demo APIs

Documentation, demos, and example code should always use current, non-deprecated APIs instead of showing deprecation warnings. When APIs are deprecated, update all demo code and examples to use the recommended replacement APIs immediately.

This prevents users from copying outdated code that generates warnings and ensures documentation serves as a reliable guide for current best practices. If deprecated API compatibility testing is needed, limit it to dedicated test files rather than user-facing examples.

Example of what to avoid:

// Bad: Demo showing deprecated API usage
<Alert onClose={handleClose} /> // Generates warning

// Good: Demo using current API
<Alert closable={{ onClose: handleClose }} />

When you see deprecation warnings in demo snapshots, update the demo source code to use the current API rather than accepting the warning as expected output.

---

preserve user input focus

When implementing reactive state updates that affect input elements, always check if the user is currently interacting with the element before applying the update. This prevents jarring user experiences where typing gets interrupted by state changes.

The most common scenario is when an input’s value is bound to reactive state that gets updated from external sources (like API responses or computed values). Without proper checks, these updates can override what the user is currently typing.

// Good: Check if input is focused before updating
if (input === document.activeElement) {
  // Skip update to preserve user's current input
  return;
}
input.value = newValue;

// Also applies to React controlled components
function SearchInput({ value, onChange }) {
  const inputRef = useRef();
  
  useEffect(() => {
    // Only update if user isn't currently typing
    if (document.activeElement !== inputRef.current) {
      inputRef.current.value = value;
    }
  }, [value]);
  
  return <input ref={inputRef} onChange={onChange} />;
}

This pattern is essential for search inputs, autocomplete fields, and any scenario where external state changes could conflict with user input. It ensures the UI “catches up” to focused inputs rather than disrupting the user’s flow.

---

Follow Vue API patterns

Always prefer Vue’s native APIs and follow official Vue patterns instead of creating custom implementations. This ensures better compatibility, maintainability, and consistency with the Vue ecosystem.

Key practices:

• Use Vue’s native composables when available (e.g., useId from Vue instead of custom implementations)
• Follow Vue’s official configuration structures and API changes from changelogs
• Match Vue Router’s API patterns when creating similar functionality (e.g., exposing useLink composable)
• Use proper Vue type definitions without redundancy

Example of migrating from custom to native Vue API:

// Before: Custom implementation
export function useId(key?: string): string {
  // Custom SSR-friendly ID generation logic...
}

// After: Use Vue's native API
import { useId as _useId } from 'vue'
export const useId = _useId

Example of following Vue Router patterns:

// Expose useLink to match RouterLink behavior
export const NuxtLink = defineComponent({
  // ... component definition
  useLink: useNuxtLink, // Matches Vue Router's RouterLink.useLink pattern
})

This approach reduces maintenance burden, improves ecosystem compatibility, and ensures your components work seamlessly with Vue tooling and development experience.

---

documentation clarity standards

Ensure all React-related documentation, comments, and descriptions maintain high standards of clarity, accuracy, and consistency. This includes using proper grammar, consistent terminology, complete descriptions, and well-structured explanations.

Key areas to focus on:

1. Grammar and Structure: Use proper grammar, punctuation, and sentence structure. Avoid incomplete sentences or unclear phrasing.

2. Terminology Consistency: Use consistent and accurate technical terms throughout. For example, prefer “Route Module API” over “Route Modules” when referring to the specific API, or “RSC-compatible bundlers” instead of “RSC-native bundlers” when the terminology is more accurate.

3. Complete Descriptions: Provide thorough explanations rather than abbreviated or incomplete descriptions. Changeset descriptions should clearly explain what changed and why.

4. Code Example Accuracy: Ensure code examples are syntactically correct and demonstrate best practices. Use proper destructuring, correct function signatures, and appropriate file extensions.

Example of improved documentation:

// Before: Incomplete and unclear
export function routes() {
  // Route Modules have been a Framework Mode only feature
}

// After: Clear and complete  
export function routes() {
  // The Route Module API has been a Framework Mode only feature
  // until now, but the lazy field unifies the APIs
}

This standard helps maintain professional documentation quality that makes React applications more maintainable and easier for developers to understand and contribute to.

---

explicit null safety

Always perform explicit null and undefined checks before processing values, and use the nullish coalescing operator (??) for safe default value assignment. Distinguish between null (explicit no value) and undefined (use default) semantics in your API design.

When providing default values, prefer nullish coalescing over logical OR to avoid falsy value issues:

// Good: Uses nullish coalescing for defaults
const severity = options.severity ?? SeverityLevelEnum.NONE;
const subscriberId = subscriber?.subscriberId ?? '';
const timezone = subscriber?.timezone ?? currentTimezone;

// Good: Explicit undefined check
if (typeof command.layoutIdOrInternalId === 'undefined') {
  // Use default layout
}

// Good: Explicit null check in sensitive code
if (!this.svix) {
  throw new BadRequestException('Webhook system is not enabled');
}

// Good: Handle null vs undefined semantics
// null = user explicitly wants no layout
// undefined = use default layout
layoutId: z.string().nullable().optional()

// Good: Explicit null check for string conversion
return value == null ? '' : String(value);

This pattern prevents null reference errors, makes default value logic clear, and ensures consistent behavior across null and undefined scenarios. Always validate these checks in sensitive code paths where null values could cause runtime failures.

---

JSDoc deprecation formatting

Ensure consistent formatting in JSDoc deprecation comments to improve API documentation clarity and developer experience. Use backticks around parameter/property names to distinguish them from regular text, use angle brackets for component names, and include “instead” for replacement suggestions.

Format Guidelines:

• Wrap parameter/property names in backticks: parameterName
• Use angle brackets for component names: <ComponentName />
• Include “instead” in replacement suggestions for clarity
• Avoid redundant explanations that the deprecation method already provides

Examples:

// ✅ Good
/** @deprecated Please use `orientation` instead */
direction?: 'horizontal' | 'vertical';

/** @deprecated Please use `railColor` instead */
trailColor?: string;

// For components
warning.deprecated(
  true,
  '<Statistic.Countdown />',
  '<Statistic.Timer type="countdown" />',
);

// ❌ Bad  
/** @deprecated please use orientation */
/** @deprecated Please use trailColor instead */
/** @deprecated Please use `tabsPlacement` instead */ // Wrong parameter name

This standardization helps developers quickly identify deprecated APIs and their replacements, improving the overall API migration experience.

---

Hook responsibility separation

Keep hooks and components focused on single, well-defined responsibilities to maintain clean architecture and avoid mixing concerns.

When designing hooks, ensure they have a clear, singular purpose. Avoid combining unrelated functionality like DOM manipulation with event handling, or complex business logic with simple state management. If a hook or component starts handling multiple distinct concerns, consider splitting it into focused, composable pieces.

For example, instead of extending a click-handling hook to also manipulate the DOM:

// Avoid mixing concerns in a single hook
const useLinks = (node, accountId) => {
  // Handles both click events AND DOM manipulation
  useEffect(() => {
    // Click handling logic
    // DOM manipulation logic - different responsibility!
  }, []);
};

// Better: Keep hooks focused
const useLinks = () => {
  // Only handles click events
};

const useHashtagDropdowns = (node, accountId) => {
  // Only handles DOM manipulation for hashtags
};

Similarly, avoid prop drilling by moving helper functions closer to where they’re used, and keep component wrappers thin by not adding unnecessary event handling logic that belongs in the underlying native elements.

This separation makes code more maintainable, testable, and follows React’s compositional patterns.

---

maintain cross-platform API consistency

When designing APIs that work across multiple platforms, ensure consistent return types and behavior to avoid breaking changes and maintain a unified developer experience. Use Platform.select() to handle platform-specific implementations rather than hardcoded conditional logic.

For APIs that need different implementations per platform, structure the code to provide consistent types while allowing platform-specific behavior:

return Platform.select({
  android: this.isLoadedFromFileSystem()
    ? this.drawableFolderInBundle()
    : this.resourceIdentifierWithoutScale(),
  ios: this.isCatalogAsset()
    ? this.assetFromCatalog()
    : this.scaledAssetURLNearBundle(),
  default: this.scaledAssetURLNearBundle()
});

When a platform cannot provide meaningful data, return a consistent placeholder value rather than undefined or void types. For example, if web platforms cannot provide an OS version, return a stable string like “1000.0.0” to maintain type consistency across all platforms. This prevents breaking changes for consumers who expect consistent API contracts regardless of the underlying platform.

---

Use descriptive, conflict-free names

Choose descriptive names that clearly convey purpose while avoiding conflicts with existing APIs, built-in functions, or established conventions. Names should follow consistent patterns across the codebase and use appropriate spelling conventions.

Key principles:

• Prefer descriptive names over abbreviated ones (e.g., dehydratedRouter instead of r)
• Avoid conflicts with built-in functions (e.g., fetchAndResolveInLoaderLifetime instead of fetch)
• Don’t clash with framework conventions (e.g., getSupabaseServer instead of useSupabase for non-hooks)
• Follow established naming patterns in the codebase (e.g., disableManifestGeneration to match disableTypes)
• Use consistent spelling conventions (e.g., US spelling: behavior not behaviour)
• Choose meaningful variable names that reflect their content (e.g., derived instead of paths)

Example:

// ❌ Avoid: Abbreviated, conflicts with built-in
const r = getRouter()
const fetch = async () => { ... }

// ✅ Good: Descriptive, conflict-free
const dehydratedRouter = getRouter()
const fetchAndResolveInLoaderLifetime = async () => { ... }

// ❌ Avoid: Misleading naming pattern
export function useSupabase() { /* not a hook */ }

// ✅ Good: Clear, follows conventions
export function getSupabaseServer() { /* server utility */ }

---

API parameter handling

Ensure consistent and safe handling of parameters and data across API endpoints. This includes using proper serialization methods, consistent parameter passing approaches, and context-aware processing when the same input may have different meanings.

Key practices:

• Use proper JSON serialization instead of string concatenation for API responses to prevent injection issues with user-provided data containing quotes or backslashes
• Maintain consistent behavior patterns across related endpoints (e.g., if login stores origin URL in cookies, signup should follow the same pattern)
• Pass parameters through appropriate channels - use hidden form fields instead of query parameters when dealing with sensitive or complex data
• Design APIs to handle context-specific interpretations where the same parameter might reference different entities based on the calling context

Example of proper JSON serialization:

// Instead of string concatenation:
return JSON.stringify(this.name) + ":" + JSON.stringify(data);

// Use proper object serialization:
const object = { name: this.name, light: {...}, dark: {...} };
return JSON.stringify(object, null, 2);

This approach prevents security vulnerabilities, ensures predictable API behavior, and provides better developer experience through consistent interfaces.

---

Configuration opt-in safety

When introducing new configuration options or making changes that could be disruptive, make them opt-in by default rather than enabled automatically. This prevents breaking existing functionality and gives users control over when to adopt new behaviors.

Key principles:

• New features should be disabled by default with explicit flags to enable them
• Potentially disruptive migrations should require explicit opt-in
• Breaking configuration changes should be avoided, or made opt-in with clear migration paths
• Validate configuration options and provide clear error messages for unsupported settings

Example from migration configuration:

// Bad: Automatically migrating potentially disruptive changes
export class NgClassMigration {
  // Always migrates multi-class keys, potentially creating verbose output
}

// Good: Making disruptive changes opt-in
export class NgClassMigration {
  constructor(private options: { migrateMultiClassKeys?: boolean } = {}) {}
  
  migrate() {
    // By default don't migrate multi-class keys
    if (!this.options.migrateMultiClassKeys) {
      return; // Skip potentially disruptive migration
    }
    // Only migrate when explicitly requested
  }
}

This approach protects users from unexpected changes while still providing access to new functionality when they’re ready to adopt it.

---

Resilient configuration patterns

When modifying or defining configuration values, use patterns that are resistant to future changes and silent failures. For configuration files, scripts, and environment variables, implement approaches that remain valid when underlying values change.

For sed-based file modifications, target the configuration key rather than specific values:

-sed -i 's/_APP_BROWSER_HOST=http:\/\/appwrite-browser:3000\/v1/_APP_BROWSER_HOST=http:\/\/invalid-browser\/v1/' .env
+# Force an invalid browser host irrespective of its previous value
+sed -i 's|^_APP_BROWSER_HOST=.*|_APP_BROWSER_HOST=http://invalid-browser/v1|' .env

For environment variable names and values, ensure correct spelling and valid defaults:

-OPR_EXECUTOR_INACTIVE_TRESHOLD=$_APP_COMPUTE_INACTIVE_THRESHOLD
+OPR_EXECUTOR_INACTIVE_THRESHOLD=$_APP_COMPUTE_INACTIVE_THRESHOLD

if [ -z "$PLATFORM" ]; then
-  PLATFORM="console"
+  PLATFORM="client"  # Using a value from the defined options
fi

These practices prevent silent failures, ensure configuration changes work reliably across environments, and improve maintainability as projects evolve.

---

Use descriptive scoped names

Prefer descriptive, scoped names over generic or vague identifiers for types, functions, and properties. Names should clearly communicate their purpose and context within the codebase.

For boolean properties, consider using getter functions with descriptive names instead of direct property access:

// Instead of direct property access
isClosed: boolean

// Consider descriptive getter
getIsClosedStatus(): boolean

For types, use specific, scoped names rather than generic ones:

// Too generic
type Resolver = { ... }

// More descriptive and scoped  
type BlockerFnResolver = { ... }
type BlockerResolver = { ... }

For object structures, maintain consistent naming patterns that support future extensibility:

// Structured approach that supports extension
export type MyRouterContext = {
  auth: AuthContextType
  // Easy to add: query: QueryContextType
}

This approach improves code readability, reduces ambiguity, and makes the codebase more maintainable by clearly communicating the intent and scope of each identifier.

---

Use design system colors

Always use design system color variables instead of hardcoded color values in stylesheets. This ensures consistent theming, automatic dark/light mode support, and maintainable code.

Replace hardcoded colors with their design system equivalents:

// ❌ Avoid hardcoded colors
.loading {
  color: #666;
  background: #f5f5f5;
}

.stat-value {
  color: #1976d2;
}

// ✅ Use design system colors
.loading {
  color: var(--secondary-contrast);
  background: var(--color-foreground);
}

.stat-value {
  color: var(--dynamic-blue-02);
}

Dynamic color variables (prefixed with --dynamic-, --color-, etc.) automatically adapt to theme changes, eliminating the need for manual theme-specific overrides. Only use theme mixins like theme.dark-theme for special cases that can’t be handled by dynamic colors.

---

Pin CI dependencies securely

Always pin CI/CD dependencies (GitHub Actions, external tools) to specific commit hashes or exact versions rather than using floating tags like @v1 or @latest. This prevents supply chain attacks and ensures reproducible builds. However, pinned dependencies must be regularly updated to avoid using outdated or vulnerable versions.

For GitHub Actions, use commit hashes with descriptive comments:

- name: verify-version
  uses: actions-cool/verify-files-modify@82e88fd0e8e5ed5b7f1a9e6a3c4b9c2d1234567 # pin to latest verified commit

When implementing automated dependency updates, ensure proper token permissions are configured so that generated PRs can run CI checks. This allows safe validation of dependency changes before merging. Consider using tokens with minimal required permissions rather than default tokens to maintain security while enabling necessary CI functionality.

---

Configuration value safety

Ensure configuration values are properly encoded and dependencies use specific versions to prevent runtime failures and security issues. When embedding dynamic values in YAML configuration files, use proper encoding methods like .to_json to handle special characters safely. For external dependencies in workflows and configuration, specify exact versions rather than using @latest or similar floating tags.

Example of proper value encoding:

# Instead of:
password: <%= ENV.fetch('SMTP_PASSWORD', nil) %>

# Use:
password: <%= ENV.fetch('SMTP_PASSWORD', nil).to_json %>

Example of proper version pinning:

# Instead of:
uses: chromaui/action@latest

# Use:
uses: chromaui/action@v1

This prevents configuration parsing errors when values contain special characters and ensures reproducible builds by avoiding unexpected dependency updates.

---

Verify authentication logic

Ensure authentication validation logic follows expected semantics and intuitive implementation. Authentication checks should correctly interpret the presence or absence of security tokens, with clear and accurate logging that reflects the actual security state.

When implementing JWT or other token-based authentication:

• Presence of valid tokens should indicate authenticated/valid states
• Absence of tokens should indicate unauthenticated/invalid states
• Log messages and condition branches should match these intuitive expectations

Example:

// Correct implementation
if (context.req.headers['x-appwrite-user-jwt']) {
  context.log('jwt-is-valid');
  // Proceed with authenticated operations
} else {
  context.log('jwt-is-invalid');
  // Handle unauthenticated state
}

This prevents security vulnerabilities that could arise from misinterpreting authentication states and ensures proper access control throughout the application.

---

Handle async operation errors

Always wrap asynchronous operations in try-catch-finally blocks to prevent unhandled promise rejections and ensure proper cleanup. When errors occur, provide users with meaningful feedback while preserving application state.

// Before: Error-prone async operation
const handleSubmit = async () => {
  setIsSubmitting(true);
  const result = await submitData(formData);
  setIsSubmitting(false); // Never executes if submitData fails
  if (result.error) {
    showError(result.error);
    return;
  }
  navigateToSuccess();
};

// After: Robust error handling
const handleSubmit = async () => {
  setIsSubmitting(true);
  try {
    const result = await submitData(formData);
    
    if (result.error) {
      showError(result.error);
      return;
    }
    
    navigateToSuccess();
  } catch (error) {
    console.error("Submission failed:", error);
    toastError({
      title: "Failed to submit data",
      description: error instanceof Error ? error.message : "Unknown error"
    });
  } finally {
    setIsSubmitting(false); // Always executes, ensuring UI state is reset
  }
};

This pattern prevents common issues like:

• Unhandled promise rejections crashing the application
• Loading indicators stuck in active state after errors
• Silent failures that confuse users
• Missing error logs that make debugging difficult

For React components fetching data, also ensure error states are properly handled in the UI:

function DataComponent() {
  const { data, error, isLoading } = useSWR('/api/data');
  
  if (error) {
    return <ErrorDisplay message="Failed to load data" />;
  }
  
  if (isLoading) {
    return <LoadingIndicator />;
  }
  
  return <DataDisplay data={data} />;
}

---

Validate environment variables strictly

Enforce strict validation of environment variables using Zod schemas with explicit environment-specific rules. Required configurations should be mandatory in production while allowing flexibility in development/test environments.

Key principles:

1. Mark critical variables as required in production
2. Provide clear error messages for missing configurations
3. Allow optional values only in development/test
4. Implement proper fallback mechanisms for optional configs

Example:

export const env = createEnv({
  server: {
    STRIPE_SECRET_KEY: z.string().refine(
      (val) => process.env.NODE_ENV === 'test' || !!val,
      'Missing STRIPE_SECRET_KEY in production',
    ),
    REDIS_URL: z.string().refine(
      (val) => process.env.NODE_ENV === 'test' || !!val,
      'Missing REDIS_URL in production',
    ),
    // Optional in all environments
    LOG_LEVEL: z.string().optional(),
  },
  client: {
    // Required in all environments
    NEXT_PUBLIC_API_URL: z.string().min(1),
  },
  // Validate on app startup
  runtimeEnv: process.env,
});

This approach prevents silent misconfigurations in production while maintaining development flexibility and providing clear error messages when required variables are missing.

---

Document complex APIs

Require comprehensive JSDoc documentation for classes, complex functions, and all exported functions to improve codebase maintainability and developer onboarding. Focus especially on code with broad reach across the codebase or non-obvious functionality.

Key requirements:

• Add JSDoc to all exported functions and classes
• Document complex methods and their purpose, not just what they do
• Ensure comments are clear without assuming excessive context knowledge
• Keep documentation current when code changes

Example of good JSDoc:

/**
 * Captures the current reactive context and returns a restore function.
 * Used to preserve effect and component state across async boundaries.
 * @param {boolean} [track=true] - Whether to track the current context
 * @returns {() => void} Function to restore the captured context
 */
export function capture(track = true) {
  // implementation
}

This practice makes the codebase significantly more approachable for new developers and reduces the cognitive load when working with complex APIs.

---

Comments versus docstrings usage

Choose between comments and docstrings based on the documentation’s purpose and scope. Use docstrings for API-level documentation of functions, classes, and methods, writing verbs as commands (e.g., “Return” not “Returns”). Use inline comments sparingly for implementation details that aren’t appropriate for the public API documentation.

Avoid redundant documentation:

• Don’t duplicate test names in docstrings when the name is sufficiently descriptive
• Avoid “what” comments that merely restate the code
• Don’t use comments for information that belongs in docstrings

Example:

# Bad - redundant docstring duplicating test name
def test_user_authentication_success(self):
    """Test that user authentication succeeds with valid credentials."""
    ...

# Bad - "what" comment that restates code
# Calculate the total price
total = price + tax

# Good - docstring with command verb
def get_user_by_email(email):
    """Return a user instance based on email address."""
    ...

# Good - implementation detail comment
def complex_calculation(x, y):
    # Adjust for floating point precision issues
    result = round((x / y) * 100, 2)
    return result

---

Measure before optimizing

Always measure performance impact before implementing optimizations and focus on changes with meaningful benefits. Python’s performance characteristics can be unintuitive - optimizations that seem beneficial might have minimal impact, while simple changes can yield significant improvements.

Key optimization patterns to consider:

1. Cache attribute lookups in loops: ```python

   Inefficient - repeated attribute lookups

   missing_instances = [i for i in instances if not self.field.is_cached(i)]

Optimized - single lookup cached in local variable

is_cached = self.field.is_cached missing_instances = [i for i in instances if not is_cached(i)]

2. **Avoid expensive operations** like materializing entire stack traces with `inspect.stack()`. Use targeted approaches instead:
```python
# Expensive - materializes all stack frames
if "aggregate" in {frame.function for frame in inspect.stack()}:
    # ...

# More efficient - only access needed frames
frame = inspect.currentframe()
for _ in range(5):
    try:
        frame = frame.f_back
    except AttributeError:
        break
else:
    is_aggregate = 'aggregate' in frame.function
del frame  # Avoid reference cycles

1. Know your standard library operations. For dictionary filtering, copy() and pop() can be more efficient than comprehensions: ```python

   ~110ns

   p = params.copy() p.pop(“q”, None)

~240ns

{k: v for k, v in params.items() if k != “q”}

Always confirm your optimizations with timings (using `timeit` or similar tools) on representative data volumes to ensure the changes provide meaningful benefits.

---

## Use environment flags consistently

<!-- source: vuejs/core | topic: Configurations | language: TypeScript | updated: 2025-07-08 -->

Feature flags like `__DEV__` and `__COMPAT__` are critical configuration mechanisms that control environment-specific behavior. Always wrap development-only code (such as warnings and debug information) in `__DEV__` conditionals to ensure they don't ship to production builds. Remember that these flags are replaced at build time through tree-shaking, so their proper usage directly impacts bundle size and performance.

```js
// Good: Warning only shown in development
if (__DEV__ && unexpectedCondition) {
  console.warn('This warning helps developers but is removed in production')
}

// Good: Feature flag affects code path selection
if (!(__COMPAT__ && compatFeature)) {
  // Modern implementation
} else {
  // Compatibility implementation
}

// Bad: Warning always included in production builds
if (unexpectedCondition) {
  console.warn('This warning will bloat production builds')
}

This practice ensures configuration is properly managed across different build environments, keeping production code lean while providing helpful development features.

---

Break lines for readability

Format code with semantic line breaks that enhance readability rather than adhering strictly to character limits. When breaking long lines:

1. Break at natural semantic boundaries
2. Place spaces at the start of continuation lines to show they are continuations
3. Aim to have one logical component per line
4. Use the full available width when it improves readability

Example:

# Less readable - breaking arbitrarily at limit
message = (f"{func_name}() takes at most {max_positional_args} positional"
          f" argument(s) (including {num_remappable_args} deprecated) but"
          f" {num_positional_args} were given.")

# More readable - semantic breaks with clear continuations
message = (
    f"{func_name}() takes at most {max_positional_args} "
    f"positional argument(s) (including {num_remappable_args} "
    f"deprecated) but {num_positional_args} were given."
)

This approach makes code easier to read and maintain while still respecting line length guidelines. The goal is to use line breaks to highlight the logical structure of the code rather than breaking lines mechanically at a specific column.

---

Use slots for composition

When designing React component APIs, implement the slots pattern using slots and slotProps props instead of specialized prop names. This approach provides a consistent, flexible, and maintainable way to customize component parts while preserving their functionality.

// Instead of specialized props:
<SpeedDial actions={[
  { icon: <FileCopyIcon />, name: 'Copy', tooltipTitle: 'Copy' },
]} />

// Use slots pattern:
<SpeedDial actions={[
  { 
    icon: <FileCopyIcon />, 
    name: 'Copy', 
    slotProps: { tooltip: { title: 'Copy' } } 
  },
]} />

This pattern separates component structure from styling and behavior, making it easier to extend components without breaking changes. It creates a consistent API across your component library, improving developer experience and making your code more maintainable. When migrating components, consider replacing specialized props with the slots pattern to achieve greater flexibility and consistency.

---

API backward compatibility

When evolving APIs, maintain backward compatibility by preserving existing public interfaces while adding new functionality through internal implementations or optional parameters. Avoid breaking changes that remove functionality without providing migration paths.

Key principles:

• Fork internal implementations to expand functionality without changing public APIs
• Support both old and new API patterns during transition periods
• Make internal utilities public when they provide value to external users
• Use optional parameters and function overloads to extend APIs gracefully

Example from the codebase:

// Good: Internal fork preserves public API
export function renderMatches(matches: RouteMatch[] | null): React.ReactElement | null {
  // Internal _renderMatches was forked to allow data-router capabilities
  // without changing the existing renderMatches public API
}

// Bad: Breaking change removes functionality
export function createRoutesStub(
  routes: StubRouteObject[],
  unstable_getContext?: () => unstable_InitialContext  // Used to take AppLoadContext
) {
  // This breaks existing usage - should support both types
}

// Better: Support both patterns
export function createRoutesStub(
  routes: StubRouteObject[],
  contextOrGetter?: AppLoadContext | (() => unstable_InitialContext)
)

Consider exposing internal utilities as public APIs when they solve common user problems, such as middleware pipeline utilities for custom data strategies.

---

Include contextual error information

Error messages should include relevant contextual information such as IDs, file paths, job identifiers, and other debugging details to make troubleshooting easier. Generic error messages make it difficult to identify the specific instance or operation that failed, especially in systems processing multiple items concurrently.

When logging errors, include:

• Entity IDs (upload_id, user_id, job_id, etc.)
• File paths or URLs being processed
• Operation context or step information
• Request IDs when available

Example of improved error logging:

# Poor: Generic error message
Rails.logger.error("Failed to handle video conversion completion")

# Good: Contextual error message  
Rails.logger.error("Failed to handle video conversion completion for upload ID #{upload.id} and job ID #{args[:job_id]}")

# Poor: Missing context in model errors
Rails.logger.error("Failed to create optimized video: #{optimized_video.errors.full_messages.join(", ")}")

# Good: Include relevant entity context
Rails.logger.error("Failed to create optimized video for upload ID #{upload.id}: #{optimized_video.errors.full_messages.join(", ")}")

This practice significantly reduces debugging time and helps identify patterns in failures across different environments and deployments.

---

Consider related object cleanup

When implementing migration operations that modify or remove database objects like fields and models, ensure all related objects (indexes, constraints, foreign keys) are properly identified and removed. Failing to handle these dependencies can leave orphaned database objects that may cause issues later.

When removing fields, check for dependencies like indexes or constraints that reference those fields:

# Example: Ensuring indexes are removed when removing fields
# Note how dependencies are explicitly defined for field removal

def _generate_removed_field(self, app_label, model_name, field_name):
    # Include dependencies such as order_with_respect_to, constraints,
    # and any generated fields that may depend on this field
    dependencies = [
        OperationDependency(
            app_label,
            model_name,
            field_name,
            OperationDependency.Type.REMOVE_INDEX_OR_CONSTRAINT,
        ),
        # Add other dependencies as needed
    ]
    
    # Add the operation with proper dependencies
    self.add_operation(
        app_label,
        operations.RemoveField(
            model_name=model_name,
            name=field_name,
        ),
        dependencies=dependencies,
    )

Write tests that verify the proper cleanup of related objects when fields or models are removed. This is especially important for complex relationships between models.

---

Organize by functionality

Place code in files that match its functionality. When functionality applies to multiple components, use a general-purpose file rather than component-specific ones. This improves maintainability and makes the codebase easier to navigate.

For example, instead of:

// In inlines.js
$('.js-inline-admin-formset fieldset.module.collapse:not(.open) details[open]').each(function() {
    this.removeAttribute('open');
});

Prefer:

// In a more general file like change_form.js
document.querySelectorAll('fieldset.module.collapse:not(.open) details[open]').forEach(details => {
    details.removeAttribute('open');
});

Additionally, use modern JavaScript patterns where appropriate to improve code consistency and readability.

---

Graceful component errors

Use descriptive error messages and appropriate error severity based on component maturity and usage patterns. For newer components, throwing errors is acceptable when constraints are violated. For established components, consider using development-mode warnings instead of throwing errors to avoid breaking existing implementations.

When writing error messages:

• Be specific about the relationship between components
• Clearly state what the developer needs to do to fix the issue

When deciding error severity:

• Consider how the component might be used in the wild
• Be more conservative with established components

Example:

// Better error message
if (ctx === null) {
  if (process.env.NODE_ENV !== 'production') {
    console.warn('Material UI: The Tab component should be used inside a Tabs component');
  }
  // Provide fallback behavior if possible
  return defaultContext;
}

// Instead of throwing:
if (ctx === null) {
  throw new Error('Material UI: Tabs component was not found in the tree');
}

This approach balances between guiding developers toward correct usage while maintaining compatibility with existing code that might use components in unexpected ways.

---

Prevent N+1 queries

The N+1 query problem is one of the most common performance bottlenecks in Django applications. This occurs when you retrieve a list of objects and then access related objects for each one individually, causing an additional database query for each parent object.

To prevent N+1 queries, follow these strategies in order of complexity:

1. Start with FETCH_PEERS mode: This is the simplest approach and should be your first consideration when optimizing queries.

from django.db.models import fetch_mode, FETCH_PEERS

# Apply to a specific code block
with fetch_mode(FETCH_PEERS):
    articles = Article.objects.all()
    for article in articles:
        print(article.reporter)  # Fetches all reporters in one query

# Or set globally in an AppConfig
from django.apps import AppConfig
from django.db.models import set_default_fetch_mode, FETCH_PEERS

class MyAppConfig(AppConfig):
    name = 'myapp'
    def ready(self):
        set_default_fetch_mode(FETCH_PEERS)

1. Use select_related() for forward ForeignKey relationships: ```python

   Instead of this (causes N+1 queries):

   for article in Article.objects.all(): print(article.reporter.name)

Do this (single query):

for article in Article.objects.select_related(‘reporter’): print(article.reporter.name)

3. **Use `prefetch_related()` for reverse or many-to-many relationships**:
```python
# Instead of this (causes N+1 queries):
for reporter in Reporter.objects.all():
    print([article.headline for article in reporter.article_set.all()])

# Do this (two queries):
for reporter in Reporter.objects.prefetch_related('article_set'):
    print([article.headline for article in reporter.article_set.all()])

1. For complex cases, combine approaches:

   queryset = Book.objects.select_related('publisher').prefetch_related('authors')
   

2. Use the RAISE fetch mode during development to catch accidental N+1 queries:

   with fetch_mode(RAISE):
    # Code that should not trigger additional queries
    render(request, "template.html", context)
   

Remember that fetching too much data can also be inefficient. Choose the appropriate strategy based on your specific access patterns.

---

Active service health checks

Replace static delays with active health checks in CI/CD workflows to ensure service readiness. Instead of using fixed sleep times, implement polling mechanisms that verify service health endpoints. This improves workflow reliability and reduces false negatives.

Example implementation:

- name: Wait for service readiness
  run: |
    for i in {1..18}; do               # 18 × 5 s = 90 s timeout
      if curl -fs http://localhost/health >/dev/null; then
        break
      fi
      echo "🕒 Waiting for service to become healthy... ($i)"
      sleep 5
    done
    curl -fs http://localhost/health >/dev/null || {
      echo "❌ Service did not become healthy in time" >&2
      exit 1
    }

This approach:

• Actively verifies service availability
• Provides clear feedback during waiting period
• Fails fast if service is unhealthy
• Accommodates varying startup times
• Includes proper error handling

---

optimize file-based routing

Implement lazy loading patterns and strategic code-splitting in file-based routing systems to improve performance and reduce unnecessary processing. Root routes should never be code-split since they’re always needed, while other routes can benefit from lazy instantiation to avoid parsing route trees when not required.

Key strategies:

1. Use lazy instantiation for route parsing to defer expensive operations until actually needed
2. Exclude root routes from code-splitting since they’re always required
3. Add clear comments explaining routing optimization decisions for future maintainers

Example implementation:

// Use lazy instantiation pattern for route parsing
export type CodeRoutesByPath<TRouteTree extends AnyRoute> =
  ParseRoute<TRouteTree> extends infer TRoutes extends AnyRoute
  
// Skip code-splitting for root routes with explanatory comment
if (createRouteFn !== 'createFileRoute') {
  // Exit early for root routes since they are never code-split
  // Root routes are always needed and should remain in the main bundle
  return
}

This approach aligns with Next.js principles of file-based routing optimization and incremental static regeneration by ensuring only necessary code is loaded when needed while maintaining fast initial page loads.

---

Names reflect semantic purpose

Choose names that reflect the semantic purpose rather than implementation details or temporal characteristics. Names should be consistent across the codebase and accurately represent their usage.

Key guidelines:

1. Use semantic names that describe the purpose rather than implementation
2. Maintain consistent naming patterns across related code
3. Ensure type/interface names accurately reflect their usage
4. Avoid encoding temporal or mutable characteristics in names

Example - Good:

// Semantic name reflecting purpose
const labelArchiveDelayed = "label_archive_delayed";
type EmailSummaryResult = z.infer<typeof schema>;
interface Message {
  date: Date;  // Required if always needed
}

Example - Avoid:

// Names tied to implementation details
const labelArchive1Week = "label_archive_1_week";
type AICheckResult = z.infer<typeof schema>;  // Misleading purpose
interface Message {
  date?: Date;  // Optional despite being required
}

---

Cache invariant computations

Avoid repeatedly computing values that don’t change frequently. For data structures, maps, or validation schemas used in hot paths, initialize them once at module scope rather than recreating them on every function call.

Examples:

Instead of:

function isValidEmail(email: string): boolean {
  return z.string().email().safeParse(email).success;
}

Prefer:

const emailSchema = z.string().email();

function isValidEmail(email: string): boolean {
  return emailSchema.safeParse(email).success;
}

For mappings used frequently:

// Bad: Recreates mapping on every call
export function getSubscriptionTier(priceId: string): Tier | null {
  for (const [tier, config] of Object.entries(PRICE_CONFIG)) {
    if (config.priceId === priceId) return tier as Tier;
  }
  return null;
}

// Good: Cache mapping once
const PRICE_ID_TO_TIER = Object.entries(PRICE_CONFIG).reduce(
  (acc, [tier, cfg]) => {
    if (cfg.priceId) acc[cfg.priceId] = tier as Tier;
    return acc;
  },
  {} as Record<string, Tier>
);

export function getSubscriptionTier(priceId: string): Tier | null {
  return PRICE_ID_TO_TIER[priceId] ?? null;
}

For frequently accessed data that rarely changes, consider Redis caching:

// Get provider for account (provider never changes after account creation)
async function getAccountProvider(accountId: string) {
  const cachedProvider = await redis.get(`account-provider:${accountId}`);
  if (cachedProvider) return cachedProvider;
  
  const provider = await prisma.account.findUnique({
    where: { id: accountId },
    select: { provider: true }
  });
  
  await redis.set(`account-provider:${accountId}`, provider, "EX", 86400);
  return provider;
}

This optimization reduces memory allocations, CPU usage, and can significantly improve performance in hot paths.

---

Sanitize all inputs

Properly sanitize or escape all user-provided inputs before using them in sensitive contexts to prevent injection attacks. This applies to multiple contexts:

1. SQL/OData queries: Use parameterized queries or properly escape special characters:

   -request = request.filter(`contains(subject, '${query}')`);
   +const escapedQuery = query.replace(/'/g, "''");
   +request = request.filter(`contains(subject, '${escapedQuery}')`);
   

2. HTML content: Use a library like DOMPurify to sanitize HTML before rendering:

   -return `<div dir="ltr">${latestReplyHtml}</div>`;
   +return DOMPurify.sanitize(`<div dir="ltr">${latestReplyHtml}</div>`);
   

3. XML construction: Escape special characters in XML:

   -<rule_name>${rule.name}</rule_name>
   +<rule_name>${escape(rule.name)}</rule_name>
   

4. AI prompts: Sanitize inputs before inclusion in prompts:

   -${user.about ? `<user_info>${user.about}</user_info>` : ""}
   +${user.about ? `<user_info>${sanitizeText(user.about)}</user_info>` : ""}
   

Input sanitization is your first line of defense against injection vulnerabilities and should be applied consistently throughout your codebase.

---

Meaningful error communication

Error handling should be designed to provide clear, actionable information to developers while avoiding redundancy. Follow these practices:

1. Don’t duplicate error reporting - If you’re throwing an exception, don’t also log the same error. This creates noise and confusion.

// BAD:
log.errorf("Error unzipping import file %s: %s", fileName, e.getMessage());
throw new IllegalStateException(String.format("Error unzipping import file %s: %s",
  fileName, e.getMessage()), e);

// GOOD:
throw new IllegalStateException(String.format("Error unzipping import file %s: %s",
  fileName, e.getMessage()), e);

1. Provide actionable error messages - Include information about what went wrong and how to fix it.

// VAGUE:
throw new DeploymentException(String.format("Class %s has no fields.", className));

// BETTER:
throw new DeploymentException(String.format("Class %s has no fields. Parameters containers are only supported if they have at least one annotated field.", className));

1. Handle unsupported operations gracefully - When a feature might not be supported by all implementations, use try-catch with informative messages:

try {
  options.setUseAlpn(sslOptions.isUseAlpn());
} catch (UnsupportedOperationException e) {
  log.warn("ALPN configuration not supported by implementation: %s. ALPN setting will be ignored."
    .formatted(options.getClass().getName()));
}

1. Use exceptions for misconfigurations - Log warnings for non-critical issues, but throw exceptions for misconfigurations that would lead to incorrect behavior:

// NOT IDEAL:
if (hasBasic && hasApiKey) {
  LOG.warn("Multiple authentication methods configured. Defaulting to Basic Authentication.");
  return EsAuth.BASIC;
}

// BETTER:
if (hasBasic && hasApiKey) {
  throw new IllegalArgumentException("Multiple authentication methods configured. Please specify only one authentication method.");
}

1. Design interfaces to prevent errors - Use language features like abstract methods when you expect implementations to provide functionality, rather than runtime exceptions.

---

Deprecated API documentation

When documenting deprecated APIs, follow consistent practices to provide clear guidance to developers while maintaining usability. Use strikethrough formatting (propertyName) to visually indicate deprecation without completely removing the documentation. Always include replacement guidance using phrases like “请使用 xxx 替换” or “Please use xxx instead” to help developers migrate. For version-specific deprecations, include version constraints such as “版本 >= 5.25.0 时请使用 Statistic.Timer 作为替代方案” to prevent confusion for users on different versions.

Example:

| ~~iconPosition~~ | 设置按钮图标组件的位置，请使用 `xxx` 替换 | `start` \| `end` | `start` | 5.17.0 |

For major component deprecations, consider using warning blocks with badges:

:::warning{title=已废弃}
版本 >= 5.25.0 时请使用 Statistic.Timer 作为替代方案。
:::

This approach ensures deprecated APIs remain discoverable for existing users while clearly guiding them toward current alternatives, preventing confusion and supporting smooth migration paths.

---

Document compatibility boundaries

Clearly communicate your API’s compatibility guarantees and limitations. When designing APIs, explicitly indicate what usage patterns are supported vs. which are experimental or might change. For functions that have multiple calling patterns, document which are stable and which might be deprecated:

// GOOD: Clear documentation about compatibility
/**
 * Creates a theme based on the options received.
 * @param {object} options - The theme options to use
 * @returns {object} A complete theme object
 * @note Only the first argument is processed by this function.
 * While passing multiple arguments currently works for backward 
 * compatibility, this behavior may be removed in future versions.
 * To ensure forward-compatibility, manually deep merge theme objects
 * and pass the result as a single object.
 */
function createTheme(options, ...args) {
  // implementation
}

When documenting API changes or limitations, use precise language that accurately reflects their status:

1. For deprecated features, provide explicit migration paths
2. For versioning decisions, clearly explain the technical reasoning
3. For import patterns and access restrictions, document what’s considered public API vs. internal implementation

This transparency helps users make informed decisions about adoption, upgrades, and implementation strategies while reducing confusion about API boundaries.

---

Standardize deprecation documentation

When marking APIs, components, or features as deprecated, use consistent JSDoc @deprecated tags with clear alternative guidance. This ensures smooth migration paths for users and maintains backward compatibility during version transitions.

Follow this format:

/** @deprecated [ComponentName] is deprecated, please use [AlternativeName] instead */

Key principles:

• Always provide a specific alternative or migration path
• Use proper JSDoc syntax for tooling compatibility
• Include the deprecated item name and recommended replacement
• Consider the deprecation timeline - items should remain functional with warnings before removal
• Document the deprecation in a way that guides users toward the preferred solution

Example:

/** @deprecated Please use `iconPlacement` instead */
icon?: React.ReactNode;

/** @deprecated DropdownButton is deprecated, please use Space.Compact + Dropdown + Button instead */

This approach helps maintain library stability while guiding users toward modern APIs and prevents breaking changes from surprising developers during upgrades.

---

Maintain configuration accuracy

Regularly audit configuration files to remove unused entries and ensure all configurations accurately reflect the project’s requirements and intended functionality. When modifying configuration files, carefully consider the purpose of each entry and verify that changes align with the desired behavior.

Examples:

1. Remove unused dependencies from package.json files: ```diff “devDependencies”: {
   • “@eslint/js”: “^9.21.0”,
   • “eslint”: “^9.21.0”,
   • “eslint-plugin-react-hooks”: “^5.0.0”,
   • “eslint-plugin-react-refresh”: “^0.4.19”,
   • “globals”: “^15.15.0”, “typescript”: “~5.7.2”, ```
2. Verify that dependency declarations accurately reflect actual requirements: ```diff “peerDependencies”: {
   • “@mui/material”: “^5.0.0”,
   • “@mui/system”: “^5.11.2”,
   • “@emotion/react”: “^11.5.0”, ```
3. When modifying configuration entries, ensure changes align with their intended purpose: ```diff { “groupName”: “node”,
   • “matchPackageNames”: [“node”],
   • “matchPackageNames”: [“node”, “cimg/node”, “actions/setup-node”], ```

By maintaining accurate configurations, you reduce technical debt, prevent unexpected behavior, and make the codebase easier to maintain over time.

---

Descriptive consistent naming

Use clear, descriptive names instead of cryptic abbreviations, and follow consistent naming patterns across your codebase. This practice enhances readability and maintainability.

For configuration properties and attributes:

• Prefer full terms over abbreviations (e.g., authentication-token instead of otac)
• Use lowercase consistently (e.g., jdk-version-latest instead of JDK-ver-latest)

For package naming:

• Follow established naming conventions (e.g., io.<organization>.<component-name>)
• Consider namespace conflicts when defining new package hierarchies
• Use descriptive package names that clearly indicate their purpose

For all identifiers, choose terms that avoid ambiguity with similar concepts in your domain to prevent confusion.

Example:

# Less clear:
quarkus.http.auth.form.otac.enabled=true

# More clear:
quarkus.http.auth.form.authentication-token.enabled=true

// Less clear package structure
package io.quarkus.cache;

// More clear and consistent package structure
package io.quarkus.extension.cache;

---

async cleanup safety

Ensure async operations include proper safety checks to prevent race conditions, memory leaks, and inconsistent state. This includes equality checks before updates, destruction status verification, and proper cleanup mechanisms.

Key safety patterns to implement:

• Equality checks: Always verify !source.equals(value) before applying updates in async contexts to prevent unnecessary side effects
• Destruction checks: Verify effects haven’t been destroyed before adding dependencies: var destroyed = active_effect !== null && (active_effect.f & DESTROYED) !== 0
• Memory leak prevention: Use WeakRef or similar patterns for long-lived async objects that reference reactions

Example of unsafe vs safe async operation:

// Unsafe - missing equality check
export function simple_set(source, value) {
  source.v = value;
  source.o?.onchange?.(); // fires even when value unchanged
}

// Safe - includes equality check
export function set(source, value) {
  if (!source.equals(value)) {
    source.v = value;
    source.o?.onchange?.();
  }
}

The “simple” optimization often becomes a “bug magnet” by removing essential safety checks that prevent race conditions in concurrent scenarios.

---

Consistent code organization

Maintain consistent patterns when organizing code elements within schema files. Place standard fields (like IDs and timestamps) first in all models to establish a predictable structure. Group similar elements together and position enum definitions at the bottom of schema files.

Example:

model SomeModel {
  // Standard fields first
  id        String   @id @default(cuid())
  createdAt DateTime @default(now())
  updatedAt DateTime @updatedAt
  
  // Model-specific fields next
  name      String
  status    Status
  
  // Relations last
  relatedItems RelatedItem[]
}

// Enums at the bottom of the file
enum Status {
  ACTIVE
  INACTIVE
}

This organization pattern improves code readability, makes navigation easier across the codebase, and helps team members quickly understand the structure of each schema file.

---

configuration resolution patterns

When defining configuration schemas, use consistent patterns for safe property access, async resolution, and default value handling. Always use optional chaining with fallback values for nested configuration properties, leverage $resolve for complex async configuration logic, and ensure proper backwards compatibility.

Key patterns to follow:

1. Safe property access: Use optional chaining with fallbacks for nested config properties:

   const extraKeys = nuxt.options?.experimental?.extraPageMetaExtractionKeys || []
   

2. Async configuration resolution: Use $resolve for complex configuration logic that requires async operations or cross-property dependencies:

   serverDir: {
     $resolve: async (val: string | undefined, get): Promise<string> => {
    return resolve(await get('rootDir') as string, val ?? 'server')
     }
   }
   

3. Default value merging: Use defu for merging configuration objects with proper defaults:

   spaLoaderAttrs: {
     $resolve: (val: undefined | null | Record<string, unknown>) => {
    return defu(val, {
      id: val?.id ?? '__nuxt-spa-loader',
    })
     }
   }
   

4. Backwards compatibility: Check for legacy configuration options when introducing new patterns:

   propsDestructure: {
     $resolve: async (val, get) => {
    // Check both new and legacy locations
    return val ?? Boolean((await get('vue') as Record<string, any>).propsDestructure)
     }
   }
   

5. Runtime config handling: Distinguish between undefined (not set) and null (explicitly set to null) values:

   // Only filter out undefined, preserve null values for runtime override capability
   if (typeof obj[key] === 'undefined') {
     // handle undefined case
   }
   

This ensures configuration is resolved consistently, safely handles missing values, and maintains backwards compatibility while supporting complex async resolution scenarios.

---

Consistent code examples

Maintain consistent formatting and styling in code examples throughout your NestJS application documentation. This ensures developers can quickly understand dependency injection patterns, module structures, and decorator usage.

When documenting your NestJS code:

1. Use consistent syntax highlighting for TypeScript code blocks
2. Include complete examples that show the context of dependency injection
3. For terminal output examples, use standardized styling with clear visual indicators
4. When showing installation instructions, always include comprehensive dependency commands

Example for documentation:

// Clear module structure with dependency injection
@Module({
  imports: [ConfigModule.forRoot()],
  controllers: [UsersController],
  providers: [
    {
      provide: 'DATABASE_CONNECTION',
      useFactory: async (configService: ConfigService) => {
        // Implementation that demonstrates the dependency clearly
        return createConnection({
          type: configService.get('DB_TYPE'),
          host: configService.get('DB_HOST')
        });
      },
      inject: [ConfigService]
    },
    UsersService
  ],
  exports: [UsersService]
})
export class UsersModule {}

For installation instructions:

$ npm install @nestjs/core @nestjs/common rxjs reflect-metadata

Consistent documentation makes onboarding easier and reduces confusion about proper implementation patterns.

---

Documentation style consistency

Maintain consistent documentation style to improve readability and user experience:

1. Use precise terminology: When referencing features or components, use their full and correct names.

   # Better
   The Apicurio Dev Services supports xref:compose-dev-services.adoc[Compose Dev Services].
      
   # Avoid
   The Apicurio Dev Services supports xref:compose-dev-services.adoc[Compose].
   

2. Address readers directly: Use “you” instead of “users” or other third-person references in documentation.

   # Better
   You must configure the annotation processor in your build tool:
      
   # Avoid
   Users are required to make an extra step of configuring the annotation processor...
   

3. Maintain consistent terminology: Choose one term for a concept and use it consistently throughout documentation. If multiple terms exist (e.g., Jakarta Validation vs. Hibernate Validator), explain the relationship once and then use a single term consistently.

4. Follow established capitalization conventions: Use lowercase for common terms unless they’re proper names or at the beginning of sentences.

   # Better
   ...automatically provides an RSA-256 key pair for you in dev mode.
      
   # Avoid
   ...automatically provides an RSA-256 key pair for you in Dev Mode.
   

When writing or updating documentation, ensure your content aligns with these style guidelines to maintain consistency across the project’s documentation.

---

Log errors for debugging

Always log errors in catch blocks and use named functions to improve debugging and error traceability. Empty catch blocks make it impossible to diagnose issues, while anonymous functions provide poor stack traces.

When handling exceptions, capture and log the error details to the console so developers have actionable information when things go wrong. Additionally, name your functions instead of using anonymous exports to improve backtraces and error messages.

Example of proper error logging:

// Bad - silent failure
try {
  await clipboardCopy(this.args.colorPalette.dump());
} catch {
  this.toasts.error({ data: { message: "Copy failed" } });
}

// Good - log error details
try {
  await clipboardCopy(this.args.colorPalette.dump());
} catch (error) {
  // eslint-disable-next-line no-console
  console.error(error);
  this.toasts.error({ data: { message: "Copy failed" } });
}

Example of named functions for better debugging:

// Bad - anonymous function
export default function (element, context) {
  // ...
}

// Good - named function improves backtraces
export default function quoteControls(element, context) {
  // ...
}

This practice ensures that when errors occur, developers have the necessary context and information to diagnose and fix issues quickly.

---

markdown formatting consistency

Establish and maintain consistent formatting standards for Markdown files to improve readability and maintainability. This includes adhering to line length limits and consistent styling choices within documents.

Key guidelines:

• Hard wrap Markdown files at 80 characters for better diff reviews and readability
• Maintain consistency in link formatting styles within each document (either all footnote-style or all inline)
• Match existing formatting patterns in the codebase when making changes

Example of proper line wrapping:

These terms of service (the "Terms") cover your access and use of Server 
Operator's ("Administrator" we," or "us") instance, located at %{domain} 
(the "Instance"). These Terms apply solely to your use of the Instance as 
operated by the Administrator.

This approach makes documents easier to read in editors, creates cleaner diffs when links change, and ensures a professional, consistent appearance across all documentation.

---

Layer security defenses

Implement multiple layers of security throughout your application rather than relying on a single protection mechanism. This defense-in-depth approach significantly improves your application’s security posture.

1. Encrypt sensitive data appropriately: ```ruby class User < ApplicationRecord # Use non-deterministic encryption for maximum security encrypts :social_security_number

# Only use deterministic encryption when queries are needed encrypts :email, deterministic: true, downcase: true

# Ensure password security beyond has_secure_password validates :password, length: { minimum: 12 } end

2. Separate authentication (identity verification) from authorization (permissions):
```ruby
# Don't mix in Authentication module
module Authorization
  extend ActiveSupport::Concern
  
  def require_admin
    redirect_to root_path unless Current.user&.admin?
  end
end

1. Use environment-specific security controls:

   # config/storage.yml
   production:
     service: S3
     environment: production
     # additional settings
   

2. Apply modern cryptographic standards (SHA256 instead of SHA1)
3. Use HTTPS for all remote resources
4. Add Content Security Policies to all responses including APIs
5. Implement rate limiting for authentication endpoints

Always document security trade-offs when making implementation decisions and regularly update security measures as standards evolve.

---

Meaningful and consistent names

Use descriptive, accurate identifiers that follow established conventions and maintain consistency throughout your codebase. Variables, parameters, and properties should clearly indicate their purpose and content.

Guidelines:

1. Use descriptive names that accurately reflect what variables contain:

   // Bad
   textarea.evaluate((event) => parseFloat(event.style.height));
      
   // Good
   textarea.evaluate((textareaElement) => parseFloat(textareaElement.style.height));
   

2. Follow standard naming patterns for common operations:

   // Bad
   demoData.relativeModules.reduce((prev, curr) => ({ ...prev, [curr.name]: curr.content }), {});
      
   // Good
   demoData.relativeModules.reduce((acc, curr) => ({ ...acc, [curr.name]: curr.content }), {});
   

3. Use conventional prop names in component APIs:

   // Bad
   interface TabsContextType {
     tabsValue?: TabsProps['value'];
   }
      
   // Good
   interface TabsContextType {
     value?: TabsProps['value'];  // Standard name when paired with onChange
   }
   

4. Maintain consistent terminology throughout your APIs to avoid confusion, especially with related concepts:

   // Bad: Mixing terms for the same concept
   renderTags?: (value: Value[], getTagProps: AutocompleteRenderGetTagProps) => React.ReactNode;
      
   // Good: Use consistent terminology
   renderItems?: (value: Value[], getItemProps: AutocompleteRenderGetItemProps) => React.ReactNode;
   

5. Choose names that reflect semantic meaning rather than just implementation details:

   // Less clear
   const hiddenSiblings = getHiddenSiblings(container);
      
   // More clear
   const hiddenElements = getHiddenElements(container);
   

Consistent naming improves code readability, maintainability, and helps prevent bugs from misinterpreting a variable’s purpose.

---

Maintain code consistency

Ensure code follows consistent patterns throughout the codebase, even when duplicating code is necessary. When similar code patterns appear in multiple places, they should maintain the same structure and approach to improve readability and reduce errors.

Key practices:

1. Use Pythonic idioms: Prefer tuple unpacking in loops rather than index access.

   # Instead of:
   for item in unsupported_attributes:
       attr, value = item[0], item[1]
          
   # Use:
   for attr, value in unsupported_attributes:
       # Code here
   

2. Organize related code together: Keep matching clauses and related logic together for better readability.

   # Group similar conditionals together
   if isinstance(origin, TypeAliasType):
       return self._type_alias_type_schema(obj)
   # Other TypeAliasType related code...
      
   if _typing_extra.origin_is_union(origin):
       # Union related code
   

3. Keep method signatures clean: Remove unused parameters from method signatures.

   # Instead of:
   def __init_subclass__(cls, **kwargs) -> None:
       # Method not using kwargs
          
   # Use:
   def __init_subclass__(cls) -> None:
       # Clean signature
   

4. Maintain consistency across repetitions: When similar code patterns must be repeated, ensure they follow the same approach.

   # Use consistent patterns for similar operations
   model_frozen = cls.model_config.get('frozen')
   field_frozen = getattr(cls.__pydantic_fields__.get(name), 'frozen', False)
   if model_frozen or field_frozen:
       # First usage
      
   # Later in code:
   model_frozen = cls.model_config.get('frozen')
   # Same pattern as before
   

5. Choose cleaner implementations: When faced with multiple functionally equivalent options, choose the cleaner one.

   # Instead of:
   field_info = FieldInfo._construct(metadata, **attr_overrides)
   if prepend_metadata is not None:
       field_info.metadata = prepend_metadata + field_info.metadata
      
   # Use:
   field_info = FieldInfo._construct(prepend_metadata + metadata, **attr_overrides)
   

Maintaining consistency reduces cognitive load when reading code, makes patterns more recognizable, and helps prevent subtle bugs from variations in similar code blocks.

---

Thread-safe state management

When managing state accessed by multiple threads, ensure thread safety through appropriate synchronization mechanisms:

1. Use thread-safe collections for multi-threaded access:

   // Incorrect
   private List<TraceListener> listeners;
      
   // Correct
   private final List<TraceListener> listeners = new CopyOnWriteArrayList<>();
   

2. Implement proper lazy initialization with either:
   • Volatile fields with double-checked locking
   • The LazyValue abstraction
   • Initialization at construction time with final fields ```java // Incorrect - not thread-safe private TraceManager traceManager;

   public TraceManager getTraceManager() { if (traceManager == null) { traceManager = new TraceManager(); // Race condition! } return traceManager; }

   // Correct - thread-safe with volatile private volatile TraceManager traceManager;

   public TraceManager getTraceManager() { TraceManager result = traceManager; if (result == null) { synchronized (this) { result = traceManager; if (result == null) { traceManager = result = new TraceManager(); } } } return result; } ```

3. For bit flag operations, use atomic operations rather than separate atomic fields:

   // Correct pattern for concurrent bit flag operations
   private boolean set(byte bitMask) {
       byte state = this.state;
       for (;;) {
           if ((state & bitMask) != 0) {
               return false;
           }
           final byte newState = (byte) (state | bitMask);
           // Use compareAndExchange for atomicity
           byte oldState = STATE_UPDATER.compareAndExchange(this, state, newState);
           if (oldState == state) {
               return true;
           }
           state = oldState;
       }
   }
   

4. Avoid storing shared mutable state in fields accessed by concurrent operations:

   // Incorrect - potential race condition
   private static AuthDevUIRecorder recorder;
      
   @BuildStep
   void doSomething(AuthDevUIRecorder recorder) {
       AuthProcessor.recorder = recorder; // Multiple build steps might race
   }
      
   // Correct - pass local parameters
   @BuildStep
   void doSomething(AuthDevUIRecorder recorder) {
       performOperation(recorder);
   }
   

---

Version annotation in docs

Always include appropriate version annotations when documenting new features or changes in behavior. Use .. versionadded:: for new features and .. versionchanged:: for modifications to existing functionality. Place these annotations immediately after the feature’s first mention in the documentation.

Example:

.. class:: NewFeature

    A new feature added to Django.

    .. versionadded:: 6.0

.. class:: ExistingFeature

    An existing feature with modified behavior.

    .. versionchanged:: 6.0
        Added support for new parameter and changed default behavior.

Key guidelines:

• Add version annotations for all new features, methods, classes, and settings
• Use versionchanged for behavioral changes, new parameters, or deprecations
• Place annotations before any detailed description or examples
• Include brief description of changes with versionchanged
• Target the next major version for changes in development

This helps users understand when features were introduced or modified, making documentation more maintainable and useful for different Django versions.

---

Validate database connections explicitly

Always implement explicit database connection validation strategies to ensure robust application behavior during startup and runtime. This includes:

1. Configure validation queries with appropriate timeouts:

   quarkus.datasource.jdbc.validation-query-timeout=3
   quarkus.datasource.jdbc.validation-query=SELECT 1
   quarkus.datasource.jdbc.validate-on-borrow=true
   

2. Control database connectivity during startup:

   # Avoid unnecessary database connections during startup
   quarkus.hibernate-orm.database.start-offline=true
   

3. Implement connection validation in critical paths: ```java @Inject AgroalDataSource dataSource;

public void validateConnection() throws SQLException { try (Connection conn = dataSource.getConnection()) { // Execute validation query try (Statement stmt = conn.createStatement()) { stmt.setQueryTimeout(3); stmt.execute(“SELECT 1”); } } }

This approach:
- Prevents application failures due to database connectivity issues
- Reduces unnecessary database connections during startup
- Enables proper error handling and recovery
- Improves application reliability in distributed environments

Consider implementing these validations in health checks and critical service initialization points.

---

## Optimize cache headers

<!-- source: rails/rails | topic: Caching | language: Other | updated: 2025-07-01 -->

Use appropriate HTTP cache headers based on content mutability. For immutable assets (like digest-stamped files), apply aggressive caching with far-future expiry and the immutable flag. For mutable files, use short cache times to balance between preventing thundering herds and allowing timely updates.

**For immutable assets:**
```ruby
# Assets in /assets/ are expected to be immutable with content-based filenames
if path.start_with?("/assets/")
  "public, immutable, max-age=#{1.year.to_i}"
else
  "public, max-age=#{1.minute.to_i}, stale-while-revalidate=#{5.minutes.to_i}"
end

Prefer simple path-based checks over regex patterns when identifying asset types, as implementation details may change. For non-asset files like robots.txt or sitemap.xml, use very short cache times (1-5 minutes) with stale-while-revalidate to improve performance while ensuring content freshness.

---

Optimize CI/CD infrastructure

Continuously optimize and maintain your CI/CD infrastructure to keep development velocity high while ensuring quality. Proactive maintenance prevents disruptions that can impact the entire team.

Key practices:

• Respond quickly to CI failures and outages to minimize disruption
• Regularly stabilize and optimize test infrastructure to reduce flaky tests
• Continuously improve build tools and linting configurations for better performance
• Standardize release processes with clear documentation and automation

For example, when adding a new release type like patch releases:

### Releasing a patch version

A patch release could happen if there is a regression fix that could not wait for the monthly release cycle.

It goes like this:
1. [Specific steps for patch release]
2. [Build steps]
3. [Publishing steps]

Invest time in automating repetitive tasks in your CI/CD pipeline. This pays dividends through faster feedback cycles, reduced manual errors, and more time for feature development.

---

Document observability context flows

When implementing observability features like OpenTelemetry exporters, metrics collection, or distributed tracing, clearly document the context flow and environment limitations. Make explicit which features are available in specific environments (development vs. production), how context is propagated between components, and provide proper error handling for unsupported configurations.

For testing scenarios, include examples of how to access telemetry data:

// Create a test-friendly exporter
@ApplicationScoped
static class InMemorySpanExporterProducer {
    @Produces
    @Singleton
    InMemorySpanExporter inMemorySpanExporter() {
        return InMemorySpanExporter.create();
    }
}

// Access the telemetry data in tests
@Inject
InMemorySpanExporter inMemorySpanExporter;

// ...

List<SpanData> traces = inMemorySpanExporter.getFinishedSpanItems();

When documenting context propagation, clearly specify where annotations should be placed (e.g., on emitter methods vs. processing methods) and how contexts flow through asynchronous boundaries. For unsupported configurations, implement descriptive error messages that guide users toward correct usage patterns.

---

Prioritize code legibility

Write clear, explicit code that prioritizes readability over brevity. Remove unnecessary operations and use straightforward syntax patterns. This is especially important in library code where clarity benefits all consumers.

Key practices:

• Eliminate redundant operations (like unnecessary object spreading of rest parameters)
• Use explicit syntax over implicit shortcuts
• Structure code for maximum legibility

Example of improvement:

// Avoid: Unnecessary spreading of rest object
).map(({ children, ...style }) => ({
  tag: 'style',
  attrs: {
    ...style,
  },

// Prefer: Direct use of rest parameter
).map(({ children, ...attrs }) => ({
  tag: 'style',
  attrs,

// Avoid: Implicit returns with complex logic
.handler(async ({ data: { name, age, pets } }) => 
  `Hello, ${name}! You are ${age + testValues.__adder} years old, and your favourite pets are ${pets.join(',')}.`
)

// Prefer: Explicit returns with clear structure
.handler(({ data: { name, age, pets } }) => {
  return `Hello, ${name}! You are ${age + testValues.__adder} years old, and your favourite pets are ${pets.join(',')}.`
})

The goal is legibility - code should be immediately understandable to any developer reading it.

---

Use modern PHPUnit attributes

Prefer modern PHPUnit attributes over PHPDoc annotations for improved type safety, IDE support, and code readability in tests. Replace legacy annotation-style test decorators with their attribute counterparts:

• Use #[DataProvider] for test data organization: ```php #[DataProvider(‘provideStrSanitizeTestStrings’)] public function testSanitize(?string $subject, ?string $expected, ?HtmlSanitizerConfig $config) { $this->assertSame($expected, Str::sanitize($subject, $config)); }

public static function provideStrSanitizeTestStrings() { return [ ‘non-empty string is returned as is’ => [‘Hello’, ‘Hello’, null], ‘XSS attack is sanitized’ => [‘’, ‘’, null], // more test cases… ]; }

- Use `#[RequiresPhp('8.4.0')]` or similar attributes instead of manual version checks:
```php
// Instead of:
if (PHP_VERSION_ID < 80400) {
    $this->markTestSkipped('Property Hooks are not available to test in PHP...');
}

// Use:
#[RequiresPhp('8.4.0')]
class DatabaseEloquentWithPropertyHooksTest extends TestCase
{
    // Test methods...
}

• For simpler test data cases, consider #[TestWith]:

  #[TestWith(['Hello', 'Hello', null])]
  #[TestWith([123, '123', null])]
  #[TestWith([null, null, null])]
  public function testSanitize(?string $subject, ?string $expected, ?HtmlSanitizerConfig $config)
  {
    $this->assertSame($expected, Str::sanitize($subject, $config));
  }
  

This approach improves code maintainability, provides better type hinting to IDEs, and follows modern PHP testing practices.

---

Name indicates clear purpose

Names should clearly indicate their purpose, type, and behavior. This applies to methods, variables, and parameters. Choose names that are self-documenting and unambiguous.

Key guidelines:

• Use prefixes for boolean methods (is, has, can)
• Use accurate type indicators (integer vs number)
• Choose domain-specific terms (digits vs length for numbers)
• Avoid abbreviated or ambiguous names

Example:

// Unclear naming
public function pan($value) { }
public function num($len = 6) { }

// Clear naming
public function formatPanNumber($value) { }
public function generateRandomInteger(int $digits = 6) { }

// Boolean method naming
public function arrayable($value) { }     // Unclear purpose
public function isArrayable($value) { }   // Clear purpose

This standard helps prevent confusion, makes code self-documenting, and maintains consistency across the codebase.

---

Name for meaning first

Choose names that prioritize domain meaning and clarity over implementation details. This applies to methods, variables, constants, and configuration properties. Names should be immediately understandable to developers working in the domain, without requiring knowledge of the underlying implementation.

Key guidelines:

• Use domain terminology over technical implementation details
• Replace magic numbers with meaningfully named constants
• Name boolean flags and masks to reflect their actual meaning
• Follow standard naming conventions when they exist

Example:

// Avoid implementation-focused naming
private static final int ELEVEN = 11;
private boolean isValid = VALID;

// Prefer domain-meaningful naming
private static final int MIN_APPLICATION_NAME_LENGTH = 11;
private boolean isInvalidated = true;

// Follow standard naming when available
public enum COSEAlgorithmIdentifier {  // Following WebAuthn standard
    // enum values...
}

This approach improves code maintainability by making the intent clear and reducing the cognitive load for developers reading the code. It also makes the code more resilient to implementation changes, as the names remain valid even if the underlying implementation evolves.

---

Write complete API examples

Always provide complete, context-rich code examples in API documentation. Examples should show the full usage context and avoid abbreviated or partial code snippets that may confuse developers.

Key guidelines:

• Show the complete context (e.g., wrapping code in create_table blocks)
• Avoid interactive prompts (like irb>)
• Use proper formatting tags for code containing spaces ()
• Include realistic variable names and values

Example:

# ❌ Unclear context
t.bigint :account_id

# ✅ Complete context
create_table :subscriptions do |t|
  t.bigint :account_id
  t.bigint :event_ids, array: true, default: []
end

---

Simple defaults, flexible overrides

Design APIs with intuitive defaults for common use cases while providing specialized options for edge cases. This approach makes your API approachable for most users while maintaining flexibility for advanced scenarios.

Key principles:

1. Identify the most common use patterns and optimize for them
2. Consolidate related parameters when they typically have the same value
3. Provide escape hatches for complex cases without complicating the common path
4. Use sensible defaults that work for most users

For example, instead of having separate configuration parameters that are usually set to identical values:

# Problematic design - requires duplicate settings for common case
config = ConfigDict(
    val_date_or_time_unit='milliseconds',
    ser_date_or_time_unit='milliseconds',
)

# Better design
config = ConfigDict(
    date_or_time_unit='milliseconds',  # Applies to both validation and serialization
    # Add specific overrides only when needed:
    val_date_or_time_unit_override=None,  # Only set when different from common setting
)

Similarly, when designing validators or constraint systems, provide high-level simple APIs for common cases, with options to bypass default behavior when needed (like the check_unsupported_field_info_attributes=False parameter that allows silencing warnings in specific contexts).

For URL schemes and other extensible systems, include the most commonly used variants by default while allowing extension for specialized cases.

---

configuration status accuracy

Ensure that configuration file status values accurately reflect the actual implementation state. Use ‘done’ only when features are fully implemented, ‘todo’ for planned but unimplemented features, and ‘exempt’ for features that don’t apply to the integration. Always provide clear, descriptive comments explaining why items are marked as exempt.

Example from quality scale configuration:

rules:
  inject-websession: todo  # Not 'done' if not actually implemented
  entity-event-setup:
    status: exempt
    comment: no explicit subscriptions to events
  dynamic-devices:
    status: exempt
    comment: |
      No dynamic devices possible.

This prevents misleading configuration states and helps maintainers understand the true implementation status and reasoning behind exemptions.

---

Feature flag isolation

Feature flags should be properly isolated and scoped to avoid mixing configuration concerns with core interfaces. When implementing feature flags, ensure they only affect behavior when explicitly enabled and don’t leak into unrelated system components.

Key principles:

• Keep feature flags out of core interfaces that will outlive the flag
• Ensure behavior changes are isolated to when flags are enabled
• Document flag limitations and dependencies clearly
• Avoid mixing UI configuration with system-level interfaces

Example of proper isolation:

// Instead of adding to core interface
public interface ReactHost {
  public fun isEdgeToEdgeEnabled(): Boolean // ❌ Avoid
}

// Use scoped utility or check flag directly where needed
if (isEdgeToEdgeFeatureFlagOn) {
  // Feature-specific behavior only when flag is on
  windowDisplayMetrics.setTo(displayMetrics)
}

Always document flag constraints:

# Enables edge-to-edge. Only works with ReactActivity and should not be used with custom Activity.
edgeToEdgeEnabled=false

This prevents configuration complexity from spreading throughout the codebase and makes it easier to remove flags when features become default.

---

Single source documentation

Maintain documentation with a single source of truth to prevent inconsistencies and reduce maintenance burden. When information exists elsewhere, link to it rather than duplicating content. This applies to code of conduct references, governance documents, and API documentation.

For example:

// Good - Links to the source
The code of conduct is located in [CODE_OF_CONDUCT.md](https://github.com/expressjs/.github/blob/HEAD/CODE_OF_CONDUCT.md)

// Bad - Duplicates content that might get out of sync
# Code of Conduct
Our project is committed to providing a welcoming community...

When writing documentation:

1. Use consistent formatting and third-person voice throughout
2. Convert bullet points to paragraphs for complex explanations
3. Organize content logically with clear section headers
4. Provide relative links to related documentation
5. Consider where documentation should live to minimize repository clutter

By following these practices, documentation stays current, accurate, and easier to maintain as the project evolves. When documentation must exist in multiple locations, establish clear processes for synchronization.

---

Follow documentation conventions

Maintain consistent formatting and style in all documentation to improve readability and professionalism:

1. Use proper formatting for code elements:
   • Wrap boolean values in backticks: true, false instead of true, false
   • Maintain prompt symbols ($) in command-line examples:

     $ rails new app_name
     

2. Use correct Rails component names:
   • Write “Active Record”, not “ActiveRecord”
   • Write “Active Model”, not “ActiveModel”
   • Write “Action View”, not “ActionView”
3. Optimize cross-references:
   • Add context links between related documentation sections:

     See the [Getting Started Guide](getting_started.html#adding-authentication) for more details.
     

   • Link to sections within the same guide when possible to avoid navigating away
   • Use standard URL patterns: api.rubyonrails.org not edgeapi.rubyonrails.org
4. Ensure example consistency:
   • Make sure code examples match their accompanying explanatory text
   • When updating code or descriptions, ensure both remain in sync

Following these conventions creates a cohesive documentation experience that helps developers find information quickly and understand it correctly.

---

Use unstable_cache directly

When implementing server-side caching in Next.js applications, prefer using unstable_cache with direct repository method calls instead of tRPC callers. This approach provides better performance and proper integration with Next.js caching mechanisms.

Instead of using tRPC callers for cached data:

const caller = await createRouterCaller(workflowsRouter);
const initialData = await caller.filteredList({ filters });

Use unstable_cache directly with repository methods:

const getWorkflowsFilteredListCached = unstable_cache(
  async (filters) => { // filters should be serializable
    return await WorkflowRepository.getFilteredList(filters);
  },
  ["getWorkflowsFilteredListCached"],
  {
    revalidate: 3600,
    tags: ["viewer.workflows.filteredList"]
  }
);

const initialData = await getWorkflowsFilteredListCached(filters);

This pattern enables proper cache revalidation using revalidateTag from next/cache in CRUD operations and eliminates unnecessary tRPC overhead for cached operations. Apply this consistently across server components where data caching is needed.

---

Standardize version transitions

When supporting multiple library versions or preparing for version deprecation in configuration-dependent code, use standardized TODO comments with consistent formatting. Always include a space after the # symbol and use the prefix “TODO:” to ensure comments can be found with standard search tools.

Example:

def pydantic_snapshot(
    *,
    v2: Snapshot,
    v1: Snapshot,  # TODO: remove v1 argument when deprecating Pydantic v1
):
    # Version-specific implementation
    if PYDANTIC_V2:
        return v2
    else:
        return v1

This practice helps teams track configuration-dependent code that will require updates during dependency upgrades, making version transitions smoother and more systematic. It also ensures that version-specific code paths are clearly documented and can be easily located when performing major configuration changes.

---

API design clarity

Maintain clear separation of concerns in API design by avoiding feature overlap and ensuring each method has a distinct, well-defined purpose. When designing APIs, resist the temptation to add convenience features that blur the boundaries between different configuration approaches, as this leads to user confusion and maintenance issues.

Key principles:

• Each API method should have a single, clear responsibility
• Avoid duplicating functionality across different configuration mechanisms
• When evolving APIs, prefer generic approaches over multiple specific functions
• Consider the conceptual clarity of the API from the user’s perspective

For example, when designing middleware configuration:

// Clear separation: route-specific timeout
app.Get("/api/reports", timeout.New(30*time.Second), handler)

// Clear separation: application-wide timeout configuration  
app.Use(timeout.NewWithConfig(timeout.Config{
    DefaultTimeout: 5 * time.Second,
}))

// Avoid: mixing route-specific config within middleware config
// This creates confusion about which timeout value actually applies
app.Get("/reports", timeout.New(handler, timeout.Config{
    Timeout: 5 * time.Second,
    Routes: map[string]time.Duration{
        "/reports": 30 * time.Second, // Confusing overlap
    },
}))

Similarly, when evolving APIs, prefer generic solutions that replace multiple specific functions rather than maintaining both approaches, as this reduces cognitive load and maintenance burden.

---

Dependency versioning consistency

Establish and maintain consistent dependency versioning strategies in package.json configuration. Choose between caret (^) and tilde (~) ranges based on stability requirements and update policies. For stable production dependencies, prefer tilde ranges to avoid unexpected breaking changes, while development dependencies can use caret ranges for latest features. Regularly review and update dependency versions to stay current with security patches and improvements.

Example:

{
  "dependencies": {
    "enter-animation": "~0.1.1",
    "@rc-component/form": "~1.2.0"
  },
  "devDependencies": {
    "tsx": "^4.20.3",
    "terser": "~5.42.0"
  }
}

For tools with known stability issues, lock to specific versions until fixes are available, as seen with “@biomejs/cli-darwin-arm64”: “2.0.0”.

---

Avoid redundant computations

Identify and eliminate redundant operations that cause performance bottlenecks by caching expensive function results, performing transformations only when necessary, and implementing lazy evaluation patterns.

Key optimization strategies:

1. Cache expensive function results that may be reused: ```javascript // Before - recalculates camelize(key) multiple times if (camelize(key) in el || key in el) { // do something }

// After - calculates once and reuses const camelKey = camelize(key) if (camelKey in el || key in el) { // do something }

2. Apply transformations selectively rather than to all elements:
```javascript
// Before - unnecessarily transforms all arguments
return arr[key](...args.map(toRaw))

// After - transforms only what's needed
return arr[key](toRaw(args[0]), ...args.slice(1))

1. Use lazy evaluation for expensive operations: ```javascript // Before - calculates expensive operation eagerly if (dep.get(effect) === effect._trackId && effect._runnings > 0) { // use result }

// After - calculates only when needed let tracking: boolean | undefined if ((tracking ??= dep.get(effect) === effect._trackId) && effect._runnings > 0) { // use tracking value }

4. Initialize data structures with values directly when possible:
```javascript
// Before - less efficient
const queue = []
queue.push(['a', 1])

// After - more efficient (benchmark: ~2.25x faster)
const queue = [['a', 1]]

1. Pass appropriate flags to avoid unnecessary work: ```javascript // Before for (let child = this.scopes; child != undefined; child = child.nextEffectScope) { child.stop(); }

// After - avoids unnecessary unlinking operations for (let child = this.scopes; child != undefined; child = child.nextEffectScope) { child.stop(true) }

These optimizations become particularly important in hot paths that execute frequently or when working with large data structures.

---

## Use connection by alias

<!-- source: django/django | topic: Database | language: Python | updated: 2025-06-27 -->

When working with database operations in Django projects that might use multiple database backends, always access database features and operations through `connections[alias]` instead of the global `connection` object. This ensures your code works correctly regardless of which database backend is being used for a specific operation.

For example, instead of:

```python
def db_returning(self):
    """Private API intended only to be used by Django itself."""
    return (
        self.has_db_default() and connection.features.can_return_columns_from_insert
    )

Use:

def db_returning(self):
    """Private API intended only to be used by Django itself."""
    return self.has_db_default()

And check the feature at the appropriate time with the correct connection:

if connections[using].features.can_return_columns_from_insert:
    # Perform operation with RETURNING clause

This approach prevents bugs in multi-database setups where features vary across backends, such as when the default database is MySQL but you’re also using PostgreSQL for specific operations.

---

Structure logs effectively

When implementing logging in your application, structure your log messages and parameters consistently to improve readability, searchability, and integration with monitoring tools. Consider these practices:

1. Use the appropriate logging method for your context:
   • Use logger.exception() only when capturing the current exception context
   • Use logger.error() with explicit exc_info=True when you need to include exception details outside of an exception handler

   # Correct: Inside an exception handler
   try:
       dangerous_operation()
   except Exception:
       logger.exception("Operation failed")  # Automatically includes traceback
      
   # Correct: Outside an exception handler
   if error_occurred:
       logger.error("Operation failed", exc_info=True)  # Explicitly include traceback
   

2. Provide structured context with log messages:
   • Use the extra parameter to add structured fields to your logs
   • Be consistent with parameter formats (dict-style vs tuple-style)
   • Include identifying information like connection aliases in database logs

   # Good: Structured logging with extra parameters
   logger.debug(
       "Query executed: %(sql)s; duration=%(duration).3f; alias=%(alias)s",
       extra={
           "duration": duration,
           "sql": sql,
           "params": params,
           "alias": connection.alias,
       }
   )
   

3. Be mindful of performance in log formatters:
   • Cache formatted values to avoid repeated expensive operations
   • Consider conditional formatting based on log levels
   • Handle both dict-style and tuple-style arguments defensively

   # Performance-aware formatter
   def format(self, record):
       # Cache formatted values to avoid repeated processing
       sql = None
       formatted_sql = None
          
       if args := record.args:
           if isinstance(args, dict) and (sql := args.get("sql")):
               args["sql"] = formatted_sql = format_sql(sql)
              
       # Reuse formatted value if it's the same SQL
       if extra_sql := getattr(record, "sql", None):
           if extra_sql == sql:
               record.sql = formatted_sql
           else:
               record.sql = format_sql(extra_sql)
                  
       return super().format(record)
   

By following these practices, you’ll create logs that are more useful for debugging, monitoring, and analysis while avoiding common performance pitfalls.

---

Transactional verified migrations

Enhance database migration reliability by wrapping changes in transactions with pre-check and post-verification steps. This pattern prevents partial migrations that could leave your database in an inconsistent state.

For any substantial schema change or data migration:

1. Begin with pre-checks to validate assumptions
2. Wrap all operations in a single transaction
3. Include post-operation verification
4. Use defensive SQL patterns (IF EXISTS clauses, pre-checks before constraints)

Example of a robust migration pattern:

BEGIN;

-- Pre-check to validate assumptions
DO $$ 
BEGIN
  IF EXISTS (
    SELECT digestFrequencyId
    FROM "EmailAccount"
    WHERE digestFrequencyId IS NOT NULL
    GROUP BY digestFrequencyId
    HAVING COUNT(*) > 1
  ) THEN
    RAISE EXCEPTION 'Duplicate values found; please resolve before migrating.';
  END IF;
END $$;

-- Safe schema changes with defensive patterns
ALTER TABLE "EmailAccount" DROP CONSTRAINT IF EXISTS "EmailAccount_digestScheduleId_fkey";
DROP INDEX IF EXISTS "EmailAccount_digestScheduleId_key";

-- For NOT NULL constraints, use a two-step approach
ALTER TABLE "CleanupJob" ADD COLUMN "email" TEXT; -- First add as nullable
UPDATE "CleanupJob" SET "email" = 'placeholder@example.com'; -- Backfill data
ALTER TABLE "CleanupJob" ALTER COLUMN "email" SET NOT NULL; -- Then set NOT NULL

-- Post-verification to confirm success
DO $$
BEGIN
  IF EXISTS (
    -- Query to verify migration succeeded as expected
    SELECT 1 FROM "CleanupJob" WHERE "email" IS NULL
  ) THEN
    RAISE EXCEPTION 'Verification failed: nullable emails found';
  END IF;
END $$;

COMMIT;

This approach makes migrations safer, more reliable, and helps prevent production incidents from failed or partial migrations.

---

Strict mode-proof hooks

Ensure your React components work correctly in both development (Strict Mode) and production environments by writing hooks that handle React’s intentional double-rendering behavior. When using side effects in initializers, guard them with refs to prevent duplicate executions:

// Bad: Side effect in initializer without guard
const [{ finalValue, assignedIndex }] = React.useState(() => {
  // This runs twice in development with Strict Mode
  registerTab(value); // Could register the same tab twice!
  return { finalValue: value || childIndex++, assignedIndex: childIndex };
});

// Good: Guard side effects with a ref
const hasRegisteredRef = React.useRef(false);

const [{ finalValue, assignedIndex }] = React.useState(() => {
  if (!hasRegisteredRef.current) {
    hasRegisteredRef.current = true;
    // Only runs once even in Strict Mode
    registerTab(value);
  }
  return { finalValue: value || childIndex, assignedIndex: childIndex };
});

For expensive calculations, use useMemo to prevent unnecessary recalculation during re-renders:

// Before: No memoization
return getThemeProps({ theme, name, props });

// After: With memoization
return React.useMemo(() => getThemeProps({ theme, name, props }), [theme, name, props]);

Remember that React’s Strict Mode intentionally calls initializers and effects twice to detect impure logic. Treat props as immutable to enable further compiler optimizations. When designing components that must work with SSR, ensure your initialization logic doesn’t cause hydration mismatches by consistently handling state across server and client renders.

---

Proper response handling

When designing APIs, ensure responses adhere to HTTP semantics by:

1. Using semantic status code constants instead of magic numbers ```python

   Bad

   raise HTTPException(status_code=400, detail=”Inactive user”)

Good

raise HTTPException( status_code=status.HTTP_400_BAD_REQUEST, detail=”Inactive user” )

2. Choosing status codes based on their semantic meaning:
   - 400: Client error (malformed request)
   - 403: Authentication succeeded but authorization failed
   - 204: Success with no content

3. Matching response types to HTTP methods:
```python
# Bad for HEAD requests
def head_item(item_id: str):
    return JSONResponse(None, headers={"x-item-id": item_id})

# Good for HEAD requests
def head_item(item_id: str):
    return Response(headers={"x-item-id": item_id})

1. Testing responses thoroughly, including both status code and content:

   # More complete test
   def test_no_content():
    response = client.get("/no-content")
    assert response.status_code == http.HTTPStatus.NO_CONTENT
    assert not response.content
   

Following these practices improves API reliability, interoperability, and compliance with HTTP standards.

---

Optimize elimination paths

When implementing algorithms that process large data structures or complex computational paths, prioritize opportunities for dead code elimination (DCE) and path optimization. Different initialization strategies (like build-time vs. runtime initialization) can dramatically affect which code paths are evaluated and optimized.

Consider the following factors in your algorithm design:

1. Identify conditional paths that could be eliminated early through proper initialization
2. Analyze the computational complexity impact of path elimination
3. Consider how initialization timing affects branch prediction and invocation paths

For example, in a system like Quarkus, build-time initialization enables more aggressive DCE:

// With proper build-time initialization, conditional paths can be eliminated
public void processData(Data input) {
    // This entire branch might be eliminated during DCE if FeatureFlag
    // is evaluated at build time
    if (FeatureFlag.isEnabled("experimental")) {
        runExperimentalAlgorithm(input);
    } else {
        runStandardAlgorithm(input);
    }
}

Without effective DCE, the system must evaluate both paths at runtime, potentially increasing computational complexity and preventing optimization of method invocation from megamorphic to direct calls. Additionally, be mindful of transitive dependencies when initializing components, as these can introduce unexpected algorithmic complexities and execution paths.

---

Optimize test case design

Write focused, efficient tests that validate core functionality without unnecessary complexity. Key principles:

1. Test one concept per case
2. Use appropriate test scope (unit vs integration)
3. Leverage modern testing tools

Instead of exhaustive parameterized tests:

@ParameterizedTest
@ValueSource(ints = { -1, 0, 100 })
void testValues(int value) {
    // Testing simple pass-through logic
}

Prefer focused single test:

@Test
void testValue() {
    // Test with representative value
}

For JSON validation, use specialized assertions:

// Instead of string contains checks:
assertThat(entity.getBody()).contains("\"name\":\"test\"");

// Use structured assertions:
JsonContent body = new JsonContent(entity.getBody());
assertThat(body).extractingPath("name").isEqualTo("test");

When testing output, prefer CapturedOutput over complex mocks:

@Test
void testOutput(CapturedOutput output) {
    // Trigger output
    assertThat(output).contains("expected message");
}

Reserve integration tests for validating system interactions that cannot be effectively tested at the unit level.

---

configuration compatibility validation

Ensure that code examples and documentation accurately reflect the constraints and requirements of different rendering modes and configurations. When documenting APIs or providing examples, verify that the suggested approach is compatible with the specific rendering context (SSR, SSG, client-side) and configuration options being used.

Key areas to validate:

• API compatibility with rendering modes (e.g., certain rendering methods may not work with specific fetch strategies)
• Accurate terminology that doesn’t make assumptions about HTTP status codes or behavior
• Clear distinction between different configuration options and their use cases
• Proper explanation of when certain features or patterns should be used

Example of problematic documentation:

// Incorrect - renderToString may not work with single fetch
export default function handleRequest(request, responseStatusCode, responseHeaders, routerContext) {
  const markup = renderToString(/* ... */);
}

Example of improved documentation:

// Correct - acknowledges configuration constraints
export default function handleRequest(request, responseStatusCode, responseHeaders, routerContext) {
  // Note: When using single fetch, use appropriate rendering method
  // for your configuration. See [link] for compatible options.
  const markup = renderToReadableStream(/* ... */);
}

This validation helps prevent runtime errors and ensures developers can successfully implement the documented patterns in their specific environment.

---

Graceful API evolution

When evolving APIs, prioritize backward compatibility and provide clear migration paths. For any significant change:

1. Add explicit deprecation warnings that explain what’s changing and how to adapt code
2. Maintain backward compatibility during deprecation periods with shims or dual implementations
3. Document specific migration steps, ideally with before/after examples
4. Consider real-world usage patterns before removing or changing behavior

Example of good practice:

# For changing from positional to keyword-only arguments:
@deprecate_posargs(RemovedInDjangoXXWarning, moved=["option1", "option2"])
def some_func(request, *, option1, option2=True):
    # Implementation

Example of maintaining compatibility when changing property behavior:

@cached_property
def params(self):
    # Keep original behavior
    return self._params.copy()  # Still includes 'q' for backward compatibility

@cached_property  
def range_params(self):
    # New API with refined behavior
    params = self._params.copy()
    params.pop("q", None)  
    return params

Even for “non-public” APIs that have been available for extended periods, consider adding deprecation shims to prevent breaking dependent code in the ecosystem.

---

Validate configuration defaults

Configuration structs should validate input values and provide sensible defaults that work well in production environments. Always check for invalid values (like negative timeouts), provide reasonable defaults for production use cases, and handle edge cases where users might set unexpected values.

Key practices:

• Validate negative or invalid values and reset to defaults
• Choose production-ready defaults (e.g., 10s timeout instead of infinite)
• Handle empty string cases appropriately for string configuration fields
• Consider security implications of default values (e.g., file permissions)

Example from timeout middleware:

func configDefault(config ...Config) Config {
    cfg := config[0]
    
    // Validate negative timeout values
    if cfg.Timeout < 0 {
        cfg.Timeout = ConfigDefault.Timeout
    }
    
    // Use production-ready defaults
    if cfg.ShutdownTimeout == 0 {
        cfg.ShutdownTimeout = 10 * time.Second // Instead of infinite
    }
    
    return cfg
}

This ensures configurations work reliably across different environments and prevents common misconfigurations that could cause issues in production.

---

Fail predictably, loudly

Design APIs that fail explicitly and predictably when used incorrectly. When an operation is attempted in an inappropriate state, raise a specific exception rather than returning None or an unexpected value. This helps developers catch misuse early rather than encountering subtle bugs later.

For example, when accessing result properties that are only valid in certain states:

def get_exception(self):
    if self.status != ResultStatus.FAILED:
        raise ValueError("Exception is only available when task has FAILED status")
    return self._exception

def get_return_value(self):
    if self.status != ResultStatus.COMPLETE:
        raise ValueError("Return value is only available when task has COMPLETE status")
    return self._return_value

Similarly, be cautious with timing-sensitive operations. When an API accepts relative time values (like timedeltas), document clearly when these values are resolved to absolute times, as this can lead to surprising behavior.

When modifying existing APIs, prioritize maintaining consistent behavior. If changing return types is necessary, ensure the new types support all previously documented behavior or provide clear migration paths. Sudden changes in return values or behavior create confusion and lead to bugs that are difficult to diagnose.

---

Clear network API documentation

Ensure networking-related API documentation and descriptions are specific, clear, and include concrete implementation details rather than vague or generic statements. This helps developers understand exactly what networking functionality does and how to implement it correctly.

Key practices:

• Use specific technical terms instead of generic descriptions (e.g., “Unix domain sockets via ListenerNetwork” instead of just “Unix socket support”)
• Include parameter names and types in method signatures for clarity
• Provide accurate grammar and consistent terminology in descriptions
• Use proper technical capitalization (e.g., “HEAD request” not “head request”)

Example improvement:

// Instead of: "Head send a head request use defaultClient, a convenient method"
// Use: "Head sends a HEAD request using the `defaultClient`, a convenience method"

func (c fiber.Ctx) Writef(format string, a ...any) (n int, err error)
// Clear parameter naming: 'format' instead of generic 'f'

This ensures networking documentation provides developers with the precise information needed to implement network functionality correctly and securely.

---

Select algorithms by complexity

Choose appropriate algorithms based on computational complexity requirements and context. When implementing lookups, prefer O(1) direct access over O(n) iterations whenever possible. For infrequent operations or small datasets, simpler linear algorithms may outperform more complex logarithmic approaches due to lower constant factors and better locality.

Example 1: Use direct map lookups instead of iterating over map keys:

// Inefficient: O(n) iteration
for bind, fn := range negotiationRenderMappings {
    if bind == accepted {
        fn(code, config, c)
        return
    }
}

// Better: O(1) direct lookup
if fn, ok := negotiationRenderMappings[accepted]; ok {
    fn(code, config, c)
    return
}

Example 2: Choose simpler algorithms when appropriate:

// Overcomplicated: Sort + binary search for simple matching
sort.Strings(extensionsAllowed)
// ...
indexFound := sort.SearchStrings(extensionsAllowed, extension)
if indexFound < len(extensionsAllowed) && extensionsAllowed[indexFound] == extension {
    // ...
}

// Better for small sets: Simple iteration
for _, v := range extensionsAllowed {
    if strings.ToLower(v) == extension {
        files = append(files, path)
    }
}

---

Preserve HTTP header semantics

HTTP headers have specific semantics that must be respected when processing, merging, or deduplicating them. Avoid naive approaches that treat headers as simple key-value pairs, as this can break protocol compliance and cause unexpected behavior.

For set-cookie headers, remember that cookies are distinct by multiple attributes (name, domain, path, secure, httpOnly, sameSite), not just their values. Simple equality checks on cookie values can incorrectly deduplicate distinct cookies that should coexist.

When handling response headers, preserve existing headers rather than flattening them. Use appropriate header manipulation functions that understand header-specific rules:

// Good: Preserve header semantics
if (header === 'set-cookie') {
  appendResponseHeader(event, header, value)  // Preserves multiple set-cookie headers
} else {
  setResponseHeader(event, header, value)
}

// Bad: Naive deduplication that breaks cookie semantics  
if (isEqual(cookie.value, existingCookie.value)) { 
  return // This ignores domain, path, and other cookie attributes
}

Always use protocol-aware utilities and libraries that understand the specific rules for each header type, rather than implementing custom string manipulation logic.

---

Remove commented code

Commented-out code should be removed from the codebase rather than left as comments. Keeping commented code:

1. Clutters the codebase and reduces readability
2. Creates confusion about which code is active and which isn’t
3. Often becomes outdated or incompatible as surrounding code evolves
4. Indicates incomplete work or indecision

Modern version control systems like Git provide better ways to preserve code history. If you need to reference previous implementations, use commit history instead of keeping commented code in the active codebase.

Instead of:

function onLabelSubmit: SubmitHandler<LabelInputs> = (data) => {
  // onSubmit(data.labelInstructions || "");
  onNext();
};

Do:

function onLabelSubmit: SubmitHandler<LabelInputs> = (data) => {
  onNext();
};

For debug statements like console.log(), ensure they’re removed before merging to production:

-console.log("API Response:", data); // Debug log
-console.log("All rules:", data.allRules); // Debug log

If you need to temporarily disable a feature, use feature flags or configuration rather than commenting out the code. For TODOs or explanatory notes, focus on explaining why rather than preserving unused code.

---

Use semantic HTML elements

Structure HTML templates using semantically appropriate elements rather than generic containers. Replace non-semantic elements like <div> and <p> with more meaningful elements such as <nav>, <ol>, <ul>, and include proper accessibility attributes like aria-labelledby and aria-current.

Example:

<!-- Instead of this -->
<p class="paginator">
  {% for i in page_range %}
    {% if i == action_list.number %}
      <span class="this-page">{{ i }}</span>
    {% else %}
      <a href="?{{ page_var }}={{ i }}">{{ i }}</a>
    {% endif %}
  {% endfor %}
</p>

<!-- Use this -->
<nav class="paginator" aria-labelledby="pagination">
  <h2 id="pagination" class="visually-hidden">Pagination</h2>
  <ul>
    {% for i in page_range %}
      {% if i == action_list.number %}
        <li><span class="this-page" aria-current="page">{{ i }}</span></li>
      {% else %}
        <li><a href="?{{ page_var }}={{ i }}">{{ i }}</a></li>
      {% endif %}
    {% endfor %}
  </ul>
</nav>

This improves code organization and readability while enhancing accessibility for users with assistive technologies. Proper semantic structure also makes templates more maintainable as the code’s purpose is clearer to other developers.

---

Self-documenting code naming

Method, parameter, and variable names should clearly describe their purpose and behavior, making code self-documenting. Choose names that indicate exactly what the code does and how it behaves with different inputs.

For methods:

• Use action verbs that precisely describe the method’s behavior
• Prefer setTileCacheEnabled(bool) over enableTileCache(bool) when a method can both enable and disable functionality
• Name methods like removeDrawablesIf rather than observeDrawablesRemove to clearly communicate intent

For parameters:

• Use descriptive nouns that indicate what the parameter represents
• Prefer meaningful types over boolean flags when possible (e.g., pass center coordinate instead of shouldCenter: YES)
• Follow platform conventions (e.g., use CoordinateBounds instead of LatLngBounds in iOS)

For constants and variables:

• Replace magic numbers with named constants, especially for special values:

// Instead of this:
if (fo == 0.0) {
    return {
        .position = float4(-2.0, -2.0, -2.0, 1.0),
        
// Prefer this:
const float4 CULLED_POSITION = float4(-2.0, -2.0, -2.0, 1.0);
if (fo == 0.0) {
    return {
        .position = CULLED_POSITION,

Clear, descriptive naming reduces the need for comments and documentation while making code more maintainable and understandable for all developers.

---

Wrap threaded code properly

When working with threads in Rails applications, always wrap application code with Rails.application.executor.wrap to ensure thread safety and proper state management. Code running outside these wrappers can cause race conditions, memory leaks, and inconsistent application state.

# INCORRECT - application code outside wrapper
Thread.new do
  user = User.find(params[:id])  # Unsafe!
  Rails.application.executor.wrap do
    # Some wrapped code
  end
end

# CORRECT - all application code inside wrapper
Thread.new do
  # No application code here
  Rails.application.executor.wrap do
    user = User.find(params[:id])
    # All application code goes here
  end
end

This applies to all scenarios where you manually create threads, including when using thread pools from libraries like Concurrent Ruby. The Rails executor ensures that your thread has proper access to autoloading, manages database connections correctly, and handles thread-local data appropriately.

For long-running operations that may be interrupted (like during deployments), also consider implementing checkpoints to preserve progress:

Rails.application.executor.wrap do
  records.find_each do |record|
    record.process
    # Create checkpoints regularly for interruptible work
    checkpoint! if should_checkpoint?
  end
end

---

prefer async/await patterns

Convert promise chains to async/await syntax for better readability, error handling, and proper cleanup operation placement. Async functions automatically return promises, so avoid redundant Promise.resolve() calls or manual promise wrapping.

Key benefits:

• Cleaner error handling with try/catch blocks
• Proper placement of finally blocks that wrap entire operations
• Elimination of unnecessary promise constructors

Example transformation:

// Before: Complex promise chain with misplaced finally
destroy(deletedBy, opts) {
  return this.setDeletedState(deletedBy).then(() => {
    // operation
  }).finally(() => {
    // cleanup only applies to inner promise
  });
}

// After: Clean async/await with proper cleanup scope
async destroy(deletedBy, opts) {
  this.set("isDeleting", true);
  try {
    await this.setDeletedState(deletedBy);
    // operation
  } finally {
    // cleanup applies to entire operation
    this.set("isDeleting", false);
  }
}

Avoid returning Promise.resolve() from async functions as they already return promises automatically.

---

API parameter design

Design API parameters with clear intent, proper validation, and thoughtful default behaviors. Parameter names should reflect their purpose rather than their source (e.g., include_original instead of client_type == 'editor'). Always validate parameters through StrongParameters to prevent security issues, and carefully consider the implications of default values - missing parameters should not trigger potentially harmful actions like forwarding to remote instances.

When evolving APIs, prefer explicit parameter migration over breaking changes. For example, redirect old parameter names to new ones while preserving all existing filters:

# Migrate old parameter names while preserving other filters
if params.include? :by_target_domain
  redirect_to admin_reports_path({
    search_type: 'target',
    search_term: params[:by_target_domain],
    # Preserve existing status filter
    status: params[:status]
  }.compact)
end

Avoid implicit behaviors based on missing parameters. Instead of defaulting to potentially destructive actions, require explicit opt-in through clear parameter names that communicate intent.

---

Normalize API responses

Design APIs to return consistent response structures across different data sources or providers. Normalize responses at the API layer rather than handling provider-specific format differences in client components. This approach:

1) Maintains type safety by ensuring predictable response shapes 2) Simplifies client components by removing conditional format handling 3) Creates a clean abstraction layer for supporting multiple providers

For example, instead of handling different message formats in UI components:

// Client-side format handling (AVOID)
const subject = "headers" in firstMessage 
  ? firstMessage.headers.subject 
  : firstMessage.subject;
const date = "headers" in firstMessage
  ? firstMessage.headers.date
  : firstMessage.receivedAt;

Normalize in your API controller/service layer:

// Server-side normalization (RECOMMENDED)
export function normalizeMessageResponse(message) {
  // Creates a unified structure regardless of provider
  return {
    id: message.id,
    subject: getMessageSubject(message),
    date: getMessageDate(message),
    snippet: getMessageSnippet(message),
    // Other normalized fields
  };
}

// Helper functions handle provider-specific logic
function getMessageSubject(message) {
  return message.headers?.subject || message.subject || "";
}

function getMessageDate(message) {
  return message.headers?.date || message.receivedAt || new Date();
}

This pattern is especially valuable for multi-provider systems where different APIs return structurally different responses for similar data.

---

Explicit configuration specifications

When writing configuration files, be explicit and precise about dependencies and versions rather than using broad patterns or tags.

For dependency declarations:

• List specific dependencies rather than relying on wildcards when possible
• Document why certain dependencies need special handling
• Maintain comprehensive lists of dependencies that require special configuration

For version specifications:

• Use semantic versioning ranges (e.g., ^6.0.0) instead of tags like latest or latest-v6
• Avoid single version identifiers when packages follow independent versioning

Example of good configuration practice:

// In build config file
export default defineConfig({
  // Explicitly list dependencies with clear comments
  ssr: {
    // Specific comment explaining the need for these dependencies
    optimizeDeps: {
      include: ['@emotion/react', '@emotion/styled', '@mui/material', '@mui/icons-material'],
    },
    noExternal: ['@emotion/react', '@emotion/styled', '@mui/material', '@mui/icons-material'],
  },
  dependencies: {
    '@mui/material': '^6.0.0',  // Explicit version range instead of 'latest'
    'react': '^18.0.0',
    'react-dom': '^18.0.0',
  }
});

This approach improves maintenance, reproduceability of issues, and makes configuration requirements explicit rather than implicit.

---

Vue context boundaries

Ensure Vue composables, reactive state, and side effects are properly scoped within Vue’s execution context to prevent SSR failures, memory leaks, and shared state across requests.

Key Rules:

1. Never call composables at module top-level - Composables must be called within <script setup>, setup() functions, or Vue lifecycle hooks where Nuxt context is available
2. Avoid side effects in root scope - Move timers, event listeners, and cleanup-requiring code into onMounted since unmount hooks don’t run during SSR
3. Don’t define reactive state outside setup - State defined outside component setup functions becomes shared across all users and requests

Examples:

❌ Incorrect - Top-level composable usage:

// utils/api.ts
const { session } = useUserSession() // Fails on server - no Nuxt context

export default defineNuxtPlugin((nuxtApp) => {
  // composable called outside proper context
})

❌ Incorrect - Root scope side effects:

<script setup>
// Timer in root scope - never cleaned up during SSR
const timer = setInterval(() => {}, 1000)

// Shared state across requests
export const myState = ref({})
</script>

✅ Correct - Proper context usage:

// utils/api.ts  
export default defineNuxtPlugin((nuxtApp) => {
  const { session } = useUserSession() // Called within plugin context
})

✅ Correct - Side effects in lifecycle hooks:

<script setup>
// Move side effects to mounted hook
onMounted(() => {
  const timer = setInterval(() => {}, 1000)
  
  onBeforeUnmount(() => {
    clearInterval(timer)
  })
})

// Use useState for proper SSR-safe state
const myState = useState('key', () => ({}))
</script>

This prevents SSR hydration mismatches, memory leaks, and ensures proper cleanup of resources across the Vue component lifecycle.

---

API polling optimization

Optimize API polling patterns to avoid excessive calls and improve performance. Use appropriate update intervals based on data freshness requirements rather than aggressive polling schedules.

Key principles:

• Avoid unnecessarily frequent polling intervals (e.g., 5-second intervals for device status)
• Implement coordinators to centralize API data management and prevent overlapping calls
• Consider on-demand updates instead of scheduled polling when appropriate
• Group related API calls to minimize total requests

Example of problematic polling:

super().__init__(
    hass,
    _LOGGER,
    name=DOMAIN,
    update_interval=timedelta(seconds=5),  # Too frequent!
)

Better approach using coordinator with reasonable intervals:

class DeviceDataCoordinator(DataUpdateCoordinator):
    def __init__(self, hass: HomeAssistant, api: DeviceAPI):
        super().__init__(
            hass,
            _LOGGER,
            name="device_coordinator",
            update_interval=timedelta(minutes=15),  # More reasonable
        )
        self.api = api

    async def _async_update_data(self):
        # Group multiple API calls together
        return await self.api.get_all_device_data()

This approach reduces API rate limit issues, improves performance, and provides better user experience while future-proofing for additional platforms.

---

Document accessibility decisions

When implementing HTML templates, add clear comments documenting accessibility-related decisions. Explain the purpose of semantic HTML elements, ARIA attributes, and screen reader considerations. This ensures that future developers understand the rationale behind these choices and preserves accessibility during code modifications.

For example:

<!-- Using <nav> with aria-labelledby provides better semantic structure for screen readers -->
<!-- Visually hidden heading allows screen reader navigation via headers while remaining invisible -->
<nav class="paginator" aria-labelledby="pagination">
    <h2 id="pagination" class="visually-hidden">{% blocktranslate with name=opts.verbose_name %}Pagination {{ name }} entries{% endblocktranslate %}</h2>
    <!-- Pagination content... -->
</nav>

<!-- Using title and aria-label attributes to provide full text content to all users -->
<!-- despite visual truncation for layout purposes -->
<a href="..." title="{{ object|to_object_display_value }}" aria-label="{{ object|to_object_display_value }}">
  {{ object|to_object_display_value|truncatechars:"80" }}
</a>

This documentation practice helps maintain accessibility standards by explaining design choices, translation considerations, and how both visual and screen reader users will experience the interface.

---

Prefer semantic CSS selectors

Use semantic attribute-based selectors instead of structural or overly specific class names when the semantic meaning is already captured in HTML attributes. This makes CSS more maintainable by connecting styles to the actual meaning of elements rather than their position in the DOM.

For example, instead of:

.paginator .this-page {
    padding: 2px 6px;
}

/* or */

ol.breadcrumbs li:last-child a {
    color: var(--breadcrumbs-fg);
    text-decoration: none !important;
    cursor: default;
}

Prefer:

.paginator a[aria-current="page"] {
    padding: 2px 6px;
}

Also, ensure interactive elements have complete selector sets that include all relevant states:

.datetimeshortcuts button:hover, .datetimeshortcuts button:focus {
    /* styles */
}

This approach improves code maintainability, better communicates intent, and naturally supports accessibility by leveraging semantic HTML attributes.

---

Choose appropriate exception types

Select exception types that match method contracts and avoid surprising behavior. Methods with names like find_or_initialize_by_* should not raise validation errors since the standard Rails method doesn’t perform validation. Use save instead of save! when you want to handle validation errors gracefully rather than raising exceptions. Prefer standard exception types like ArgumentError for invalid parameters over custom exceptions when possible.

# Avoid - surprising exception from find_or_initialize method
def self.find_or_initialize_by_domain(domain)
  normalized_domain = TagManager.instance.normalize_domain(domain&.strip)
  raise ActiveRecord::RecordInvalid if normalized_domain.blank?  # Surprising!
end

# Better - use appropriate exception type or remove the method
def self.find_or_initialize_by_domain(domain)
  normalized_domain = TagManager.instance.normalize_domain(domain&.strip)
  raise ArgumentError, "Invalid domain" if normalized_domain.blank?
end

# Avoid - save! raises exceptions instead of allowing error handling
tag.save!  # Causes bogus 422 responses

# Better - use save for graceful error handling
tag.save   # Allows proper error annotation on the model

Consider reusing existing exception classes like Mastodon::ValidatorError instead of creating new custom exceptions when the behavior matches existing patterns.

---

avoid unnecessary conversions

Choose direct, efficient methods over approaches that require additional parsing, conversion, or processing steps. This reduces computational overhead and improves performance by eliminating intermediate operations.

When equivalent alternatives exist, prefer:

• Direct constructors over string parsing (e.g., Color.rgb(11, 6, 0) instead of parsing hex strings)
• Native method calls over wrapper methods that add conversion layers
• Conditional execution over forced operations (check if work is needed before performing expensive operations)

Example from code reviews:

// Avoid: String parsing with conversion overhead
val color = if (isDarkMode) "#0b0600" else "#f3f8ff"

// Prefer: Direct constructor
val color = if (isDarkMode) Color.rgb(11, 6, 0) else Color.rgb(243, 248, 255)

This principle applies to any situation where you can eliminate intermediate processing steps, type conversions, or unnecessary method calls that don’t add functional value but consume computational resources.

---

Multi-indicator configuration detection

When detecting configuration states, use multiple indicators rather than relying on a single source of truth, especially when dealing with ambiguous or transitional states. Provide clear documentation explaining the detection logic and reasoning behind each check.

Configuration detection often requires examining multiple signals because:

• Single indicators can be misleading (e.g., tsconfig.json presence doesn’t guarantee TypeScript usage)
• Transitional states may need special handling (e.g., “maybe_runes” mode)
• Legacy compatibility requires fallback detection methods

Example from TypeScript detection:

uses_ts:
    // Some people could use jsdoc but have a tsconfig.json, so double-check file for jsdoc indicators
    (use_ts && !source.includes('@type {')) ||
    !!parsed.instance?.attributes.some(
        (attr) => attr.name === 'lang' && attr.value[0].data === 'ts'
    )

Example from runes mode detection:

// Components not explicitly in legacy mode might be expected to be in runes mode (especially since we didn't
// adjust this behavior until recently, which broke people's existing components), so we also bail in this case.
// Kind of an in-between-mode.
if (context.state.analysis.runes || context.state.analysis.maybe_runes) {

Always document the rationale behind complex detection logic, particularly when handling edge cases or backward compatibility scenarios.

---

prefer findBy async queries

When testing components that require waiting for elements to appear, prefer using findBy* queries over waitFor + getBy* combinations. The findBy* queries have built-in waiting functionality that makes tests more readable and reliable.

Instead of:

await waitFor(() => canvas.getByRole('button'));
await userEvent.click(canvas.getByRole('button'));

Use:

const button = await canvas.findByRole('button');
await userEvent.click(button);

This approach reduces code duplication, improves readability, and leverages the testing library’s built-in async waiting mechanisms. While some scenarios may still require waitFor for complex conditions, findBy* should be the default choice for waiting for elements to appear.

---

defensive error handling

Add defensive checks and proper error handling to prevent crashes and handle edge cases gracefully. This includes using try-catch blocks around potentially unsafe operations, adding guard conditions to prevent infinite loops or invalid states, and ensuring the system can recover from unexpected inputs or conditions.

Key practices:

• Wrap property access or function calls that might fail in try-catch blocks, especially in contexts where external factors could cause failures
• Add guard flags or conditions to prevent recursive error scenarios (e.g., preventing error handlers from triggering more errors)
• Handle unknown or future cases by logging warnings and providing fallback behavior rather than throwing fatal errors
• Add defensive resets or cleanup calls to prevent state corruption during error scenarios

Example from the codebase:

// Add defensive try-catch around potentially unsafe operations
try {
    if ((a === b) !== (get_proxied_value(a) === get_proxied_value(b))) {
        w.state_proxy_equality_mismatch(equal ? '===' : '!==');
    }
} catch {
    // Handle case where property access might be disallowed
}

// Add guard flags to prevent recursive error handling
if (calling_on_error) {
    w.reset_misuse();
    throw error;
}

// Provide fallback for unknown cases instead of crashing
default:
    console.warn(`Unknown operator ${expression.operator}`);
    this.values.add(UNKNOWN);

This approach ensures the system remains stable and provides meaningful feedback even when encountering unexpected conditions or edge cases.

---

Defend against nulls

Always use defensive programming techniques when handling potentially null or empty values to avoid runtime errors. Consider these practices:

1. Use specialized methods when checking for default values or null states rather than direct comparisons: ```python

   Prefer this

   if self.has_default(): # handle default case

Instead of this

if self.default and self.default is not NOT_PROVIDED: # handle default case

2. Use `getattr()` with a default value when accessing attributes that might be None:
```python
# Safer approach
on_delete = getattr(field.remote_field, "on_delete", None)

# Instead of directly accessing which might raise AttributeError
# on_delete = field.remote_field.on_delete  # Risky if field.remote_field is None

1. Check if collections are non-empty before applying operations that could fail on empty sequences: ```python

   Safe handling of potentially empty collections

   if objs and (order_wrt := self.model._meta.order_with_respect_to): # process objects

Instead of assuming collection is non-empty

4. Be aware of different types of nulls in specialized contexts (e.g., SQL NULL vs JSON null):
```python
# SQL NULL
obj.json_field = None
# JSON null (different semantics in queries)
obj.json_field = Value(None, output_field=JSONField())

These defensive patterns prevent common null-related errors and make code more robust.

---

Define schema relations correctly

When designing database schemas, ensure relations and constraints are explicitly and correctly defined:

1. Every model must have a properly defined primary key:

   model EmailAccount {
     email String @id  // Primary key, not just @unique
     // OR
     id String @id @default(cuid())  // UUID as primary key
     email String @unique  // Unique but not primary key
   }
   

2. Always use explicit @relation directives with field references:

   model EmailAccount {
     accountId String @unique
     account Account @relation(fields: [accountId], references: [id])
   }
   

3. Avoid redundant foreign keys that Prisma implicitly manages:

   -  digestSchedule Schedule?
   -  digestScheduleId String? @unique
   +  digestSchedule Schedule? // Let Prisma handle the relation
   

4. Carefully evaluate unique constraints to ensure they won’t restrict valid use cases: ```prisma // ❌ Too restrictive - prevents multiple actions of same type @@unique([executedRuleId, actionType])

// ✅ Better - includes distinguishing field @@unique([executedRuleId, actionType, targetIdentifier])

Proper relation definitions improve schema clarity, prevent migration issues, and avoid runtime errors from phantom fields or missing constraints.

---

## leverage existing configuration sources

<!-- source: mastodon/mastodon | topic: Configurations | language: TypeScript | updated: 2025-06-23 -->

When implementing configuration logic, prefer using built-in configuration mechanisms and existing framework parameters over creating custom configuration options. This reduces complexity, improves maintainability, and follows established patterns.

Key principles:
- Use framework-provided configuration objects instead of passing custom parameters
- Leverage type inference from existing interfaces rather than explicit type annotations
- Simplify state management by avoiding context-specific parameters when a single configuration can serve multiple use cases
- Handle undefined configuration values consistently with existing error handling patterns

Example from plugin configuration:
```typescript
// Instead of passing custom parameters
export function MastodonThemes(projectRoot: string): Plugin {
  return {
    name: 'mastodon-themes',
    config: () => {
      // custom logic with projectRoot
    }
  }
}

// Leverage built-in config object
export function MastodonThemes(): Plugin {
  return {
    name: 'mastodon-themes',
    async config(userConfig) { // Type inferred from Plugin interface
      const root = userConfig.root || process.cwd();
      // Use framework-provided configuration
    }
  }
}

This approach reduces the API surface, eliminates redundant parameters, and ensures consistency with framework conventions.

---

consistent naming patterns

Establish and maintain consistent naming conventions across similar components and contexts. Inconsistent naming patterns make code harder to understand, discover, and maintain.

Key areas to focus on:

• Path naming consistency: Use consistent singular/plural forms in variable paths (e.g., steps.X.eventCount not step.digest.eventCount)
• Composite identifier formats: Follow established patterns for multi-part identifiers (e.g., org_${orgId}:user_${userId})
• Trigger and delimiter patterns: Maintain consistent syntax for special markers and triggers across the system

Example of inconsistent naming:

// Inconsistent - mixing singular and plural
const digestVar = 'step.digest.countSummary';  // singular 'step'
const otherVar = 'steps.workflow.events';      // plural 'steps'

// Consistent approach
const digestVar = 'steps.digest.countSummary'; // plural 'steps'
const otherVar = 'steps.workflow.events';      // plural 'steps'

Before introducing new naming patterns, verify they don’t conflict with existing validation rules or system constraints, and ensure they follow the established conventions in similar contexts.

---

prefer established configuration patterns

When making configuration choices, prioritize existing centralized configuration values and established patterns over ad-hoc solutions or deprecated frameworks. This reduces technical debt and maintains consistency across the codebase.

Use centralized configuration exports instead of direct API calls:

// Avoid direct browser API calls
const prefersReducedMotion = window.matchMedia('(prefers-reduced-motion: reduce)');

// Prefer existing centralized configuration
import { reduceMotion } from 'mastodon/initial_state';

Similarly, avoid deprecated frameworks when the team is actively migrating away from them:

// Avoid if migrating away from rails-ujs
Rails.delegate(/* ... */);

// Consider alternative approaches that align with migration plans

Before introducing new configuration approaches, check if equivalent centralized values or patterns already exist in the codebase. This ensures consistency and reduces maintenance overhead during framework migrations or refactoring efforts.

---

Pin problematic dependencies

When external dependencies or tools in CI/CD pipelines have known regressions or bugs, pin them to stable versions and document the reasoning with issue links. Include TODO comments to track when temporary measures can be reverted.

This prevents CI/CD pipeline failures and ensures build stability while maintaining visibility into when constraints can be lifted.

Example:

# PLEASE KEEP THIS PINNED TO 1.4.10 to avoid a regression in 1.5.*
# See https://github.com/changesets/action/issues/465
uses: changesets/action@v1.4.10

# TODO: Track and re-enable once this has been fixed: https://github.com/google/wireit/issues/1297
# - uses: google/wireit@setup-github-actions-caching/v2

Always include the specific issue URL and a clear explanation of what regression or problem the pinning/disabling prevents.

---

Standardize configuration formats

Use consistent, explicit, and well-documented formats in all configuration files to improve readability and prevent misunderstandings. When defining configuration values:

1. Use consistent units for numerical values (e.g., prefer 2g instead of 2048m for memory settings)
2. Explicitly configure all necessary goals/options for build tools rather than relying on defaults
3. Be specific about file type configurations when appropriate rather than using overly broad wildcards

Example:

// Gradle properties - consistent format for memory
org.gradle.jvmargs=-Xmx2g

// Build configurations - explicit plugin configuration
plugins {
    id 'io.spring.javaformat' version "${javaFormatVersion}"
}

// Explicitly configure all required tasks
tasks.named('format') {
    // Configuration here
}

// Editor configurations - specific rather than overly broad when needed
// .editorconfig example with targeted file types
[*.{java,xml,properties}]
charset = utf-8

Following these practices ensures configs are more maintainable, easier to understand at a glance, and less prone to unexpected behavior.

---

Design fluent HTTP APIs

When designing HTTP-related APIs, prioritize readability and intuitiveness through well-crafted fluent interfaces. API methods should read naturally in code, expressing the developer’s intent clearly and concisely.

Key principles:

1. Use intuitive method names that directly express their purpose
2. Provide concise shortcuts for common operations
3. Ensure method chains read like natural sentences
4. Arrange methods in a logical sequence that mirrors user intent

Example (Improved):

// Preferred style - intuitive and readable
httpSecurity
    .get("/public/*").permit()
    .path("/api/*").authenticated()
    .path("/admin/*").roles("admin");

Example (Avoid):

// Avoid - less intuitive naming and structure
httpSecurity
    .path("/public/*").methods("GET").authorization().permit()
    .path("/api/*").authenticationMechanism(new CustomAuthMechanism()).authorization().authenticated()
    .path("/admin/*").authorization().roles("admin");

When designing security-related APIs, prefer direct method names like .authenticated() instead of more verbose alternatives like .authenticationMechanism(). For HTTP method operations, provide shortcuts (get(), post(), put(), delete()) rather than requiring verbose method specification.

The goal is to create APIs that are not only powerful but also immediately understandable, reducing cognitive load and making the most common use cases the easiest to express.

---

Enforce user scoping

All database queries must include appropriate user scoping to prevent unauthorized data access and Insecure Direct Object Reference (IDOR) vulnerabilities. Every query should filter results based on the authenticated user’s context using emailAccountId, userId, or equivalent identifiers in WHERE clauses.

Why it matters: Without proper user scoping, attackers could potentially access or modify data belonging to other users by manipulating input parameters or request data.

Implementation:

// ❌ VULNERABLE: Missing user scoping
const schedule = await prisma.schedule.findUnique({
  where: { id: scheduleId }
});

// ✅ SECURE: Properly scoped to authenticated user
const schedule = await prisma.schedule.findUnique({
  where: { id: scheduleId, emailAccountId }
});

Security checks:

• Run security audit scripts regularly to identify unscoped queries
• When reviewing code, always verify that database queries include user context filters
• For relations, ensure that lookups verify ownership through proper joins or nested where clauses
• Be especially vigilant with findUnique, findFirst, and any query that returns specific records

---

Isolate configuration concerns

Keep configuration settings separate from application code by using environment variables or dedicated configuration files. This promotes better maintainability, security, and flexibility across different deployment environments.

Key practices:

1. Use environment variables for sensitive or environment-specific configuration

   import os
      
   # Read configuration from environment variables with defaults
   database_url = os.getenv("DATABASE_URL", "sqlite:///default.db")
   debug_mode = os.getenv("DEBUG_MODE", "False") == "True"
   

2. Isolate project dependencies with virtual environments Create virtual environments for each project to manage dependencies independently and avoid conflicts:

   $ python -m venv .venv
   $ source .venv/bin/activate  # Linux/macOS
   $ .venv\Scripts\Activate.ps1  # Windows PowerShell
   

3. Document configuration options clearly Provide comprehensive documentation of all configuration options, including:
   • Expected variable types
   • Default values
   • Example usage
   • Possible values and their impact
4. Consider using a centralized configuration manager For more complex applications, implement a dedicated configuration class:

   from pydantic_settings import BaseSettings
      
   class Settings(BaseSettings):
       database_url: str = "sqlite:///default.db"
       api_key: str
       debug_mode: bool = False
          
       class Config:
           env_file = ".env"
      
   settings = Settings()
   

By separating configuration from code, you can adapt your application to different environments without changing the codebase, simplify testing, and enhance security by keeping sensitive information out of your repository.

---

Write resilient tests

Tests should be designed to validate behavior without being brittle or sensitive to implementation details. Avoid direct string comparisons for complex data structures or binary data, as these tests can break due to formatting changes or encoding issues that don’t reflect actual functional problems.

Instead:

1. For binary data, compare raw byte slices: ```go // Instead of this (brittle): assert.Equal(t, string(bsonData), w.Body.String())

// Do this (more robust): assert.Equal(t, bsonData, w.Body.Bytes())

2. For structured data like JSON/YAML/XML, unmarshal back to a comparable structure:
```go
// Instead of string comparisons:
assert.Equal(t, "{\"foo\":\"bar\"}", w.Body.String())

// Parse and compare structurally:
var result map[string]interface{}
err := json.Unmarshal(w.Body.Bytes(), &result)
require.NoError(t, err)
assert.Equal(t, expectedData, result)

1. For complex strings with variable ordering (like HTTP headers): ```go // Instead of exact string matching: assert.Equal(t, “user=gin; Path=/; Domain=localhost; Max-Age=1; HttpOnly; Secure”, cookie)

// Check each component individually: setCookie := w.Header().Get(“Set-Cookie”) assert.Contains(t, setCookie, “user=gin”) assert.Contains(t, setCookie, “Path=/”) assert.Contains(t, setCookie, “Domain=localhost”)

These approaches ensure tests remain valid even when non-functional aspects of the implementation change, reducing maintenance burden and avoiding false test failures.

---

## Semantic naming clarity

<!-- source: tanstack/query | topic: Naming Conventions | language: Markdown | updated: 2025-06-21 -->

When introducing names for APIs/docs and for contribution metadata, ensure the naming is semantic and cannot be mistaken for a requirement that isn’t real.

**Apply this rule**
1) **Avoid misleading implied constraints**: If two keys/identifiers are shown together, make it explicit whether they *must* match or are simply examples.
2) **Prefer domain-based, unambiguous identifiers**: Name commit scopes by library/framework area (e.g., `react-query`, `query-core`) rather than narrowly duplicated code-level terms.
3) **Use the team/standard vocabulary for commit types**: Only use commit type labels that match the accepted conventional-commit configuration (e.g., `types` only if it’s allowed by your commitlint rules).

**Example (docs/config helper)**
```ts
function groupMutationOptions() {
  return mutationOptions({
    mutationKey: ['groups'], // required: identifies the mutation
    mutationFn: addGroup,
    // Note: mutationKey does NOT need to equal the queryKey used by the invalidation.
  })
}

useMutation({
  ...groupMutationOptions(),
  onSuccess: () => queryClient.invalidateQueries({ queryKey: ['groups'] }),
})

Example (commit scope/type naming)

• Prefer: types(react-query): add mutationOptions typing support
• Prefer: chore(query-core): update build tooling
• Avoid scopes like useQuery if they can be duplicated across adapters; prefer the library/framework area instead.

---

Avoid render cycle allocations

Creating new objects, arrays, or functions inside a component’s render cycle causes unnecessary allocations on every render, which can degrade performance, especially in frequently-rendered components.

For non-derived values that don’t depend on props or state:

• Extract object/function declarations to module scope outside components
• Use useRef or custom hooks like useLazyRef for mutable references
• Prefer styled over inline sx props for static styling

// Inefficient: New allocations on every render
function Component() {
  const valueToIndex = new Map(); // ❌ Creates new Map each render
  const handleClick = () => {...}; // ❌ Creates new function each render
  return <Box sx={{ color: 'red' }}>...</Box>; // ❌ Creates new object each render
}

// Optimized: Stable references and static optimizations
const createMap = () => new Map(); // ✅ Defined once in module scope
const StyledBox = styled(Box)({ color: 'red' }); // ✅ Styled component

function Component() {
  const valueToIndex = useLazyRef(createMap).current; // ✅ Stable reference
  const handleClick = useCallback(() => {...}, []); // ✅ Memoized function
  return <StyledBox>...</StyledBox>; // ✅ No new style object created
}

For values derived from props or state, use appropriate memoization with useMemo and useCallback with correct dependency arrays.

Additionally, when working with DOM updates, prefer direct manipulation of CSS variables over context-driven updates when it provides a performance benefit.

---

Use specific test assertions

Always use the most specific test assertion method available for your test case rather than generic assertions. Specific assertions provide better error messages and make test failures easier to debug.

For string comparisons, use EXPECT_STREQ instead of ASSERT_TRUE with string equality:

// Instead of:
ASSERT_TRUE(json == testValue);

// Use:
EXPECT_STREQ(json.c_str(), testValue.c_str());

For exception testing, use EXPECT_THROW to properly verify exceptions instead of manually catching them:

// Instead of:
try {
    lru.evict();
    // Test will pass even if no exception is thrown
} catch (...) {
    // ...
}

// Use:
EXPECT_THROW(lru.evict(), SomeExceptionType);

Specific assertions like these will print the actual and expected values when tests fail, making debugging much faster and providing clearer failure messages in test reports.

---

use Guardian authorization classes

Always implement authorization checks using Guardian classes rather than ad-hoc permission logic. Guardian classes provide a centralized, consistent approach to authorization that helps prevent security vulnerabilities from inconsistent or missing permission checks.

The main Guardian class is defined in lib/guardian.rb, with additional Guardian classes available in the lib/guardian/ directory. These classes encapsulate authorization logic and should be used for all permission-related decisions in the application.

Example usage:

# In a controller
def show
  guardian.ensure_can_see!(@topic)
  # ... rest of action
end

# In a service or model
if guardian.can_edit_post?(@post)
  # ... perform edit operation
end

This pattern ensures that authorization logic is:

• Centralized and maintainable
• Consistently applied across the application
• Easier to audit for security vulnerabilities
• Following established architectural patterns

Avoid implementing custom authorization logic directly in controllers or services, as this can lead to inconsistent security enforcement and potential authorization bypass vulnerabilities.

---

Consistent terminology propagation

When changing terminology or naming conventions in a codebase, ensure complete and consistent propagation across all related code artifacts. This includes variable names, method names, parameters, error messages, documentation, comments, and any other references. Inconsistent terminology creates cognitive overhead, leads to bugs, and hampers maintainability.

For example, when transitioning from ‘collection’ to ‘table’ terminology:

// Update method names
- public function testDeleteCollection(array $data)
+ public function testDeleteTable(array $data)

// Update variable names
- $moviesCollectionId = $data['moviesId'];
+ $moviesTableId = $data['moviesId'];

// Update error messages
if (!$dbForProject->deleteDocument('database_' . $db->getInternalId(), $tableId)) {
-    throw new Exception(Exception::GENERAL_SERVER_ERROR, 'Failed to remove collection from DB');
+    throw new Exception(Exception::GENERAL_SERVER_ERROR, 'Failed to remove table from DB');
}

// Update parameter descriptions
-    ->param('name', null, new Text(128), 'Collection name. Max length: 128 chars.')
+    ->param('name', null, new Text(128), 'Table name. Max length: 128 chars.')

// Update event labels
-    ->label('scope', 'collections.write')
+    ->label('scope', 'tables.write')

Inconsistent terminology not only confuses developers but can lead to runtime errors when methods or variables with old names are referenced.

---

Enforce API endpoint consistency

When implementing or modifying API endpoints, ensure consistency across related routes by checking:

1. Parameter naming matches between route definition and handler: ```php // BAD: Parameter name mismatch ->setHttpPath(‘/v1/databases/:databaseId/tables/:collectionId/rows’) ->action(function(string $databaseId, string $tableId) { … })

// GOOD: Parameter names align ->setHttpPath(‘/v1/databases/:databaseId/tables/:tableId/rows’) ->action(function(string $databaseId, string $tableId) { … })

2. Response formats are consistent for similar operations:
```php
// BAD: Inconsistent responses for related operations
incrementEndpoint->returns(200, documentModel);
decrementEndpoint->returns(204, noContent);

// GOOD: Consistent response pattern
incrementEndpoint->returns(200, documentModel);
decrementEndpoint->returns(200, documentModel);

1. Permission scopes and event names follow the same pattern: ```php // BAD: Mixed terminology in related endpoints ->label(‘scope’, ‘collections.write’) ->label(‘event’, ‘databases.[databaseId].tables.[tableId].update’)

// GOOD: Consistent terminology ->label(‘scope’, ‘tables.write’) ->label(‘event’, ‘databases.[databaseId].tables.[tableId].update’)

When reviewing API changes, compare against related endpoints to maintain a consistent interface. This helps prevent subtle bugs from parameter mismatches and reduces cognitive load for API consumers.

---

## Documentation translation guidelines

<!-- source: fastapi/fastapi | topic: Documentation | language: Markdown | updated: 2025-06-19 -->

Maintain consistency and accuracy when translating documentation. Ensure technical terms and special formatting elements are handled properly according to project guidelines.

When translating documentation:
1. **Preserve special formatting**: Keep formatting elements like admonitions intact, following project-specific patterns. For example with info boxes:
   ```markdown
   /// tip | Dica
   Content goes here
   ///

Don’t change the word immediately after /// as it determines the box’s styling.

1. Handle technical terms appropriately: Consider whether technical terms should be translated or kept in their original form based on common usage in the target language.

   # In Korean translation
   # Better: "오버헤드" (keeping technical term "overhead")
   # Instead of: "추가적인 시간" (translating as "additional time")
   

2. Maintain consistent terminology: Use the same translation for recurring terms throughout the documentation.

3. Add context when needed: Include examples for abbreviations or technical concepts to improve clarity.

4. Don’t modify original content: When translating, avoid changing the source code examples unless translating comments.

---

Keep documentation paths current

Maintain accurate and consistent documentation paths, references, and descriptions across the codebase. When terminology or architecture changes, ensure all documentation references are updated to reflect the current state.

Example of proper documentation path updates:

// In SDK method definition
-description: '/docs/references/databases/update-attribute-enum.md',
+description: '/docs/references/databases/update-column-enum.md',

// In parameter description
-->param('attribute', '', new Key(), 'Document ID.')
+->param('attribute', '', new Key(), 'Attribute key.')

Key points:

• Update documentation paths when endpoints or features are renamed
• Ensure parameter descriptions accurately reflect their purpose
• Maintain consistency between code terminology and documentation
• Review all related files when making terminology changes
• Keep API references synchronized with implementation changes

---

Secure authorization skip handling

When using authorization bypass mechanisms like Authorization::skip(), ensure proper security validation is maintained. Authorization skipping should only be used for internal system operations where the caller already has appropriate permissions, never for user-facing operations that require access control.

Common pitfalls to avoid:

1. Don’t skip authorization checks just to verify resource existence
2. Don’t expose internal collection access through authorization bypasses
3. Ensure consistent authorization handling across related operations

Example of proper authorization handling:

- // BAD: Skips auth check entirely
- $database = Authorization::skip(fn () => 
-     $dbForProject->getDocument('databases', $databaseId)
- );
-
- if ($database->isEmpty()) {
-     throw new Exception(Exception::DATABASE_NOT_FOUND);
- }

+ // GOOD: Let DB layer handle authorization
+ try {
+     $database = $dbForProject->getDocument('databases', $databaseId);
+     
+     if ($database->isEmpty()) {
+         throw new Exception(Exception::DATABASE_NOT_FOUND);
+     }
+ } catch (AuthorizationException $e) {
+     // Convert to generic error to avoid information disclosure
+     throw new Exception(Exception::USER_UNAUTHORIZED);
+ }

Only use Authorization::skip() when:

• Accessing internal system collections that don’t have user-level permissions
• Performing privileged operations where authorization was already verified
• Working with metadata that shouldn’t block access to the main resource

Always document why authorization skipping is necessary and safe in that specific context.

---

Cache expensive operations

Identify and cache results of expensive operations that may be called repeatedly during a request lifecycle, especially recursive functions or operations performed in loops. This reduces redundant processing and can significantly improve application performance.

For example, when working with trait detection or class hierarchy traversal:

// Instead of repeatedly calling an expensive function
public function isPrunable(): bool
{
    return in_array(Prunable::class, class_uses_recursive(static::class)) || static::isMassPrunable();
}

// Cache the result for the lifetime of the request
protected static $classTraitsCache = [];

public function isPrunable(): bool
{
    $class = static::class;
    
    // Only perform the expensive operation once per class
    if (!isset(static::$classTraitsCache[$class])) {
        static::$classTraitsCache[$class] = class_uses_recursive($class);
    }
    
    return in_array(Prunable::class, static::$classTraitsCache[$class]) || static::isMassPrunable();
}

Similarly, when selecting methods for array operations, favor efficient approaches. For instance, use array_search() over array_flip() followed by key lookup for better performance with large arrays.

When implementing expensive transformations (like toArray() on models), use memoization techniques to avoid recalculating the same values multiple times during a single request.

---

Environment variable fallbacks

Always implement proper fallback chains for environment variables and handle missing configuration gracefully. When introducing new environment variables, maintain backward compatibility with existing ones, and apply environment-specific behavior conditionally to avoid issues across different deployment contexts.

Key practices:

• Use fallback chains with multiple environment variable options
• Provide sensible defaults or graceful degradation when configuration is missing
• Apply conditional logic based on deployment environment (e.g., IS_DOCKER_HOSTED)
• Maintain backward compatibility when renaming environment variables

Example implementation:

export function resolveLogging(providedLogging?: boolean): boolean {
  if (providedLogging !== undefined) {
    return providedLogging;
  }
  // Support both new and legacy environment variables
  if (process.env.LOGGING_LEVEL || process.env.LOG_LEVEL) {
    return (process.env.LOGGING_LEVEL || process.env.LOG_LEVEL) === 'true';
  }
  
  // Graceful fallback based on environment
  return !['test', 'production'].includes(process.env.NODE_ENV);
}

// Conditional behavior based on deployment context
const options = process.env.IS_DOCKER_HOSTED === 'true' 
  ? { priority: command.priority } 
  : {};

For optional services, avoid initialization entirely when configuration is missing rather than using empty defaults, allowing the application to bootstrap gracefully without the optional functionality.

---

Semantic descriptive naming

Choose names that clearly communicate purpose, behavior, and semantics of code elements. Names should be self-explanatory and convey their intended functionality without requiring additional context.

Guidelines:

1. Use semantic names for HTML elements and attributes
   • Assign proper ARIA roles that match component functionality (e.g., role="switch" for toggle components)
   • This enhances accessibility and code clarity
2. Create descriptive UI labels and tooltips
   • Prefer specific, action-oriented labels over generic ones
   • Example: “Open standalone demo” is clearer than “Open in new tab”
3. Choose component and function names that indicate behavior and limitations
   • If a function has specific trade-offs or constraints, reflect this in its name
   • Example: Prefix with “fast” when performance is prioritized over complete correctness ```javascript // Good: Name indicates performance optimization with potential limitations import fastDeepAssign from ‘@mui/utils/fastDeepAssign’;

   // Alternative: More generic name requires additional documentation import deepAssign from ‘@mui/utils/deepAssign’; ```

4. Use consistent naming patterns for component props
   • Select prop names that clearly indicate their purpose
   • Follow established naming conventions within your codebase
   • Example: For props that modify component behavior, use descriptive prefixes: ```jsx // Clear naming pattern for skipping option highlight
   Skip highlight

   ```

When choosing between multiple naming options, prioritize clarity and predictability over brevity. Well-named elements reduce the need for comments and make code more maintainable.

---

Environment variable validation

Environment variables should be properly validated with correct type checking and without redundant conditions. Common issues include comparing strings to integers and using unnecessary double-checks that can lead to unexpected behavior.

Key principles:

1. Avoid redundant checks: Don’t check if an environment variable exists and then check its value in the same condition
2. Use correct types: Environment variables are always strings, so compare against string values
3. Simplify boolean logic: Use direct comparisons instead of complex conditional chains

Examples of issues and fixes:

❌ Problematic patterns:

# Redundant checking
if ENV["RCT_USE_PREBUILT_RNCORE"] && ENV["RCT_USE_PREBUILT_RNCORE"] == "1"

# Type mismatch - comparing string to integer
return ENV["RCT_NEW_ARCH_ENABLED"] == 0 ? false : true

✅ Improved patterns:

# Direct value check
if ENV["RCT_USE_PREBUILT_RNCORE"] == "1"

# Correct string comparison with simplified logic
return ENV["RCT_NEW_ARCH_ENABLED"] != "0"

This approach prevents runtime errors, improves code readability, and ensures consistent behavior across different environments and deployment scenarios.

---

Follow established naming conventions

Ensure all identifiers (variables, methods, classes) adhere to the project’s established naming conventions and accurately reflect their purpose. Consistency in naming patterns improves code readability and maintainability across the codebase.

Key principles:

• Follow documented naming conventions (e.g., “REACT_NATIVE is shortened to RCT”)
• Use semantically clear names that match the actual behavior
• Maintain consistency with existing patterns in the codebase

Example from codebase:

# Instead of inconsistent naming:
REACT_NATIVE_DEPS_BUILD_FROM_SOURCE

# Follow the established convention:
RCT_USE_DEP_PREBUILD

# Ensure method names match their actual purpose:
# If method handles release builds, name it appropriately
def podspec_source_download_prebuild_release_tarball()
    url = release_tarball_url(@@react_native_version, :release) # not :debug
end

Before introducing new naming patterns, verify they align with existing conventions or update documentation if establishing new standards.

---

Handle errors gracefully always

Always implement graceful error handling for resource lookups, data parsing, and system operations. Catch specific exceptions, provide clear error messages, and ensure the system can continue operating in a degraded state rather than failing completely.

Key practices:

1. Wrap resource lookups in try/catch blocks
2. Handle parsing errors explicitly
3. Provide fallback behavior
4. Use clear error messages

Example:

try {
    $data = json_decode($input, true);
    if (json_last_error() !== JSON_ERROR_NONE) {
        throw new Exception(Exception::GENERAL_BAD_REQUEST, 'Invalid JSON input');
    }
    
    $document = Authorization::skip(
        fn() => $dbForProject->getDocument('collection', $id)
    );
    
    if ($document->isEmpty()) {
        // Graceful degradation - use empty document
        $document = new Document();
        Console::warning("Document {$id} not found - using empty document");
    }
} catch (Throwable $e) {
    // Log error for debugging
    Console::error("Failed to process document {$id}: {$e->getMessage()}");
    // Return safe fallback state
    return new Document();
}

This approach ensures that:

• Resource lookups don’t crash the application
• Data parsing errors are caught early with clear messages
• The system can continue operating even when components fail
• Errors are logged for debugging while maintaining stability

---

Complete API documentation

Documentation should be complete, accurate, and follow Spring Framework conventions. Ensure your Javadocs include:

1. Clear and accurate descriptions that precisely explain behavior and purpose ```java /**
   • Returns a concise description of this {@code HandlerMethod}, which is used
   • in log and error messages.

   • The description should typically include the method signature of the

   • underlying handler method for clarity and debugging purposes. */ ```
2. Complete parameter documentation for all parameters, especially in interfaces ```java /**
   • Called before every retry attempt.
   • @param retryExecution the current retry execution context */ default void beforeRetry(RetryExecution retryExecution) { ```

3. Class-level Javadoc for all public classes and interfaces

4. Format standards:
   • Wrap Javadoc around 90 characters
   • Don’t end @param or @return descriptions with periods unless they contain sentences
   • Include @since tags for all new public methods
5. Contextual information about when and how to use the API: ```java /**
   • Create a builder with the method, URI, headers, cookies, attributes, and body of the given request.
   • @param other the request to copy the method, URI, headers, cookies, attributes, and body from
   • @return the created builder
   • @since 5.3 */ ```
6. Clear behavioral documentation for methods with special handling: ```java /**
   • Create a builder with the given method and given string base URI template.

   • The given URI template may contain URI variable placeholders that can be expanded using

   • the methods of the built request.
   • @param method the HTTP method (GET, POST, etc)
   • @param uri the URI template
   • @return the created builder
   • @since 5.3 */ ```

Documentation should be specific to the code at hand rather than copied from similar classes, and should clarify edge cases and expected behaviors.

---

Document configuration comprehensively

Configuration properties should be thoroughly documented with explicit details about constraints, units, default values, and behavior implications. This helps users understand how to use them correctly and troubleshoot issues.

When documenting time-related properties, always specify the time unit and mention any rounding behavior:

/**
 * The amount of time a client will wait until it closes the TCP connection after sending a close frame.
 * Note: This duration is rounded to the nearest second.
 */
Optional<Duration> closeTimeout();

For error messages related to configuration, make them actionable by mentioning the relevant configuration property:

// Instead of:
return errorDataSet("The persistence unit datasource points to a non-allowed datasource");

// Better:
return errorDataSet("The persistence unit datasource points to a non-allowed datasource " +
        "(by default, only local databases are allowed). To allow remote databases, set quarkus.hibernate-orm.dev-ui.allowed-hosts=*");

Choose property names that follow consistent naming conventions and reflect their purpose clearly. For example, prefer quarkus.rest-client.logging.scope over logLevel to better express hierarchical relationships and maintain consistency with similar properties.

When deprecating configuration properties, provide clear migration paths with links to documentation:

/**
 * @deprecated Use interfaces annotated with @ConfigMapping instead. 
 * See https://quarkus.io/guides/config-mappings for more info
 */
@Deprecated(since = "3.24", forRemoval = true)

For optional configuration, use Optional<> to avoid breaking changes when adding new properties:

/**
 * Decrypt ID token.
 */
Optional<Boolean> decryptIdToken = Optional.empty();

---

Secure Input Validation Rules

When validating security-sensitive inputs (IDs, hostnames, tokens, IPs, payment-like numbers), ensure the implementation is strict, resilient, portable, and non-leaky:

• Be explicit about sanitation/normalization: don’t name or treat data as “sanitized” unless the required transformation is actually applied before validation.
• Validate the real accepted grammar and edge cases: tighten patterns/logic so you don’t over-accept (e.g., punycode hostnames must include a complete form; JWT header typ checks should tolerate valid variants like JWT-at).
• Harden regex to reduce ReDoS risk: if a regex is used on attacker-controlled input, prefer patterns that avoid catastrophic backtracking and ensure security tooling/lint rules are satisfied (or justify the exception).
• Keep parsing runtime-portable: don’t use Node-only APIs (e.g., Buffer) if the code must run in browsers; prefer atob/universal helpers.
• Avoid leaking user-controlled input in error messages: security-related validation errors should not echo “received” raw values back to clients.

Example (portable JWT header decode + non-leaky error style):

function decodeHeader(headerB64: string) {
  // Convert base64url to base64, then decode in browser-compatible way
  const b64 = headerB64.replace(/-/g, "+").replace(/_/g, "/")
    .padEnd(headerB64.length + ((4 - (headerB64.length % 4)) % 4), "=");
  return JSON.parse(atob(b64));
}

function validateTyp(decoded: any) {
  if ("typ" in decoded && !decoded.typ?.startsWith("JWT")) return false;
  return true;
}

// Error message should not include the raw received discriminator/token/input.
const message = "Invalid discriminator value. Expected one of: ...";

Apply this checklist to every change involving validation/parsing logic, regexes, and security-related error reporting.

---

Document APIs clearly

When designing and documenting APIs, prioritize clarity and completeness through concrete examples and accurate parameter descriptions. Your documentation should help developers understand both the basic usage and edge cases of your API.

For parameter documentation:

• Explain what each parameter does and its default value
• Clearly indicate parameter limitations (like when they apply)
• Use proper formatting for parameter names (e.g., api_timestamp_field:)

Always include practical examples:

# Good - shows parameter usage with examples
# acts_as_api_resource api_timestamp_field: :last_api_access
#
# Example:
class Product < ApplicationRecord
  acts_as_api_resource api_timestamp_field: :last_accessed_at
end

When designing callback-style APIs, follow Rails conventions where possible:

# Option 1: Named options with method references or lambdas
has_one_attached :image, after_attached: :process_image

# Option 2: Configuration within blocks
has_one_attached :image do |attachable|
  attachable.after_attached do |blob|
    process_image(blob)
  end
end

Keep documentation consistent across all locations (guides and API reference), with simpler cases in guides and more complex edge cases in API reference documentation. This approach ensures developers can find the right information at the right time as they progress from basic to advanced usage.

---

Initialize nil-prone variables

Always initialize variables that might be nil to appropriate default values to prevent unexpected behavior. For boolean flags, explicitly initialize to false in constructors or initialization methods:

def initialize
  @unsubscribed = false  # Clear and explicit boolean state
end

For collections, initialize to empty arrays or hashes rather than nil. When setting defaults, use ||= or Hash#reverse_merge! to assign values only when current value is nil:

@options[:autocomplete] ||= "off"  # Only assigns if nil
# or
@options.reverse_merge!(autocomplete: "off")

When implementing predicate methods, use explicit == true comparison to ensure they return true or false, never nil:

def define_predicate_method(name)
  define_method("#{name}?") { public_send(name) == true }
end

For complex types like JSON, provide sensible defaults:

# When handling JSON type
when :json then {}  # Or use a more descriptive example structure

This proactive approach prevents nil-related errors and ensures consistent behavior throughout your application lifecycle.

---

Validate security-related inputs

Always validate and sanitize all inputs that influence security-related functionality at the application level, rather than relying on underlying systems to handle invalid inputs. This prevents potential security vulnerabilities and provides clearer error messages to developers.

When implementing security features:

1. Sanitize user inputs before using them in security contexts
2. Validate configuration values against expected types and ranges
3. Provide informative error messages that aid debugging without exposing sensitive details

Example 1: Sanitizing search inputs to prevent injection

def psql_escape(query: str):
    """Replace unsafe chars with space and convert multiple spaces to single."""
    return normalize_spaces(_spec_chars_re.sub(" ", query))

Example 2: Validating security configuration values

def validate_csp_setting(name, value):
    if value is not None and not isinstance(value, dict):
        raise ValueError(
            f"The Content Security Policy setting '{name}' must be a dictionary (got {value!r} instead)."
        )

Example 3: Validating security-critical parameters

def set_weight(self, weight):
    if weight is not None and weight.upper() not in ('A', 'B', 'C', 'D'):
        raise ValueError(f"Weight must be one of A, B, C, or D (got {weight!r} instead).")
    self.weight = weight

Always perform input validation as early as possible in your code, before the values are used in any security-critical operations. This prevents security vulnerabilities and provides better developer experience with meaningful errors.

---

Use design system tokens

Always use design system tokens (theme values, breakpoints, spacing units) instead of hard-coded values. This ensures consistency across the codebase and makes maintenance easier when design changes are needed.

Bad:

<Grid sx={{ 
  width: '44px',
  fontWeight: 'bold',
  '@media (max-width: 640px)': {
    // ...
  }
}} />

Good:

<Grid sx={{ 
  width: theme.spacing(5.5), // or appropriate token
  fontWeight: theme.typography.fontWeightBold,
  [theme.breakpoints.down('sm')]: {
    // ...
  }
}} />

This practice:

• Maintains visual consistency
• Simplifies theme customization
• Makes responsive design more maintainable
• Reduces the need for magic numbers in the code

---

Follow platform naming conventions

Adhere to the established naming conventions and namespacing practices of your target platform. This includes following language-specific patterns for method names, avoiding namespace pollution in headers, and properly namespacing exported functions.

For Objective-C:

• Methods prefixed with get should return results via pointer arguments, not return values directly
• Exported functions should include appropriate prefixes (e.g., RCT prefix)
• Avoid using namespace declarations in header files to prevent namespace pollution

Example violations and fixes:

// ❌ Violates Objective-C naming convention
+ (std::pair<CGPoint, CGPoint>)getPointsForCAGradientLayerLinearGradient:(CGPoint)startPoint

// ✅ Follows convention by removing 'get' prefix
+ (std::pair<CGPoint, CGPoint>)pointsForCAGradientLayerLinearGradient:(CGPoint)startPoint

// ❌ Missing namespace prefix for exported function
RCT_EXTERN RCTFontWeight weightOfFont(UIFont *font);

// ✅ Properly namespaced
RCT_EXTERN RCTFontWeight RCTGetFontWeight(UIFont *font);

Platform naming conventions exist for good reasons - they improve code readability, prevent naming conflicts, and ensure consistency with the broader ecosystem.

---

Configuration over hardcoding

When designing APIs, prefer exposing behavior through configuration options rather than hardcoding logic, especially for aspects that might vary across implementations or require customization. This creates more flexible APIs that can adapt to changing requirements without code modifications.

For example, instead of hardcoding mappings between Unicode ranges and font files:

// Hardcoded approach requiring code changes for new languages
if (isInDevanagari(ch)) return GlyphIDType::Devanagari;
if (isInKhmer(ch)) return GlyphIDType::Khmer;

Design a configuration-driven approach:

// Configuration-driven approach
"fonts": [
  {
    "name": "devanagari",
    "url": "https://example.com/devanagari.ttf",
    "unicode-range": "U+0900-097F"
  },
  {
    "name": "khmer",
    "url": "https://example.com/khmer.ttf",
    "unicode-range": "U+1780-17FF"
  }
]

This pattern applies to many API aspects like URI scheme handling, internationalization support, and feature flags. Configuration-driven APIs are more adaptable, easier to extend, and give API consumers more control without requiring changes to the underlying implementation.

---

comprehensive null checks

When checking for null or undefined values in conditional statements, ensure all related nullable dependencies are validated together in the same condition. Partial null checks can lead to runtime errors when some dependencies are validated while others are not.

This prevents scenarios where code proceeds with some required values present but others potentially null or undefined. Always group related null checks to maintain consistency and prevent edge cases.

Example:

// Before - incomplete null checking
if (!user || !currentEnvironment) {
  return;
}
// currentOrganization could still be null/undefined

// After - comprehensive null checking  
if (!user || !currentEnvironment || !currentOrganization) {
  return;
}

Additionally, consider simplifying complex union types that include nullable variants, as they can make comprehensive null checking more difficult and error-prone.

---

organize accessibility attributes

Systematically organize HTML elements by adding appropriate accessibility attributes (aria-label, role) to improve code structure and semantic clarity. Place accessibility attributes immediately after class attributes for consistent code organization and enhanced readability.

When working with semantic HTML elements like headings and images, ensure each element includes descriptive accessibility attributes that clearly identify their purpose and content. This creates more organized, self-documenting code that follows accessibility best practices.

Example:

<!-- Before -->
<h1 class="flex flex-col gap-y-4 items-center justify-center">
<svg class="h-8 sm:h-12" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 800 200">

<!-- After -->
<h1 class="flex flex-col gap-y-4 items-center justify-center" aria-label="Nuxt {{ version }}">
<svg role="img" aria-label="Nuxt" class="h-8 sm:h-12" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 800 200">

This approach ensures consistent attribute organization while making the code more accessible and maintainable.

---

Enforce permission-based UI controls

Always implement proper authorization checks in UI components that expose sensitive functionality. Wrap buttons, forms, and other interactive elements that perform create, update, delete, or other privileged operations with permission-based controls to prevent unauthorized access.

Use permission wrapper components or conditional rendering based on user roles/permissions to ensure that only authorized users can see and interact with sensitive functionality. This prevents both accidental and malicious access to restricted operations.

Example implementation:

<PermissionButton
  permission={PermissionsEnum.WORKFLOW_WRITE}
  // ... other props
>
  Create Layout
</PermissionButton>

This pattern should be consistently applied to all UI elements that trigger sensitive operations like creating, deleting, duplicating, or modifying critical resources. The authorization check should happen both at the UI level (for user experience) and at the API level (for security enforcement).

---

Use transactions for consistency

Always wrap multiple related database operations in a transaction to ensure data consistency and prevent partial updates. This applies to operations across different tables or when coordinating database updates with external services (e.g., Redis cache).

Example:

- const dbPromise = prisma.label.upsert({ ... })
- const redisPromise = saveUserLabel({ ... })
- await Promise.all([dbPromise, redisPromise])

+ await prisma.$transaction(async (tx) => {
+   const dbResult = await tx.label.upsert({ ... });
+   await saveUserLabel({ ... });
+ });

Key benefits:

• Ensures all operations succeed or fail together
• Prevents inconsistent state between related data
• Maintains referential integrity
• Simplifies error handling and rollbacks

Apply this pattern when:

• Updating multiple related records
• Coordinating DB changes with cache updates
• Performing data migrations or merges
• Managing cross-service data consistency

---

optimize algorithm performance

When implementing algorithms, prioritize performance optimization through careful algorithm selection, query structure, and evaluation strategy choices. Key considerations include:

Algorithm Selection: Choose appropriate algorithms for the task. Avoid inefficient patterns like flawed cycle detection that only checks subsets of data or tree walking when more efficient alternatives exist.

Query Optimization: Structure database queries and datalog rules for optimal performance. Place filter clauses early in the query to reduce the search space: (or [?block :logseq.task/scheduled ?n] [?block :logseq.task/deadline ?n]) [(>= ?n ?start-time)] [(<= ?n ?end-time)] rather than filtering later.

Evaluation Strategy: Understand the difference between lazy and eager evaluation. Use mapv or doseq instead of map when side effects are needed, as map is lazy and won’t execute the operations.

Rule Optimization: For recursive queries, carefully order clauses for performance. Write rules optimized for your primary access pattern - descendant queries vs ancestor queries require different clause ordering.

Example of inefficient cycle detection to avoid:

;; Problematic - only checks every 100 steps, misses cycles in smaller datasets
(when (and (zero? steps)
           (seq (set/intersection (set @seen) (set uuids-to-add))))
  ;; cycle detection logic

Consider computational complexity early in design and choose data structures and algorithms that scale appropriately with expected input sizes.

---

Optimize algorithmic operations

Before implementing or modifying algorithms, carefully evaluate data structure properties and operation costs. Always:

1. Understand data structure guarantees: Choose structures that provide the necessary ordering and performance characteristics. For instance, when replacing one structure with another, be aware of their different behaviors:

// Problematic: PriorityBlockingQueue doesn't guarantee ordering for equal priorities
private final PriorityBlockingQueue<ShutdownTask> shutdownTasks = new PriorityBlockingQueue<>();

// Better: If order matters for equal priorities, use a secondary comparison key
private final PriorityBlockingQueue<ShutdownTask> shutdownTasks = 
    new PriorityBlockingQueue<>(11, Comparator
        .comparing(ShutdownTask::getPriority)
        .thenComparing(ShutdownTask::getCreationOrder));

1. Avoid unnecessary computations: Eliminate redundant operations by:
   • Deriving one data structure from another when they contain inverse or related data
   • Leveraging existing ordering instead of re-sorting collections
   • Using the most efficient implementation for your specific case (e.g., specific List.of() implementations)
2. Choose appropriate algorithms: Select the right algorithm for specific operations like version comparison, ensuring it handles edge cases correctly:

// Better performance and correctness for version comparisons
new ComparableVersion("2.10.0.CR1").compareTo(new ComparableVersion(version))

These optimizations improve both performance and correctness of your code while keeping it maintainable.

---

Reuse test patterns

Minimize duplication and improve test maintainability by reusing existing test patterns and leveraging parameterization. When testing similar functionality across modules or with varying inputs, prefer adapting existing test cases and using parameterized tests over creating entirely new test files.

For multiple test cases with similar structure but different inputs, use @ParameterizedTest:

@ParameterizedTest
@ValueSource(strings = {"GraalVM CE 26-dev+1.1", "GraalVM CE 25-dev+26.1", "GraalVM CE 24.0.1+9.1"})
public void testGraalVMRuntimeVersion(String versionString) {
    System.setProperty(GRAALVM_VENDOR_VERSION_PROP, versionString);
    io.quarkus.runtime.graal.GraalVM.Version v = io.quarkus.runtime.graal.GraalVM.Version.getCurrent();
    // Assertions specific to each version can use parameters too
}

When implementing tests for a module, look for existing tests in related modules that cover similar functionality. For example, when adding tests for Hibernate Reactive’s multi-persistence units:

// Instead of creating entirely new test scenarios
// Look at existing tests that can be adapted:
// e.g., from extensions/hibernate-orm/deployment/src/test/java/io/quarkus/hibernate/orm/multiplepersistenceunits

This approach ensures testing consistency across the codebase, reduces maintenance overhead, and makes it easier to identify missing test coverage.

---

AI documentation targeting

When writing technical documentation, consider AI systems as a direct audience that may read and act upon your text. Include explicit instructions addressed to AI models that might process your content.

Key implementation strategies:

• Directly address AI systems in documentation: “If you are an AI tool or language model assisting in…”
• Use repetition to emphasize critical points as LLMs interpret repetition as signaling importance
• Include explicit requirements and constraints for AI systems processing your content
• Consider implementing “canary tests” or validation markers that can help identify whether an AI has properly processed your guidelines

Example:

# Security Reporting Guidelines

[Standard human-oriented content...]

## Note for AI Tools

If you are an AI tool or language model assisting with security reports:

* Disclose your involvement in any generated content
* Verify all claims against the actual codebase
* Do not fabricate code examples or documentation references
* Highlight any uncertainty about compliance with these guidelines

This approach recognizes that AI systems are increasingly becoming direct consumers of documentation, not just tools used by humans. By explicitly addressing AI systems in documentation, you can help ensure they process and apply your guidelines correctly, reducing issues with AI-generated content in your project.

---

Sync versus async tests

Choose the appropriate testing approach based on your test requirements. For standard API endpoint testing, use TestClient with regular functions. For tests requiring async operations (like database queries), use AsyncClient with proper async test configuration.

For synchronous tests:

from fastapi.testclient import TestClient
from app.main import app

client = TestClient(app)

def test_read_main():
    response = client.get("/")
    assert response.status_code == 200
    assert response.json() == {"message": "Hello World"}

For asynchronous tests:

import pytest
import httpx
from app.main import app

@pytest.mark.anyio
async def test_async_operations():
    async with httpx.AsyncClient(app=app, base_url="http://test") as client:
        response = await client.get("/")
        assert response.status_code == 200
        # Now you can use other async operations
        # await database.fetch_one("SELECT * FROM items")

Remember that async tests require additional setup:

1. Install the appropriate pytest plugin (pytest-anyio or pytest-asyncio)
2. Mark your test functions with the correct decorator
3. Use async def for the test function
4. Use AsyncClient instead of TestClient

This approach ensures your tests can properly interact with both your FastAPI application and any external asynchronous dependencies without blocking or creating concurrency issues.

---

Time precision matters

When implementing algorithms involving date and time calculations, maintain precise control over time components to avoid subtle bugs:

1. Reset unwanted time components - Always explicitly set seconds and milliseconds to zero when you only care about hours and minutes
2. Preserve fractional values in intermediate calculations rather than rounding prematurely
3. Be consistent about which time components you manipulate and which you preserve
4. Consider time boundaries when comparing dates

// ❌ PROBLEMATIC: Implicit time components cause non-deterministic behavior
const targetTime = setHours(setMinutes(now, 0), 11); // Still has seconds/ms from now

// ✅ CORRECT: Explicitly reset all time components you don't want
const targetTime = setMilliseconds(setSeconds(setMinutes(now, 0), 0), 0) |> 
                   (d => setHours(d, 11));

// ❌ PROBLEMATIC: Rounding can collapse distinct slots
const slotDate = addDays(intervalStart, Math.round(i * slotLength));

// ✅ CORRECT: Preserve fractional precision in intermediate calculations
const wholeDays = Math.floor(i * slotLength);
const slotDate = addDays(intervalStart, wholeDays);

// ❌ PROBLEMATIC: Missing boundary check
if (daysOfWeek & nextDayMask) {
  nextDate.setHours(0, 0, 0, 0);
  return nextDate; // Could return a time in the past
}

// ✅ CORRECT: Check time boundaries
if (daysOfWeek & nextDayMask) {
  nextDate.setHours(0, 0, 0, 0);
  if (daysToAdd === 0 && nextDate <= fromDate) {
    daysToAdd++;
    continue; // Skip to next day
  }
  return nextDate;
}

Time-related bugs can be subtle and hard to detect. They often manifest only in specific situations (like date boundaries or daylight saving time changes). Implement thorough tests that cover edge cases, and always be explicit about which time components you’re manipulating.

---

Automate style enforcement

Implement automated code style enforcement using complementary tools rather than relying on manual reviews. Configure multiple tools to work together, as each has unique strengths and blind spots.

Key practices:

• Configure formatters to automatically apply fixes (not just check) to prevent build failures while ensuring consistency
• Use overlapping tools like formatter-maven-plugin, spotless, and PMD together for comprehensive coverage
• Add static analysis rules to catch common style and quality issues
• Automate organizational concerns like import ordering and POM file element sorting

Example configuration:

<plugin>
    <groupId>com.diffplug.spotless</groupId>
    <artifactId>spotless-maven-plugin</artifactId>
    <configuration>
        <java>
            <removeUnusedImports />
            <formatAnnotations />
            <!-- Additional style rules -->
        </java>
    </configuration>
    <executions>
        <execution>
            <goals>
                <goal>apply</goal>
            </goals>
            <phase>process-sources</phase>
        </execution>
    </executions>
</plugin>

When introducing new tools, prefer those that can automatically fix issues rather than just reporting them. This reduces manual work and ensures consistent style across the codebase.

---

Pin GitHub Actions SHA

GitHub Actions should be pinned to specific SHA commits rather than mutable tag references to ensure security and reproducibility. Tags can be moved or updated by malicious actors, potentially introducing supply chain vulnerabilities, while SHA commits are immutable and provide guaranteed consistency across builds.

When referencing GitHub Actions, always use the full SHA commit hash followed by a comment indicating the version for readability:

# Instead of:
uses: cypress-io/github-action@v6

# Use:
uses: cypress-io/github-action@6c143abc292aa835d827652c2ea025d098311070 # v6.10.1

This practice protects against supply chain attacks, ensures reproducible builds, and maintains clear version tracking while providing the security benefits of immutable references.

---

Semantic naming consistency

Ensure all model and field names semantically reflect their actual purpose and maintain consistency with their usage throughout the codebase:

1. Choose names that accurately represent the entity’s role without misleading prefixes.
2. Verify correct spelling in all identifiers.
3. Ensure data types match the documented usage patterns.

Example:

// Misleading model name with inappropriate type
- model UserFrequency {
-   timeOfDay DateTime?  // Comment says only time portion used
-   lastOcurrenceAt DateTime?  // Spelling error
- }

// Improved semantic naming and type consistency
+ model Schedule {
+   timeOfDay String?  // Stores time in "HH:mm" format as documented
+   lastOccurrenceAt DateTime?  // Correct spelling
+ }

This standard helps prevent confusion, improves code readability, and reduces the cognitive load for developers working with your schema.

---

Numerical precision considerations

When implementing algorithms involving floating-point calculations, choose epsilon values based on the specific domain requirements rather than defaulting to system-defined constants. Standard values like std::numeric_limits<double>::epsilon() are often too small for practical geometric or graphical applications.

Instead:

1. Select appropriate epsilon values that account for the scale and precision needs of your specific algorithm
2. Document any precision limitations in code comments
3. Consider defining common epsilon values as named constants for consistency across the codebase

// Bad: Using system epsilon which may be too small
if (std::abs(a - b) < std::numeric_limits<double>::epsilon()) {
    // ...
}

// Good: Using domain-appropriate epsilon with documentation
const auto epsilon = 1e-10; // Suitable for geometric calculations at this scale
// Document precision limitations: Results may be unreliable beyond zoom level X
if (std::abs(a - b) < epsilon) {
    // ...
}

This approach helps prevent subtle bugs that can occur when numerical comparisons fail due to inappropriate precision thresholds, particularly in geometry processing, graphics rendering, and spatial algorithms.

---

configuration consistency standards

Ensure configuration options, flags, and environment settings are handled consistently across all commands and modules. This includes supporting the same configuration flags across CLI commands, using standardized approaches for environment detection, and implementing clear precedence rules.

Key principles:

• Support configuration flags consistently across all CLI commands (like --config flag)
• Use build-time constants (__DEV__) instead of runtime environment checks (process.env.NODE_ENV) for library code
• Implement clear precedence rules where explicit parameters override inferred configuration
• Provide informative error messages that guide users toward solutions
• Calculate derived configuration flags using consistent logic

Example of good configuration precedence:

function resolveRootDirectory(root?: string, flags?: { config?: string }) {
  if (root) {
    return path.resolve(root); // Explicit root takes precedence
  }
  // Fall back to inferring from config file location
  return inferRootFromConfig(flags?.config);
}

Example of consistent environment handling:

// Good: Build-time constant for libraries
if (__DEV__ && !alreadyWarned[message]) {
  console.warn(message);
}

// Good: Runtime environment for CLI tools
process.env.NODE_ENV = process.env.NODE_ENV ?? 
  (command === "dev" ? "development" : "production");

This ensures predictable behavior and reduces confusion when the same configuration concepts are used in different parts of the system.

---

Guarantee cleanup execution

When implementing features that require cleanup or state restoration, always use try-finally blocks to ensure cleanup code executes even when errors occur. This pattern prevents resources from being leaked, components from becoming stuck in intermediate states, and operations from remaining incomplete after exceptions.

For example, instead of:

if (element._isSpecial) {
  element._beginOperation()
}
performComplexAction()
if (element._isSpecial) {
  element._endOperation()
}

Use the more robust pattern:

const isSpecial = !!element._isSpecial
try {
  if (isSpecial) {
    element._beginOperation()
  }
  performComplexAction()
} finally {
  if (isSpecial) {
    element._endOperation()
  }
}

This approach:

• Prevents components from remaining in an inconsistent state if errors occur
• Ensures all resources are properly released
• Makes your code more resilient to unexpected failures
• Maintains proper balance of paired operations (begin/end, open/close)

When handling multiple cleanup operations, consider whether to wrap each in its own try-catch to prevent one failure from blocking other cleanups, especially in shutdown sequences.

---

Use Existing Abstractions

Prefer existing framework/library abstractions for both types and layout styling to avoid redundant code and one-off visual tweaks.

• Types: If the framework exposes a prop type, reuse it instead of introducing a duplicate interface.
• Spacing/Layout: Apply spacing at the container/layout level and make breakpoint-specific changes explicit (e.g., mobile-only), rather than removing padding/margins on a deeper inner element.

Example:

"use client";

import Image, { type ImageProps } from "next/image";

type SidebarLogoProps = ImageProps; // reuse library type

export function SidebarLogo(props: SidebarLogoProps) {
  return (
    <div className="mb-2 md:mb-0"> {/* spacing controlled at container */}
      <Image {...props} />
    </div>
  );
}

Apply this during review by checking: (1) are we duplicating types already provided by the dependency? (2) are spacing changes implemented in a maintainable place (container/layout + explicit responsive behavior) rather than ad hoc on an inner div?

---

Enforce style with linters

Use automated linting tools to enforce consistent code style across the project, but be deliberate about which rules to include or exclude. When adding new linters or rules, evaluate their impact on the codebase before fully adopting them.

For configuration files like pyproject.toml:

[tool.ruff]
select = [
    'D1',     # pydocstyle
    'PIE',    # flake8-pie
]
# Ignore rules with explicit reasoning
ignore = ['D105', 'D107', 'PIE804']  # Document exceptions with comments

When making style-related changes, prefer solutions that can be automatically enforced rather than relying on manual review. Consider adding appropriate pre-commit hooks for consistent formatting. If a tool would generate too many changes at once (like the discussed toml-fmt), consider gradual adoption or documenting the manual style requirements clearly.

---

Keep configurations current

Always use the latest stable and supported versions in configuration files. This applies to runtime environments, build plugins, and dependencies. Outdated configurations can limit functionality, miss security updates, or prevent access to newer features.

For runtime environments:

# AVOID
Properties:
  Handler: io.quarkus.funqy.lambda.FunqyStreamHandler::handleRequest
  Runtime: java8

# PREFER
Properties:
  Handler: io.quarkus.funqy.lambda.FunqyStreamHandler::handleRequest
  Runtime: java17  # Or java21 if supported

For build plugins and dependencies, regularly evaluate if newer alternatives provide better functionality or consolidate multiple tools:

• Consider tools that solve multiple problems (e.g., “spot covering impsort-maven-plugin”)
• Verify license compatibility when introducing new configuration dependencies
• Look for options that “go beyond whitespaces fixing real issues and flaws”

Periodically review all configuration files as part of your maintenance routine to ensure they reflect current best practices and supported versions.

---

Precise type annotations

Always use the most specific and accurate type information possible in PHPDoc comments to improve static analysis, IDE autocompletion, and code clarity. Pay special attention to array types using appropriate syntax:

• For associative arrays with string keys: array<string, mixed> instead of just array
• For arrays of strings: string[] rather than generic array
• For complex generics: maintain template type parameters like Collection<int, TPivotModel>
• For method parameters accepting string or array of strings: string|string[] instead of string|array

Include full namespaces in type references (e.g., \Illuminate\Support\Collection instead of just Collection).

When documenting specialized types, use appropriate annotations:

/**
 * Get JSON casting flags for the specified attribute.
 *
 * @param  string  $key
 * @return int-mask-of<JSON_*>
 */
protected function getJsonCastingFlags($key)

Precise type annotations help both developers and tools understand your code better, reducing potential errors and improving maintainability.

---

Enforce atomic database operations

Replace check-then-act patterns with atomic database operations to prevent race conditions in concurrent environments. Use transactions for multi-step operations and leverage database-level constraints instead of application-level checks.

Example - Transform this race-prone code:

// DON'T: Check-then-act pattern
const existing = await prisma.newsletter.findUnique({
  where: { email_userId: { email, userId } }
});
if (!existing?.analyzed) {
  await prisma.newsletter.create({
    data: { email, userId, analyzed: true }
  });
}

Into atomic operation:

// DO: Use upsert for atomic operation
await prisma.newsletter.upsert({
  where: { email_userId: { email, userId } },
  update: { analyzed: true },
  create: { email, userId, analyzed: true }
});

// DO: Use transactions for multi-step operations
await prisma.$transaction(async (tx) => {
  const result = await tx.newsletter.findUnique({/*...*/});
  if (result) {
    await tx.newsletter.update({/*...*/});
  }
});

Key practices:

• Use upsert instead of separate find/create
• Wrap related operations in transactions
• Handle unique constraint violations (e.g., Prisma P2002 errors)
• Add database-level constraints rather than relying on application checks
• Consider using advisory locks for complex operations

---

Cleanup error handling

When handling resources that require cleanup (like streams, connections, or transactions), ensure that errors during the cleanup phase don’t overshadow or silently replace the original error. This applies to both try-with-resources and traditional try/finally blocks.

Key practices:

1. For critical cleanup operations that might fail, catch and log errors rather than letting them propagate and possibly mask the original exception.
2. Use try-with-resources only when appropriate - consider whether exceptions from close() should be suppressed or logged.
3. When errors occur in cleanup phases of transactions or connection management, log them at an appropriate level but don’t throw new exceptions.
4. Preserve the original cause when wrapping exceptions.

Example of good error handling during cleanup:

// Handle errors in cleanup without losing original exception
Mono<Void> safeCleanupStep(String stepDescription, Mono<Void> stepMono) {
    if (!logger.isDebugEnabled()) {
        return stepMono.onErrorComplete();
    }
    return stepMono
        .doOnError(e -> logger.debug(String.format("Error ignored during %s: %s", 
                                                  stepDescription, e)))
        .onErrorComplete();
}

// Usage in transaction cleanup
if (shouldDoCleanup) {
    Mono<Void> step = safeCleanupStep("transaction cleanup", 
                                      cleanupOperation());
    afterCleanup = afterCleanup.then(step);
}

When using traditional try/finally blocks, explicitly catch and log exceptions in the finally block:

InputStream in = null;
try {
    in = resource.getInputStream();
    // Process the stream...
    return result;
}
catch (Exception ex) {
    // Handle primary operation exception
    throw ex;
}
finally {
    if (in != null) {
        try {
            in.close();
        }
        catch (IOException ex) {
            // Log but don't throw to avoid masking original exception
            logger.warn("Error closing resource", ex);
        }
    }
}

Remember that try-with-resources doesn’t silently swallow exceptions from close() methods - they’re suppressed but attached to the primary exception, so choose this pattern carefully based on your error handling needs.

---

Avoid request-path blocking

Minimize blocking operations in request-handling paths to ensure responsive application performance. Implement caching and asynchronous processing for expensive operations to reduce latency and improve throughput.

When implementing APIs and services:

1. Cache external service calls to avoid repeated expensive operations. For authentication services like LDAP, enable caching to prevent roundtrips on every request:

   quarkus.security.ldap.cache.enabled=true
   

2. Use asynchronous operations for tasks that could block requests. For example, configure asynchronous token refreshing instead of having clients wait during the request cycle:

   # Configure asynchronous token refresh rather than blocking during requests
   quarkus.oidc-client.async-refresh=true
   

3. Choose efficient API methods that avoid hidden performance costs. Select methods without unnecessary internal handlers or callbacks: ```java // Less efficient: registers a reply handler internally bus.requestAndForget(“greeting”, name)

// More efficient: direct send without handler overhead bus.send(“greeting”, name)

Remember to consider the trade-offs: caching improves performance but introduces staleness (e.g., LDAP cache has a default max-age of 60s), while asynchronous operations add complexity but maintain responsiveness.

---

## accessibility interaction security

<!-- source: mastodon/mastodon | topic: Security | language: TSX | updated: 2025-06-13 -->

Ensure that accessibility features do not create security vulnerabilities by allowing unintended interactions or providing misleading information to assistive technologies. This includes proper ARIA attribute usage and ensuring hidden or inactive elements are truly inaccessible.

Key practices:
1. **Choose appropriate ARIA attributes**: Use `aria-describedby` for plain text descriptions and `aria-details` for complex content that requires navigation
2. **Make inactive elements inert**: Use the `inert` attribute on hidden or inactive UI elements (like carousel slides) to prevent screen reader interaction
3. **Test with assistive technologies**: Verify that custom emojis, images, and interactive elements provide appropriate feedback to screen readers

Example of proper implementation:
```tsx
// Good: Inactive carousel slides are made inert
<animated.div
  className='featured-carousel__slide'
  data-index={index}
  inert={index !== slideIndex}
>
  <StatusContainer id={statusId} />
</animated.div>

// Good: Appropriate ARIA attribute for text content
<button
  aria-describedby={descriptionId}
  onClick={onClick}
>
  Show content
</button>
<p id={descriptionId}>{textContent}</p>

This prevents accessibility-related security issues where users might inadvertently interact with hidden elements or receive incorrect information through assistive technologies.

---

avoid deprecated SASS syntax

Always use modern SASS and CSS syntax instead of deprecated functions to ensure future compatibility and avoid build warnings. Replace deprecated division operators with calc() or math.div(), and use native CSS functions instead of deprecated SASS color functions.

Common deprecated patterns to avoid:

• Division with / operator: margin: (24px - 12px) / 2;
• SASS color functions like lighten(): fill='#{hex-color(lighten($ui-base-color, 12%))}'

Use these modern alternatives instead:

• For division: margin: calc((24px - 12px) / 2); or margin: math.div(24px - 12px, 2);
• For color manipulation: Use CSS color mixing or native CSS color functions

This prevents deprecation warnings during builds and ensures your stylesheets remain compatible with future SASS versions. When you encounter deprecation warnings, address them immediately rather than deferring the updates.

---

Isolate DOM security boundaries

When developing UI components, establish clear DOM manipulation boundaries to prevent security risks. Components that modify aria attributes (like aria-hidden) on parent or ancestor elements can create security vulnerabilities by unexpectedly exposing content that was intentionally hidden from assistive technologies or hiding content that should be accessible.

For example, in the code below, removing aria-hidden attributes from ancestor elements might expose content that was intentionally hidden for security reasons:

// Risky pattern - modifies DOM outside component boundaries
function ariaHiddenElements(container, mountElement, currentElement, elementsToExclude, show) {
  let current = container;
  
  while (current != null && html !== current) {
    // Traversing up the DOM tree
    for (let i = 0; i < current.children.length; i += 1) {
      // Removing aria-hidden could expose sensitive content
      if (isPreviousElement && !isNotExcludedElement && show) {
        ariaHidden(element, !show); // Removes aria-hidden
      }
    }
    current = current.parentElement;
  }
}

Instead, limit aria attribute modifications to elements within your component’s scope, or provide clear documentation and configuration options if cross-boundary modifications are necessary for functionality. If you must modify parent elements, implement a tracking mechanism to distinguish between attributes set by your component versus those set intentionally by developers for security purposes.

---

Parameter interaction design

Design APIs with clear parameter interactions and priority rules to create intuitive interfaces. When multiple parameters could affect the same behavior, establish and document a consistent priority order rather than making parameters conditionally required.

Consider this Modal component example:

// Good: Clear parameter priority without conditional requirements
const resolvedContainer = disablePortal
  ? ((mountNodeRef.current ?? modalRef.current)?.parentElement ?? getDoc().body)
  : getContainer(container) || getDoc().body;

This approach gives disablePortal priority over container without requiring users to provide container when using disablePortal.

Avoid redundant type definitions when parameters are inherited. For example, don’t redefine callbacks in component props if they’re already defined in a hook that the component extends. Instead, rely on the type hierarchy to provide proper documentation and type checking:

// Avoid: Redundant type definition
interface AutocompleteProps extends UseAutocompleteProps {
  // Already defined in UseAutocompleteProps
  onScrollToBottom?: (event: React.SyntheticEvent) => void;
}

Always document parameter interactions and priorities clearly in component and function API references to help developers understand the expected behavior.

---

prefer Kotlin idioms

Use Kotlin-specific constructs and syntax patterns instead of Java-style code to improve readability and maintainability. This includes leveraging Kotlin’s expressive syntax features and standard library functions.

Key practices to follow:

Expression body syntax for simple functions:

// Instead of
override fun contentType(): MediaType? {
    return responseBody.contentType()
}

// Use
override fun contentType(): MediaType? = responseBody.contentType()

Kotlin collection builders:

// Instead of
ArrayList<JavaModuleWrapper>().apply { ... }

// Use
buildList { ... } or mutableListOf()

When expressions for complex conditionals:

// Instead of multiple if-else chains
return when (value) {
    null -> ReadableType.Null
    is Boolean -> ReadableType.Boolean
    is Number -> ReadableType.Number
    else -> ReadableType.Null
}

Properties over getter methods:

// Instead of
fun getLifecycleState(): LifecycleState = state

// Use
val lifecycleState: LifecycleState
    get() = state

Functional interfaces:

// Use fun interface to enable lambda syntax
public fun interface BatchEventDispatchedListener {
    fun onBatchEventDispatched()
}

Kotlin string builders:

// Instead of StringBuilder
// Use
buildString { ... }

These patterns make code more concise, readable, and leverage Kotlin’s strengths while reducing boilerplate compared to Java-style implementations.

---

Document code rationale

Add clear comments that explain the “why” behind non-obvious code decisions, complex logic, or special-case handling. This is especially important when:

• Implementing conditional logic that isn’t self-explanatory
• Creating helper functions with non-obvious purposes
• Working with complex subsystems like type handling or schema generation
• Adding warnings or deprecation notices
• Overriding methods with potential side effects

Good documentation reduces cognitive load for future readers, prevents accidental breakage during refactoring, and provides context when switching between specialized domains.

For example, instead of:

def _add_unique_postfix(name: str):
    """Used to prevent namespace collision."""
    # implementation

Write:

def _add_unique_postfix(name: str):
    """Used to prevent namespace collision when resolving forward references.
    
    This is necessary because we might encounter the same named reference in 
    different modules, and without unique postfixes, references from different
    contexts could be incorrectly resolved to the same object.
    """
    # implementation

Similarly, when implementing complex operations like schema cleaning or discriminator handling, include explanations with basic examples that help readers understand the underlying principles and reasons behind the implementation approach.

---

Optimize computational complexity

Identify and reduce computational complexity in your code by minimizing redundant operations and simplifying algorithms. Focus especially on code that processes large datasets or is called frequently.

Key practices:

1. Reduce redundant operations, especially in loops and function calls:

   # Inefficient - O(2N+1) function calls
   for obj in objs:
       filter_kwargs = get_filter_kwargs_for_object(obj)
       # ...process...
       filter_kwargs = get_filter_kwargs_for_object(obj)  # Called again!
          
   # Optimized - O(N) function calls
   for obj in objs:
       filter_kwargs = get_filter_kwargs_for_object(obj)
       # ...use filter_kwargs throughout...
   

2. Use appropriate data structures to improve access patterns:

   # Creating a lookup map for faster access
   max_orders_map = {
       tuple(key_values): max_order
       for key_values, max_order in zip(keys, values)
   }
   # Now O(1) lookups instead of repeated O(n) searches
   

3. Simplify complex conditionals without sacrificing functionality:

   # Verbose approach
   if isinstance(rel, ForeignKey) or isinstance(rel, OneToOneField):
       # do something
      
   # Simplified equivalent
   if isinstance(rel, (ForeignKey, OneToOneField)):
       # do something
   

4. Choose algorithms with appropriate complexity for your data size:

   # Less efficient for large datasets (potentially O(n²))
   return min(desired_types, key=lambda t: self.accepted_types.index(t[0]))[1]
      
   # More efficient direct comparison (O(n))
   return max(desired_types, key=lambda t: t[0].quality)[1]
   

Remember that the most important optimizations target the inner loops and frequently called functions. Document the time and space complexity of critical algorithms to help future developers understand performance considerations.

---

Optimize collection operations

When processing collections of data, choose efficient algorithms and data structures that minimize computational complexity. Use appropriate array methods (filter, find, map, reduce) and consider batching operations when possible.

Key principles:

• Use find() for single item searches instead of filtering entire arrays
• Leverage Map for deduplication and fast lookups by key
• Batch operations when processing multiple items to reduce API calls or iterations
• Consider the scope and context when searching collections to limit search space

Example from the codebase:

// Efficient: Use find() for single item lookup
const localVariable = scopedVariables.find((v) => v.name === prefix);

// Efficient: Use Map for deduplication
const baseVariables = Array.from(new Map([...jitVariables, ...variables].map((item) => [item.name, item])).values());

// Efficient: Batch operations instead of individual updates
const bulkUpdatePreferences = (preferences: Preference[]) => async (channels: ChannelPreference) => {
  await novu.preferences.bulkUpdate(
    preferences.map((el) => {
      const channelsToUpdate = Object.keys(channels)
        .filter((channel) => oldChannels.includes(channel))
        .reduce((acc, channel) => {
          acc[channel] = channels[channel];
          return acc;
        }, {});
      return { preference: el, channels: channelsToUpdate };
    })
  );
};

This approach reduces time complexity and improves performance, especially when dealing with large datasets or frequent operations.

---

Avoid unnecessary operations

Check conditions early to skip unnecessary processing and reuse computed values where possible to optimize performance. This reduces CPU cycles and improves execution speed, especially in performance-critical code paths.

Early condition checking example:

# Less performant approach
def process_value(assigned_value):
    # Perform expensive operations regardless of value state
    result = complex_calculation(assigned_value)
    if assigned_value is PydanticUndefined:
        return default_value
    return result

# More performant approach
def process_value(assigned_value):
    # Early check avoids unnecessary processing
    if assigned_value is PydanticUndefined:
        return default_value
    result = complex_calculation(assigned_value)
    return result

Value caching example:

def get_schema(cls: type) -> Schema:
    # Check if schema already exists before regenerating
    schema = cls.__dict__.get('__schema__')
    if (
        schema is not None
        and not isinstance(schema, MockSchema)
        and conditions_for_reuse_met(cls)
    ):
        return schema
    
    # Only build new schema when necessary
    return build_new_schema(cls)

Apply these patterns whenever you find yourself performing expensive operations that might be unnecessary based on input conditions or when values can be safely reused across calls.

---

Cross-platform CI validation

Always verify that code changes work across all CI platforms before submitting. When addressing a CI issue for one platform, ensure your fix doesn’t break other environments. Common cross-platform CI issues include:

1. Missing includes: Add all necessary includes required by different compilers/platforms.

   // Add includes needed by all platforms, even if your primary dev environment doesn't require them
   #include <array>  // Required by Node.js CI
   

2. Unused code: Either remove unused code, move it to an appropriate implementation file, or conditionally compile it for specific platforms.

   #ifdef PLATFORM_DARWIN
   // Darwin-specific implementation
   #endif
   

3. Build configuration: Make build parameters configurable rather than hardcoded.

   // In config.bzl or equivalent
   BUILD_MODE = "bazel"  // Can be configured per developer or environment
   

When CI fails on any platform, investigate thoroughly and implement a solution that works across all environments. This prevents development bottlenecks from recurring platform-specific issues and ensures consistent behavior across the entire build pipeline.

---

Pin dependency versions

Always pin dependency versions by removing caret (^) and tilde (~) prefixes in package.json files to prevent build failures and ensure consistency across different environments and packages in a monorepo.

Version ranges can cause unexpected issues when different packages resolve to different minor or patch versions of the same dependency, leading to build failures, API incompatibilities, or subtle runtime bugs. This is especially critical in monorepo setups where multiple packages may depend on the same library.

Example of problematic versioning:

{
  "dependencies": {
    "react-icons": "^5.0.1",
    "@nestjs/common": "^10.4.1"
  }
}

Example of properly pinned versions:

{
  "dependencies": {
    "react-icons": "5.0.1",
    "@nestjs/common": "10.4.1"
  }
}

For complex scenarios involving peer dependencies, leverage package manager features like PNPM overrides to ensure consistent version resolution across production and development environments.

---

platform API consistency

When implementing cross-platform functionality, prioritize consistency and avoid replicating platform-specific bugs or inconsistencies. Consider the broader architectural impact of API choices, especially when they require significant migrations or affect multiple components.

For example, when choosing between platform-specific APIs (like AndroidX ComponentActivity.enableEdgeToEdge()) versus custom implementations, evaluate:

• Migration scope and complexity across the codebase
• Consistency requirements across different UI contexts (Activities, Dialogs, Modals)
• Whether platform-specific behaviors should be replicated or corrected

// Avoid replicating iOS bugs for the sake of parity
if (data.mAnimated) {
  scrollView.reactSmoothScrollTo(data.mDestX, data.mDestY);
  scrollView.handleSmoothScrollMomentumEvents(); // Only for animated scrolls
} else {
  scrollView.scrollTo(data.mDestX, data.mDestY);
  // Don't emit momentum events for non-animated scrolls
}

Note: These discussions focus on UI/platform concerns rather than networking protocols, which suggests a category mismatch in the analysis request.

---

Verify token security level

When refreshing or updating authentication tokens, always verify the new token maintains or exceeds the original token’s security level. This applies to WebSocket connections, step-up authentication scenarios, or any case where tokens are refreshed during an active session.

For security integrity, implement these essential checks:

1. Verify principal identity remains consistent (same user)
2. Confirm required roles and permissions are preserved
3. Validate that Authentication Context Class Reference (ACR) values meet or exceed requirements

// Example for WebSocket token refresh
@OnTextMessage
String processMessage(RequestDto request) {
    // 1. Verify same principal/subject
    if (!securityIdentity.getPrincipal().getName().equals(newTokenPrincipal)) {
        throw new SecurityException("Principal mismatch during token refresh");
    }
    
    // 2. Re-apply security checks with new token
    if (!hasRequiredRoles(newToken, originalRequiredRoles)) {
        throw new SecurityException("Insufficient privileges in new token");
    }
    
    // 3. Check ACR values for step-up authentication
    if (requiredAcr != null && !newToken.getClaim("acr").contains(requiredAcr)) {
        throw new SecurityException("Required authentication level not met");
    }
    
    // Update token only after all checks pass
    webSocketSecurity.updateSecurityIdentity(newToken);
}

Failing to verify these security properties when refreshing tokens could allow privilege escalation or unauthorized access if a compromised or less-privileged token replaces a more secure one.

---

batch similar operations

When performing multiple similar operations (database queries, Redis calls, job enqueues, or data lookups), batch them together or eliminate redundancy to reduce overhead and improve performance.

Common patterns to optimize:

• Job enqueueing: Use perform_bulk instead of multiple perform_async calls
• Redis operations: Pipeline multiple Redis commands instead of separate round-trips
• Data lookups: Cache or memoize results to avoid repeated parsing/querying
• Duplicate operations: Reuse lookup results instead of performing the same operation multiple times

Example transformation:

# Before: Multiple individual operations
@domain_block_event.affected_local_accounts.find_each do |account|
  LocalNotificationWorker.perform_async(account.id, event.id, 'AccountRelationshipSeveranceEvent', 'severed_relationships')
end

# After: Batched operations
notification_jobs_args = []
@domain_block_event.affected_local_accounts.find_in_batches do |accounts|
  accounts.each do |account|
    notification_jobs_args.push([account.id, event.id, 'AccountRelationshipSeveranceEvent', 'severed_relationships'])
  end
  LocalNotificationWorker.perform_bulk(notification_jobs_args)
  notification_jobs_args.clear
end

This approach reduces network round-trips, memory usage, and processing overhead while maintaining the same functionality.

---

Use contextually descriptive names

Names should clearly indicate their purpose and context to avoid confusion, especially when similar concepts exist in the same scope. Generic names like “api”, “params”, or “arg1” create ambiguity and make code harder to understand. Instead, use specific, meaningful identifiers that describe what they represent or do.

Examples of improvements:

• Change generic labels like “expand”/”collapse” to contextual ones like “Expand/collapse lists menu”
• Replace confusing names like params (which resembles useParams hook) with descriptive alternatives like target
• Use meaningful parameter names like index instead of generic arg1, arg2
• Replace non-specific names like api with descriptive alternatives that indicate their actual purpose

This practice becomes especially important when multiple similar concepts exist in the same scope, as clear naming prevents confusion and improves code maintainability.

---

Configure CSS layers

When integrating Material UI with other styling solutions like Tailwind CSS v4, proper configuration of CSS layers is essential to ensure correct style precedence and override behavior.

Follow these framework-specific steps to enable and configure CSS layers:

1. Client-side applications (Vite/SPA):

   import { StyledEngineProvider } from '@mui/material/styles';
   import GlobalStyles from '@mui/material/GlobalStyles';
   
   ReactDOM.createRoot(document.getElementById('root')!).render(
     <React.StrictMode>
       <StyledEngineProvider enableCssLayer>
         <GlobalStyles styles="@layer theme, base, mui, components, utilities;" />
         {/* Your app */}
       </StyledEngineProvider>
     </React.StrictMode>,
   );
   

2. Next.js App Router:

   import { AppRouterCacheProvider } from '@mui/material-nextjs/v15-appRouter';
   import GlobalStyles from '@mui/material/GlobalStyles';
   
   export default function RootLayout() {
     return (
       <html lang="en" suppressHydrationWarning>
         <body>
           <AppRouterCacheProvider options={{ enableCssLayer: true }}>
             <GlobalStyles styles="@layer theme, base, mui, components, utilities;" />
             {/* Your app */}
           </AppRouterCacheProvider>
         </body>
       </html>
     );
   }
   

3. Next.js Pages Router:

   import { AppCacheProvider } from '@mui/material-nextjs/v15-pagesRouter';
   import GlobalStyles from '@mui/material/GlobalStyles';
   
   export default function MyApp(props: AppProps) {
     const { Component, pageProps } = props;
     return (
       <AppCacheProvider {...props}>
         <GlobalStyles styles="@layer theme, base, mui, components, utilities;" />
         <Component {...pageProps} />
       </AppCacheProvider>
     );
   }
   

Always ensure that the mui layer comes before the utilities layer so that utility classes can properly override Material UI styles without using the !important directive.

---

prefer early returns

Use early returns and guard clauses to reduce nested conditionals and improve code readability. This pattern makes the main logic flow clearer by handling edge cases upfront and avoiding deeply nested if-else structures.

Instead of complex nested conditions:

const handleClick = (e: MouseEvent) => {
  const target = (e.target as HTMLElement).closest('a');
  
  if (e.button !== 0 || e.ctrlKey || e.metaKey) {
    return;
  }
  
  if (isHashtagLink(target)) {
    // main logic here with multiple nested conditions
    if (condition1) {
      if (condition2) {
        // deeply nested logic
      }
    }
  }
};

Prefer early returns to flatten the structure:

const handleClick = (e: MouseEvent) => {
  const target = (e.target as HTMLElement).closest('a');
  
  if (e.button !== 0 || e.ctrlKey || e.metaKey) {
    return;
  }
  
  if (!isHashtagLink(target)) {
    return;
  }
  
  if (!condition1) {
    return;
  }
  
  if (!condition2) {
    return;
  }
  
  // main logic here at the top level
};

This approach also applies to component logic where complex conditional rendering can be simplified by handling edge cases early and returning null or alternative components before the main render logic.

---

Write user-centric documentation guides

Documentation should be written with the user’s perspective in mind, using clear, action-oriented language and intuitive organization. Follow these principles:

1. Use active voice and direct “you” statements instead of passive voice
2. Structure content with informative question-based headers that anticipate user needs
3. Provide complete, self-contained examples that can be copied and used directly
4. Write one sentence per line for better readability and maintainability

Example:

- ## Overview
- The component can be configured with various options that are found in the API documentation.
+ ## How do I configure the component?
+ You can customize the component using these key options:
+ 
+ 1. Set the `variant` prop to change the visual style
+ 2. Use the `size` prop to adjust dimensions
+ 3. Add the `disabled` prop to control interactivity
+
+ ```jsx
+ // Complete, ready-to-use example
+ import { Button } from '@mui/material';
+ 
+ export default function CustomButton() {
+   return (
+     <Button
+       variant="contained"
+       size="large"
+       disabled={false}
+     >
+       Click me
+     </Button>
+   );
+ }
+ ```

---

minimize public API surface

Carefully evaluate whether functionality needs to be exposed as public API. Keep implementations private when they’re only used internally, and avoid creating public APIs that increase maintenance burden without clear benefit.

Before exposing new public APIs, consider:

• Can the functionality be handled with existing patterns (e.g., platform checks in JavaScript instead of native module calls)?
• Is this API only used internally and can remain private?
• Are experimental APIs properly gated behind feature flags?
• Will adding parameters break API stability for existing callers?

Example from the codebase:

// Instead of exposing this in the header as public API:
RCT_EXTERN UIDeviceOrientation RCTDeviceOrientation(void);

// Keep it private in the .mm file since it's only used internally:
static UIDeviceOrientation RCTDeviceOrientation(void) {
  // implementation
}

For experimental features, use feature flags rather than exposing unstable APIs:

// Experimental APIs should be clearly marked and gated
textInputEventEmitter.experimental_flushSync([state = _state, data = std::move(data)]() mutable {
  // experimental functionality
});

This approach reduces maintenance overhead, prevents API bloat, and gives teams flexibility to refactor internal implementations without breaking public contracts.

---

Database type best practices

Select appropriate data types and defaults for database columns to ensure data integrity and simplify application code. For timestamp columns, use timezone-aware types (TIMESTAMPTZ) when working across different timezones or with UTC offsets. For ID columns, configure auto-generation at the database level using functions like gen_random_uuid() rather than relying on application code to generate identifiers.

CREATE TABLE "Entity" (
  -- Auto-generated UUID for primary key
  "id" TEXT NOT NULL DEFAULT gen_random_uuid(),
  -- Timezone-aware timestamps for accurate time handling
  "createdAt" TIMESTAMPTZ(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
  "updatedAt" TIMESTAMPTZ(3) NOT NULL,
  -- Other columns
  "name" TEXT NOT NULL,
  -- JSON for flexible structured data
  "metadata" JSONB
);

This approach reduces bugs related to timezone confusion, simplifies code by delegating ID generation to the database, and ensures consistent handling of data types across the application.

---

Document dependency versions

When managing dependency versions in configuration files, provide clear documentation to help maintainers understand version choices and relationships. Include links to repositories where versions can be verified, keep related versions aligned when appropriate, and add explanatory comments for version-related decisions.

Examples of good practices:

1. Add repository links for easier version checking: ```xml

1.69.1

2. Explain dependencies between related versions:
```xml
<grpc.version>1.69.1</grpc.version> <!-- when updating, verify if com.google.auth and perfmark.version should not be updated too -->

1. When relocating version properties, provide clear location comments:

   <!--jakarta.persistence-api.version is located in the root pom -->
   

2. Document the rationale for version alignment or divergence between related components: ```xml

9.0.1 9.0.1

Clear version documentation reduces maintenance burden, prevents accidental version mismatches, and helps team members understand the reasoning behind specific version choices.

---

## Test network performance

<!-- source: ant-design/ant-design | topic: Networking | language: JavaScript | updated: 2025-06-10 -->

Always validate network performance and connectivity before suggesting alternative endpoints or making routing decisions. Implement timeout-based checks to ensure alternatives are actually faster or more accessible for the user's specific network conditions.

When offering mirror sites, CDN alternatives, or fallback endpoints, first test the current connection quality and the proposed alternative's performance. This prevents suggesting slower alternatives to users who may have different network conditions (e.g., overseas users accessing domestic mirrors).

Example implementation:
```javascript
function checkMirrorAvailable(timeout = 1500) {
  return new Promise((resolve) => {
    const img = new Image();
    let done = false;
    img.onload = () => {
      if (!done) {
        done = true;
        resolve(true);
      }
    };
    img.onerror = () => {
      if (!done) {
        done = true;
        resolve(false);
      }
    };
    img.src = `https://mirror.example.com/test-resource?_t=${Date.now()}`;
    setTimeout(() => {
      if (!done) {
        done = true;
        resolve(false);
      }
    }, timeout);
  });
}

This approach ensures network routing decisions are based on actual performance data rather than assumptions about user location or network conditions.

---

Place configurations appropriately

Choose the right location and scope for your Rails configuration options to improve maintainability and clarity:

1. Use appropriate namespaces - For truly global configurations, place them on the module rather than on a specific class: ```ruby

   Preferred for global settings

   ActiveRecord.configuration_option = value

Avoid for global settings

ActiveRecord::Base.configuration_option = value

2. **Use environment-specific files** for environment-specific configurations:
```ruby
# config/environments/development.rb
config.active_record.verbose_query_logs = true

1. Use load hooks for adapter-specific configurations:

   # config/application.rb or an initializer
   ActiveSupport.on_load(:active_record_postgresqladapter) do
     self.datetime_type = :timestamptz
   end
   

2. Prefer simplified syntax when available: ```ruby

   Instead of

   config.yjit = true config.yjit_options = { stats: true }

Prefer

config.yjit = { stats: true }

Using appropriate configuration placement improves organization, reduces conflicts between environments, and makes your application more maintainable.

---

## Use proper documentation format

<!-- source: facebook/react-native | topic: Documentation | language: Kotlin | updated: 2025-06-09 -->

Use the appropriate documentation format for the target programming language. In Kotlin files, use KDoc formatting instead of Javadoc formatting for consistency and proper tooling support.

**Key differences:**
- Use `[ClassName]` instead of `{@link ClassName}` for type references
- Use `[Runnable]` instead of `{@code Runnable}` for code references  
- Avoid dots before method names in references (use `[setApplication]` not `[.setApplication]`)

**Example:**
```kotlin
// ❌ Incorrect (Javadoc style in Kotlin)
/**
 * Throws an {@link AssertionException} if the current thread is not the UI thread.
 * Before calling build, the following must be called:
 * * [.setApplication]
 */

// ✅ Correct (KDoc style in Kotlin)  
/**
 * Throws an [AssertionException] if the current thread is not the UI thread.
 * Before calling build, the following must be called:
 * * [setApplication]
 */

This ensures documentation renders correctly in IDEs and documentation generators, and maintains consistency with language conventions.

---

Precise Validation Documentation

When documenting inputs/validators, explicitly state (a) the units/meaning of any parameters (e.g., file size units), (b) what is truly validated (syntactic/format via regex vs semantic correctness), and (c) timezone/offset semantics using unambiguous wording (avoid phrasing that suggests an offset is “missing” when “Z” explicitly means zero offset). This prevents common user misunderstandings and support churn.

Example (documentation style):

// Size constraints are in bytes.
const imageFile = z.file({
  required_error: "file is required",
  invalid_type_error: "This object must be a file",
}).size({ min: 100000, max: 200000 }); // bytes

// These string datetime checks validate the expected ISO format via regex,
// not calendar correctness.
// e.g., the parser may accept a syntactically valid shape even if the date is impossible.
const dt = z.string().datetime(); // ISO 8601; default is UTC zero offset ('Z')

// If you also add date/time helpers, document their format basis and options.
const date = z.string().date(); // ISO short date format
const time = z.string().time(); // 24-hour time of day format

Checklist for contributors:

• Any “size”, “length”, “min/max”, or unit-based parameter: name the unit.
• Any “datetime/date/time” validator: clarify format-vs-correctness behavior.
• Any timezone/offset defaults: describe how UTC is represented (e.g., via ‘Z’) and avoid ambiguous phrases like “without UTC offset.”

---

avoid Hungarian notation

Do not use Hungarian notation prefixes (like m, s) in variable and field names. Use descriptive, semantic names that clearly indicate the variable’s purpose without encoding type or scope information in the name.

Hungarian notation makes code less readable and goes against Kotlin naming conventions. Instead of prefixing variables with their scope or type, choose names that describe what the variable represents.

Examples:

// ❌ Avoid Hungarian notation
private val mObject: Any? = null
private val sHelperRect: Rect = Rect()
public val mBackingMap: ReadableMap = props
private val mDecoder: CharsetDecoder = charset.newDecoder()

// ✅ Use semantic names
private val value: Any? = null
private val helperRect: Rect = Rect()
public val backingMap: ReadableMap = props
private val decoder: CharsetDecoder = charset.newDecoder()

This applies to all variable types including fields, parameters, and local variables. Focus on choosing names that communicate the variable’s role and meaning in the context of your code.

---

Async resource cleanup guarantees

When implementing async context managers, always ensure proper resource cleanup even during task cancellation. Use try/finally blocks to guarantee that resources are released and context state is properly restored regardless of how execution terminates.

Consider this flawed implementation:

async def __aexit__(self, exc_type, exc_value, traceback):
    # This may never complete if a CancelledError is raised
    await self.connection.aclose()
    await self.cleanup_state()

If a task is cancelled while in this context, aclose() might never be called, leading to connection leaks and inconsistent state. Instead, implement:

async def __aexit__(self, exc_type, exc_value, traceback):
    try:
        # Handle normal cleanup first
        if not exc_type:
            await self.connection.acommit()
        else:
            await self.connection.arollback()
    finally:
        # Always execute these operations, even during cancellation
        await self.connection.aclose()
        await self.cleanup_state()

This pattern ensures that critical cleanup operations always execute, preventing resource leaks when tasks are cancelled. When working with resource pools or connection stacks, this approach is essential to maintain system integrity and prevent gradual resource exhaustion.

Additionally, use distinct naming for async methods (like aclose vs close) rather than overloading, to avoid confusing errors and make debugging easier when async/sync boundaries are crossed incorrectly.

---

Document performance implications

Clearly document the performance implications of features and configurations to help users make informed decisions. Avoid overstating or understating performance impacts. Instead, provide specific context about when certain features might impact performance and in what environments they are appropriate.

For example, when adding a feature with potential performance impact:

# GOOD
# In documentation:
# The :source_location option can slow down query execution, so consider its impact
# if using in production environments where query volume is high.

# BAD
# WARNING: Never use :source_location in production! It will destroy performance!

# BETTER
# When implementing configurable features:
config.feature.enabled = true # in development.rb
config.feature.enabled = false # in production.rb (default)

Consider providing environment-specific defaults for performance-impacting features, making them opt-in for production rather than requiring users to opt-out. When performance tradeoffs exist (like between different checksum algorithms or between observability and optimization), document these tradeoffs to help users select the most appropriate option for their specific use case.

---

Eliminate documentation redundancy

Documentation should be concise and avoid repeating the same information in multiple places. Redundant content confuses readers, makes maintenance more difficult, and can lead to inconsistencies when only one copy gets updated.

When maintaining markdown files, READMEs, implementation plans, or other technical documentation:

1. Check for duplicate information before adding new content
2. Consolidate similar sections into a single, comprehensive section
3. Use cross-references instead of duplicating information
4. Regularly review documentation to identify and eliminate redundancy

Example of documentation improvement:

# Project Setup Guide

## Getting Started
...

- # Redundant Docker instructions
- ```bash
- docker-compose up
- ```

## Official Docker Setup
...

By maintaining a single source of truth for each piece of information, documentation remains clearer, more maintainable, and more trustworthy for all developers on the team.

---

consistent dependency versioning

Maintain consistent version constraint patterns across all dependencies in configuration files and avoid unstable versions that can cause build issues. Use caret (^) constraints uniformly for predictable updates within compatible ranges, and employ resolutions when necessary to prevent automatic resolution to beta or unstable versions.

When package managers resolve to unstable versions, use explicit resolutions to enforce stable versions:

{
  "devDependencies": {
    "@vitest/browser": "^3.2.1",
    "@vitest/coverage-v8": "^3.2.0",
    "@vitest/ui": "^3.2.1"
  },
  "resolutions": {
    "vite": "^6.3.5"
  }
}

This prevents issues like TypeScript compatibility problems from beta releases while maintaining consistent constraint patterns. Remember to remove forced resolutions once stable versions become available.

---

Handle AI operation failures

Always implement proper error handling for AI service operations. AI services can fail due to rate limiting, network issues, or service outages. Wrap AI service calls in try-catch blocks to gracefully handle potential failures, log relevant error information, and provide appropriate fallbacks.

// ❌ Without error handling
const result = await chatCompletionObject({
  userAi: user,
  system,
  prompt,
  schema,
  userEmail: user.email,
  usageLabel: "AI Operation",
});

return result.object;

// ✅ With proper error handling
try {
  const result = await chatCompletionObject({
    userAi: user,
    system,
    prompt,
    schema,
    userEmail: user.email,
    usageLabel: "AI Operation",
  });
  
  logger.trace("Output", { result });
  
  return result.object;
} catch (error) {
  logger.error("AI operation failed", { error });
  return fallbackValue; // Return a sensible default
}

This pattern ensures that AI-dependent features degrade gracefully when AI services are unavailable, preventing unhandled exceptions from propagating and disrupting user experience. Consider defining standardized error handling functions for common AI operation patterns in your codebase.

---

Avoid synchronous main dispatch

Avoid using RCTUnsafeExecuteOnMainQueueSync and similar synchronous main queue dispatch methods as they can cause deadlocks, especially in initialization code, dispatch_once blocks, or when called from background threads that may already hold main queue dependencies.

Deadlocks occur when the main queue is waiting for a background queue, and that background queue then tries to synchronously dispatch back to the main queue. This creates a circular dependency where both queues are blocked waiting for each other.

Instead, use asynchronous alternatives like RCTExecuteOnMainQueue which avoids the jump if already on the main queue, or standard dispatch_async(dispatch_get_main_queue(), ...) when you need to ensure execution at the end of the main queue.

Example of problematic code:

// BAD - Can cause deadlock
- (void)invalidate {
  RCTUnsafeExecuteOnMainQueueSync(^{
    if (_didInvalidate) {
      return;
    }
    // ... invalidation logic
  });
}

Example of safer alternative:

// GOOD - Uses async dispatch to avoid deadlock
- (void)invalidate {
  RCTExecuteOnMainQueue(^{
    if (_didInvalidate) {
      return;
    }
    // ... invalidation logic
  });
}

This pattern is particularly important in React Native’s multi-threaded environment where JavaScript, UI, and background threads frequently interact.

---

Next.js async behavior

Understand and correctly implement the asynchronous behavior of Next.js APIs and components. Follow these guidelines:

1. Add <Suspense> boundaries around components that use hooks that can trigger suspense, such as useSearchParams in the Next.js App Router:

<Suspense>
  <ComponentUsingSearchParams />
</Suspense>

1. Don’t await synchronous Next.js functions. For example, cookies() from ‘next/headers’ returns a synchronous object:

// Incorrect
const cookieStore = await cookies();

// Correct
const cookieStore = cookies();

1. Next.js page props like searchParams are regular objects, not Promises - handle them correctly:

// Incorrect
export default async function Page(props: {
  searchParams: Promise<{ param?: string }>;
}) {
  const searchParams = await props.searchParams;
  // ...
}

// Correct
export default async function Page({ 
  searchParams 
}: {
  searchParams: { param?: string };
}) {
  // ...
}

Correctly identifying when to use asynchronous patterns like Suspense and await improves application stability and performance.

---

environment-aware API usage

Always detect the runtime environment before using environment-specific APIs or utilities. This is crucial for networking applications that may run in browsers, Node.js servers, or cross-platform contexts.

Key practices:

1. Use platform-specific utilities when available (e.g., path.posix.join for consistent path handling)
2. Check for environment-specific globals before accessing them (e.g., typeof window !== 'undefined' && 'CSS' in window before using window.CSS.supports())
3. Use explicit module prefixes for built-in modules (e.g., "node:url" instead of "url" for Node.js built-ins)

Example of proper environment detection:

// Check for browser environment before using browser APIs
if (!this.isServer && typeof window !== 'undefined' && 'CSS' in window) {
  this.isViewTransitionTypesSupported = window.CSS.supports(...)
}

// Use Node.js module prefix for built-in modules
import { fileURLToPath } from 'node:url'

// Use platform-specific path utilities
path.posix.join(routesDirectoryFromRoot, v.filePath as string)

This approach prevents runtime errors and ensures your networking code works reliably across different deployment environments.

---

Respect annotation processing order

When designing Spring components, pay careful attention to the order in which annotations are processed, especially for inheritance scenarios. Spring processes annotations in a specific sequence that can affect bean initialization and override behavior.

1. Ensure interface-level annotations are processed before class-level annotations when appropriate. This ordering allows local annotations to override behavior from inherited interfaces.

// DO: Process interface annotations before local class annotations
for (SourceClass ifc : sourceClass.getInterfaces()) {
    collectImports(ifc, imports, visited);
}
imports.addAll(sourceClass.getAnnotationAttributes(Import.class.getName(), "value"));

1. Validate annotation usage at appropriate scope levels. Throw exceptions when annotations are used at an incorrect scope rather than silently ignoring them:

// DO: Validate annotation usage
if (executionPhase == ExecutionPhase.BEFORE_TEST_CLASS && !isClassLevel) {
    throw new IllegalArgumentException("Class-level phase cannot be used on method-level annotation");
}

1. When managing bean definitions, be cautious about bean overrides. Redefinitions of beans with the same name but different definitions can lead to unpredictable behavior if allowed silently:

// Consider explicitly handling bean definition conflicts
if (!isAllowBeanDefinitionOverriding() && existingDefinition != null 
        && !existingDefinition.equals(beanDefinition)) {
    throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
}

1. When implementing autowiring for components with potential duplicates, prefer clear methods that show the intent rather than relying on Optional parameters:

// Better approach for single-instance configurers
@Autowired(required = false)
void setAsyncConfigurer(AsyncConfigurer asyncConfigurer) {
    if (asyncConfigurer != null) {
        this.executor = asyncConfigurer::getAsyncExecutor;
        this.exceptionHandler = asyncConfigurer::getAsyncUncaughtExceptionHandler;
    }
}

---

Optimize common search paths

Implement dedicated fast paths for common search patterns while maintaining a complete fallback path for edge cases. This optimization pattern significantly improves performance for frequent operations while ensuring correctness for all scenarios.

Key implementation guidelines:

1. Identify the most common usage patterns
2. Create type-specific or pattern-specific fast paths
3. Maintain a complete fallback path for edge cases
4. Consider adding configuration options for traversal depth

Example:

function optimizedSearch(values, target) {
  // Fast path for primitive type comparisons
  if (typeof target === 'number' || typeof target === 'string') {
    return values.includes(target)
  }

  // Fast path for same-type objects
  if (values.some(v => typeof v === typeof target)) {
    return values.some(v => String(v) === String(target))
  }

  // Fallback path for complex comparisons
  return values.some(v => looseEqual(v, target))
}

This pattern is especially valuable in framework code where the same operations are performed frequently. The fast paths handle common cases efficiently while the fallback ensures correctness for all scenarios.

---

Use proper logging

Always use the project’s standard logging system (mbgl::Log) with appropriate log levels instead of ad-hoc solutions like std::cout, printf, or custom logging macros. This ensures consistent log formatting, proper filtering, and integration with test frameworks.

Key guidelines:

1. Use mbgl::Log with the appropriate event type and level:

   // Instead of:
   // std::cout << "-------- HASTILE - FOUND IN TILES\n";
   // or:
   #if MLN_PLUGIN_LAYER_LOGGING_ENABLED
   std::cout << "Working on: " << name << "\n";
   #endif
   
   // Use:
   Log::Debug(Event::General, "HASTILE - FOUND IN TILES");
   // or for errors:
   Log::Error(Event::OpenGL, "Failed to open X display, retrying...");
   

2. Choose the correct log level based on message importance:
   • Debug: Detailed information useful during development
   • Info: General operational messages
   • Warning: Concerning but non-fatal issues
   • Error: Serious problems that need attention
3. Add logging for error conditions and edge cases to improve visibility:

   if (!checkAndSetMode(Mode::Primitives)) {
       Log::Warning(Event::Render, "Cannot add triangle with current mode");
       return;
   }
   

4. Remove commented-out debug prints from production code or convert them to proper logging calls.

Be mindful that log levels can affect test behavior - some test fixtures may filter specific log levels.

---

Avoid unnecessary allocations

Minimize object creation and memory allocations, especially in frequently called methods and hot code paths, to reduce garbage collection pressure and improve performance.

Key practices:

1. Avoid varargs methods like Objects.hash() in hashCode() implementations for objects that will be used as map keys, as they allocate arrays with each call: ```java // Instead of this: public int hashCode() { return Objects.hash(name, params, returnType); // Creates array allocation }

// Prefer this: public int hashCode() { int result = name.hashCode(); result = 31 * result + params.hashCode(); result = 31 * result + returnType.hashCode(); return result; }

2. Cache method results that would otherwise create new collections on each call:
```java
// Instead of repeatedly calling:
method.parameterTypes().size() // Creates new collection each time

// Cache the result or use alternatives:
int paramCount = method.parametersCount(); // Doesn't create collection

1. Optimize collection creation for small, known sizes:

   // Use specialized factories for small collections:
   this.params = switch (method.parametersCount()) {
    case 0 -> List.of();
    case 1 -> List.of(method.parameterTypes().get(0).name());
    case 2 -> List.of(method.parameterTypes().get(0).name(), method.parameterTypes().get(1).name());
    default -> {
        List<DotName> ret = new ArrayList<>(method.parametersCount());
        for (Type i : method.parameterTypes()) {
            ret.add(i.name());
        }
        yield ret;
    }
   };
   

2. Create specialized non-collection return methods for hot paths: ```java // Instead of always returning collections: public List<RequestMatch> mapFromPathMatcher(...) { ... }

// Provide specialized method for common cases: public RequestMatch map(String path) { // Direct return without collection creation }

Be conscious of underlying collection implementations when choosing iteration patterns (for-loops vs iterators) as using index-based access on LinkedLists can lead to O(n²) performance.

---

## Collections use plural names

<!-- source: elie222/inbox-zero | topic: Naming Conventions | language: TSX | updated: 2025-06-04 -->

Always use plural names for properties representing collections (arrays/lists) in interfaces, types, and destructuring patterns. This ensures consistency between interface definitions and their usage throughout the codebase.

Example:
```typescript
// ❌ Inconsistent naming
interface DigestEmailProps {
  newsletter?: EmailItem[];  // singular for array
  receipt?: EmailItem[];     // singular for array
}

// ✅ Consistent plural naming
interface DigestEmailProps {
  newsletters?: EmailItem[];  // plural matches array type
  receipts?: EmailItem[];    // plural matches array type
}

// Usage remains consistent with interface
const { newsletters, receipts } = props;

This convention:

• Makes array types immediately recognizable
• Prevents confusion between single items and collections
• Reduces bugs from property name mismatches
• Follows common JavaScript/TypeScript conventions

---

Organize tests for clarity

Structure tests to maximize clarity and maintainability by:

1. Placing related tests together in appropriate test files
2. Using built-in assertion helpers instead of raw assertions
3. Extracting common test helpers when patterns emerge
4. Preferring fixtures over hardcoded values for test data

Example of applying these principles:

# Bad
def test_content_changes
  message = Message.create!(content: "Hello")
  message.content = ""
  message.save
  assert_equal 0, message.content.embeds.count
end

# Good
def test_content_changes
  message = messages(:greeting)  # Use fixture
  assert_changes -> { message.content.embeds.count }, from: 1, to: 0 do
    message.update!(content: "")
  end
end

# Extract shared assertions into helpers when pattern emerges
def assert_content_embeds_change(message, from:, to:, &block)
  assert_changes -> { message.content.embeds.count }, from: from, to: to, &block
end

---

avoid !! operator

Avoid using the not-null assertion operator (!!) as it can cause runtime crashes if the assumption about non-nullability is incorrect. Instead, use safer alternatives that provide better error handling and code clarity.

Preferred alternatives:

1. Use checkNotNull() or requireNotNull() for explicit null validation with meaningful error messages: ```kotlin // Instead of: drawable = draweeHolder.topLevelDrawable!!

// Use: drawable = checkNotNull(draweeHolder.topLevelDrawable) { “Drawable should not be null” }

2. **Use Elvis operator (`?:`)** for providing fallback values or throwing exceptions:
```kotlin
// Instead of:
val local = instance().connectNative(pageId, remote)
local ?: throw IllegalStateException("Can't open failed connection")

// Use:
instance().connectNative(pageId, remote) ?: throw IllegalStateException("Can't open failed connection")

1. Use smart casting with is checks to avoid unnecessary null states: ```kotlin // Instead of: if (value !is Boolean) { throw ClassCastException(“Dynamic value from Object is not a boolean”) } return value as Boolean

// Use: if (value is Boolean) { return value } throw ClassCastException(“Dynamic value from Object is not a boolean”)

The `!!` operator should only be used when you have absolute certainty that the value cannot be null, and even then, consider if a more explicit null check would make the code clearer and safer for future maintainers.

---

## Minimize public API surface

<!-- source: rails/rails | topic: API | language: Ruby | updated: 2025-06-03 -->

Design APIs with a minimal public surface area by carefully controlling which methods and properties are exposed. Start with a restricted set of public methods and expand only when there's clear evidence of need. This approach makes APIs easier to maintain and evolve while reducing the risk of breaking changes.

Key principles:
- Expose only methods that are essential for client usage
- Prefer specific, focused public methods over general-purpose ones
- Document the rationale for making methods public

Example:
```ruby
class ErrorReporter
  # BAD: Exposing internal state directly
  attr_accessor :context_middlewares

  # GOOD: Controlled public interface
  def add_middleware(&block)
    context_middlewares << block
  end

  private
    attr_reader :context_middlewares
end

When adding new public methods, consider:

1. Is this functionality truly needed by API consumers?
2. Could this be implemented using existing public methods?
3. Are we prepared to support this method long-term?

Remember: It’s easier to add methods later than to remove them, as removal requires a deprecation cycle.

---

Extract repeated patterns

Extract repeated code patterns, CSS classes, and constants to improve maintainability and reduce duplication. When the same values, classes, or logic appear multiple times, consolidate them into reusable constants or utilities.

For CSS classes, extract repeated combinations into constants:

// Instead of duplicating classes
const tabTriggerClasses = "relative text-xs font-medium text-[#525866] transition-colors hover:text-[#dd2476] data-[state=active]:text-[#dd2476]";

<TabsTrigger value="cli" className={tabTriggerClasses}>CLI</TabsTrigger>
<TabsTrigger value="manual" className={tabTriggerClasses}>Manual</TabsTrigger>

For animations and transitions, reuse predefined constants:

// Use existing animation constants
import { fadeIn } from './animations';

<motion.div {...fadeIn} />

For callbacks and event handlers, define once and reuse:

// Define callback once
const handleSave = () => saveForm();

// Reuse across multiple props
<QueryBuilder 
  onAddRule={handleSave}
  onUpdateRule={handleSave}
  onRemoveRule={handleSave}
/>

Use proper utility functions for className concatenation instead of string interpolation:

// Use cn utility for proper class merging
className={cn('base-classes', conditionalClass && 'conditional-classes', className)}

This approach reduces maintenance burden, prevents inconsistencies, and makes the codebase more readable and reliable.

---

Cypress test isolation

Ensure end-to-end tests are properly isolated and follow best practices for reliability. Tests should avoid side effects that can impact other tests and eliminate practices that cause flaky results.

Key practices:

1. Avoid fixed waits:

   // ❌ Bad: Makes tests slow and potentially flaky
   cy.get('.element').click();
   cy.wait(1000);
      
   // ✅ Good: Cypress automatically waits for elements
   cy.get('.element').click();
   cy.get('.result').should('be.visible');
   

2. Extract common setup code:

   // ❌ Bad: Repeating login flow in every test
   it('Test one', () => {
     cy.visit('/login');
     cy.get('#email').type('user@example.com');
     cy.get('#password').type('password');
     cy.get('button').contains('Sign in').click();
     // Test-specific code
   });
      
   // ✅ Good: Using beforeEach for common setup
   beforeEach(() => {
     cy.login('user@example.com', 'password');
   });
      
   it('Test one', () => {
     // Test-specific code only
   });
   

3. Clean up test-created resources:

   // ❌ Bad: Files persist between test runs
   it('writes to a file', () => {
     cy.writeFile('cypress/fixtures/users.json', data);
   });
      
   // ✅ Good: Clean up after tests
   it('writes to a file', () => {
     cy.writeFile('cypress/fixtures/users.json', data);
   });
      
   after(() => {
     cy.task('deleteFile', 'cypress/fixtures/users.json');
   });
   

4. Restore modified configurations:

   // ❌ Bad: Changes affect other tests
   it('changes timeout', () => {
     Cypress.config('pageLoadTimeout', 20000);
     // Test code
   });
      
   // ✅ Good: Save and restore original config
   it('changes timeout', () => {
     const originalTimeout = Cypress.config('pageLoadTimeout');
     Cypress.config('pageLoadTimeout', 20000);
     // Test code
     Cypress.config('pageLoadTimeout', originalTimeout);
   });
   

Following these practices helps create a reliable test suite that provides consistent results regardless of which tests are run or in what order.

---

Self-contained test scenarios

Tests should be fully self-contained to ensure reliability and prevent unexpected failures. Each test scenario should:

1. Create any prerequisite data it needs rather than assuming it exists
2. Explicitly clean up data after test execution
3. Avoid dependencies on other test scenarios
4. Use parameterized values instead of hardcoded data

Benefits:

• Tests can run independently and in any order
• Test suites are more reliable and less prone to cascading failures
• Test maintenance becomes simpler when individual tests are isolated

Example - Before:

Escenario: Como administrador, puedo renombrar un proyecto existente
  Dado que la API está disponible
  Y dado que existe un proyecto "ProyectoPrueba" con ID $projectId
  Cuando el Actor envía PATCH /v1/projects/$projectId con:
    | name | "ProyectoRenombrado" |
  Entonces el código de respuesta debe ser 200

Example - After:

Escenario: Como administrador, puedo renombrar un proyecto existente
  Dado que la API está disponible
  Y que creo un proyecto "ProyectoPrueba" y guardo su ID como $projectId
  Cuando el Actor envía PATCH /v1/projects/$projectId con:
    | name | "ProyectoRenombrado" |
  Entonces el código de respuesta debe ser 200
  Y el JSON retornado debe tener name "ProyectoRenombrado"
  Y limpio el proyecto creado

---

Consistent language in naming

Use a single language (preferably English) consistently throughout your codebase for all identifiers including interface names, classes, variables, and properties. Avoid mixing languages as this reduces code readability and creates inconsistent naming patterns.

Before:

export interface ModeloBaseDeDatos {
    $id: string;
    name: string;
    permissions: string[];
    // Otros campos: createdAt, updatedAt, etc.
}

After:

export interface DatabaseModel {
    $id: string;
    name: string;
    permissions: string[];
    createdAt: string;
    updatedAt: string;
    enabled?: boolean;
}

This standard improves code maintainability and helps prevent confusion, especially in projects with international contributors. When choosing names, prefer English for broader accessibility and alignment with most programming languages and frameworks.

---

Flexible network handling

When working with network connections and HTTP requests, implement flexible configuration patterns and robust response handling to prevent flaky behavior and ensure compatibility across environments.

For network configurations:

• Always specify complete endpoint information including port numbers
• Use environment variables for configurable network settings

// Instead of:
baseUrl: 'http://localhost', // May cause connection issues

// Use:
baseUrl: process.env.CYPRESS_BASE_URL || 'http://localhost:80', // Configurable with explicit port

For HTTP response handling:

• Accept all valid status codes for a given scenario rather than requiring a specific one
• Consider cache-related status codes (like 304) alongside traditional success codes

// Instead of:
cy.wait('@request').its('response.statusCode').should('eq', 200)

// Use:
cy.wait('@request').its('response.statusCode').should('be.oneOf', [200, 304])

This approach accommodates legitimate response variations and different deployment environments, resulting in more reliable and maintainable network code.

---

Optimize algorithmic choices

When implementing algorithms, prioritize both correctness and efficiency by selecting the most appropriate data structures and computational approaches for each specific task. Ensure mathematical calculations follow established specifications and standards, and choose data structures that match the operation’s requirements.

For geometric calculations, verify that mathematical transformations account for all relevant parameters. For example, when calculating inner corner radii with border insets, adjust the radii based on border thickness according to specifications like the W3C CSS spec.

For data operations, select the most efficient data structure. Instead of using regular expressions for simple character filtering operations, consider more direct approaches like NSCharacterSet:

// Less efficient: regex for simple character filtering
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"[^a-z0-9_]" options:0 error:nil];

// More efficient: character set for the same operation
NSCharacterSet *allowedChars = [NSCharacterSet characterSetWithCharactersInString:@"abcdefghijklmnopqrstuvwxyz0123456789_"];

This approach reduces computational overhead while maintaining code clarity and correctness.

---

Secure credentials management

Never store sensitive credentials (passwords, API keys, tokens, etc.) in plain text within code repositories. This practice poses a significant security risk as it can lead to unauthorized access if the repository is compromised or accidentally made public.

Instead:

1. Use environment-specific configuration files that are excluded from version control
2. Implement secrets management tools or services
3. Use environment variables for runtime injection of sensitive values
4. Include commented placeholder examples in configuration templates

Example of good practice:

-DOCKERHUB_PULL_USERNAME=actual_username
-DOCKERHUB_PULL_PASSWORD=actual_password
-DOCKERHUB_PULL_EMAIL=actual_email@example.com
+# DOCKERHUB_PULL_USERNAME=your_username
+# DOCKERHUB_PULL_PASSWORD=your_password  
+# DOCKERHUB_PULL_EMAIL=your_email

Make sure to add these sensitive files to your .gitignore file and document the required environment variables in your project documentation.

---

Secure file uploads

Always implement and maintain robust scanning mechanisms for user-uploaded files to prevent malware distribution. When modifying infrastructure or services related to file handling, ensure alternative security controls are in place before removing existing protections.

Examples:

1. When removing an antivirus service like ClamAV: ```yaml

   Incorrect - commenting out without alternative

   services: appwrite: depends_on:

   • mariadb
   • redis

     - clamav # Security risk: Removed without replacement

Correct - either keep the service or document alternative

services: appwrite: depends_on: - mariadb - redis - clamav # Maintain file scanning # Alternative: Implement cloud-based scanning solution as documented in security.md

2. Ensure application logic handles scanning failure gracefully:
```php
// Verify uploads are always scanned before processing
if (!$scanService->isAvailable() && !$alternativeScanner->isAvailable()) {
    throw new SecurityException('No file scanning service available');
}

---

Variable evaluation context

Be mindful of when and where environment variables and configuration values are evaluated in shell scripts, especially when working across different execution contexts (like host vs. container environments). Improper quoting can cause variables to be evaluated in the wrong context, leading to unexpected behavior.

For example, when providing instructions for command execution in output messages:

# INCORRECT - $PWD would evaluate inside the container
echo "  docker run --rm -it -v \"$PWD:/app/\" -v \"$PWD/docker/.cache:/home/$USERNAME/.cache\" maplibre-native-image"

# CORRECT - Using single quotes to preserve $PWD for host evaluation
echo '  docker run --rm -it -v "$PWD:/app/" -v "$PWD/docker/.cache:/home/'"$USERNAME"'/.cache" maplibre-native-image'

Similarly, when referencing configuration files in scripts, use variables consistently to avoid hardcoded references:

# Use variables for file paths
echo "::error::Invalid version '$version' in $(realpath "$version_file")"

This approach makes scripts more robust, maintainable, and less prone to configuration errors across different environments.

---

Consolidate duplicate configurations

Maintain a single source of truth for configuration files instead of duplicating them across the codebase. Duplicated configurations (like banned-signatures.txt files) lead to maintenance challenges, potential inconsistencies, and confusion about which version is authoritative.

For shared configuration rules like import bans or code quality checks:

• Create a common configuration file (e.g., banned-signatures-common.txt)
• Reference this common file from different modules when needed
• Document the location of the common file

Example: Instead of having multiple copies:

// In module1/banned-signatures.txt
@defaultMessage Don't use Maven classes. They won't be available when using Gradle.
org.apache.maven.**

// In module2/banned-signatures.txt
@defaultMessage Don't use Maven classes. They won't be available when using Gradle.
org.apache.maven.**

Consolidate into a common file:

// In common/banned-signatures-common.txt
@defaultMessage Don't use Maven classes. They won't be available when using Gradle.
org.apache.maven.**

This approach ensures that when configuration rules need to be updated, the change happens in a single place, maintaining consistency across the codebase.

---

Ensure comprehensive test coverage

All code paths, error conditions, and edge cases must have corresponding unit tests to ensure robust functionality and prevent regressions. This includes testing both success and failure scenarios, boundary conditions, and error handling paths.

Key areas requiring test coverage:

• Error handling and validation logic (empty inputs, malformed data, decode failures)
• Edge cases and boundary conditions (negative offsets, missing values, empty collections)
• Both positive and negative test scenarios for configuration flags
• All public functions and methods, especially newly exposed APIs
• Complete coverage of new features and functionality

Example of comprehensive edge case testing:

// Test both positive and negative cases
func Test_Ctx_Subdomains_EdgeCases(t *testing.T) {
    t.Run("negative_offset", func(t *testing.T) {
        c.Request().URI().SetHost("john.doe.google.com")
        require.Empty(t, c.Subdomains(-1), "negative offset should return empty slice")
    })
    
    t.Run("offset_too_high", func(t *testing.T) {
        c.Request().URI().SetHost("john.doe.is.awesome.google.com")
        require.Empty(t, c.Subdomains(10))
    })
}

// Test error handling paths
func Test_parseAndClearFlashMessages_DecodeError(t *testing.T) {
    // Test when hex.DecodeString fails
    cookieValue, err := hex.DecodeString(invalidHexString)
    if err != nil {
        // Verify that no flash messages are processed
        require.Len(t, r.c.flashMessages, 0, "Expected no flash messages when decode fails")
    }
}

Missing test coverage often indicates incomplete validation of functionality and can lead to production bugs. Use code coverage tools to identify untested paths and ensure critical error handling is properly validated.

---

Configuration method selection

Choose the appropriate configuration method based on when values are needed and whether they can change at runtime. Use runtimeConfig for values that need to be set via environment variables after build (especially secrets), app.config for public build-time configuration that won’t change, and process.env only in server contexts when outside the Nuxt framework.

Key guidelines:

• runtimeConfig: Private or public tokens that need to be specified after build using environment variables
• app.config: Public tokens determined at build time, for website configuration such as theme variant, title, and any project configuration that is not sensitive
• process.env: Only use in server contexts outside Nuxt framework (like nuxt.config.ts at build time)

Remember that nuxt.config.ts only runs at build time, so you cannot change anything in it using environment variables at runtime (including runtimeConfig).

// nuxt.config.ts - build time only
export default defineNuxtConfig({
  runtimeConfig: {
    // Private keys (only available on server-side)
    apiSecret: process.env.API_SECRET,
    // Public keys (exposed to client-side)
    public: {
      apiBase: process.env.API_BASE_URL || '/api'
    }
  }
})

// app.config.ts - build time, public values
export default defineAppConfig({
  theme: {
    primaryColor: '#ababab'
  },
  title: 'My App'
})

// In components/composables - runtime
const config = useRuntimeConfig()
const appConfig = useAppConfig()

---

Consistent, clear naming

Use naming that is unambiguous, consistent with the codebase, and semantically accurate.

Apply:

• Avoid shadowing: don’t reuse the same parameter name in a nested scope; either rename or move the nested function out.
• Follow established terminology: if the repo uses *Params*, don’t introduce *Opts* for the same concept (and avoid opts vs params drift).
• Avoid misleading or shadowy identifiers: don’t use generic built-in-like names (e.g. toString) for domain helpers—prefer explicit names (e.g. errToString).
• Keep aliases/shortcuts truthful: if an alias suggests transformation but it only adds validation, rename it to reflect intent and/or align with existing API vocabulary.

Example (shadowing + rename):

function isValidCreditCard(cardNumber: string): boolean {
  const isLuhnAlgo = (sanitizedCardNumber: string): boolean => {
    // ...
    return true;
  };

  return isLuhnAlgo(cardNumber);
}

Example (terminology + semantics):

• Prefer params.async (not opts.async) if the repo’s standard is Params.
• Prefer step over a confusing alias like mod when it’s meant to align with “step” semantics from familiar APIs.

---

Avoid wildcard imports

Wildcard (star) imports like import java.util.*; are prohibited in the codebase as they reduce code readability and can cause naming conflicts. Always import specific classes individually.

Configure your IDE to disallow wildcard imports:

• In IntelliJ IDEA: Navigate to Editor -> Code Style -> Java -> Imports and set ‘Class count to use import with *’ to 999.
• The same setting should be applied for ‘Names count to use static import with *’.

Instead of:

import java.util.*;

Use:

import java.util.List;
import java.util.Map;
import java.util.Set;

This makes dependencies explicit and avoids potential name conflicts when classes with the same name exist in different packages.

---

Human-readable configuration values

When writing configuration files, prioritize human readability and maintainability by using descriptive expressions instead of magic numbers or cryptic values. This makes code more understandable and easier to maintain.

For time-based configurations, prefer using expressions like 1.year.to_i or 1.hour.to_i instead of hard-coded seconds:

# Avoid this
config.public_file_server.headers = { "cache-control" => "public, max-age=31556952" }

# Prefer this
config.public_file_server.headers = { "cache-control" => "public, max-age=#{1.year.to_i}" }

Keep configuration formatting consistent and pay attention to spacing, especially around conditional statements:

# Incorrect
t.options = "--profile"if ENV["CI"]

# Correct
t.options = "--profile" if ENV["CI"]

Document configuration options clearly, especially when they relate to environment variables or external settings. Use precise language that accurately describes the expected value format:

# Vague
# similar environment variable prefixed with the configuration key in uppercase.

# Clear and precise
# similar environment variable prefixed with the connection name appended to `DATABASE_URL`.

Maintaining consistent, readable configuration across all environments helps prevent unexpected behavior and makes your application easier to debug and maintain.

---

analyze transitive dependencies

When implementing dependency analysis algorithms, ensure comprehensive tracking of both direct and transitive dependencies to avoid missing critical relationships. Many bugs arise from incomplete dependency graphs that fail to account for indirect connections.

Key algorithmic considerations:

• Implement proper transitive closure when analyzing dependency chains
• Account for indirect mutations and reactive updates that propagate through multiple levels
• Use graph traversal algorithms (DFS/BFS) to identify all reachable dependencies, not just immediate ones

Example scenarios:

• In reactivity systems: if A depends on B and B depends on C, changes to C should invalidate A
• In usage analysis: when checking if rules are used, consider nested relationships and child dependencies
• In mutation tracking: indirect mutations through function calls or property access chains should be detected

This prevents common issues where dependency analysis algorithms miss edge cases due to incomplete graph traversal or failure to consider multi-hop relationships in the dependency graph.

---

Restrict administrative access

Implement proper authorization controls for sensitive operations that can modify system configuration or create new entries. Administrative functions like service calls that create config entries should be restricted to admin-level access at minimum, or better yet, exposed as scoped integration APIs rather than general-purpose services. Additionally, ensure that authentication flows are thoroughly tested to verify that reauth mechanisms trigger correctly when authorization fails.

Example of problematic code:

# Unrestricted service that can create config entries
hass.services.async_register(
    DOMAIN,
    "register_irk", 
    service_register_irk,
    vol.Schema({vol.Required("irk"): cv.string}),
    supports_response=SupportsResponse.NONE,
)

Better approach:

# Restrict to admin access or expose as integration API
hass.services.async_register(
    DOMAIN,
    "register_irk",
    service_register_irk, 
    vol.Schema({vol.Required("irk"): cv.string}),
    supports_response=SupportsResponse.NONE,
    required_features=[FEATURE_ADMIN_ACCESS]  # Restrict access
)

Always test that reauth flows trigger properly:

async def test_token_refresh_reauth():
    aioclient_mock.post(TOKEN_URL, status=HTTPStatus.UNAUTHORIZED)
    assert not await setup_integration()
    assert mock_config_entry.state is ConfigEntryState.SETUP_ERROR
    # Verify reauth flow has started
    assert len(hass.config_entries.flow.async_progress()) == 1

---

proper synchronization practices

Ensure thread safety by using appropriate synchronization mechanisms and understanding thread context. When working with shared mutable state, protect critical sections with proper synchronization to prevent race conditions and concurrent modifications. Choose the right synchronization approach for your use case - prefer language-provided utilities over manual implementations when possible.

Key practices:

1. Use synchronized blocks or methods to protect shared collections from concurrent modification
2. Leverage language features like Kotlin’s lazy delegation for thread-safe initialization instead of manual double-checked locking
3. Understand your execution context - avoid unnecessary thread switching when already on the correct thread

Example of proper synchronization:

// Instead of risking ConcurrentModificationException
val snapshot = ArrayList(beforeUIBlocks)
beforeUIBlocks.clear()

// Use proper synchronization
val blocksToExecute: List<UIBlock> = synchronized(this) {
    if (beforeUIBlocks.isEmpty()) return
    beforeUIBlocks.toList().also { beforeUIBlocks.clear() }
}

// Prefer lazy delegation over manual double-checked locking
private val mainHandler: Handler by lazy {
    Handler(Looper.getMainLooper())
}

This approach prevents race conditions, reduces complexity, and makes concurrent code more maintainable and less error-prone.

---

Strategic error handling

Implement strategic error handling by properly checking exception types and using try/catch blocks to distinguish between user errors and system errors. Avoid runtime errors from improper type checking and categorize exceptions based on their source and required response.

Key principles:

1. Proper exception type checking: Verify exception structure before using operators like in to avoid runtime errors on primitive values
2. Strategic try/catch placement: Use try/catch blocks to separate critical system operations from user input validation
3. Error categorization: Distinguish between user input errors (which don’t need immediate action) and system errors (which require investigation)

Example:

// Bad - can cause runtime error on primitive exceptions
const isBadRequestExceptionFromValidationPipe =
  exception instanceof Object &&
  'response' in exception &&  // This fails on primitive values
  'message' in (exception as any).response;

// Good - proper type checking
const isBadRequestExceptionFromValidationPipe =
  exception instanceof Object &&
  typeof exception === 'object' &&
  exception !== null &&
  'response' in exception;

// Strategic try/catch - separate system errors from user errors
try {
  // Critical system operations that indicate internal failures
  scheduledJob = await this.createScheduledUnsnoozeJob(notification, delayAmount);
  snoozedNotification = await this.markNotificationAsSnoozed(command);
  await this.queueJob(scheduledJob, delayAmount);
} catch (error) {
  // Transform to InternalServerErrorException - needs immediate attention
  throw new InternalServerErrorException('System error during snooze operation');
}
// User validation errors outside try/catch bubble up as-is

This approach prevents runtime errors from improper exception handling while ensuring system errors are properly categorized and logged for investigation.

---

Explicit null handling

Use explicit identity comparisons for null checks and leverage modern PHP null-handling features to create more reliable, readable code.

Key practices:

1. Use identity operators for null checks instead of functions

// Avoid
if (is_null($value)) { ... }
if (empty($path)) { ... }

// Prefer
if ($value === null) { ... }
if ($path === '') { ... }
if ($array === []) { ... }

Identity comparisons (===, !==) are more precise than functions like is_null() or empty(). They clearly communicate your intent and avoid unexpected behavior with falsy values like '0' or 0.

2. Leverage null coalescing operators

// Avoid
$name = (string) (is_null($this->argument('name')) 
    ? $choice 
    : $this->argument('name'));

// Prefer
$name = (string) ($this->argument('name') ?? $choice);

The null coalescing operator (??) simplifies conditional logic and makes your code more concise and readable.

3. Add proper null annotations in docblocks and types

// Avoid
/** @param string $string The input string to sanitize. */
public static function sanitize($string) 
{
    if ($string === null) {
        return null;
    }
}

// Prefer
/** @param string|null $string The input string to sanitize. */
/** @return string|null The sanitized string. */
public static function sanitize(?string $string) 
{
    if ($string === null) {
        return null;
    }
}

Accurately document nullable parameters and return types for better static analysis and IDE support.

4. Check for null before method calls

// Avoid direct method calls on possibly null values
$using($this->app);

// Prefer
if ($using !== null) {
    $this->app->call($using);
}

Always check if variables are null before calling methods on them to prevent null reference exceptions.

5. Be careful with null in array and object relationships

// Check if a relation exists before accessing properties
if (isset($relation)) {
    $attributes[$key] = $relation;
}

Remember that isset() returns false for null values, which may not be what you expect when working with relationships or arrays that might legitimately contain null values.

---

Preserve error handling context

When handling exceptions, preserve the original error context and provide clear, actionable error messages. This helps with debugging and improves the developer experience. Key practices:

1. Avoid swallowing exception details during serialization or logging
2. Include specific information about what caused the error
3. Use appropriate exception types for different error scenarios
4. Consider adding fallback error representations

Example of good error handling:

def handle_task_error(exc):
    try:
        # Attempt full error serialization
        return {
            "error_type": type(exc).__name__,
            "error_details": str(exc),
            "traceback": "".join(format_exception(type(exc), exc, exc.__traceback__)),
        }
    except Exception:
        # Fallback to basic error information if serialization fails
        return {
            "error_type": type(exc).__name__,
            "error_message": str(exc),
            "note": "Full error details unavailable - serialization failed"
        }

This approach ensures that error information is preserved as much as possible, with a fallback mechanism when full details cannot be captured. It helps maintain debuggability while being robust against serialization or logging failures.

---

Prefer standard library functions

When implementing algorithms, prioritize using standard library functions over manual implementations when they provide equivalent or better performance. The standard library is typically optimized and well-tested, making it a more reliable choice for common operations.

For example, instead of manually copying map entries:

// Avoid manual iteration
for k, v := range m {
    c[k] = v
}

// Prefer standard library function
maps.Copy(c, m)

Similarly, for string operations, the standard library is often more efficient:

// Use strings.ToLower() instead of custom utilities
origin := strings.ToLower(c.Get(fiber.HeaderOrigin))

This approach reduces code complexity, leverages optimized implementations, and improves maintainability. The standard library functions are particularly efficient when input data is already in the expected format, as noted: “standard lib is faster if it is already lower case, which should be the case in most cases.”

---

HTTP protocol compliance

Ensure code adheres to HTTP protocol standards and handles different protocol versions correctly. This includes respecting protocol limitations, using appropriate status codes, and implementing proper fallbacks.

Key considerations:

• HTTP/2 doesn’t support status messages, so avoid setting statusMessage for HTTP/2 connections
• Use reliable endpoints for server health checks that return success status codes rather than application logic that might fail
• Handle redirect status codes appropriately with proper fallback mechanisms

Example implementation:

// Good: Check protocol version before setting status message
export async function toNodeRequest(res: Response, nodeRes: ServerResponse) {
  nodeRes.statusCode = res.status;
  // HTTP/2 doesn't support status messages
  // https://datatracker.ietf.org/doc/html/rfc7540#section-8.1.2.4
  if (nodeRes.httpVersion !== '2.0') {
    nodeRes.statusMessage = res.statusText;
  }
}

// Good: Use reliable endpoint for health checks
await waitOn({
  resources: [
    `http://${args.host ?? "localhost"}:${args.port}${args.basename ?? "/favicon.ico"}`,
  ]
});

// Good: Handle redirect status codes with appropriate fallbacks
if (redirectStatusCodes.has(response.status)) {
  let location = response.headers.get("Location");
  let delay = response.status === 302 ? 2 : 0;
  // Implement meta refresh fallback
}

This ensures network communication follows established protocols and handles edge cases gracefully across different HTTP versions and scenarios.

---

Follow modern C++ guidelines

Adhere to the C++ Core Guidelines for improved code quality, readability, and maintainability. Follow these key practices:

1. Use enum class instead of regular enums for type safety and scope: ```cpp // Avoid enum { collisionTextureCount };

// Prefer enum class CollisionTexture { Count };

2. **Use `using` over `typedef`** for improved readability:
```cpp
// Avoid
typedef CollisionUBO CollisionBoxUBO;

// Prefer
using CollisionBoxUBO = CollisionUBO;

1. Mark methods as const when they don’t modify object state: ```cpp // Avoid std::vector<std::string> getLog();

// Prefer std::vector<std::string> getLog() const;

4. **Use override without redundant virtual**:
```cpp
// Avoid
virtual void setSynchronous(bool value) override { synchronousFrame = value; }

// Prefer
void setSynchronous(bool value) override { synchronousFrame = value; }

These practices align with modern C++ standards, reduce potential bugs, and make the code easier to understand and maintain. The C++ Core Guidelines provide comprehensive recommendations for writing clear, correct, and efficient C++ code.

---

Modern C++ style practices

Apply modern C++ features and consistent syntax patterns to improve code readability and safety. Follow these guidelines:

1. Use modern C++ features:
   • Prefer structured bindings for tuple unpacking: ```cpp // Instead of: for (const auto& tuple : glyphsToUpload) { const auto& texHandle = std::get<0>(tuple); const auto& glyph = std::get<1>(tuple); }

// Use: for (auto [texHandle, glyph, fontStack] : glyphsToUpload) { // … }

2. Use safe casting practices:
- Prefer static_cast over C-style casts:
```cpp
// Instead of:
auto i = (mbgl::style::PluginLayer::Impl*)baseImpl.get();

// Use:
auto i = static_cast<mbgl::style::PluginLayer::Impl*>(baseImpl.get());

1. Maintain consistent syntax:
   • Always use braces for multi-line conditionals
   • Always initialize variables, even if immediately set
   • Use default comparison operators where possible in C++20: ```cpp // Instead of: bool operator==(const TileEntry& other) const noexcept { return id == other.id && sourceID == other.sourceID && op == other.op; }

// Use: bool operator==(const TileEntry& other) const = default;

These practices improve code safety, readability, and maintainability while leveraging modern C++ features.

---

## Write comprehensive test cases

<!-- source: vuejs/core | topic: Testing | language: TypeScript | updated: 2025-05-27 -->

Tests should thoroughly cover all code paths and edge cases. Each test case should:
1. Test distinct scenarios in separate test cases
2. Cover all logical branches and code paths
3. Use clear, specific test names that describe the scenario being tested
4. Include both positive and negative test cases

Example:
```js
// ❌ Incomplete test coverage
test('isRef check', () => {
  expect(isRef(computed(() => 1))).toBe(true)
})

// ✅ Comprehensive test coverage
describe('isRef', () => {
  test('returns true for computed values', () => {
    expect(isRef(computed(() => 1))).toBe(true)
  })

  test('returns false for primitive values', () => {
    expect(isRef(0)).toBe(false)
    expect(isRef(1)).toBe(false)  // Test truthy primitive
    expect(isRef('')).toBe(false) // Test falsy primitive
  })
  
  test('returns true for ref values', () => {
    expect(isRef(ref(1))).toBe(true)
    expect(isRef(ref(null))).toBe(true)
  })
})

---

Write focused efficient tests

Tests should be focused, efficient and meaningful. Follow these guidelines:

1. Avoid testing implementation details or already-tested functionality
2. Use clear, direct assertions that test actual behavior
3. Prefer simple class-based tracking over complex mocks
4. Keep tests fast by avoiding unnecessary test cases

Example of a good test:

def test_bulk_create_with_existing_children(self):
    """
    bulk_create() should continue _order sequence from existing children.
    """
    question = Question.objects.create(text="Test Question")
    Answer.objects.create(question=question, text="Existing 1")
    Answer.objects.create(question=question, text="Existing 2")

    new_answers = [
        Answer(question=question, text=f"New Answer {i}") 
        for i in range(2)
    ]
    created_answers = Answer.objects.bulk_create(new_answers)

    # Clear assertions testing actual behavior
    self.assertEqual(len(created_answers), 2)
    self.assertEqual(created_answers[0]._order, 2)
    self.assertEqual(created_answers[1]._order, 3)

This test is focused on specific functionality, uses clear assertions, and avoids unnecessary complexity while still thoroughly testing the behavior.

---

Document public API completely

All public APIs (files in include/) must have comprehensive documentation using either Doxygen-style or triple-slash comments. Documentation should include:

1. Class-level documentation describing purpose and usage
2. Method documentation with parameters, return values, and behavior
3. Enum documentation including individual value descriptions
4. Clear indication of public vs private API boundaries

Example:

/// This enum defines color blending equations
enum class ColorBlendEquationType : uint8_t {
    Add,            ///< Adds source and destination colors
    Subtract,       ///< Subtracts destination from source color
    ReverseSubtract ///< Subtracts source from destination color
};

/**
 * @brief Adds a polyline to the drawable layer
 * 
 * @param coordinates Geographic coordinates of the polyline
 * @return true if polyline was successfully added, false otherwise
 */
bool addPolyline(const LineString<double>& coordinates);

Private implementation files (in src/) may have lighter documentation, focusing on complex logic or non-obvious implementations.

---

Group related properties

Design APIs by organizing related properties into purpose-specific structures rather than flat parameter lists. This improves clarity about which properties apply in different contexts, enhances API documentation, and makes interfaces more maintainable as they evolve.

When designing APIs that handle multiple property types or target different use cases, create specialized structures that clearly indicate their purpose. This practice:

1. Makes code more self-documenting
2. Reduces confusion about which properties are applicable in different contexts
3. Provides better organization as APIs grow
4. Simplifies future extensions

For example, instead of placing multiple property setters at the interface level:

// Less clear approach
class Interface {
public:
    void setColor(Color color);
    void setBlur(float blur);
    void setWidth(float width);
    
    void addPolyline(/* parameters */);
    void addFill(/* parameters */);
};

Group related properties into purpose-specific structures:

// Better organized approach
class Interface {
public:
    struct LineOptions {
        Color color;
        float blur;
        float width;
    };
    
    struct FillOptions {
        Color color;
        float opacity;
    };
    
    void addPolyline(const LineOptions& options, /* other parameters */);
    void addFill(const FillOptions& options, /* other parameters */);
};

This pattern also helps with API evolution - when adding new properties, you can clearly see which structure they belong to, and clients only need to consider properties relevant to their use case.

---

catch specific exceptions

Always catch specific exception types rather than generic Exception to avoid masking unexpected errors and ensure intentional error handling. This practice helps distinguish between expected failure scenarios that should be handled gracefully and unexpected errors that indicate bugs.

When handling known failure cases, catch the specific exception type that the API contract specifies. For example, when setting font variation settings which throws IllegalArgumentException for invalid input, catch only that specific exception:

try {
    fontVariationSettings = fontVariationSettingsParam
} catch (e: IllegalArgumentException) {
    Log.w(TAG, "Invalid font variation settings: $fontVariationSettingsParam", e)
    // Handle gracefully - continue without font variations
}

Avoid generic exception catching which can hide programming errors:

// DON'T DO THIS - masks all errors including unexpected ones
try {
    fontVariationSettings = fontVariationSettingsParam
} catch (e: Exception) {
    // This could hide NullPointerException, OutOfMemoryError, etc.
}

Additionally, validate inputs early to prevent crashes from edge cases, and remove unnecessary try blocks that have no catch or finally clauses as they create misleading code structure without providing error handling benefits.

---

Optimize CI platform builds

When configuring CI/CD build pipelines, limit builds to only the platforms your project actively supports and avoid building for out-of-tree (OOT) platforms that maintain separate forks. This reduces unnecessary CI overhead and build times. Additionally, design your build configuration to support parallelization by allowing platforms to be passed as separate parameters.

For example, instead of building for all possible platforms, focus on core supported platforms:

// Only build for actively supported platforms
const supportedPlatforms = ['iOS', 'iOS simulator', 'macOS,variant=Mac Catalyst'];

// Design for parallel execution in CI
const buildPlatform = (platform) => {
  const buildCommand = `xcodebuild -scheme React -destination "generic/platform=${platform}" ...`;
  // Build logic here
};

// Can be parallelized in CI by passing platforms separately
supportedPlatforms.forEach(buildPlatform);

This approach improves CI efficiency by avoiding builds for platforms that won’t be used while maintaining the flexibility to parallelize builds across the platforms that matter.

---

Prefer modern security

When implementing security features (such as artifact signing), use current best practices and prefer pure-Java security libraries over native executables whenever possible. This approach simplifies configuration, improves portability, and reduces security risks associated with native executable dependencies and their complex configurations.

For example, when configuring Maven GPG plugin, prefer:

<configuration>
    <bestPractices>true</bestPractices>
    <useAgent>false</useAgent>
    <signer>bc</signer>
</configuration>

Instead of manual configurations with native executables:

<configuration>
    <!-- Prevent gpg from using pinentry programs -->
    <gpgArguments>
        <arg>--pinentry-mode</arg>
        <arg>loopback</arg>
    </gpgArguments>
</configuration>

This leverages libraries like BouncyCastle (Java-based cryptography) that eliminate the need for native GPG executable installation and complex signature setup.

---

Synchronize configuration values

Ensure all configuration values, particularly version numbers and environment variables, are consistent across related files to prevent subtle bugs and deployment issues. When updating configurations:

1. Identify all related occurrences of the same value across different files (e.g., docker-compose.yml, .phtml templates)
2. Update all instances to use the same value or parameter
3. For renamed variables, remove the deprecated ones to prevent ambiguity
4. When backward compatibility is needed, explicitly support both legacy and current values

Example for version synchronization:

# In app/views/install/compose.phtml
- image: openruntimes/executor:0.7.14
+ image: openruntimes/executor:0.7.16  # Match version in docker-compose.yml

Example for environment variables:

# Remove deprecated variable to avoid confusion
-      - _APP_MAINTENANCE_DELAY
       - _APP_MAINTENANCE_START_TIME

Example for maintaining backward compatibility:

# Support both legacy and current runtime versions
- OPR_EXECUTOR_RUNTIME_VERSIONS=v5
+ OPR_EXECUTOR_RUNTIME_VERSIONS=v2,v5

---

Prefer Optional over nulls

Use Java’s Optional API instead of null checks to improve code readability, safety, and maintainability. When dealing with potentially absent values:

1. Return Optional instead of T that might be null
2. Use Optional’s functional methods (ifPresent, map, flatMap, orElse) rather than null checks
3. Avoid Optional.get() without first checking isPresent()
4. When comparing values that might be null, use Objects.equals() or place potentially null values on the right side of equals comparisons

Example:

// Not recommended
String principalClaim = resolvedContext.oidcConfig().token().principalClaim().orElse(null);
if (principalClaim != null && !tokenJson.containsKey(principalClaim)) {
    // do something with principalClaim
}

// Recommended
resolvedContext.oidcConfig().token().principalClaim().ifPresent(claim -> {
    if (!tokenJson.containsKey(claim)) {
        // do something with claim
    }
});

For performance-critical code paths, consider using specialized patterns like returning pre-defined constants (e.g., Collections.emptyMap()) instead of allocating new objects when a value is absent.

---

Database-specific query optimization

Leverage database-specific features to optimize queries and improve performance. Different database engines have unique capabilities that can significantly enhance query efficiency when used appropriately.

For PostgreSQL:

• Use ANY operator instead of IN for queries with large arrays of values to improve query plan caching
• Handle joins in UPDATE statements properly to avoid unnecessary subqueries
• Consider PostgreSQL-specific data types (arrays, JSONB) for more efficient storage and querying

For example, with PostgreSQL:

# Rails can optimize this to use PostgreSQL's more efficient ANY operator:
User.where(id: large_array_of_ids)
# SQL: user.id = ANY('{1,2,3}') instead of user.id IN (1,2,3)

When updating with joins, be aware of database-specific limitations:

# PostgreSQL supports UPDATE with FROM for inner joins
Post.joins(:author).where(authors: {active: true}).update_all(featured: true)

# But for left joins or complex conditions, Rails may need to use subqueries
# Be mindful of how these are translated to SQL for your specific database

Examine the SQL generated by your ORM and understand how database-specific optimizations are applied. This helps you write ActiveRecord queries that translate to efficient SQL for your database engine.

---

Design evolution-ready APIs

Design APIs that are both explicit in their usage and provide clear evolution paths. When designing APIs:

1. Prefer structured objects with named fields over primitive collections or multiple parameters to improve clarity and self-documentation

// Avoid this:
CameraPosition getCameraForLatLngBounds(LatLngBounds bounds, int[] padding, double bearing, double pitch);

// Prefer this:
CameraPosition getCameraForLatLngBounds(LatLngBounds bounds, CameraPadding padding, double bearing, double pitch);

// Where CameraPadding is a well-defined class:
public class CameraPadding {
    public final int left;
    public final int top;
    public final int right;
    public final int bottom;
    
    // Constructor and other methods
}

1. When modifying existing APIs, analyze compatibility impacts (binary vs. source compatibility) and provide proper deprecation paths:

/**
 * @deprecated Use {@link #onDidFinishRenderingFrame(boolean, RenderingStats)} instead.
 */
@Deprecated
void onDidFinishRenderingFrame(boolean fully, double frameEncodingTime, double frameRenderingTime);

/**
 * Called when the map has finished rendering a frame
 *
 * @param fully true if all frames have been rendered, false if partially rendered
 * @param stats rendering statistics
 */
void onDidFinishRenderingFrame(boolean fully, RenderingStats stats);

1. Consider using more generic interfaces for parameters when appropriate to allow for greater flexibility, but evaluate compatibility impacts before changing existing signatures.

Following these practices leads to more maintainable, self-documenting APIs that can evolve gracefully over time without causing unnecessary pain for API consumers.

---

avoid unnecessary allocations

When implementing algorithms and data structure operations, avoid unnecessary memory allocations, object creation, and data copying that can impact performance. Look for opportunities to leverage existing objects, references, and lazy evaluation patterns.

Key optimization strategies:

• Use polymorphism instead of creating new objects when type compatibility exists (Liskov Substitution Principle)
• Prefer const references over copying when data won’t be modified
• Implement lazy evaluation with optional types to defer expensive operations until needed

Example of unnecessary allocation:

// Avoid: Creating unnecessary shared_ptr when type already matches
dispatchEvent("scrollEndDrag", std::make_shared<ScrollEndDragEvent>(scrollEvent));

// Better: Let polymorphism handle the type conversion
dispatchScrollViewEvent("scrollEndDrag", scrollEvent);

Example of unnecessary copying:

// Avoid: Always copying the list
auto children = shadowNode.getChildren();

// Better: Use reference when no modification needed
const auto& children = shadowNode.getChildren();

// Or: Use lazy evaluation for conditional modification
std::optional<ListOfShared> modifiedChildren;
// Only copy when first modification is needed

This approach reduces computational complexity and memory pressure in performance-critical code paths.

---

Optimize for code readability

Prioritize code readability over clever solutions by:

1. Using early returns to reduce nesting
2. Leveraging modern PHP features when they improve clarity
3. Maintaining consistent style patterns
4. Simplifying complex logic

Example - Before:

protected function parseIds($value)
{
    if (is_null($value)) {
        return [];
    }

    if (is_string($value)) {
        return array_map('trim', explode(',', $value));
    }

    check_type($value, 'array', $key, 'Environment');

    return $value;
}

Example - After:

protected function parseIds($value)
{
    return match (true) {
        $value === null => [],
        is_string($value) => array_map('trim', explode(',', $value)),
        default => check_type($value, 'array', $key, 'Environment'),
    };
}

The improved version:

• Uses match expression for cleaner flow control
• Maintains consistent null comparison style
• Reduces nesting and cognitive load
• Leverages modern PHP features appropriately

Choose simpler constructs when they improve readability, but avoid sacrificing clarity for brevity. The goal is to write code that is easy to understand and maintain.

---

check all error returns

Always check and handle error returns from function calls, even for operations that seem unlikely to fail. Ignoring errors can lead to silent failures, resource leaks, and unpredictable behavior in production.

Common patterns to avoid:

• Missing error checks: ln.Close() without checking the error
• Silent error ignoring: returning without handling errors from critical operations
• Assuming operations never fail: even operations like certificate parsing can fail

Proper error handling patterns:

• Check errors immediately after function calls
• Use early returns to avoid unnecessary processing when errors occur
• Log errors appropriately before returning or handling them
• For operations in defer statements, still check errors when meaningful

Example of missing error check:

// Bad: Missing error check
file, err := os.Open(path)
if err != nil {
    return err
}
defer file.Close() // Error ignored

// Good: Proper error handling
file, err := os.Open(path)
if err != nil {
    return err
}
defer func() {
    if closeErr := file.Close(); closeErr != nil {
        log.Errorf("failed to close file: %v", closeErr)
    }
}()

Example of early error return:

// Bad: Continuing processing after error
key, err := parseParamSquareBrackets(key)
// ... rest of function continues regardless

// Good: Early error return
key, err := parseParamSquareBrackets(key)
if err != nil {
    return err
}
// ... continue processing

This practice is essential for building robust applications that handle failure scenarios gracefully and provide meaningful error information for debugging.

---

Optimize loop operations

When writing loops, optimize for both readability and performance by following these key principles:

1. Exit early when a decision can be made: ```php // Instead of this: foreach ($keys as $key) { if (! static::has($array, $key)) { $result = false; } } return $result;

// Do this: foreach ($keys as $key) { if (! static::has($array, $key)) { return false; } } return true;

2. **Move invariant operations outside loops**:
```php
// Instead of this:
foreach ($array as $key => $item) {
    $groupKey = is_callable($groupBy) ? $groupBy($item, $key) : static::get($item, $groupBy);
    // ...
}

// Do this:
$groupBy = is_callable($groupBy) ? $groupBy : fn ($item) => static::get($item, $groupBy);
foreach ($array as $key => $item) {
    $groupKey = $groupBy($item, $key);
    // ...
}

1. Use O(1) operations where possible instead of O(n): ```php // Instead of this: if (in_array(InteractsWithQueue::class, $uses) && in_array(Queueable::class, $uses)) { // … }

// Do this: if (isset($uses[InteractsWithQueue::class], $uses[Queueable::class])) { // … }

4. **Add early termination conditions** for algorithms that can complete before processing all elements:
```php
// Add early exit:
foreach ($map as $roman => $value) {
    while ($number >= $value) {
        $result .= $roman;
        $number -= $value;
    }
    
    if ($number === 0) {
        return $result;
    }
}

These optimizations help reduce computational complexity and unnecessary operations, resulting in more efficient and maintainable code.

---

Validate configuration formatting

Ensure all JSON configuration files adhere to proper syntax and formatting conventions. Common issues to avoid include:

1. Invalid key-value syntax: All JSON properties must use proper key-value format with double-quoted keys. ```diff // Incorrect
   • hi am sairam

   // Correct

   • “message”: “hi am sairam”, ```

   ```

Run a JSON validator on configuration files before committing changes to catch these issues early. Proper JSON formatting ensures reliable parsing, prevents runtime errors, and maintains code consistency across the project.

---

optimize network configurations

Optimize network configurations by eliminating redundancy, using modern compression standards, and properly configuring load balancing. This includes setting sensible defaults to avoid duplicative parameters, leveraging efficient compression algorithms like zstd alongside gzip for better data transfer, and implementing proper load balancing with health checks for high-availability services.

Examples:

• Set crossorigin defaults to avoid repetitive crossorigin: 'anonymous' parameters
• Use encode zstd gzip for better compression (zstd supported by 70% of users)
• Configure load balancing with health checks:

  handle /api/v1/streaming* {
    reverse_proxy localhost:4000 localhost:4001 {
        lb_policy least_conn
        health_uri /api/v1/streaming/health
    }
  }
  

This approach reduces configuration bloat, improves network performance, and ensures reliable service delivery.

---

Document code behavior

Document the “why” and “how” of your code, not just what it does. Add clear comments to explain:

1. Non-obvious behaviors and edge cases
2. Special input handling and transformations
3. Implementation rationale for tests
4. Usage examples for new APIs

Follow Go documentation conventions: use // for comments, don’t use dashes after function names, and follow the format: // FunctionName verb phrase.

Examples:

// Bad
func TestBindingBSON(t *testing.T) {
    data, _ := bson.Marshal(&obj)
    testBodyBinding(t, BSON, "bson", "/", "/", string(data), string(data[1:]))
}

// Good
func TestBindingBSON(t *testing.T) {
    data, _ := bson.Marshal(&obj)
    // Slicing the first byte simulates invalid BSON input for testing error handling
    testBodyBinding(t, BSON, "bson", "/", "/", string(data), string(data[1:]))
}

// Bad
if val == "" {
    // Code that handles empty values

// Good
if val == "" {
    // Empty string values are intentionally mapped to zero time to avoid parsing errors
    
// Bad
// RunLimited - use netutil.LimitListener to limit inbound accepts

// Good
// RunLimited attaches the router to a http.Server and starts listening and 
// serving HTTP requests using netutil.LimitListener to limit inbound accepts

Document behavior of both exported and non-exported elements when they implement important functionality. Include usage examples for new APIs, especially when they introduce patterns like go:embed.

---

Use theme utilities consistently

Always use theme utilities for consistent styling across the application instead of hard-coded values. Replace direct pixel values with theme functions like theme.spacing() for spacing, and access theme variables directly with theme.vars.* for theme-aware styling:

// Don't
padding: 16,
paddingBottom: 24,

// Do
padding: theme.spacing(2),
paddingBottom: theme.spacing(3),

For complex component styling, prefer the styled API over the sx prop as it offers better performance and readability, especially with longer style definitions:

// Less optimal for complex styling
<ToggleButtonGroup
  sx={(theme) => ({
    gap,
    ...(orientation === 'horizontal' && {
      // many complex styles...
    })
  })}
/>

// Better for complex styling
const StyledToggleButtonGroup = styled(ToggleButtonGroup)(({ theme }) => ({
  gap: props.gap,
  ...(props.orientation === 'horizontal' && {
    // many complex styles...
  })
}));

Choose the simplest CSS solutions possible and avoid unnecessary inline comments for self-explanatory style changes. When modifying properties, use specific CSS properties (like overflowY: 'auto' instead of overflow: 'auto') when the intent is clear.

---

Documentation formatting standards

Maintain consistent documentation formatting to ensure proper rendering and readability. Follow these key practices:

1. Consistent code output display: Standardize how objects are printed in examples. Either use print(<inst>) or print(repr(<inst>)) consistently throughout the documentation.

2. Proper markdown list formatting:
   • Always include a blank line after a list item when followed by a code block
   • Use 4-space indentation (not 2 or 3) for code blocks within lists to ensure proper rendering
3. Newline consistency: Be mindful of how newlines affect rendering, especially in lists and admonitions.

Example of proper markdown list formatting with code:

- List item with code example:

    ```python
    from pydantic import BaseModel
    
    class Example(BaseModel):
        field: str
        
    print(Example(field="value"))
    ```

Following these standards will prevent broken documentation rendering and maintain a consistent look and feel throughout the codebase.

---

optimize component memoization

When implementing React.memo for performance optimization, ensure props are structured to enable effective memoization. Pass individual primitive props separately rather than complex objects to allow React.memo to correctly detect unchanged props and prevent unnecessary re-renders.

Example:

// Before - complex object prop prevents effective memoization
<FormBuilderField field={{ ...field, hidden }} readOnly={readOnly} />

// After - individual props enable React.memo optimization  
<MemoizedField field={field} hidden={hidden} readOnly={readOnly} />

This approach is particularly important in components that render frequently or contain expensive operations. Consider the performance impact of data fetching patterns as well - avoid duplicate API calls by leveraging client-side query caching or strategic prop passing when the same data is needed in multiple components.

---

Documentation audience appropriateness

Ensure documentation content matches its intended audience and location. High-level documentation like README files should focus on essential information for the primary audience, while detailed technical information should be placed in developer-specific documentation. Avoid adding overly detailed or redundant information that may confuse or overwhelm readers.

Consider these guidelines:

• Top-level README files should contain information relevant to all users, not just developers
• Detailed codebase structure explanations belong in developer guides, not general documentation
• Auto-generated files should not be manually edited as changes will be overwritten
• When in doubt, ask whether the information serves the document’s primary purpose and audience

For example, instead of adding detailed directory structure to a README:

### Codebase structure
├──app                               // The app frontend  
├──bin                               // Scripts for running and hosting Mastodon
├──config                            // Code files relating to federated hosting

Consider whether this information is necessary for the README’s audience, or if it would be better placed in a dedicated developer documentation file.

---

Measure performance impact

Before making performance-related changes, measure the actual impact with benchmarks and profiling. Many performance assumptions can be misleading without data.

When performance concerns arise, create realistic benchmarks that reflect actual usage patterns. For example, when evaluating DOM operations:

function run(n = 1e6) {
  const els = Array(n);
  let i = n;
  while (i--) {
    let div = document.createElement('div');
    document.body.append(div);
    els[i] = div;
  }
  console.time('test');
  i = n;
  while (i--) {
    const div = els[i];
    div.nodeName.includes('-');
    div.namespaceURI === 'http://www.w3.org/1999/xhtml';
  }
  console.timeEnd('test');
}

Consider algorithmic complexity when choosing data structures. For operations like array lookups, analyze whether O(n*m) approaches like array.indexOf() should be replaced with O(n+m) alternatives using Set:

// O(select.options.length * value.length)
option.selected = ~value.indexOf(get_option_value(option));

// O(select.options.length + value.length)  
const values = new Set(value);
option.selected = values.has(get_option_value(option));

Add performance guards for expensive operations, but validate they’re actually needed. Avoid premature optimization while ensuring real bottlenecks are addressed with measurable improvements.

---

Consistent error patterns

Implement consistent error handling patterns throughout your codebase to improve readability and maintainability.

Key guidelines:

1. Use named error variables instead of inline error creation

   // Instead of
   return errors.New("invalid request")
      
   // Use
   var ErrInvalidRequest = errors.New("invalid request")
   return ErrInvalidRequest
   

2. Add explicit returns after error handling to avoid nested conditionals and improve readability

   // Instead of
   if err != nil {
       c.JSON(http.StatusInternalServerError, gin.H{
           "error": err.Error(),
       })
   } else {
       c.JSON(http.StatusOK, gin.H{
           "result": data,
       })
   }
      
   // Use
   if err != nil {
       c.JSON(http.StatusInternalServerError, gin.H{
           "error": err.Error(),
       })
       return
   }
   c.JSON(http.StatusOK, gin.H{
       "result": data,
   })
   

3. Reduce duplication in error handling by separating decision logic from response actions

   // Instead of duplicating similar code
   if errors.As(err, &maxBytesErr) {
       c.AbortWithError(http.StatusRequestEntityTooLarge, err).SetType(ErrorTypeBind)
   } else {
       c.AbortWithError(http.StatusBadRequest, err).SetType(ErrorTypeBind)
   }
      
   // Use
   var statusCode int
   switch {
   case errors.As(err, &maxBytesErr):
       statusCode = http.StatusRequestEntityTooLarge
   default:
       statusCode = http.StatusBadRequest
   }
   c.AbortWithError(statusCode, err).SetType(ErrorTypeBind)
   

Consistent error handling patterns make code more predictable, reduce bugs, and make it easier for other developers to understand error flows.

---

Distinguish Next.js routers

Always provide separate implementation instructions for Next.js App Router (13+) and Pages Router. These routing systems have different file structures, initialization requirements, and component placement:

• App Router: Place components and configuration in the appropriate files within the app directory:

  // app/layout.tsx for root configuration
  export default function RootLayout(props: { children: React.ReactNode }) {
    return (
      <html lang="en" suppressHydrationWarning>
        <body id="__next"> {/* Manually add ID for styling hooks */}
          <AppRouterCacheProvider options={{ enableCssLayer: true }}>
            {props.children}
          </AppRouterCacheProvider>
        </body>
      </html>
    );
  }
  

• Pages Router: Use custom files in the root directory:

  // pages/_document.tsx (needs to be manually created)
  export default function Document() {
    return (
      <Html>
        <Head />
        <body>
          <Main />
          <NextScript />
        </body>
      </Html>
    );
  }
  

When documenting features, clearly indicate which router approach is being used and provide separate examples for each. Always note router-specific requirements like manually adding element IDs (id="__next") for App Router that were automatically handled in earlier versions.

---

Understand query method behavior

When working with database queries in Active Record, it’s essential to understand the precise behavior of query methods to avoid unexpected results and performance issues.

Key considerations:

1. Method Override Behaviors: Some methods replace previous configurations rather than augmenting them. For example, pluck ignores any previous select clauses:

# This ignores the select(:email) - only id is selected
Customer.select(:email).pluck(:id)
# => SELECT "customers"."id" FROM customers

# For raw SQL in pluck, use Arel.sql:
Customer.pluck(Arel.sql("DISTINCT id"))
# => SELECT DISTINCT id FROM customers

1. Query Merging Complexity: When combining queries with merge, or, and and, be careful about how conditions are combined to avoid incorrect SQL generation:

# Complex queries can generate unexpected SQL if not carefully constructed
base = Comment.joins(:post).where(user_id: 1).where("recent = 1")
base.merge(base.where(draft: true).or(Post.where(archived: true)))

1. Index Usage Control: For performance optimization, understand how to control which indexes are used in queries:

# When using implicit_order_column with multiple columns
# Adding nil at the end prevents appending the primary key
add_index :users, [:created_at, :id], name: "optimal_recent_users_query"
User.implicit_order_column = [:created_at, nil] # Prevents adding id twice to ORDER BY

Carefully understanding these behaviors helps you write more predictable, efficient database queries and avoid unexpected results when refactoring.

---

Precompute over recalculate

Perform expensive calculations during initialization rather than on each request, and avoid unnecessary operations in frequently executed code paths. This significantly improves performance in high-traffic applications.

Key practices:

• Cache computed values that don’t change between requests
• Avoid redundant parsing operations on each request
• Eliminate unnecessary pointer operations in hot paths

Example:

// Instead of this:
func (c *Context) ClientIP() string {
    // Parse trusted proxies on every request
    for _, trustedProxy := range e.TrustedProxies {
        // Parse CIDR each time
    }
    return ip
}

// Do this:
type Engine struct {
    // Precomputed during initialization
    trustedCIDR []*net.IPNet
    // ...
}

func (e *Engine) Run() {
    // Precompute once during startup
    e.trustedCIDR = parseTrustedProxies(e.TrustedProxies)
    // ...
}

func (c *Context) ClientIP() string {
    // Use precomputed values
    return ip
}

Similarly, for operations like BSON marshaling, avoid unnecessary pointer indirection:

// Prefer this when possible:
bytes, err := bson.Marshal(r.Data)

// Over this:
bytes, err := bson.Marshal(&r.Data)

---

Initialize before null-checking

When handling potentially nil values, ensure proper initialization order to prevent race conditions and null reference errors. This is critical for maintaining thread safety and following idiomatic Go patterns.

For shared resources, acquire locks before performing null checks and initialization:

// Good: Lock first to prevent race conditions
c.KeysLocker.Lock()
if c.Keys == nil {
    c.Keys = make(map[string]interface{})
}

// Problematic: May miss concurrent initialization
if c.Keys == nil {
    c.KeysLocker.Lock()
    c.Keys = make(map[string]interface{})
}

When checking for specific error types, declare target variables before using them:

// Good: Declare before use
var maxBytesErr *http.MaxBytesError
if errors.As(err, &maxBytesErr) {
    // handle error
}

// Avoid: Creates unnecessary struct instance
maxBytesErr := &http.MaxBytesError{}
if errors.As(err, &maxBytesErr) {
    // handle error
}

This approach ensures proper resource handling, reduces memory allocation, and follows Go’s conventions for null safety patterns.

---

Preserve security configurations

Always respect explicitly set security attributes and properly sanitize user inputs to prevent security vulnerabilities. When modifying security-related configurations:

1. Only apply default values when the attribute is not explicitly set
2. Thoroughly validate and sanitize URL paths and other user inputs to prevent path traversal attacks

Example 1: When handling cookie security attributes:

// Good: Only override SameSite when not explicitly set
if cookie.SameSite == http.SameSiteDefaultMode {
    cookie.SameSite = c.sameSite
}

// Bad: Unconditionally overriding security attributes
cookie.SameSite = c.sameSite

Example 2: For URL path sanitization:

// Good: Initialize regex patterns once, outside of functions
var pathSanitizer = regexp.MustCompile("[^a-zA-Z0-9/-]+")

// Use the pre-compiled pattern to sanitize paths
sanitizedPath := pathSanitizer.ReplaceAllString(path, "")

Properly preserving security configurations and sanitizing inputs helps prevent CSRF, XSS, and path traversal vulnerabilities.

---

Extract duplicate logic

When code blocks become large or contain repetitive patterns, extract them into separate functions to improve readability and maintainability. This follows Clean Code principles of keeping functions short and focused on single responsibilities.

Key indicators for extraction:

• Configuration setup blocks that have grown large
• Identical or nearly identical code patterns across multiple locations
• Functions that handle multiple concerns or have grown beyond a reasonable size
• Repetitive error handling or validation logic

Example of extracting configuration logic:

// Before: Large configuration block in main function
func (r *Redirect) Route(name string, config ...RedirectConfig) error {
    cfg := RedirectConfig{CookieConfig: CookieConfigDefault}
    if len(config) > 0 {
        cfg = config[0]
    }
    if cfg.CookieConfig == (CookieConfig{}) {
        cfg.CookieConfig = CookieConfigDefault
    }
    // ... more configuration logic
}

// After: Extract to dedicated function
func (r *Redirect) Route(name string, config ...RedirectConfig) error {
    cfg := r.buildConfig(config...)
    // ... rest of route logic
}

func (r *Redirect) buildConfig(config ...RedirectConfig) RedirectConfig {
    cfg := RedirectConfig{CookieConfig: CookieConfigDefault}
    if len(config) > 0 {
        cfg = config[0]
    }
    // ... configuration logic
    return cfg
}

Example of extracting duplicate logic:

// Before: Duplicate proxy logic
func Do(c *fiber.Ctx, addr string, clients ...*fasthttp.Client) error {
    // ... setup code
    return cli.Do(req, res)
}

func DoRedirects(c *fiber.Ctx, addr string, maxRedirects int, clients ...*fasthttp.Client) error {
    // ... identical setup code
    return cli.DoRedirects(req, res, maxRedirects)
}

// After: Extract common logic
func do(c *fiber.Ctx, addr string, action func(*fasthttp.Client, *fasthttp.Request, *fasthttp.Response) error, clients ...*fasthttp.Client) error {
    // ... common setup code
    return action(cli, req, res)
}

This practice reduces code duplication, makes functions easier to test, and improves overall code organization.

---

Handle nulls with types

Enforce type safety by properly handling null and undefined values through TypeScript types and explicit checks. Avoid using non-null assertions (!) or type assertions (as any), and instead:

1. Use union types with null/undefined: ```typescript // Bad function process(value: string!) { return value.length; }

// Good function process(value: string | null) { if (!value) return 0; return value.length; }

2. Provide explicit defaults using nullish coalescing:
```typescript
// Bad
const count = data?.count || 0;  // '' and 0 are treated as false
const name = user?.name || "Anonymous";  // '' is treated as false

// Good
const count = data?.count ?? 0;  // only null/undefined trigger default
const name = user?.name ?? "Anonymous";

1. Use type guards for complex objects: ```typescript // Bad interface Response { data: any } const result = (response as Response).data;

// Good interface Response { data: string | null } function isResponse(value: unknown): value is Response { return typeof value === ‘object’ && value !== null && ‘data’ in value; } const result = isResponse(response) ? response.data : null;

This approach prevents runtime errors, makes null handling explicit, and leverages TypeScript's type system for better safety.

---

## Contextual error messages

<!-- source: rails/rails | topic: Error Handling | language: Ruby | updated: 2025-05-19 -->

Error messages should provide sufficient context to understand and debug the problem efficiently. Include both the expected and actual values in error messages, along with specific information about what failed. This makes troubleshooting much more straightforward and reduces debugging time.

**Good practice:**
```ruby
# Clear about what was expected and what was received
unless value == true || value == false
  raise ArgumentError, "distinct expects a boolean value, got: #{value.inspect}"
end

# Shows both expected and actual values
actual_checksum = service.compute_checksum(file) 
unless actual_checksum == checksum
  raise ActiveStorage::IntegrityError, "Checksum verification failed expecting #{checksum}, but downloaded file having #{actual_checksum}"
end

# Specific about which value caused the problem
unless ActiveStorage.supported_image_processing_methods.any? { |method| method_name == method }
  raise UnsupportedImageProcessingMethod, "Method '#{method_name}' is not supported. Supported methods: #{ActiveStorage.supported_image_processing_methods.join(', ')}"
end

Bad practice:

# Vague error message with no context
unless value == true || value == false
  raise ArgumentError, "Invalid value"
end

# Missing the actual values causing the failure
unless actual_checksum == checksum
  raise ActiveStorage::IntegrityError, "Checksum verification failed"
end

Contextual error messages make your API more user-friendly and significantly reduce troubleshooting time when problems occur. They also serve as implicit documentation about parameter constraints and expected behaviors.

---

Prefer direct property access

When property names are known at development time, use direct property access (e.g., object.property) over computed property access (e.g., object[propertyName]). This approach enhances code readability, enables better IDE autocompletion, improves type checking, and makes the code more maintainable.

Example - Instead of:

output[propName] = clsx(
  defaultProps?.[propName] as string,
  props?.[propName] as string,
);

output[propName] = {
  ...(defaultProps?.[propName] ?? ({} as React.CSSProperties)),
  ...(props?.[propName] ?? ({} as React.CSSProperties)),
};

Prefer:

output.className = clsx(
  defaultProps.className,
  props.className,
);

output.style = {
  ...defaultProps.style,
  ...props.style,
};

This approach eliminates unnecessary dynamic property access, type assertions, and optional chaining when the property name is statically known. Code becomes more concise and the intent is clearer.

---

referrer header privacy

When implementing features that link to external sites, carefully consider referrer policies to prevent unintended disclosure of sensitive information about users or the origin server. HTTP referrer headers can inadvertently expose details about what type of community, instance, or service users belong to, which may have privacy or safety implications.

This is particularly important in contexts where the origin server URL itself reveals sensitive information about users’ identities, affiliations, or communities. For example, users from specialized community servers (LGBTQ+, political, religious, etc.) could be inadvertently “outed” when clicking external links if the referrer header reveals their origin server.

Consider implementing referrer policies like no-referrer or same-origin for external links, and provide configuration options to allow administrators to control this behavior based on their community’s privacy needs.

Example configuration approach:

# config/locales/en.yml
allow_referrer_origin:
  desc: When your users click links to external sites, their browser may send the address of your server as the referrer. Disable this if this would uniquely identify your users, e.g. if this is a personal server.

---

Self-documenting identifier names

Use clear, self-documenting names for variables, methods, and classes that express intent without exposing unnecessary implementation details.

For methods and variables:

• Avoid abbreviations unless universally understood (use connection instead of conn, source_location instead of line)
• Follow natural language patterns with adjectives before nouns (use allowed_redirect_hosts instead of redirect_hosts_allowed)
• Remove implementation details from public API names (use compute_checksum instead of compute_checksum_in_chunks)

For error classes:

• Follow the “what? kind?” pattern (e.g., ChecksumUnsupportedError instead of UnsupportedChecksumError)
• Make names descriptive enough to understand the problem (use MissingRequiredOrderError instead of OrderError)
• Match existing conventions (like AssociationNotFoundError for consistency with HasManyThroughAssociationNotFoundError)

For method signatures:

• Choose concise yet descriptive names for parameters and methods
• Avoid overly verbose names like supports_disabling_use_of_index_for_queries? when supports_disabling_indexes? would suffice

Remember that code is read far more often than it’s written. Thoughtful naming reduces cognitive load for future readers.

---

Use language-specific syntax

Code snippets must use the correct language-specific syntax and include all necessary imports to compile properly. When writing examples:

1. Include all required imports for the libraries and data structures used
2. Use language-appropriate collection initializers and factories
3. Ensure code is placed in the correct language directory
4. Avoid mixing syntax from different languages (e.g., Kotlin syntax in Java files)

Bad Example (Java file with Kotlin syntax):

import io.appwrite.services.Databases;

Databases databases = new Databases(client);
databases.updateDocuments(
    "<DATABASE_ID>",
    "<COLLECTION_ID>",
    mapOf("a" to "b"),  // Wrong: Using Kotlin syntax in Java
    listOf()            // Wrong: Using Kotlin syntax in Java
);

Good Example (Java file with Java syntax):

import io.appwrite.services.Databases;
import java.util.Map;
import java.util.List;

Databases databases = new Databases(client);
databases.updateDocuments(
    "<DATABASE_ID>",
    "<COLLECTION_ID>", 
    Map.of("a", "b"),   // Correct: Using Java Map factory
    List.of()           // Correct: Using Java List factory
);

Proper language-specific syntax improves code readability and ensures examples actually compile and run correctly for developers.

---

validate configuration schemas

Always validate configuration objects using proper schema validation (like Zod) before type casting or using the configuration values. Avoid unsafe type casting from input types to output types without validation, as this can lead to runtime errors when expected properties are undefined.

Configuration resolution should follow a clear hierarchy: file-based config → inline config → defaults. Parse and validate configurations at the appropriate boundaries, not after unsafe casting.

Example of the problem:

// Risky - casting before validation
let userConfig = options as Config
// userConfig.routesDirectory may not be defined yet

// Better approach
const validatedConfig = configSchema.parse({
  ...fileConfig,
  ...inlineConfig,
  ...defaults
})

When building configuration utilities, accept optional directory parameters to avoid hardcoded paths, and leverage existing config resolution functions rather than duplicating logic. This ensures consistent behavior across different entry points and prevents configuration drift.

---

Ensure proper async context

Always wrap asynchronous operations (await, suspend functions, try-await) in the appropriate language-specific async context. Top-level await is generally not supported and will cause runtime errors.

JavaScript/Node.js (CommonJS):

// ❌ Incorrect - top-level await
const result = await databases.createDocuments(...);

// ✅ Correct - async IIFE with error handling
(async () => {
  try {
    const result = await databases.createDocuments(...);
    console.log(result);
  } catch (error) {
    console.error(error);
  }
})();

Swift:

// ❌ Incorrect - try-await outside async context
let documentList = try await databases.upsertDocuments(...);

// ✅ Correct - Task with do-catch
Task {
  do {
    let documentList = try await databases.upsertDocuments(...);
    print(documentList);
  } catch {
    print("Error:", error);
  }
}

C#:

// ❌ Incorrect - await outside async method
DocumentList result = await databases.CreateDocuments(...);

// ✅ Correct - async method
public static async Task Main(string[] args)
{
    DocumentList result = await databases.CreateDocuments(...);
    Console.WriteLine(result);
}

Always include appropriate error handling for asynchronous operations to prevent unhandled promise/task rejections and improve debugging.

---

Efficient data processing

When implementing algorithms that process large data streams or collections, use a chunking approach rather than processing the entire input at once. This improves memory efficiency and prevents out-of-memory errors for large inputs.

Key practices to follow:

1. Process data in manageable chunks when dealing with potentially large inputs
2. Be consistent in chunking strategy across related operations
3. Remember to properly initialize data structures that will grow during processing
4. Reset stream positions (e.g., rewind) after processing when the data needs to be reused

# Efficient implementation with chunking
def compute_checksum_in_chunks(io, algorithm: default_algorithm)
  raise ArgumentError, "io must be rewindable" unless io.respond_to?(:rewind)
  
  digest = checksum_implementation(algorithm).new.tap do |checksum|
    read_buffer = "".b  # Binary string buffer for reuse
    while io.read(5.megabytes, read_buffer)  # Process in 5MB chunks
      checksum << read_buffer  # Update digest with each chunk
    end
    
    io.rewind  # Reset stream position for reuse
  end.base64digest
end

# Properly initialize a hash that will hold growing collections
@collection_map = Hash.new { |h, k| h[k] = {} }  # Each key gets its own hash

Always consider the memory implications of your algorithm implementation, especially when processing user-generated content of unpredictable size. Using chunked processing patterns helps ensure your code performs well at scale while maintaining consistent memory usage.

---

Guard database query results

Always validate database query results before accessing their methods or properties. Methods like findOne(), getDocument(), and similar database operations can return null or empty documents. Failing to check these results before access leads to runtime errors.

Example of unsafe code:

$latestDeployment = $dbForProject->findOne('deployments', [ /* ... */ ]);
$latestBuild = $dbForProject->getDocument('builds', 
    $latestDeployment->getAttribute('buildId', '')  // May throw if $latestDeployment is null
);

Safe pattern:

$latestDeployment = $dbForProject->findOne('deployments', [ /* ... */ ]) 
    ?? new Document();  // Provide empty fallback

if (!$latestDeployment->isEmpty()) {  // Check before accessing
    try {
        $latestBuild = $dbForProject->getDocument(
            'builds',
            $latestDeployment->getAttribute('buildId', '')
        );
    } catch (Throwable $e) {
        $latestBuild = new Document();  // Handle failure gracefully
    }
}

Key practices:

1. Provide fallback empty documents when queries may return null
2. Check document existence before accessing properties
3. Use try-catch when chaining dependent queries
4. Consider logging failed lookups in production environments

---

OpenAPI spec compliance

Ensure all API definitions strictly follow OpenAPI specification standards to maintain compatibility with tooling and clients. This includes:

1. Match default values with their defined types:

   "data": {
     "type": "object",
     "description": "Document data as JSON object.",
   -  "default": [],
   +  "default": {},
   }
   

2. Place custom properties under vendor extensions (x-prefix):

   - "methods": [
   + "x-appwrite-methods": [
     {
    "name": "createDocument",
    ...
     }
   ]
   

3. Use proper variable syntax for URL templates:

   - "url": "https://<REGION>.cloud.appwrite.io/v1"
   + "url": "https://{region}.cloud.appwrite.io/v1",
   + "variables": {
   +   "region": {
   +     "description": "Regional subdomain (e.g., us-east-1)",
   +     "default": "us-east-1"
   +   }
   + }
   

Maintaining specification compliance ensures API documentation is accurate, enables proper code generation, and provides a consistent developer experience.

---

Context-appropriate API authentication

Always use the authentication method appropriate for your API client’s execution context. Server-side SDKs should use API key authentication (with setKey()) rather than session-based authentication, which is meant for client-side applications.

Why it matters:

• Server SDKs are designed to work with API keys for secure backend operations
• Session-based authentication (setSession()) won’t function properly in server contexts
• Consistent authentication patterns improve maintainability across projects

Example - PHP Server SDK:

$client = (new Client())
    ->setEndpoint('https://<REGION>.cloud.appwrite.io/v1') 
    ->setProject('<YOUR_PROJECT_ID>')
    ->setKey('<YOUR_API_KEY>'); // Correct: Using API key for server authentication
    // ->setSession(''); // Incorrect: Session auth doesn't work server-side

Example - Kotlin Server SDK:

val client = Client()
    .setEndpoint("https://<REGION>.cloud.appwrite.io/v1")
    .setProject("<YOUR_PROJECT_ID>")
    .setKey("<YOUR_API_KEY>") // Correct: Using API key for server authentication
    // .setSession("") // Incorrect: Session auth doesn't work server-side

---

Match defaults to types

When specifying default values in schemas or configurations, ensure they match the declared type to prevent validation errors and unpredictable behavior. For object types, use empty objects ({}) not null, undefined, or arrays. For string types that should be empty by default, use empty strings ("") not null. This practice improves type safety and prevents runtime type errors.

// INCORRECT: Type mismatch between declared type and default
{
  "type": "object",
  "description": "Document data as JSON object.",
  "default": [],  // An array default for an object type
}

// CORRECT: Type-consistent defaults
{
  "type": "object",
  "description": "Document data as JSON object.",
  "default": {},  // An object default for an object type
}

// CORRECT: Empty string default for optional string
{
  "type": "string",
  "description": "Optional document ID",
  "default": "",  // Empty string instead of null
}

---

Prevent API documentation duplication

When maintaining API specification files (like OpenAPI or Swagger), ensure consistency and avoid duplication that can confuse documentation generators and API consumers:

1. Eliminate duplicate service definitions - Remove or merge tags that represent the same service with different names (e.g., “projects” and “project”).

2. Standardize naming conventions - Use consistent casing and plural/singular forms for similar entities across all documentation.

3. Maintain consistent style - Ensure all descriptions:

   • End with proper punctuation (typically periods)
   • Use correct grammar
   • Maintain consistent tone and formatting

Example:

// BAD: Duplicate tags with inconsistent descriptions
"tags": [
  {
    "name": "projects",
    "description": "The Project service allows you to manage all the projects in your Appwrite server."
  },
  {
    "name": "project",
    "description": "The Project service allows you to manage all the projects in your Appwrite server."
  }
]

// GOOD: Single, well-defined tag
"tags": [
  {
    "name": "projects",
    "description": "The Projects service allows you to manage all the projects in your Appwrite server."
  }
]

This consistency helps maintain clear documentation and prevents confusion in generated code or documentation.

---

Use proper authentication

Always implement the correct authentication method for API clients as specified in the SDK documentation. Incorrect authentication methods can lead to security vulnerabilities, API access failures, or unintended behavior.

Incorrect example:

Client client = new Client()
    .setEndpoint("https://<REGION>.cloud.appwrite.io/v1")
    .setProject("<YOUR_PROJECT_ID>")
    .setSession(""); // INCORRECT: Empty session token

Correct examples:

// For API key authentication (server-side)
Client client = new Client()
    .setEndpoint("https://<REGION>.cloud.appwrite.io/v1")
    .setProject("<YOUR_PROJECT_ID>")
    .setKey("<YOUR_API_KEY>");

// For JWT authentication
Client client = new Client()
    .setEndpoint("https://<REGION>.cloud.appwrite.io/v1")
    .setProject("<YOUR_PROJECT_ID>")
    .setJWT("<YOUR_JWT>");

Using the proper authentication method ensures your application interacts securely with external services and prevents unauthorized access.

---

Pause tracking during side-effects

When executing side-effects in reactive systems (like event handlers, cleanup functions, or async operations), always pause reactivity tracking to prevent unintended dependencies from being captured. This prevents infinite loops, race conditions, and unexpected behavior that can occur when reactive state is accessed during side-effects.

Use pauseTracking() before and resetTracking() after such operations, and ensure tracking is reset even when errors occur by using try/finally blocks:

// Bad: Side-effect might track unwanted dependencies
function handleEvent() {
  callEventHandler();  // Might access reactive state
}

// Good: Pausing tracking during side-effect
function handleEvent() {
  pauseTracking();
  try {
    callEventHandler();  // Safe to access reactive state
  } finally {
    resetTracking();  // Always reset, even if errors occur
  }
}

For reusable patterns, consider implementing pausable effects:

class PausableEffect extends ReactiveEffect {
  private _isPaused = false;
  
  pause() {
    this._isPaused = true;
  }
  
  resume() {
    this._isPaused = false;
    // Additional logic as needed
  }
  
  update() {
    if (!this._isPaused) {
      return super.run();
    }
  }
}

This pattern is essential for maintaining reactivity system integrity, especially when dealing with event handlers, cleanup functions, and asynchronous operations that could otherwise cause unpredictable behavior or performance issues.

---

Remove commented out code

Delete commented-out code instead of retaining it in the codebase. Commented code creates confusion, adds maintenance overhead, and clutters the source files. If code is no longer needed, remove it entirely - version control systems will preserve the history if it needs to be referenced later.

Example of what to avoid:

// export function isActionError(error: any): error is ActionError {
//   return error && typeof error === "object" && "error" in error && error.error;
// }

export function newFunction() {
  // Implementation
}

Instead, simply delete unused code:

export function newFunction() {
  // Implementation
}

If you need to temporarily disable code during development:

1. Use feature flags or environment variables for toggling functionality
2. Create a separate branch for experimental changes
3. Use TODO comments to mark incomplete work, but don’t retain commented implementation

This keeps the codebase clean, reduces cognitive load when reading code, and prevents outdated commented code from becoming misleading over time.

---

validate before accessing

Always validate parameters for both null values and correct types before accessing their properties or methods. Provide safe fallback values when validation fails to prevent crashes and undefined behavior.

This pattern prevents common crashes from null dereference and type mismatches. Instead of assuming parameters are valid, explicitly check both nullability and type before use.

Example from the codebase:

// Bad - assumes parameters are valid
std::string([type UTF8String])

// Good - validates type and null, provides fallback
const char *typeCStr = [type isKindOfClass:[NSString class]] && type ? [type UTF8String] : "";

For JavaScript/C++ interop:

// Bad - direct access without validation
jsi::String stringValue = value.getString(*runtime);

// Good - check type first, use safe conversion
if (value.isString()) {
  jsi::String stringValue = value.asString(*runtime);
}

Apply this pattern when:

• Converting between different type systems (JS/Objective-C/C++)
• Accessing properties of potentially null objects
• Working with optional or nullable parameters
• Processing user input or external data

The key is to fail gracefully with meaningful defaults rather than crashing on unexpected null or wrong-type values.

---

Consistent database parameters

Maintain consistency and clarity in database-related parameters and configuration variables. Follow these practices:

1. Use descriptive variable names that match parameter names for clarity
2. Follow established naming patterns for database configuration
3. Use ‘enabled’/’disabled’ instead of boolean values for configuration flags
4. Avoid unnecessary complexity in database parameter handling

Example 1 - Simplifying parameter handling:

// Instead of:
$dbService = $this->getParam('database', 'mariadb') === 'mariadb' ? 'mariadb' : 'postgresql';

// Use:
$database = $this->getParam('database', 'mariadb');

Example 2 - Consistent naming for database configuration flags:

// Instead of:
_APP_SLOW_QUERIES=true

// Use:
_APP_SLOW_QUERIES_BLOCK=enabled

These practices improve code readability, maintainability, and reduce the potential for errors in database-related code.

---

consistent authentication patterns

Use standardized authentication decorators consistently across all endpoints to ensure proper security coverage and follow the principle of least privilege. Always use @RequireAuthentication() as the primary way to protect endpoints, and explicitly use @SkipPermissionsCheck() for authenticated routes that don’t require permission validation.

This approach prevents accidentally leaving endpoints unprotected and maintains consistency in security patterns. The authentication decorator should automatically apply both user authentication and permission guards, with explicit opt-out for permission checks when not needed.

Example:

// Standard protected endpoint (requires auth + permissions)
@RequireAuthentication()
async updateEnvironment() { ... }

// Authenticated but no permission check needed
@RequireAuthentication()
@SkipPermissionsCheck()
async listMyEnvironments() { ... }

// Within the endpoint, check specific permissions for sensitive data
if (user.permissions.includes(PermissionsEnum.API_KEY_READ)) {
  // Return sensitive data like API keys
}

This pattern ensures security by default while allowing granular control when needed, reducing the risk of security vulnerabilities from inconsistent authentication handling.

---

Event listener management

Implement comprehensive event listener management by registering listeners on multiple relevant sources and providing appropriate fallback mechanisms. This ensures robust event handling across different environments and prevents missed events that could lead to inconsistent application state.

When handling events that may originate from multiple sources, register listeners on all relevant targets rather than relying on a single source. Additionally, implement feature detection and fallbacks for environments that may not support newer APIs.

Example implementation:

// Register on multiple event sources
document.body.addEventListener('click', handleClickOutside);
containerElement()?.addEventListener('click', handleClickOutside);

// Use feature detection with fallbacks
const supportsInterpolateSize = CSS.supports('interpolate-size', 'allow-keywords');
if (contentRef && !supportsInterpolateSize) {
  resizeObserver.observe(contentRef);
}

// Ensure proper cleanup
onCleanup(() => {
  document.body.removeEventListener('click', handleClickOutside);
  containerElement()?.removeEventListener('click', handleClickOutside);
  resizeObserver.disconnect();
});

This pattern is particularly important for network event handling where events may come from multiple connection sources, protocols, or fallback mechanisms, and proper cleanup prevents resource leaks in long-running network applications.

---

Use constructor.name context

Always set logger context using this.constructor.name and configure it via the setContext() method rather than hardcoding context strings or passing context as parameters to individual log calls.

This approach ensures consistency across the codebase and proper context display in logs. Hardcoded context strings can become outdated when classes are renamed, while this.constructor.name automatically reflects the current class name.

Correct approach:

@Injectable()
export class SendWebhookMessage {
  constructor(private logger: PinoLogger) {
    this.logger.setContext(this.constructor.name);
  }

  async execute() {
    // Context is already set, no need to pass it
    this.logger.error({ err: error }, 'Failed to create execution details');
  }
}

Avoid:

// Don't use hardcoded context strings
const LOG_CONTEXT = 'SendWebhookMessageUseCase';
this.logger.setContext(LOG_CONTEXT);

// Don't pass context as parameter - it won't be used properly
this.logger.error({ err: error }, 'Failed to create execution details', LOG_CONTEXT);

Setting context once in the constructor ensures all log messages from that class instance include the proper context automatically, making logs more traceable and maintainable.

---

Prevent metrics cardinality explosion

When implementing metrics and telemetry in your application, avoid using dynamic values like path parameters or user IDs directly as metric tags or dimensions. This practice causes cardinality explosion, which leads to excessive memory usage, degraded performance, and can overwhelm your monitoring systems.

Instead:

1. Use route templates rather than actual paths:
   • Good: /client-endpoint-with-path-param/{name} as a metric tag
   • Bad: /client-endpoint-with-path-param/123 as a metric tag
2. For high-cardinality data like tenant IDs or user identifiers:
   • Store them in span attributes for tracing
   • Use exemplars to correlate metrics with traces
   • Query APM systems for detailed analysis

Example of proper implementation:

// WRONG: Will cause cardinality explosion
@Path("template/path/{value}")
public class PathTemplateResource {
    @GET
    public String get(@PathParam("value") String value) {
        // Don't do this - adds a high-cardinality tag
        ContextLocals.put("metric-tag", value);
        // ...
    }
}

// CORRECT: Uses route templates instead
@Path("template/path/{value}")
public class PathTemplateResource {
    @GET
    public String get(@PathParam("value") String value) {
        // For tracing/debugging, put in span attributes instead
        Span.current().setAttribute("path.value", value);
        // ...
    }
}

Remember that for each unique tag value, you multiply the number of time series across all other dimensions (methods, status codes, endpoints), which can quickly overwhelm your metrics system.

---

API evolution strategy

Design APIs with future extensibility in mind by using parameter objects instead of direct method parameters. When an API might need additional parameters in the future, encapsulate them in an interface or class:

// Instead of adding parameters directly:
<K, V> Uni<V> get(K key, Function<K, V> valueLoader, Duration expiresIn);

// Prefer an encapsulating approach:
<K, V> Uni<V> get(K key, Function<K, V> valueLoader, CacheOptions options);

For parameter objects, prefer interfaces over concrete classes to allow for extension without breaking changes. When naming parameters or methods, align with established industry standards (e.g., use “expiresAfter” instead of “expiresIn” to match Caffeine’s terminology).

Choose clear, descriptive method names over abbreviations (e.g., authenticationContextInterceptorCreator() rather than authCtxInterceptorCreator()). For methods with similar functionality, maintain a consistent pattern - if you have send() and sendAndAwait(), consider also adding sendAndForget() for completeness.

When providing builder-style APIs, ensure utility methods that don’t contribute to object construction are placed in appropriate utility classes rather than in the builder itself.

---

Feature flags over vendors

When checking for database backend capabilities, always use feature flags rather than checking specific vendor names. This makes your code more maintainable and vendor-agnostic while allowing third-party backends to implement support through the feature flag system.

Instead of explicitly checking the vendor:

if connection.vendor == "sqlite":
    # SQLite-specific implementation
    ...
else:
    # Implementation for other databases
    ...

Declare and use feature flags:

# In database feature definition
class DatabaseFeatures:
    supports_json_absent_on_null = property(lambda self: self.connection.vendor != "sqlite")

# In your code
if connection.features.supports_json_absent_on_null:
    # Use feature requiring JSON ABSENT ON NULL
    ...
else:
    # Use alternative implementation or raise NotSupportedError
    raise NotSupportedError("This database does not support ABSENT ON NULL")

This pattern centralizes capability detection in feature flags rather than spreading vendor-specific checks throughout the codebase, making it easier to update support for features across different database backends.

---

Optimize build scripts

Improve CI/CD pipeline efficiency by optimizing package.json scripts. Run compatible tasks in parallel using pattern matching capabilities of your package manager, and implement thorough cleanup scripts that remove all build artifacts and caches. This reduces build times and ensures consistent build environments.

{
  "scripts": {
    // Run multiple lint tasks in parallel
    "lint": "pnpm run \"/^lint:eslint|^lint:ox/\"",
    
    // Comprehensive cleanup of all build artifacts and caches
    "clean": "rimraf packages/*/dist temp .eslintcache"
  }
}

---

Follow naming patterns

Maintain consistent naming conventions throughout the codebase by following established patterns and avoiding redundancy. Key principles include:

1. Error naming: Use the pattern Err + [Subject] + [Error Condition] (e.g., ErrStorageRetrievalFailed instead of ErrNotGetStorage)

2. Test/benchmark naming: Include underscores for consistency (Test_ and Benchmark_ prefixes)

3. Constant naming: Use descriptive names that indicate purpose (DefaultFormat instead of FormatDefault)

4. Avoid redundant prefixes: Don’t repeat package context in type names (KeyLookupFunc instead of KeyauthKeyLookupFunc)

5. Use proper English: Avoid non-standard plurals or constructions (AllFormData() instead of FormDatas())

6. Function naming: Choose concise, clear names that match existing patterns (FromContext() instead of FromGoContext(), Logger() to match similar functions)

Example of consistent error naming:

// Good - follows Err + Subject + Condition pattern
ErrStorageRetrievalFailed = errors.New("unable to retrieve data from CSRF storage")
ErrStorageSaveFailed      = errors.New("unable to save data to CSRF storage")

// Avoid - inconsistent pattern
ErrNotGetStorage = errors.New("unable to retrieve data from CSRF storage")

This ensures code readability and helps developers quickly understand naming conventions when contributing to the project.

---

Descriptive configuration keys

Configuration keys should clearly indicate their value type, units, or expected format to prevent misunderstandings and errors. Include unit information directly in key names when appropriate and ensure documentation accurately reflects the default values and behavior.

For example, instead of using a generic key with ambiguous units:

// Unclear - are these hours or minutes?
'maintenance_bypass_cookie_lifetime' => (int) env('SESSION_MAINTENANCE_BYPASS_COOKIE_LIFETIME', 720),

Use a more descriptive key that includes the unit:

'maintenance_bypass_cookie_lifetime_minutes' => (int) env('SESSION_MAINTENANCE_BYPASS_COOKIE_LIFETIME_MINUTES', 720),

This approach makes configuration self-documenting, reduces the need to consult documentation, and prevents errors from unit mismatches or incorrect assumptions about value types. When environment variables serve as configuration sources, maintain this same naming convention to ensure consistency across your application’s configuration system.

---

Prevent workflow recursion

Control GitHub Actions workflow execution to avoid infinite loops and unnecessary builds. Implement these practices:

1. Add paths-ignore filters for generated files that might trigger the workflow again:

on:
  push:
    branches: ["main"]
    paths-ignore:
      - version.txt  # Skip when only version files change

1. Explicitly specify branch references when checking out code to ensure the correct version is processed:

- name: Checkout code
  uses: actions/checkout@v4
  with:
    ref: main  # Explicitly reference the target branch
    fetch-depth: 0

1. Target the correct branch when pushing changes to avoid misdirected commits:

- name: Push changes
  uses: ad-m/github-push-action@master
  with:
    github_token: ${{ secrets.GITHUB_TOKEN }}
    branch: trails  # Explicitly specify the target branch

1. Restrict event triggers to only required events to prevent premature actions:

on:
  push:
    branches: [ "main" ]
  # pull_request:  # Remove if not needed for publishing operations
  #   branches: [ "main" ]

These practices ensure your workflows run only when needed and operate on the correct code, preventing wasteful CI resources and confusing version history.

---

Leverage Kotlin null-safety

Utilize Kotlin’s null-safety features effectively to create cleaner, more robust code:

1. For class properties that will be initialized before use, prefer lateinit var over nullable types with ?: ```kotlin // Avoid private var server: MockWebServer? = null

// Prefer private lateinit var server: MockWebServer

2. Design API signatures to minimize forcing clients to use the unsafe `!!` operator:
```kotlin
// Avoid
suspend fun <T : Any> TransactionalOperator.executeAndAwait(f: suspend (ReactiveTransaction) -> T?): T?

// Prefer
suspend fun <T> TransactionalOperator.executeAndAwait(f: suspend (ReactiveTransaction) -> T): T

1. Avoid redundant null checks when Kotlin’s null-safety operators are already in use: ```kotlin // Redundant val ctor = BeanUtils.findPrimaryConstructor(SomeClass::class.java)!! assertThat(ctor).isNotNull() // Unnecessary since !! already asserts non-null

// Cleaner val ctor = BeanUtils.findPrimaryConstructor(SomeClass::class.java)!! // Continue using ctor directly

---

## remove redundant code

<!-- source: mastodon/mastodon | topic: Code Style | language: TypeScript | updated: 2025-05-13 -->

Identify and remove code elements that no longer serve a purpose, including unused imports, redundant function calls, and obsolete ESLint disable directives. This improves code readability and maintainability by eliminating unnecessary clutter.

When refactoring or updating configurations, review the codebase for:
- Imports that are no longer used after removing function calls
- Function calls that duplicate functionality already handled elsewhere (e.g., in application layouts)
- ESLint disable directives that are no longer needed due to rule changes

Example of cleanup:
```typescript
// Before - redundant code
import { start } from 'mastodon/common';
import { loadLocale } from 'mastodon/locales';

// eslint-disable-next-line import/no-default-export
start();

// After - cleaned up
import { loadLocale } from 'mastodon/locales';

Regularly audit your code during reviews to ensure only necessary code remains, especially after configuration changes or architectural updates.

---

Externalize configuration values

Configuration files should not contain hardcoded values for usernames, credentials, hostnames, or environment-specific settings. Instead, use environment variables, templated values, or dynamic references that can adapt to different deployment contexts.

This approach improves:

• Security: Prevents credentials from being checked into source control
• Portability: Allows configurations to work across different environments
• Collaboration: Makes it easier for teams to work on the same codebase without conflicts

For Docker and CI/CD configurations:

# In docker-compose.yml
- DATABASE_URL: "postgresql://postgres:password@db:5432/inboxzero?schema=public"
+ DATABASE_URL: ${DATABASE_URL:-postgresql://${POSTGRES_USER:-postgres}:${POSTGRES_PASSWORD}@db:5432/${POSTGRES_DB:-inboxzero}?schema=public}

# In GitHub workflows
- DOCKER_USERNAME: "elie222"
+ DOCKER_USERNAME: "${{ github.repository_owner }}"

# In Docker images
- image: ghcr.io/elie222/inbox-zero:latest
+ image: ghcr.io/${ORGANIZATION:-$USER}/inbox-zero:latest

For sensitive values, consider using secrets management systems for production environments. For local development, provide .env.example files as templates that developers can copy to create their own .env files, which should be excluded from version control.

---

prefer specific cryptographic libraries

When adding cryptographic dependencies, critically evaluate whether broad libraries like OpenSSL are necessary or if more specific, focused alternatives can meet your requirements. Broad cryptographic libraries often include extensive functionality that may not be needed, potentially increasing the attack surface and complexity.

Before adding general-purpose cryptographic libraries, consider:

• Whether a specific library (like RSA for RSA operations) can fulfill your needs
• The principle of least privilege - only include what you actually need
• Maintenance and security update considerations for smaller, focused libraries

Example from the codebase:

# Instead of:
openssl = "0.10"

# Consider using:
rsa = "0.9"  # If you only need RSA functionality

This approach reduces dependency bloat, minimizes potential security vulnerabilities, and makes your cryptographic intentions more explicit in the codebase.

---

Minimize redundant operations

Optimize application performance by preventing unnecessary renders, calculations, and network operations. Implement proper memoization strategies, lift shared operations to parent components, and batch related tasks.

Memoization best practices:

• Ensure comparison functions in memo() accurately evaluate prop changes: ```jsx // Incorrect: Always returns true, preventing needed updates export const Component = memo(PureComponent, () => true);

// Correct: Uses default shallow comparison or provides accurate comparison export const Component = memo(PureComponent); // Or with custom comparison when needed: export const Component = memo(PureComponent, (prev, next) => prev.id === next.id && prev.status === next.status );

**Data operations:**
- Move shared hooks and state to parent components instead of repeating in list items
- Batch related network calls and updates with Promise.all:
```jsx
// Inefficient: Serial execution with multiple updates
const handleBulkOperation = async () => {
  for (const id of selected) {
    await apiCall(id);  // N network requests
    mutate();           // N re-validations
  }
};

// Optimized: Parallel execution with single update
const handleBulkOperation = async () => {
  const calls = selected.map(id => apiCall(id));
  await Promise.all(calls);  // Parallel requests
  mutate();                  // Single re-validation
};

Expensive calculations:

• Extract expensive calculations into memoized functions with useMemo or into callbacks that execute only when needed, not on every render

---

Complete hook dependency arrays

Ensure all hooks (useEffect, useCallback, useMemo) explicitly list every dependency used within their callback functions. Missing dependencies can lead to stale closures, unexpected behaviors, and hard-to-debug issues.

Example of proper dependency management:

// ❌ Incomplete dependencies
useEffect(() => {
  if (textareaRef.current) {
    const finalValue = domValue || localStorageInput || "";
    setInput(finalValue);
    adjustHeight();
  }
}, []); // Missing localStorageInput and setInput

// ✅ Complete dependencies
useEffect(() => {
  if (textareaRef.current) {
    const finalValue = domValue || localStorageInput || "";
    setInput(finalValue);
    adjustHeight();
  }
}, [localStorageInput, setInput]);

// Same applies for useCallback
const handleAction = useCallback(
  async (index: number, action: string) => {
    const item = items[index];
    if (!item) return;
    onAction(item);
    refreshData();
  },
  [items, onAction, refreshData] // List all used dependencies
);

Key points:

• List every variable, function, and prop used inside the callback
• Don’t silence linter warnings without proper justification
• Consider refactoring if dependency arrays become too large
• Use dependency arrays to optimize re-renders and prevent infinite loops

---

maintain API backwards compatibility

When modifying existing public APIs, prioritize backwards compatibility to avoid breaking external consumers. Before making changes that alter method signatures, property access patterns, or introduce new abstract methods, first investigate whether existing functionality can be preserved or extended.

For property access changes, provide alternative access methods while maintaining the original interface:

// Instead of only changing:
// mEventEmitterCallback.invoke("onPress"); 
// to:
// getEventEmitterCallback().invoke("onPress");

// Provide both approaches - keep the property accessible AND add the getter
protected EventEmitterCallback mEventEmitterCallback; // Keep original
protected final EventEmitterCallback getEventEmitterCallback() { // Add new getter
    return mEventEmitterCallback;
}

For new functionality, leverage existing methods rather than creating new abstract methods:

// Instead of adding:
// public abstract void invalidate();

// Use existing method:
public void clear() {
    // Add invalidation logic here
    // existing clear logic...
}

This approach protects downstream consumers, reduces migration burden, and maintains API stability. Always check if your changes affect external packages before finalizing API modifications.

---

Prevent async race conditions

Always guard against race conditions when working with asynchronous code. Implement these patterns to avoid unpredictable behavior:

1. Always await async operations

   // Incorrect: Potential race condition
   processPreviousSentEmailsAction(emailAccountId);
      
   // Correct: Ensures operation completes before continuing
   await processPreviousSentEmailsAction(emailAccountId);
   

2. Disable interactive elements during async operations

   const [isLoading, setIsLoading] = useState(false);
      
   return (
     <Button
       disabled={isLoading}
       onClick={async () => {
         if (isLoading) return;
         setIsLoading(true);
         try {
           await someAsyncAction();
           // Handle success
         } finally {
           setIsLoading(false);
         }
       }}
     >
       {isLoading ? 'Processing...' : 'Submit'}
     </Button>
   );
   

3. Clean up event listeners in useEffect hooks

   useEffect(() => {
     if (!api) return;
        
     const handler = () => {
       // Handle event
     };
     api.on("select", handler);
        
     return () => {
       // Clean up to prevent memory leaks
       api.off("select", handler);
     };
   }, [api]);
   

These practices prevent issues like duplicate submissions, unhandled promises, memory leaks, and unpredictable UI behavior resulting from concurrent operations interfering with each other.

---

Review configuration currency

Regularly audit and update configuration to align with current tool capabilities and best practices. Remove obsolete settings that are no longer needed due to tool evolution, and consolidate fragmented configuration approaches into more unified solutions.

When underlying tools gain new capabilities, review existing configuration to identify opportunities for simplification. For example, when build tools natively support language features, remove explicit transformation rules. When libraries provide consolidated configuration options, prefer them over fragmented environment variables.

Example from database configuration:

// Avoid fragmented approach with multiple environment variables
if (env.DB_SSLMODE) {
  logger.warn(
    'Using DB_SSLMODE is not recommended, instead use DATABASE_URL with SSL options',
  );
}

// Prefer consolidated configuration
config = toClientConfig(parse(env.DATABASE_URL, { useLibpqCompat: true }));

Establish a regular review cycle to assess whether configuration reflects current standards and tool capabilities. Document the reasoning behind configuration choices to help future maintainers understand when updates may be appropriate.

---

Use semantic exceptions

Choose exception types that accurately reflect the nature of the error. Use LogicException for developer errors like incorrect usage, InvalidArgumentException for invalid inputs, OutOfBoundsException for range violations, and specialized exceptions for domain-specific errors.

This improves error diagnostics, enables selective exception handling, and communicates intent more clearly than using generic exceptions or returning magic values.

// Instead of this
throw new Exception("Invalid compression mode");

// Do this
if ($mode < 1 || $mode > 9) {
    throw new OutOfBoundsException('Compression mode must be between 1 and 9.');
}

// Instead of this
throw (new ModelNotFoundException)->setModel(get_class($this), $value);

// Do this
throw (new InvalidIdFormatException)->setModel(get_class($this), $value);

// Instead of using assertions that may be disabled
assert(is_object($model), 'Resource collection guesser expects objects.');

// Do this
if (!is_object($model)) {
    throw new InvalidArgumentException('Resource collection guesser expects objects.');
}

// For related exceptions, create hierarchies for better error handling
class ViteException extends Exception {}
class ViteManifestNotFoundException extends ViteException {}

When creating exception hierarchies, consider extending from framework exceptions like HttpException for web applications to ensure proper HTTP status codes are returned. This allows consumers to handle entire categories of errors with a single catch block while still providing appropriate responses.

Good exception selection is the foundation of effective error handling and leads to more maintainable, self-documenting code.

---

Secure authentication defaults

Configure authentication mechanisms with secure default settings to prevent security vulnerabilities. When implementing WebAuthn or similar authentication protocols:

1. Avoid attestation bypasses: Do not include verifiers that allow skipping attestation checks.

   // INCORRECT: Allows attestation bypass
   return new WebAuthnAsyncManager(
       Arrays.asList(
           new NoneAttestationStatementAsyncVerifier(),
           // other verifiers
       )
   );
   

2. Use recommended timeouts: Follow standard security recommendations for timeout values.

   // INCORRECT: Too short for authentication ceremonies
   this.timeout = config.timeout().orElse(Duration.ofSeconds(60));
      
   // CORRECT: Use recommended 5 minutes
   this.timeout = config.timeout().orElse(Duration.ofMinutes(5));
   

3. Enable security verifications by default: Features like user presence verification should be enabled by default.

   // INCORRECT: Security feature disabled by default
   this.userPresenceRequired = config.userPresenceRequired().orElse(false);
      
   // CORRECT: Security feature enabled by default
   this.userPresenceRequired = config.userPresenceRequired().orElse(true);
   

4. Prevent information disclosure: Avoid endpoints that expose account information to unauthenticated requests, which could enable account enumeration attacks.

   // VULNERABLE: Returns user-specific credential information
   // to unauthenticated requests
   .map(challenge -> security.toJsonString(challenge))
   .subscribe().with(challenge -> ok(ctx, challenge), ctx::fail);
   

---

descriptive specific naming

Use descriptive and specific names that clearly communicate purpose and context. Method names should indicate their platform target when applicable, test names should describe the expected behavior, and function names should follow consistent conventions.

Platform-specific methods: Include the platform in the method name to avoid confusion:

// Instead of
isCatalogAsset(): boolean

// Use
isIOSCatalogAsset(): boolean

Test naming: Test names should be self-explanatory so engineers understand the purpose without reading implementation:

// Instead of
it('Should view properly submit cancel text', async function () {

// Use  
it('Press Cancel Button - Validates cancel confirmation message displays', async function () {

Function naming consistency: Use camelCase for functions and underscore prefix for private methods:

// Instead of
function _download_prebuild_release_tarball(

// Use
function _downloadPrebuildReleaseTarball(

Names should eliminate ambiguity about what code does, which platform it targets, or what behavior it tests. When reviewing code, ask: “Can I understand this element’s purpose from its name alone?”

---

Consistent package naming

Use consistent and meaningful naming patterns for packages based on their purpose, visibility, and scope. This improves clarity in build scripts, dependencies, and during development.

For regular packages:

• Use descriptive names that clearly indicate the package’s purpose or technology
• Example: @app/pigment-css-next-app instead of @app/next-app

For special-purpose packages:

• Apply consistent prefixes based on package visibility:
  • @mui/internal-* for internal packages used across the codebase
  • @mui/private-* for packages not intended for external consumption
  • @mui/test-* for testing utilities

In package.json:

{
  "name": "@mui/internal-bundle-size",
  // or
  "name": "@app/pigment-css-next-app"
}

This naming consistency makes it easier to understand package purposes when referenced in scripts (e.g., --ignore @app/pigment-css-next-app) and helps developers immediately recognize the intended usage scope of each package.

---

Use appropriate log levels

Choose logging levels that match the intended audience and purpose of the message. Use debug or silent logging for internal operations, optional behaviors, and retry logic that shouldn’t be visible to end users. Reserve console output and higher log levels (info, warning, error) for user-relevant information.

Internal operations like workspace detection, file system probing, and retry mechanisms should use debug logging to avoid cluttering user output during normal operation. This is especially important for optional behaviors that may fail gracefully.

Example of appropriate level selection:

// For internal/optional operations - use debug logging
try {
  const workspaceConfig = detectWorkspace(packagePath);
} catch (err) {
  if (err.code !== 'ENOENT') {
    logger.debug(`Failed getting workspace root from ${packagePath}:`, err);
  }
}

// For user-facing messages - use appropriate console levels
function prebuildLog(
  message /*: string */,
  level /*: 'info' | 'warning' | 'error' */ = 'warning',
) {
  const prefix = '[Prebuild] ';
  let colorFn = (x /*:string*/) => x;
  if (process.stdout.isTTY) {
    if (level === 'info') colorFn = x => `\x1b[32m${x}\x1b[0m`;
    else if (level === 'error') colorFn = x => `\x1b[31m${x}\x1b[0m`;
    else colorFn = x => `\x1b[33m${x}\x1b[0m`;
  }
  console.log(colorFn(prefix + message));
}

This approach prevents information overload while maintaining useful debugging capabilities for developers.

---

Ensure API contract integrity

Maintain strict consistency between API implementation and contract by ensuring:

1. Request/response schemas match exactly between client and server
2. All required parameters are validated and documented
3. HTTP status codes accurately reflect response types
4. OpenAPI documentation stays synchronized with implementation

Example of proper implementation:

// API Route implementation
export const POST = withError(async (request: Request) => {
  // 1. Validate request against documented schema
  const body = checkoutSessionSchema.parse(await request.json());
  
  // 2. Return appropriate status codes
  if (!session?.user?.email) {
    return NextResponse.json(
      { error: "Not authenticated" }, 
      { status: 401 }
    );
  }

  // 3. Include all required parameters
  const checkout = await stripe.checkout.sessions.create({
    customer: stripeCustomerId,
    success_url: `${env.NEXT_PUBLIC_BASE_URL}/api/stripe/success`,
    mode: "subscription",
    line_items: [{
      price: env.STRIPE_PRICE_ID,
      quantity: 1
    }]
  });

  return NextResponse.json({ checkout });
});

// OpenAPI documentation
registry.registerPath({
  method: "post",
  path: "/checkout",
  description: "Create checkout session",
  request: {
    body: {
      content: {
        "application/json": {
          schema: checkoutSessionSchema
        }
      }
    }
  },
  responses: {
    200: { description: "Success" },
    401: { description: "Not authenticated" }
  }
});

This ensures reliable API behavior, reduces runtime errors, and maintains clear contracts with API consumers.

---

Enforce clear data ownership

Always establish and maintain clear ownership semantics in concurrent code to prevent data races. This includes:

1. Use RAII patterns for resource management (especially locks)
2. Ensure data lifetime matches synchronization scope
3. Prefer value semantics over references for shared data
4. Be explicit about ownership transfer in async operations

Example of proper RAII lock usage:

void DynamicTexture::reserveSize(const Size& size, int32_t uniqueId) {
    std::lock_guard<std::mutex> guard(mutex); // RAII lock
    // ... protected operations ...
} // Auto-unlock on scope exit

// Instead of:
void DynamicTexture::reserveSize(const Size& size, int32_t uniqueId) {
    mutex.lock();
    // ... operations that might throw ...
    mutex.unlock(); // Might never be reached!
}

For shared data access:

// Avoid:
std::string_view getData() {
    std::shared_lock<std::shared_mutex> lock(mutex);
    return string_view{buffer.data()}; // Dangerous! View might outlive lock
}

// Prefer:
std::string getData() {
    std::shared_lock<std::shared_mutex> lock(mutex);
    return std::string{buffer}; // Safe copy
}

---

DRY class hierarchies

Follow the Don’t Repeat Yourself (DRY) principle when designing class hierarchies. Extract common functionality into base classes and avoid duplicating state or methods in subclasses. When extending a class, delegate to parent implementations rather than redefining functionality.

Examples of issues to avoid:

// AVOID: Duplicating state in subclass
public class TransformAuto extends Transform {
    @Nullable
    private CameraPosition cameraPosition; // Duplicate of parent state
    
    @UiThread
    public CameraPosition getCameraPosition() {
        if (cameraPosition == null) {
            cameraPosition = invalidateCameraPosition();
        }
        return cameraPosition;
    }
}

// BETTER: Delegate to parent
public class TransformAuto extends Transform {
    // No duplicate cameraPosition variable
    
    @UiThread
    public CameraPosition getCameraPosition() {
        return super.getCameraPosition(); // Delegate to parent
    }
}

For similar implementations across different technologies (e.g., GL and Vulkan renderers), extract shared code into common base classes. This improves maintainability and prevents bugs from inconsistent implementations.

---

Prefer values over pointers

When designing classes and interfaces, prefer passing lightweight objects by value rather than using raw pointers or converting smart pointers to raw pointers using .get(). This eliminates the risk of null dereferences and dangling pointer issues.

For example, instead of:

// Risky approach with raw pointers
class Parser {
public:
    std::string spriteURL;
    std::vector<std::unique_ptr<Sprite>> sprites;
    
    Sprite* getSprite() {
        return sprites[0].get();  // Dangerous: consumer could hold onto this raw pointer
    }
};

Prefer value semantics:

// Safer approach with value objects
class Parser {
public:
    std::string spriteURL;
    std::vector<Sprite> sprites;  // Store as values
    
    const Sprite& getSprite() {   // Return reference with clear lifetime
        return sprites[0];
    }
    
    // Or return by value if the object is lightweight
    Sprite getSpriteCopy() {
        return sprites[0];
    }
};

When values aren’t suitable (e.g., for polymorphic types), use smart pointers consistently throughout the API rather than mixing smart and raw pointers. This approach prevents null reference exceptions and makes ownership semantics clearer in your codebase.

---

leverage build tool automation

Modern build tools like Vite automatically handle many performance optimizations that previously required manual implementation. Trust these automated capabilities rather than duplicating effort with manual resource hints and preloading directives.

Build tools automatically preload chunks that entrypoints depend on, including support for early hints when available. This eliminates the need for manual preload directives in most cases.

However, be aware of exceptions where manual intervention may still be beneficial:

• Dynamically imported scripts are not preloaded by default
• Critical resources that need explicit prioritization

Example of removing redundant manual preloading:

- content_for :header_tags do
  - if user_signed_in?
    -# These can be removed - Vite handles preloading automatically
    -# = preload_pack_asset 'features/compose.js', crossorigin: 'anonymous'
    -# = preload_pack_asset 'features/home_timeline.js', crossorigin: 'anonymous'

Additionally, choose performance analysis tools based on testing and proven effectiveness rather than convenience. Tools like rollup-plugin-visualizer may provide better insights than default options for bundle analysis and optimization decisions.

---

Minimize unnecessary object allocations

Avoid creating unnecessary objects, especially in frequently executed code paths. This includes being mindful of implicit object allocations from common Ruby operations like array methods, string concatenations, and temporary variable creation.

Key practices:

1. Avoid unnecessary array allocations from methods like first(n), flatten, or map
2. Use direct iteration instead of intermediate collections when possible
3. Consider using mutation methods (e.g., <<) over concatenation (+) for strings
4. Cache computed values that are reused frequently

Example - Before:

def process_items
  first_two = items.first(2)  # Creates new array
  result = first_two.map { |x| x.to_s }  # Creates another array
  result.flatten.compact  # Creates more arrays
end

Example - After:

def process_items
  result = []
  items.each_with_index do |item, index|
    break if index >= 2
    result << item.to_s  # Single array, built incrementally
  end
  result
end

This optimization is especially important in hot code paths, such as request processing or data transformation pipelines, where the cumulative effect of unnecessary allocations can impact performance and trigger more frequent garbage collection.

---

Clear database configuration examples

Database configuration examples in documentation should be correct, minimal, and include proper context. Provide only essential configuration properties rather than defaults or environment-specific values that would change in production. Use proper syntax and be precise about component interactions.

For configuration properties, always use the correct syntax:

# Good: Using proper equals sign syntax
quarkus.datasource."named-datasource".reactive = true
quarkus.datasource."named-datasource".db-kind = postgresql

# Bad: Using incorrect comma syntax
quarkus.datasource."named-datasource".reactive", true
quarkus.datasource."named-datasource".db-kind", postgresql

When documenting multiple database access approaches (like Hibernate ORM and Hibernate Reactive), clearly explain their boundaries:

# Note: When using both ORM and Reactive, they won't share the same persistence context
# It's recommended to use ORM in blocking endpoints, and Reactive in reactive endpoints

For complex configurations like transaction recovery, include explanatory notes about the consequences of configuration choices:

# Only disable recovery if you understand the implications
# May result in data loss if disabled incorrectly
quarkus.datasource.jdbc.enable-recovery = false

Organize related examples in dedicated sections rather than mentioning capabilities in passing or pointing to test code, which can confuse users.

---

Standardize code formatting patterns

Maintain consistent code formatting patterns across the codebase to improve readability and maintainability. This includes:

1. Use consistent spacing and indentation
2. Group related code blocks logically
3. Break long lines for better readability
4. Use clear and descriptive naming

Example of good formatting:

// Good: Clear organization and spacing
import React from 'react';
import { createTheme, ThemeProvider } from '@mui/material/styles';

const theme = createTheme({
  modularCssLayers: true,
});

export default function AppTheme({ children }: { children: React.ReactNode }) {
  return <ThemeProvider theme={theme}>{children}</ThemeProvider>;
}

// Bad: Inconsistent spacing and organization
import React from 'react'
import {createTheme,ThemeProvider} from '@mui/material/styles'
const theme=createTheme({modularCssLayers:true})
export default function AppTheme({children}:{children:React.ReactNode}){return(
  <ThemeProvider theme={theme}>{children}</ThemeProvider>
)}

This pattern helps maintain code quality by:

• Making code easier to read and understand
• Reducing cognitive load during code reviews
• Facilitating easier maintenance and updates
• Promoting consistency across the team

---

Framework-aware text composition

When writing user-facing text (error messages, notifications, labels), understand how your framework automatically processes and modifies that text before it reaches users. Many frameworks like Rails automatically combine messages with attribute names or apply other transformations that can result in redundant or grammatically incorrect output.

Before finalizing any user-facing text, consider:

• How the framework will process or modify your text
• Different contexts in which the message might appear (past vs future events, different user states)
• Whether automatic prefixes or suffixes will create redundant phrasing

Example from Rails localization:

# Problematic - Rails prefixes with "Fields"
errors:
  fields_with_values_missing_names: Names of extra profile fields with values cannot be empty
# Result: "Fields Names of extra profile fields..."

# Better - Account for Rails' automatic prefixing
errors:
  fields_with_values_missing_names: with values cannot have empty names
# Result: "Fields with values cannot have empty names"

Always test your messages in their actual runtime context to ensure they read naturally and provide clear guidance to users.

---

Validate configuration changes

Before modifying default configuration settings, thoroughly understand and test their implications. Django’s default configurations often include important safeguards that prevent subtle bugs.

For example, the ENQUEUE_ON_COMMIT setting in task backends defaults to True for good reason:

@task
def my_task():
    Thing.objects.get(id=thing_id)  # Could fail if transaction hasn't committed yet

with transaction.atomic():
    thing = Thing.objects.create()
    my_task.enqueue(thing_id=thing.id)
    # With ENQUEUE_ON_COMMIT=False, task might run before transaction commits

Similarly, the QUEUES restriction in task backends prevents typos that could cause tasks to be enqueued but never executed.

When working with time-sensitive data, be particularly careful with timezone configurations as they can lead to unexpected query results when using functions like Trunc across different environments.

Always test configuration changes across all target environments before deployment, as some issues only manifest in specific contexts or at scale.

---

optimize collection iterations

Avoid multiple passes through the same data structure when a single iteration can accomplish the same work. This reduces computational complexity and improves performance, especially for large datasets.

Instead of using multiple array traversals like filter_map chains:

# Inefficient: multiple traversals
params = uris.filter_map { |uri| uri_to_local_account_params(uri) }
usernames = params.filter_map { |param, value| value.downcase if param == :username }
ids = params.filter_map { |param, value| value if param == :id }

Use a single iteration to collect all needed data:

# Efficient: single traversal
usernames = []
ids = []

uris.each do |uri|
  param, value = uri_to_local_account_params(uri)
  usernames << value.downcase if param == :username
  ids << value if param == :id
end

This principle also applies to avoiding duplicate iteration logic in collection processing services and preventing redundant recursive operations by checking if work has already been completed before proceeding.

---

Hook dependencies stability

Ensure hook dependencies are minimal, stable, and follow React’s rules to prevent unnecessary re-renders and maintain predictable behavior. This includes:

1. Remove unnecessary dependencies: Only include dependencies that actually change the hook’s behavior. For example, remove state.revalidation from dependency arrays when the function doesn’t need to recreate on state changes.

2. Avoid writing to refs during render: Never write to ref.current inside useMemo or during component render, as this violates React’s rules and can cause unpredictable behavior with transitions.

3. Use stable references: Ensure objects passed as dependencies maintain stable identity to prevent cascading re-renders.

4. Proper useEffect cleanup: Don’t return promises from useEffect and ensure dependency arrays include all referenced values.

Example of problematic code:

// Bad - writes to ref during render in useMemo
const searchParams = useMemo(() => {
  searchParamsRef.current = getSearchParamsForLocation(location.search);
  return searchParamsRef.current;
}, [location.search]);

// Bad - unstable state object in dependencies
useEffect(() => {
  navigate(to, { replace, state, relative });
}, [navigate, to, replace, state, relative]); // state might be unstable

Example of improved code:

// Good - use useEffect to update ref
useEffect(() => {
  searchParamsRef.current = getSearchParamsForLocation(location.search);
}, [location.search]);

// Good - resolve path outside effect for stability
const path = resolveTo(to, matches, locationPathname, relative);
const jsonPath = JSON.stringify(path);
useEffect(() => {
  navigate(JSON.parse(jsonPath), { replace, state, relative });
}, [navigate, jsonPath, relative, replace, state]);

This approach ensures components re-render only when necessary and maintains predictable behavior across React’s concurrent features.

---

Enhance code clarity

Ensure all code examples and documentation are as clear and complete as possible for developers. This includes adding clarifying inline comments to explain non-obvious behavior, including all necessary import statements, and structuring information for maximum readability.

Key practices:

• Add inline comments to clarify behavior, especially for files or configurations that might be confusing (e.g., // 👈🏼 ignored for excluded files)
• Include complete import statements in code examples rather than assuming developers know what to import
• Break complex statements into separate, digestible points
• Use proper grammar and standard abbreviations (e.g., “i.e.” not “ie”)

Example of good clarity:

// Include all imports
import { Link, createLink } from '@tanstack/react-router'
import { Button } from '@mui/material'

// Clear file structure with explanatory comments
routes/
├── posts.tsx
├── -posts-table.tsx // 👈🏼 ignored from route generation
├── -components/
│   ├── header.tsx // 👈🏼 ignored from route generation
│   └── footer.tsx // 👈🏼 ignored from route generation

This approach reduces confusion, speeds up developer onboarding, and prevents common implementation mistakes by making examples self-contained and immediately understandable.

---

Document public APIs

All public APIs, interfaces, and methods should include comprehensive JavaDoc that clearly explains their purpose, parameters, return values, and any non-obvious behaviors. This is especially important for:

1. Public interfaces and SPIs that will be used by external developers
2. Methods with complex parameters (like priority values)
3. Methods with non-obvious execution order or side effects
4. Build items and integration points

JavaDoc should be added at the time the code is written, not as an afterthought. For deprecations, ensure to include forRemoval=true to clearly document the API lifecycle.

Example:

/**
 * Context for handling application shutdown.
 * Tasks can be registered with different priorities to control execution order.
 */
public interface ShutdownContext {

    int DEFAULT_PRIORITY = Interceptor.Priority.LIBRARY_AFTER;
    int SHUTDOWN_EVENT_PRIORITY = DEFAULT_PRIORITY + 100_000;

    /**
     * Adds a shutdown task with the default priority.
     * 
     * @param runnable The task to execute during shutdown
     */
    default void addShutdownTask(Runnable runnable) {
        addShutdownTask(DEFAULT_PRIORITY, runnable);
    }

    /**
     * Adds a shutdown task with the specified priority.
     * Higher priority tasks are executed first during shutdown.
     * 
     * @param priority Task execution priority - higher values run before lower values
     * @param runnable The task to execute during shutdown
     */
    void addShutdownTask(int priority, Runnable runnable);
}

---

Standardize configuration paths

Follow consistent patterns for storing and referencing configuration files across projects. Place custom configuration files in standardized locations (e.g., src/main/docker for Dockerfiles, .s2i for S2I environment files) and use consistent naming conventions. When referencing file paths in configuration properties, use relative paths from the project root to ensure portability.

For example, to use a custom Dockerfile for OpenShift deployment:

# Place custom Dockerfiles in the standard location
quarkus.openshift.native-dockerfile=src/main/docker/Dockerfile.custom-native

Or for S2I deployment configuration:

# Create a standard .s2i/environment file with proper settings
MAVEN_S2I_ARTIFACT_DIRS=target/quarkus-app
S2I_SOURCE_DEPLOYMENTS_FILTER=app lib quarkus quarkus-run.jar
JAVA_OPTIONS=-Dquarkus.http.host=0.0.0.0
JAVA_APP_JAR=/deployments/quarkus-run.jar

Using standardized paths improves maintainability and helps team members quickly locate configuration files across different projects. It also prevents confusion when multiple configuration files serve similar purposes but are stored in different locations. Always verify the correct property names when referencing paths (e.g., using native-dockerfile for native builds, not jvm-dockerfile).

---

preserve component patterns

When refactoring React components, maintain essential component patterns including type annotations, ref forwarding capabilities, and thoughtful component composition. Avoid losing important functionality during simplification.

Key considerations:

• Preserve component type annotations when converting between component patterns (e.g., forwardRef to regular functions)
• Ensure ref forwarding remains functional for parent components that need to pass refs
• Consider component hierarchy and whether wrapper components can be simplified or consolidated
• Maintain consistency with similar components in the codebase

Example of preserving component type during refactoring:

// Before: forwardRef with component type
const View: component(...) = React.forwardRef(...)

// After: regular function but preserve the type
function View({...}: Props): React.Node {
  // component logic
}

export default View as component(
  ref?: React.RefSetter<React.ElementRef<typeof ViewNativeComponent>>,
  ...props: ViewProps
);

For ref forwarding, ensure parent components can still pass refs by merging internal refs with forwarded ones, similar to patterns used in TouchableOpacity. When restructuring component hierarchies (like SafeAreaView/View combinations), evaluate whether the nesting serves a purpose or can be simplified while maintaining the same functionality.

---

Choose efficient algorithms

Prefer built-in methods and appropriate data structures over manual implementations to improve both performance and code readability. Consider the computational complexity and trade-offs of different approaches.

When processing collections, leverage optimized built-in methods instead of manual loops:

// Instead of manual reduce loop
const allParams = matches()
  .flatMap((m) => m.params)
  .reduce((prev, curr) => {
    const keys = Object.keys(curr)
    for (const key of keys) {
      if (prev[key] === undefined) {
        prev[key] = curr[key]
      }
    }
    return prev
  }, {})

// Use built-in methods with appropriate ordering
const allParams = Object.assign(
  {},
  ...matches()
    .reverse()
    .flatMap((m) => m.params),
)

Choose data structures based on your specific use case requirements. For detecting property additions, consider the trade-offs: Proxy for plain objects, or redesign to use Array.push() or Map.set() which can be more easily intercepted.

Avoid expensive type operations that can impact development performance. Default generic type parameters to simple types (like string) rather than large unions when the constraint already provides the necessary flexibility.

---

consistent code formatting

Maintain consistent formatting standards across code and documentation to improve readability and maintainability. This includes proper ordering of logical conditions and consistent use of backticks for code values in comments.

For complex conditional statements, organize conditions in a logical order that enhances readability:

// Better: Group related conditions and order logically
if (
  viewTransitionMode === false ||
  prefersNoTransition ||
  hasUAVisualTransition ||
  !isChangingPage(to, from)
) {
  // handle condition
}

In JSDoc comments and documentation, wrap code values and boolean literals in backticks for proper formatting:

/**
 * Whether the component should render when `pending` is `true`
 * @param {boolean} showPending - Set to `true` to show loading state
 */

This practice ensures code is more readable for team members and maintains professional documentation standards that are especially important in React component libraries and shared codebases.

---

Use semantic null handling

When designing APIs and data structures, be intentional about null and undefined usage. Use null and undefined with distinct semantic meanings rather than interchangeably. For example, undefined can indicate “not yet loaded” while null indicates “does not exist”. However, avoid nullable types when simpler alternatives serve the same purpose - if an empty string conveys the same meaning as null (like “no description available”), prefer the empty string to simplify type handling.

Example of meaningful null/undefined distinction:

// Good: Semantic distinction
function useAccountId() {
  // undefined = not fetched yet, null = doesn't exist
  if (accountId) {
    return accountId;
  }
  return undefined; // or null, depending on semantic meaning
}

Example of avoiding unnecessary nullables:

// Instead of: avatar_description: string | null
// Prefer: avatar_description: string (empty string when no description)
interface AccountShape {
  avatar_description: string; // "" means no description
  header_description: string; // "" means no description
}

---

Use direct path imports

For optimal performance, use direct path imports instead of barrel imports when working with UI component libraries like Material UI. This practice improves both production bundle size through better tree-shaking and significantly enhances development server performance.

Recommended:

// Good - Direct path import
import Button from '@mui/material/Button';

Avoid:

// Avoid - Barrel import
import { Button } from '@mui/material';

While modern bundlers (Vite, Webpack 5+, Next.js 13.5+) handle tree-shaking well for production builds, barrel imports can severely slow down development server startup time and hot module reloading.

For enforcing this pattern across your team, consider configuring your editor to discourage barrel imports:

// .vscode/settings.json
{
  "typescript.preferences.autoImportSpecifierExcludeRegexes": ["^@mui/[^\\/]+$"]
}

This small change can lead to significant performance improvements in large applications without requiring additional Babel plugins or complex configuration.

---

Write targeted, specific tests

Tests should validate specific, well-defined behaviors with clear assertions that directly relate to what’s being tested. Avoid writing overly general or unfocused tests that try to cover too much at once, as these are often harder to maintain and debug when they fail.

Good tests:

1. Have a clear, singular purpose evident from their name and implementation
2. Include specific assertions that validate exactly what you’re testing
3. Provide helpful error messages that make failures easy to diagnose
4. Are separated by functionality rather than combining different test cases

For example, instead of writing a general test:

# Too general and unfocused
def test_model_attributes():
    model = Model()
    # Testing too many things at once
    assert model.field == "default"
    assert model._private_attr is not None
    assert callable(model.method)

Write specific, targeted tests:

def test_private_attribute_not_skipped_during_ns_inspection() -> None:
    # Clear comment explaining the test's purpose
    # It is important for the enum name to start with the class name
    # (it previously caused issues with qualname comparisons):
    class Fullname(str, Enum):
        pass

    class Full(BaseModel):
        _priv: object = Fullname

    # Specific assertion testing exactly one behavior
    assert isinstance(Full._priv, ModelPrivateAttr)

When parameterizing tests, ensure each parameter set tests a distinct case that belongs together. If test cases require different assertion logic or warning checks, they should be in separate test functions.

---

Spring DI precedence rules

When developing Quarkus extensions that interact with classes containing Spring annotations (like @Service, @Component, etc.), ensure your extension respects Spring DI’s scope definitions by setting appropriate annotation transformer priorities.

Spring DI extension uses the default priority of 1000 for its transformers. If your extension also adds scopes or bean-defining annotations to classes, it should use a lower priority value to allow Spring annotations to take precedence.

For example, when implementing an annotation transformer that adds scopes:

@Override
public int priority() {
    return 500; // Lower priority than Spring DI's 1000
}

Alternatively, if using the AutoAddScopeBuildItem pattern:

@BuildStep
AutoAddScopeBuildItem autoAddScope() {
   return AutoAddScopeBuildItem.builder()
      .containsAnnotations(YOUR_ANNOTATIONS) 
      .defaultScope(BuiltinScope.YOUR_SCOPE)
      .priority(500) // Lower than Spring DI's priority
      .build();
}

This approach prevents conflicts when multiple extensions try to add “auto” scopes to the same classes, ensuring Spring annotations are properly honored in the application.

---

Extract test helpers

Create reusable helper functions for common test setup patterns to reduce duplication and improve maintainability. When you find yourself repeating the same mock objects, test data structures, or setup code across multiple tests, extract them into shared utilities.

This approach provides several benefits:

• Changes to data structures only need to be made in one place
• Tests become more readable and focused on the actual behavior being tested
• Consistency is maintained across the test suite
• New fields or properties can be added without touching every individual test

For example, instead of duplicating complex mock objects:

// Before: Repeated in every test
let context: FrameworkContextObject = {
  routeModules: { root: { default: () => null } },
  manifest: {
    routes: {
      root: {
        hasLoader: false,
        hasAction: false,
        hasErrorBoundary: false,
        id: "root",
        module: "root.js",
      },
    },
    entry: { imports: [], module: "" },
    url: "",
    version: "",
  },
};

// After: Centralized helper
let context = mockFrameworkContext();

Similarly, when adding new fields to test data arrays, update all existing entries to maintain consistency, even if the new field has the same value as existing ones. This ensures that assertions against the new field work correctly across all test cases.

---

prefer explicit readable constructs

Choose explicit and semantic code constructs that enhance readability over more concise but less clear alternatives. This improves code maintainability and reduces cognitive load for developers.

Key practices:

• Use ternary operators instead of && in JSX to make the conditional logic explicit and avoid potential rendering issues
• Use semantic methods like endsWith() instead of manual string indexing operations
• Structure complex conditionals with clear if/else branches rather than nested ternaries when there are multiple conditions

Example transformations:

// Avoid: && operator in JSX (can cause rendering issues)
{ENABLE_DEV_WARNINGS && heyDeveloper}

// Prefer: explicit ternary
{ENABLE_DEV_WARNINGS ? heyDeveloper : null}

// Avoid: manual string operations
toPathname[toPathname.length - 1] === "/"

// Prefer: semantic methods
toPathname.endsWith("/")

This approach makes code intentions clearer, reduces the chance of subtle bugs, and makes the codebase more accessible to developers of varying experience levels.

---

Evaluate nil check necessity

Before adding nil checks, evaluate whether they are actually necessary or if they represent false positives from static analysis tools. Consider Go’s built-in nil safety patterns and semantics.

Key principles:

1. Add explicit nil validation for public API parameters that could reasonably be nil, especially when the function would panic or behave unexpectedly
2. Question nil checks flagged by static analysis tools - tools like nilaway can produce false positives where nil states are impossible given the code flow
3. Leverage Go’s nil-safe operations - operations like len(data) return 0 for nil slices/maps, making explicit nil checks often redundant
4. Distinguish between nil and zero values - understand that []string{} (empty slice) and []string(nil) (nil slice) have different semantics, though both have length 0

Example of necessary nil check:

// NewWithClient creates a client from an existing fasthttp.Client
func NewWithClient(c *fasthttp.Client) *Client {
    if c == nil {
        panic("client cannot be nil")
    }
    return &Client{client: c}
}

Example of unnecessary nil check:

func parseToStruct(data map[string][]string) error {
    // Unnecessary: len(nil) == 0 in Go
    if data == nil {
        return nil
    }
    // Better: direct length check handles nil case
    if len(data) == 0 {
        return nil
    }
}

When in doubt, consider: “Can this value actually be nil given the calling context?” and “Does Go already handle this nil case safely?”

---

Benchmark algorithmic optimizations

Always validate performance improvements with benchmarks rather than assuming algorithmic optimizations provide benefits. Many seemingly faster approaches may not deliver measurable gains or may even perform worse in practice.

When proposing algorithmic changes for performance reasons:

1. Provide benchmark evidence comparing the old and new approaches
2. Test with realistic data sizes and conditions
3. Consider maintainability costs versus performance gains
4. Implement “fast path” optimizations only when measurements justify the complexity

Example from a filtering optimization attempt:

// Proposed "faster" in-place filtering
function turboFilterInPlace(data, predicate) {
  for (let i = data.length; i--; i >= 0) {
    if (!predicate(data[i], i, data)) {
      const lastItem = data[data.length - 1]
      if (i < --data.length) data[i] = lastItem;
    }
  }
  return data;
}

// Result: Benchmark showed it's "not faster than the existing implementation"

Before implementing complex optimizations, measure whether simpler approaches like using appropriate data structures (Set for deduplication, Map for lookups) provide sufficient performance gains with better code clarity.

---

Implement least privilege

Apply the principle of least privilege for all repository and system access to enhance security. Each role should be granted only the permissions necessary to perform their specific responsibilities:

1. Repository maintainers should have “maintain access” rather than “admin rights” for day-to-day operations
2. Security reports should follow a dedicated triage process through security teams first
3. Release capabilities should be restricted to authorized individuals with appropriate permissions

This practice reduces the attack surface and limits the potential impact of compromised accounts.

Example implementation in team documentation:

# Repository Access Levels

- TC Members: Admin access
- Repository Captains: Maintain access and package publication rights
- Contributors: Write access to specific repositories
- Security Triage Team: Access to security reports

Security vulnerabilities must be reported to the security triage team first, who will involve repository captains after initial assessment.

---

consistent dependency formatting

Maintain consistent formatting and organization when managing dependencies in package.json files. Use semver range notation (^) consistently for all dependencies to allow compatible updates, and make targeted changes rather than bulk updates to preserve clean git history and blame information.

Example:

// Good - consistent semver ranges and targeted updates
"@biomejs/biome": "^1.0.0",
"@babel/runtime": "^7.27.0"

// Avoid - missing semver range and bulk updates
"@biomejs/biome": "1.0.0"  // Missing ^ prefix

When updating dependencies, only modify the specific packages you intend to upgrade rather than running broad update commands that change multiple unrelated dependencies simultaneously.

---

Choose meaningful identifier names

Names for variables, methods, and classes should be descriptive, semantically accurate, and consistent with established conventions. Follow these guidelines:

1. Use names that clearly describe the purpose or content:

   // Bad
   const val: any = getValue();
      
   // Good
   const fileOrFiles: File | File[] = getUploadedFiles();
   

2. Follow semantic naming conventions:
   • Boolean variables/methods should use “is”, “has”, or “should” prefixes
   • Error classes should be specific (e.g., RouterAliasError instead of Error)
   • Maintain consistent pluralization (e.g., PostsService for a service handling multiple posts)
3. Align with framework and library conventions:
   • Match external library naming patterns when extending their functionality
   • Follow project’s established naming patterns for consistency
   • Preserve meaningful naming from referenced libraries
4. Avoid generic or ambiguous names:
   • Replace generic names like ‘data’, ‘value’, ‘info’ with context-specific alternatives
   • Use type-specific prefixes/suffixes when appropriate
   • Consider the scope and usage when choosing names

Remember that good names serve as self-documentation and improve code maintainability.

---

Guard against null chains

Prevent null pointer exceptions by validating object chains before accessing nested properties. Use early returns with null checks instead of optional chaining when the rest of the function depends on a non-null value.

Example of problematic code:

const messages = user.account.access_token
  ? await getMessagesBatch(messageIds, user.account.access_token)
  : [];

Better approach:

const accessToken = user.account?.access_token;
if (!accessToken) {
  logger.warn("No access token available");
  return [];
}
const messages = await getMessagesBatch(messageIds, accessToken);

Key practices:

1. Extract nested values early with optional chaining
2. Validate critical values before proceeding
3. Use early returns to handle null cases
4. Add logging for null cases to aid debugging
5. Consider using nullish coalescing (??) for providing default values

This pattern improves code reliability by catching null cases early and explicitly, rather than letting them propagate through the codebase.

---

Ensure schema-migration consistency

When modifying database schemas, ensure complete alignment between schema definitions and SQL migration scripts. Every field, column, constraint, or relationship defined in your schema must have a corresponding migration operation.

Common issues to avoid:

• Adding fields to schema models without corresponding ADD COLUMN statements in migrations
• Changing field attributes without updating migration constraints
• Forgetting to add columns before defining foreign keys that reference them

Example of problematic changes:

// Schema changes:
model EmailAccount {
-  id           String   @id @default(cuid())
+  email        String   @id
   writingStyle String?
+  userId       String
+  accountId    String   @unique
}

Without matching migration statements:

-- Missing corresponding SQL operations:
-- ADD COLUMN "writingStyle" TEXT
-- ADD COLUMN "userId" TEXT NOT NULL
-- ADD COLUMN "accountId" TEXT NOT NULL UNIQUE

Failing to maintain this consistency will cause migration failures at runtime. Always verify that every schema field change has a matching migration operation before submitting your PR.

---

Documentation Must Explain

Ensure inline docs and comments are accurate, clear, and justified:

• Match implementation defaults: If JSDoc mentions “default”, it must reflect what the code actually does. If there’s a real default value, document it (e.g., with an @default tag).
• Explain non-obvious concepts: For API terms or behaviors that may be unfamiliar (e.g., specific encodings), add a brief comment describing what the term means and how it should be interpreted.
• Justify suppressions: Any lint/test ignores or other “silence” directives must include a short explanation of why the suppression is necessary and what it’s protecting against.

Example:

interface Options {
  /** Registry used to look up metadata. */
  metadata?: $ZodRegistry<Record<string, any>>;

  /** Target JSON Schema version.
   * - "draft-2020-12" — Default.
   * - "draft-7"
   */
  target?: "draft-7" | "draft-2020-12";
}

// Clearly document uncommon terms/encodings
get isBase64url() {
  // base64url is a URL-safe variant of base64 encoding ("-" and "_" instead of "+" and "/").
  return !!this._def.checks.find((ch) => ch.kind === "base64url");
}

// Always explain ignore directives
// biome-ignore lint/complexity/noBannedTypes: `{}` is intentionally used here as the empty object type.
type T = {};

---

Filter sensitive data server-side

Always filter sensitive data at the API/server level before sending responses to the client. Never rely on client-side filtering or assume that data not displayed in the UI is secure. Any data sent to the client should be considered public and accessible to anyone with malicious intent.

Key principles:

• APIs should only return the specific fields that the client needs
• Use server-side data transformation to exclude sensitive fields like passwords, internal IDs, or private user information
• Avoid exposing entire database entities or objects that may contain sensitive fields
• Configuration files accessible to the client (like app.config) must never contain secrets or sensitive values

Example of proper server-side filtering:

// ❌ Bad: Returning entire user entity
export default defineEventHandler(async (event) => {
  const user = await db.query.users.findFirst()
  return user // Contains password, internal fields, etc.
})

// ✅ Good: Return only necessary fields
export default defineEventHandler(async (event) => {
  const user = await db.query.users.findFirst()
  return {
    id: user.id,
    email: user.email,
    name: user.name
    // password and other sensitive fields excluded
  }
})

Remember: “An API is and should always be considered as something public and accessible.” Even if sensitive data isn’t displayed in your UI, it can still be accessed by inspecting network requests or the client bundle.

---

Extract complex logic

Break down complex methods into smaller, well-named private methods to improve readability and maintainability. When a method contains multiple responsibilities, nested conditionals, or complex logic blocks, extract these into descriptive private methods.

This approach makes code easier to understand, test, and modify. Instead of having long methods with inline complexity, create focused methods that clearly communicate their purpose through their names.

Example of improvement:

# Before: Complex logic inline
def require_functional!
  if current_user.functional?
    nil
  elsif !current_user.confirmed?
    redirect_to new_user_confirmation_path
  elsif current_user.pending_reconfirmation?
    redirect_to edit_user_registration_path
  else
    redirect_to edit_user_registration_path
  end
end

# After: Extracted to descriptive method
def require_functional!
  return if current_user.functional?
  redirect_to non_functional_user_setup_path
end

private

def non_functional_user_setup_path
  return new_user_confirmation_path unless current_user.confirmed?
  edit_user_registration_path
end

Apply this pattern when you find yourself writing complex conditional logic, data transformation blocks, or any logic that requires inline comments to explain its purpose. The extracted method name should clearly describe what the logic accomplishes.

---

Avoid nested ternaries

Avoid using nested ternary operators as they significantly reduce code readability and make debugging difficult. Complex conditional logic should be refactored into clear, readable structures using if-else statements, early returns, or extracted helper functions.

Why this matters:

• Nested ternaries create cognitive overhead and are hard to parse
• They become “a nightmare to debug” when logic gets complex
• Code readability is crucial for maintainability and team collaboration

How to refactor:

Instead of nested ternaries like this:

slotStartTime = slotStartTime.minute() % interval !== 0
  ? showOptimizedSlots
    ? rangeEnd.diff(slotStartTime, "minutes") % interval > interval - slotStartTime.minute()
      ? slotStartTime.add(interval - slotStartTime.minute(), "minute")
      : slotStartTime.add(rangeEnd.diff(slotStartTime, "minutes") % interval, "minute")
    : slotStartTime.startOf("hour").add(Math.ceil(slotStartTime.minute() / interval) * interval, "minute")
  : slotStartTime;

Refactor to clear conditional blocks:

if (slotStartTime.minute() % interval === 0) {
  // No adjustment needed
  return slotStartTime;
}

if (showOptimizedSlots) {
  const timeDiff = rangeEnd.diff(slotStartTime, "minutes") % interval;
  const minutesToAdd = timeDiff > interval - slotStartTime.minute() 
    ? interval - slotStartTime.minute()
    : timeDiff;
  return slotStartTime.add(minutesToAdd, "minute");
}

return slotStartTime
  .startOf("hour")
  .add(Math.ceil(slotStartTime.minute() / interval) * interval, "minute");

Additional guidelines:

• Use early returns to reduce nesting levels
• Extract complex conditions into well-named boolean variables
• Consider breaking complex logic into smaller, focused functions
• Add comments to explain the business logic when conditions are complex

---

Document implementation decisions

Add explanatory comments for non-obvious implementation details, especially when maintaining backward compatibility or implementing complex logic that isn’t immediately clear without context. This helps other developers understand the reasoning behind design decisions and implementation choices.

Example:

const focusItem = useEventCallback((itemToFocus) => {
  if (itemToFocus === -1) {
    inputRef.current.focus();
  } else {
    // data-tag-index is kept for backward compatibility
    const indexType = renderValue ? 'data-item-index' : 'data-tag-index';
    anchorEl.querySelector(`[${indexType}="${itemToFocus}"]`).focus();
  }
});

This practice is especially important when:

• Maintaining backward compatibility with older APIs
• Making decisions based on usage metrics (e.g., keeping both CodeSandbox and StackBlitz)
• Creating navigation paths or references that might not be intuitive to users
• Implementing workarounds or temporary solutions

Well-documented implementation decisions reduce confusion, prevent regressions, and help new team members understand the codebase more quickly.

---

documentation formatting consistency

Ensure consistent formatting throughout documentation by applying these standards: wrap code terms, variable names, and boolean values in backticks (data, error, status, true, false), use proper markdown link syntax with leading slashes (/docs/guide/... instead of docs/guide/...), maintain consistent punctuation and spacing in code examples, and fix syntax errors in code blocks.

Example of proper formatting:

The `pending` object returned from `useAsyncData` is now a computed property that is `true` only when `status` is also pending.

See [route middleware](/docs/guide/directory-structure/middleware) for more details.

```vue
<template>
  <NuxtLink :to="{ name: 'posts-id', params: { id: 123 } }">
    Post 123
  </NuxtLink>
</template>

This consistency improves readability, ensures proper rendering of documentation, and provides a better developer experience when reading technical content.

---

Use configuration constants

Always use predefined constants from homeassistant.const instead of string literals when accessing configuration data. For required configuration keys that must be present, use direct dictionary access (entry.data[CONF_KEY]) rather than .get() with defaults, as this provides better error handling and makes the required nature of the configuration explicit.

# Bad - using string literals and .get() for required keys
email = user_input.get("email")
password = user_input.get("password") 
api_key = entry.data.get("api_key", "")

# Good - using constants and direct access for required keys
from homeassistant.const import CONF_EMAIL, CONF_PASSWORD, CONF_API_KEY

email = user_input.get(CONF_EMAIL)
password = user_input.get(CONF_PASSWORD)
api_key = entry.data[CONF_API_KEY]  # Will raise KeyError if missing, which is appropriate

This approach improves code maintainability, prevents typos in configuration key names, and makes the required vs optional nature of configuration values clear through the access pattern used.

---

Deterministic Test Assertions

For tests, prefer deterministic, intention-revealing assertions and keep runtime tests and type-only tests strictly separated.

Apply: 1) Use the right matcher for the claim

• Identity: use toBe instead of deep equality when referential identity matters.
• Async rejections: prefer matcher-based assertions over try/catch.

2) Make timer-based tests fast and stable

• If you must use timers, prefer fake timers and advance/run them deterministically.
• Keep real timer durations extremely short.

3) Don’t mix runtime and type-only tests

• Put compile-time checks into *.test-d.tsx and use expectTypeOf(...).toEqualTypeOf(...).
• In *.test-d.tsx, don’t rely on runtime behavior inside it blocks.

4) Ensure the test can prove which code path executed

• When a hook can call different queryFns (e.g., prefetch vs render), use distinct spies and assert call counts. Clear mocks after setup calls.

Example (async rejection + timers + type-only):

// runtime test
await expect(promise).rejects.toBe(testError)

// timer test (prefer fake timers)
vi.useFakeTimers()
vi.runAllTimersAsync()
expect(spy).toHaveBeenCalledTimes(0)

// type-only test in *.test-d.tsx
expectTypeOf(result4[0]).toEqualTypeOf<UseQueryResult<string, Error>>()

This reduces brittle/flaky tests, improves signal-to-noise, and guarantees type coverage lives where it’s actually executed by the tooling.

---

Respect Angular DI

When integrating with Angular’s DI and reactivity, follow these rules:

• Dependency access: For hook-like utilities, accept an optional Injector (or injector-derived path) so the function can be executed both inside and outside the normal injection context. Use Angular’s injection-context/assert-injector helpers to resolve dependencies from the Injector when provided.
• Effect lifecycle + teardown: If you use effect(...) to keep signals in sync, add/propagate cleanup via the effect onCleanup argument wherever long-lived listeners/subscriptions are created.
• Signal write semantics: If an effect updates a signal, ensure signal writes follow Angular’s expectations: use allowSignalWrites: true and wrap option reads in untracked when needed to avoid unintended tracking loops.
• Modern HTTP interceptors: Prefer functional interceptors via withInterceptors(...) over DI-provided interceptor classes. Also avoid redundant HttpClientModule wiring when using provideHttpClient(...).

Example pattern for effect-driven signal updates:

import { DestroyRef, effect, inject, signal, untracked, type Injector } from '@angular/core';

export function injectSomething(optionsFn = () => ({}), injector?: Injector) {
  // resolve dependencies from injector / injection context here
  return ((): any => {
    const destroyRef = inject(DestroyRef);
    const value = signal(0);

    effect(
      () => {
        const opts = untracked(() => optionsFn());
        // imperative signal update inside effect
        value.set(opts.someValue);
      },
      { allowSignalWrites: true }
    );

    return value;
  })();
}

Applying this set of practices will make utilities safer to use across injection contexts, reduce lifecycle leaks, and align with Angular’s current HTTP interceptor direction.

---

Strategic dependency configuration

Configure dependencies in package.json strategically based on how they’re used in your project:

1. Direct dependencies - Only for packages required for normal operation
2. Peer dependencies - For lazy-loaded packages or optional integrations
3. Optional peer dependencies - Use peerDependenciesMeta to indicate optionality

{
  "dependencies": {
    "core-package": "1.0.0"
  },
  "peerDependencies": {
    "lazy-loaded-package": ">=1.0.0",
    "axios": ">=0.18.0"
  },
  "peerDependenciesMeta": {
    "lazy-loaded-package": {
      "optional": true
    }
  }
}

For packages with 0.x versions (pre-1.0), use inclusive ranges (>=0.18.0) rather than caret ranges (^0.18.0) to allow compatible updates.

Avoid including type packages (@types/*) when the library already provides its own type definitions. For example, modern versions of Sequelize include built-in types, making @types/sequelize unnecessary.

---

Package dependency configuration

Configure dependencies appropriately in package.json based on usage patterns and requirements. This improves package maintainability, flexibility, and reduces unnecessary dependencies.

• Use peerDependencies instead of direct dependencies for libraries that are loaded lazily or optionally used
• Add peerDependenciesMeta to mark peer dependencies as optional when appropriate
• Use flexible version ranges for stable libraries (e.g., ">=0.18" or "^0.18.0 || ^0.19.0")
• Avoid redundant type packages when libraries include their own TypeScript definitions

Example:

{
  "dependencies": {
    "required-package": "2.3.1"
  },
  "peerDependencies": {
    "lazily-loaded-package": "^2.0.0",
    "optional-package": ">=1.0.0"
  },
  "peerDependenciesMeta": {
    "optional-package": {
      "optional": true
    }
  }
}

This approach ensures that your package properly declares its requirements while maintaining flexibility and avoiding unnecessary dependencies.

---

Defensively handle nullables

When working with values that could be null or undefined, implement defensive coding patterns to prevent runtime errors. This practice is essential for robust React applications.

Three key techniques to apply:

1. Use double-bang (!!) to safely convert to boolean: ```js // Risky - may cause unexpected behavior if selected is undefined props: ({ selected }) => selected,

// Safe - explicitly converts to boolean props: ({ selected }) => !!selected,

2. **Apply optional chaining (`?.`) for property access and method calls:**
```js
// Risky - will throw if child or props is null/undefined
child.props.onKeyDown(event);

// Safe - gracefully handles null/undefined at any level
child?.props?.onKeyDown?.(event);

1. Use ternary operators for conditional rendering: ```js // Risky - if productName is undefined, renders “undefined” ${title} - ${productName}

// Safe - handles undefined case explicitly ${title}${productName ? - ${productName} : ''}

These patterns create more resilient code by anticipating and gracefully handling potential null or undefined values throughout your application.

---

## Environment file management

<!-- source: TanStack/router | topic: Configurations | language: Other | updated: 2025-04-10 -->

Ensure proper handling of environment files by following these practices: (1) Add actual environment files (`.env`, `.env.local`, etc.) to `.gitignore` to prevent sensitive data from being committed, (2) Include example environment files (`.env.example`) in version control to help other developers understand required configuration, and (3) Add clear documentation in example files explaining how to use them.

Example `.gitignore` entry:

Environment files

.env .env.local .env.*.local

Example `.env.example` with documentation:

Copy this file as .env.local and fill in these values from your service console

VITE_FIREBASE_API_KEY= VITE_FIREBASE_AUTH_DOMAIN=

This approach ensures projects remain cloneable while protecting sensitive configuration data and providing clear setup instructions for new developers.

---

## Write timeless documentation

<!-- source: mui/material-ui | topic: Documentation | language: TypeScript | updated: 2025-04-10 -->

Documentation should be written to remain clear and useful regardless of when it's read. Avoid references to temporary contexts like "in this PR," "original behavior," or "current implementation" that will lose meaning over time. Instead, precisely describe behaviors, changes, and functionality in a way that will remain clear to developers reading the code months or years later. This applies to API documentation, inline code comments, and technical documentation.

Example:
```javascript
// Instead of:
// If no layer is specified, use the original behavior

// Write:
// If no layer is specified, add style and clean it on unmount

When documenting breaking changes, be explicit about what needs to be updated and why the change was made, rather than relying on contextual knowledge that may be forgotten.

---

precise language usage

Use precise, natural language in documentation to improve clarity and readability. Focus on accurate word choice, proper grammar, and natural phrasing that flows well for readers.

Key areas to address:

Word Choice Precision: Choose specific, accurate terms over vague ones:

• Use “several” instead of “a number of”
• Use “must” instead of “have to” for requirements
• Use “accessible” instead of “directly served” for clarity

Natural Phrasing: Write in a way that sounds natural when read aloud:

• “We recommend using” instead of “We recommend to use”
• “call the API directly” instead of “directly call the API”
• “you can use” instead of “you will need to use” (unless truly required)

Grammar Accuracy: Pay attention to conjunctions and sentence structure:

• Use “or” vs “and” correctly: “setup function or lifecycle hooks” (not both required)
• Place commas carefully as they affect meaning: “only works during setup, inside plugins” vs “only works during setup inside plugins”
• Ensure parallel structure in lists: “Moving” vs “Move” - keep consistent verb forms

Example improvements:

- This function can also return a Promise and a value
+ This function can be asynchronous

- Never combine next() callback with a legacy middleware that is async
+ Never combine the next() callback with an async legacy middleware

- We recommend to use useHead() in app.vue
+ We recommend using useHead() in app.vue

These language improvements make documentation more professional, easier to understand, and reduce cognitive load for developers reading the content.

---

Run Type Resolution Checks

Add a CI/pre-release gate that validates your published package’s JavaScript + TypeScript type resolution. Use @arethetypeswrong/cli to catch broken exports/subpath import mappings across CJS/ESM and Node versions, and configure it to your supported runtime matrix (e.g., ignore known/unavoidable legacy Node failures via --profile).

Example (package-level CI step):

# install in repo (or as a package devDependency)
# npx @arethetypeswrong/cli --profile node16
# or, if you want multiple profiles:
# npx @arethetypeswrong/cli --profile node16 --profile bundler

Apply this when you change package.json fields like exports, main/module/types, or build outputs, so latest/release candidates are actually safe for consumers relying on subpath imports.

---

Use safe type guards

When implementing type guards for nullable or unknown types, use the in operator and property existence checks instead of type casting. This approach provides better null safety by verifying that properties exist before accessing them, preventing runtime errors from null or undefined values.

Build layered type guards that check for basic validity first, then use the in operator to verify specific properties exist. This creates a chain of safety checks that handles null, undefined, and missing property cases gracefully.

Example:

// Instead of unsafe type casting:
const isMenuItem = (item: unknown): item is MenuItem => {
  return !!(item as MenuItem)?.text;
};

// Use safe property checks:
const isMenuItem = (item: unknown): item is MenuItem => {
  if (item === null) {
    return true;
  }
  return typeof item === 'object' && 'text' in item;
};

// Build on existing guards for complex types:
const isActionItem = (item: unknown): item is ActionMenuItem => {
  if (!item || !isMenuItem(item)) {
    return false;
  }
  return 'action' in item;
};

This pattern ensures that you never attempt to access properties on null or undefined values, and TypeScript can properly narrow the types based on your checks.

---

Validate configuration formats

Ensure configuration values use the correct data format expected by target systems and avoid duplication by sourcing from authoritative locations when possible. Mismatched formats can cause runtime failures, while duplicated configurations create maintenance overhead and inconsistency risks.

When configuring external tools or actions, verify the expected input format:

# Wrong: JSON array format when comma-separated string expected
discord_ids: "[ \"${{ env.oncall1 }}\", \"${{ env.oncall2 }}\" ]"

# Correct: Comma-separated string format
discord_ids: "${{ env.oncall1 }}, ${{ env.oncall2 }}"

For deployment targets and version specifications, prefer reading from authoritative sources rather than hardcoding:

# Consider reading from package.json or project config instead of:
IOS_DEPLOYMENT_TARGET: "13.4"
XROS_DEPLOYMENT_TARGET: "1.0" 
MAC_DEPLOYMENT_TARGET: "10.15"

Always validate configuration formats against documentation and test with actual usage to prevent integration issues.

---

Strategic component loading

Choose component loading strategies based on when interactivity is actually needed, not just code splitting. Lazy prefixed components only control chunk size but still load eagerly with the page’s scripts. Use delayed hydration for components that don’t need immediate interactivity, avoiding unnecessary JavaScript execution during initial page load. Be cautious with server components and nested islands as they can create request waterfalls and add overhead.

<template>
  <div>
    <!-- ❌ Lazy component still loads eagerly -->
    <LazyMountainsList v-if="show" />
    
    <!-- ✅ Delayed hydration loads component just-in-time -->
    <LazyMyComponent hydrate-on-visible />
    
    <!-- ❌ Avoid nesting islands (creates waterfall) -->
    <ServerComponentA>
      <ServerComponentB /> <!-- Each island adds overhead -->
    </ServerComponentA>
  </div>
</template>

Prioritize delayed hydration for below-the-fold components, use lazy components primarily for code organization, and avoid patterns that create request waterfalls or unnecessary overhead during the critical rendering path.

---

Standardize build configurations

When configuring module builds, maintain consistent and explicit configuration for different module formats (CJS, ESM, modern) to ensure compatibility across environments. Package exports should be clearly defined with appropriate conditions for each module system.

Best practices:

1. Use explicit file extensions (.js, .mjs, .cjs) to avoid reliance on package.json lookups for determining module type:

   const packageExports = {
     '.': {
    types: './index.d.ts',
    import: './index.mjs',     // ESM with .mjs extension
    'mui-modern': './index.modern.mjs',  // Modern build with condition
    require: './index.js',     // CJS with .js extension
     },
     // Other exports...
   };
   

2. Consider build output organization that supports multiple module formats while maintaining backward compatibility:
   • Either use separate directories (cjs/, esm/) for different formats
   • Or use a flat structure with distinct file extensions (.mjs, .cjs)

3. Ensure all necessary metadata (like sideEffects) is included in all package.json configurations

4. Document module resolution strategy and compatibility with different Node.js versions, especially when supporting legacy environments

---

Explicit configuration resolution

Always use explicit path resolution and document ordering requirements in configuration files to prevent environment-dependent issues. This makes configurations more reliable and self-documenting.

For file paths in configuration files:

• Use require.resolve() instead of relative paths to ensure consistent resolution across environments
• Document plugin or dependency ordering requirements with clear comments
• Include references to official documentation when specific ordering is required

Example:

// Bad
module.exports = {
  extends: [
    'eslint-config-airbnb',
    './eslint/config-airbnb-typescript.js',
  ]
};

// Good
module.exports = {
  extends: [
    'eslint-config-airbnb',
    require.resolve('./eslint/config-airbnb-typescript.js'),
  ]
};

// Even better - with documentation
const plugins = [];

// must be loaded last: https://github.com/tailwindlabs/prettier-plugin-tailwindcss?tab=readme-ov-file#compatibility-with-other-prettier-plugins
plugins.push('prettier-plugin-tailwindcss');

// For complex environment variables, include thorough documentation
/**
 * Fun facts about the `process.env.CONTEXT`:
 * - It is defined by Netlify environment variables
 * - `process.env.CONTEXT === 'production'` means...
 */

This approach prevents subtle configuration bugs that only appear in certain environments, reduces onboarding friction for new developers, and creates self-documenting configuration files.

---

Next.js integration patterns

When integrating with Next.js, follow framework-specific patterns carefully and stay updated with API changes to ensure proper server-side rendering and optimal code.

For SSR styling with libraries like Emotion:

• Call initialization functions in the correct sequence
• Document critical side effects that affect rendering

// ✅ DO: Call createEmotionServer immediately after cache creation with explanatory comment
const cache = createEmotionCache();
// The createEmotionServer has to be called directly after the cache creation due to the side effect of cache.compat = true,
// otherwise the styles won't be properly placed in the head tag
const { extractCriticalToChunks } = createEmotionServer(cache);

// ❌ DON'T: Call functions without understanding sequence dependencies
const cache = createEmotionCache();
// Other code...
const { extractCriticalToChunks } = createEmotionServer(cache); // Too late, SSR styling will be broken

Additionally, regularly review the official Next.js documentation to remove deprecated patterns (like unnecessary passHref props in newer versions) and adopt current recommended practices.

---

Validate security inputs

Always validate security-critical inputs to prevent DoS attacks and injection vulnerabilities. Implement size limits, scheme restrictions, and format validation for user-controlled data that affects security mechanisms.

Key practices:

• Set reasonable size limits (e.g., 4KB for cookie values) to prevent DoS through oversized inputs
• Validate URL schemes for security-sensitive operations (only allow http/https for proxies)
• Follow standard library patterns for input sanitization and validation
• Avoid logging sensitive input values that could be exploited

Example implementation:

// Validate proxy URL scheme
pURL, err := urlPkg.Parse(proxyURL)
if err != nil {
    return err
}
if pURL.Scheme != "http" && pURL.Scheme != "https" {
    return errors.New("unsupported proxy scheme")
}

// Limit cookie value size to prevent DoS
func (c *DefaultCtx) sanitizeCookieValue(v string) string {
    const maxCookieSize = 4096 // 4KB limit
    if len(v) > maxCookieSize {
        // Log generic message without exposing value
        log.Warn("cookie value exceeds size limit, truncating")
        v = v[:maxCookieSize]
    }
    // Continue with sanitization...
}

This prevents common attack vectors while maintaining functionality and following security best practices established in standard libraries.

---

extract complex logic

Break down complex functions and large files into smaller, focused units with clear responsibilities. Extract complex logic into well-named helper functions, split large files into focused modules, and prefer const over let for variables that won’t be reassigned.

When functions become difficult to understand or do multiple things, extract the complex parts:

// Instead of one large function doing everything
function parseRadialGradientCSSString(gradientContent) {
  // 50+ lines of parsing logic for shape, size, and position
  const firstPartTokens = firstPartStr.split(/\s+/);
  while (firstPartTokens.length > 0) {
    // complex parsing logic...
  }
}

// Extract into focused functions
function parseRadialGradientCSSString(gradientContent) {
  const position = parseRadialGradientPosition(firstPartStr);
  const shape = parseRadialGradientShape(firstPartStr);
  // cleaner, more focused logic
}

Similarly, prefer const for immutable variables to signal intent:

// Instead of
let restPropsWithDefaults = {
  ...defaultProps
};

// Use
const restPropsWithDefaults = {
  ...defaultProps
};

When files grow beyond 200-300 lines or handle multiple distinct responsibilities, split them into focused modules organized by functionality (e.g., StyleSheet/BackgroundImage/linearGradient.js, radialGradient.js).

---

Use context for configuration

When accessing application state or configuration within request handlers, always use the context method c.App().State() instead of direct app instance references. This pattern ensures proper context isolation, supports dependency injection, and works correctly in multi-file applications where the app instance may not be directly accessible.

Direct app references create tight coupling and break when handlers are moved to separate files or packages. The context-aware approach maintains loose coupling and follows proper architectural patterns.

Example:

// ❌ Avoid: Direct app reference
app.Get("/config", func(c fiber.Ctx) error {
    config := map[string]any{
        "apiUrl": fiber.GetStateWithDefault(app.State(), "apiUrl", ""),
        "debug":  fiber.GetStateWithDefault(app.State(), "debug", false),
    }
    return c.JSON(config)
})

// ✅ Prefer: Context-aware access
app.Get("/config", func(c fiber.Ctx) error {
    config := map[string]any{
        "apiUrl": fiber.GetStateWithDefault(c.App().State(), "apiUrl", ""),
        "debug":  fiber.GetStateWithDefault(c.App().State(), "debug", false),
    }
    return c.JSON(config)
})

This pattern is especially important when handlers are defined in separate packages or when using dependency injection, as it ensures configuration access works regardless of the application’s structure.

---

Manage dependencies wisely

When configuring dependencies in composer.json files, follow these guidelines to ensure maintainable and reliable configurations:

1. Only include direct dependencies: Add dependencies only when they are directly used by your package. If a dependency is accessed through another package, don’t include it directly.

// AVOID - including unused direct dependencies
{
    "require": {
        "illuminate/contracts": "^12.0",
        "psr/simple-cache": "^1.0|^2.0|^3.0"  // Already included via illuminate/contracts
    }
}

// BETTER - only include what you directly use
{
    "require": {
        "illuminate/contracts": "^12.0"
    }
}

1. Use appropriate dependency categories: Place non-essential extensions and packages in the “suggest” section rather than “require” when they’re only needed for optional features.

// BETTER - use suggest for optional dependencies
{
    "require": {
        "php": "^8.2"
    },
    "suggest": {
        "ext-zlib": "For compression features",
        "spatie/fork": "For alternative concurrency driver"
    }
}

1. Evaluate maintainer activity: Before adding third-party dependencies, consider the package’s maintenance status. For critical functionality, prefer actively maintained packages or consider implementing the functionality internally if maintenance is questionable.

2. Use proper version constraints: Format version constraints consistently and appropriately (use pipe

   without spaces) and ensure they’re compatible with all other dependencies.

// AVOID
"laravel/serializable-closure": "^2.0@dev",
"laravel/prompts": "^0.1.20 || ^0.2 || ^0.3"

// BETTER
"laravel/serializable-closure": "^1.3|^2.0",
"laravel/prompts": "^0.1.20|^0.2|^0.3"

Following these practices helps maintain reliable, clearly defined configuration files that minimize surprises during updates and installations.

---

validate before operations

Always explicitly check for null, undefined, or missing properties/methods before performing operations that could fail. JavaScript’s loose typing and the fact that typeof null === 'object' can lead to runtime errors if values aren’t validated first.

Key patterns to implement:

• Check for null/undefined objects: if (params == null) { return; }
• Verify method existence: if (typeof child.removeParent === 'function') { child.removeParent(this); }
• Validate array elements: if (_backPressSubscriptions[i] && _backPressSubscriptions[i]()) { ... } or use optional chaining _backPressSubscriptions[i]?.()

This prevents common runtime errors and makes code more robust by handling edge cases where expected values or methods might not be present.

---

safe error data handling

When processing error data that may contain unsafe or undefined values, use safe parsing methods and defensive programming techniques to prevent secondary exceptions during error handling.

Use safe JSON parsing libraries like destr() instead of JSON.parse() when parsing potentially malformed JSON data from error objects:

// Instead of:
ssrError.data = JSON.parse(ssrError.data)

// Use:
ssrError.data = destr(ssrError.data)

Apply destructuring with fallback values when accessing potentially undefined error data:

// Instead of:
const caller = stack[stack.length - 1]
const explanation = `${fileURLToPath(caller.source)}:${caller.line}:${caller.column}`

// Use:
const {source, line, column} = stack[stack.length - 1] ?? {}
const explanation = source ? ` (used at ${fileURLToPath(source)}:${line}:${column})` : ''

This approach prevents error handling code from becoming a source of additional errors, ensuring that the original error information is preserved and properly communicated to users or logging systems.

---

Fail fast explicitly

When critical components or operations fail, throw explicit errors rather than silently continuing or returning nil. Silent failures can mislead users into thinking operations succeeded when they didn’t, potentially causing data loss or inconsistent application state.

Key principles:

• Throw explicit errors when required dependencies are missing (e.g., database workers, required parameters)
• Avoid catch-all handlers that suppress errors without proper handling
• Use meaningful error messages that help users understand what went wrong
• Prefer failing fast over graceful degradation when data integrity is at risk

Example of problematic silent failure:

(when-let [^Object sqlite @db-browser/*worker]
  ;; operation continues only if worker exists
  ;; but silently does nothing if worker is nil
  (.transact sqlite repo tx-data tx-meta))

Better approach with explicit failure:

(if-let [^Object sqlite @db-browser/*worker]
  (.transact sqlite repo tx-data tx-meta)
  (throw (js/Error. "Database worker not initialized - data cannot be persisted")))

This prevents users from losing data silently and makes debugging easier by surfacing issues immediately rather than allowing them to compound.

---

complete React ESLint setup

When configuring ESLint for React projects, ensure you include comprehensive React-specific configurations beyond the basic setup. Include both the React import plugin configuration and JSX runtime configuration to get enhanced linting rules and automatic fixes.

Essential React ESLint configurations to include:

• importPlugin.flatConfigs.react for React-specific import rules
• react.configs.flat["jsx-runtime"] for automatic JSX configuration and fixes

Example configuration:

extends: [
  js.configs.recommended,
  react.configs.flat.recommended,
  react.configs.flat["jsx-runtime"], // Auto-configures JSX handling
  reactHooks.configs['recommended-latest'],
  jsxA11Y.flatConfigs.recommended,
  importPlugin.flatConfigs.recommended,
  importPlugin.flatConfigs.react, // React-specific import rules
  // ... other configurations
],

These additional configurations provide automatic fixes for common React patterns and ensure comprehensive linting coverage for React-specific code patterns, imports, and JSX usage.

---

dependency version ranges

When configuring dependencies in package.json, use version ranges that maintain backwards compatibility and follow semantic versioning principles. For peer dependencies, prefer ranges that support multiple major versions when possible to avoid forcing consumers to upgrade unnecessarily.

Key practices:

• Use || syntax for backwards-compatible peer dependencies: "wrangler": "^3.28.2 || ^4.0.0"
• Prefer broader version ranges over specific versions: ^4.0.0 instead of ^4.2.0 to support 4.0.x and 4.1.x
• In monorepo root package.json, dependencies can be placed in dependencies rather than devDependencies since end users never consume the root package
• Use version placeholders like "*" in templates that get replaced by build tools: "react-router": "*"
• Be pragmatic about pre-release versions when the usage is limited and well-tested, but document the reasoning

Example of proper peer dependency configuration:

{
  "peerDependencies": {
    "typescript": "^5.1.0",
    "vite": "^5.1.0 || ^6.0.0",
    "wrangler": "^3.28.2 || ^4.0.0"
  }
}

This approach reduces dependency conflicts, improves compatibility, and makes packages more consumable across different project configurations.

---

Optimize IO with async

FastAPI’s performance advantage comes from its asynchronous foundation built on Starlette and Uvicorn, using uvloop which is significantly faster than Python’s default asyncio implementation. To maximize application performance, use asynchronous programming patterns for IO-bound operations such as database queries, API requests, and file operations.

Converting blocking operations to async versions prevents the server from stalling while waiting for external resources, allowing it to handle more concurrent requests:

# Less efficient - blocks the server while waiting for response
@app.get("/external-data/")
def get_external_data():
    response = requests.get("https://api.example.com/data")
    data = response.json()
    return {"result": data}

# More efficient - releases the event loop while waiting
@app.get("/external-data/")
async def get_external_data():
    async with httpx.AsyncClient() as client:
        response = await client.get("https://api.example.com/data")
        data = response.json()
    return {"result": data}

For CPU-bound operations that can’t be made asynchronous, consider running FastAPI with multiple workers to utilize all available CPU cores:

uvicorn app:app --workers 4

This deployment strategy improves throughput for high-traffic applications while maintaining FastAPI’s performance benefits.

---

Descriptive identifier names

Choose identifier names (variables, functions, parameters, classes) that clearly describe their purpose, content, or behavior. Replace generic terms like value, data, or options with more specific alternatives that convey meaning.

For parameters:

// Poor: Generic parameter name
async validateFilesOrFile(value: any): Promise<void> {
  // ...
}

// Better: Descriptive parameter name
async validateFilesOrFile(fileOrFiles: any): Promise<void> {
  // ...
}

For method names:

// Poor: Ambiguous method name
protected mergeOptions(opts1, opts2) { ... }

// Better: Purpose-specific method name
protected mergePacketOptions(opts1, opts2) { ... }

For properties:

// Poor: Vague property name
private readonly signalsListening: string[] = new Array<string>();

// Better: Purpose-specific property name
private readonly activeShutdownSignals: string[] = new Array<string>();

For boolean variables, use names that clearly indicate the condition they represent:

// Poor: Cryptic boolean name
const cacheManagerIsv5OrGreater = 'memoryStore' in cacheManager;

// Better: Clear condition description
const isCacheManagerV5OrLater = 'memoryStore' in cacheManager;

Methods with prefixes like “is”, “has”, or “should” must return boolean values:

// Misleading: Method name suggests boolean return
public shouldFlushLogsOnOverride() {
  // Method updates state but doesn't return boolean
}

// Better: Property for state, method returns boolean
public shouldFlushLogsOnOverride: boolean;
public flushLogsOnOverride(): void { /* ... */ }

Clear, descriptive naming reduces cognitive load, improves code readability, and helps prevent bugs from misinterpreting an identifier’s purpose.

---

Optimize migration code

When writing database migration code, prioritize clarity and efficiency to ensure migrations are reliable and maintainable across environments. Apply these practices:

1. Use early returns for better flow control Instead of nesting conditions or using complex branching, return early when a condition is met:

   // Instead of this:
   if ($this->shouldSkipMigration($migration)) {
       $this->write(Task::class, $name, fn () => MigrationResult::Skipped);
   } else {
       // other operations
   }
   
   // Prefer this:
   if ($this->shouldSkipMigration($migration)) {
       $this->write(Task::class, $name, fn () => MigrationResult::Skipped);
       return;
   }
   // other operations
   

2. Prefer array emptiness checks over count operations For better readability and potentially better performance:

   // Instead of this:
   if (count($options['selected']) > 0) {
       // ...
   }
   
   // Prefer this:
   if ($options['selected'] !== []) {
       // ...
   }
   

3. Use method reference syntax when appropriate Replace arrow functions with direct method references when the function is simply passing through arguments:

   // Instead of this:
   ->keyBy(fn($file) => $this->getMigrationName($file))
   
   // Prefer this:
   ->keyBy($this->getMigrationName(...))
   

These practices help create more readable and maintainable migration code, reducing the chance of errors during database schema changes.

---

Use environment-independent defaults

When designing configuration options, avoid relying on environment-specific defaults such as system character encodings, file paths, or platform-specific features. Instead, specify explicit defaults that work consistently across all supported environments. This prevents subtle bugs that manifest only in specific environments.

For example, instead of using default charset for file operations:

// Problematic: relies on environment-specific default charset
new String(Files.readAllBytes(path), Charset.defaultCharset());

// Better: explicitly specifies charset (usually UTF-8)
new String(Files.readAllBytes(path), StandardCharsets.UTF_8);

Be especially careful when changing defaults, as this can break existing configurations. Consider IDE compatibility issues when using specific language features or imports, as seen in discussion #3 where a private constant was needed instead of a direct import to avoid Eclipse compilation errors. When updating defaults is necessary, reserve such changes for major version releases to prevent breaking existing tests and deployments.

---

state boundary management

Ensure proper state management when passing reactive values across component and function boundaries. State reactivity can be lost when values are read at the point of return rather than through getters, setters, or object properties.

When passing state between components or extracting logic into functions, maintain reactivity by:

1. Use object properties or class instances - Objects and classes maintain “live” references to their properties
2. Use getters/setters or functions - These preserve the reactive connection by deferring the read/write
3. Avoid direct value extraction - Reading reactive values at return time fixes them to that moment

// ❌ Loses reactivity - values are read at return time
function createState(initial) {
  let count = $state(initial);
  return { count }; // count is fixed at return time
}

// ✅ Maintains reactivity - using getter/setter
function createState(initial) {
  let count = $state(initial);
  return {
    get count() { return count },
    set count(v) { count = v }
  };
}

// ✅ Maintains reactivity - returning the whole object
function createState(initial) {
  const state = $state({ count: initial });
  return state; // object properties remain reactive
}

Props passed from parent components maintain their reactivity only if the parent passed reactive state. Fallback values and non-reactive objects will not trigger updates when mutated. Avoid updating state inside effects as this creates unpredictable behavior and difficult-to-debug applications.

---

Choose descriptive property names

Property and configuration field names should clearly communicate their purpose, behavior, and relationships to other components. Avoid ambiguous or misleading names that require additional context to understand.

When naming properties, consider:

• Semantic accuracy: Names should precisely reflect what the property represents or does
• Behavioral clarity: If a property has specific behavior (like fallback order), include that in the name
• Consistency: Follow established naming patterns within your codebase

Examples of improvements:

// Poor: Ambiguous about whether it's for custom or predefined formats
CustomFormat string

// Better: Clear that it handles both predefined and custom formats
Format string

// Poor: Doesn't indicate these are fallback options
AdditionalKeyLookups []string

// Better: Clearly indicates fallback behavior and order
FallbackKeyLookups []string

// Poor: Inconsistent with standard naming patterns
IsLiveEndpoint string

// Better: Consistent with conventional endpoint naming
LivenessEndpoint string

Well-chosen names reduce cognitive load, improve code maintainability, and make APIs more intuitive for other developers to use.

---

Consistent terminology usage

Always use consistent terminology for the same concept throughout your codebase, documentation, and user interfaces. When multiple terms could describe the same thing, choose one definitive term and use it consistently everywhere.

For example, when referring to database configuration elements, don’t alternate between calling them “configuration keys” and “connection names” - pick the most semantically accurate term (e.g., “connection name”) and use it consistently:

# GOOD:
# Connection URLs for non-primary databases can be configured using
# environment variables. The variable name is formed by concatenating the
# connection name with `_DATABASE_URL`.

# BAD:
# Similar environment variable prefixed with the configuration key...
# ...prefixed with the connection name...
# (Using inconsistent terminology for the same concept)

Terminology consistency reduces cognitive load for readers and maintainers, prevents confusion, and makes documentation more accessible. This principle applies equally to code comments, user-facing labels, and semantic HTML elements.

---

Use pytest fixtures effectively

Tests should use pytest fixtures to improve organization, promote test isolation, and avoid code duplication. Fixtures provide a clean way to set up test dependencies, manage test state, and create reusable test components.

Key principles:

• Use fixtures for test setup instead of global variables to prevent test pollution
• Monkeypatch environment variables and dependencies within fixtures
• Extract repetitive test code into parameterized fixtures
• Use session or module-level fixtures for expensive setup operations
• Store test constants in fixtures or dedicated constant files

Example:

# Before: Using global variables and repetitive code
counter_holder = {"counter": 0, "parsing_counter": 0}  # Risky global state

def get_client_with_custom_config(config_value):
    app = FastAPI(config=config_value)
    return TestClient(app)

def test_feature_a():
    client = get_client_with_custom_config("value1")
    # Test implementation...

def test_feature_b():
    client = get_client_with_custom_config("value2")
    # Test implementation...

# After: Using pytest fixtures
@pytest.fixture
def counter():
    return {"counter": 0, "parsing_counter": 0}  # Isolated for each test

@pytest.fixture
def client(request):
    config_value = request.param
    app = FastAPI(config=config_value)
    return TestClient(app)

@pytest.mark.parametrize("client", ["value1", "value2"], indirect=True)
def test_features(client, counter):
    # Test implementation using client and counter...

Using fixtures properly improves test isolation, prevents unexpected side effects between tests, and makes test maintenance easier by centralizing common setup logic.

---

Modern TypeScript style

Use modern TypeScript syntax and conventions throughout the codebase. This includes:

• Using const instead of var for variable declarations unless reassignment is needed
• Using ES module syntax (import express from 'express') instead of CommonJS require()
• Explicitly typing function parameters and return values

Example (before):

const express = require("express");

const app: import("express").Application = module.exports = express();

app.get('/', function(request, response) {
    console.log(request.url);

Example (after):

import express from 'express';
import { Request, Response } from 'express';

const app = express();

app.get('/', function(request: Request, response: Response) {
    console.log(request.url);
});

---

Component initialization state

Ensure components properly handle initialization state during their lifecycle, particularly when being recycled or updated. Components should explicitly track whether they have been initialized and force initial value setting when necessary, rather than relying on property comparison alone.

When implementing component updates, check for initialization state before comparing old and new properties:

// Instead of just comparing properties
if (oldSwitchProps.value != newSwitchProps.value) {
  [_switchView setOn:newSwitchProps.value animated:shouldAnimate];
}

// Include initialization check
if (!_isInitialValueSet || oldSwitchProps.value != newSwitchProps.value) {
  BOOL shouldAnimate = _isInitialValueSet == YES;
  [_switchView setOn:newSwitchProps.value animated:shouldAnimate];
}

This pattern prevents issues where recycled components retain default values that don’t match the intended initial state, and ensures proper state preservation during component updates. Always consider the component’s lifecycle stage when determining whether to apply property changes.

---

Documentation clarity principles

When writing technical documentation, adhere to these core principles to ensure clarity and effectiveness:

1. Use precise technical terminology: Choose the most accurate terms for technical concepts and be consistent with product names. Remove unnecessary qualifiers when context is clear.

   # Prefer
   This is especially useful for Container beans, as they keep their state despite the application restart.
      
   # Instead of
   This is especially useful for Testcontainer javadoc:org.testcontainers.containers.Container[] beans...
   

2. Follow formatting conventions: Use correct admonition formats (e.g., NOTE not Note), keep one sentence per line, and use idiomatic language.

   # Prefer
   NOTE: The OpenTelemetry Logback appender and Log4j appender are not part of Spring Boot.
   You have to provide and configure them yourself.
      
   # Instead of
   Note: The OpenTelemetry Logback appender and Log4j appender are not part of Spring Boot. You have to provide and configure them yourself.
   

3. Simplify when possible: Document only recommended approaches rather than all possible variations to reduce cognitive load. When multiple approaches exist, clearly indicate the preferred method.

4. Keep information current: Regularly review and remove outdated information that no longer applies to current versions of the software.

5. Use idiomatic language: Choose proper prepositions and phrases that sound natural in technical contexts (e.g., “over HTTP” rather than “via HTTP” when discussing protocols).

Following these principles creates documentation that is more accessible, maintainable, and valuable to users.

---

Test behavior not implementation

Focus tests on user behavior and outcomes rather than implementation details. Structure tests to simulate real user interactions and verify expected results. This creates more robust tests that remain valid even when implementation changes.

Example:

// Good - Simulates user behavior
const textbox = screen.getByRole('combobox');
await user.type(textbox, 'new value');
await user.keyboard('{ArrowDown}');
expect(screen.getByText('dropdown option')).to.be.visible;

// Avoid - Tests implementation details
expect(component.state.inputValue).to.equal('new value');
expect(component.state.isOpen).to.be.true;

Use testing-library’s user-centric queries (getByRole, getByText) via the screen object rather than targeting DOM elements directly. When testing events, verify their effect rather than just their occurrence. This approach makes tests more maintainable and provides better confidence that components work correctly from the user’s perspective.

---

explicit response types

Always specify explicit response types when making API calls, especially for prerendered routes or external APIs. In production environments, response headers may not be preserved as expected, leading to incorrect content-type detection that can break applications in unpredictable ways.

When fetching prerendered API routes, always set the responseType parameter:

// Always specify responseType for prerendered routes
const articleContent = await $fetch('/api/content/article/name-of-article', {
  responseType: 'json'
})

// Also apply when using useFetch
const { data } = await useFetch('/api/data', {
  responseType: 'json'
})

Additionally, exercise extreme caution when proxying headers to external APIs. Only include headers you specifically need, as not all headers are safe to forward and may introduce unwanted behavior. This practice prevents content-type mismatches and ensures reliable API communication across different deployment environments.

---

maintain clean linter configs

Ensure linter configuration files are well-maintained by avoiding duplicate entries, using current non-deprecated options, and implementing security-conscious restrictions. Remove any duplicate configuration blocks, replace deprecated linters with their modern equivalents, and configure restrictive policies for dangerous imports that require explicit justification.

Example of good practices:

# Remove duplicates - avoid this:
- name: unhandled-error
  arguments: ['bytes\.Buffer\.Write']
- name: unhandled-error  # Duplicate!
  disabled: true

# Use current linters - replace deprecated ones:
# - varcheck  # Deprecated
- unused      # Current alternative

# Configure security restrictions:
depguard:
  packages:
    - unsafe  # Require //nolint:depguard // Justification

This ensures configuration files remain clean, current, and secure while preventing maintenance issues and security oversights.

---

Design flexible APIs

When designing APIs, prioritize flexibility and developer experience by:

1. Accept broader parameter types - Use callable instead of Closure to support various invocation patterns:

// Instead of this (restrictive):
public function throw(?Closure $callback = null)

// Do this (flexible):
public function throw(?callable $callback = null)

1. Support fluent method chaining - Allow methods to return the instance for chainable calls:

// Example from date formatting:
public function format(string $format): static
{
    $this->format = $format;
    return $this;
}

// Usage:
$date->format('Y-m-d')->after('2023-01-01');

1. Accept multiple parameter formats - Make your API handle different input types intelligently:

// Example with status code handling:
if (is_numeric($callback) || is_string($callback) || is_array($callback)) {
    $callback = static::response($callback);
}

1. Use enums for constrained options - Instead of arbitrary integers, use typed enums:

// Instead of:
public static function query($array, $encodingType = PHP_QUERY_RFC3986)

// Do this:
public static function query($array, HttpQueryEncoding $encodingType = HttpQueryEncoding::Rfc3986)

Flexible APIs improve developer experience by being intuitive, reducing errors, and accommodating different coding styles while maintaining robustness and clarity.

---

explicit CI/CD configuration

Always use explicit configuration in CI/CD workflows rather than relying on defaults or convenience shortcuts. This includes pinning exact tool versions, specifying action parameters explicitly, and choosing reliable installation methods.

Key practices:

• Pin exact versions across all environments (e.g., version: v1.64.7 instead of version: v1.64)
• Use go install for Go tools instead of third-party GitHub actions that may become unmaintained
• Explicitly set action parameters even when overriding defaults (e.g., cache: false for setup-go)

Example of explicit configuration:

- name: Install Go
  uses: actions/setup-go@v4
  with:
    go-version: 1.21.0  # exact version
    cache: false        # explicit cache setting

- name: Install gotestsum
  run: go install gotest.tools/gotestsum@v1.11.0  # exact version via go install

This approach ensures reproducible builds, reduces dependency on external maintainers, and makes workflow behavior predictable across different environments and over time.

---

avoid timing-dependent tests

Tests should not rely on fixed delays, arbitrary timeouts, or assume deterministic ordering of asynchronous operations. Instead, use proper waiting mechanisms and sort results when order doesn’t matter.

Replace fixed delays like await sleep(LOADER_LATENCY_MS) with conditional waiting:

// Bad: Fixed delay
await sleep(LOADER_LATENCY_MS);
expect(router.getBlocker("KEY", fn)).toEqual({
  state: "unblocked",
  proceed: undefined,
});

// Good: Wait for condition
await waitFor(() =>
  expect(router.getBlocker("KEY", fn)).toEqual({
    state: "unblocked", 
    proceed: undefined,
  })
);

For non-deterministic collections, sort before comparison:

// Bad: Assumes request order
expect(requests).toEqual([...]);

// Good: Sort for deterministic comparison  
expect(requests.sort()).toEqual([...]);

This prevents flaky tests that fail intermittently due to timing variations across different environments and browsers.

---

Maintain consistent naming patterns

Follow established naming patterns and conventions throughout the codebase to ensure consistency and clarity. This includes:

1. Use existing naming patterns for similar concepts:
   • Follow established suffixes (e.g., *BuilderCustomizer for builder customization interfaces)
   • Maintain consistent method naming patterns across related classes
   • Use consistent property naming schemes (avoid mixing kebab-case and camelCase)
2. Choose clear, descriptive names that avoid jargon:

   // Avoid unclear or ambiguous names
   enum SameSite {
     UNSET("Unset")  // Makes readers stop and think
   }
      
   // Use clear, descriptive names
   enum SameSite {
     OMITTED("Omitted")  // Clearly describes the behavior
   }
   

3. Write descriptive test method names that explain the test scenario:

   // Avoid vague names
   @Test
   void customizer() { }
      
   // Use descriptive names that explain the test
   @Test
   void whenCustomizerBeanIsDefinedThenItIsConfiguredOnSpringLiquibase() { }
   

4. Avoid unnecessary renaming that doesn’t add value but increases diff complexity and makes code reviews harder.

---

React rendering safeguards

This standard ensures your React components render correctly and efficiently, preventing common pitfalls that cause errors or performance issues.

Proper key usage

Always use stable, unique identifiers as keys when rendering lists:

// ❌ Avoid using array index as key when items can reorder
{payload.map((item, index) => (
  <div key={index}>...</div>
))}

// ✅ Use a unique, stable identifier when available
{payload.map((item) => (
  <div key={item.value || `${item.dataKey}-${item.name}`}>...</div>
))}

Hydration safety

When dealing with components that might render differently on server vs. client, implement hydration safety checks:

const [isMounted, setMounted] = React.useState(false);

React.useEffect(() => {
  setMounted(true);
  // Additional initialization if needed
}, []);

// Avoid hydration mismatch by not rendering on server
if (!isMounted) {
  return null;
}

return <Component {...props} />;

Context-aware rendering

When conditionally showing UI elements or handling state that depends on browser APIs:

1. Check for document/window availability
2. Use useLayoutEffect for DOM measurements
3. Defer client-side-only logic to useEffect

This prevents hydration errors, improves SSR compatibility, and ensures consistent rendering across environments.

---

Structured log message quality

Design log messages to be clear, concise, and properly structured to maximize their utility for debugging and monitoring. When using structured logging, configure reasonable limits for data complexity to prevent resource exhaustion and ensure logs remain usable.

Key practices:

1. Set appropriate limits for structured logging depth (prefer lower values like 32 instead of excessively high values like 1000) to prevent both stack overflow and log storage issues.
2. Consolidate related log messages when possible to improve readability and reduce log noise.
3. Provide context in log messages to make them self-contained and meaningful.

Example of consolidated logging (preferred):

if (dataSourceList.size() == 1) {
    logger.info("H2 console available at '{}'. Database '{}' available at '{}'", 
                path, dataSourceList.get(0).getName(), connectionUrl);
} else {
    logger.info("H2 console available at '{}'", path);
    dataSourceList.forEach(ds -> 
        logger.info("Database '{}' available at '{}'", ds.getName(), ds.getUrl()));
}

Instead of separate log messages:

logger.info("H2 console available at '" + path + "'.");
dataSource.orderedStream().forEachOrdered((available) -> {
    try (Connection connection = available.getConnection()) {
        logger.info("Database available at '" + connection.getMetaData().getURL() + "'");
    }
    // ...
});

---

Maintain API types

Ensure API type definitions accurately reflect current implementations. When maintaining TypeScript definitions for APIs, regularly audit them against the actual source code to prevent developers from using non-existent or deprecated features.

For API type definitions:

1. Remove outdated type declarations that no longer exist in the implementation
2. Add clear comments for deprecated features or known limitations
3. Document version changes that affect API types

Example:

// INCORRECT: Keeping outdated type definitions
/**
 * This function no longer exists in Express 5.0+
 */
export function query(options: qs.IParseOptions): Handler;

// CORRECT: Properly documenting API changes
/**
 * @deprecated Removed in Express 5.0 (2014-11-06)
 * @see https://github.com/expressjs/express/blob/master/History.md#500-alpha1--2014-11-06
 */
// export function query(options: qs.IParseOptions): Handler;

Accurate type definitions prevent confusion, reduce runtime errors, and improve developer experience when working with your API.

---

Maintain backward compatibility

When evolving APIs, always maintain backward compatibility to avoid breaking existing user code. Support both old and new syntax during transition periods, and use deprecation warnings to guide users toward new patterns.

Key practices:

• Use function overloads or runtime type checking to support multiple API signatures
• Add deprecation warnings for old patterns while keeping them functional
• Follow semantic versioning - breaking changes only in major versions
• When changing parameter names or structure, support both old and new formats

Example from useBlocker API evolution:

// Support both old and new syntax
export function useBlocker(
  blockerFnOrOpts: BlockerFn | BlockerOpts,
  condition?: boolean | any
): BlockerResolver {
  if (typeof blockerFnOrOpts === 'function') {
    // Legacy function signature
    return useBlockerInternal(blockerFnOrOpts, condition)
  } else {
    // New object-based signature
    return useBlockerInternal(blockerFnOrOpts.blockerFn, blockerFnOrOpts.condition)
  }
}

This approach allows gradual migration while preventing immediate breakage for existing users. Always consider the impact on downstream consumers before changing public API surfaces.

---

Environment-aware configuration management

Ensure configuration management accounts for different environments and maintains backward compatibility during migrations. This includes using safe access patterns for global objects, versioning configuration keys, and preserving environment-specific behavior.

Key practices:

1. Safe Global Access: Use optional chaining when accessing global objects that may not exist in all environments
2. Version Configuration Keys: Include version identifiers in storage/configuration keys to prevent conflicts during major updates
3. Environment-Specific Behavior: Maintain different configuration behavior for production vs development environments
4. Migration Strategy: Use proxy exports to maintain backward compatibility when restructuring packages

Example from the discussions:

// Safe global access with optional chaining
__html: `(${restoreScroll.toString()})(${JSON.stringify(storageKey)},${JSON.stringify(resolvedKey)});__TSR__?.cleanScripts?.()`

// Versioned configuration keys
export const storageKey = 'tsr-scroll-restoration-v1-3'

// Proxy exports for backward compatibility
export { TanStackRouterDevtoolsInProd as TanStackRouterDevtools } from '@tanstack/react-router-devtools'

This approach prevents runtime errors in different environments, avoids configuration conflicts during updates, and ensures smooth transitions during package migrations.

---

explicit API design

Design APIs with explicit parameters, consistent return types, and clear interfaces to improve usability and maintainability. Avoid boolean flags in favor of option objects, ensure consistent return types across all code paths, and use proper TypeScript overloads for type safety.

Key principles:

• Use option objects instead of boolean parameters for extensibility
• Provide consistent return types to avoid type juggling
• Omit optional properties when not present rather than including undefined values
• Use TypeScript overloads to provide type-safe API variants

Example of explicit parameter design:

// Instead of boolean flags
const start = (force: boolean = true) => { ... }

// Use option objects for clarity and extensibility
const start = (options: { force?: boolean } = {}) => { ... }

Example of consistent return types:

// Instead of conditional return types that require type juggling
export function useObserver(): { observe: ObserveFn } | undefined

// Provide consistent interface with noop fallback
export function useObserver(): { observe: ObserveFn }

Example of proper property omission:

// Omit optional properties when not present
const result = {
  path: pathname,
  ...(search && { query: parseQuery(search) }),
  ...(hash && { hash })
}

This approach makes APIs more predictable, reduces the need for runtime type checking, and provides better developer experience through clear interfaces and consistent behavior.

---

Meaningful consistent identifiers

Choose descriptive, semantically accurate names for variables, types, and components that clearly communicate their purpose. Maintain consistency throughout your codebase by:

1. Using established naming patterns for similar concepts (e.g., ComponentNameProps for interface props)
2. Avoiding duplicate type/interface names that cause confusion
3. Reusing defined types instead of redefining them
4. Using specific type definitions rather than generic indexing to preserve IDE autocompletion

// ❌ Poor naming practices
import { Slot } from "radix-ui"
// Duplicate interface name causes confusion
interface TimelineConent extends React.HTMLAttributes<HTMLParagraphElement> {}
// Generic typing disables autocompletion
type IconComponents = { [key: string]: (props: IconProps) => JSX.Element }
// Type redefinition instead of reuse
interface MultiSelectProps {
  options: Record<"value" | "label", string>[]
}

// ✅ Better naming practices
import { Slot as SlotPrimitive } from "radix-ui"
// Consistent naming pattern
interface TimelineHeadingProps extends React.HTMLAttributes<HTMLParagraphElement> {}
// Specific typing enables autocompletion
type IconComponents = {
  logo: (props: IconProps) => JSX.Element;
  // other specific icon components...
}
// Reusing defined types
export type OptionType = Record<"value" | "label", string>
interface MultiSelectProps {
  options: OptionType[]
}

When choosing between similar terms (like “mode” vs “theme”), select the one that most accurately represents the concept’s purpose in your codebase, and document the distinction to maintain consistency.

---

Cache lifecycle management

Implement comprehensive cache lifecycle management that includes proper key management, invalidation strategies, and cleanup mechanisms. Cache implementations should handle the full lifecycle from creation to cleanup to prevent memory leaks, stale data, and unbounded growth.

Key practices:

1. Proper cache keys: Use unique, collision-free cache keys and avoid object mutation issues
2. Invalidation strategies: Implement TTL mechanisms and handle cache invalidation on updates
3. Error handling: Preserve cache-control headers and clear cache on promise rejections
4. Cleanup mechanisms: Implement garbage collection for long-lived caches

Example implementation:

// Proper cache key management with cleanup
const metaCache = new Map()
const cacheKey = `${absolutePath}:${hash}`

// Handle cache with TTL and error recovery
let manifest: Promise<NuxtAppManifest> | null = null
export function getAppManifest(): Promise<NuxtAppManifest> {
  if (!manifest) {
    manifest = $fetch(manifestUrl).catch(error => {
      manifest = null // Clear on error for retry
      throw error
    })
  }
  return manifest
}

// Preserve cache headers for proper browser caching
setResponseHeaders(event, {
  'Cache-Control': defaultError.headers['cache-control'],
  ...defaultError.headers
})

// Implement GC for build caches
// Keep `.cache/nuxt/builds.json` with id + date for cleanup

This approach prevents common caching pitfalls like stale data, memory leaks, and cache corruption while ensuring proper browser caching behavior.

---

Document deployment strategy constraints

Always document and enforce appropriate deployment strategies for different application types in your CI/CD pipeline configuration. Different deployment strategies have specific constraints that must be considered for successful application delivery.

For example, when deploying Quarkus applications:

• Use Docker build strategy for native executable deployments to OpenShift
• S2I (Source-to-Image) can be used for JVM-based deployments, but is not suitable for native deployments
• Binary builds are appropriate for simpler deployment scenarios

Include clear configuration examples in your CI/CD documentation:

# For native application deployment using Docker build strategy
quarkus.openshift.build-strategy=docker
quarkus.native.container-build=true

# Optional: Container runtime specification
quarkus.native.container-runtime=docker  # or podman

# Additional configuration for your environment
quarkus.kubernetes-client.trust-certs=true
quarkus.openshift.route.expose=true

Ensure your pipeline documentation explains the implications of each strategy, including customization options, security considerations, and verification steps appropriate for each deployment approach.

---

Document all responses

When designing APIs, thoroughly document all possible responses your endpoints can return, not just the “happy path” success cases. Include documentation for:

1. Success responses with different status codes (e.g., 200 OK, 201 Created)
2. Error responses with appropriate status codes (400-range for client errors, 500-range for server errors)
3. Response structure for each status code
4. Conditions that trigger each response type

For example, in FastAPI you can document multiple response scenarios using the responses parameter:

@app.get(
    "/items/{item_id}",
    responses={
        200: {
            "description": "Successful Response",
            "content": {"application/json": {"schema": {"$ref": "#/components/schemas/Item"}}}
        },
        404: {
            "description": "Item Not Found",
            "content": {"application/json": {"schema": {"$ref": "#/components/schemas/Message"}}}
        }
    }
)
def read_item(item_id: int):
    if item_id not in items:
        return JSONResponse(
            status_code=404,
            content={"message": "Item not found"}
        )
    return items[item_id]

By documenting all possible responses, you provide API consumers with the information they need to properly handle all scenarios, improving the robustness of applications built on your API and reducing integration time.

---

Explicit Undefined Defaults

Prevent undefined/void/falsy values from becoming accidental runtime states.

Apply these rules:

1. Eliminate transient undefined: If a value can be absent (e.g., localStorage, optional query data), wire an explicit defaultValue so hooks/state initialize to a concrete value and consumers never render an “undefined first frame”.
   • Prefer setting the useState initial value from defaultValue inside the utility hook rather than letting it be undefined and patching later.
2. Guard globals by environment: Never assume browser APIs exist—use a shared “is server/client” check before touching window/DOM.
3. Treat void/no-arg and falsy as testable cases: When designing/using optional variables or cached data, add type and runtime tests for void (no variables) and for falsy cached values (e.g., '', 0, false) so “absent” isn’t conflated with “no result”.
4. Don’t rely on undefined being “missing” during key/hash matching: If keys are serialized/hashed (e.g., via JSON.stringify) or displayed via hashes, undefined may be removed, making different logical keys collide or fail to match.
   • Prefer key shapes where absence is explicit (e.g., use a dedicated sentinel or omit the property at the call site) and document/align hashing with comparison semantics.

Example (default to avoid initial undefined):

function useLocalStorage<T>(key: string, defaultValue: T) {
  const [value, setValue] = React.useState<T>(() => {
    const raw = localStorage.getItem(key)
    return raw == null ? defaultValue : (JSON.parse(raw) as T)
  })
  // ...sync back to localStorage
  return [value, setValue] as const
}

If a behavior constraint exists (e.g., a function must not return undefined), encode it in types and tests—don’t “test” impossible states.

---

avoid expensive operations

Identify and eliminate computationally expensive operations through early termination, better data structures, and algorithmic optimizations. Look for opportunities to short-circuit loops, cache results, and choose more efficient algorithms.

Key strategies:

• Early termination: Stop processing when the desired condition is already met
• Efficient data structures: Use Sets instead of arrays for membership testing to reduce O(n²) to O(n)
• Minimize traversals: Avoid expensive tree walking or DOM traversal operations when possible
• Optimize bit operations: Use combined bit checks for better performance

Example of early termination:

// Before: continues checking even after condition is met
for (const item of items) {
  if (checkCondition(item)) {
    hasCondition = true;
  }
  // continues processing...
}

// After: stops as soon as condition is found
for (const item of items) {
  if (checkCondition(item)) {
    hasCondition = true;
    break; // early termination
  }
}

Example of better data structure choice:

// Before: O(n²) complexity with array includes
const needsVersionIncrease = !s.reactions?.every(r => version.reactions?.includes(r));

// After: O(n) complexity with Set
const vReactions = version.reactions === null ? null : new Set(version.reactions);
const needsVersionIncrease = vReactions === null || !s.reactions?.every(r => vReactions.has(r));

---

Consistent style conventions

Apply consistent formatting and organization conventions throughout the codebase to enhance readability and maintainability:

1. Follow the project’s .editorconfig settings for indentation style (tabs vs spaces) and other formatting rules.

2. Sort dependencies alphabetically in build scripts:

   dependencies {
     optional("io.micrometer:context-propagation")
     optional("io.micrometer:micrometer-observation")
     optional("io.projectreactor:reactor-test")
     optional("org.jetbrains.kotlinx:kotlinx-coroutines-core")
     optional("org.jetbrains.kotlinx:kotlinx-coroutines-reactor")
   }
   

3. Store stateless implementations as final fields rather than creating getter methods:

   // Preferred:
   private final RowMapper<Actor> actorRowMapper = (rs, rowNum) -> {
       Actor actor = new Actor();
       actor.setFirstName(rs.getString("first_name"));
       actor.setLastName(rs.getString("last_name"));
       return actor;
   };
      
   // Not preferred:
   private RowMapper<Actor> getActorMapper() {
       return (rs, rowNum) -> {
           // implementation
       };
   }
   

4. Prefer inline lambda expressions for simple operations rather than creating separate variables:

   // Preferred:
   jdbcTemplate.update(connection -> {
       PreparedStatement ps = connection.prepareStatement(INSERT_SQL, new String[] { "id" });
       ps.setString(1, name);
       return ps;
   }, keyHolder);
      
   // Not preferred:
   PreparedStatementCreator statementCreator = connection -> {
       // implementation
   };
   jdbcTemplate.update(statementCreator, keyHolder);
   

---

Environment variables best practices

When working with environment variables in configuration files, follow these practices to ensure reliability and testability:

1. Use placeholder syntax ${ENV_VAR} to reference environment variables in both properties and YAML configuration files
2. Provide default values using the ${ENV_VAR:default-value} syntax to ensure the application functions even when environment variables are not set
3. For testing environment variable-dependent code, design components to accept injectable Map objects rather than using reflection-based libraries

Example of proper environment variable usage in YAML:

environments:
  dev:
    url: ${DEV_ENV_URL}
    name: ${DEV_ENV_NAME:development-environment}

When testing code that depends on environment variables, prefer dependency injection instead of reflection:

// Instead of using reflection-based libraries to modify System.getenv()
public class ConfigReader {
    private final Map<String, String> env;
    
    // For production use
    public ConfigReader() {
        this(System.getenv());
    }
    
    // For testing use
    public ConfigReader(Map<String, String> env) {
        this.env = env;
    }
    
    public String getConfig(String key, String defaultValue) {
        return env.getOrDefault(key, defaultValue);
    }
}

---

Use parameterized testing

When testing multiple scenarios with similar logic, use your testing framework’s built-in parameterized testing features (test.each, describe.each, it.each) instead of manual forEach loops or duplicated test functions. This approach reduces code duplication, improves readability, and makes it easier to add new test cases.

Instead of writing repetitive test functions or using manual iteration:

// ❌ Avoid manual forEach loops
[
  { path: '/', expected: undefined },
  { path: '/single', expected: '/single' },
  { path: '/path/example', expected: '/example' }
].forEach(({ path, expected }) => {
  it(`should handle ${path}`, () => {
    expect(getLastPathSegment(path)).toBe(expected)
  })
})

Use the framework’s parameterized testing features:

// ✅ Use test.each for cleaner parameterized tests
it.each([
  ['/', undefined, 'root path'],
  ['/single', '/single', 'single segment'],
  ['/path/example', '/example', 'multiple segments']
])('should return %s for path %s (%s)', (path, expected, description) => {
  expect(getLastPathSegment(path)).toBe(expected)
})

This pattern works well for testing multiple input/output combinations, different browser scenarios, or various configuration states. It makes tests more maintainable and provides clearer test output when failures occur.

---

Clear informative errors

Error messages should be clear, specific, and provide enough context to understand the issue without exposing unnecessary implementation details. When handling errors:

1. Include specific details about what went wrong rather than using generic messages
2. Consider using appropriate attributes of the exception (like e.msg) rather than the entire exception
3. For common error cases, provide tailored error messages with appropriate status codes
4. Keep error handling code clean by avoiding unnecessary control structures

Example - Before:

except Exception as e:
    http_error = HTTPException(
        status_code=400, detail="There was an error parsing the body"
    )
    
# And with unnecessary else:
if is_multipart_body and has_dict_error:
    raise RequestInvalidContentTypeException(
        status_code=415,
        detail="Unsupported media type: multipart/form-data (expected application/json)",
    )
else:
    raise RequestValidationError(errors, body=body)

Example - After:

except Exception as e:
    http_error = HTTPException(
        status_code=400, detail=f"There was an error parsing the body: {e.msg}"
    )
    
# Without unnecessary else (since the first raise will exit):
if is_multipart_body and has_dict_error:
    raise RequestInvalidContentTypeException(
        status_code=415,
        detail="Unsupported media type: multipart/form-data (expected application/json)",
    )
raise RequestValidationError(errors, body=body)

---

Document configuration relationships

When designing configuration options that interact with each other, clearly document these relationships and consider implementing safeguards against invalid combinations. This is especially important for boolean flags controlling related behaviors.

1. Document interdependencies explicitly in configuration documentation
2. Consider automatic adjustments when one setting implies another
3. Provide warnings when potentially conflicting values are detected

For example, in discussion #8, the validate_by_alias and validate_by_name settings have a critical relationship:

class ConfigDict:
    validate_by_alias: bool
    """
    Whether an aliased field may be populated by its alias. Defaults to `True`.

    !!! tip
        If you set `validate_by_alias` to `False`, you should set `validate_by_name` to `True` 
        to ensure that the field can still be populated.
    """
    
    validate_by_name: bool
    """
    Whether a field may be populated by its name. Defaults to `False`.
    """

Consider adding automatic adjustments to handle common patterns:

# When a user sets one configuration, automatically adjust related ones if needed
if config.get('validate_by_alias') is False and config.get('validate_by_name') is None:
    config['validate_by_name'] = True
    warnings.warn(
        'Setting validate_by_name=True automatically because validate_by_alias=False',
        UserWarning,
        stacklevel=2,
    )

---

Meaningful Identifier Naming

Use names that clearly reflect the thing being identified, and ensure renamed identifiers don’t accidentally couple to old data or misleading conventions.

• When an identifier backs persisted/external state (e.g., localStorage keys), rename the storage key as well to prevent reusing stale values after refactors.

  // Before: reads old stored values
  const [sortDesc, setSortDesc] = useLocalStorage('reactQueryDevtoolsSortDesc', '')
  
  // After: new state name, use a new storage key
  const [baseSort, setBaseSort] = useLocalStorage('reactQueryDevtoolsBaseSort', '')
  

• Name test files/identifiers for the specific scenario being tested; avoid redundant labels when the suffix/extension already implies the category.

  # Prefer a scenario/feature name
  mutations.test-d.tsx
  

Applying this keeps naming semantically aligned with behavior and prevents accidental cross-contamination from previously persisted names.

---

Test helpers for maintainability

Create reusable helper methods for common testing operations to improve test maintainability and consistency. Design these helpers to be appropriate for their specific test context (integration vs system tests) and resilient to implementation changes.

For authentication in integration tests:

def sign_in_as(user)
  Current.session = user.sessions.create!
  
  ActionDispatch::TestRequest.create.cookie_jar.tap do |cookie_jar|
    cookie_jar.signed[:session_id] = Current.session.id
    cookies[:session_id] = cookie_jar[:session_id]
  end
end

For authentication in system tests:

def sign_in(user)
  session = user.sessions.create!
  Current.session = session
  request = ActionDispatch::Request.new(Rails.application.env_config)
  cookies = request.cookie_jar
  cookies.signed[:session_id] = { value: session.id, httponly: true, same_site: :lax }
end

When accessing test data, avoid hardcoding references to specific fixtures which are likely to change. Instead, use approaches that are more resilient:

# Instead of:
test "create" do
  post passwords_path, params: { email_address: users(:one).email_address }
end

# Prefer:
setup do
  @user = User.take
end

test "create" do
  post passwords_path, params: { email_address: @user.email_address }
end

This approach reduces test brittleness and maintenance overhead when fixtures or underlying implementations change.

---

Secure dependency management

Always maintain secure dependencies by following these two critical security practices:

1. Keep dependencies updated with the latest security patches - Regularly check for and apply updates that contain security fixes. Pin to specific versions but review them frequently.

2. Always maintain a lockfile for security auditing - Ensure your project has a lockfile (package-lock.json, yarn.lock, etc.) to enable proper vulnerability scanning.

Example implementation:

{
  "scripts": {
    "start": "node build/index.js",
    "build": "tsc && node -e \"require('fs').chmodSync('build/index.js', '755')\"",
    "audit": "npm audit",
    "update-check": "npm outdated"
  },
  "dependencies": {
    "@modelcontextprotocol/sdk": "1.6.1",  // Updated to latest version with security patches
    "zod": "3.24.2"
  }
}

To validate dependencies:

1. Run npm i --package-lock-only to generate/update the lockfile
2. Execute npm audit to check for known vulnerabilities
3. Use npm outdated to identify packages with available updates

---

Technical term consistency

When working with multilingual codebases or documentation, maintain consistent naming conventions for technical terms across all languages. Consider the following practices:

1. Context over literalism: Translate technical terms based on their semantic meaning in context rather than word-for-word. For example, in Korean, JWT’s “subject” field should be translated as “주체” (entity/subject) rather than “주제” (topic) because it refers to the entity who owns the token.

2. Preserve framework terminology: For framework-specific concepts or methods, consider keeping the original term or providing a consistent translation. Treat them as proper nouns (e.g., Pydantic’s “Configuration”).

3. Be consistent with existing translations: If a technical term has already been translated in your codebase (e.g., “issue” → “이슈”), maintain that translation throughout.

4. Programming keywords: Consider whether programming language keywords (like Python’s import) should be translated or kept in their original form for clarity.

# Example of consistent technical terminology in comments
# 경로 작업 (path operation)
@app.get("/items/")
async def read_items():
    # 토큰의 주체(subject)를 확인
    return {"message": "Consistent terminology helps users understand your API"}

Maintaining terminology consistency helps users build a mental model of your API and prevents confusion when switching between languages.

---

Eliminate redundant computation

Identify and eliminate redundant or duplicate computation paths in your code, especially for expensive operations like schema generation, type resolution, or recursive traversals. This improves performance and reduces resource usage.

Key practices to follow:

1. Cache expensive computation results when they won’t change between calls
2. Analyze code paths to identify duplicate work
3. Use appropriate method ordering to avoid repeated expensive operations
4. Consider specialized implementations for frequently used operations

Example of problematic code:

def _display_complex_type(obj: Any) -> str:
    # Expensive recursive operation called frequently
    if get_origin(obj):
        args = get_args(obj)
        # Recursive processing of each argument...
    # ...

# Called in multiple places
repr_args = _display_complex_type(type_)  # Called repeatedly for same types

Improved approach:

@cached_property  # Or use functools.lru_cache
def _validator(self) -> SchemaValidator:
    """Cache validator to avoid rebuilding for each validation"""
    if not self._core_schema:
        self._build_schema()  # Build only once
    return SchemaValidator(self._core_schema)

For frequently used utility functions, consider specialized implementations that avoid repeated work or use more efficient algorithms for common cases.

---

Semantic over syntactic

Choose names that clearly communicate the purpose and behavior of your code elements, focusing on semantic meaning rather than just syntax. Names should instantly convey what something is or does without requiring readers to investigate implementation details.

For properties and variables:

• Use nouns that represent what the data is, not how it’s implemented
• Avoid names that suggest actions when they’re actually retrieving data

# Misleading - suggests an action of setting constraints
@property
def set_constraints(self) -> dict[str, Any]: ...

# Better - clearly indicates a property that returns defined constraints
@property
def defined_constraints(self) -> dict[str, Any]: ...

For functions and classes:

• Make names specific enough to differentiate from similar entities
• Add clarifying words to prevent ambiguity

# Unclear - what kind of "invalid" is this?
class CollectedInvalid(Exception): ...

# Better - clearly indicates the domain and purpose
class CollectedInvalidSchema(Exception): ...

For type variables and parameters:

• Use descriptive names that indicate their purpose

# Cryptic - what is R used for?
_R = TypeVar('_R')

# Better - indicates the purpose of the type variable
ReturnType = TypeVar('ReturnType')

Names that accurately reflect semantics make code more maintainable, self-documenting, and less prone to misuse.

---

Use early returns

Decrease indentation levels in your code by using early returns for edge cases and guard conditions. This approach improves readability by reducing nesting and making the code flow more linear.

Instead of wrapping your main logic in conditional blocks:

def process_data(data):
    if data is not None:
        # Process data here (indented)
        result = transform(data)
        return result
    else:
        return None
        
# In loops:
for param in parameters:
    if field_info.include_in_schema:
        # Process parameter (indented)
        # Many lines of code

Prefer checking conditions that allow early exit, then handle the main logic with less indentation:

def process_data(data):
    if data is None:
        return None
    # Process data here (not indented)
    result = transform(data)
    return result
    
# In loops:
for param in parameters:
    if not field_info.include_in_schema:
        continue
    # Process parameter (not indented)
    # Many lines of code

Similarly, avoid unnecessary else blocks after returns, and use early continues in loops to keep your code flat and easier to follow.

---

Balance documentation thoroughness

Documentation should balance completeness with avoiding redundancy. When documenting complex features:

1. Centralize detailed explanations in a single location
2. Use cross-references and links to connect related concepts
3. Include essential information in overview sections
4. Avoid duplicating content across sections

For example, when documenting multiple related features:

# Good - Using cross-references
"""
Field validation works similarly to [model validation](./models.md#validation).
See the [validation reference](../api/validators.md) for detailed options.
"""

# Avoid - Duplicating detailed explanations
"""
Field validation supports mode='before', mode='after', and mode='wrap'.
The before mode runs before type validation, after mode runs after, etc.
(Repeating all details that are already in the validation reference)
"""

This approach makes documentation easier to maintain (changes only need to be made in one place) and helps users find comprehensive information through intuitive navigation. When uncertain whether to include information in multiple places, prefer using links to a canonical source rather than duplicating content.

---

Consistent configuration patterns

When working with configurations in Pydantic models, maintain consistency by using ConfigDict() instead of plain dictionaries for better type checking support and IDE assistance. This provides explicit typing and makes your configuration intentions clearer.

# Recommended - using ConfigDict for type checking support
from pydantic import BaseModel, ConfigDict

class Model(BaseModel):
    model_config = ConfigDict(str_max_length=10, validate_by_name=True)
    
    field: str
    
# Alternative approach - using class arguments (useful for 'frozen')
class FrozenModel(BaseModel, frozen=True):
    id: int
    name: str

Be aware of how configurations merge in inheritance hierarchies - child class settings override parent class settings for the same configuration keys. Document clearly which configurations are being overridden when implementing class inheritance.

Remember that runtime method parameters can override model configurations when explicitly provided, but default method parameters do not override model configurations. For example, when using validation methods, the default behavior follows the model configuration unless explicitly changed:

# The model's configuration takes precedence unless explicitly overridden
model = Model.model_validate(data)  # Uses model_config settings
model = Model.model_validate(data, by_alias=False)  # Explicitly overrides config

---

Preserve language conventions

When designing APIs that bridge between programming languages and external data formats (like JSON, XML, etc.), maintain language-specific naming conventions in your code while using aliases to accommodate external data formats. For Python APIs:

1. Use snake_case for internal field names following Python conventions
2. Define aliases for external formats that use different conventions (e.g., camelCase in JSON)
3. Document methods clearly with parentheses in references (e.g., model_dump() not just model_dump)
4. Present JSON examples with proper formatting for readability

Example:

from pydantic import BaseModel, Field

class UserProfile(BaseModel):
    user_id: int = Field(validation_alias="userId", serialization_alias="userId") 
    first_name: str = Field(validation_alias="firstName", serialization_alias="firstName")
    
    # Python-native usage in code
    # user = UserProfile(user_id=1, first_name="John")
    
    # External data validation (JSON)
    # user = UserProfile.model_validate({"userId": 1, "firstName": "John"})
    
    # Example of well-formatted JSON output in documentation
    # import json
    # print(json.dumps(user.model_dump(by_alias=True), indent=2))
    # """
    # {
    #   "userId": 1,
    #   "firstName": "John"
    # }
    # """

This approach creates a clear separation between your language-specific implementation and external API contracts, improving code readability while maintaining compatibility with external systems. It also ensures your API documentation is consistent and easily understood by developers.

---

Parameterize build processes

When designing build scripts for multi-package repositories, use parameterization to handle special cases rather than creating duplicate scripts with minor variations. This approach maintains consistency while accommodating package-specific needs. For example, instead of hardcoding different behaviors, add flags that can modify behavior:

"scripts": {
  "build": "standard-build-script --skipEsmPkg",
  "build:esm-pkg": "node ./scripts/create-esm-package-json.mjs"
}

Similarly, prefer built-in parameterization of tools (like pnpm’s --dry-run flag) over custom implementations for common CI/CD operations. This improves maintainability and leverages well-tested functionality.

---

Configuration validation and defaults

Always validate configuration structure before accessing properties and provide sensible defaults while preserving explicit user overrides. Configuration code should defensively check for the existence of nested properties and gracefully handle missing or malformed configuration.

When implementing configuration logic:

1. Validate structure before access - Check that nested configuration objects exist before accessing their properties
2. Provide meaningful defaults - Implement sensible default behavior when configuration is missing or incomplete
3. Respect explicit overrides - Allow users to explicitly disable automatic behavior by providing their own configuration
4. Handle edge cases gracefully - Consider scenarios where configuration might be partially defined or in unexpected formats

Example of problematic code:

// Crashes when dependency.platforms is undefined
Object.keys(dependency.platforms).forEach(platform => {
  if (dependency.platforms[platform] == null) {
    notLinkedPlatforms.push(platform);
  }
});

Example of improved code:

// Defensive validation before access
if (dependency.platforms) {
  Object.keys(dependency.platforms).forEach(platform => {
    if (dependency.platforms[platform] == null) {
      notLinkedPlatforms.push(platform);
    }
  });
}

For default vs explicit configuration:

// Provide defaults but respect explicit user configuration
if (!config.watchFolders.some(folder => folder !== ctx.root)) {
  // Apply auto-detection only when user hasn't specified custom folders
  overrides.watchFolders = getWatchFolders(ctx.root);
}

This approach prevents runtime crashes from malformed configuration while maintaining flexibility for users to customize behavior when needed.

---

Protocol-specific error handling

Handle errors and responses appropriately based on the network protocol being used. Different protocols have different mechanisms for error reporting and communication patterns.

For HTTP endpoints:

• Use appropriate HTTP status codes to communicate the nature of the response
• Return 2xx codes for successful operations, 4xx for client errors, 5xx for server errors
• Include descriptive error messages in the response body for client errors
• Configure CORS headers correctly, especially when using credentials:

  # When allow_credentials is True, avoid wildcards
  app.add_middleware(
      CORSMiddleware,
      allow_origins=["https://specific-origin.com"],  # Not ['*']
      allow_methods=["GET", "POST"],  # Not ['*']
      allow_headers=["X-Custom-Header"],  # Not ['*']
      allow_credentials=True
  )
  

For WebSockets:

• Don’t raise HTTP exceptions in WebSocket handlers
• Close the connection directly with an appropriate code when errors occur:

  @app.websocket("/ws")
  async def websocket_endpoint(websocket: WebSocket):
      await websocket.accept()
      try:
          while True:
              data = await websocket.receive_text()
              # Process data
              if error_condition:
                  # Don't use HTTPException here
                  await websocket.close(code=1008)  # Policy violation
                  return
      except Exception:
          await websocket.close(code=1011)  # Internal error
  

For custom headers:

• Use ‘X-‘ prefix for custom headers in server-to-server communication
• When browsers need to access custom headers in cross-origin requests, add them to your CORS configuration with the expose_headers parameter

---

Respect async execution order

When working with asynchronous code, always be mindful of the execution order of operations, particularly with regards to yielded dependencies, middleware, and background tasks. This affects resource management, error handling, and overall application flow.

Key considerations:

• Code after yield in dependencies runs after middleware completes processing
• For file operations, remember FastAPI executes file methods in a thread pool with proper awaiting
• Always use up-to-date async APIs (e.g., avoid deprecated event loop policies in favor of asyncio.Runner)
• Be explicit about execution flow in documentation and comments

Example with yielded dependencies:

async def get_db():
    db = Database()  # This executes when dependency is called
    try:
        yield db  # Flow returns here after dependency is used
    finally:
        # This executes after response is generated and middleware completes
        await db.close()  # Always clean up resources

@app.get("/items/")
async def read_items(db: Database = Depends(get_db)):
    # db is available here from the yield statement above
    return await db.get_items()

Understanding async execution order prevents resource leaks, race conditions, and helps ensure proper cleanup even in error scenarios. This is especially important in FastAPI applications where dependencies with yield are common for database connections and other resources.

---

Ensure semantic naming accuracy

Names should accurately reflect the actual behavior, purpose, and scope of functions, variables, and classes. Misleading or inaccurate names create confusion and maintenance burden.

Key principles:

• Function names should match their actual behavior, not initial assumptions
• Avoid ambiguous abbreviations that could have multiple meanings
• Choose names that accommodate future extensions rather than overly specific ones
• Use descriptive names over cryptic shortcuts for better maintainability

Examples of improvements:

;; Bad: Name suggests uniqueness per view but acts like a type
:logseq.property.view/identity

;; Good: Accurately describes what it represents  
:logseq.property/ui-type

;; Bad: Overly specific, requires changes when extended
:logseq.property/checkbox-default-value

;; Good: Generic enough to support other non-ref types
:logseq.property/scalar-default-value

;; Bad: Ambiguous abbreviation
[frontend.encrypt :as e]  ; could be event, error, etc.

;; Good: Clear and unambiguous
[frontend.encrypt :as encrypt]

;; Bad: Predicate naming convention but returns a key
(defn block-or-page? [id] ...)

;; Good: Either follow predicate convention or use descriptive name
(defn block-or-page-type [id] ...)

This prevents bugs caused by incorrect assumptions about functionality and makes code self-documenting for future maintainers.

---

Categorize error types

Distinguish between different categories of errors and handle each appropriately. Specifically:

1. Validation errors occur during normal operation when input data doesn’t match expectations. These should be caught and handled gracefully.
2. Usage errors indicate developer mistakes in using your API and generally shouldn’t be caught.

Document these distinctions clearly for API users and provide correct alternatives for common error scenarios.

# BAD: Catching usage errors that indicate developer mistakes
try:
    # Code that might produce both validation and usage errors
    result = model(invalid_input)
except Exception:  # Too broad!
    log_error("An error occurred")
    
# GOOD: Only catch expected validation errors
try:
    result = model(user_input)
except ValidationError as e:
    # Handle validation errors gracefully
    log_error(f"Validation failed: {e}")
    show_user_friendly_message()
    
# Usage errors (like PydanticUserError) aren't caught,
# allowing them to crash during development when they can be fixed

# In documentation, clearly explain error categories:
"""
## Error Types

### Validation Errors
Errors that happen during data validation when user input doesn't match schema.
These can be caught and handled at runtime.

### Usage Errors 
Errors that happen when using the API incorrectly.
These indicate developer mistakes and shouldn't be caught.
"""

---

Standardize dependency management

Maintain consistent dependency management practices across CI workflows to ensure reliable builds and tests. Use the same tool (e.g., UV, PDM) throughout workflows and specify Python versions explicitly. Avoid redundant dependency specifications when dependencies are already included in other groups.

Example:

- uses: astral-sh/setup-uv@v5
  with:
    python-version: ${{ matrix.python-version }}
    enable-cache: true

- name: Install dependencies
  run: uv sync --python ${{ matrix.python-version }} --group testing --extra timezone

When installing dependencies, verify that you’re not specifying extras that are already included in other groups. Keep tool configurations as close as possible to the upstream project’s CI when working with third-party integrations.

---

Choose descriptive names

Prioritize semantic clarity and descriptive naming over brevity or convenience. Avoid esoteric, abbreviated, or ambiguous identifiers that require mental translation to understand their purpose.

Key principles:

• Replace esoteric terms with clear alternatives (e.g., value instead of clazz, createSubscriber instead of createStartStopNotifier)
• Use semantically meaningful parameter names (e.g., disallow_loose instead of is_each, attribute instead of node_or_nodes)
• Prefer positive boolean names over negatives (e.g., track_owner instead of skip_derived_source)
• Ensure function names match their return behavior (functions starting with is_ should return boolean, not mixed types)

Example:

// Avoid esoteric or ambiguous names
function to_class(clazz, hash, classes) { // ❌ "clazz" is esoteric
function to_class(value, hash, classes) { // ✅ "value" is clear

// Use semantically meaningful parameters  
function read_expression(parser, opening_token, is_each) { // ❌ unclear purpose
function read_expression(parser, opening_token, disallow_loose) { // ✅ clear intent

// Prefer positive boolean names
export function source(v, skip_derived_source = false) { // ❌ negative logic
export function source(v, track_owner = true) { // ✅ positive logic

This approach reduces cognitive load, improves code readability, and makes the codebase more maintainable by ensuring names clearly communicate their purpose and behavior.

---

Document configuration logic

Always add clear, explanatory comments for conditional configuration logic, architectural decisions, and platform-specific handling. Configuration code often involves complex decision trees, temporary solutions during transitions, and platform-specific workarounds that may not be immediately obvious to other developers.

When implementing conditional configuration logic, explain the reasoning behind the conditions and what each branch accomplishes. For architectural transitions, document the temporary nature of solutions and migration plans. For platform-specific code, explain why the special handling is necessary.

Example from CMake configuration:

# We check if the user is providing a custom OnLoad.cpp file. If so, we pick that
# for compilation. Otherwise we fallback to using the `default-app-setup/OnLoad.cpp` 
# file instead.
if(override_cpp_SRC)
    # Use custom implementation
else()
    # Use default setup
endif()

# On Windows, backslashes in file paths are interpreted as escape characters
# Convert to forward slashes for consistent path handling across platforms
if(CMAKE_HOST_WIN32)
    string(REPLACE "\\" "/" BUILD_DIR ${BUILD_DIR})
    string(REPLACE "\\" "/" REACT_ANDROID_DIR ${REACT_ANDROID_DIR})
endif()

This practice prevents confusion during code reviews, helps with maintenance during architectural transitions, and makes platform-specific workarounds understandable to developers working on different operating systems.

---

Secure JWT authentication

Implement secure authentication using JWT tokens by following these best practices:

1. Use secure libraries: Prefer well-maintained libraries like PyJWT for JWT handling and passlib with bcrypt for password hashing:

from passlib.context import CryptContext
import jwt

# Password hashing setup
pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")

# JWT configuration
SECRET_KEY = "your-secure-secret-key"  # Generate with: openssl rand -hex 32
ALGORITHM = "HS256"
ACCESS_TOKEN_EXPIRE_MINUTES = 30

# Functions for security
def verify_password(plain_password, hashed_password):
    return pwd_context.verify(plain_password, hashed_password)
    
def get_password_hash(password):
    return pwd_context.hash(password)
    
def create_access_token(data: dict, expires_delta: timedelta):
    to_encode = data.copy()
    expire = datetime.utcnow() + expires_delta
    to_encode.update({"exp": expire})
    return jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)

1. Never store plaintext passwords: Always hash passwords before storage and compare hashed values during verification.

2. Set appropriate token expiration: Balance security with user experience by setting reasonable token expiration times.

3. Distinguish authentication from authorization: Authentication verifies user identity while authorization determines their permissions. Implement both correctly.

4. Configure secure settings: Avoid security risks in configurations. For example, never use allow_credentials=True with allow_origins=['*'] in CORS settings, as this would allow any third-party origin to access sensitive cookie information.

5. Protect JWT tokens: Store tokens securely (HTTP-only cookies or secure client-side storage), validate them on each request, and implement proper token revocation strategies.

---

Escape untrusted input

Always use appropriate escaping mechanisms when handling input from untrusted sources to prevent injection attacks. User-provided data that contains special characters or operators can be interpreted in unintended ways if not properly escaped, leading to security vulnerabilities like XSS, SQL injection, or command injection.

For example, when working with search functionality where user input might contain special operators:

# Unsafe approach - user could inject search operators
query = request.GET.get('q')
results = Entry.objects.filter(search_vector=query)  # Vulnerable to injection

# Secure approach using Lexeme objects to escape special characters
from django.contrib.postgres.search import SearchQuery, Lexeme
query = request.GET.get('q')
search_query = SearchQuery(Lexeme(query))  # Operators in the query string are escaped
results = Entry.objects.filter(search_vector=search_query)

Similarly, use appropriate escaping mechanisms in other contexts:

• HTML: Use template systems with auto-escaping or dedicated HTML escaping functions
• SQL: Use parameterized queries or ORM methods that handle escaping
• Command execution: Avoid shell=True with subprocess and validate all inputs
• URL parameters: Use proper URL encoding functions

The principle applies to any situation where user input is incorporated into operations that interpret special characters. When in doubt, assume all external input is potentially malicious and apply context-appropriate escaping.

---

Safe attribute access pattern

Always use safe attribute access patterns to handle potentially null or undefined attributes. Instead of direct attribute access that might raise AttributeError, use getattr() with a default value. This pattern prevents null reference errors and makes code more robust.

Example:

# Unsafe:
version = obj.__version__
value = obj.as_tuple()

# Safe:
version = getattr(obj, '__version__', '')
try:
    value = getattr(obj, 'as_tuple')()
except AttributeError:
    value = None

This approach:

1. Provides fallback values for missing attributes
2. Makes null cases explicit and handled
3. Reduces runtime errors from missing attributes
4. Makes code more maintainable by centralizing null handling

When using this pattern, choose meaningful default values that make sense in the context rather than always defaulting to None.

---

Use universally understandable identifiers

When naming variables, functions, routes, and other code elements, use clear, neutral terminology that will be understood by all developers regardless of their cultural or domain-specific knowledge. This is especially important in tests, examples, and documentation where context may not be obvious.

For test names, use descriptive identifiers that clearly indicate what’s being tested, including test conditions and parameters:

# Less clear:
def test_create_item():
    # ...

# More clear:
def test_create_item_when_separate_input_output_schemas_is():
    # ...

For route paths and other public-facing code, prefer neutral, generic terms over domain-specific or culturally-bound terminology:

# Potentially confusing:
@app.get("/pita/shuli")
def get_pita_shuli():
    # ...

# Clearer for all developers:
@app.get("/category/item")
def get_category_item():
    # ...

Clear naming reduces the cognitive load for all developers interacting with the codebase, especially those who are new to the project or from different cultural backgrounds.

---

Use descriptive identifier names

Choose clear, descriptive names for variables, functions, and classes that accurately convey their purpose and follow framework conventions. Avoid abbreviations, single-letter names, or generic placeholders that might confuse readers.

Key guidelines:

• Replace abbreviated names with their full form (e.g., ‘pagination’ instead of ‘p’)
• Avoid meaningless placeholder names (e.g., ‘Foo’, ‘Bar’) in favor of domain-specific terms
• Use semantic naming that reflects the actual behavior
• For class-returning methods, include ‘class’ suffix in the name

Example:

# Poor naming
def get_pagination(self, request, **kwargs):
    p = self.pagination_cls()
    return p

# Better naming
def get_pagination_class(self, request, **kwargs):
    pagination_instance = self.pagination_class()
    return pagination_instance

This approach improves code readability, maintains consistency with framework patterns, and makes the codebase more maintainable.

---

Event-triggered network requests

When implementing user interactions that trigger network requests, use precise event handling techniques to ensure reliable network operations. Specifically, check event properties like event.button (which button was pressed) rather than event.buttons (which buttons are currently pressed) to correctly handle user intent.

For mouse events that initiate network calls:

// Only handle network request when the main button is pressed (left click)
const handleRequestButtonClick = (event) => {
  if (event.button === 0) {  // 0 represents left mouse button
    fetchDataFromAPI();
  }
};

For keyboard events, use appropriate event management to prevent unintended network activity:

const handleKeyDown = (event) => {
  // Prevent navigation shortcuts from triggering network requests
  if (event.altKey && (event.key === 'ArrowLeft' || event.key === 'ArrowRight')) {
    event.stopPropagation();
    return;
  }
  
  // Proceed with network request if Enter key is pressed
  if (event.key === 'Enter') {
    fetchDataFromAPI();
  }
};

This prevents accidental network requests from middle/right clicks or keyboard shortcuts, improving user experience and reducing unnecessary server load.

---

Network resource limits

Implement protective limits for network operations to prevent resource exhaustion and denial-of-service attacks. Network operations should have bounded resource consumption to avoid overwhelming servers or clients.

Key areas to address:

1. Pagination limits: Set maximum page counts and track visited pages to prevent infinite loops in collection traversal
2. Connection management: Consume response bodies within reasonable limits (e.g., 1MB) for persistent connections, closing connections when limits are exceeded
3. Subscription churn: Avoid creating excessive per-resource network channels that cause high subscribe/unsubscribe load

Example implementation for pagination protection:

def collection_items(collection_or_uri)
  visited_pages = Set.new
  page_count = 0
  max_pages = 50
  
  while collection.is_a?(Hash) && page_count < max_pages
    return if visited_pages.include?(collection['id'])
    visited_pages.add(collection['id'])
    
    # Process items...
    page_count += 1
    collection = collection['next'].present? ? fetch_collection(collection['next']) : nil
  end
end

This prevents attackers from creating infinite pagination loops while ensuring legitimate large collections can still be processed within reasonable bounds.

---

Bean lifecycle management

When using containers and external services in Spring applications (especially with Testcontainers), declare them as Spring beans rather than static fields to ensure proper lifecycle management. This approach ensures that the application context will shut down clients first and then containers, preventing connection errors during shutdown.

For example, instead of:

@TestConfiguration
class TestConfig {
    // Not recommended for services like Kafka, ActiveMQ, etc.
    private static final KafkaContainer kafka = new KafkaContainer();
    
    @Bean
    public KafkaClient kafkaClient() {
        return new KafkaClient(kafka.getBootstrapServers());
    }
}

Prefer:

@TestConfiguration
class TestConfig {
    @Bean
    public KafkaContainer kafkaContainer() {
        return new KafkaContainer();
    }
    
    @Bean
    public KafkaClient kafkaClient(KafkaContainer container) {
        return new KafkaClient(container.getBootstrapServers());
    }
}

This pattern is especially important for messaging systems like ActiveMQ, Kafka, and Pulsar, where connection handling during shutdown is critical. The Spring container manages the lifecycle correctly, destroying client beans before container beans, which prevents errors caused by clients trying to access already-stopped services.

---

simplify redundant logic

Eliminate redundant conditional logic, extract duplicated code, and choose simpler patterns over complex implementations. This improves code readability and maintainability by reducing cognitive load.

Key practices:

• Simplify redundant conditionals: Instead of checking both directions of a condition, calculate once and use the result directly
• Extract duplicated code: When the same logic appears multiple times, extract it into a shared function or variable
• Use existing properties: Before creating new instance variables, check if existing properties can serve the same purpose
• Avoid complex initialization patterns: Prefer straightforward initialization in constructors over complex flag-based approaches
• Choose simpler function designs: Prefer return values over output parameters when possible

Example of simplifying redundant logic:

// Instead of:
if (textHeight > lineHeight) {
    CGFloat difference = textHeight - lineHeight;
    verticalOffset = difference / 2.0;
} else if (textHeight < lineHeight) {
    CGFloat difference = lineHeight - textHeight;
    verticalOffset = -(difference / 2.0);
}

// Use:
CGFloat difference = textHeight - lineHeight;
CGFloat verticalOffset = difference / 2.0;

Example of using existing properties:

// Instead of creating _initialProps, use existing _props:
if (_props) {
    // Use _props directly
}

---

Meaningful exception design

Design exceptions to provide clear context, preserve stack traces, and propagate correctly through your system. Key practices include:

1. Choose the most appropriate exception type based on the error condition:
   • Use IllegalArgumentException for invalid inputs
   • Use IllegalStateException for invalid state
   • Avoid generic exceptions when more specific ones exist

// Poor practice
throw new ValidationException("Cannot unwrap to " + type);

// Better practice
throw new IllegalArgumentException("Cannot unwrap " + target + " to " + type.getName());

1. Avoid unnecessary exception wrapping that obscures the original cause. Let original exceptions propagate when they provide sufficient context:

// Unnecessary wrapping
try {
  this.jobLauncher.launch(job, jobParameters);
} catch (NoSuchJobException ex) {
  throw new JobExecutionException(ex.getMessage(), ex);
}

// Better approach - NoSuchJobException is already a JobExecutionException
// Remove the try/catch completely
this.jobLauncher.launch(job, jobParameters);

1. For cleanup operations during error handling, capture secondary failures as suppressed exceptions:

catch (RuntimeException ex) {
  try {
    WebServer webServer = getWebServer();
    if (webServer != null) {
      webServer.stop();
    }
  }
  catch (Exception shutdownEx) {
    ex.addSuppressed(shutdownEx);
  }
  throw ex;
}

1. Prefer failing fast with specific exceptions when unexpected conditions occur rather than continuing with defensive fallbacks that might mask issues:

// Defensive (might mask issues)
Method initializeMethod = ReflectionUtils.findMethod(this.tester, "initialize", Class.class, ResolvableType.class);
if (initializeMethod == null) {
  throw new IllegalStateException("unable to find initialize method for " + this.tester);
}

// Fail-fast (better for critical components)
Method initializeMethod = ReflectionUtils.findMethod(this.tester, "initialize", Class.class, ResolvableType.class);
// Let the NPE happen naturally if the method isn't found

1. Ensure proper error propagation in asynchronous contexts where traditional exception handling might not work:

// Errors suppressed:
webClient.post()
  .bodyValue(body)
  .retrieve()
  .toBodilessEntity()
  .subscribe((__) -> {}, (__) -> {});

// Proper error handling:
webClient.post()
  .bodyValue(body)
  .retrieve()
  .toBodilessEntity()
  .subscribe((__) -> {}, (error) -> errorHandler.handleError(error));

---

Check SSR context

Always verify execution context (server vs client) before running client-specific operations in SSR applications. Many hydration errors and unexpected behaviors stem from client-only code executing during server-side rendering.

Key practices:

• Use import.meta.client checks before client-specific operations like polling, timers, or browser APIs
• Ensure context availability before using composables that depend on client state
• Be aware that some operations like useHead() may not work properly in server components without proper context

Example from polling implementation:

const startPolling = () => {
  if (import.meta.client && options.pollEvery && !pollTimer) {
    // Client-only polling logic
  }
}

This prevents server-side execution of client-specific code and reduces hydration mismatches that can break SSR applications.

---

Redact Transported Errors

When you serialize/dehydrate async results (queries, promises, RSC/RPC payloads), treat error objects as sensitive and do not transport raw server error details to the client/shared layer. Use a default redaction policy and make the behavior explicitly configurable and documented.

Apply this rule:

• Redact error message/stack (and any other sensitive fields) before dehydration/transport.
• Provide a single option/hook to control redaction (e.g., shouldRedactError) rather than hard-coding framework-specific assumptions.
• Decide and document how to handle special transport metadata (e.g., a digest field used for correlation): either preserve it intentionally for logging/correlation or redact it to prevent client exposure.

Example pattern:

function shouldRedactError(error: unknown): boolean {
  // default: redact to prevent leaking server-side details
  return true
}

function dehydratePromise(promise: Promise<unknown>) {
  return promise.catch((error) => {
    if (shouldRedactError(error)) throw new Error('redacted')
    throw error
  })
}

---

dependency management strategy

When configuring dependencies in package.json, follow these strategic principles to ensure stable and maintainable package management:

Peer Dependencies: Use peer dependencies judiciously to enable proper package hoisting while avoiding forced installations for all consumers. As noted: “We still need it here for it to be hoisted correctly. But we can make it optional and make it a direct dependency in the template.” Consider making peer dependencies optional when appropriate and satisfy requirements through direct dependencies in consuming packages.

Version Locking: Lock critical dependencies to specific versions that are known to work, especially for testing and tooling packages. Avoid using loose version ranges for packages that frequently introduce breaking changes. This prevents situations where “updates break testing” and ensures consistent behavior across environments.

Local vs Global Dependencies: Prefer local package dependencies over global installations to ensure reproducible builds and proper dependency resolution. Instead of requiring global installations, include dependencies directly in package.json: “You don’t need to install globally if installing here.”

Minimize Changes During Migrations: During monorepo transitions or major refactoring, “limit the changes to those packages to only the necessary ones” to reduce complexity and potential issues.

Example of proper dependency configuration:

{
  "peerDependencies": {
    "@react-native-community/cli-server-api": "*"
  },
  "peerDependenciesMeta": {
    "@react-native-community/cli-server-api": {
      "optional": true
    }
  },
  "devDependencies": {
    "appium": "2.0.0",
    "appium-uiautomator2-driver": "^2.29.0"
  }
}

---

Prefer simpler expressions

Always choose the simplest, most readable way to express your code logic. Unnecessary complexity makes code harder to understand and maintain.

When writing conditionals, method calls, or data transformations, ask yourself: “Is there a clearer way to express this?”

Examples of simplifying expressions:

1. Remove redundant conditionals when context makes them obvious: ```ruby

   Instead of this

   if reflection.belongs_to? && model.ignored_columns.include?(reflection.foreign_key.to_s)

Use this (when already in a belongs_to context)

if model.ignored_columns.include?(reflection.foreign_key.to_s)

2. Format array display consistently:
```ruby
# Instead of this verbose approach
filter_names = @filters.length == 1 ? @filters.first.inspect : "[#{@filters.map(&:inspect).join(", ")}]"

# Use the built-in inspect method
filter_names = @filters.length == 1 ? @filters.first.inspect : @filters.inspect

1. Use direct array methods instead of custom iterations: ```ruby

   Instead of searching with any?

   unless ActiveStorage.supported_image_processing_methods.any? { |method| method_name == method }

Use the more direct include?

unless ActiveStorage.supported_image_processing_methods.include?(method_name)

4. Optimize iterations when appropriate:
```ruby
# Instead of filtering then iterating
enums_to_create = columns.select { |c| c.type == :enum && c.options[:values] }
enums_to_create.each do |c|
  # process enum
end

# Check inside the loop to avoid an extra iteration
columns.each do |c|
  next unless c.type == :enum && c.options[:values]
  # process enum
end

1. Use modern language features when they improve readability: ```ruby

   Instead of ignoring block arguments

   def add_binds(binds, proc_for_binds = nil, &_)

Use anonymous block syntax (Ruby 2.7+)

def add_binds(binds, proc_for_binds = nil, &)

Remember that code is read far more often than it's written. Optimizing for readability pays dividends throughout the lifecycle of your application.

---

## platform-aware configuration messages

<!-- source: facebook/react-native | topic: Configurations | language: C++ | updated: 2025-02-13 -->

Configuration-related error messages, troubleshooting guidance, and feature flags should be accurate and account for platform-specific differences. When providing configuration instructions or enabling features conditionally, ensure the guidance reflects the actual capabilities and limitations of each target platform.

For error messages, provide clear, actionable troubleshooting steps that are relevant to the user's environment:

```cpp
// Good: Platform-aware error message with specific guidance
throw std::runtime_error(folly::to<std::string>(
    "Unable to load script.\n\n"
    "Make sure you're running Metro or that your "
    "bundle '", assetName, "' is packaged correctly for release.\n\n"
    "The device must be on the same Wi-Fi network as your laptop to connect to Metro.\n\n"
    "To use USB instead, shake the device to open the Dev Menu and set "
    "the bundler location to \"localhost:8081\" and run:\n"
    "  adb reverse tcp:8081 tcp:8081"));

For feature flags, consider platform capabilities when enabling conditional compilation:

#if AUTOLINKING_AVAILABLE
// Feature only enabled where actually supported
// Note: Android can't disable new arch at runtime unlike iOS
#endif

This ensures users receive relevant guidance and prevents configuration mismatches that could lead to runtime failures or unexpected behavior across different platforms.

---

Cache expensive computations

Implement strategic caching and memoization for expensive or frequently repeated computations to avoid redundant work. This can significantly improve performance in hot code paths.

Key implementation strategies:

1. Memoize frequently used functions or handlers - Store the results of expensive lookups or computations that are repeatedly accessed with the same inputs
2. Reuse complex structures - When working with schemas, validators, or other complex objects, compute them once and reuse them where possible
3. Implement proper cache invalidation - Ensure caches are cleared or updated when the underlying data changes

Example of effective memoization:

class BaseModel(metaclass=ModelMetaclass):
    __pydantic_setattr_handlers__: ClassVar[Dict[str, Callable[[BaseModel, Any], None]]]
    """__setattr__ handlers. Memoizing the setattr handlers leads to a dramatic 
    performance improvement in `__setattr__`"""
    
    def __setattr__(self, name: str, value: Any) -> None:
        # Use memoized handler for performance
        if (handler := self.__pydantic_setattr_handlers__.get(name)) is not None:
            handler(self, value)
            return
        # Fall back to slower path

For schema generation, reuse existing schemas rather than rebuilding them:

# Previously: schema was generated twice for nested models
# Now: schema is only generated once and reused
schema = cls.__dict__.get('__pydantic_core_schema__')
if schema is not None and not isinstance(schema, MockCoreSchema):
    # Reuse the existing schema instead of rebuilding
    return schema

Remember to implement appropriate cache clearing when needed:

# Clear cached values when they need to be rebuilt
for attr in ('__pydantic_core_schema__', '__pydantic_validator__', '__pydantic_serializer__'):
    if attr in cls.__dict__:
        delattr(cls, attr)

---

Simplify configuration setup

Avoid redundant configuration parameters and prefer automated solutions over manual maintenance. Remove configuration options that duplicate library defaults, replace manual dependency lists with programmatic detection, and eliminate unused configuration logic when usage patterns change.

Key practices:

• Remove parameters that duplicate library defaults (e.g., argv: process.argv.slice(2) when it’s already the default)
• Replace manual lists with automated detection where possible (e.g., external: (id) => isBareModuleId(id) instead of maintaining a hardcoded external dependencies array)
• Simplify configuration when requirements change (e.g., using transformIgnorePatterns: [] instead of complex modulePaths setup)
• Clean up conditional logic and prompts that are no longer needed due to changed usage patterns

Example of improvement:

// Before: Redundant and manual
let args = arg({}, { argv: process.argv.slice(2), stopAtPositional: true });
external: ["history", "@remix-run/router", "react", "react-dom"]

// After: Simplified and automated  
let args = arg({}, { permissive: true });
external: (id) => isBareModuleId(id)

This approach reduces maintenance burden, prevents configuration drift, and ensures setups work consistently across different environments and package managers.

---

Update documentation proactively

When code behavior changes, new features are added, or potential usage pitfalls are identified, proactively update all relevant documentation including API docs, inline comments, and usage warnings. This ensures developers have accurate information about execution order, blocking operations, and proper usage patterns.

Key areas requiring documentation updates:

• Behavioral changes (e.g., execution order modifications)
• New public methods and their purpose
• Usage warnings for blocking operations or common pitfalls
• Migration notes when functionality is moved or refactored

Example from the codebase:

// Important: app.Listen() must be called in a separate goroutine, otherwise shutdown hooks will not work
// as Listen() is a blocking operation. Example:
//
//	go app.Listen(":3000")
//	// ...

This proactive approach prevents confusion, reduces support burden, and improves the overall developer experience by keeping documentation synchronized with code reality.

---

avoid redundant computations

Identify and eliminate repeated expensive operations to improve performance. Cache computationally expensive objects like regex patterns, API results, or complex calculations outside of loops and repeated execution contexts. Implement early exit conditions when possible to avoid unnecessary processing.

Examples of optimization opportunities:

• Move regex compilation outside loops: const match = segment.match(/^:([\w-]+)(\?)?/) should have the regex cached
• Cache function results: Track previously computed values in a Set or Map to avoid re-calling expensive functions like patchRoutesOnMiss
• Add early bail-out conditions: Check simple conditions first before performing complex iterations or comparisons

Focus on hot paths and frequently executed code where redundant work has the most impact on performance.

---

Use streaming generators

When processing large files or datasets, implement generator functions that yield data incrementally rather than loading everything into memory at once. This approach significantly improves memory efficiency and enables handling of arbitrarily large datasets that wouldn’t fit in memory.

def stream_file(filename):
    # Use a context manager to ensure the file is properly closed
    with open(filename, "rb") as file_like:
        # Yield from delegates iteration to the file object
        # Each chunk is yielded without loading the entire file
        yield from file_like
        
# Usage with FastAPI streaming response
@app.get("/large-file/")
def get_large_file():
    generator = stream_file("large_video.mp4")
    return StreamingResponse(generator, media_type="video/mp4")

Benefits of this pattern:

• Constant memory usage regardless of file size
• Immediate first byte to client response time
• Works well with asynchronous frameworks
• Compatible with cloud storage and remote data sources

For optimal performance, carefully choose appropriate chunk sizes when implementing custom generators. Too small chunks can create unnecessary overhead, while too large chunks defeat the purpose of streaming.

---

Provide explicit error handling

Create custom, descriptive errors instead of allowing external dependencies or systems to fail with generic messages. Use consistent error handling utilities throughout the codebase rather than implementing ad-hoc error responses.

When a file or resource is missing, provide a clear custom error rather than letting the underlying system (like Vite) fail:

// Instead of letting Vite fail when loading a missing file
if (reactRouterConfigFile) {
  try {
    let configModule = await viteNodeContext.runner.executeFile(
      reactRouterConfigFile
    );
  } catch (error) {
    // Provide our own descriptive error
    return err(`Failed to load React Router config file: ${reactRouterConfigFile}`);
  }
}

// Check for missing exports explicitly
if (typeof configModule.default !== "object") {
  return err("Config file must export a default object");
}

Consolidate defensive error handling into reusable utilities:

// Instead of scattered invariant checks
function abortFetcher(key: string) {
  let controller = fetchControllers.get(key);
  // Flatten defensive check into the method itself
  if (!controller) return; // Handle gracefully
  controller.abort();
}

// Use consistent error utilities
if (!response) {
  // Use shared utility instead of ad-hoc response
  let error = new Error('Unhandled request');
  return returnLastResortErrorResponse(error, serverMode);
}

This approach improves debugging by providing clear error messages, reduces inconsistency across the codebase, and makes error handling more maintainable by centralizing common patterns.

---

Handle errors with care

Always implement comprehensive error handling for asynchronous operations, external API calls, and database operations. Catch errors at appropriate levels, log them with sufficient context for debugging, and provide meaningful error responses or recovery mechanisms.

Key principles:

1. Use try/catch blocks for error-prone operations
2. Log errors with relevant context
3. Implement recovery or fallback mechanisms
4. Return consistent error responses

Example:

async function processUserData(userId: string) {
  try {
    // Attempt primary operation
    const result = await database.users.findUnique({
      where: { id: userId },
    });
    
    if (!result) {
      logger.warn("User not found", { userId });
      return { error: "User not found" };
    }
    
    try {
      // Attempt secondary operation
      await externalApi.process(result);
      return { success: true };
    } catch (error) {
      // Handle specific operation failure
      logger.error("API processing failed", {
        userId,
        error: error instanceof Error ? error.message : String(error),
      });
      // Attempt fallback or recovery
      return { error: "Processing failed", retry: true };
    }
  } catch (error) {
    // Handle critical failures
    logger.error("Critical database error", {
      userId,
      error: error instanceof Error ? error.stack : String(error),
    });
    throw new Error("Internal server error");
  }
}

This approach ensures:

• Errors are caught and handled appropriately
• Error context is preserved for debugging
• Users receive meaningful error messages
• System can attempt recovery when possible

---

Sanitize external content

Always sanitize and validate external content before processing or rendering it to prevent security vulnerabilities like XSS (Cross-Site Scripting) and injection attacks. This applies to HTML content from emails, user inputs, URL parameters, and any data from untrusted sources.

For HTML content:

import DOMPurify from "dompurify";

// When displaying HTML content
export function HtmlEmail({ html }: { html: string }) {
  const srcDoc = useMemo(() => {
    try {
      const sanitizedHtml = DOMPurify.sanitize(html);
      return getIframeHtml(sanitizedHtml);
    } catch (error) {
      console.error("Failed to process HTML:", error);
      return "<p>Failed to load email content</p>";
    }
  }, [html]);
  // Rest of component...
}

// When converting text to HTML
const nudgeHtml = nudge
  ? nudge
      .split("\n")
      .filter((line) => line.trim())
      .map((line) => `<p>${DOMPurify.sanitize(line)}</p>`)
      .join("")
  : "";

For URL parameters:

// Instead of string concatenation:
// const url = `/api/endpoint?param=${value}&other=${otherValue}`;

// Use URLSearchParams to properly encode parameters
const url = `/api/endpoint?${new URLSearchParams({
  param: value,
  other: otherValue,
})}`;

This approach prevents malicious code execution, data theft, session hijacking, and other security vulnerabilities that can arise from improperly handled external content.

---

comprehensive authorization checks

Always implement thorough authorization checks at the earliest appropriate point in request processing, rather than relying solely on downstream filtering. This includes verifying user permissions, access rights, and relationship constraints (such as blocking status) before granting access to resources.

Even when additional filtering occurs at the message or data level, upfront authorization prevents unnecessary processing and provides clearer security boundaries. Consider all relevant access control factors including user relationships, privacy settings, and resource ownership.

Example from streaming access:

case 'profile':
  if (!params.account_id) {
    reject(new RequestError('Missing account id parameter'));
    return;
  }
  
  // Add comprehensive authorization check
  if (isAccountBlocked(params.account_id, req.accountId)) {
    reject(new AuthenticationError('Access denied'));
    return;
  }

This approach prevents security gaps where authorization logic is incomplete or missing entirely, as seen in cases where only basic parameter validation occurs without proper permission verification.

---

Precise testing dependency versioning

When specifying testing library dependencies, always use explicit minimum patch versions rather than development branches or broad version constraints. This practice ensures consistent and reproducible test environments across development, CI systems, and production builds.

Example of good practice:

"dependencies": {
  "phpunit/phpunit": "^10.5.35|^11.3.6|^12.0.1",
  "orchestra/testbench-core": "^9.9.3"
}

Example of practices to avoid:

"dependencies": {
  "phpunit/phpunit": "^10.5|^11.0", // Too broad, may include versions with issues
  "orchestra/testbench-core": "9.x-dev" // Development branch, not stable
}

This standard helps prevent subtle test failures due to dependency changes and makes test behavior more predictable across all environments. Using precise version constraints is particularly important for testing frameworks as unexpected behavior in these dependencies can lead to false positives or negatives in your test results.

---

Data structure correctness

Ensure data structures are accurately represented with their proper constraints and valid implementations, particularly for recursive structures. When documenting or implementing collections:

1. Explicitly state data structure constraints
   • For set-like structures, clearly document hashability requirements
   • For tree-like structures, describe node relationships precisely
2. Validate that recursive type examples actually terminate
   • Include escape conditions in recursive type definitions
   • Ensure examples represent structures that can be instantiated

# Incorrect recursive type definition (infinite recursion)
type B = list[C]
type C = B  # No termination condition!

# Correct recursive type definition with termination
type A = list[A] | None  # Terminates with None

Properly defined data structures not only prevent runtime errors but also enable more efficient algorithm implementations.

---

Configure rendering modes clearly

Ensure clear distinction and proper handling between different rendering modes (SSR, SSG, SPA) with appropriate conditional logic for each mode’s specific requirements.

Different rendering modes have distinct behaviors and asset generation needs:

• SPA Mode (ssr: false, no prerender): Generates only a single index.html that can hydrate for any path
• SSG Mode (ssr: false + prerender paths): Generates multiple HTML pages, enabling loaders and build-time data
• SSR Mode (ssr: true): Handles rendering and manifests via server handler

Apply mode-specific logic consistently:

function isSpaModeEnabled(reactRouterConfig) {
  // SPA Mode means we will only prerender a *single* `index.html` file
  // which prerenders only to the root route and can hydrate for _any_ path
  return (
    reactRouterConfig.ssr === false &&
    (reactRouterConfig.prerender == null || reactRouterConfig.prerender === false)
  );
}

// Conditionally remove exports based on rendering mode
if (!options?.ssr) {
  removeExports(ast, SERVER_ONLY_ROUTE_EXPORTS);
}

// Generate appropriate assets per mode
if (hasLoaders && isPrerenderingEnabled(reactRouterConfig)) {
  await prerenderData(handler, path, clientBuildDirectory);
}

This prevents configuration conflicts and ensures each mode generates the correct assets and applies the appropriate optimizations.

---

Test all code paths

Write comprehensive tests that cover all code paths including edge cases, error conditions, and different parameter combinations. Each test file should include:

1. Basic functionality tests
2. Edge case scenarios
3. Error handling cases
4. Different parameter combinations

Example of comprehensive test coverage:

describe("findMatchingRule", () => {
  it("handles basic matching", async () => {
    const rule = getRule({ from: "test@example.com" });
    // ... basic test implementation
  });

  it("handles AND operator with multiple conditions", async () => {
    const rule = getRule({
      from: "test@example.com",
      subject: "Important",
      conditionalOperator: LogicalOperator.AND,
    });
    // ... test multiple conditions
  });

  it("handles error conditions", async () => {
    const invalidRule = getRule({ from: null });
    // ... test error handling
  });

  it("handles edge cases", async () => {
    const rule = getRule({
      from: "",
      subject: "".padEnd(1000, "a"), // Very long subject
    });
    // ... test edge cases
  });
});

This approach ensures robust code quality by verifying behavior across different scenarios and preventing potential bugs from reaching production.

---

Early returns prevent waste

Add early return statements and duplicate checks to avoid unnecessary computations, memory allocations, and API calls. This pattern prevents performance degradation by stopping expensive operations before they begin.

Key strategies:

1. Check for duplicates before adding to collections to prevent memory leaks
2. Validate preconditions early to avoid unnecessary processing
3. Return immediately when work is not needed instead of continuing execution

Example implementation:

__addChild(child: AnimatedNode): void {
  // Prevent adding duplicate animated nodes
  if (this._children.includes(child)) {
    return;
  }
  // Continue with expensive operations only if needed
  this._children.push(child);
  // ... rest of implementation
}

_maybeCallOnEndReached() {
  const {onEndReached} = this.props;
  // Early return if callback doesn't exist
  if (!onEndReached) {
    return;
  }
  // Early return if scrolling in wrong direction
  if (offset <= 0 || dOffset <= 0) {
    return;
  }
  // ... continue with expensive calculations
}

This approach reduces unnecessary memory allocations, prevents duplicate processing, and eliminates redundant API calls, leading to better overall performance and resource utilization.

---

Optimize dependency automation

Configure automated dependency update tools (like Dependabot) to balance security needs against developer cognitive load. Set monthly intervals instead of weekly to reduce PR noise, limit the number of concurrent PRs, and consider excluding major version updates that could cause compatibility issues.

Example configuration for Dependabot:

version: 2
updates:
  - package-ecosystem: npm
    directory: /
    schedule:
      interval: monthly
      time: "23:00"
      timezone: Europe/London
    open-pull-requests-limit: 10
    ignore:
      - dependency-name: "*"
        update-types: ["version-update:semver-major"]

This configuration reduces PR noise with monthly updates, limits open PRs to 10, schedules updates during off-hours, and avoids major version updates that might break compatibility.

---

Explicit exception propagation

Always be explicit about how exceptions are handled, propagated, and recovered from in your code. When catching exceptions, either re-raise them or raise appropriate new exceptions to ensure proper error flow through the system.

When using dependencies with yield, be particularly careful with exception handling:

async def get_db():
    try:
        db = DBSession()
        yield db  # This value is injected into path operations
    except InternalError as e:
        # Either re-raise the original exception
        raise
        # Or raise a more specific exception
        # raise HTTPException(status_code=500, detail="Database error")
    finally:
        db.close()

Without explicitly re-raising exceptions or raising new ones, your application might silently fail or return unexpected 500 errors without proper logging. This is especially important in frameworks like FastAPI where dependency execution order and exception handling patterns greatly impact application behavior.

Format exception-related code with proper backticks in documentation (HTTPException, raise, except) and use technically accurate terminology when describing error flows to ensure other developers correctly understand error handling patterns in your codebase.

---

Avoid blocking in async

When working with asynchronous code, ensure that I/O operations (like file reads/writes) don’t block the event loop. Blocking operations in async contexts can lead to performance degradation, deadlocks, or unexpected behavior.

• Use asynchronous alternatives for I/O operations (aiofiles instead of built-in open, etc.)
• If a blocking operation cannot be avoided, consider offloading it to a separate thread

Example:

# Problematic - blocking I/O in async context
async def shutdown_event():
    with open("log.txt", "w") as f:  # Blocking operation
        f.write("Application shutdown")

# Better - using async I/O
import aiofiles
async def shutdown_event():
    async with aiofiles.open("log.txt", "w") as f:
        await f.write("Application shutdown")

# Alternative - offload blocking I/O to a thread
from concurrent.futures import ThreadPoolExecutor
thread_pool = ThreadPoolExecutor()

async def shutdown_event():
    def write_log():
        with open("log.txt", "w") as f:
            f.write("Application shutdown")
    
    await asyncio.get_event_loop().run_in_executor(thread_pool, write_log)

---

use modern null-safe operators

Prefer modern JavaScript null-safe operators over verbose conditional checks to improve code readability and prevent null-related errors. Use optional chaining (?.) for safe property access, nullish coalescing (??) for default values, and nullish coalescing assignment (??=) for lazy initialization.

Key patterns to adopt:

1. Optional chaining for safe property access: ```javascript // Instead of verbose null checks if (reaction.parent !== null && (reaction.parent.f & DERIVED) !== 0)

// Use optional chaining if ((reaction.parent?.f & DERIVED) !== 0)

2. **Nullish coalescing for default values:**
```javascript
// Instead of logical OR
parent: parent_derived || active_effect

// Use nullish coalescing to handle only null/undefined
parent: parent_derived ?? active_effect

1. Nullish coalescing assignment for lazy initialization: ```javascript // Instead of separate checks and assignments if (to_animate === undefined) to_animate = new Set(); to_animate.add(item);

// Use nullish coalescing assignment (to_animate ??= new Set()).add(item);

4. **Optional chaining for method calls:**
```javascript
// Instead of conditional calls
if (handler) {
    return handler.call(this, event);
}

// Use optional chaining
return handler?.call(this, event);

These operators provide cleaner, more expressive code while maintaining the same null-safety guarantees. They’re particularly valuable in complex expressions where traditional null checks would require nested conditionals or temporary variables.

---

Consistent term capitalization

Follow consistent capitalization rules for technical terms, acronyms, and library names throughout your codebase and documentation:

1. Capitalize standard acronyms: Use ‘URL’, ‘JSON’, ‘API’, ‘HTML’, ‘CSS’, ‘Unicode’, etc. rather than lowercase versions.

2. Capitalize product/library names: Use ‘Pydantic’, ‘Django’, ‘React’, etc. when referring to them as proper nouns in documentation, comments, and string literals.

3. Preserve lowercase in code contexts: Keep technical names lowercase when used in import statements, function calls, or paths where they must match the actual implementation:

   # Correct:
   import pydantic  # lowercase in import statements
      
   # In documentation or comments:
   # Pydantic provides validation for Python data types  # capitalized as proper noun
   

This consistency enhances readability, maintains technical accuracy, and provides a more professional appearance in your documentation and user-facing messages.

---

avoid unnecessary workflow restrictions

Remove unnecessary approval gates, custom tokens, and restrictive conditions in CI/CD workflows when existing security measures are sufficient. Over-restrictive workflows create friction without meaningful security benefits.

For example, avoid adding approval requirements when contributor workflows already require approval:

jobs:
  preview:
    name: Preview
    # Remove unnecessary approval check
    # if: github.event.review.state == 'APPROVED'

Similarly, use built-in tokens when appropriate instead of custom secrets:

- uses: actions/labeler@v4.3.0
  with:
    repo-token: ${{ secrets.GITHUB_TOKEN }}  # Use built-in token

Evaluate each workflow condition to ensure it adds genuine security value rather than just creating additional steps.

---

avoid unnecessary component complexity

When designing React components and their APIs, resist the temptation to add features, props, or methods that provide limited or no real value to developers. Components should expose only functionality that serves genuine use cases and avoids introducing maintenance burden or developer confusion.

Consider whether new props or features will actually be useful in practice. For example, adding a backgroundColor prop to a navigation component might seem comprehensive, but if it has no effect with modern gesture navigation, it creates false expectations and API bloat.

Before adding new component features, evaluate:

• Will this prop/feature work consistently across different environments?
• Does it solve a real problem developers face?
• Will it require deprecated APIs or workarounds?
• Does it align with platform conventions and best practices?

Example of what to avoid:

// Avoid adding props that don't work consistently
<NavigationBar 
  backgroundColor="#ff0000"  // No effect with gesture navigation
  barStyle="dark"           // Automatic based on contrast
  translucent={true}        // Limited utility
/>

Instead, focus on essential functionality that provides clear value:

// Focus on props that serve real purposes
<NavigationBar 
  hidden={false}  // Actually controls visibility
/>

This principle helps maintain clean, predictable component APIs that developers can rely on without encountering unexpected limitations or deprecated functionality.

---

Use Kotlin testing idioms

When writing tests in Kotlin, prefer Kotlin-specific testing libraries and language features over their Java equivalents. Use Mockito Kotlin instead of standard Mockito for more idiomatic syntax, and leverage Kotlin language features like apply blocks to make test setup code more concise and readable.

For example, instead of:

import org.mockito.Mockito.verify
// ...
val field = OkHttpClientProvider::class.java.getDeclaredField("sClient")
field.isAccessible = true
field.set(null, null)

Use:

import org.mockito.kotlin.verify
// ...
val field = OkHttpClientProvider::class.java.getDeclaredField("sClient").apply {
  isAccessible = true
  set(null, null)
}

This approach improves test code readability, reduces boilerplate, and takes advantage of Kotlin’s expressive syntax to make tests more maintainable.

---

Use descriptive semantic names

Choose variable, function, and type names that clearly communicate their purpose and context. Prioritize readability and semantic meaning over brevity.

Key principles:

• Use full descriptive names over abbreviations when clarity benefits (State instead of S, handlerContext instead of context)
• Choose readable prefixes over cryptic ones (__ReactRouter_SerializesTo instead of $__RR_SerializesTo)
• Align naming with existing patterns in the codebase (navigationType to match useNavigationType hook)
• Rename variables when their scope or purpose changes to maintain clarity

Example from codebase:

// Before: Generic and unclear
let context = await loadRouteData(...)

// After: Specific and descriptive  
let handlerContext = await loadRouteData(...)

// Before: Cryptic prefix
export type SerializesTo<T> = {
  $__RR_SerializesTo?: [T];

// After: Clear, readable prefix
export type SerializesTo<T> = {
  __ReactRouter_SerializesTo?: [T];

This approach reduces cognitive load for developers and makes code self-documenting, especially important in large codebases where context switching is frequent.

---

Build documentation clarity

Ensure build and deployment documentation clearly explains processes, outputs, and environment options to prevent CI/CD pipeline issues. Documentation should comprehensively cover build context separation, deployment targets, and generated artifacts.

When documenting build processes, include:

• Clear explanation of build outputs and their purposes (e.g., index.html, 200.html, 404.html for prerendering)
• Deployment environment options with specific examples
• Build vs runtime context separation to prevent configuration errors

Example:

## Build Output
When prerendering a client-rendered app, Nuxt generates `index.html`, `200.html` and `404.html` files by default. You can deploy this output on any system supporting JavaScript, including serverless and edge environments, or pre-render for static hosting.

## Context Separation  
`nuxt.config` and Nuxt Modules extend the build context, whereas Nuxt Plugins extend runtime. These contexts are isolated and should not share state.

This prevents CI/CD pipeline failures caused by unclear build requirements, incorrect deployment configurations, or context mixing issues.

---

Optimize React hooks

Avoid unnecessary useCallback and useEffect dependencies to improve performance and code clarity. When event handlers are only used within a useEffect, define them locally inside the effect rather than using useCallback. This eliminates the need for the callback hook and reduces re-renders. Additionally, understand that refs don’t need to be included in useEffect dependency arrays since they maintain stable references across renders.

Example of optimization:

// Instead of this:
const handleDocumentClick = useCallback(() => {
  onClose();
}, [onClose]);

useEffect(() => {
  document.addEventListener('click', handleDocumentClick);
  return () => document.removeEventListener('click', handleDocumentClick);
}, [handleDocumentClick]);

// Do this:
useEffect(() => {
  const handleDocumentClick = () => {
    onClose();
  };
  
  document.addEventListener('click', handleDocumentClick);
  return () => document.removeEventListener('click', handleDocumentClick);
}, [onClose]); // refs like nodeRef don't need to be dependencies

This approach reduces unnecessary re-renders and makes the code more readable by keeping related logic together.

---

improve code readability

Add line breaks and proper spacing between logical blocks within functions to improve code readability. When functions become complex with multiple logical sections, consider extracting nested logic into separate functions.

For example, instead of cramped code:

function uniquePlugins (plugins: NuxtPlugin[]) {
  const pluginFlags = new Set<string>()
  const bucket: NuxtPlugin[] = []
  for (const plugin of [...plugins].reverse()) {
    const name = plugin.name ? plugin.name : filename(plugin.src)
    const mode = plugin.mode ? plugin.mode : 'all'
    const flag = `${name}.${mode}`
    if (pluginFlags.has(flag)) {
      continue
    }
    pluginFlags.add(flag)
    bucket.push(plugin)
  }
  return bucket.reverse()
}

Use proper spacing between logical sections:

function uniquePlugins (plugins: NuxtPlugin[]) {
  const pluginFlags = new Set<string>()
  const bucket: NuxtPlugin[] = []

  for (const plugin of [...plugins].reverse()) {
    const name = plugin.name ? plugin.name : filename(plugin.src)
    const mode = plugin.mode ? plugin.mode : 'all'
    const flag = `${name}.${mode}`

    if (pluginFlags.has(flag)) {
      continue
    }

    pluginFlags.add(flag)
    bucket.push(plugin)
  }

  return bucket.reverse()
}

Additionally, when complex logic can be extracted for better organization and readability, move it out of nested contexts into separate functions or higher-level scopes.

---

Follow consistent style conventions

Spring Boot projects maintain specific coding style conventions for consistency and readability. When contributing code, adhere to the following style guidelines:

1. Explicit type declarations: Don’t use var keyword for variable declarations. Always declare variable types explicitly: ```java // Incorrect: var sessionStore = new MaxIdleTimeInMemoryWebSessionStore(timeout);

// Correct: MaxIdleTimeInMemoryWebSessionStore sessionStore = new MaxIdleTimeInMemoryWebSessionStore(timeout);

2. **String comparison pattern**: Use "literal".equals(variable) pattern instead of Objects.equals():
```java
// Incorrect:
return Objects.equals(postgresAuthMethod, "trust");

// Correct:
return "trust".equals(postgresAuthMethod);

1. Lambda expressions: Use parentheses around single lambda parameters: ```java // Incorrect: .map(exporter -> BatchSpanProcessor.builder(exporter).build())

// Correct: .map((exporter) -> BatchSpanProcessor.builder(exporter).build())

4. **Annotation consistency**: Explicitly declare annotations even when using default values for readability:
```java
// Keep annotations with default values for consistency
@Order(Ordered.LOWEST_PRECEDENCE)

1. Regular expression syntax: Be consistent with character escaping in regular expressions - if you escape opening brackets, also escape closing brackets: ```java // Inconsistent: Pattern.compile(“^(.)\[(.)\]$”);

// Consistent: Pattern.compile(“^(.)\[(.)]$”);

6. **Ordering**: Sort enum values and similar collections alphabetically for ease of finding items.

Following these conventions helps maintain a consistent codebase that's easier to read, review, and maintain.

---

## Structure exception handling patterns

<!-- source: nestjs/nest | topic: Error Handling | language: TypeScript | updated: 2025-01-21 -->

Implement consistent exception handling using framework-provided mechanisms rather than ad-hoc try-catch blocks or manual error propagation. Use appropriate exception classes and interceptors to handle errors at the right architectural level.

Key guidelines:
1. Use built-in exception classes with proper status codes
2. Leverage exception interceptors for cross-cutting error handling
3. Avoid mixing different error handling approaches

Example - INCORRECT approach:
```typescript
@Controller('cats')
export class CatsController {
  @Post()
  async create(@Body() createCatDto: CreateCatDto) {
    try {
      await this.catsService.create(createCatDto);
    } catch(error) {
      console.error(error);
      return []; // Swallowing error, returning empty result
    }
  }
}

CORRECT approach:

@Controller('cats')
export class CatsController {
  @Post()
  async create(@Body() createCatDto: CreateCatDto) {
    // Let exception filter handle errors
    return await this.catsService.create(createCatDto);
  }
}

// In a custom exception filter
@Catch()
export class AllExceptionsFilter implements ExceptionFilter {
  catch(exception: unknown, host: ArgumentsHost) {
    // Proper error handling with status codes and logging
    const status = exception instanceof HttpException 
      ? exception.getStatus()
      : HttpStatus.INTERNAL_SERVER_ERROR;
    // Handle error appropriately...
  }
}

---

Propagate errors properly

Always forward errors to the framework’s error handling pipeline instead of swallowing them or handling them inconsistently. This enables centralized error handling, consistent user experiences, and proper error logging.

Bad practice:

try {
  await someAsyncOperation();
} catch (err) {
  res.status(404).json(err.message); // Direct response, bypassing error pipeline
}

Good practice:

try {
  await someAsyncOperation();
} catch (err) {
  // Forward to Express error handling middleware
  return next(err); 
}

For “fire-and-forget” operations where you don’t want to interrupt the main flow:

try {
  // Non-critical operation
  await redisClient.hSet('online_users', user, now.toString());
} catch (err) {
  console.error('Error setting user activity:', err);
  // Don't call next(err) for non-critical errors
}

When handling streams or events, properly forward errors but be mindful of potential recursive error handling:

inputStream.on('error', (err) => {
  // Remove handlers first to avoid recursive error handling
  inputStream.removeAllListeners();
  res.removeAllListeners('error');
  
  // Then forward the error
  next(err);
});

Using the error handling pipeline allows your application to:

1. Provide consistent error responses
2. Centralize error logging
3. Customize error pages based on environment (development vs production)
4. Set appropriate HTTP status codes based on error types

---

Serialize dynamic code inputs

Always serialize or sanitize user-controlled data before embedding it in dynamically generated code to prevent code injection vulnerabilities. Unsanitized inputs containing special characters like quotes can break JavaScript syntax or enable malicious code execution.

When injecting values into generated JavaScript, use proper serialization methods rather than direct string concatenation:

// Vulnerable - direct injection without serialization
this.injectScript(`__TSR__.streamedValues['${key}'] = { value: ${value}}`)

// Secure - serialize inputs before injection  
this.injectScript(`__TSR__.streamedValues.push([${this.serializer?.(key)}, ${this.serializer?.(value)}])`)

This applies to any scenario where user input is embedded in generated code, including SQL queries, HTML templates, JavaScript snippets, and configuration files. Use appropriate escaping or serialization functions for the target context to maintain both functionality and security.

---

Environment-specific logger configuration

Configure loggers in environment-specific files rather than in application.rb or initializers. Different environments (development, test, production) typically require different logging levels and configurations, and Rails is designed to support this pattern.

When setting up loggers or modifying logging levels, place the configuration in the appropriate environment file:

# AVOID
# config/application.rb
config.logger = Logger.new(STDOUT)
config.log_level = :warn

# PREFER
# config/environments/production.rb
config.logger = Logger.new(STDOUT)
config.log_level = :warn

This approach ensures that each environment can have tailored logging settings appropriate for its context (e.g., verbose in development, minimal in production). It also follows Rails conventions, making your codebase more maintainable and aligned with standard practices.

---

Extract view complexity

Keep views clean and readable by extracting complex logic to appropriate locations. Move database queries with complex conditions to model scopes, extract reusable form fields to partials, and move complex conditional logic to helper methods.

For database queries, use explicit ordering and create named scopes:

# Instead of in the view:
options_from_collection_for_select(CustomEmojiCategory.order(:name).all, 'id', 'name')

# Create a model scope:
class CustomEmojiCategory
  scope :alphabetic, -> { order(name: :asc) }
end

# Then use in view:
options_from_collection_for_select(CustomEmojiCategory.alphabetic, 'id', 'name')

For reusable forms, extract fields to partials even for single-use forms to improve consistency and mental parsing:

# Instead of inline form fields:
= simple_form_for @generator do |form|
  .fields-group
    = form.input :field1
    = form.input :field2

# Extract to _form.html.haml:
= render 'form', generator: @generator

For complex conditional blocks in views, move the logic to helper methods to improve readability and testability. This separation of concerns makes views easier to scan and understand while keeping business logic properly organized.

---

Configure platform-specific builds

Ensure build and distribution configurations are properly documented and optimized for each target platform. For cross-platform projects, explicitly document which configuration flags are needed for different build scenarios and package manager integrations.

When configuring build systems like Bazel or CMake, provide complete examples with all required flags for different contexts:

# Building application directly
bazel build //platform/ios:App --//:renderer=metal --//:use_rust

# Generating project files requires different configuration
bazel run //platform/ios:xcodeproj --@rules_xcodeproj//xcodeproj:extra_common_flags="--//:renderer=metal --//:use_rust"

For repository configuration, optimize for platform-specific package managers. Document the preferred distribution method (source vs. binary) for each platform, as different platforms have different requirements:

# Clone with submodules for complete source access
git clone --recurse-submodules git@github.com:maplibre/maplibre-native.git

# For Apple platforms, source distribution may be preferred for package manager integration
# "Source-only distribution is the preferred way of distribution for Apple platforms now"

Test all documented configurations regularly to ensure they remain valid as the codebase evolves, particularly when introducing new dependencies or build targets.

---

Eliminate unnecessary computations

Identify and remove redundant operations, unnecessary copies, and repeated computations that add algorithmic overhead without providing value. This includes avoiding redundant hash operations, using const references instead of copies, implementing memoization for expensive lookups, and making conscious space-time tradeoffs.

Key patterns to watch for:

• Hash functions that perform unnecessary operations (e.g., hash_combine with seed 0 instead of returning the hash directly)
• Using auto instead of const auto& when working with existing objects, causing unnecessary copies
• Repeated expensive operations like NSClassFromString that can be cached with static variables
• Storing precomputed state vs recomputing on-demand based on access patterns

Example optimization:

// Instead of redundant hash_combine:
facebook::react::hash_combine(seed, color.getUIColorHash());

// Return hash directly:
return color.getUIColorHash();

// Use const references to avoid copies:
const auto& orientation = gradient.orientation;
const auto& colorStops = gradient.colorStops;

Consider the frequency of operations and choose the approach that minimizes total computational cost while maintaining code clarity.

---

Simplify and deduplicate code

Write concise, non-redundant code by eliminating unnecessary duplication and using simpler syntax where possible. This improves readability and maintainability.

Key practices:

• Remove redundant property definitions when extending interfaces or classes that already provide them
• Extract common logic into shared functions to prevent duplication across files
• Use direct function references instead of arrow function wrappers when the signature matches
• Make exported types comprehensive to avoid forcing users to combine multiple types

Examples:

// Instead of redundant property definitions:
export interface Derived<V = unknown> extends Value<V> {
  r_version: number; // ❌ Already defined in Value
}

// Use inheritance properly:
export interface Derived<V = unknown> extends Value<V> {
  // ✅ Only add new properties
}

// Instead of arrow function wrappers:
elements.forEach(element => detach(element)); // ❌

// Use direct function reference:
elements.forEach(detach); // ✅

// Make exported types complete:
export type ClassValue = string | ClassArray | ClassDictionary; // ✅

---

Standardize dependency version notation

When specifying dependencies in package.json, follow consistent version notation patterns that align with your project’s stability and compatibility requirements:

1. Choose the appropriate notation based on your project type:
   • Use caret notation (^) for libraries that properly follow semver when you want to receive compatible updates automatically
   • Use tilde notation (~) for patch-level updates only
   • Use exact versions (without prefix) for critical dependencies where any change might introduce risks

2. Maintain consistency across the project and document your versioning strategy in contributing guidelines.

3. Consider backward compatibility with older npm versions and user environments when selecting notation style.

Example:

{
  "dependencies": {
    "express": "^4.18.2",     // Library following semver - accepts compatible updates
    "body-parser": "~1.20.1", // Accepts patch updates only
    "crypto-library": "2.0.1" // Exact version for critical security dependency
  },
  "engines": {
    "node": "^14 || ^16 || ^18 || ^20" // Clear specification of supported versions
  }
}

Remember that some projects may have strict policies prohibiting certain notation types based on their ecosystem requirements. Always follow project-specific guidelines when they exist.

---

Structured configuration management

Configuration files should follow official standards, have up-to-date tool settings, and appropriate dependency constraints. This ensures consistent behavior across environments and compatibility with the project’s requirements.

For pyproject.toml:

1. Organize sections according to packaging specifications (e.g., place dependency-groups under the project section)
2. Keep tool configuration versions aligned with project requirements:

   [tool.ruff]
   target-version = 'py39'  # Should match minimum supported Python version
   

3. Manage dependency constraints carefully, considering Python version compatibility:

   # Option 1: Version constraints with conditions
   "sqlalchemy>=2.0,<3.0; python_version < '3.13'"
      
   # Option 2: Simpler constraints when appropriate
   "sqlalchemy>=2.0,<3.0"
   

Regular audits of configuration files should be performed when upgrading dependencies or changing supported Python versions to ensure configurations remain correct and optimal.

---

Avoid shared structure mutation

When implementing algorithms that manipulate complex nested data structures, avoid directly mutating shared objects that might be referenced elsewhere in the system. Mutations can lead to unexpected side effects and hard-to-trace bugs, particularly when the same structure is referenced in multiple places.

Instead:

1. Create copies of data structures before modifying them
2. Use immutable data structures where possible
3. Consider the reference implications when extracting or moving properties between structures

For example, rather than:

# Dangerous: directly mutating a schema that might be shared
schema = inner_schema['schema']
ref = schema.pop('ref', None)  # This modifies the original schema!
if ref:
    outer_schema['ref'] = ref

Prefer:

# Safer: extract values without mutation
if 'ref' in inner_schema['schema']:
    ref = inner_schema['schema']['ref']
    outer_schema['ref'] = ref
    # Create a new structure without the ref if needed
    new_schema = {**inner_schema['schema']}
    new_schema.pop('ref')

This approach is especially important in schema generation, type systems, and other algorithms where complex nested structures with cross-references are common.

---

Extract workflow scripts

Move complex scripts out of workflow YAML files into separate, dedicated script files in your repository. This practice significantly improves workflow maintainability, enables local testing of CI logic, and makes code reviews more effective.

Benefits:

• Scripts can be tested locally before committing changes
• Workflow files remain clean and readable
• Shell syntax errors can be caught before CI runs
• Scripts can be reused across multiple workflows
• Proper syntax highlighting in code editors

Example:

Instead of:

# .github/workflows/example.yml
steps:
  - name: Upload external data for benchmark
    run: |
      mkdir -p /tmp/benchmark-data
      curl -L https://example.com/data.zip -o /tmp/benchmark-data/data.zip
      unzip /tmp/benchmark-data/data.zip -d /tmp/benchmark-data
      # many more lines of complex logic...

Prefer:

# .github/workflows/example.yml
steps:
  - name: Upload external data for benchmark
    run: ./scripts/ci/upload-benchmark-data.sh

With script file:

# scripts/ci/upload-benchmark-data.sh
#!/bin/bash
set -euo pipefail

mkdir -p /tmp/benchmark-data
curl -L https://example.com/data.zip -o /tmp/benchmark-data/data.zip
unzip /tmp/benchmark-data/data.zip -d /tmp/benchmark-data
# many more lines of complex logic...

When scripts become more complex, consider also adding comments about their purpose and relationship to the build process to help other developers understand the workflow.

---

Standard configuration files

Use standardized, tool-specific configuration files instead of embedding configurations in CI scripts or other build files. This improves discoverability, ensures consistency between local development and CI environments, and provides self-documentation for required settings.

However, be mindful of introducing dependencies on specific tooling ecosystems. Ensure your configuration approach works well with all build systems your project might interact with.

Example:

# Instead of this in a CI workflow file:
- name: Add targets for Rust toolchain
  run: rustup target add --toolchain stable-x86_64-unknown-linux-gnu aarch64-linux-android

# Use a standard configuration file (rust-toolchain.toml):
# [toolchain]
# targets = ["aarch64-linux-android", "armv7-linux-androideabi"]

This approach documents required settings in conventional locations that tools automatically recognize, reducing the need for extra documentation while ensuring consistency across environments.

---

Content security policy configuration

Implement Content Security Policy (CSP) configurations appropriately for your application’s context. Use report-only mode during implementation to avoid breaking functionality while testing policies.

For API endpoints, implement stricter policies:

# In controllers serving API endpoints
content_security_policy only: :api do |policy|
  policy.default_src :none
  policy.frame_ancestors :none
  policy.sandbox        # Additional protection with minimal overhead
end

For user-facing pages, implement policies that balance security and functionality:

# In application controller or specific controllers
content_security_policy do |policy|
  policy.default_src :self
  policy.script_src :self
  policy.style_src :self
  # Add sources as needed, but be as restrictive as possible
end

# Test new policies in report-only mode before enforcing
content_security_policy_report_only do |policy|
  # Configure your new policy here
  # It will be reported but not enforced
end

Always prefer hash or nonce-based source validation over ‘unsafe-inline’ when script execution from inline elements is required. Remove unnecessary CSP configurations to avoid confusion and maintain clean security controls.

---

Documentation clarity standards

Ensure technical documentation clearly distinguishes between similar but different concepts, uses precise language, and provides unambiguous explanations. When documenting Vue features, explicitly label and differentiate between reactive and non-reactive data, different directive behaviors, and component patterns.

Use clear, descriptive comments in code examples to highlight important distinctions:

// reactive data - changes trigger re-renders
const reactiveUser = reactive({name: "Alice", age: 18});

// plain object - changes do not trigger re-renders  
const plainUser = {name: "Bob", age: 21};

Avoid ambiguous phrasing that could confuse readers about technical behavior. Choose words that clearly convey the intended meaning and relationship between concepts. Review documentation for grammatical errors and ensure consistent terminology throughout.

---

Structure documentation effectively

Documentation should prioritize clear organization with a logical flow to help developers find information quickly. Apply these practices:

1. Use descriptive headings and titles that directly communicate content purpose

   # Ways to Configure the Map
   ## XML Configuration
   ## Programmatic Configuration
   ## Using MapLibreMapOptions
   

2. Focus on specialized or unique content rather than explaining widely understood concepts

   // Instead of explaining JSON basics:
   ## Using GeoJSON in MapLibre
   This guide focuses on MapLibre-specific GeoJSON implementation details.
   

3. Include complete, explicit instructions that readers can follow without additional context ```markdown // Instead of: You need to have the correct Rust toolchain(s) installed.

// Write: Install the required Rust toolchain with:

rustup install 1.68.0
rustup default 1.68.0

1. Ensure all substantive code examples are referenced or tested to verify they remain valid as the codebase evolves

   // Reference to a working example in the codebase
   // See: examples/MapOptionsDemo.kt
   val mapOptions = MapLibreMapOptions.Builder()
    .camera(CameraPosition.Builder()
        .target(LatLng(51.50550, -0.07520))
        .zoom(10.0)
        .build())
    .build()
   

---

Configure at proper scope

Place configuration options at their proper scope within the framework hierarchy. Avoid tight coupling between components and ensure user configurations aren’t accidentally overridden.

When working with configurations:

1. Avoid direct framework references in components

   Instead of accessing global constants directly:

   def perform(event)
     ex = event.payload[:exception_object]
     if ex
       cleaned_backtrace = Rails.backtrace_cleaner.clean(ex.backtrace)
       # ...
     end
   end
   

   Pass dependencies through proper configuration channels:

   # In the railtie
   initializer "active_job.backtrace_cleaner" do
     ActiveJob::LogSubscriber.backtrace_cleaner = Rails.backtrace_cleaner
   end
      
   # In the component
   def perform(event)
     ex = event.payload[:exception_object]
     if ex
       cleaned_backtrace = self.class.backtrace_cleaner.clean(ex.backtrace)
       # ...
     end
   end
   

2. Respect user configuration

   Check if user has already set a configuration before applying defaults:

   # Bad: Overwrites user configuration
   initializer "active_record.attributes_for_inspect" do |app|
     ActiveRecord::Base.attributes_for_inspect = :all if app.config.consider_all_requests_local
   end
      
   # Good: Respects user configuration
   initializer "active_record.attributes_for_inspect" do |app|
     if app.config.consider_all_requests_local && app.config.active_record.attributes_for_inspect.nil?
       ActiveRecord::Base.attributes_for_inspect = :all
     end
   end
   

3. Avoid mutating shared configuration objects

   Always duplicate default configuration objects before modification:

   # Bad: Mutates shared constant
   route_set_config = DEFAULT_CONFIG
   route_set_config[:some_setting] = value
      
   # Good: Works with a copy
   route_set_config = DEFAULT_CONFIG.dup
   route_set_config[:some_setting] = value
   

4. Use environment-specific configuration via config, not conditionals

   Instead of hardcoding environment checks:

   # Bad: Direct environment checking in middleware
   if (Rails.env.development? || Rails.env.test?) && logger(request)
     # ...
   end
   

   Make behavior configurable:

   # Good: Configurable behavior
   def initialize(app, warn_on_no_content_security_policy = false)
     @app = app
     @warn_on_no_content_security_policy = warn_on_no_content_security_policy
   end
      
   # Later in code
   if @warn_on_no_content_security_policy && logger(request)
     # ...
   end
   

Following these practices ensures components remain properly isolated and configurations behave predictably across different environments and application setups.

---

Complete code examples

Ensure all code examples are complete, functional, and accurately demonstrate the intended concepts. Code examples should include all necessary imports, variable declarations, and interactive elements to be self-contained and runnable.

Key requirements:

• Include all necessary imports at the top of examples
• Declare all variables used in the example (e.g., let visible = $state(false);)
• Add interactive elements when demonstrating dynamic behavior (e.g., checkboxes to toggle state)
• Ensure syntax matches the concept being demonstrated (avoid quotes when showing unquoted syntax)
• Make examples functional rather than just illustrative fragments

Example of a complete code example:

<script>
  import { fade, fly } from 'svelte/transition';
  
  let visible = $state(false);
</script>

<label>
  <input type="checkbox" bind:checked={visible}>
  visible
</label>

{#if visible}
  <div in:fly={{ y: 200, duration: 2000 }} out:fade>
    flies in, fades out
  </div>
{/if}

This approach helps developers understand the full context and makes examples immediately usable for learning and testing.

---

avoid unclear abbreviations

Use clear, descriptive names instead of abbreviated variable names that reduce code readability. Abbreviations like mult should be replaced with more conventional or descriptive alternatives. Additionally, maintain consistent naming conventions: use snake_case for internal code and camelCase for user-facing APIs.

// ❌ Avoid unclear abbreviations
export function multiplier(initial, mult) {
  return initial * mult;
}

// ✅ Use clear, conventional names
export function multiplier(initial, k) {
  return initial * k;
}

// ❌ Inconsistent naming between internal and external
component.$destroy(run_outro); // user-facing API using snake_case

// ✅ Consistent naming patterns
component.$destroy(runOutro); // user-facing API using camelCase

This approach improves code maintainability by making variable purposes immediately clear to other developers and ensures consistent patterns across different parts of the codebase.

---

Consistent dependency versioning

When updating dependency version constraints in requirements files, ensure consistency with versions pinned by other dependencies in your project. Check what versions are used by major dependent packages before setting your own constraints to avoid compatibility issues.

For example, if a dependency like Starlette already pins a specific version range for a shared dependency:

# Instead of setting arbitrary version constraints:
anyio[trio] >=3.2.1,<5.0.0

# Check what related packages require and align with them:
anyio[trio] >=3.6.2,<5.0.0  # Aligned with Starlette's requirements

This practice prevents dependency conflicts, reduces troubleshooting time, and ensures your configuration files maintain a coherent dependency strategy across the project.

---

Separate user system data

Separate user-facing data from system/implementation data using proper namespacing and schema design to prevent data pollution and improve user experience.

System-generated properties, internal attributes, and feature-specific data should be clearly separated from user-accessible data through namespacing or dedicated attributes. This prevents implementation details from appearing in user interfaces like autocompletion, queries, and property dropdowns.

Implementation approaches:

1. Namespace system properties: Use prefixed namespaces for feature-specific data
2. Hide internal attributes: Mark implementation details as non-public and hidden
3. Scope data appropriately: Store configuration at the correct level (graph-level vs global)

Example - Whiteboard properties separation:

;; Bad - mixes user and system data
{:block/properties 
 {:user-title "My Note"
  :id "system-generated-id"  ; system data pollutes user space
  :fill "black"              ; tldraw-specific
  :stroke "#ababab"}}        ; tldraw-specific

;; Good - namespaced separation  
{:block/properties
 {:user-title "My Note"
  :logseq.tldraw.shape {:id "system-generated-id"
                        :fill "black" 
                        :stroke "#ababab"}}}

Example - Internal attribute hiding:

:block/order {:title "Node order"
              :attribute :block/order  
              :schema {:type :string
                       :public? false    ; Hidden from user queries
                       :hide? true}}     ; Hidden from autocompletion

This separation improves query performance, prevents user confusion, and makes the system more maintainable by clearly delineating data boundaries.

---

Effect hook best practices

When using React effect hooks, follow these practices to ensure predictable behavior and prevent memory leaks:

1. Use stable dependency arrays: Create a reusable constant for empty dependency arrays rather than creating a new array on each render.

// ❌ Avoid: Creates a new array reference on each render
useEnhancedEffect(timeout.disposeEffect, []);

// ✅ Better: Use a stable reference
const EMPTY = [] as unknown[];
useEnhancedEffect(timeout.disposeEffect, EMPTY);

1. Choose the appropriate effect type: Use useLayoutEffect for DOM operations that need to be synchronized with painting (like aria-hidden management), and useEffect for everything else. Consider using a utility like useEnhancedEffect that handles SSR scenarios.

// For DOM manipulations that affect visual appearance
React.useLayoutEffect(() => {
  // DOM operations that need to happen before painting
}, [dependency]);

// For side effects that don't require synchronous DOM updates
React.useEffect(() => {
  // Other side effects
}, [dependency]);

1. Always implement cleanup functions: Ensure that all event listeners, subscriptions, and other resources are properly released in the effect’s cleanup function.

React.useEffect(() => {
  // Add event listener
  media.addListener(handler);
  handler(media);
  
  // Properly clean up in the return function
  return () => {
    media.removeListener(handler);
  };
}, []);

These practices prevent unexpected behavior, memory leaks, and render inconsistencies in your React components.

---

Minimize HTML attack surface

When allowing HTML attributes or rendering user-generated content, explicitly limit the attack surface by restricting allowed properties to a minimal, vetted set rather than permitting broad categories of attributes.

The principle is to be conservative about what HTML/CSS properties you allow, as even “safe” attributes can introduce vulnerabilities or increase the attack surface significantly. When sanitizing HTML, prefer explicit allow-lists of specific properties over general categories.

Example of problematic approach:

# Risky - allows all style attributes
'iframe' => %w(allowfullscreen height scrolling src style width)

Better approach:

# Safer - explicit property restrictions
css: {
  properties: ['border']  # Only allow specific, vetted CSS properties
}

# Or avoid style attributes entirely when possible
'iframe' => %w(allowfullscreen height scrolling src width)

When rendering user content like markdown, ensure proper sanitization is applied and be cautious with html_safe usage. If you’re unsure about the safety of rendering user input, err on the side of caution and seek additional review for HTML/CSS attribute additions.

---

Transaction-aware task enqueuing

When working with background tasks that depend on database changes, ensure tasks are enqueued only after the related transaction has successfully committed. This prevents tasks from operating on uncommitted or rolled-back data, avoiding race conditions and inconsistent states.

The ENQUEUE_ON_COMMIT setting (defaulting to True) is crucial when using database-backed task queues as it enables atomic operations where both application data and tasks are committed together:

from django.tasks import task
from django.db import transaction

@task()  # Uses default enqueue_on_commit=True
def process_order(order_id):
    # This task will only run after the transaction commits
    # ensuring the order exists in the database
    ...

# In your view or service:
with transaction.atomic():
    order = Order.objects.create(...)
    # The task will be enqueued when the transaction commits
    process_order.enqueue(order.id)

When testing or developing, you might choose different backends with appropriate transaction behavior, but always be mindful of how transaction handling will differ in production. Consider organizing tasks in a dedicated tasks.py module within each app to maintain consistent task discovery patterns.

---

Escape column names properly

Always use the appropriate wrapping/escaping mechanism when generating SQL to prevent syntax errors and SQL injection vulnerabilities, especially when handling:

1. Functional expressions in columns: When dealing with columns that contain SQL functions or expressions, use a detection method before applying escaping:

protected static function isFunctionalExpression(string $column): bool
{
    return preg_match('/\(.+\)/', $column);
}

// Usage when building queries
$columns = collect($command->columns)
    ->map(fn (string $column) => self::isFunctionalExpression($column) ? $column : $this->wrap($column))
    ->implode(', ');

1. Column names that are SQL keywords: Database column names might conflict with SQL reserved keywords (like ‘create’, ‘table’, ‘order’). Always properly wrap these identifiers:

// DON'T rely on plain string interpolation
$query = "SELECT $column FROM users";

// DO use the query builder or wrap method
$query = $this->builder->select($this->wrap($column))->from('users');

1. Cross-database compatibility: Different database systems use different identifier quoting (MySQL uses backticks, PostgreSQL uses double quotes). Always use the database grammar’s wrap() method instead of hardcoding quote characters.

This practice prevents SQL errors when working with reserved words as column names, functional expressions in indexes, and ensures consistent behavior across different database systems.

---

Descriptive idiomatic identifiers

Use descriptive names for variables, types, and interfaces that follow Go language idioms. Avoid single-letter variables or cryptic abbreviations that reduce code readability.

Key guidelines:

1. Follow Go interface naming conventions by using the “-er” suffix for interfaces that describe behavior (e.g., Validator instead of ValidatorImp).

2. Don’t repeat the package name in type names. When a type is in a package that describes its domain: ```go // AVOID package json type JsonApi interface { … }

// PREFER package json type API interface { … }

3. Choose descriptive variable names, especially avoiding single letters that can be confused with numbers:
```go
// AVOID
for l := len(skippedNodes); l > 0; l-- {
    // ...
}

// PREFER
for length := len(skippedNodes); length > 0; length-- {
    // ...
}

1. Avoid cryptic abbreviations like ldi or ri in favor of complete words like levelOneRouterIndex or recordIndex.

Clear, descriptive, and idiomatic naming improves code readability and maintenance, making it easier for team members to understand the code’s purpose and behavior without additional context.

---

prefer existing APIs

When adding new functionality, prioritize reusing existing methods and interfaces rather than creating new ones. This maintains API consistency, reduces cognitive load for developers, and prevents unnecessary duplication.

Before introducing new methods or interfaces, evaluate whether existing APIs can be extended or composed to achieve the same goal. Consider method chaining, variadic parameters, or interface composition as alternatives to separate implementations.

Example of preferred approach:

// Instead of creating a separate CustomJSON method
func (c *Ctx) CustomJSON(data interface{}, ctype string) error {
    err := c.JSON(data)
    if err != nil {
        return err
    }
    c.fasthttp.Response.Header.SetContentType(ctype)
    return nil
}

// Or better yet, extend existing method with variadic params
func (c *Ctx) JSON(data interface{}, ctype ...string) error {
    raw, err := c.app.config.JSONEncoder(data)
    if err != nil {
        return err
    }
    c.fasthttp.Response.SetBodyRaw(raw)
    
    if len(ctype) > 0 {
        c.fasthttp.Response.Header.SetContentType(ctype[0])
    } else {
        c.fasthttp.Response.Header.SetContentType(MIMEApplicationJSON)
    }
    return nil
}

Similarly, prefer existing interfaces like fiber.Storage over creating new specialized interfaces when the existing interface provides sufficient functionality, even if some methods remain unused.

---

optimize test organization

Organize tests to minimize factory creation, reduce duplication, and improve performance by chaining assertions and extracting common values.

Key practices:

• Chain assertions to test multiple aspects of the same response instead of creating separate examples
• Extract repeated values to private methods or let blocks to reduce duplication
• Minimize factory creation by using single examples with multiple change blocks instead of separate examples
• Use build over create when database persistence isn’t required

Example:

# Instead of multiple examples creating many factories:
let!(:invite_unlimited) { Fabricate(:invite, user: user, max_uses: nil, created_at: 10.days.ago) }
let!(:invite_huge_max_uses) { Fabricate(:invite, max_uses: 100, created_at: 10.days.ago) }

# Use single example with chained expectations:
it 'processes invites correctly' do
  expect { subject.perform }
    .to change(Invite.where(max_uses: nil), :count).by(-1)
    .and change(Invite.where('max_uses > ?', retention_max_uses), :count).by(-1)
end

# Extract common datetime values:
let(:default_datetime) { DateTime.new(2024, 11, 28, 16, 20, 0) }

# Chain response assertions:
expect(response)
  .to have_http_status(403)
  .and have_content('error message')

This approach reduces test execution time, improves maintainability, and makes test intent clearer by grouping related assertions together.

---

Avoid subscription race windows

When code derives state from an external cache/store (or wraps promises), treat subscription setup and promise resolution as concurrent events. Ensure your implementation is race-safe and doesn’t use stale inputs.

Apply these rules: 1) Close the “init-before-subscribe” race: after creating/obtaining the source (store/cache) and before/while wiring the subscription callback, immediately sync derived state so updates that occur in the setup window aren’t missed. 2) Resubscribe when dependencies change: if filters/select/query keys change, recreate the subscription (don’t keep listening with old options). 3) Don’t let non-critical async failures abort whole batches: avoid throwing inside Promise.all-mapped work for cases you can ignore; handle per-item errors and continue. 4) For promise/thenable proxies and concurrent fetch/cancel/resolve, define expected behavior and add tests for ordering edge-cases.

Example pattern (React-like):

useEffect(() => {
  // 1) Sync immediately to avoid missing updates in the setup window
  setResult(getResult(store, optionsRef.current))

  // 2) Subscribe for subsequent updates
  const unsubscribe = store.subscribe(() => {
    setResult(getResult(store, optionsRef.current))
  })

  return unsubscribe
}, [store /* and ensure resubscribe when options/select changes if needed */])

Example pattern (Solid-like):

createEffect(() => {
  const unsub = mutationCache().subscribe(() => {
    setResult(getResult(mutationCache(), options()))
  })
  onCleanup(unsub)
})

Example for Promise.all: don’t throw for “not-a-thing we care about”.

await Promise.all(
  Object.keys(deps ?? {}).map(async dep => {
    const depPackage = packages.find(p => p.name === dep)
    if (!depPackage) return // ignore non-critical/non-matching deps
    // ...do work for relevant deps
  })
)

---

Quote shell substitutions

Always enclose command substitutions in double quotes when assigning to variables or using in shell scripts to prevent word splitting vulnerabilities. Unquoted command substitutions can lead to unexpected behavior or security vulnerabilities if the output contains spaces or special characters, potentially enabling command injection attacks.

Example:

# Vulnerable - may allow word splitting if output contains spaces
- echo "STORE_PATH=$(pnpm store path --silent)" >> $GITHUB_ENV

# Secure - properly quotes the command substitution
+ echo "STORE_PATH=\"$(pnpm store path --silent)\"" >> $GITHUB_ENV

Use automated tools like shellcheck to identify and fix these vulnerabilities in your CI/CD workflows and shell scripts.

---

Environment-specific database configuration

Configure database connections differently based on the environment. Use lightweight file-based databases like SQLite for development and testing, but deploy robust server-based databases like PostgreSQL in production. This approach simplifies local development while ensuring your application has appropriate scalability and reliability in production.

import os
from sqlalchemy import create_engine

# Get environment from configuration
environment = os.getenv('APP_ENV', 'development')

# Configure database based on environment
if environment == 'development':
    # SQLite for local development
    DATABASE_URL = "sqlite:///./app.db"
elif environment == 'testing':
    # In-memory SQLite for testing
    DATABASE_URL = "sqlite:///./test.db"
else:
    # PostgreSQL for production
    DATABASE_URL = f"postgresql://{user}:{password}@{host}/{db_name}"

# Create engine with appropriate configurations
engine = create_engine(
    DATABASE_URL,
    # Add production-specific settings like connection pooling
    pool_size=5 if environment == 'production' else 0,
    max_overflow=10 if environment == 'production' else 0
)

This pattern ensures developers can work efficiently with lightweight database setups while maintaining robust configurations for production environments. Remember to properly manage the engine object throughout your application as it maintains database connections. For production applications, consider additional settings like connection pooling, timeouts, and SSL configurations appropriate for your specific database provider.

---

prefer built-in React types

Favor React’s built-in types over custom interfaces when possible, and consolidate to standard library types for better maintainability and type safety. Use PropsWithChildren instead of creating custom component prop interfaces, leverage generics for type flexibility, and migrate away from deprecated types in favor of type-safe alternatives.

Example:

// Instead of custom interface
export interface LayoutComponentProps {
  children: ReactNode
}

// Use built-in React type
export type LayoutComponentProps = PropsWithChildren;

// For additional props, extend with generics
export type LayoutComponentProps = PropsWithChildren<{
  extraProp: string;
}>;

// Use generics for flexibility
export type RouteManifest<R = AgnosticDataRouteObject> = Record<
  string,
  R | undefined
>;

This approach reduces code duplication, improves type safety, leverages React’s established patterns, and makes the codebase more maintainable by using well-tested standard types.

---

Complete translatable sentences

Use complete sentences in translatable strings rather than breaking them into fragments, even if this results in some repetition. Sentence fragments make translation difficult or impossible for languages with different grammatical structures, and they provide insufficient context for translators.

When you need rich formatting within translatable text, use placeholder-based approaches with complete sentences rather than splitting the text:

This approach gives translators full context and flexibility to restructure the sentence according to their language’s grammar while maintaining the desired visual formatting.

---

Document error conditions clearly

Always provide clear documentation for error conditions, unsafe usage patterns, and failure scenarios in API documentation. Include explicit warnings about potential data races, undefined behavior, and error propagation to help developers avoid common pitfalls.

When documenting methods that can lead to unsafe states or have specific error behaviors, use prominent warning blocks and describe the exact consequences:

**Close** releases both the associated `Request` and `Response` objects back to their pools.

⚠️ **WARNING**: After calling `Close`, any attempt to use the request or response may result in data races or undefined behavior. Ensure all processing is complete before closing.

For systems with error propagation, clearly state the behavior:

If any request hook returns an error, the request is interrupted and the error is returned immediately.

This practice helps developers understand failure scenarios upfront, enabling them to write more robust error handling code and avoid runtime issues.

---

prefer explicit code

Write code that explicitly states its intent rather than relying on implicit behavior or complex constructs. This improves readability and maintainability by making the code’s purpose immediately clear to other developers.

Key practices:

• Set default values explicitly instead of using empty initializers like {}
• Structure conditional logic with clear if-else blocks rather than complex ternary operations or intermediate variables
• Add intent-clarifying comments when the logic serves multiple purposes

Example of explicit default values:

// Prefer explicit default
disableKeyboardShortcuts(convertRawProp(
    context,
    rawProps,
    "disableKeyboardShortcuts",
    sourceProps.disableKeyboardShortcuts,
    {false}))  // explicit default value

// Instead of implicit empty default
disableKeyboardShortcuts(convertRawProp(
    context,
    rawProps,
    "disableKeyboardShortcuts",
    sourceProps.disableKeyboardShortcuts,
    {}))  // unclear what the default is

Example of clear conditional structure:

// Prefer clear if-else structure
if (ignoreYogaStyleProps_ || filterObjectKeys != nullptr) {
  // We need to filter props
  return jsi::dynamicFromValue(*runtime_, value_, [&](const std::string& key) {
    if (ignoreYogaStyleProps_ && isYogaStyleProp(key)) {
      return false;
    }
    if (filterObjectKeys) {
      return filterObjectKeys(key);
    }
    return true;
  });
} else {
  // We don't need to filter, just include all props by default
  return jsi::dynamicFromValue(*runtime_, value_, nullptr);
}

// Instead of complex ternary with intermediate variables
const std::function<bool(const std::string&)> filterFunctionOrNull =
    ignoreYogaStyleProps_ || filterObjectKeys != nullptr
    ? propFilterFunction
    : nullptr;
return jsi::dynamicFromValue(*runtime_, value_, filterFunctionOrNull);

---

Mark sensitive parameters

Always use the #[\SensitiveParameter] attribute for parameters containing sensitive information such as passwords, tokens, API keys, and personal identifiable information. This prevents accidental exposure of sensitive data in logs, stack traces, and debugging information, which could otherwise lead to security breaches.

// Before - security risk
public function __construct(
    public ?string $username = null,
    public ?string $pass = null,
) {}

// After - secure
public function __construct(
    public ?string $username = null,
    #[\SensitiveParameter]
    public ?string $pass = null,
) {}

// Also use in method parameters
public function validateCredentials(
    $username, 
    #[\SensitiveParameter] $password
) {
    // Password won't appear in logs or stack traces
}

For legacy PHP versions without attribute support, consider using alternative patterns such as:

1. Accepting sensitive data through non-logged channels
2. Sanitizing log output manually before writing
3. Using specialized secure input handlers

Additionally, ensure proper error handling for security-critical functions. Avoid using error suppression operators (@) in favor of try-catch blocks that capture errors without exposing implementation details.

---

ensure exception safety

Always ensure proper exception safety by placing cleanup code in @finally blocks, using stack-allocated exceptions, and implementing comprehensive exception handling for different types. Resource cleanup must occur even when exceptions are thrown to prevent memory leaks.

Key practices:

• Place cleanup code like [retainedObjectsForInvocation removeAllObjects] in @finally blocks, not after catch blocks
• Use throw std::runtime_error(...) instead of throw new std::runtime_error(...) for C++ exceptions
• Implement comprehensive exception handling for different types (NSException, NSError, NSString, std::exception, etc.)

Example:

@try {
  [inv invokeWithTarget:strongModule];
} @catch (NSException *exception) {
  caughtException = maybeCatchException(shouldCatchException, exception);
} @catch (NSError *error) {
  caughtException = maybeCatchException(shouldCatchException, error);
} @finally {
  [retainedObjectsForInvocation removeAllObjects]; // Always cleanup
}

// For C++ exceptions, use stack allocation
throw std::runtime_error("Error message");

This ensures robust error handling while preventing resource leaks and maintaining proper exception semantics.

---

Configure React build environments

Ensure proper environment and module configuration for React applications to load the correct versions and entrypoints across different build contexts. This includes setting NODE_ENV appropriately and configuring import paths for optimal React loading.

For environment configuration, set NODE_ENV before React initialization to ensure the proper version loads:

// Set NODE_ENV before calling CLI or initializing React
process.env.NODE_ENV = process.env.NODE_ENV ?? "production";

For build tooling, configure import paths to point to appropriate React entrypoints:

// In build configuration (e.g., rollup.config.js)
paths: {
  "react-router": "./index.mjs",
}

This prevents issues where React loads incorrect versions or modules, which can cause runtime errors or suboptimal performance. Always verify that your build configuration explicitly handles React’s environment-specific loading behavior.

---

SSR documentation clarity

Ensure server-side rendering documentation is grammatically correct and clearly explains the differences between server and client contexts. Documentation should explicitly describe hydration behavior, performance implications, and function availability constraints.

When documenting SSR features, avoid ambiguous language and provide specific context about when certain behaviors occur. For example, instead of vague references to “render,” specify whether you mean “server render” or “client render.”

Example improvements:

• Change “If the a {@html ...} value changes” to “If the {@html ...} value changes”
• Clarify “not during the server render” vs “not during render” based on the specific context
• Explain performance rationale: “change detection during hydration is expensive and usually unnecessary”

This ensures developers understand SSR limitations and behaviors, reducing confusion during implementation and debugging.

---

Prefer micro-optimizations

Apply small performance improvements that accumulate to significant gains. Focus on efficient memory usage, API choices, and avoiding unnecessary operations.

Key practices:

• Use references instead of copies when possible: auto& dynamic = std::get<folly::dynamic>(value_) instead of folly::dynamic dynamic = std::get<folly::dynamic>(value_)
• Prefer faster API variants: use getObject() instead of asObject() when you’ve already validated with isObject() - it’s faster because it uses an assert
• Use move semantics and emplace for containers: result.emplace(propertyNameString, std::move(property)) instead of result[propertyNameString] = property for better performance with no unnecessary copies
• Avoid expensive memory operations: use stack allocation CGFloat locations[colorStops.size()] instead of malloc(sizeof(CGFloat) * colorStops.size())

These micro-optimizations are especially important in performance-critical code paths where small improvements compound across many operations.

---

Prevent async race conditions

Design async operations to prevent race conditions, memory leaks, and ensure proper resource cleanup. Key principles:

1. Avoid mutating shared state in async operations
2. Ensure proper cleanup of resources when async operations complete or are cancelled
3. Use appropriate data structures for async streaming to prevent event loop blocking

Example of problematic code:

// BAD: Mutating shared state in async context
Object.assign(socket, {
  getPattern: () => this.reflectPattern(callback)
});

// BAD: Potential memory leak with async timing
this.routingMap.set(packet.id, callback);
await this.serialize(packet.data);

Better approach:

// GOOD: Maintain request-scoped state
class RequestContext {
  constructor(private pattern: string) {}
  getPattern() { return this.pattern; }
}

// GOOD: Ensure cleanup on unsubscribe
const cleanup = new AbortController();
try {
  if (cleanup.signal.aborted) return;
  const data = await this.serialize(packet.data);
  this.routingMap.set(packet.id, callback);
  cleanup.signal.addEventListener('abort', () => {
    this.routingMap.delete(packet.id);
  });
} catch (err) {
  this.routingMap.delete(packet.id);
}

For streaming operations, use appropriate async scheduling:

// GOOD: Non-blocking stream processing
return from(items).pipe(
  concatMap(item => defer(() => processItem(item))),
  observeOn(asyncScheduler)
);

---

Remove obsolete configuration options

Proactively remove configuration options that are no longer functional or relevant to prevent developer confusion and potential bugs. When configuration options become obsolete due to architectural changes or package migrations, removing them from type definitions and interfaces is preferable to keeping them as non-functional placeholders.

This approach provides several benefits:

• Prevents developers from using non-functional configuration
• Surfaces potential bugs through compile-time errors rather than silent failures
• Maintains clean, accurate configuration interfaces
• Guides developers toward correct alternatives

For example, when a timeout configuration becomes non-functional:

// Before: Keeping obsolete option
export interface ServerRouterProps {
  context: EntryContext;
  url: string | URL;
  abortDelay?: number; // Non-functional but still present
}

// After: Remove and force migration
export interface ServerRouterProps {
  context: EntryContext;
  url: string | URL;
  // Use streamTimeout instead of abortDelay
}

Similarly, when packages become obsolete due to tooling changes, update imports and remove references:

// Before: Obsolete package import
import { cssBundleHref } from "@remix-run/css-bundle";

// After: Updated or removed based on new tooling
// Package removed as it's obsolete in vite-only environments

The resulting TypeScript errors serve as helpful migration guides, alerting developers to update their configuration and fix potential functional issues.

---

comprehensive test validation

Tests should validate all relevant aspects of the system to ensure comprehensive coverage. This includes incorporating type checking into test execution, validating file operations and generation processes, and ensuring end-to-end functionality works correctly. Different types of tests serve different validation purposes and should be used strategically.

For example, when running tests, include type checking alongside runtime tests:

"scripts": {
  "test:lib": "vitest --typecheck"
}

Additionally, consider separate e2e tests when they validate distinct functionality like file reading, code generation, or navigation flows that unit tests might not cover. As one developer noted: “I wanted a test, without the routeTree.gen.ts committed into git so that on every CI run, it generated the routeTree.gen.ts from the routes.ts and ensured the navigations were successful.”

This approach ensures that both compile-time correctness (through type checking) and runtime behavior (through comprehensive test scenarios) are validated, providing confidence in the system’s reliability across different operational contexts.

---

Include practical examples

Documentation should include practical, working examples that demonstrate real-world usage scenarios. When introducing new features, methods, or concepts, provide concrete code examples that show users how to apply them in practice. This is especially important when mentioning functionality multiple times without demonstration, or when documenting complex features that users need to understand to adopt effectively.

Examples should be complete and runnable where possible, showing both the setup and expected output. For features with multiple use cases or configuration options, demonstrate the differences with separate examples.

// Good: Shows practical usage with complete example
func (r *Request) Headers() iter.Seq2[string, []string]

// Example demonstrating real usage
req := client.AcquireRequest()
req.AddHeader("Content-Type", "application/json")
req.AddHeader("Authorization", "Bearer token123")

// Collect all headers into a map
headers := maps.Collect(req.Headers())
for key, values := range headers {
    fmt.Printf("Header: %s = %v\n", key, values)
}

The principle “only a feature that is understandable and well documented will be found and used” should guide documentation decisions. Users need to see how features work in context, not just understand their signatures or theoretical capabilities.

---

optimize algorithmic efficiency

When implementing algorithms, especially in performance-critical paths like scroll handlers or layout methods, prioritize computational efficiency and avoid expensive operations. Consider algorithmic complexity and choose more efficient approaches when dealing with large datasets or frequently called methods.

Key strategies:

1. Use efficient search algorithms: Replace linear searches with binary search when data is sorted or can be organized efficiently
2. Avoid expensive recomputations: Reuse existing calculations and data structures rather than recreating them (e.g., use existing layout accessors instead of creating new layouts)
3. Choose optimal data structures: Use primitive collections to avoid boxing overhead and memory retention issues
4. Implement early termination: Add condition checks to avoid deep traversals or unnecessary processing

Example from scroll view optimization:

// Instead of linear search through all children
for (int i = minIdx; i < contentView.getChildCount(); i++) {
    // Process each child...
}

// Consider binary search for better O(log n) complexity
// when dealing with sorted or organized data structures

This is particularly important for methods called frequently (scroll handlers, layout callbacks) or when processing large collections, where algorithmic improvements can significantly impact user experience.

---

Avoid expensive allocations

Minimize object creation and expensive operations in performance-critical code paths, particularly in frequently called methods like onDraw, layout operations, and UI updates.

Key strategies:

1. Lazy allocation: Only create objects when actually needed. For example, allocate collections like HashSet only when the feature requiring them is used, rather than eagerly during initialization.

2. Reuse objects in hot paths: Avoid creating new instances in frequently called methods. Instead, create reusable objects as instance variables and reset them before use:

// Instead of creating new Path in onDraw:
public void onDraw(Canvas canvas) {
    Path path = new Path(); // BAD - creates object every draw
    // ...
}

// Create reusable instance variable:
private Path mReusablePath = new Path();

public void onDraw(Canvas canvas) {
    mReusablePath.reset(); // GOOD - reuse existing object
    // ...
}

1. Guard expensive operations: Before performing costly computations, check if they’re actually necessary. Add conditional checks to avoid redundant expensive calls like layout calculations or complex measurements.

This approach prevents memory pressure from frequent allocations, reduces garbage collection overhead, and improves overall application performance, especially in UI rendering and animation scenarios.

---

configuration consistency management

Maintain consistent configuration references across all code branches and document temporary configuration code for future cleanup. Configuration inconsistencies can lead to compilation errors and maintenance debt.

When using feature flags or configuration classes, ensure the same class names and method signatures are used consistently across different branches or versions. For example, avoid mixing ReactFeatureFlags.enableBridgelessArchitecture and ReactNativeFeatureFlags.enableBridgelessArchitecture() in different parts of the codebase.

For temporary configuration code (such as version checks or compatibility shims), add clear comments indicating when the code should be removed:

// TODO: Remove when minSdk is bumped to 26
int justificationMode = (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) 
    ? 0 : Layout.JUSTIFICATION_MODE_NONE;

This practice prevents accumulation of obsolete configuration code and makes it easier to clean up when constraints change.

---

Clear structured logging documentation

Document structured logging implementations with clarity, explicitly noting precedence rules and interactions with other logging configurations. Always highlight important considerations (such as custom configurations taking precedence) prominently in the main documentation rather than as footnotes or warnings that might be missed.

When providing configuration examples:

1. Keep examples as simple as possible for the common case
2. Avoid unnecessary conditional logic unless required for specific scenarios
3. For complex configurations, reference default implementations or provide links to more detailed documentation

Example of good structured logging documentation:

# Structured Logging

To enable structured logging, set the property `logging.structured.format.console` (for console output) 
or `logging.structured.format.file` (for file output) to the format ID you want to use.

IMPORTANT: Custom log configurations take precedence over these settings. If you're using custom log 
configuration, you must manually configure structured logging as shown below:

## Basic Implementation
```xml
<encoder class="org.springframework.boot.logging.logback.StructuredLogEncoder">
    <format>${CONSOLE_LOG_STRUCTURED_FORMAT}</format>
    <charset>${CONSOLE_LOG_CHARSET}</charset>
</encoder>

For advanced configurations with conditionals, see our default configurations.

This approach ensures that developers have clear guidance for common cases while maintaining access to more complex options when needed.

---

## Organize tailwind classes

<!-- source: shadcn-ui/ui | topic: Code Style | language: TSX | updated: 2024-12-04 -->


Structure your Tailwind CSS classes for readability and maintainability. Instead of long chains of conditional classes with `&&` operators, use object syntax with clear naming patterns. This improves code readability and makes maintenance significantly easier.

**Instead of this:**
```jsx
className={cn(
  "h-9 w-9 p-0 font-normal",
  modifiers?.today && "bg-accent text-accent-foreground",
  modifiers?.selected && "bg-primary text-primary-foreground hover:bg-primary hover:text-primary-foreground",
  modifiers?.outside && "text-muted-foreground opacity-50 pointer-events-none",
  // many more conditions
)}

Do this instead:

className={cn({
  "h-9 w-9 p-0 font-normal": true,
  "bg-accent text-accent-foreground": modifiers?.today,
  "bg-primary text-primary-foreground hover:bg-primary hover:text-primary-foreground": modifiers?.selected,
  "text-muted-foreground opacity-50 pointer-events-none": modifiers?.outside,
  // cleaner and easier to read
})}

Additional recommendations:

• Use Tailwind classes instead of inline styles (e.g., use touch-manipulation instead of style={{ touchAction: "manipulation" }})
• Use standard classes like rounded-md instead of inline styles for border radius
• For text alignment that respects RTL languages, use text-start rather than text-left
• Maintain consistent class ordering, with structural classes first, followed by visual styles

These practices make your code more maintainable, easier to review, and better for internationalization.

---

Validate nulls properly

Always use appropriate null validation mechanisms to prevent NullPointerExceptions and ensure code robustness.

For string parameters:

• Use Assert.hasText(profile, "Profile must have text") instead of Assert.notNull() when you need to validate both null and empty strings
• This handles both null checks and empty string validation in one call

For equals methods:

• Always check for null before comparing class types:

  @Override
  public boolean equals(Object obj) {
    if (this == obj) {
        return true;
    }
    if (obj == null || getClass() != obj.getClass()) {
        return false;
    }
    // Continue with comparison
  }
  

For collections and arrays:

• Always validate that collection parameters are not null before processing them
• For optional collections, consider:

  if (resolvers != null) {
    // process resolvers
  }
  

• Or enforce non-null values through constructor validation

Using these patterns consistently will reduce null-related bugs and improve code quality across the codebase.

---

Specific types for performance

Using concrete types instead of abstract container classes in data models improves validation performance. More specific types require fewer checks and coercion attempts, resulting in faster validation. Additionally, ensure proper model parametrization to prevent unnecessary revalidation, which can trigger validators repeatedly.

For example, prefer:

from pydantic import BaseModel

class Model(BaseModel):
    items: list[str]  # Concrete type

Instead of:

from collections.abc import Sequence
from pydantic import BaseModel

class Model(BaseModel):
    items: Sequence[str]  # Abstract type - incurs more validation overhead

This optimization is particularly important in performance-sensitive code paths where validation occurs frequently.

---

Thread-safe shared state

Ensure that shared mutable state is properly protected against concurrent access to prevent race conditions and data corruption. When multiple threads can access the same mutable data, use appropriate synchronization mechanisms such as ThreadLocal, locks, or atomic operations.

Key indicators that thread safety is needed:

• Static mutable fields accessed by multiple threads
• Shared objects modified during overlapping operations
• State that assumes single-threaded access but may be accessed concurrently

Common solutions:

• Use ThreadLocal for thread-specific instances of shared data
• Implement proper state tracking for overlapping operations
• Add null checks and validation for data that may be modified concurrently

Example transformation from unsafe to thread-safe code:

// UNSAFE: Static arrays shared across threads
private static final Object[] VIEW_MGR_ARGS = new Object[2];

// SAFE: ThreadLocal ensures each thread has its own instance
private static final ThreadLocal<Object[]> VIEW_MGR_ARGS =
    new ThreadLocal<Object[]>() {
        @Override
        protected Object[] initialValue() {
            return new Object[2];
        }
    };

For overlapping operations, maintain proper state tracking:

// Track multiple concurrent operations instead of single boolean flag
private Set<Integer> transitioningChildren = new HashSet<>();

public void startViewTransition(View view) {
    transitioningChildren.add(view.getId());
}

public void endViewTransition(View view) {
    transitioningChildren.remove(view.getId());
    // Only clear state when no more transitions are active
    if (transitioningChildren.isEmpty()) {
        clearTransitionState();
    }
}

Always consider the timing and ordering of operations that modify shared state, and add appropriate null checks for data that may be modified by concurrent operations.

---

simplify logging integrations

When implementing custom logging integrations, prioritize simplicity and completeness over complex abstractions. Avoid creating overly complicated wrapper structures that developers must recreate for basic logging functionality. Instead, provide simple, reusable patterns that support all necessary logging levels and are easy to understand and maintain.

For example, when creating logger adapters, use straightforward approaches like anonymous structs with embedded functions rather than complex type definitions:

func LoggerToWriter(customLogger fiberlog.AllLogger, level fiberlog.Level) io.Writer {
    return &struct {
        Write func(p []byte) (n int, err error)
    }{
        Write: func(p []byte) (n int, err error) {
            switch level {
            case fiberlog.LevelDebug:
                customLogger.Debug(string(p))
            case fiberlog.LevelInfo:
                customLogger.Info(string(p))
            case fiberlog.LevelWarn:
                customLogger.Warn(string(p))
            case fiberlog.LevelError:
                customLogger.Error(string(p))
            }
            return len(p), nil
        },
    }
}

Ensure that logging integrations support all relevant logging levels, not just a subset, and consider providing these patterns as reusable utilities rather than requiring each developer to implement them from scratch.

---

organize test scripts properly

Keep base test scripts generic and create specialized variants for specific workflows. Base scripts like “test” should remain simple and flexible, allowing developers to pass additional arguments via CLI. For specialized workflows, create separate scripts with descriptive names.

For example, instead of modifying the base test script:

{
  "scripts": {
    "test": "jest --projects packages/react-router --watch"
  }
}

Keep the base script generic and create specialized variants:

{
  "scripts": {
    "test": "jest",
    "test:integration": "pnpm build && pnpm test:integration:run",
    "test:integration:run": "pnpm playwright:integration"
  }
}

This approach allows developers to use npm test -- --projects packages/react-router --watch for custom CLI arguments while providing convenient shortcuts for common workflows. It also enables iterative testing without unnecessary rebuilds by separating build and execution steps.

---

Externalize configuration values

Use environment variables and external configuration mechanisms instead of hard-coding values in build scripts. This makes your build system more flexible, maintainable, and adaptable to different environments.

Why it matters:

• Hard-coded values like file paths (e.g., /usr/bin/ccache) limit where tools can be installed
• Project-specific constraints (e.g., spaces in project names causing Dokka errors) should be externalized
• Configuration options should be adaptable across different environments

How to implement:

1. Replace hard-coded paths with environment variable lookups
2. Use properties files or command-line parameters for configurable values
3. Document configuration requirements clearly

Example: Instead of:

// Hard-coded paths that limit where ccache can be installed
val ccachePaths = listOf("/usr/bin/ccache", "/usr/local/bin/ccache")

Better approach:

// Use environment variables with fallbacks
val ccachePath = System.getenv("CCACHE_PATH") 
    ?: listOf("/usr/bin/ccache", "/usr/local/bin/ccache").firstOrNull { file(it).exists() }

if (ccachePath != null) {
    arguments("-DANDROID_CCACHE=$ccachePath")
}

Similarly, for dependency exclusions, use a consistent pattern:

configurations {
    getByName("implementation") {
        exclude(group = "commons-logging", module = "commons-logging")
        exclude(group = "commons-collections", module = "commons-collections")
    }
}

---

Consistent component API patterns

Design component APIs with consistent patterns that promote extensibility and clear usage. Prefer generic prop structures like slotProps over specific props (such as InputProps, InputLabelProps) for better maintainability and consistency across components.

When evolving APIs, provide clear migration paths and documentation to minimize breaking changes. Consider backward compatibility by supporting both old and new patterns during transition periods:

// When migrating from specific props to slotProps pattern
// Support both patterns temporarily
<Autocomplete
    renderInput={(params) => (
        <TextField
            {...params}
            // New pattern
            slotProps={{
                input: {...params.slotProps.input, ref},
            }}
            // Legacy pattern (deprecated but supported)
            InputProps={{...params.InputProps, ref}}
        />
    )}
/>

For function parameters in component APIs, ensure they match their intended use and are properly typed. Use dedicated comparison functions rather than repurposing other APIs:

// Prefer this
isOptionEqualToValue(option, value)

// Over repurposing other functions
getOptionLabel(option) === getOptionLabel(value)

When organizing component APIs across packages, establish clear patterns for importing and extension points that allow for customization without causing namespace collisions or duplicating functionality.

---

manage component state dependencies

Ensure React components have all necessary state information before rendering and that lifecycle events don’t cause unintended state interactions. Components should validate they have required data (like sizing information) before updating, and state changes should be carefully managed to prevent side effects.

When removing state updates, verify that components still receive essential information for proper rendering. For example, modal components need viewport size data even when not directly using it for layout calculations.

When adding state management to lifecycle events, consider all scenarios where the event might trigger to avoid unintended behaviors:

// Before: Focus logic in onLayout can cause unintended selection
public void requestFocusFromJS() {
    requestFocusInternal();
    // This could trigger selection even when focus didn't actually change
}

// After: Explicitly manage the state dependency
public void requestFocusFromJS() {
    requestFocusInternal();
    hasSelectedTextOnFocus = true; // Clear intent for this specific case
}

Always investigate the root cause when component behavior changes between architectures, as missing state dependencies often manifest as subtle rendering or interaction issues.

---

Keep CI configurations minimal

When configuring CI workflows, include only the extensions, tools, and settings that are necessary for the specific tests being run. Avoid adding unnecessary PHP extensions (such as xml or xdebug) to workflow configurations unless they’re explicitly required. Similarly, keep coverage disabled (coverage: none) in CI pipelines by default to improve performance.

Example:

- name: Setup PHP
  uses: shivammathur/setup-php@v2
  with:
    php-version: 8.3
    extensions: dom, curl, libxml, mbstring, zip, pcntl, pdo, pdo_mysql, :php-psr
    coverage: none

This approach keeps CI workflows efficient, reduces execution time, and avoids potential issues from unnecessary dependencies.

---

Disable coverage in workflows

Keep code coverage tools disabled in CI/CD workflows unless they’re specifically needed for generating coverage reports. Enabling coverage tools like xdebug in GitHub Actions can significantly slow down pipeline execution without providing value when reports aren’t being collected or analyzed.

When configuring PHP environments in workflows, explicitly set coverage: none and avoid including coverage extensions like xdebug unless they serve a specific purpose:

uses: shivammathur/setup-php@v2
with:
  php-version: 8.2
  extensions: dom, curl, libxml, mbstring, zip, pcntl, pdo, pdo_mysql, :php-psr
  tools: composer:v2
  coverage: none  # Keep coverage disabled for better performance

Reserve coverage tools for dedicated testing jobs that specifically generate and process coverage reports. This helps maintain faster CI pipelines while still allowing coverage analysis when needed.

---

Follow existing naming conventions

When adding new variables, methods, or constants, always follow the naming conventions already established in the codebase. Before introducing new identifiers, examine existing code in the same file and related files to understand the established patterns, including prefixes, suffixes, and naming styles.

For example, when adding boolean fields to a class that uses ‘m’ prefixes and ‘Did’ prefixes for state variables, maintain consistency:

// Existing code shows the pattern:
private boolean mContextMenuHidden = false;
private boolean mDidAttachToWindow = false;
private boolean mSelectTextOnFocus = false;

// Follow the established convention:
private boolean mDidSelectTextOnFocus = false;  // ✓ Correct

// Rather than breaking the pattern:
private boolean hasSelectedTextOnFocus = false;  // ✗ Inconsistent

This applies to all identifiers including constants, where numbering and naming should be synchronized across related files to maintain architectural consistency. Consistent naming conventions improve code readability, reduce cognitive load, and make the codebase easier to maintain.

---

Robust error messaging

Create clear, specific, and actionable error messages that help users understand and resolve issues, while implementing defensive error handling to maintain system integrity. Follow these principles:

1. Write user-focused error messages that explain what went wrong and how to fix it
2. Use defensive error handling with specific exception types and cleanup mechanisms
3. Defer expensive error computations until actually needed

Example of good error handling:

def validate_path(path: Path) -> Path:
    try:
        # Check path length before accessing filesystem
        if isinstance(path, PosixPath) and path.parent.exists():
            try:
                if os.statvfs(path.parent).f_namemax < len(path.name):
                    raise PydanticCustomError('path_too_long', 'Path name is too long')
            except OSError:
                # Handle specific error when path is inaccessible
                raise PydanticCustomError('path_error', f'Path "{path}" cannot be accessed')
                
        if not path.exists():
            # Specific, actionable error message
            raise PydanticCustomError('path_not_found', f'Path "{path}" does not exist')
            
        return path
    except Exception as e:
        # Preserve original error information while adding context
        raise ValueError(f"Invalid path: {e}") from e

When modifying functions or objects that might raise exceptions, always use try/finally blocks to ensure cleanup:

original_qualname = function.__qualname__
try:
    # Potentially risky modifications
    function.__qualname__ = new_qualname
    # Additional operations...
    return function
finally:
    # Ensure cleanup on failure
    if some_error_condition:
        function.__qualname__ = original_qualname

For performance-critical code, defer expensive error message construction:

# Instead of computing expensive messages upfront:
# error_msg = f"Complex {expensive_calculation()} message"
# raise ValueError(error_msg)

# Use a lazy approach:
def get_error_message():
    return f"Complex {expensive_calculation()} message"

# Only computed when an error actually occurs
if error_condition:
    raise ValueError(get_error_message())

---

Runtime HTML escaping

HTML escaping must occur at runtime, not during compilation or build time, to properly prevent XSS vulnerabilities. When content is escaped too early in the process, it may not account for dynamic values or runtime context that could introduce security risks.

Compile-time escaping can miss dynamic content that gets injected at runtime, leaving applications vulnerable to XSS attacks. Always ensure that HTML escaping functions are called when the content is actually being rendered or output.

Example of incorrect approach (escaping at compile time):

// DON'T: Escaping template quasis at compile time
export function escape_template_quasis(template, is_attr) {
    walk(template, {}, {
        TemplateLiteral(node, { next }) {
            for (let quasi of node.quasis) {
                quasi.value.raw = escape_html(quasi.value.raw, is_attr);
            }
            next();
        }
    });
}

Instead, ensure escaping happens when content is rendered:

// DO: Import and use runtime escaping
import { escape_html } from '../../../escaping.js';

// Apply escaping when content is actually output/rendered
function renderContent(dynamicContent) {
    return escape_html(dynamicContent);
}

---

Prefer safe null handling

Use explicit, safe practices when dealing with potentially null resources to prevent memory leaks and undefined behavior.

Key guidelines:

1. Use nullptr instead of NULL in all C++ code, even when calling C functions: ```cpp // Poor: Uses outdated NULL macro sqlite3_vfs* os_fs = sqlite3_vfs_find(NULL);

// Better: Uses modern nullptr keyword sqlite3_vfs* os_fs = sqlite3_vfs_find(nullptr);

2. **With `unique_ptr`, prefer `.reset()` over `.release()`** when clearing resources:
```cpp
// Poor: Memory is leaked after release()
response.error.release();

// Better: Properly destroys the managed object
response.error.reset();

1. Explicitly handle ownership after move operations to prevent accessing invalid objects: ```cpp // Poor: Using pendingReleases after moving it threadPool.schedule( this, wrap_{CaptureWrapper{std::move(pendingReleases)}} { // pendingReleases is now in an invalid state pendingReleases.push_back(…); // Undefined behavior! });

// Better: Clear or reinitialize after move threadPool.schedule( this, wrap_{CaptureWrapper{std::move(pendingReleases)}} { // Code that uses wrap_ instead of pendingReleases }); // Reset pendingReleases to known state here if needed pendingReleases.clear();

4. **Avoid raw pointers** when ownership semantics are needed; use appropriate smart pointers instead:
```cpp
// Poor: Raw pointer ownership is unclear
gpuExpression = other.gpuExpression ? new gfx::GPUExpression(*(other.gpuExpression)) : nullptr;

// Better: Ownership is explicit with smart pointers
gpuExpression = other.gpuExpression ? std::make_unique<gfx::GPUExpression>(*(other.gpuExpression)) : nullptr;

These practices make code more robust by eliminating common sources of null-related bugs and memory leaks.

---

minimize public API exposure

Keep internal implementation details private to reduce security attack surface. Public properties in header files can be accessed and potentially manipulated by external code, creating security vulnerabilities. Store internal state using private instance variables in the implementation file instead of exposing them through public properties.

Example of the security issue:

// ❌ Bad - exposes internal state publicly
@property (nonatomic, assign) BOOL isFirstRender;
@property (nonatomic, strong) NSArray<UIBarButtonItemGroup *> *initialValueLeadingBarButtonGroups;

Secure alternative:

// ✅ Good - keep internal state private
@implementation ClassName {
    BOOL isFirstRender;
    NSArray<UIBarButtonItemGroup *> *initialValueLeadingBarButtonGroups;
}

This follows the principle of least privilege by only exposing what external consumers actually need to access, reducing the potential for security exploits through API misuse.

---

memoize for render optimization

Use React memoization techniques strategically to prevent unnecessary re-renders and recomputations when values change infrequently. Apply React.memo to components that receive stable props, and useMemo for expensive computations that depend on rarely-changing values.

Removing memoization can significantly degrade performance by causing excessive re-renders. Conversely, adding memoization to frequently recomputed values that remain stable can provide substantial performance benefits.

Example of proper memoization:

// Memoize component to prevent unnecessary re-renders
export const MatchInner = React.memo(function MatchInnerImpl({
  matchId,
}: { matchId: string }) {
  // Memoize expensive computation when dependencies are stable
  const Comp = useMemo(() => 
    route.options.component ?? router.options.defaultComponent,
    [route.options.component, router.options.defaultComponent]
  )
  
  return <Comp />
})

Focus memoization efforts on components and computations where the cost of re-execution outweighs the overhead of memoization checks.

---

Purposeful style changes

Code style modifications should accompany functional improvements rather than being submitted as standalone changes. When improving code, prefer modern JavaScript syntax like object spread over older patterns or external dependencies.

Example:

// Instead of using external dependencies:
const merged = require('utils-merge')(obj1, obj2);

// Prefer native JavaScript features:
const merged = {...obj1, ...obj2};

The project prioritizes meaningful contributions that improve functionality or fix issues over purely cosmetic changes. Pull requests focused solely on code style updates without functional benefits are generally not accepted.

---

Explicit over implicit

Always prefer explicit configuration settings over relying on implicit defaults or environmental behaviors in CI workflows and build configurations. This is particularly important for:

1. Python version specifications: Always explicitly specify the Python version in commands even when tools might detect it automatically.

# Good - explicitly specifies Python version
- name: Set up Python 3.12
  run: uv python install 3.12

- name: Install dependencies
  run: uv sync --python 3.12 --group docs

1. Dependency extras and groups: Clearly state which extras and dependency groups are being included in installation commands.

# Good - explicitly states which extras are being installed
- name: Install dependencies
  run: uv sync --extra timezone

# Good - step name clearly indicates what's being tested
- name: Test without email-validator
  run: ...

This approach prevents unexpected behaviors from implicit configurations (like .python-version files) and makes workflows more maintainable and predictable, especially in CI environments where consistency is critical.

---

Enforce secure TLS configuration

Always configure TLS connections with secure minimum version requirements and proper certificate handling. Network communications should enforce TLS 1.2 or higher to prevent security vulnerabilities from outdated protocols.

When configuring TLS in clients or servers, explicitly set the minimum version and validate certificate configurations:

// Server TLS configuration
tlsConfig := &tls.Config{
    MinVersion: tls.VersionTLS12, // Enforce TLS 1.2 minimum
}

// Client TLS configuration with certificates
func (c *Client) TLSConfig() *tls.Config {
    if c.tlsConfig == nil {
        c.tlsConfig = &tls.Config{
            MinVersion: tls.VersionTLS12,
        }
    }
    return c.tlsConfig
}

Additionally, ensure comprehensive testing of TLS compatibility scenarios, including cases where client and server have different TLS version requirements. Test handshake failures when version mismatches occur (e.g., server only allows TLS 1.3 but client attempts TLS 1.2). This prevents production issues and ensures robust network security across different deployment environments.

---

Safe proxy configuration

When configuring proxy settings for network applications, always use proper compilation methods to prevent runtime errors and ensure consistent IP address handling across different connection types. Improper proxy configuration can cause server crashes when IP addresses are accessed, particularly when using string-based configurations with multiple values.

Use proxyaddr.compile() to safely process proxy configurations and define IP properties consistently:

const trustProxy = proxyaddr.compile(
  process.env.TRUSTED_PROXY_IP ?
    process.env.TRUSTED_PROXY_IP.split(/(?:\s*,\s*|\s+)/) :
    ['loopback', 'uniquelocal']
);

// For websocket connections, define IP property to match Express behavior
Object.defineProperty(request, 'ip', {
  configurable: true,
  enumerable: true,
  get() {
    return proxyaddr(this, trustProxy);
  }
});

This approach prevents server crashes from malformed proxy configurations and ensures that IP address access works uniformly across HTTP and WebSocket connections, enabling consistent network security features like IP blocking.

---

leverage framework cache mechanisms

When implementing caching functionality, prefer using framework-provided cache mechanisms over manual cache management. Frameworks typically offer optimized cache handling that includes automatic error propagation, efficient multi-level cache checking, and built-in performance optimizations that are difficult to replicate manually.

Manual cache checking often leads to inefficient implementations that duplicate work, miss optimization opportunities, and require custom error handling. Framework mechanisms handle these complexities automatically and provide better performance characteristics.

For example, instead of manually checking cache availability:

// Avoid: Manual cache checking
val imagePipeline = Fresco.getImagePipeline()
val dataSource = imagePipeline.isInDiskCache(uri)
dataSource.subscribe(object : BaseDataSubscriber<Boolean>() {
  override fun onNewResultImpl(dataSource: DataSource<Boolean>) {
    val isInCache: Boolean = dataSource.getResult() ?: false
    if (isInCache) {
      setupImageRequest(uri, cacheControl, postprocessor, resizeOptions)
    } else {
      // Custom error handling needed
    }
  }
})

// Prefer: Framework cache mechanism
val requestLevel = if (cacheControl == ImageCacheControl.ONLY_IF_CACHED) 
  RequestLevel.DISK_CACHE else RequestLevel.FULL_FETCH

val imageRequestBuilder = ImageRequestBuilder.newBuilderWithSource(uri)
  .setLowestPermittedRequestLevel(requestLevel)

This approach leverages the framework’s comprehensive cache checking (bitmap, encoded memory, and disk caches), automatic error propagation, and avoids duplicate cache reads while ensuring optimal performance.

---

Consistent Scoped Naming

Use consistent, semantic naming patterns for externally visible identifiers—especially package names and command/script names.

• Packages/registry entries: Prefer the correct scope and canonical name format (typically @scope/name) aligned with ownership and established ecosystem conventions. If the project belongs under a scope (e.g., @zod), use @zod/zod-style naming rather than an unrelated owner-scope.
  • Example: change a JSR name to @zod/zod (or equivalent @zod/*) instead of keeping an @colinhacks/* identity when ownership/pattern indicates @zod/*.
• Grouped scripts/commands: When defining related commands, use a consistent hierarchy delimiter such as : to make relationships obvious.
  • Example:

    {
      "scripts": {
        "fix:lint": "eslint --fix --ext .ts ./src",
        "fix:format": "prettier --write \"src/**/*.ts\"",
        "fix": "yarn fix:lint && yarn fix:format"
      }
    }
    

---

Documentation quality standards

Ensure documentation follows proper formatting standards and provides complete, practical information for developers. Use JSDoc tags correctly - @default should contain actual TypeScript values, not descriptive sentences. When the default value is conditional or complex, use plain text descriptions instead.

Additionally, include usage examples in API documentation to make it more accessible and helpful. Synchronize examples across different documentation sources (README, inline docs, etc.) to maintain consistency.

Example of incorrect JSDoc usage:

/**
 * Configure whether Ink should only render the last frame of non-static output.
 * @default true if in CI or stdout is not a TTY
 */
patchConsole?: boolean;

Example of correct approach:

/**
 * Configure whether Ink should only render the last frame of non-static output.
 * Default: true if in CI or stdout is not a TTY
 */
patchConsole?: boolean;

For API documentation, include practical usage examples:

/**
 * Hook that calls inputHandler callback with input that program received.
 * Additionally contains helpful metadata for detecting when arrow keys were pressed.
 * 
 * @example
 * ```typescript
 * useInput((input, key) => {
 *   if (key.leftArrow) {
 *     // Handle left arrow key
 *   }
 * });
 * ```
 */

---

Simplify parsing algorithms

When implementing parsing or processing algorithms, prioritize simplification and reusability over complex custom solutions. Convert complex conditional logic into simpler, well-defined data structures and reusable functions. Use established, proven algorithms from reliable sources rather than deriving custom implementations.

For example, instead of complex nested conditionals for parsing gradient directions:

// Before: Complex conditional parsing
if (typeof bgImage.direction === 'undefined') {
  points = TO_BOTTOM_START_END_POINTS;
} else if (ANGLE_UNIT_REGEX.test(bgImage.direction)) {
  const angle = parseAngle(bgImage.direction);
  if (angle != null) {
    points = calculateStartEndPointsFromAngle(angle);
  }
} else if (DIRECTION_REGEX.test(bgImage.direction)) {
  // More complex logic...
}

// After: Simplified with reusable orientation structure
let orientation: LinearGradientOrientation = DEFAULT_ORIENTATION;
if (bgImage.direction != null && ANGLE_UNIT_REGEX.test(bgImage.direction)) {
  const parsedAngle = getAngleInDegrees(bgImage.direction);
  if (parsedAngle != null) {
    orientation = { type: 'angle', value: parsedAngle };
  }
}

This approach makes algorithms more maintainable, testable, and allows for better code reuse across different parts of the system. When dealing with complex patterns like URL validation, prefer established regex patterns from trusted sources over custom derivations.

---

TypeScript configuration setup

Ensure proper TypeScript configuration for generated types and development workflow. This includes setting up gitignore patterns, configuring tsconfig.json for type generation, and integrating typegen into build scripts.

When working with frameworks that generate types (like React Router v7), follow these configuration steps:

1. Add generated directories to gitignore:

   .react-router/
   

2. Configure tsconfig.json for generated types:

   {
     "include": [".react-router/types/**/*"],
     "compilerOptions": {
    "rootDirs": [".", "./.react-router/types"]
     }
   }
   

3. Integrate typegen into build scripts:

   {
     "scripts": {
    "typecheck": "react-router typegen && tsc"
     }
   }
   

This configuration ensures that generated types are properly excluded from version control, TypeScript can locate and use the generated types correctly, and the development workflow includes type generation as part of the build process. The rootDirs configuration allows importing generated types as if they were sibling files, improving developer experience.

---

Validate noexcept guarantees

Only mark functions as noexcept when you can guarantee they won’t throw exceptions under any circumstances. Common pitfalls include:

1. Hidden allocations: Operations like vector operations, std::make_tuple, or working with collections might allocate memory and throw.
2. Dependent types: When using templates, the operations performed on template parameters might throw.
3. Non-noexcept components: If a class member or base class has non-noexcept operations, derived classes shouldn’t blindly use noexcept.

For complex templated code, consider compile-time validation:

// Before marking a templated function as noexcept
template <typename DataDrivenPaintProperty, typename Evaluated>
static bool isConstant(const Evaluated& evaluated) noexcept {
    // How do you know all operations here are truly noexcept?
    return evaluated.template get<DataDrivenPaintProperty>().isConstant();
}

// Better: Add compile-time verification
template <typename DataDrivenPaintProperty, typename Evaluated>
static bool isConstant(const Evaluated& evaluated) noexcept {
    using ReturnType = decltype(evaluated.template get<DataDrivenPaintProperty>());
    static_assert(std::is_nothrow_invocable_v<decltype(&ReturnType::isConstant), ReturnType&>,
                  "isConstant() must be noexcept");
    return evaluated.template get<DataDrivenPaintProperty>().isConstant();
}

When in doubt, err on the side of caution and omit noexcept. Incorrect noexcept specifications can lead to program termination if an exception is thrown, which is worse than having a potentially throwing function not marked as noexcept.

---

optimize array operations

Pre-allocate arrays when the final size is known and consolidate multiple iterations into single loops to reduce memory allocations and improve performance.

When you know the array size in advance, use new Array(length) instead of starting with an empty array and using push(). JavaScript engines allocate extra space (typically 8-16 slots) when using push(), leading to wasted memory.

Combine multiple array operations (map, filter, forEach) into a single loop when possible to reduce iterations and temporary array creation.

Example - Array pre-allocation:

// Instead of this:
const vnodes = []
for (const item of items) {
  vnodes.push(processItem(item))
}

// Do this when size is known:
const vnodes = new Array(items.length)
for (let i = 0; i < items.length; i++) {
  vnodes[i] = processItem(items[i])
}

Example - Consolidating iterations:

// Instead of multiple operations:
const filtered = items.filter(item => item.enabled)
const mapped = filtered.map(item => transform(item))
const processed = mapped.forEach(item => process(item))

// Use single loop:
const results = []
for (const item of items) {
  if (item.enabled) {
    const transformed = transform(item)
    results.push(transformed)
    process(transformed)
  }
}

This approach reduces both memory allocations and CPU cycles, especially beneficial when processing large datasets or in performance-critical code paths.

---

Replace magic numbers

Replace magic numbers with named constants to improve code readability and maintainability. Magic numbers make code harder to understand and maintain, as their purpose and significance are not immediately clear to other developers.

When you encounter numeric literals in your code that have specific meaning or significance, extract them into well-named constants. This practice makes the code self-documenting and easier to modify in the future.

Example:

// Instead of:
if (Math.abs(deltaX) > 1) {
    // handle scroll delta
}

// Use:
private static final int SCROLL_DELTA_EPSILON = 1;

if (Math.abs(deltaX) > SCROLL_DELTA_EPSILON) {
    // handle scroll delta
}

Additionally, avoid using arbitrary placeholder values that won’t be used. If a value is not meaningful in certain contexts, consider using more explicit approaches like early returns with appropriate sentinel values rather than meaningless numbers.

---

Format complex CSS selectors

When working with complex CSS selectors that include multiple nested pseudo-selectors like :is(), :where(), :not(), and :has(), maintain consistent formatting and consider breaking long selector chains for better readability. This is particularly important in Svelte components where selectors may need :global() wrappers.

For complex nested selectors, consider adding multiple selector options within pseudo-selectors to improve maintainability:

/* Good: Multiple selectors within :is() for flexibility */
div :is(:global(.class:is(span:is(:hover)), .x)){}

/* Instead of: Single complex nested chain */
div :is(:global(.class:is(span:is(:hover)))){}

This approach makes selectors more maintainable and allows for easier extension when additional selector variants are needed.

---

conditional component bundling

When adding conditional components to your application, ensure they are only bundled when actually needed to avoid unnecessary bundle bloat. This is especially important for optional features or components that depend on specific configurations.

Protect conditional components by checking if the feature is actually used before including the component. For example, if adding a component that only applies when certain route metadata exists, guard against always bundling it:

<!-- Bad: Always bundles NuxtPage even when not needed -->
<LazyNuxtPage v-else-if="route.meta?.isolate" />

<!-- Better: Only bundle when isolate metadata actually exists in routes -->
<LazyNuxtPage v-else-if="hasIsolateRoutes && route.meta?.isolate" />

This approach ensures that if no routes have the required metadata, there will be no changes to the bundle at all. Consider the trade-offs between lazy loading and bundle size, but prioritize avoiding unnecessary inclusions that impact all users regardless of feature usage.

---

use modern JavaScript patterns

Adopt modern JavaScript syntax and patterns to improve code quality and maintainability. This includes using current language features over deprecated alternatives, proper variable declarations, and modern conditional operators.

Key practices to follow:

• Replace deprecated methods like substr() with modern equivalents like substring()
• Use const instead of let when variables won’t be reassigned
• Prefer optional chaining (?.) and ternary operators over logical AND (&&) in JSX conditional rendering
• Follow established best practices for conditional rendering patterns

Example of improved JSX conditional rendering:

// Instead of:
{actionData && actionData.error && (
  <div>Error occurred</div>
)}

// Use:
{actionData?.error ? (
  <div>Error occurred</div>
) : null}

This approach reduces potential runtime errors, improves readability, and follows current JavaScript and React best practices.

---

Descriptive named constants

Replace magic numbers and unclear variables with descriptive named constants using appropriate naming conventions. This improves code readability, maintainability, and prevents errors.

Guidelines:

1. Use constexpr variables with descriptive names instead of raw numbers
2. Follow camelCase naming for constants (reserve ALL_CAPS for macros only)
3. Include comments explaining the origin of special values when relevant
4. Use meaningful names for array indices and limits

Example:

// Poor readability:
resource.dataRange = std::make_pair<uint64_t, uint64_t>(0, 16383);

// Improved with named constants:
// https://github.com/protomaps/PMTiles/blob/main/spec/v3/spec.md#3-header
constexpr uint64_t pmtilesHeaderOffset = 0;
constexpr uint64_t pmtilesHeaderMaxSize = 16383;
resource.dataRange = std::make_pair(pmtilesHeaderOffset, pmtilesHeaderMaxSize);

// Array indices should have names:
bool propUpdateFlags[4] = {propertiesUpdated, propertiesUpdated, propertiesUpdated, propertiesUpdated};
// Better:
constexpr size_t linePropFlagIndex = 0;
bool propUpdateFlags[4] = {/*...*/};
if (!linePropertiesBuffer || propUpdateFlags[linePropFlagIndex]) {
    // ...
}

// Context for numeric parameters:
Context::Context(RendererBackend& backend_)
    : gfx::Context(16), // TODO
// Better:
constexpr uint32_t maximumVertexBindingCount = 16;
Context::Context(RendererBackend& backend_)
    : gfx::Context(maximumVertexBindingCount),

This approach makes code self-documenting, easier to maintain, and less prone to errors when numbers need to be updated.

---

Descriptive migration comments

When adding migration task comments, always include specific details about why manual intervention is required rather than using generic instructions. This helps developers understand the underlying issue and implement the correct fix more efficiently.

Migration comments should explain the root cause of the migration failure, such as invalid identifiers, syntax conflicts, or breaking changes. This context is crucial for successful manual migration.

Example:

<!-- Bad: Generic comment -->
<!-- @migration-task: migrate this slot by hand -->

<!-- Good: Specific comment with reason -->
<!-- @migration-task: migrate this slot by hand, `cool:stuff` is an invalid identifier -->
<!-- @migration-task: migrate this slot by hand, `cool stuff` is an invalid identifier -->

The specific reason helps developers immediately understand what needs to be fixed - in this case, slot names containing colons or spaces that are not valid identifiers in the new syntax.

---

Inherit organization security policies

Before implementing custom security documentation or procedures, check if your organization already provides standardized security policies that your repository can inherit. This avoids duplication, ensures consistency across projects, and leverages platform-specific security features. For GitHub repositories, organization-level security policies (.github repository) are automatically inherited and should be used instead of repository-specific implementations when applicable.

Example:

# Instead of creating a repository-specific SECURITY.md file with custom content:
# Reporting a Vulnerability
Please, [open a draft security advisory](https://github.com/org-name/security-advisories/security/advisories/new) if you need to disclose a security issue.

# Simply reference the organization-wide policy:
For reporting security vulnerabilities, please see our [security policy](https://github.com/org-name/repo-name/security/policy).

---

Use consistent terminology

Prioritize consistent, clear, and beginner-friendly terminology throughout your codebase and documentation. Choose names that are intuitive for users rather than technically precise but confusing. Maintain consistency with established patterns and style guidelines.

Key principles:

• Favor clarity over technical accuracy: Use ViteConfig instead of UserConfig when the context makes it clearer that it’s Vite configuration
• Use beginner-friendly terms: Prefer “client-side” over “front-end” and “server-side” over “back-end” for accessibility
• Maintain consistency: Use “user interface” consistently instead of mixing with “UI”, and follow established import patterns like ~/ over @/
• Follow style guidelines: Apply proper capitalization rules (e.g., “TypeScript-Friendly” following APA style, “vs” lowercase in “ESM vs CJS”)
• Match existing APIs: When naming new parameters, consider existing patterns (e.g., refreshEvery to match native functions rather than pollEvery)

Example of good terminology consistency:

// Good - clear and consistent
interface ViteConfig {
  clientSide: boolean;
  serverSide: boolean;
}

// Avoid - technically correct but less intuitive
interface UserConfig {
  frontEnd: boolean;
  backEnd: boolean;
}

---

configure build tools properly

Ensure build configurations use proper package.json exports fields and TypeScript settings to avoid hard-coded paths and module format inconsistencies. Build tools should be configured to handle module resolution and output formats correctly to prevent runtime issues.

Use package.json exports field instead of hard-coding file paths:

// Instead of hard-coded paths
input: `${SOURCE_DIR}/index.ts`,

// Use multiple inputs with proper exports configuration
input: [`${SOURCE_DIR}/index.ts`, `${SOURCE_DIR}/install.ts`],

Configure TypeScript and Babel properly for consistent module formats:

typescript({
  tsconfig: path.join(__dirname, "tsconfig.json"),
  exclude: ["__tests__"],
  noEmitOnError: !WATCH,
  noForceEmit: true, // Prevents incorrect CJS exports in ESM builds
}),
babel({
  babelHelpers: "bundled",
  exclude: /node_modules/,
  extensions: [".ts"],
  ...remixBabelConfig, // Use shared configuration
})

This prevents build-time issues that can cause deployment failures and ensures consistent module handling across different environments.

---

Preallocate collection capacity

When the final size of a collection is known before adding elements, use reserve() to preallocate memory capacity. This optimization eliminates multiple reallocations and copy operations during insertions, improving both performance and memory usage patterns. This is particularly beneficial in performance-critical code paths where collections are frequently constructed or modified.

// Inefficient approach - may cause multiple reallocations
std::vector<AnchorOffsetPair> collection;
for (const auto& anchorOffset : variableAnchorOffset) {
    collection.emplace_back(anchorOffset);
}

// Optimized approach - single allocation
std::vector<AnchorOffsetPair> collection;
collection.reserve(variableAnchorOffset.size());  // Pre-allocate memory
for (const auto& anchorOffset : variableAnchorOffset) {
    collection.emplace_back(anchorOffset);
}

Even for small collections, this practice improves code efficiency. For vectors that grow incrementally with push_back or emplace_back operations, each reallocation requires copying all existing elements to a new memory location, which becomes increasingly expensive as the collection grows.

---

Meaningful documentation practices

Documentation should enhance code understanding rather than duplicate information already present in the code. Avoid redundant type annotations in JSDoc when type systems like Flow are already used. Instead, focus on explaining intent, complex logic, and providing context that aids debugging and maintenance.

For test descriptions, use clear, descriptive names that explain the feature being tested:

// Good: Explains the feature being tested
describe('Testing Cancel Button Functionality', function () {

// Avoid: Vague or redundant descriptions  
describe('Test is checking cancel button', function () {

For complex patterns like regular expressions, add explanatory comments:

// Good: Explains what the regex matches
const colorStopRegex = 
  // matches color values like rgba(0,0,0,1), #fff, or named colors with optional percentages
  /\s*((?:(?:rgba?|hsla?)\s*\([^)]+\))|#[0-9a-fA-F]+|[a-zA-Z]+)(?:\s+(-?[0-9.]+%?)(?:\s+(-?[0-9.]+%?))?)?\s*/gi;

Prioritize documentation that tells developers why something exists or how it works, not what is already evident from well-written code.

---

Vue component type safety

When defining Vue components with TypeScript, use appropriate component definition patterns to ensure proper type inference and avoid breaking type changes.

For proper typing of component props:

1. Use the correct helper for your component definition needs. For example, DeclareComponent may be more appropriate than defineComponent when you need to expose prop types in a specific way.

2. When providing default values for function props, remember they’re handled differently than object/array defaults:

// Correct way to define function props with defaults
props: {
  handler: {
    type: Function,
    // Function props don't need to be wrapped in factory functions
    default() {
      return (value) => console.log(value)
    }
  },
  // While object defaults need factory functions
  objProp: {
    type: Object,
    default: () => ({ key: 'value' })
  }
}

1. Be cautious when modifying type definitions or signatures of public APIs, as these can introduce breaking changes for consumers. Maintain the expected type argument order for exported types like DefineComponent.

By following these practices, you’ll ensure your Vue components have proper TypeScript support while maintaining compatibility with Vue’s type system.

---

Validate security-sensitive inputs

Always use appropriate validation mechanisms for security-sensitive inputs to prevent vulnerabilities. When implementing validation for headers, origins, user inputs, or any security-related data, consult security documentation and use established validators rather than creating custom validation logic.

For example, when validating CORS requests, ensure proper validation of the Origin header:

// Bad - Missing validation
public static boolean isCorsRequest(HttpServletRequest request) {
    String origin = request.getHeader(HttpHeaders.ORIGIN);
    if (origin == null) {
        return false;
    }
    // No validation of origin value before using it
    return true;
}

// Good - Using proper validation
public static IsCorsRequestResult isCorsRequest(HttpServletRequest request) {
    String origin = request.getHeader(HttpHeaders.ORIGIN);
    if (origin == null) {
        return IsCorsRequestResult.IS_NOT_CORS_REQUEST;
    }
    // Using established validation mechanism
    if (!(new UrlValidator().isValid(origin))) {
        return IsCorsRequestResult.INVALID_CORS_REQUEST;
    }
    // Continue with additional validation if needed
    return IsCorsRequestResult.VALID_CORS_REQUEST;
}

Using established validators ensures that your security checks benefit from community-vetted logic that properly handles edge cases. Before implementing security validation, research existing issues and security best practices to ensure you’re using the most secure approach.

---

Accurate documentation references

Ensure all code documentation includes appropriate reference links that are current and accurate. When porting code or migrating between frameworks, preserve all documentation comments with their external references. For API documentation, verify that links point to the correct and up-to-date specification documentation.

Example:

/**
 * The circle manager allows to add circles to a map.
 * 
 * Learn more about circle properties in the 
 * [Style specification](https://maplibre.org/maplibre-style-spec/).
 * 
 * For implementation details, see the 
 * [KhronosGroup repository](https://github.com/KhronosGroup/...)
 */
class CircleManager {
    // Implementation
}

Maintaining accurate documentation references helps developers find the correct information quickly and prevents them from following outdated or incorrect links. This is especially important when migrating code between frameworks (like Mapbox to MapLibre) or when porting from one language to another (like Groovy to Kotlin).

---

Preprocess data early

Transform and prepare data structures at their source rather than during consumption. This includes flattening nested objects, sorting collections, and other manipulations that make data more efficient to process downstream.

When working with nested structures like configuration objects, flatten them early:

// Instead of:
function processColors(colors) {
  return typeof colors === "string" ? { [name]: colors } : colors;
  // This doesn't handle deeply nested color objects properly
}

// Prefer:
function processColors(colors) {
  return typeof colors === "string" ? { [name]: colors } : flatten(colors);
  // Flattens all nested objects into a simple key-value format
}

Similarly, when generating datasets for visualization or processing, sort or transform the data at its source:

// Instead of sorting inside the consuming component:
const generateRandomData = (days) => {
  const data = [];
  // ... generate data
  return data; // Unsorted
};

// Prefer:
const generateRandomData = (days) => {
  const data = [];
  // ... generate data
  return data.sort((a, b) => new Date(a.date) - new Date(b.date)); // Pre-sorted
};

This approach improves performance by avoiding redundant operations, creates cleaner separation of concerns, and makes algorithms more maintainable by handling data preparation at the appropriate level of abstraction.

---

Clone network headers carefully

When working with HTTP or WebSocket headers in networking code, be cautious about header manipulation, cloning, and lifecycle management. Native headers in server implementations are often pooled and may be recycled after initial processing.

Specific considerations:

1. Preserve case-insensitivity of HTTP headers when copying them
2. For WebSocket handshakes, create a deep copy of headers as they may be needed after the original headers are recycled
3. Avoid adding duplicate headers when reading after headers are written

Example:

// Incorrect - May lose case-insensitivity of header names
this.headers = new HttpHeaders(new LinkedMultiValueMap<>(original.getHeaders()));

// Correct - Create a proper copy that preserves HTTP header behavior
HttpHeaders headers = new HttpHeaders();
headers.addAll(request.getHeaders());

These practices help prevent subtle bugs related to header handling in network communication.

---

Clear contextual error messages

Error messages should be specific, contextually relevant, and provide actionable guidance to developers. Avoid generic or ambiguous error text that could apply to multiple scenarios.

In tests, use distinct error messages for different components or scenarios so that test failures clearly indicate the expected outcome:

const rootRoute = createRootRoute({
  errorComponent: () => <span>Rendering errorComp message</span>,
  component: () => {
    throw new Error('Throwing from route component')
  }
})

For runtime errors, provide context about where the error occurred and suggest specific solutions:

// Instead of generic: "No match found while rendering useMatch()"
// Use contextual: "No match found for route '/' while rendering the '/about' route. Did you mean to pass '{ strict: false }' instead?"

This approach helps developers quickly identify the source of errors and understand how to resolve them, whether during development, testing, or debugging production issues.

---

Document design decisions

When making architectural choices or modifying existing APIs, document your reasoning directly in the code or in type definitions. This helps other developers understand the “why” behind changes and prevents future regressions.

For API changes:

// Document parameter changes in type definitions, even for internal components
interface GetTabbableProps {
  // Added third parameter to support focusing the first element
  container: HTMLElement;
  firstFocus: boolean;
  forceFirst?: boolean;
}

For architectural decisions:

// MuiMeta.tsx
// This component is separated from layout components to:
// 1. Minimize changes to core files
// 2. Isolate metadata logic for easier maintenance
// 3. Allow users to update metadata without modifying root structures
import theme from "./theme";

export default function MuiMeta() {
  // Metadata implementation
}

By documenting the reasoning behind your decisions, you make the codebase more maintainable and help other developers understand your design choices, reducing questions during code review and simplifying future updates.

---

Configurable logging controls

Make logging behavior configurable rather than hardcoded, and avoid manipulating global state for logging purposes. Provide configuration options to enable/disable specific log messages, especially for warnings or debug information that could become spammy. Instead of overwriting global variables like os.Stdout and os.Stderr for testing, use dependency injection or proper logging interfaces that can be mocked or redirected.

Example of configurable logging:

type Config struct {
    EnableWarnings bool
    Logger         Logger // injectable logger interface
}

func FromContext(c fiber.Ctx) *Middleware {
    m, ok := c.Locals(middlewareContextKey).(*Middleware)
    if !ok && cfg.EnableWarnings {
        cfg.Logger.Warn("session: Session middleware not registered")
        return nil
    }
    return m
}

This approach prevents misleading or excessive log output while maintaining flexibility for different deployment environments and testing scenarios.

---

Alphabetical ordering requirement

Always maintain alphabetical ordering for lists of elements including dependencies, modules, configuration entries, and other similar collections. This convention improves code organization, makes it easier to locate items, prevents duplications, and ensures consistency across the codebase.

When adding new elements to existing lists, ensure they are placed in the correct alphabetical position:

dependencies {
  // Correct: alphabetically ordered
  dockerTestRuntimeOnly("com.ibm.db2:jcc")
  dockerTestRuntimeOnly("io.r2dbc:r2dbc-mssql")
  dockerTestRuntimeOnly("org.postgresql:postgresql")
  dockerTestRuntimeOnly("org.postgresql:r2dbc-postgresql")
  
  // Incorrect: not alphabetically ordered
  dockerTestRuntimeOnly("io.r2dbc:r2dbc-mssql")
  dockerTestRuntimeOnly("org.postgresql:postgresql")
  dockerTestRuntimeOnly("org.postgresql:r2dbc-postgresql")
  dockerTestRuntimeOnly("com.ibm.db2:jcc")  // Wrong position
}

This rule applies to all list-like structures including gradle dependencies, spring.factories entries, module definitions, and similar configuration files throughout the project.

---

Implement recursive safeguards

When implementing recursive algorithms, always include cycle detection and early termination conditions to prevent infinite recursion and improve performance. This is especially critical in graph traversal, AST processing, and dependency analysis where circular references can occur.

Key safeguards to implement:

1. Visited set tracking: Maintain a set of already-processed nodes/paths
2. Early returns: Skip processing if an item has already been handled
3. Cycle detection: Check for circular dependencies before recursing

Example from AST traversal:

function getDependentIdentifiersForPath(path, { visited, identifiers }) {
  // Ensure we don't recurse indefinitely
  if (visited.has(path)) {
    return identifiers;
  }
  
  visited.add(path);
  
  // We can skip all of this work if we've already processed this identifier
  if (identifiers.has(path)) {
    return;
  }
  
  // Continue with recursive processing...
}

Consider the algorithmic complexity and don’t assume data structures are in any particular order. Design algorithms that can handle arbitrary arrangements and potential cycles, as this adds minimal cost while significantly improving robustness.

---

Choose semantic descriptive names

Names should be clear, descriptive and follow consistent patterns. Choose names that accurately reflect the purpose and behavior of the code element:

1. Use semantic prefixes/suffixes that match established patterns:
   • State flags should use consistent prefixes (e.g., isActivated not deactive)
   • Type names should start with uppercase (e.g., PluginParam not pluginParam)
   • Internal implementations should use descriptive suffixes (e.g., ComputedRefImpl not _ComputedRef)
2. Pick clear, unambiguous names that convey intent:
   • Prefer descriptive names over abbreviated ones (e.g., immediate over runOnce)
   • Use complete words rather than shortened forms
   • Follow framework conventions (e.g., VNodeKey over VKey)

Example:

// Bad
class _ComputedRef {
  isDeactive: boolean
  runOnce: boolean
}

// Good
class ComputedRefImpl {
  isActivated: boolean
  immediate: boolean
}

---

Reference existing configurations

When setting up configuration files, reference existing configuration sources rather than duplicating values or logic. This creates a single source of truth, reduces maintenance overhead, and prevents inconsistencies between different environments.

For example, when configuring tools that depend on version information that exists elsewhere in your project:

# Instead of hardcoding Java version installation:
tasks:
  - init: yes | sdk install java && ./gradlew build

# Reference the version specified in .sdkmanrc:
tasks:
  - init: sdk env install && ./gradlew build

Similarly, when configuring service dependencies like health checks, prefer application-aware approaches over hardcoded values:

# Instead of arbitrary wait times:
healthcheck:
  test: [ 'CMD', 'sleep', '115' ]

# Consider log pattern matching or status checks:
healthcheck:
  test: [ 'CMD', 'grep', '"Setup has completed"', '/var/log/application.log' ]

This approach ensures configuration changes only need to be made in one place and propagate automatically to dependent configurations, while also leveraging appropriate application-specific behaviors.

---

Consistent terminology usage

When referring to technical concepts in documentation and code comments, use proper full names and consistent terminology:

1. Use full official names instead of abbreviations or shortened forms (e.g., “Kubernetes” instead of “K8s”)
2. When describing actions related to annotations, use the verb form without the @ symbol (e.g., use “autowire” as a verb rather than “@Autowire”)
3. Follow terminology conventions established in the framework or library documentation

Example:

// Incorrect:
// You can @Autowire JdbcTemplate directly into your beans when working with K8s

// Correct:
// You can autowire JdbcTemplate directly into your beans when working with Kubernetes

Maintaining consistent terminology improves documentation readability and prevents confusion, especially for developers who are new to the project or technology.

---

Write clear test cases

Tests should be written with clear intent and expectations. Use descriptive names that accurately reflect what the test validates, and include both positive and negative test cases to demonstrate expected behavior through contrast. Organize tests in appropriate suites based on their purpose (e.g., validation tests vs. runtime tests).

For example, when testing error conditions, include a passing case above the failing case:

function validFunction() {
    return $state(1); // This should pass
}

function invalidFunction() {
    return $state(1); // This should throw, as expected
}

Avoid confusing names like importing something called “broken” when it’s actually working correctly. Instead, use names that clearly indicate the test’s purpose and expected outcome.

---

avoid redundant computations

Identify and eliminate computations that are performed repeatedly when they could be executed once. This includes moving loop-invariant checks outside of loops and reducing callback overhead that creates unnecessary function declarations.

Common patterns to optimize:

• Loop invariants: Move conditions that don’t depend on individual loop items outside the loop
• Repeated function calls: Cache results of expensive operations that don’t change
• Callback overhead: Minimize complex function declarations that cause GC churn

Example from file upload validation:

// Before: checking upload limit for every file
filesArray.some(file => {
  // ... file-specific checks ...
  || (files.length + media.size + pending > maxMediaAttachments)  // This doesn't depend on individual file!
})

// After: check upload limit once before processing files
if (files.length + media.size + pending > maxMediaAttachments) {
  // handle error
  return;
}
// Then process individual files without redundant check

This optimization reduces computational overhead and improves performance, especially in scenarios with loops, callbacks, or frequently called functions.

---

Spring code style

Follow Spring Framework’s code style guidelines to ensure consistency across the codebase. Key rules include:

1. Import statements:
   • Use specific imports rather than wildcard imports
   • Maintain consistent import ordering
   • Avoid static imports except in specific cases
2. Field and variable references:
   • Always prefix instance field references with this.
   • Don’t declare local variables as final unless there’s a compelling reason
   • Don’t use var in production code
3. Formatting:
   • Use tabs for indentation, not spaces
   • Remove unnecessary spaces inside parentheses
   • Aim for 90 characters per line (maximum 120), with 80 for Javadoc
   • Place opening braces on the same line, else statements on a new line
4. Before submitting:
   • Run ./gradlew check to catch style violations automatically

Example of proper style:

public class MyClass {
    private final String field;

    public MyClass(String parameter) {
        this.field = parameter;
    }

    public void doSomething(String input) {
        if (input == null) {
            return;
        }
        else {
            String result = processInput(this.field, input);
            processResult(result);
        }
    }
}

---

Complete configuration paths

Always verify that configuration files include all necessary file paths and extensions, particularly for framework-specific settings. Common issues include missing file extensions for TypeScript files, incorrect directory paths, and configurations that don’t account for framework-specific directory structures.

When configuring Tailwind CSS with TypeScript support:

module.exports = {
  content: [
    "./src/**/*.{html,js,jsx,tsx,ts}", // Include all relevant extensions
    "./app/**/*.{js,ts,jsx,tsx}", // For Next.js 13 app directory
    "./pages/**/*.{js,ts,jsx,tsx}", // For traditional Next.js pages
    "./components/**/*.{js,ts,jsx,tsx}",
  ],
  // Add comments to explain non-obvious configuration choices
  // ...
}

For framework-specific configurations like Laravel, double-check paths against the framework’s expected directory structure (e.g., resources/css/app.css not resources/app.css). Adding comments to clarify framework-specific settings will help other developers understand your configuration choices, especially when supporting multiple versions or experimental features.

---

graceful error handling

Implement error handling that gracefully degrades when operations fail, uses consistent reporting patterns, and considers security implications. Always wrap potentially failing operations in try-catch blocks, provide meaningful fallback behavior, and follow established error reporting conventions.

Key principles:

• Use environment-aware error information disclosure (preserve debugging details in development, sanitize in production)
• Follow consistent error reporting patterns across the codebase
• Implement defensive programming against unexpected error types
• Provide graceful degradation when non-critical operations fail

Example implementation:

try {
  sessionStorage.setItem(storageKey, JSON.stringify(data));
} catch (error) {
  warning(
    false,
    `Failed to save data in sessionStorage, feature will not work properly. ${error}`
  );
  // Continue execution - don't let storage failure break the app
}

// Environment-aware error disclosure
error.stack = process.env.NODE_ENV === "development" ? val.stack : "";

// Proper error propagation with meaningful responses
if (res.status === 404) {
  throw new ErrorResponseImpl(404, "Not Found", true);
}

This approach ensures applications remain functional even when individual operations fail, while maintaining appropriate security boundaries and consistent user experience.

---

Comprehensive dependency security checks

Regularly check dependencies for security vulnerabilities using multiple sources, not just npm audit. As shown in the discussion, some vulnerabilities may not be reported by npm audit but are still present and documented elsewhere.

When a security vulnerability is identified:

1. Promptly update the affected dependency to a patched version
2. Consult release notes to verify the fix
3. Document the update reason in commit messages

Example:

// Before - vulnerable dependency
{
  "dependencies": {
    "@fastify/middie": "8.3.1"  // Has security vulnerability
  }
}

// After - updated dependency
{
  "dependencies": {
    "@fastify/middie": "8.3.3"  // Security vulnerability fixed
  }
}

Consider implementing automated tools or scheduled workflows to periodically check for dependency vulnerabilities beyond what npm audit reports.

---

Proactive dependency security

Always maintain dependencies at their latest secure versions, even when automated vulnerability scanning tools (like npm audit) don’t report issues. Regularly check release notes and security advisories for your dependencies, as some security fixes may not be detected by automated tools.

When a team member identifies a security vulnerability:

1. Verify the vulnerability exists
2. Upgrade to the fixed version promptly
3. Document the change

Example:

// Update vulnerable dependencies immediately when discovered
{
  "dependencies": {
    "@fastify/middie": "8.3.3",  // Updated from 8.3.1 which had security issues
    // Other dependencies...
  }
}

Consider implementing a regular dependency review process, occurring at least monthly, to proactively identify and address security vulnerabilities.

---

Cross-platform test management

When working with tests that run across multiple platforms (iOS, Android, etc.), ensure proper configuration and handling of platform-specific issues:

1. Place test files in all relevant platform-specific directories to ensure they’re properly recognized:

   metrics/linux-gcc8-release/render-tests/...
   ios-render-test-runner/...
   android-render-test-runner/...
   

2. When excluding a test that fails on specific platforms:
   • Document the reason for exclusion with a clear comment or issue link
   • Specify the exclusion only for affected platforms when possible
   • Create a follow-up issue to investigate and fix the root cause
3. For inconsistent test results that vary by device or environment:
   • Document the specific conditions where failures occur
   • Consider conditional test execution rather than complete exclusion

This approach maintains test coverage across platforms while providing clear documentation for temporarily disabled tests.

---

Follow snake_case convention

Consistently use snake_case naming throughout the codebase for variables, methods, and identifiers to maintain established conventions. When the codebase has adopted snake_case as the standard, all new code should follow this pattern rather than introducing camelCase or other naming styles.

Example:

// Preferred - follows codebase snake_case convention
const class_name = `__svelte_${hash(rule)}`;
function push_quasi(q: string) { ... }

// Avoid - inconsistent with established convention
const className = `__svelte_${hash(rule)}`;
function pushQuasi(q: string) { ... }

This ensures consistency across the codebase, improves readability, and prevents confusion when different naming conventions are mixed within the same project.

---

Document configuration properties completely

Configuration properties should be fully documented with clear descriptions, explicit default values, and proper metadata. This helps users understand and configure the application correctly.

Key requirements:

• Provide explicit default values in the property definition
• Include short, simple property descriptions without Javadoc tags
• Add enum defaults to additional-spring-configuration-metadata.json
• Use consistent property naming within property groups

Example:

@ConfigurationProperties("spring.example")
public class ExampleProperties {
    /**
     * Maximum number of connections to create.
     */
    private int maxConnections = 100;
    
    /**
     * Connection timeout duration.
     */
    private Duration timeout = Duration.ofSeconds(30);
    
    // Getters/setters
}

For enums:

{
  "properties": [
    {
      "name": "spring.example.mode",
      "defaultValue": "auto"
    }
  ]
}

---

Property description conventions

When documenting configuration properties in Spring Boot applications, follow these conventions for clarity and consistency:

1. Avoid starting descriptions with articles like “the” or “a”

   // INCORRECT:
   /** The max time to wait for the container to start. */
      
   // CORRECT:
   /** Time to wait for the container to start. */
   

2. Begin boolean property descriptions with “Whether…”

   // INCORRECT:
   /** This signals to Brave that the propagation type... */
      
   // CORRECT:
   /** Whether the propagation type and tracing backend support sharing the span ID... */
   

3. Omit phrases like “by default” since defaults are processed separately

   // INCORRECT:
   /** Sub-protocol to use in websocket handshake signature. Null by default. */
      
   // CORRECT:
   /** Sub-protocol to use in websocket handshake signature. */
   

4. Ensure all properties have descriptions that clearly explain their purpose

   // INCORRECT:
   private final Map<String, Duration> expiry = new LinkedHashMap<>();
      
   // CORRECT:
   /**
    * Duration after which the value expires from the distribution.
    */
   private final Map<String, Duration> expiry = new LinkedHashMap<>();
   

5. Align descriptions with other similar properties in the same class for consistency

Following these conventions improves documentation readability and maintainability while providing a consistent experience for developers using your API.

---

Complete optional chaining

When using optional chaining (?.), ensure that all subsequent operations in the chain are also protected from null/undefined values. A common mistake is only protecting the initial object access while leaving subsequent method calls or property accesses vulnerable.

Problems to avoid:

1. Unprotected method returns:

   // PROBLEMATIC: scrollSnapList() result is unprotected
   api?.scrollSnapList().map(...)
   

2. Incorrect control flow with void returns:

   // PROBLEMATIC: OR operator doesn't work with void returns
   onClick={() => onClickStep?.(index, setStep) || onClickStepGeneral?.(index, setStep)}
   

Better approaches:

1. Protect the entire chain: ```typescript // BETTER: Both api and its method result are protected api?.scrollSnapList()?.map(…)

// BEST: Add length check for extra safety api?.scrollSnapList()?.length > 0 && api.scrollSnapList().map(…)

2. Use proper conditionals for control flow:
```typescript
// Option 1: Explicit conditional
onClick={() => {
  if (onClickStep) {
    onClickStep(index, setStep);
  } else {
    onClickStepGeneral?.(index, setStep);
  }
}}

// Option 2: Execute both with separate optional chaining
onClick={() => {
  onClickStep?.(index, setStep);
  onClickStepGeneral?.(index, setStep);
}}

Always trace through the entire chain of operations when working with potentially null/undefined values to ensure each step is properly protected.

---

Prevent object recreations

Avoid creating new objects and functions repeatedly during renders to reduce memory pressure and improve performance. Implement these practices:

1. Move static data outside components:

   // Instead of this:
   function MyComponent() {
     const spinnerBars = [
       { animationDelay: -1.2, rotate: 0 },
       { animationDelay: -1.1, rotate: 30 },
       // ...more items
     ];
     // component code
   }
   
   // Do this:
   const spinnerBars = Array.from({ length: 12 }, (_, index) => ({
     animationDelay: -1.2 + 0.1 * index,
     rotate: 30 * index
   }));
   
   function MyComponent() {
     // component code
   }
   

2. Avoid inline function definitions in event handlers:

   // Instead of this:
   <Button onClick={() => scrollTo(index)} />
   
   // Do this:
   const handleScrollTo = (index) => () => scrollTo(index);
   <Button onClick={handleScrollTo(index)} />
   

3. Prevent unnecessary object instantiation:

   // Instead of this:
   return new Date(date) >= new Date(now)
   
   // Do this when objects already exist:
   return date >= now
   

These optimizations reduce garbage collection overhead and improve rendering performance, especially in components that render frequently or in large lists.

---

Spring annotation best practices

When working with Spring annotations, follow these guidelines to avoid common issues:

1. Use interface types for dependency injection: When autowiring dependencies, declare fields using the interface type rather than the implementation class. This ensures proper behavior with proxies and AOP.

// RECOMMENDED
@Autowired
private Pojo self;  // Interface type

// AVOID (unless you're certain CGLIB proxies are being used)
@Autowired
private SimplePojo self;  // Implementation type

1. Remember @Bean flexibility: Methods annotated with @Bean can be defined in any @Component-annotated class, not just in @Configuration classes.

2. Avoid annotation-based injection in infrastructure classes: Do not use @Autowired, @Inject, or @Resource annotations within BeanFactory implementations or their dependencies. This can cause BeanCurrentlyInCreationException due to initialization timing issues. Use programmatic lookups instead for these infrastructure components.

Following these practices will help prevent subtle runtime errors and improve the maintainability of your Spring applications.

---

Defer expensive operations

Avoid performing expensive computations until they are actually needed, and eliminate redundant work in hot code paths. This includes delaying database pulls, moving expensive object creation outside functions, and removing unnecessary operations.

Key strategies:

• Delay expensive operations: Only perform costly operations like database pulls when actually needed, especially in exception/error branches
• Hoist expensive computations: Move expensive object creation (like compiled regexes, composed functions) outside of frequently called functions
• Use defonce for static values: For expensive computations that produce static results, use defonce to avoid recomputation
• Eliminate redundant operations: Remove unnecessary function calls, file system operations, or data transformations

Example of delaying expensive operations:

;; Bad - always pulls data even if not used
(let [full-data (d/pull db pattern entity-id)]
  (if error
    (throw (ex-info "Error" {:data full-data}))
    (process full-data)))

;; Good - only pull when needed
(if error
  (let [full-data (d/pull db pattern entity-id)]
    (throw (ex-info "Error" {:data full-data})))
  (process (d/pull db pattern entity-id)))

Example of hoisting expensive computations:

;; Bad - recreates function on every call
(defn remove-nils [nm]
  (into {} (remove (comp nil? second)) nm))

;; Good - create function once
(def remove-nils
  (let [f (comp nil? second)]
    (fn [nm]
      (into {} (remove f) nm))))

---

Document non-obvious behavior

Write documentation that explains behavior and context that may not be obvious to newcomers, even if it seems clear to experienced developers. Include explanations for domain-specific concepts, data structure representations, and implicit behaviors that could confuse someone unfamiliar with the codebase.

For example, when documenting complex data structures, explain what arrays represent and why certain design decisions were made:

/**
 * Quoted/string values are represented by an array, even if they contain 
 * a single expression like `"{x}"`, since they may be a combination of 
 * text and expression values such as `style="color: {color} !important"`.
 */
value: Array<Text | ExpressionTag> | true;

Rather than assuming knowledge, provide context that helps developers understand the reasoning behind the implementation. What feels obvious after working with a codebase for months may be completely unclear to someone encountering it for the first time.

---

Deterministic Error Propagation

When handling async work, cancellation, retries, or hydration/prefetch, ensure errors are propagated consistently and control flow can’t leave callers stuck.

Apply these rules: 1) Always settle: any Promise constructed (or thenable returned) must end in either resolve(...) or reject(...) along every code path—no “neither called” cases. 2) Stop after error: in try/catch, once you call onError(...) (or reject(...)), immediately return so success handlers don’t run. 3) Failover, don’t strand: when an auxiliary path fails (e.g., restore from storage), catch the failure and fall back to the normal execution path (e.g., proceed to queryFn), rather than leaving the query stuck in error/loading forever. 4) Boundary-aware behavior: when you disable retries/throwing based on ErrorBoundary reset state, still preserve correct error propagation (don’t prevent settlement).

Example (fixing missed return):

try {
  this.setData(data)
} catch (error) {
  onError(error as TError)
  return // critical: don’t run onSuccess after an error
}

Example (never leave a hung promise):

return new Promise((resolve, reject) => {
  observer.subscribe((result) => {
    notifyManager.batchCalls(() => {
      if (result.isError) return reject(result.error)
      // always resolve on success; if you intentionally skip, still resolve
      return resolve(result.data as any)
    })
  })
})

---

Conditional observability instrumentation

Wrap all tracing, profiling, and debugging instrumentation in appropriate conditional compilation blocks (like MLN_TRACY_ENABLE) to prevent performance overhead in production builds. When adding trace points:

1. Use proper scoping for trace zones to control their lifetime
2. Include contextual information with zone annotations to maximize debugging value
3. Consider the performance impact of unique identifiers and other debug-only information

Example:

// Good practice - scoped and conditionally compiled
#ifdef MLN_TRACY_ENABLE
{
    MLN_TRACE_FUNC()
    MLN_ZONE_STR(name)  // Adds context about which component is being processed
}
#endif

// For debug IDs or other observability-only fields
class MyClass {
private:
#ifdef MLN_TRACY_ENABLE
    int64_t uniqueDebugId{generateDebugId()};
#endif
    // other members
};

This approach ensures that observability instrumentation provides maximum value during development and debugging while having zero impact on production performance.

---

consistent route nesting

Maintain consistent URL patterns and nesting structures across similar API endpoints to ensure predictable and intuitive interfaces. When designing routes for related resources, apply the same nesting strategy throughout the application rather than mixing top-level and nested approaches.

In the example, instance notes were nested under instances (/admin/instances/:instance_id/notes/:id) while similar resources like account moderation notes and report notes used top-level routes (/admin/account_moderation_notes/:id, /admin/report_notes/:id). This inconsistency makes the API harder to understand and use.

Choose one approach and apply it consistently:

# Consistent nested approach
/admin/instances/:instance_id/notes/:id
/admin/accounts/:account_id/moderation_notes/:id  
/admin/reports/:report_id/notes/:id

# OR consistent top-level approach
/admin/instance_notes/:id
/admin/account_moderation_notes/:id
/admin/report_notes/:id

Additionally, ensure resources are properly addressable by providing unique identifiers (like DOM IDs) that allow direct linking to specific items, enabling permalink functionality for better user experience and API usability.

---

Lock responsibly, always

Ensure proper management of locks and concurrent resources throughout their lifecycle. When implementing concurrency:

1. Encapsulate locking/unlocking in appropriate methods rather than duplicating code
2. Be mindful of which threads acquire locks and consider thread-safety implications
3. Implement proper timeout handling for waiting on concurrent operations
4. Account for race conditions during cleanup of concurrent resources

Example:

// Good: Locks encapsulated in methods where they're used
public String getResourcesCachePath() {
    resourcesCachePathLoaderLock.lock();
    try {
        // critical section operations
        return resourcesCachePath;
    } finally {
        resourcesCachePathLoaderLock.unlock();
    }
}

// For waiting on task queues, implement timeouts and handle potential race conditions
public int waitForEmpty(long timeoutMillis) {
    // Implementation that respects timeout and returns remaining tasks
    // without resetting timeout if new tasks are added
}

Avoid duplicating locking code across methods, and ensure locks are released in finally blocks to prevent deadlocks. When implementing methods that wait for concurrent operations to complete, provide sensible timeout options and consider the implications of race conditions.

---

Strict props event handling

Enforce strict typing and consistent handling of component props and events to ensure type safety, runtime validation, and maintainable component interfaces. Key guidelines:

1. Always declare prop types explicitly with runtime validators:

   export default {
     props: {
    value: {
      type: Number,
      required: true,
      validator: (val) => val >= 0
    },
    options: {
      type: Array,
      default: () => [] // Use function for object/array defaults
    }
     }
   }
   

2. Use typed emits declaration to enable proper type checking:

   export default {
     emits: {
    'update:modelValue': (value: number) => value >= 0,
    'change': (value: number, oldValue: number) => true
     }
   }
   

3. Maintain consistent event naming:
   • Use kebab-case for event names (e.g., ‘item-selected’)
   • Prefix v-model events with ‘update:’
   • Document event payload types
4. Validate props access:
   • Access props through defineProps in setup
   • Avoid direct mutation of props
   • Use computed properties for derived prop values

This ensures components are type-safe, self-documenting, and maintainable while preventing common runtime errors.

---

Maintain consistent code style

Follow project-wide code style conventions to ensure consistency and readability. Key practices include:

1. Use consistent spacing and formatting:
   • Maintain blank lines between test cases
   • Proper indentation and line breaks for imports
   • Follow established quote style (single vs double)
2. Prefer clean control flow:
   • Use early returns instead of nested if/else chains
   • Avoid unnecessary conditional nesting

Example of clean control flow:

// Instead of:
function isCoreComponent(tag: string): symbol | void {
  if (isBuiltInType(tag, 'Teleport')) {
    return TELEPORT
  } else if (isBuiltInType(tag, 'Suspense')) {
    return SUSPENSE
  } else if (isBuiltInType(tag, 'KeepAlive')) {
    return KEEP_ALIVE
  }
}

// Prefer:
function isCoreComponent(tag: string): symbol | void {
  if (isBuiltInType(tag, 'Teleport')) {
    return TELEPORT
  }
  if (isBuiltInType(tag, 'Suspense')) {
    return SUSPENSE
  }
  if (isBuiltInType(tag, 'KeepAlive')) {
    return KEEP_ALIVE
  }
}

Use automated tools like ESLint and Prettier to enforce consistent formatting. When making changes, ensure they align with the existing codebase style rather than introducing new patterns.

---

defensive null checking

Always perform explicit null and undefined checks before accessing object properties or methods to prevent runtime errors. This defensive programming approach ensures code robustness when dealing with potentially missing data.

When working with objects that might be null or undefined, implement multiple layers of validation:

const breadcrumbs = matches.map(({ pathname, routeContext }) => {
    if (!routeContext) return null
    if (!('getTitle' in routeContext)) return null
    if (!routeContext.getTitle) return null
    
    return {
        title: routeContext.getTitle(),
        path: pathname,
    }
})

This pattern prevents null reference errors by:

1. First checking if the object exists (!routeContext)
2. Then verifying the property exists ('getTitle' in routeContext)
3. Finally ensuring the method/property is truthy (!routeContext.getTitle)

Apply this approach consistently when accessing nested properties, calling methods on potentially undefined objects, or working with data that may not be fully populated. The small overhead of these checks prevents runtime crashes and makes code more reliable.

---

Configurable log formatting

Design logging systems with customizable formatting and output options. Separate formatting logic into protected methods that can be overridden by derived logger implementations.

Key practices:

1. Use consistent parameter naming (prefer json over asJSON)
2. Separate color handling from message composition
3. Make core formatting components overridable
4. Support environment variables for controlling features like colored output

Example of a well-structured logger with configurable formatting:

export class CustomizableLogger implements LoggerService {
  // Allow configuring output format
  constructor(protected options: { json?: boolean, timestamp?: boolean }) {}

  // Core logging implementation
  log(message: any, context?: string) {
    const formattedMessage = this.formatMessage(message, context, 'log');
    process.stdout.write(formattedMessage);
  }

  // Protected method for formatting - can be overridden
  protected formatMessage(message: unknown, context: string, logLevel: string): string {
    // For JSON output
    if (this.options.json) {
      return JSON.stringify({
        level: logLevel,
        message,
        context,
        timestamp: new Date().toISOString()
      }) + '\n';
    }

    // Regular formatted output with optional coloring
    const output = this.stringifyMessage(message);
    const contextMsg = context ? `[${context}] ` : '';
    const timestamp = this.options.timestamp ? this.getTimestamp() : '';
    const formattedLevel = this.colorize(logLevel.toUpperCase().padStart(7, ' '));
    
    return `${timestamp} ${formattedLevel} ${contextMsg}${output}\n`;
  }

  // Helper methods that can also be overridden
  protected stringifyMessage(message: unknown): string {
    return typeof message === 'object' ? JSON.stringify(message, null, 2) : String(message);
  }
  
  protected colorize(text: string, color?: (text: string) => string): string {
    // Default implementation or delegate to provided color function
    return color ? color(text) : text;
  }
  
  protected getTimestamp(): string {
    return new Date().toISOString();
  }
}

---

## Standardize logger configuration patterns

<!-- source: nestjs/nest | topic: Logging | language: TypeScript | updated: 2024-08-12 -->

Maintain consistent logger configuration and usage patterns across the application while leveraging built-in customization options. This promotes maintainable logging practices and ensures uniform log output.

Key guidelines:
1. Configure logging options at the application level rather than scattered throughout the code
2. Use protected methods for custom formatting when needed
3. Keep logger instances at the class level rather than creating new instances repeatedly
4. Utilize the built-in formatting options before creating custom solutions

Example of proper logger configuration and customization:

```typescript
// Global configuration
const app = await NestFactory.create(AppModule, {
  logger: {
    json: true,  // Configure JSON logging globally
  }
});

// Custom formatting when needed
class CustomLogger extends ConsoleLogger {
  protected formatMessage(
    pid: number,
    logLevel: string,
    context: string,
    timestampDiff: number,
    output: string,
  ): string {
    // Custom format implementation
    return `[${logLevel}] ${context}: ${output}`;
  }
}

// Class-level logger instance
@Injectable()
class MyService {
  private readonly logger = new Logger(MyService.name);
  
  someMethod() {
    this.logger.log('Operation completed');
  }
}

---

Reserve container capacity early

When using containers like unordered_map, unordered_set, or vectors in performance-critical code, always pre-allocate space by calling reserve() before adding elements. This prevents expensive rehashing or reallocation operations during insertion, which can cause significant performance degradation, especially in rendering loops or frequently called functions.

For string-heavy lookups and comparisons, consider using specialized containers like StringIndexer with unordered_set<StringIdentity> instead of storing and comparing raw strings directly.

Example:

// Suboptimal: May cause multiple reallocations
std::unordered_map<TextureID, TextureDesc> textureMap;
// Add many elements...

// Better: Pre-allocate expected capacity
std::unordered_map<TextureID, TextureDesc> textureMap;
textureMap.reserve(expectedCount); // Prevent rehashing during insertion
// Add many elements...

// Even better for string comparisons in hot paths:
std::unordered_set<StringIdentity> propertiesAsUniforms;
propertiesAsUniforms.reserve(expectedPropertyCount);
// This optimization can help with performance in methods called per frame

This simple practice can significantly reduce memory allocation overhead, especially in data structures accessed in rendering loops or hot paths in your graphics code.

---

Structured coroutine management

Always bind coroutine scopes to appropriate lifecycles and follow consistent patterns for asynchronous operations. Prefer suspending functions over class-based approaches when possible, and ensure proper job cancellation to prevent memory leaks.

For internal Kotlin code without Java interoperability requirements:

// Preferred: suspending function approach
suspend fun requestLocalUrl(url: String): ByteArray? = withContext(Dispatchers.IO) {
    loadFile(...)
}

// Instead of class-based approach with callback
class RequestTask(private val scope: CoroutineScope, private val onCompletion: ((ByteArray?) -> Unit)?) {
    fun execute(url: String) {
        scope.launch(Dispatchers.IO) { ... }
    }
}

When a class-based approach is necessary:

1. Document the intended lifecycle of the coroutine scope
2. Implement proper cancellation mechanism
3. Tie the scope to an appropriate lifecycle object
4. Consider returning the Job from launch operations for granular control

class AsyncOperation(lifecycleOwner: LifecycleOwner) {
    // Scope tied to lifecycle
    private val scope = lifecycleOwner.lifecycleScope
    
    fun execute(): Job = scope.launch(Dispatchers.IO) {
        // Work here
    }
    
    // Or with SupervisorJob for managing multiple concurrent tasks
    private val job = SupervisorJob()
    private val scope = CoroutineScope(Dispatchers.IO + job)
    
    fun cancel() {
        job.cancel() // Cancels all child jobs
    }
}

For any asynchronous work, maintain consistency by using coroutines with appropriate dispatchers rather than raw threads.

---

Align configurations with usage

Configuration files should accurately reflect the actual requirements and characteristics of your codebase. When setting up TypeScript configurations:

1. Match language settings to feature usage: Ensure settings like target and lib correctly align with the ECMAScript features your code actually uses.

// Good: Correctly specified to support Array.prototype.includes
{
  "compilerOptions": {
    "target": "es2015",
    "lib": ["es2016", "dom"]
  }
}

// Bad: Using inconsistent or inappropriate settings
{
  "compilerOptions": {
    "target": "es2015",
    "lib": ["esnext", "dom"] // Too broad, or "es2015" would be too restrictive
  }
}

1. Create modular configurations: Maintain separate configuration files for different parts of the project instead of overloading a single configuration file. This provides better control over component-specific settings.

For example, consider creating a separate tsconfig for private packages rather than adding them to the root configuration’s include paths.

---

Benchmark before optimizing

When making performance-critical decisions, always validate your approach with benchmarks using realistic data sizes and use cases rather than relying on theoretical assumptions.

For data access patterns, benchmark different approaches with varying data sizes:

// Example benchmark comparing Array, Map and Object lookups
function runBenchmark(dataSize, iterations) {
  const data = generateTestData(dataSize);
  const structures = prepareDataStructures(data);

  const structureTypes = ['array', 'map', 'object'];
  const results = {};
  const queryKeys = Array.from({ length: iterations }, () =>
    structures.arr[Math.floor(Math.random() * dataSize)].key
  );

  structureTypes.forEach(structure => {
    const start = performance.now();
    queryKeys.forEach(key => runQuery(structure, key, structures));
    const end = performance.now();
    results[structure] = end - start;
  });

  console.log(`Data size: ${dataSize}, Iterations: ${iterations}`);
  structureTypes.forEach(structure => {
    console.log(`${structure}: ${results[structure]}ms`);
  });
}

When optimizing loops or operations on collections, compare functional approaches (map/filter) against traditional loops with measurements rather than intuition:

// Quick performance comparison
function benchmarkApproaches() {
  console.time('functional');
  const result1 = array.map(process).filter(isValid);
  console.timeEnd('functional');
  
  console.time('for-loop');
  const result2 = [];
  for (const item of array) {
    const processed = process(item);
    if (isValid(processed)) {
      result2.push(processed);
    }
  }
  console.timeEnd('for-loop');
}

Consider early termination when applicable (finding first match vs processing all elements), and test with various data sizes that represent your actual workload. Balancing readability with performance is essential - only sacrifice readability when benchmarks demonstrate a significant performance advantage in performance-critical paths.

---

Handle errors by severity

Choose error handling mechanisms based on error severity and recoverability:

1. Use throws for unrecoverable errors that prevent system operation:

   VkResult result = vmaCreateAllocator(&allocatorCreateInfo, &allocator);
   if (result != VK_SUCCESS) {
    throw std::runtime_error("Vulkan allocator init failed");
   }
   

2. Use callbacks/return values for recoverable errors:

   HeadlessFrontend::RenderResult render(Map& map, std::exception_ptr *error) {
    map.renderStill([&](const std::exception_ptr& e) {
        if (e) { *error = e; }
    });
   }
   

3. Use assertions only for developer-time invariant checking, not for runtime error handling.

Critical errors that prevent system operation should throw exceptions. Recoverable errors should be propagated via return values or callbacks to allow graceful handling. Assertions should only validate development-time invariants and not be used for runtime error handling since they’re removed in release builds.

---

Externalize config values

Replace hardcoded “magic numbers” and environment-specific logic with externally configurable values. Use preprocessor definitions, build flags, or configuration constants to make your code adaptable to different environments and requirements.

For numeric constants, define them as configurable parameters:

// BAD: Hardcoded magic numbers
const std::vector<vk::DescriptorPoolSize> poolSizes = {
    {vk::DescriptorType::eUniformBuffer, 10000},
    {vk::DescriptorType::eCombinedImageSampler, 5000},
};

// GOOD: Configurable via build flags
#ifndef MLN_VULKAN_DESCRIPTOR_POOL_SIZE
#define MLN_VULKAN_DESCRIPTOR_POOL_SIZE 10000
#endif

const std::vector<vk::DescriptorPoolSize> poolSizes = {
    {vk::DescriptorType::eUniformBuffer, MLN_VULKAN_DESCRIPTOR_POOL_SIZE},
    {vk::DescriptorType::eCombinedImageSampler, MLN_VULKAN_DESCRIPTOR_POOL_SIZE/2},
};

For feature-specific or platform-specific code, use preprocessor conditionals:

// Only load extensions when the related feature is enabled
#ifdef MLN_USE_TRACY
extension::loadTimeStampQueryExtension(fn);
#endif

// Handle platform-specific behavior
#if !defined(__QT__)
TEST(Image, WebPTile) {
    // Test implementation
}
#endif

This approach improves maintainability, makes platform-specific behavior explicit, and allows for customization without code changes.

---

prefer testing libraries

When testing components, use established testing libraries like @testing-library/svelte instead of low-level DOM manipulation approaches. Low-level testing with direct mount/unmount and querySelector calls is brittle and requires frequent updates when component structure changes. Testing libraries provide user-focused APIs that are more robust to implementation changes.

// Avoid: Low-level DOM testing
test('Component', () => {
  const component = mount(Component, {
    target: document.body,
    props: { initial: 0 }
  });
  
  expect(document.body.innerHTML).toBe('<button>0</button>');
  document.body.querySelector('button').click();
  flushSync();
  expect(document.body.innerHTML).toBe('<button>1</button>');
  
  unmount(component);
});

// Prefer: Testing library approach
test('Component', async () => {
  const user = userEvent.setup();
  render(Component, { props: { initial: 0 } });
  
  const button = screen.getByRole('button');
  expect(button).toHaveTextContent('0');
  
  await user.click(button);
  expect(button).toHaveTextContent('1');
});

Testing libraries focus on how users interact with your components rather than implementation details, making tests more maintainable and less likely to break when refactoring component structure.

---

Document containerized builds

When using Docker for build environments, provide complete, tested instructions that users can copy-paste without modification. Include proper user permission handling to prevent file ownership issues, and ensure commands work as documented.

For example, instead of generic placeholders:

# DON'T
docker run --rm -it -v "$PWD:/code/" -u $(id -u):$(id -g) maplibre-native-image ___any_build_command___

Provide specific working examples:

# DO
docker build \
  -t maplibre-native-image \
  --build-arg USER_ID=$(id -u) \
  --build-arg GROUP_ID=$(id -g) \
  -f platform/linux/Dockerfile \
  platform/linux

# Run all build commands using the docker container
docker run --rm -it -v "$PWD:/code/" maplibre-native-image

This ensures reproducible builds across different developer environments and CI/CD pipelines, reduces setup time, and prevents “works on my machine” issues.

---

Style-compliant example code

Example code in documentation and tutorials should adhere to project style guidelines and demonstrate best practices. Avoid using internal classes or implementation details that are inaccessible to users. Instead, use public APIs and concrete resources that developers can directly copy into their applications.

For instance, instead of using test-specific utilities:

this.maplibreMap.setStyle(
    Style.Builder().fromUri(TestStyles.getPredefinedStyleWithFallback("Streets"))
)

Use concrete, accessible resources:

this.maplibreMap.setStyle(
    Style.Builder().fromUri("https://demotiles.maplibre.org/style.json")
)

Similarly, when demonstrating architecture patterns (like in SwiftUI), follow established best practices even if they require additional complexity. Since developers often copy example code directly into their projects, prioritize teaching proper patterns over shortcuts. This principle extends to all examples regardless of language or framework—always prefer clarity, correctness, and adherence to project style guidelines over brevity.

---

Use proper HTTP utilities

When handling HTTP cookies and headers, use dedicated utility functions instead of manual string manipulation. Manual parsing of HTTP headers, especially cookies, can lead to incorrect behavior due to the complexity of HTTP header formats.

For cookie handling, prefer established utilities like splitCookiesString from h3 or native browser APIs like headers.getSetCookie() over manual string splitting:

// ❌ Avoid manual cookie parsing
const cookies = (res.headers.get('set-cookie') || '').split(',')

// ✅ Use proper utilities
import { splitCookiesString } from 'h3'
const cookies = splitCookiesString(res.headers.get('set-cookie') || '')

// ✅ Or use native browser API
const cookies = res.headers.getSetCookie()

This approach ensures correct parsing of complex cookie values that may contain commas, semicolons, or other special characters that would break simple string splitting. Always verify that utility functions are available in your target environment before using them.

---

Include database-specific migration dependencies

When implementing database migrations with tools like Flyway, ensure you include the appropriate database-specific dependency for your target database. As of Flyway V10.0.0, all databases except in-memory or file-based ones (such as H2 or SQLite) require their own specific dependency package.

For example:

• For PostgreSQL: org.flywaydb:flyway-database-postgresql
• For MySQL: org.flywaydb:flyway-mysql

Note that not all database modules follow the same naming pattern. Always consult the official documentation (https://documentation.red-gate.com/flyway/flyway-cli-and-api/supported-databases) for the most current information about required dependencies for your specific database platform.

Including the correct database-specific dependency is essential for successful schema migrations and prevents runtime errors when your application attempts to initialize the database.

---

prefer != null comparisons

When checking for null or undefined values, prefer the concise != null comparison over explicit checks or array-based methods. This pattern effectively handles both null and undefined while preserving other falsy values like false, 0, or empty strings.

The != null pattern is more readable and performant than alternatives:

// Preferred: Concise and clear
const hasCachedData = () => options.getCachedData!(key) != null

// Avoid: Verbose explicit checks
const hasCachedData = () => {
  const data = options.getCachedData!(key)
  return data !== null && data !== undefined
}

// Avoid: Array-based inclusion checks
const hasCachedData = () => ![null, undefined].includes(options.getCachedData!(key) as any)

For cases requiring additional type safety, combine null checks with type validation:

// Good: Null check with type validation
if (!rawVersion || typeof rawVersion !== 'string') {
  return
}

// Good: Explicit equality for specific values
if (result === true) {
  // Handle confirmed true, not just truthy
}

This approach maintains null safety while keeping code concise and avoiding unnecessary complexity in most common scenarios.

---

Exclude sensitive configurations

Do not commit sensitive, time-limited, or environment-specific configuration files to version control. Instead:

1. For files with expiration dates (like SSL certificates):
   • Provide clear generation instructions in documentation
   • Consider using auto-generation tools or modules
   • Add these files to .gitignore
2. For environment-specific configurations:
   • Use template files with placeholders (e.g., config.example.js)
   • Document the required configuration parameters
   • Ensure all sensitive files are in .gitignore

Example of proper .gitignore usage:

# npm
node_modules
package-lock.json
npm-shrinkwrap.json

# Security
*.pem
*.key
*.crt

Example of documentation in README.md:

## Setup
Before running the example, generate the required SSL certificates:

```bash
openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365 -nodes

---

## Add interactive element roles

<!-- source: shadcn-ui/ui | topic: Security | language: TSX | updated: 2024-06-30 -->

When adding event handlers like `onClick` to non-interactive elements such as `div`, always include appropriate ARIA roles and keyboard event handlers. This prevents accessibility issues and reduces security vulnerabilities by ensuring all interactive elements are properly identified and managed.

Non-interactive elements with click handlers but without proper roles can be overlooked in security audits and create potential attack vectors through inconsistent input validation.

**Bad:**
```jsx
<div 
  className="stepper__vertical-step"
  onClick={() => handleStepClick(index)}
>
  {content}
</div>

Good:

<div 
  className="stepper__vertical-step"
  role="button"
  tabIndex={0}
  onClick={() => handleStepClick(index)}
  onKeyDown={(e) => {
    if (e.key === 'Enter' || e.key === ' ') {
      handleStepClick(index);
    }
  }}
>
  {content}
</div>

Better yet, use a semantic element when possible:

<button 
  className="stepper__vertical-step"
  onClick={() => handleStepClick(index)}
>
  {content}
</button>

This approach ensures both accessibility compliance and proper security by ensuring all interactive elements are consistently implemented and validated.

---

validate client inputs

Always validate and sanitize client-provided data on the server side before processing. Client-side data, including form inputs, query parameters, and request bodies, should never be trusted without proper validation as it can be easily manipulated by malicious users.

This applies to all data sources from the client:

• Form data (including hidden fields)
• URL parameters
• Request headers
• JSON payloads

Example of proper server-side validation:

const yourFn = createServerFn('POST', async (formData: FormData) => {
  const rawVal = formData.get('val');
  
  // Validate and sanitize the input
  if (typeof rawVal !== 'string' || !rawVal.trim()) {
    throw new Error('Invalid input: val must be a non-empty string');
  }
  
  const val = rawVal.trim();
  
  // Additional validation based on expected format
  if (!/^\d+$/.test(val)) {
    throw new Error('Invalid input: val must be numeric');
  }
  
  const numericVal = parseInt(val, 10);
  // Now safe to use numericVal
})

Never assume client data is safe or correctly formatted, even if your client-side code generates it correctly.

---

Cancel aborted async operations

When working with async operations that can be aborted (like HTTP requests), ensure proper cancellation of related promises and deferred operations to prevent memory leaks and unnecessary work. This applies to both operations created after abortion has occurred and those created before abortion.

For operations created after abortion, check the abort signal before proceeding:

let result = await handler(args);
if (args.request.signal.aborted && isDeferredData(result)) {
  result.cancel();
}

For operations created before abortion, set up abort listeners to handle cancellation:

if (isDeferredData(result)) {
  if (request.signal.aborted) {
    result.cancel();
  } else {
    let deferResult = result;
    request.signal.addEventListener("abort", () => deferResult.cancel());
  }
}

This pattern prevents resource leaks and ensures that aborted requests don’t continue consuming system resources. Always consider both the proactive case (already aborted) and reactive case (abort during execution) when implementing cancellation logic.

---

Handle SSR hydration mismatches

When implementing server-side rendering, proactively handle scenarios where server and client rendering may produce different outputs to prevent hydration errors. This commonly occurs with dynamic URLs, route matching, and encoded characters.

Implement defensive coding practices that gracefully handle these mismatches:

1. Clear conflicting server state when client routing takes precedence:

   // Clear SSR 404s when client routes match
   if (matchedPropRoute) {
     for (let [routeId, error] of Object.entries(hydrationData.errors)) {
    if (isRouteErrorResponse(error) && error.status === 404) {
      delete hydrationData.errors[routeId];
    }
     }
   }
   

2. Normalize URLs to match client-side encoding:

   function safelyEncodeSsrHref(to: To, href: string): string {
     let path = typeof to === "string" ? parsePath(to).pathname : to.pathname;
     if (!path || path === ".") {
    try {
      let encoded = new URL(href, "http://localhost");
      return encoded.pathname + encoded.search;
    } catch (e) {
      // no-op - no changes if we can't construct a valid URL
    }
     }
     return href;
   }
   

While some hydration flickering may be unavoidable in edge cases, proper error handling ensures the application recovers gracefully and maintains functionality.

---

Document mutex usage

Always document mutex fields and their purpose, ensure proper locking/unlocking patterns, and avoid redundant locks when underlying structures are already thread-safe. When using mutexes, clearly indicate what data they protect and why the synchronization is necessary.

Add comments for mutex fields explaining their purpose:

// sendfilesMutex protects concurrent access to sendfiles slice
sendfilesMutex sync.RWMutex

Avoid redundant locking when underlying structures already provide thread safety:

// The mu mutex in the Middleware struct might be redundant for operations 
// on the Session since Session struct itself already ensures thread-safety

Use proper defer patterns to prevent race conditions, even if slightly slower:

mutex.Lock()
defer mutex.Unlock() // Prevents race conditions on shared data access
return c.Status(fiber.StatusOK).JSON(data)

Consider performance implications when choosing between sync.Map and regular maps with RWMutex, but prioritize correctness and clarity over micro-optimizations.

---

optimize CI/CD configurations

Review CI/CD workflow configurations for both performance optimizations and accuracy in conditional logic. This includes minimizing resource usage where possible and ensuring all conditional statements use correct values.

For performance, avoid fetching unnecessary git history by using minimal fetch depth:

- uses: actions/checkout@v4
  with:
    ref: ${{ steps.pr.outputs.head_sha }}
    fetch-depth: 1  # Only fetch the specific commit, not full history

For accuracy, verify that conditional statements reference correct repository names, environment variables, and other identifiers:

if: ${{github.event_name == 'push' || github.repository == 'nuxt/nuxt'}}  # Correct repo name

These optimizations reduce build times, minimize resource consumption, and prevent workflow failures due to incorrect conditions.

---

Validate CI/CD timing checks

When implementing timing-based security checks in CI/CD workflows, ensure that timestamp comparisons use tamper-proof data sources that cannot be manipulated through commit history manipulation or force pushes. Always verify that the timestamps being compared (such as PR updated_at vs comment created_at) come from authoritative sources that reflect actual events rather than potentially forgeable commit metadata.

Example from GitHub workflows:

- name: Get PR Info
  run: |
    pr="$(gh api /repos/${GH_REPO}/pulls/${PR_NUMBER})"
    updated_at="$(echo "$pr" | jq -r .updated_at)"
    # Use PR updated_at (push date) rather than commit timestamps
    # which could potentially be manipulated
    if [[ $(date -d $updated_at) > $(date -d $COMMENT_AT) ]]; then exit 1; fi

This prevents timing-based bypass attempts where an attacker might try to manipulate commit timestamps or use force pushes to circumvent security checks. The PR updated_at field represents the actual push date and cannot be forged through commit manipulation.

---

Use Suspense Only When Ready

In Next.js SSR/app-router, do not use useSuspenseQuery unless your server prefetch + hydration setup guarantees the data is already in the cache such that the component will not suspend.

Why: with standard hydration, if the query isn’t actually present on the client yet, useSuspenseQuery may suspend and you’ll get undesirable loading/empty HTML or server/client state mismatch. If you can’t guarantee “no suspend,” prefer useQuery (so the component renders with isLoading/pending state instead of relying on Suspense streaming).

Apply this rule:

• If you use the “dehydrate pending queries” + streaming-friendly pattern (v5.40+), useSuspenseQuery can be appropriate because pending promises can be hydrated and consumed.
• Otherwise (common case with the standard HydrationBoundary + awaited prefetch), use useQuery in the client component to avoid Suspense-related mismatches.

Also keep SSR hydration details correct:

• For non-JSON serialization, deserialize on the client via hydrate.transformPromise.
• Ensure prefetchQuery({ queryFn }) uses a function queryFn: () => getPosts().then(serialize).

Example (safe default for app-router with awaited prefetch):

// app/posts/page.tsx (Server)
import { dehydrate, HydrationBoundary, QueryClient } from '@tanstack/react-query'
import Posts from './posts'
import { getPosts } from './api'

export default async function PostsPage() {
  const queryClient = new QueryClient()
  await queryClient.prefetchQuery({
    queryKey: ['posts'],
    queryFn: getPosts,
  })

  return (
    <HydrationBoundary state={dehydrate(queryClient)}>
      <Posts />
    </HydrationBoundary>
  )
}

// app/posts/posts.tsx (Client)
'use client'
import { useQuery } from '@tanstack/react-query'
import { getPosts } from './api'

export default function Posts() {
  const { data } = useQuery({ queryKey: ['posts'], queryFn: getPosts })
  return <div>{data?.length}</div>
}

---

Minimize lock contention

When implementing thread-safe code, minimize the scope and duration of locks to reduce contention and improve performance. Keep critical sections small, avoid redundant operations under locks, and consider whether pessimistic locking is appropriate for your use case.

Key practices:

1. Keep critical sections small and focused:

   // Bad: Doing extra work under lock
   synchronized (lock) {
       result = computeExpensiveOperation();
       sharedState.update(result);
   }
      
   // Good: Only synchronize the state update
   result = computeExpensiveOperation();
   synchronized (lock) {
       sharedState.update(result);
   }
   

2. Avoid redundant writes to shared/volatile fields:

   // Bad: Multiple writes to volatile field
   synchronized (this) {
       this.cachedFieldValue = desc;
       // More logic...
       this.cachedFieldValue = new ShortcutDependencyDescriptor(...);
   }
      
   // Good: Single write using local variable
   synchronized (this) {
       Object cachedFieldValue = desc;
       // More logic...
       if (condition) {
           cachedFieldValue = new ShortcutDependencyDescriptor(...);
       }
       this.cachedFieldValue = cachedFieldValue;
   }
   

3. Choose appropriate concurrency primitives:
   • Use ReadWriteLock for read-heavy workloads
   • Consider lock-free alternatives like ConcurrentHashMap and atomic variables
   • In reactive code, prefer optimistic locking with CAS operations over pessimistic locks
4. Be aware of hidden performance costs:
   • Collection operations like size() on linked structures may require traversal
   • Improper lock granularity can cause contention hotspots
   • Consider thread scheduling and context switching overhead

---

Optimize hot paths

When writing code that will be executed frequently (hot paths), prioritize performance optimizations that reduce overhead. This includes:

1. Move expensive operations out of frequently executed blocks: Place resource-intensive operations like require() calls at module initialization rather than in request handlers or response methods.

// Poor performance: Loading module on every response
res.send = function send(body) {
  // ...
  if (isChunkBlob) {
    var WritableStream = require('stream/web').WritableStream; // ❌ Executed on each call
    // ...
  }
};

// Improved: Load once at module initialization
const { WritableStream } = require('stream/web'); // ✅ Loaded once

res.send = function send(body) {
  // ...
  if (isChunkBlob) {
    // WritableStream is already available
    // ...
  }
};

1. Use direct property assignments when values are trusted: Avoid unnecessary method calls that add function invocation overhead.

// Less efficient with method call overhead:
this.status(status); // ❌ Additional function call overhead

// More efficient direct assignment when appropriate:
this.statusCode = status; // ✅ Direct assignment is faster

1. Prefer traditional loops over higher-order functions: Use for loops instead of array methods with callbacks to avoid closure creation overhead.

// Less efficient with closure overhead:
this.tracers.forEach(function(tracer) { // ❌ Creates closures
  tracer(app, req, res, event, date, args);
});

// More efficient:
for (let i = 0; i < this.tracers.length; i++) { // ✅ Avoids closure overhead
  this.tracers[i](app, req, res, event, date, args);
}

1. Minimize object creation: Avoid creating temporary objects in frequently executed paths, as object allocation and garbage collection are expensive.

// Expensive - creating objects in a loop:
for (var i = 0; i < this.root.length; i++) {
  context = { root: this.root[i] }; // ❌ Creating objects each iteration
  match = this.lookup.call(context, path);
}

// Better - reuse objects or restructure code:
const context = {}; // ✅ Create once
for (var i = 0; i < this.root.length; i++) {
  context.root = this.root[i]; // Modify existing object
  match = this.lookup.call(context, path);
}

These optimizations are most impactful in code that executes frequently, such as middleware, request handlers, and utility functions used in tight loops. Always verify performance improvements with benchmarks when making changes to critical paths.

---

Explicit security configurations

When configuring security-related features, always use the most specific configurer classes to make security decisions explicit and improve code readability. For example, when disabling CSRF protection in Spring Security, use CsrfConfigurer::disable instead of the more generic AbstractHttpConfigurer::disable:

// Prefer this (explicit about what security feature is being disabled)
http.csrf(CsrfConfigurer::disable);

// Instead of this (less explicit)
http.csrf((csrf) -> csrf.disable());
// or
http.csrf(AbstractHttpConfigurer::disable);

This practice improves code clarity, makes security decisions more visible during code reviews, and helps prevent misunderstandings about which security features are being modified. By using type-specific configurers, the code self-documents which security features are being configured, making it easier to audit and maintain security settings over time.

---

Document platform requirements

When setting or changing minimum platform version requirements, always document the specific technical reasons for these decisions. Include:

1. Features or APIs that necessitate the change (e.g., std::filesystem requiring macOS 10.15+)
2. Impact analysis on backward compatibility
3. Market considerations (e.g., iOS version distribution)

For libraries, consider using conditional compilation to support optional features that require newer platform versions while maintaining core functionality for older versions:

// Example showing conditional use of std::filesystem
#if defined(__APPLE__)
  #include <TargetConditionals.h>
  #if TARGET_OS_MAC
    #if MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_15
      // Use std::filesystem
      #include <filesystem>
      namespace fs = std::filesystem;
    #else
      // Use alternative implementation
      #include "custom_filesystem.hpp"
      namespace fs = custom_filesystem;
    #endif
  #endif
#endif

// Similarly for iOS:
#if defined(__APPLE__) && TARGET_OS_IOS
  #if __IPHONE_OS_VERSION_MIN_REQUIRED >= __IPHONE_13_0
    // Use iOS 13+ features
  #else
    // Fallback implementation
  #endif
#endif

Always validate platform-specific dependencies against your minimum version requirements. When library dependencies change (e.g., GLES versions), ensure compatibility with your stated platform minimums to avoid runtime failures.

---

Default to minimum permissions

Always default to the least invasive privacy settings and explicitly request elevated permissions only when necessary for specific functionality. For location-based features, start with reduced accuracy and request precise location only when required with a clear purpose explanation.

Configure your app’s Info.plist with keys like NSLocationDefaultAccuracyReduced to indicate your app can function with reduced permissions by default. This follows the security principle of least privilege and respects user privacy.

Example:

// In your view model
@Published var locationAccuracy: LocationAccuracyState = .unknown

// Only request higher permissions when necessary with clear purpose
func requestPreciseLocation() {
    if locationAccuracy == .reducedAccuracy {
        let purposeKey = "PreciseLocationPurposeKey" // Defined in InfoPlist.strings
        locationManager.requestTemporaryFullAccuracyAuthorization(withPurposeKey: purposeKey)
    }
}

When implementing location features, be careful with properties like showsUserLocation = true that might trigger permission requests immediately. Instead, design your app to request permissions contextually when users access specific features that require those permissions.

---

Accessible security indicators

Ensure all security-related UI elements such as warnings, error messages, and destructive action buttons meet WCAG contrast standards. Poor contrast in these elements creates an accessibility issue that can prevent users from noticing important security warnings or destructive actions, potentially leading to security vulnerabilities.

Before implementing color changes, verify contrast ratios using tools like WebAIM’s contrast checker (https://webaim.org/resources/contrastchecker/).

Example:

/* GOOD: Verified accessible destructive color */
:root {
  --destructive: 0 72.8% 47%;
  --destructive-foreground: 210 20% 98%; /* Ensure this has sufficient contrast with destructive */
}

/* Before committing color changes, add a comment confirming accessibility */
/* Contrast ratio verified: 4.6:1 against white background, passes WCAG AA */

---

Maintain Predictable Configs

Configuration files should be predictable for every developer and remain maintainable over time.

• Prefer explicit, stable values in runtime/version files (pin a specific version) so nvm use/install instructions work consistently. If you use an alias (like an LTS channel), ensure the exact alias form is supported (e.g., correct casing) and document why the alias is used.
• Keep config exception lists (spellchecks, dictionaries, rule overrides) small and scoped. Avoid large catch-all lists; instead, prune them, and for test/local-only terms prefer exclusions or consistent “known words.”

Example (.nvmrc):

# Pin for predictability
v22.2.0

# Or, if using an alias, ensure it matches what nvm supports
lts/iron

Example (cspell in ESLint config):

// Don’t let words[] grow unbounded—only keep truly shared terms.
// For test/local-only terms, prefer updating the spelling in code,
// adding targeted ignore patterns, or using exclusions rather than expanding the global list.

---

Evolve APIs gracefully

When modifying or extending APIs, prioritize backward compatibility while providing clear migration paths for future changes. Follow these practices:

1. Mark deprecated APIs clearly rather than removing them immediately:

   // Good: Keeping backward compatibility with clear deprecation notice
   export const isGloballyAllowed = /*#__PURE__*/ makeMap(GLOBALS_ALLOWED)
   /** @deprecated use `isGloballyAllowed` instead */
   export const isGloballyWhitelisted = isGloballyAllowed
   

2. Support both old and new parameters by normalizing internally:

   // Good: Supporting both boolean and string namespace types
   mount(
     rootContainer: HostElement | string,
     isHydrate?: boolean,
     namespace?: ElementNamespace | boolean // Support both forms
   ) {
     // Internally normalize boolean to string representation
     if (typeof namespace === 'boolean') {
    namespace = namespace ? 'svg' : undefined
     }
     // ...implementation
   }
   

3. Consider custom renderer implementations when adding new methods to core interfaces, as they constitute breaking changes for implementers.

4. Follow web standards when implementing attribute behaviors, particularly for custom elements:

   // Following HTML spec for boolean attribute behavior
   if (name === 'bar' && value === '') {
     // Treat empty string as true per HTML spec
     return true
   }
   

5. Use TypeScript interfaces to enforce precise API contracts and accurately reflect browser behavior for event types and DOM interactions.

When uncertain about a change, consider adding a deprecation notice and providing the new approach in parallel rather than breaking existing code.

---

Design for API extension

When designing APIs, prioritize extensibility by providing clear extension points and avoiding direct exposure of implementation details. This allows for future enhancements without breaking compatibility.

Key practices:

1. Use interface-based designs over concrete classes
2. Provide extension hooks through protected methods or customization functions
3. Consider future use cases in method signatures
4. Favor composition over inheritance for flexibility

Example of good API design with extension points:

// Instead of directly exposing implementation:
public class HttpConnector {
    private HttpContext createContext() {
        return new HttpContext();
    }
}

// Provide extension hooks:
public class HttpConnector {
    // Allow customization through function
    public HttpConnector(BiFunction<HttpMethod, URI, HttpContext> contextProvider) {
        this.contextProvider = contextProvider;
    }
    
    // Protected methods for subclass customization
    protected HttpContext createContext(HttpMethod method, URI uri) {
        return contextProvider.apply(method, uri);
    }
}

This approach:

• Enables customization without breaking changes
• Keeps implementation details private
• Provides clear extension points
• Maintains backward compatibility

---

Prefer safe DOM manipulations

When manipulating DOM content, prefer safer alternatives to innerHTML when possible to prevent Cross-Site Scripting (XSS) vulnerabilities. For example, when clearing element content, use textContent instead of innerHTML:

// Avoid this (potential XSS risk)
container.innerHTML = '';

// Prefer this (safer alternative)
container.textContent = '';

For cases where HTML parsing is necessary, implement Trusted Types policies with minimal permissions, defining only the functions you absolutely need (e.g., just createHTML if that’s all you’re using). When supported by browsers, consider using built-in helpers like emptyHTML() for better performance and security.

---

distinguish falsy vs nullish

When handling potentially null or undefined values, carefully choose between the logical OR (||) and nullish coalescing (??) operators based on whether you want to preserve other falsy values.

The || operator treats all falsy values (null, undefined, false, 0, “”, NaN) as “missing” and provides the fallback. The ?? operator only treats null and undefined as “missing”, preserving other falsy values like empty strings or false booleans.

Use || when: You want to reject all falsy values and provide a default.

// Reject empty strings, use default
pathname: locationProp.pathname || "/"

Use ?? when: You want to preserve legitimate falsy values but handle null/undefined.

// Allow false, "", 0 but handle null/undefined
state: locationProp.state ?? null

Avoid || when falsy values are valid: Using || can cause bugs by rejecting legitimate values.

// BAD: Rejects "", false, 0, NaN as valid state values
state: locationProp.state || null

// GOOD: Only rejects null/undefined
state: locationProp.state ?? null

Consider bundle size implications when using ?? in environments with older transpilation targets, and use explicit null checks as an alternative: value != null ? value : fallback.

---

Follow library recommendations

When writing tests, prioritize following the official recommendations and best practices of testing libraries (like Playwright) even if they appear more verbose than alternatives. Library recommendations typically address edge cases, improve reliability, and future-proof your tests.

For example, prefer:

// Recommended approach
const errorSelector = page.locator('.MuiInputBase-root.Mui-error');
await errorSelector.waitFor();

Instead of:

// Discouraged approach
await page.waitForSelector('.MuiInputBase-root.Mui-error');

This applies to all testing libraries and frameworks. While deprecated or discouraged methods might sometimes appear cleaner or more straightforward, the recommended approaches usually incorporate lessons learned from the wider community and prevent subtle issues from arising in different environments or future versions.

---

Define Validation Contracts

When adding/maintaining API validation schemas, make the input contract explicit: specify exactly what input types are accepted, and whether the schema is parsing (strict mapping) or coercing/converting values. Don’t rely on assumptions about built-in JS semantics or on a single runtime’s concrete types.

Apply these rules:

• Boolean: If the API accepts boolean-like strings, confirm the semantics. z.string().boolean() does not match Boolean()/MDN behavior—use z.coerce.boolean() when you want JS Boolean()-style coercion.
• Dates: Use z.date() only for actual Date objects. If the API accepts date strings too, explicitly convert via z.preprocess.
• Cross-runtime files: Don’t couple validation to “browser File only” if your API is used in Node/Deno too. Validate a shared file contract (e.g., size, type, etc.) or create separate schemas per runtime.
• Deprecations: Avoid deprecated Zod helpers in public schemas; use current equivalents (e.g., z.string().min(1) instead of deprecated nonempty).

Example (date + boolean semantics):

import { z } from "zod";

// Dates: accept both Date and ISO strings
const dateSchema = z.preprocess((arg) => {
  if (typeof arg === "string" || arg instanceof Date) return new Date(arg);
}, z.date());

// Booleans: choose semantics explicitly
const strictLogicalBool = z.string().boolean(); // accepts specific strings like "TRUE"/"False"
const jsBooleanLike = z.coerce.boolean();       // matches JS Boolean() coercion semantics

---

Explicit null handling

Treat null/undefined and “absence vs presence” as first-class concerns.

• TypeScript: Keep null safety effective by ensuring strictNullChecks is enabled and not overridden by extended configs (explicitly set it to true if needed).
• Zod runtime: Decide what should happen when input is undefined vs when it is a wrong value or null.
  • Use .default(value) for absent inputs (typically undefined).
  • Use .catch(fallback) for parsing failures (including wrong strings), not as a substitute for handling undefined.
• Form inputs: Don’t assume “required field” means “non-empty”. Browsers/DOM often send "" for an “empty” required field; z.string() will accept "" as a valid string. If you require non-empty content, validate it explicitly (e.g., .min(1)).

Example:

import { z } from "zod";

const boolSchema = z.string().boolean();

// absent (undefined) -> fallback
const withDefault = boolSchema.default(false);

// wrong value (including "other" / null if you pass it in) -> fallback
const withCatch = boolSchema.catch(false);

// non-empty string required by UI
const requiredText = z.string().min(1, "Required");

Apply these consistently so validation behavior matches what your types and UI expectations actually mean.

---

Deterministic Parse Fallbacks

When parsing inputs that may be invalid (e.g., string → boolean), do not rely on implicit/unclear failure behavior. Instead, decide explicitly how parse errors should be handled and make it deterministic.

Apply this by:

• Using a safe fallback for parse errors (e.g., Zod .catch(...)) so invalid values consistently map to a chosen boolean.
• Ensuring the parsing semantics match your intent: z.string().boolean() uses logical string values (like “true”/”false”), which may differ from TypeScript/JS Boolean() behavior—use z.coerce.boolean() when you want coercion semantics.

Example (explicit error recovery to a boolean):

import { z } from "zod";

// Logical boolean parsing with deterministic fallback on error
const b = z.string()
  .boolean()
  .catch(() => false); // whenever parsing fails

b.parse("true");   // true
b.parse("False");  // false
b.parse("other");  // false (fallback)

If you expect JS-like coercion semantics instead of strict logical strings, prefer:

const b = z.coerce.boolean();

---

Pin action commit hashes

Always pin third-party GitHub Actions to specific commit hashes rather than semantic version tags (like @v1). This prevents automatic execution of potentially malicious code if the maintainer updates the tag. Additionally, minimize permission scopes for any tokens used in workflows, and consider replacing third-party actions with direct implementations when feasible.

Example - Instead of:

- name: Repository Dispatch
  uses: peter-evans/repository-dispatch@v1

Use commit hash pinning:

- name: Repository Dispatch
  uses: peter-evans/repository-dispatch@a328d6e8c37ac0b002f76abbdd3cfe2908502656

Even better, consider replacing with native functionality:

- name: Repository Dispatch
  run: |
    curl -X POST \
      -H "Authorization: token ${{ secrets.GITHUB_TOKEN }}" \
      -H "Accept: application/vnd.github.v3+json" \
      https://api.github.com/repos/owner/repo/dispatches \
      -d '{"event_type":"build_application"}'

---

Semantic HTML usage

Use HTML elements according to their semantic purpose to ensure proper accessibility and code organization. Choose elements based on their intended role, not just how they appear visually:

1. Use <nav> only for sections containing navigation links, not for containers with single links or static content
2. Place <footer> appropriately within document structure (can be inside <article> or <section>)
3. Use role="button" for links that behave like buttons rather than navigation

Example of proper semantic structure:

<main>
  <article>
    <header id="feature">
      <!-- article introduction -->
      <!-- chapter index / toc -->
    </header>   

    <!-- article contents with headings -->    

    <footer>
      <h2>Feedback</h2>
      <!-- feedback explanation -->
    </footer>
  </article>
</main>

When HTML semantics aren’t consistently recognized by screen readers, add explicit ARIA roles and attributes to enhance accessibility. This improves both code organization and the experience for users of assistive technologies.

---

Consistent observability data

When implementing observability features, always ensure consistency in your data model, especially with tags and attributes. This helps prevent issues with backends that expect consistent tag sets.

1. Use consistent tag sets across metrics: Always include the same set of tag keys for metrics of the same type, even when some values are missing.

2. Provide defaults for missing values: Use standardized defaults like “unknown” or “N/A” rather than omitting tags when values are unavailable.

// INCORRECT: Inconsistent tag sets
Gauge.builder("git.info", () -> 1L)
    .tag("branch", props.getBranch()) // May be omitted if null
    .tag("id", props.getShortCommitId())
    .register(registry);

// CORRECT: Consistent tag sets with defaults
Gauge.builder("git.info", () -> 1L)
    .tag("branch", props.getBranch() != null ? props.getBranch() : "unknown")
    .tag("id", props.getShortCommitId() != null ? props.getShortCommitId() : "unknown")
    .register(registry);

1. Document metrics clearly: Use descriptive names that indicate what’s being measured and from which perspective:

// INCORRECT: Ambiguous description
builder.description("Duration of requests made to HTTP Server")

// CORRECT: Clear perspective
builder.description("Duration of HTTP server request handling")

1. Be explicit about propagation behavior: When configuring trace context propagation, explicitly define extraction order and format preferences to ensure reliable tracing across service boundaries.

These practices help avoid issues with observability backends (like Prometheus) that may not handle inconsistent tag sets well and improve the overall reliability and usability of your observability data.

---

Use AssertJ correctly

Spring Framework tests must use AssertJ for assertions rather than JUnit’s Assertions, Spring’s Assert class, or plain assert statements. Follow these AssertJ best practices:

1. Use fluent assertions with proper methods:

   // PREFERRED
   assertThat(collection).hasSize(2);
      
   // AVOID
   assertThat(collection.size()).isEqualTo(2);
   

2. For exception testing, use:

   // PREFERRED
   assertThatExceptionOfType(BadSqlGrammarException.class).isThrownBy(() -> {
       jdbcTemplate.queryForList("SELECT name FROM user", String.class);
   });
      
   // AVOID
   try {
       jdbcTemplate.queryForList("SELECT name FROM user", String.class);
       fail("BadSqlGrammarException should have been thrown");
   }
   catch (BadSqlGrammarException expected) {
   }
   

3. For code that shouldn’t throw exceptions:

   // PREFERRED
   assertThatCode(() -> {
       Assert.noNullElements(asList("foo", "bar"), "enigma");
   }).doesNotThrowAnyException();
      
   // AVOID
   Assert.noNullElements(asList("foo", "bar"), "enigma"); // Missing verification
   

Using AssertJ consistently provides more readable tests, better failure messages, and ensures test consistency throughout the codebase.

---

API boundary null handling

Establish consistent null handling patterns at API boundaries to prevent null pointer exceptions and improve code clarity:

1. Validate method parameters using explicit null checks:

   public void setHttpClient(HttpClient httpClient) {
    Assert.notNull(httpClient, "HttpClient must not be null");
    this.httpClient = httpClient;
   }
   

2. Return empty collections instead of null:

   public List<PropertyAccessor> getPropertyAccessors() {
    return Collections.emptyList();  // Instead of returning null
   }
   

3. Use Optional only as a return type, never as a field: ```java // DON’T private Optional errorStatus; // Avoid Optional as field

// DO public Optional findUserById(String id) { // OK as return type // ... }

4. For nullable return values in internal APIs, prefer explicit @Nullable annotation over Optional:
```java
@Nullable
protected Class<?> getReturnType(Method method) {
    // ...
}

These patterns ensure consistent null handling, improve code readability, and reduce the likelihood of null-related bugs. They also help maintain clear contracts between components while avoiding unnecessary Optional usage.

---

Early return pattern

Prefer returning early from functions rather than nesting conditions. When a condition can lead to an early exit, handle it immediately and return rather than wrapping the main logic in else blocks. This approach reduces nesting, improves code readability, and reduces cognitive load.

Instead of this:

func debugPrint(format string, values ...interface{}) {
  if IsDebugging() {
    if DebugPrintFunc == nil {
      if !strings.HasSuffix(format, "\n") {
        format += "\n"
      }
      fmt.Fprintf(DefaultWriter, "[GIN-debug] "+format, values...)
    } else {
      DebugPrintFunc(format, values...)
    }
  }
}

Use this:

func debugPrint(format string, values ...interface{}) {
  if !IsDebugging() {
    return
  }

  if DebugPrintFunc != nil {
    DebugPrintFunc(format, values...)
    return
  }

  if !strings.HasSuffix(format, "\n") {
    format += "\n"
  }
  fmt.Fprintf(DefaultWriter, "[GIN-debug] "+format, values...)
}

The early return pattern simplifies the code flow, making it easier to understand at a glance. It also helps prevent the “arrow code” or “pyramid of doom” where multiple nested conditions create deeply indented code blocks.

---

Document configuration rationale

When adding or modifying configuration files, always include clear comments or documentation explaining the reasoning behind non-obvious choices, especially when suppressing warnings, excluding files, or making decisions that deviate from defaults.

Configuration decisions often involve trade-offs or address specific operational issues that may not be immediately apparent to other developers. Documenting the rationale helps prevent future confusion and accidental reversions.

Examples of good documentation:

# .npmrc
# Suppress workspace cycle warnings for dev dependencies in test code
ignore-workspace-cycles=true

# Keep pre/post script behavior during migration to minimize changes
enable-pre-post-scripts=true

# .eslintignore
# Exclude lock file to prevent CI formatting loops between pnpm and Prettier
pnpm-lock.yaml

This practice is particularly important for suppressions, exclusions, and migration-related configurations where the reasoning may not be obvious from the configuration itself.

---

Use screen queries

When writing component tests, prefer using global screen queries from Testing Library instead of container-specific queries or passing query functions as parameters. This approach keeps the test environment simple and consistent across the codebase.

Instead of:

const { container } = render(<TextareaAutosize style={{ backgroundColor: 'yellow' }} />);
const input = container.querySelector<HTMLTextAreaElement>('textarea')!;

Use:

render(<TextareaAutosize style={{ backgroundColor: 'yellow' }} />);
const input = screen.getByRole('textbox');

Similarly, avoid passing query functions as parameters to test utilities when the global screen object can be used directly. This reduces complexity and follows the Testing Library’s recommendation of using queries that resemble how users interact with your components.

---

Document configuration behaviors

Always document configuration options thoroughly, especially for module and service settings. For each configuration property:

1. Provide clear descriptions of what the option does
2. Specify default values using the @default JSDoc tag when appropriate
3. Document different behaviors in different contexts (e.g., client vs server)
4. Add examples for complex configuration scenarios

This prevents developers from spending hours debugging unexpected behaviors. When default values differ between contexts or cannot use @default tags, explicitly explain the behavior in comments.

export interface CacheModuleOptions extends CacheManagerOptions {
  /**
   * If "true', register `CacheModule` as a global module.
   * Note: This applies only at the top level CacheModuleAsyncOptions.isGlobal,
   * and will be ignored in useFactory return values.
   * @default false
   */
  isGlobal?: boolean;
}

For optional features or configurations that aren’t enabled by default in examples, consider adding commented code with explanatory notes:

// Uncomment these lines to enable Redis adapter
// const redisIoAdapter = new RedisIoAdapter(app);
// await redisIoAdapter.connectToRedis();
// app.useWebSocketAdapter(redisIoAdapter);

This approach significantly improves developer experience by preventing confusion and reducing time spent debugging configuration-related issues.

---

avoid -count=1 flag

Avoid using the -count=1 flag in Go test commands unless specifically required to disable test caching. Removing this flag enables concurrent test execution, which not only improves test performance but more importantly allows for better detection of data races during testing.

The -count=1 flag disables Go’s test caching mechanism and forces tests to run sequentially. While this was historically used to work around caching issues, modern Go testing benefits from concurrent execution for race detection.

Example of preferred approach:

# Preferred - enables concurrency and race detection
go test -v -race ./...

# Avoid unless caching must be disabled
go test -v -race -count=1 ./...

When tests run concurrently with the -race flag, they are more likely to expose data races and concurrency issues that might be missed in sequential execution. This approach has proven effective in practice, as concurrent test execution can immediately surface race conditions that would otherwise remain hidden.

---

justified nolint exceptions

When style linters cannot be applied universally across a codebase due to architectural constraints or legitimate use cases, use targeted //nolint comments with clear explanations rather than disabling the linter entirely. This approach maintains code style standards while allowing necessary exceptions.

For example, when a linter like interfacebloat conflicts with a core interface design, apply a specific exemption:

//nolint:interfacebloat // Ignore fiber.Ctx - core interface requires many methods
type Ctx interface {
    // ... many methods
}

Similarly, for packages that are dangerous but sometimes necessary:

//nolint:depguard // Using unsafe for performance-critical memory operations
import "unsafe"

This strategy preserves the value of style linters by catching violations in most of the codebase while providing documented exceptions where the rules don’t apply. Each exception should include a brief explanation of why the violation is justified, making the codebase more maintainable and helping future developers understand the reasoning behind style rule exceptions.

---

Use concise methods

Prefer built-in methods and properties that achieve the same result with less code. This improves readability, reduces potential bugs, and makes your code more maintainable.

For DOM manipulations, use specialized methods like classList.toggle() instead of conditional add/remove operations:

// Instead of this:
document.documentElement.classList[isDark ? 'add' : 'remove']('dark');

// Use this more concise approach:
document.documentElement.classList.toggle('dark', isDark);

Similarly, avoid redundant styling properties when fewer properties can achieve the desired effect. Review your CSS classes to eliminate unnecessary declarations that don’t contribute to the intended visual outcome:

// Instead of potentially redundant classes:
<SheetContent className="w-[400px] sm:w-[540px] sm:max-w-none">

// Use only what's necessary:
<SheetContent className="w-[400px] sm:w-[540px]">

These simplifications make code easier to read and maintain while reducing the possibility of conflicting declarations.

---

Preserve API interface stability

When modifying or extending public API interfaces, ensure backward compatibility and proper versioning. Follow these guidelines:

1. Make interface additions optional to avoid breaking changes: ```typescript // Instead of adding required methods interface HttpServer { get(): void; newMethod(): void; // Breaking change! }

// Make additions optional interface HttpServer { get(): void; newMethod?(): void; // Non-breaking change }

2. Support versioning through explicit version types:
```typescript
// Allow flexible version handling
export interface CustomVersioningOptions {
  type: VersioningType.CUSTOM;
  extractor: (request: any) => string | string[];
}

@Controller({
  version: '1',
  versioningOptions: customOptions
})

1. When evolving interfaces:
   • Add new methods as optional properties
   • Use union types for backward compatibility
   • Document breaking changes for major version releases
   • Consider providing migration paths for deprecated features

This approach maintains API stability while enabling controlled evolution of the interface contract.

---

Preserve public API stability

When modifying or extending public interfaces, ensure changes maintain backward compatibility and follow proper versioning practices. Key guidelines:

1. Make interface additions optional: ```typescript // Instead of interface HttpServer { newMethod(): void; }

// Do this interface HttpServer { newMethod?(): void; }

2. Use union types for extending existing types:
```typescript
// Instead of
type Version = string;

// Do this
type Version = string | (string & {}) | ((version: string) => boolean);

1. When adding new functionality that could break existing implementations:
   • Create a new interface/type that extends the base
   • Add configuration options to enable new features
   • Wait for major version releases for breaking changes
2. Document version support clearly: ```typescript @Controller({version: ‘2.x’}) class MyController { @Version(‘>=2.5.1’) @Get(‘:id’) newMethod() {}

@Version(‘<2.5.0’) @Get(‘:id’) legacyMethod() {} }

These practices ensure API consumers can upgrade safely and maintain compatibility with their existing implementations.

---

## Descriptive specific names

<!-- source: spring-projects/spring-framework | topic: Naming Conventions | language: Java | updated: 2024-02-06 -->

Choose names that are specific, descriptive, and accurately reflect the purpose and domain of variables, methods, classes, and constants. Avoid overly generic terms that could be ambiguous or conflict with future features.

When naming constants, qualify them to avoid collisions:
```java
// Avoid
public static final String ATTRIBUTES_CHANNEL_KEY = "attributes";

// Prefer
public static final String ATTRIBUTES_CHANNEL_KEY = 
    ReactorClientHttpRequest.class.getName() + ".attributes";

For methods, use names that clearly describe their specific purpose:

// Too generic
private PreparedStatementCallback<int[]> getPreparedStatementCallback(...) { }

// More descriptive
private PreparedStatementCallback<int[]> getPreparedStatementCallbackForBatchUpdate(...) { }

For parameters and variables, select names that accurately reflect their type and domain:

// Potentially confusing (suggests java.nio.ByteBuffer)
public DataBuffer encodeValue(ByteBuf byteBuffer, ...) { }

// Clear and accurate
public DataBuffer encodeValue(ByteBuf byteBuf, ...) { }

When adding similar methods to existing APIs, choose names that align with established patterns:

// Doesn't align with Optional's terminology
UriBuilder optionalQueryParam(String name, Optional<?> optionalValue);

// Aligns with terminology and sorts better alphabetically
UriBuilder queryParamIfPresent(String name, Optional<?> optionalValue);

---

Optimize documentation for usability

When creating component documentation, prioritize the developer experience by providing clear, usable examples and configurations. For Storybook components, configure props documentation thoughtfully—rather than removing props like children from the table entirely, consider using more specific controls:

// Instead of hiding children completely:
children: {
  table: {
    disable: true,
  },
},

// Better approach - disable only the control:
children: {
  control: false,
},

// Or constrain to text when appropriate:
children: {
  control: 'text',
},

Organize documentation in a logical structure that matches user expectations (such as aligning with your public documentation structure) and leverage specialized documentation blocks like ColorPalette and TypeSet for design systems. This makes documentation more intuitive and helps developers quickly find and implement components.

---

Minimize allocation hotspots

Reduce object creation in performance-critical paths by carefully evaluating allocation patterns. For frequently instantiated objects, consider caching instances or using static helpers, but always validate improvements with proper benchmarks.

Key practices:

1. Identify allocation hotspots with profiling tools before optimizing
2. Size collections appropriately to avoid resizing: new HashMap<>(expectedSize * 4/3 + 1)
3. Reuse objects in loops rather than creating new ones each iteration
4. Cache frequently used utility objects as static variables
5. Use pooled resources (buffers, connections) with proper release mechanisms

Example of object creation optimization with benchmark validation:

// Before: Creates new factory for every request
public URI getUrl() {
    final DefaultUriBuilderFactory factory = new DefaultUriBuilderFactory();
    factory.setEncodingMode(DefaultUriBuilderFactory.EncodingMode.URI_COMPONENT);
    return factory.expand(uriTemplate.toString(), uriVariables);
}

// After: Uses static factory instance
private static final DefaultUriBuilderFactory URI_BUILDER_FACTORY;

static {
    URI_BUILDER_FACTORY = new DefaultUriBuilderFactory();
    URI_BUILDER_FACTORY.setEncodingMode(DefaultUriBuilderFactory.EncodingMode.URI_COMPONENT);
}

public URI getUrl() {
    return URI_BUILDER_FACTORY.expand(uriTemplate.toString(), uriVariables);
}

Always verify optimizations with JMH benchmarks that prevent dead-code elimination:

@Benchmark
public Object measureOptimizedCode(Blackhole blackhole) {
    Object result = optimizedOperation();
    blackhole.consume(result); // Prevent JVM optimization from removing code
    return result;
}

---

Concrete bean return types

When defining @Bean methods in Spring configurations, use concrete return types rather than interfaces while using interface types in @ConditionalOnMissingBean annotations. This approach maximizes type information available to the Spring bean factory while maintaining flexibility in bean overriding.

For example, instead of:

@Bean
@ConditionalOnMissingBean
PulsarConsumerFactory<?> pulsarConsumerFactory(PulsarClient pulsarClient) {
    return new DefaultPulsarConsumerFactory<>(/* parameters */);
}

Prefer:

@Bean
@ConditionalOnMissingBean(PulsarConsumerFactory.class)
DefaultPulsarConsumerFactory<?> pulsarConsumerFactory(PulsarClient pulsarClient) {
    return new DefaultPulsarConsumerFactory<>(/* parameters */);
}

This provides Spring with precise type details during bean creation while allowing applications to override the bean with any implementation of the interface. The bean factory will have more complete information about the actual implementation, which helps with autowiring, debugging, and type safety throughout the application context.

---

Maintain documentation consistency

When modifying documentation structure or content, ensure all cross-references remain valid and avoid creating inconsistencies between related documents. Before renaming files or restructuring documentation, search for and update all internal links that reference the changed content. When platform-specific documentation exists alongside general guides, focus each document on its specific scope rather than duplicating information that could become out of sync.

For example, when updating a Windows-specific setup guide, reference the main development guide for common steps rather than duplicating them:

# Build Logseq Desktop on Windows

This guide covers Windows-specific setup requirements. 
For general development instructions, see [develop-logseq.md](develop-logseq.md).

## Windows Pre-requisites
* Visual Studio (required for desktop app)
* Windows-specific Node.js setup via winget

Always include relevant cross-references to help developers find related documentation, and verify that structural changes don’t break the documentation navigation flow.

---

Type Parameter Naming

Enforce a single, strict naming convention for TypeScript generic type parameters using ESLint, and migrate the rule to error after a short “warn” rollout.

Rules:

• Use PascalCase for type parameters.
• Forbid leading/trailing underscores on type parameters.
• Use a small allowlist-style regex (e.g., allow either T or a PascalCase identifier such as TUser, TItem2).
• Start as warn, then switch to error once the codebase is compliant.

Example ESLint config:

// .eslintrc.cjs
module.exports = {
  rules: {
    '@typescript-eslint/naming-convention': [
      'error', // start as 'warn' for gradual rollout
      {
        selector: 'typeParameter',
        format: ['PascalCase'],
        leadingUnderscore: 'forbid',
        trailingUnderscore: 'forbid',
        custom: {
          regex: '^(T|T[A-Z][A-Za-z]+[0-9]*|[A-Z][a-zA-Z]+[0-9]*)$',
          match: true,
        },
      },
    ],
  },
}

Apply this to every generic type parameter (<TUser>, <TData2> etc.) so the meaning of identifiers stays consistent and automatically enforced across the codebase.

---

Preserve API compatibility

When evolving APIs, maintain backward compatibility to avoid breaking client code. Consider these guidelines:

1. Add overloaded methods instead of modifying signatures: When adding parameters, create a new method rather than changing an existing one.

// AVOID: Breaking change by modifying existing method
- public DockerConfiguration withHost(String address, boolean secure, String certificatePath) {
+ public DockerConfiguration withHost(String address, boolean secure, String certificatePath, Integer socketTimeout) {

// PREFER: Add an overloaded method
public DockerConfiguration withHost(String address, boolean secure, String certificatePath) {
    return withHost(address, secure, certificatePath, null);
}

public DockerConfiguration withHost(String address, boolean secure, String certificatePath, Integer socketTimeout) {
    // Implementation
}

1. Use more general types when specializing parameters: When changing parameter types, prefer changes that won’t break existing code:

// AVOID: Breaking change by narrowing type
- protected Function<String, String> getDefaultValueResolver(Environment environment) {
+ protected UnaryOperator<String> getDefaultValueResolver(Environment environment) {

// PREFER: Keep compatible types or provide adaptation layer
protected Function<String, String> getDefaultValueResolver(Environment environment) {
    // Implementation
}

1. For functional interfaces, avoid changing the abstract method signature: This preserves lambda compatibility.

2. When breaking changes are unavoidable:
   • Deprecate the old API first with clear migration notes
   • Keep both implementations for at least one release cycle
   • Provide automated migration tooling if possible
3. Expand types to be more inclusive rather than restrictive: Consider future use cases when designing parameter types:

// AVOID: Restrictive single value
private String audience;

// PREFER: More flexible collection that handles current and future cases
private List<String> audiences;

These practices help maintain a stable API contract while allowing your library to evolve.

---

Optimize compilation flags

When optimizing application performance, carefully select compiler flags based on your optimization goals. For size-critical applications or accurate size measurements, use -Oz to prevent aggressive inlining that can distort metrics. Additionally, implement compiler caching with tools like ccache to significantly improve build times in development and CI environments.

For CMake-based projects, enable ccache with:

# For direct CMake invocation
cmake . -B build -G Ninja -DCMAKE_CXX_COMPILER_LAUNCHER=ccache -DCMAKE_BUILD_TYPE=Release

# For npm/cmake-js projects
npm config set cmake_CMAKE_CXX_COMPILER_LAUNCHER ccache

When analyzing binary size with tools like Bloaty, ensure you’re comparing equivalent architectures by isolating specific targets:

# Example extracting ARM64 binary from multi-architecture framework
cp MapLibre.xcframework/ios-arm64/MapLibre.framework/MapLibre MapLibre_arm64

These practices ensure both efficient development cycles and optimized production artifacts.

---

Simplify code readability

Write code that prioritizes clarity and simplicity over cleverness. Use appropriate Clojure idioms to make code more readable and maintainable.

Key practices:

• Use thread macros (-» ->) to make data transformations easier to follow
• Simplify conditional logic with descriptive let bindings instead of complex nested expressions
• Avoid unnecessary function nesting (e.g., nested str calls)
• Choose semantic functions that clearly express intent (seq vs not-empty)
• Eliminate unnecessary complexity like delay when simpler alternatives exist

Example of improvement:

;; Instead of complex nested logic:
{:visibility (if (or (not can-open?) (and @*highlight-mode? new?)) "hidden" "visible")}

;; Use descriptive let bindings:
(let [is-new-highlight (and selection @*highlight-mode? new?)
      is-existing-highlight (and selection @*highlight-mode? (not new?))
      should-display-for-new-highlight (and is-new-highlight (state/sub :pdf/auto-open-ctx-menu?))]
  {:visibility (if (or is-existing-highlight should-display-for-new-highlight) "visible" "hidden")})

;; Instead of nested function calls:
(str (string/join ", " (map name (keys (:plugin/installed-plugins @state/state)))))

;; Use thread macros for clarity:
(->> (:plugin/installed-plugins @state/state)
     keys
     (map name)
     (string/join ", "))

This approach makes code more maintainable, especially for team members who may not be familiar with complex Clojure patterns, and reduces cognitive load when reading and debugging code.

---

Explicit default configurations

Always provide explicit default values for configuration options to improve code readability and maintainability. Use helper methods consistently for default value management, and document defaults clearly.

When setting configuration options:

1. Use helper methods like getOptionsProp() with explicit default values: ```typescript // Good - default value is explicit this.port = this.getOptionsProp(options, ‘port’, TCP_DEFAULT_PORT); this.rawOutputPackets = this.getOptionsProp(options, ‘rawOutputPackets’, false);

// Avoid - implicit default through || operator this.port = this.getOptionsProp(options, ‘port’) || TCP_DEFAULT_PORT;

2. Conditionally add configuration options only when needed:
```typescript
// Good - only add config when value exists
const serverOptions = {
  ...this.maxSendMessageLength ? 
    { 'grpc.max_send_message_length': this.maxSendMessageLength } : 
    {}
};

// Avoid - setting undefined values
const serverOptions = {
  'grpc.max_send_message_length': this.maxSendMessageLength
};

1. Document default values using appropriate JSDoc tags: ```typescript /**
   • Defines if file parameter is optional.
   • @default false */ optional?: boolean;

// When defaults differ between contexts (e.g., client vs server): /**

• Defaults to "-server" on server side and "-client" on client side. */ clientId?: string; ```

1. Avoid duplicating default values that are already defined by dependencies. Instead, rely on the dependency’s defaults unless you have a specific reason to override them.

Following these practices makes configuration behavior more predictable and self-documenting, reduces bugs from unexpected undefined values, and makes code easier to maintain.

---

Use documentation features properly

Utilize Asciidoc features correctly when writing or updating Spring Framework documentation. Instead of hardcoded links, use defined attributes where available. For example, replace:

[its `META-INF/spring.factories` properties file](https://github.com/spring-projects/spring-framework/blob/main/spring-test/src/main/resources/META-INF/spring.factories)

With:

[its `META-INF/spring.factories` properties file]{spring-framework-code}

When cross-referencing content within the same document, use simplified section references (e.g., <<webflux>> instead of <<web/webflux.adoc#webflux>>). This improves documentation consistency, maintainability, and reduces the effort needed for future updates. Proper use of Asciidoc features also helps maintain a consistent style across the entire codebase and makes documentation more resilient to structural changes.

---

Lifecycle effects management

Properly manage component lifecycle effects and cleanup in React components to prevent memory leaks and performance issues. Use appropriate dependency arrays in useEffect hooks, and ensure cleanup functions are implemented for subscriptions, event listeners, and other side effects.

When working with async components or operations:

1. Make sure effects properly handle both resolved and pending states
2. Consider component mounting/unmounting timing when dealing with async operations

// Poor implementation
useEffect(() => {
  const subscription = someAPI.subscribe(data => {
    setData(data);
  });
  // Missing cleanup function
}, []); // Missing proper dependencies

// Better implementation
useEffect(() => {
  let isMounted = true;
  const subscription = someAPI.subscribe(data => {
    if (isMounted) {
      setData(data);
    }
  });
  
  return () => {
    isMounted = false;
    subscription.unsubscribe();
  };
}, [someAPI]); // Proper dependencies listed

Effects in parent components can impact child component performance. Be mindful of effect hierarchies and consider using more targeted state management approaches when effects cascade across many components.

---

Template instantiation trade-offs

When designing algorithms that accept callbacks or function parameters, consider the trade-off between template functions and std::function:

1. Templates generate code - Each unique lambda passed to a template function creates a new instance of that entire function body, which can significantly increase binary size for large functions.

2. Use std::function for large function bodies - When a function body is substantial (like in polyline generation), the code duplication cost from templates outweighs the indirection cost of std::function.

// Prefer std::function for large function bodies with multiple callers
std::size_t visitDrawables(const std::function<void(gfx::Drawable&)>& f) {
    for (const auto& item : drawables) {
        if (item) {
            f(*item);
        }
    }
    return drawables.size();
}

// Templates are appropriate for small, performance-critical code
template <typename Hasher>
size_t computeHash(const T& value) {
    return Hasher{}(value);
}

1. Extract complex operations - For operations like hash combining, extract the logic to a shared function rather than duplicating it across template instantiations.

2. Consider compile time - Templates increase compile time, especially for complex algorithms, which can slow down the development cycle.

---

Use factory providers

Prefer useFactory over useValue for better performance in NestJS dependency injection, especially for large objects or complex configurations. Using useValue with large objects can significantly slow down application bootstrapping due to expensive module serialization.

When defining providers in a module, implement them as factory functions:

// Less optimal - may cause performance issues with large objects
{ 
  provide: MULTER_MODULE_OPTIONS, 
  useValue: complexConfigObject 
}

// Better performance
{ 
  provide: MULTER_MODULE_OPTIONS, 
  useFactory: () => complexConfigObject 
}

This optimization prevents deep serialization of object structures during module token creation. The serialization process in NestJS needs to stringify providers to create unique identifiers, and complex objects can significantly impact performance.

If your application has slow startup times, check for warnings about module serialization exceeding 10ms, which indicates potential performance bottlenecks. Converting value providers to factory providers can substantially reduce initialization time in larger applications with complex dependency graphs.

---

Consistent API practices

Maintain consistency in API design, documentation, and implementation across all supported platforms to improve developer experience and reduce friction.

API Documentation Standards:

• Use code formatting (backticks) when referencing API methods: initialize, de_initialize, not initialize, de_initialize
• Use correct capitalization for platform names: iOS, Android (not ios, android)
• Refer to the library consistently as “MapLibre Native” rather than variations like “maplibre-gl”

Cross-Platform Implementation:

• Implement new API features across all supported platforms simultaneously when possible
• When implementing features in phases, document the limitation and provide a timeline for complete implementation
• Ensure consistent behavior across platforms for identical API methods

Example: Cross-platform implementation Instead of:

// Adding feature only for Android
// platform/android/CHANGELOG.md
* Add support for the [`slice` expression](https://maplibre.org/maplibre-style-spec/expressions/#slice) ([#1113](https://github.com/maplibre/maplibre-native/pull/1133))

Prefer:

// Implementing across platforms
// CHANGELOG.md
* Add support for the [`slice` expression](https://maplibre.org/maplibre-style-spec/expressions/#slice) across all platforms ([#1133](https://github.com/maplibre/maplibre-native/pull/1133))

Following these practices ensures that developers have a consistent experience regardless of which platform they are using and reduces confusion when working with MapLibre Native APIs.

---

Leverage framework defaults

Avoid redundant or unnecessary configuration by understanding and utilizing default behaviors provided by frameworks and tools. Remove explicit configuration when the underlying framework already handles it automatically, which reduces maintenance overhead and prevents configuration drift.

For example, when using Storybook with NextJS, you can simplify your configuration by removing redundant settings:

// .storybook/main.ts
const config: StorybookConfig = {
  stories: ["../stories/**/*.stories.@(js|jsx|ts|tsx|mdx)"],
  addons: [
    "@storybook/addon-links",
    "@storybook/addon-essentials",
    "@storybook/addon-interactions",
-    {
-      name: "@storybook/addon-styling",
-      options: {
-        postCss: true,
-      },
-    },
  ],
}

Similarly, when writing utility functions for configuration, prefer simple, direct implementations:

// Instead of complex nested conditionals
export function resolveProjectDir(appDir: boolean, srcDir: boolean) {
  if (appDir && srcDir) return "src/app"
  if (appDir) return "app"
  if (srcDir) return "src"
  return ""
}

Always research framework capabilities before adding custom configuration to avoid duplicating functionality that’s already built-in.

---

organize tests clearly

Structure tests with clear organization, focused scope, and minimal duplication to improve maintainability and debugging. Each test should have a single, well-defined purpose that correlates directly to its name. Group related tests using describe blocks and extract common setup code to reduce duplication.

Key principles:

• Split complex tests with multiple expectations into smaller, focused test cases
• Use descriptive test names that clearly indicate what is being tested
• Group related tests under describe blocks and remove redundant prefixes from individual test names
• Extract duplicated setup code into beforeEach hooks or shared helper functions
• Ensure each test validates one specific behavior or scenario

Example of improved test organization:

// Instead of:
it('OnEndReached should not be called after initial rendering', () => {
  const ITEM_HEIGHT = 100;
  // setup code...
  // test logic...
});

it('OnEndReached should be called once after scrolling', () => {
  const ITEM_HEIGHT = 100; // duplicated
  // same setup code... // duplicated
  // test logic...
});

// Prefer:
describe('onEndReached', () => {
  const ITEM_HEIGHT = 100;
  let component, instance, data, onEndReached;
  
  beforeEach(() => {
    // shared setup code
  });

  it('should not be called after initial rendering', () => {
    // focused test logic only
  });

  it('should be called once after scrolling', () => {
    // focused test logic only
  });
});

This approach makes tests easier to understand, debug, and maintain while reducing code duplication and improving test reliability.

---

Silence Unused Query Updates

To optimize performance, prevent components from re-rendering when they don’t need to react to query updates.

Rule: If you use useQuery/useFocusEffect for prefetching or side effects and intentionally ignore the result, disable change notifications so the hook doesn’t subscribe to updates that would trigger re-renders.

Apply to React Query prefetching (ignore result)

When you “prefetch by calling useQuery but not using data”, you still create an observer and can cause re-renders. Pass an empty notifyOnChangeProps to avoid notifications.

function Article({ id }: { id: string }) {
  // Critical data used by UI
  const { data: articleData, isPending } = useQuery({
    queryKey: ['article', id],
    queryFn: getArticleById,
  })

  // Prefetch-only: prevent re-renders
  useQuery({
    queryKey: ['article-comments', id],
    queryFn: getArticleCommentsById,
    notifyOnChangeProps: [],
  })

  if (isPending) return 'Loading article...'
  return <Comments id={id} articleData={articleData} />
}

Apply to React Navigation focus

If screen UI should not update while out of focus, gate notifications so query-driven state won’t re-render off-screen.

In practice, implement a focus-aware notifyOnChangeProps (optionally using navigation.isFocused() if available) so that updates are suppressed while unfocused and re-enabled when focused again.

---

Buffer bounds validation

Always validate buffer boundaries before performing memory operations to prevent buffer overflow vulnerabilities. When copying data into a buffer at a specified offset, verify that the combination of size and offset doesn’t exceed the buffer’s allocated capacity.

Example implementation for the update method:

void BufferResource::update(const void* data, std::size_t size, std::size_t offset) {
    if (buffer && data) {
        // Security check to prevent buffer overflow
        if (size + offset > buffer->length()) {
            // Handle error appropriately: log, throw exception, or return error code
            return; // Abort operation
        }
        
        if (void* content = buffer->contents()) {
            std::memcpy(static_cast<uint8_t*>(content) + offset, data, size);
        }
    }
}

This validation is crucial for preventing memory corruption, application crashes, and potential security exploits that could lead to arbitrary code execution. Never trust input parameters without validation, even when they come from internal code.

---

Database-agnostic SQL syntax

Write SQL statements that conform to standard SQL rather than relying on vendor-specific dialects to ensure portability across different database systems.

When working with SQL identifiers (table names, column names, etc.), obtain the appropriate quote characters from the database metadata rather than hardcoding them:

// Get the appropriate quote character for the database
String quoteChar = databaseMetaData.getIdentifierQuoteString();

Remember to quote schema and table names independently:

// Correct - Schema and table quoted independently
"INSERT INTO " + quoteChar + "SCHEMA" + quoteChar + "." + quoteChar + "TABLE" + quoteChar

// Incorrect - Combined quoting
"INSERT INTO " + quoteChar + "SCHEMA.TABLE" + quoteChar

For database sequences, use standard-compliant syntax:

// Good - standard syntax
"VALUES NEXT VALUE FOR sequence_name"

// Avoid - vendor-specific (Oracle-style)
"select sequence_name.nextval from dual"

Some databases like MS SQL Server may have unique quoting requirements or special syntax. Always verify functionality across all target database platforms and avoid compatibility modes or features that are specific to a single database vendor.

---

optimize iteration patterns

When implementing loops and iteration logic, evaluate whether your current approach is the most efficient and readable option available. Look for opportunities to simplify complex iteration patterns and eliminate unnecessary loops.

Common optimizations to consider:

• Use for (let [index, item] of array.entries()) when you need both index and value, rather than manual index tracking
• Replace loops that handle simple conditional logic with direct conditional statements
• Consider whether character-by-character or element-by-element processing can be simplified

Example of optimization:

// Instead of manual index tracking:
for (let index = 0; index < lines.length; index++) {
  const line = lines[index];
  // process line and index
}

// Use entries() for cleaner code:
for (let [index, line] of lines.entries()) {
  // process line and index
}

// Instead of unnecessary loops for simple cases:
for (let dx = 1; dx < charWidth; dx++) {
  currentLine[offsetX + dx] = '';
}

// Use direct conditional when appropriate:
if (char.fullWidth) {
  currentLine[offsetX + 1] = '';
}

This approach reduces computational complexity, improves code readability, and often eliminates potential off-by-one errors in index management.

---

Pin dependency versions

Explicitly pin or constrain dependency versions in CI/CD configurations instead of using latest tags. This prevents unexpected build failures when new incompatible versions are released. Consider using parameterized versions to centralize version management while maintaining stability.

For tool installations in CI pipelines:

# Avoid this:
- run:
    name: Update NPM version
    command: 'sudo npm install -g npm@latest'

# Prefer this:
- run:
    name: Update NPM version
    command: 'sudo npm install -g npm@^8'

# Or better, use parameters:
parameters:
  npm-version:
    type: string
    default: "^8"
  
jobs:
  build:
    # ...
    steps:
      - run:
          name: Update NPM version
          command: 'sudo npm install -g npm@<< pipeline.parameters.npm-version >>'

For GitHub Actions or other external dependencies, specify exact versions or follow a semantic versioning strategy that matches your risk tolerance. Consider establishing a regular process to review and update dependency versions.

---

Parameterize version requirements

Always parameterize tool and runtime versions in CI/CD configurations rather than hardcoding them. This makes your pipelines more maintainable when dependencies need updates and provides a single source of truth for version requirements.

For critical dependencies like Node.js or package managers:

1. Define versions as parameters at the top of your configuration
2. Reference these parameters throughout your configuration
3. Consider separate parameters for maintenance and legacy versions
4. Use version ranges when appropriate to get compatible updates

Example:

# Good practice
parameters:
  maintenance-node-version:
    type: string
    default: "16.20"
  
jobs:
  build:
    docker:
      - image: cimg/node:<< pipeline.parameters.maintenance-node-version >>
    steps:
      - run:
          command: 'npm install -g npm@^8'  # Version range for compatible updates

This approach helps prevent CI failures when new incompatible versions are released and simplifies the process of updating dependencies across multiple workflow steps.

---

log complete error objects

Always log complete error objects rather than just error messages to preserve stack traces, error codes, and debugging context. Use the application’s logger instead of hardcoded console statements in modules.

When catching errors, log the entire error object to capture all available debugging information:

// ❌ Avoid - loses valuable debugging context
catch (error) {
  this.logger.error(`unable to install dependencies: ${error.message}`)
}

// ✅ Preferred - preserves complete error information
catch (error) {
  this.logger.fatal(error)
  // or with additional context
  this.logger.error('Unable to install dependencies', error)
}

Modern loggers can handle error objects properly without manual formatting like JSON.stringify(). Reserve console methods only for user-facing messages that must remain separate from structured application logs.

---

Consistent import paths

Establish and follow consistent import path conventions throughout the codebase. Prefer aliased imports using the project’s path aliases (e.g., @/src/utils/get-initial-values) over relative imports to ensure consistency and improve maintainability. This practice creates uniform import statements across files regardless of their location in the project structure.

// Preferred
import { getInitialValues } from "@/src/utils/get-initial-values"

// Instead of
import { getInitialValues } from "../utils/get-initial-values"

Using aliased imports makes code more portable and easier to refactor, as moving files doesn’t require updating multiple relative import paths. This approach also avoids the confusion that can arise from nested relative paths (e.g., ../../utils/ vs ../utils/).

---

Explicit nullish checks

When checking for the absence of values, use explicit nullish checks rather than relying on JavaScript’s falsy behavior. This prevents issues with valid falsy values like empty strings, zero, or false being treated as non-existent.

Bad:

// This will skip empty strings, zero, and false
if (vars[key]) {
  style.setProperty(`--${key}`, vars[key])
}

// Similarly problematic for numeric inputs
if (props.value) {
  el.setAttribute('value', props.value)
}

Good:

// Handles empty strings correctly
if (vars[key] || vars[key] === '') {
  style.setProperty(`--${key}`, vars[key])
}

// Even better - explicitly checks for null/undefined
if (vars[key] !== undefined && vars[key] !== null) {
  style.setProperty(`--${key}`, vars[key])
}

// Or use loose equality for brevity when appropriate
if (props.value != null) {
  el.setAttribute('value', props.value)
}

Remember that value == null checks for both null and undefined, while value === null only checks for null. Choose the appropriate check based on your requirements. When handling form inputs, DOM properties, or CSS variables, be especially careful as empty strings and zero are often valid values that should be preserved.

---

Justify configuration changes

When making configuration changes, especially dependency upgrades, provide clear justification for why the change is necessary rather than simply updating to the latest version. Explain the specific benefits, required features, or problems being solved.

For dependency upgrades, identify the minimum version needed and the specific features that require the upgrade. Consider the impact on related tools and dependencies that may also need updating.

Example from a TypeScript upgrade discussion:

// Instead of just upgrading to latest
"typescript": "^4.0.0"

// Provide justification in PR description:
// "TypeScript 3.7+ needed for optional chaining feature used in new code.
// Updated to 3.9.7 (minimum required) rather than 4.0.0 to minimize compatibility risks.
// Also updated sucrase dependency which requires compatible TypeScript version."

This approach helps reviewers understand the necessity of changes and prevents unnecessary upgrades that could introduce instability or compatibility issues.

---

REST principles first

When designing APIs with Express, prioritize proper REST principles and HTTP semantics over convenience. This ensures your API is predictable, standards-compliant, and maintainable:

1. Use appropriate HTTP verbs for different operations:
   • GET for retrieval
   • POST for creation
   • PUT for complete entity updates
   • PATCH for partial updates
   • DELETE for removal

// Implement both PUT and PATCH for different update scenarios
router.put('/:id', controller.replaceEntity.bind(controller));    // Full entity replacement
router.patch('/:id', controller.updateFields.bind(controller));   // Partial update

1. Handle HTTP headers correctly:
   • Respect existing Content-Type headers before applying defaults
   • Follow established patterns for setting headers (use res.type() where appropriate)
   • Handle Link headers according to RFC specifications
   • Process Accept headers intelligently, considering priorities
2. Follow consistent response patterns:
   • Use res.status() with appropriate status codes (200 OK, 201 Created, 204 No Content)
   • For error responses, use semantic status codes (400 Bad Request, 404 Not Found)
   • Use res.sendStatus() for simple status-only responses

Remember that proper HTTP semantics help clients understand your API intuitively without requiring extensive documentation for basic operations.

---

Add explanatory documentation

Add docstrings to functions and comments to explain complex logic, especially when the purpose or reasoning isn’t immediately clear from the code itself. This includes documenting function parameters, explaining non-obvious conditions, and clarifying implementation decisions or workarounds.

Functions should have docstrings that explain their purpose and parameters:

(defn convert-index
  "Converts a numeric index to different formats based on delta value.
   Args:
     idx - numeric index to convert
     delta - format selector (0=numeric, 1=letters, else=roman)"
  [idx delta]
  (cond
    (zero? delta) idx
    (= delta 1) (some-> (util/convert-to-letters idx) util/safe-lower-case)
    :else (util/convert-to-roman idx)))

Complex conditions and workarounds should be explained with comments:

;; hovering on page ref in page-preview does not show another page-preview 
;; if {:preview? true} was passed to page-blocks-cp
(page-reference false page {:preview? true} nil)

;; Check if edit input exists to prevent navigation when not editing
(not (state/get-edit-input-id))

Configuration options should include clear explanations and usage examples, especially for potentially risky settings or complex features.

---

Prefer behavior-true names

Use naming that clearly communicates the real behavior/intent of the API and avoids misleading abbreviations or borrowed terms whose common meaning differs.

Apply this when adding/renaming methods:

• Match semantics to behavior: if the method “checks and returns input as-is,” don’t name it after an operation that “returns an array without duplicates.”
• Prefer full, intention-revealing names over short/ambiguous ones when they reduce clarity.
• If a common ecosystem term may imply different semantics, choose a name that reflects the actual operation (or explicitly document the difference).
• For domain terms that overlap with other systems (e.g., “forms”), ensure the wording/dox strings align with the library’s/TypeScript’s meaning to prevent confusion.

Example rule in practice:

• ❌ Confusing due to semantic mismatch: a method named like lodash uniq when it does not dedupe/transform.
• ✅ Clearer alternative: choose a name that reflects what happens (e.g., “unique/ distinct” only if the operation truly enforces/derives uniqueness as that name implies), or pick another verb that matches intent (as in the naming exploration for .check).

---

Handle streams properly

When transferring data over HTTP, properly implement streaming mechanisms to prevent memory exhaustion and potential denial-of-service vulnerabilities. Handle backpressure appropriately to ensure that slow clients cannot overwhelm server resources.

Key considerations:

1. For large data transfers, use appropriate streaming APIs instead of loading entire payloads into memory
2. Always handle backpressure in custom stream implementations
3. Be aware of client disconnections and abort events to free resources promptly
4. Choose the right stream API based on data source and Node.js version compatibility
5. Ensure HTTP header consistency with your streaming approach (avoid setting Content-Length with Transfer-Encoding)

Example of properly handling a Blob response with backpressure consideration:

// Good: Using stream.Readable.from with proper error handling
if (isChunkBlob) {
  var res = this;
  var blob = chunk;
  
  if (typeof blob.stream === 'function') {
    var Readable = require('stream').Readable;
    var nodeStream = Readable.from(blob.stream());
    
    // Handle errors and cleanup on request termination
    nodeStream.on('error', req.next);
    res.on('error', req.next);
    
    // Use pipe to automatically handle backpressure
    nodeStream.pipe(res);
  } else {
    // Fallback for blobs without stream support
    blob.arrayBuffer()
      .then(function(arrayBuffer) {
        res.end(Buffer.from(arrayBuffer));
      })
      .catch(req.next);
  }
} else {
  this.end(chunk, encoding);
}

For custom streaming implementations, always account for backpressure by responding to write events that return false, and implement proper error handling to release resources when connections terminate unexpectedly.

---

Classify configuration properties appropriately

Ensure configuration properties and settings are properly categorized based on their intended use, visibility, and user interaction requirements. Built-in system properties should be classified as hidden, editable, or user-visible depending on whether end users should interact with them directly.

For built-in properties that control system behavior:

• Use hidden-built-in-properties for internal system properties that users should never see or modify
• Use editable-built-in-properties for system properties that users can modify but shouldn’t clutter UI elements like query builders
• Avoid exposing internal configuration properties in user-facing interfaces unless explicitly needed

For user-facing configuration options:

• Provide multiple installation/setup methods to accommodate different user preferences and environments
• Document all available configuration approaches rather than removing options
• Consider cross-platform compatibility when designing configuration workflows

Example from the codebase:

// Good: Properly categorized table properties
const editableBuiltInProperties = [
  'logseq.table.version',
  'logseq.table.hover', 
  'logseq.table.stripes'
];

// Avoid: Exposing internal properties in user UI
// These shouldn't appear in query builder dropdowns

This ensures users can configure what they need without being overwhelmed by internal system properties, while maintaining flexibility for different development environments and user preferences.

---

Explicit security documentation

Always provide explicit and accurate documentation for security-related configurations, including:

1. Use proper configuration property syntax with validation where possible (e.g., configprop:spring.security.oauth2.resourceserver.jwt.audiences[])

2. Clearly document default security behaviors, especially which endpoints or features are exposed/protected by default

3. Include explicit warnings when documenting configurations that relax security for development tools

4. When showing how to disable security features, clearly state the security implications

Example for development tool security configuration:

// SECURITY WARNING: This configuration exposes the H2 console to anyone 
// and disables CSRF protection. Only use in development environments.
@Bean
public WebSecurityCustomizer h2ConsoleSecurityCustomizer() {
    return (web) -> web.ignoring().requestMatchers(PathRequest.toH2Console());
}

In documentation, prefer phrasing like “only the /health endpoint is exposed over HTTP by default” rather than vague terms like “secret” to clearly communicate security boundaries.

---

Configuration option lifecycle

When adding new configuration options, follow a systematic approach to ensure consistency and maintainability across the application. This prevents incomplete implementations that can break existing functionality or create inconsistent user experiences.

The proper lifecycle for configuration options includes:

1. Add to config schema - Define the option’s structure and validation rules
2. Update config template - Add documentation and examples to the default config template
3. Provide default values - Add fallback values in the appropriate config module (avoid hardcoding in templates as this breaks global config)
4. Create accessor functions - Implement getter and setter functions for the config option
5. Use accessor functions consistently - Always access config through the defined functions, never directly

Example of proper config option implementation:

;; In config schema
:new-feature/enabled? {:type :boolean :default false}

;; In config template with documentation
;; Enable new feature functionality
;; Default value: false
:new-feature/enabled? false

;; Accessor functions
(defn new-feature-enabled? []
  (get (get-config) :new-feature/enabled? false))

;; Usage
(when (new-feature-enabled?)
  (enable-new-feature))

This systematic approach prevents issues like incomplete config implementations, missing documentation, hardcoded defaults that override global settings, and inconsistent access patterns. It also ensures that configuration changes are properly validated and don’t silently break existing functionality.

---

Verify operation semantics

When implementing algorithms that process collections or use conditional logic, always verify the exact semantics of operations across different data structures.

For conditional operators like the Elvis operator (?:), be aware they may follow specific evaluation rules rather than intuitive reference semantics. For example, in SpEL, the Elvis operator checks for values that are non-null AND non-empty for Strings, which is more specific than general truthy/falsy rules from other languages:

// This will inject 25 if pop3.port is null OR an empty string
@Value("${pop3.port ?: 25}")
private int port;

For operations that process collections, verify which data structures are actually supported. Selection operations in SpEL work not just on lists and maps, but also on arrays and anything implementing java.lang.Iterable or java.util.Map interfaces:

// Works on lists, arrays, and any Iterable implementation
inventors.?[nationality == 'Serbian']

Understanding these semantics ensures your algorithms behave as expected across different data structures and prevents subtle bugs.

---

Ensure test completion

Tests must properly terminate by following appropriate asynchronous patterns. For asynchronous tests, always invoke the done() callback after assertions or use returned Promises. For synchronous tests, omit the done parameter entirely. Use Mocha’s built-in assertion handling rather than manual try-catch blocks.

Poor pattern (test may hang on assertion failure):

it('should verify response data', function(done) {
  request(app)
    .get('/notes')
    .expect(200, function(err, res) {
      if (res.body.length === 1 && res.body[0].title === "Text") {
        done(); // No 'else' path - test will hang if check fails
      }
    });
});

Better pattern:

it('should verify response data', function(done) {
  request(app)
    .get('/notes')
    .expect(200, function(err, res) {
      if (err) return done(err);
      assert.strictEqual(res.body.length, 1);
      assert.strictEqual(res.body[0].title, "Text");
      done();
    });
});

Best pattern (using testing framework assertions):

it('should verify response data', function(done) {
  request(app)
    .get('/notes')
    .expect(200)
    .expect(res => {
      assert.strictEqual(res.body.length, 1);
      assert.strictEqual(res.body[0].title, "Text");
    })
    .end(done);
});

For long-running tests, set appropriate timeouts to prevent false failures:

it('should process many routes', function(done) {
  this.timeout(7500); // Extend timeout for complex operations
  // Test implementation
  // ...
  done();
});

---

Multi-arity backward compatibility

When extending existing API functions with new parameters, use multi-arity function definitions to maintain backward compatibility. This allows existing code to continue working unchanged while providing enhanced functionality through additional arities.

The pattern involves defining the original function signature that delegates to the extended version with default values, then defining the extended signature with the new parameters. This approach prevents breaking changes for existing callers while enabling new functionality.

Example implementation:

(defn eval-string
  ([s]
   (eval-string s {}))
  ([s ns]
   (try
     (sci/eval-string s {:bindings {'sum sum
                                    'average average}
                        :namespaces ns}))))

(defn resolve-input
  ([input]
   (resolve-input input nil))
  ([input current-block-uuid]
   (cond
     (= :current-block input)
     (when current-block-uuid
       (some-block-lookup current-block-uuid))
     :else input)))

This pattern is especially important for APIs used by external consumers like plugins, where breaking changes can cause widespread compatibility issues. Always validate that the default parameter values work correctly across all intended usage contexts.

---

Filter nil values defensively

Proactively filter out nil values from collections and validate non-empty states before processing to prevent runtime errors. This defensive approach prevents common issues like “Cannot read properties of null” errors and ensures robust data handling.

When working with collections that may contain nil values, filter them out before processing:

;; Before: Risk of null pointer errors
(let [blocks (util/sort-by-height blocks)]
  ...)

;; After: Safe processing
(let [blocks (util/sort-by-height (remove nil? blocks))]
  ...)

Use seq instead of seq? to check for non-empty collections:

;; Check if collection has content before processing
(when (seq paths)
  ;; Process paths safely
  ...)

While this pattern requires callers to handle nil states (leading to (remove nil?) throughout the codebase), it prevents more serious downstream errors and makes error handling explicit rather than allowing silent failures or confusing secondary errors.

---

Use 404 over 403

When blocking access to security-sensitive endpoints or directories, return HTTP 404 (Not Found) instead of 403 (Forbidden) to prevent information disclosure. A 403 response reveals that the resource exists but access is denied, which can provide valuable reconnaissance information to attackers. A 404 response makes it harder for attackers to determine what resources are actually present on the server.

This principle applies to endpoints like certificate validation paths, admin interfaces, API endpoints, or any resource where revealing its existence could aid an attacker’s reconnaissance efforts.

Example nginx configuration:

# Instead of allowing discovery with 403
location /.well-known/acme-challenge/ { 
  deny all;  # This would return 403
}

# Use 404 to hide existence
location /.well-known/acme-challenge/ { 
  return 404;  # Appears as if path doesn't exist
}

Apply this pattern when the security benefit of hiding resource existence outweighs the need for clear error messaging.

---

Secure API endpoints

Always implement appropriate security measures for API endpoints that perform sensitive operations. This includes:

1. Verify request authenticity: Ensure requests come from legitimate sources using mechanisms like SDK verification, API keys, or signatures.

2. Validate HTTP methods: Restrict non-idempotent operations (create/update/delete) to appropriate methods like POST, and reject GET/HEAD requests for these operations.

Example:

exports.handler = async (event) => {
  // 1. Verify HTTP method
  if (event.httpMethod !== 'POST') {
    return {
      statusCode: 404,
      body: 'Not found'
    };
  }
  
  // 2. Verify request authenticity
  // Using SDK verification or custom validation
  const isAuthentic = verifyRequestSignature(event);
  if (!isAuthentic) {
    return {
      statusCode: 401,
      body: 'Unauthorized request'
    };
  }
  
  // Continue with handling the authenticated request
  // ...
}

These measures prevent unauthorized access and protect against security exploits where sensitive operations might be triggered unintentionally through link following, bots, or prefetching.

---

Use descriptive parameter names

Choose parameter names that clearly communicate their purpose and avoid confusion with similar concepts. Avoid generic or ambiguous names that could be misinterpreted.

When naming parameters, consider:

• What the parameter actually represents, not just its technical type
• Whether the name could be confused with other common programming concepts
• If the parameter type changes, update the name to match

Example of unclear naming:

export function useInput(
	inputHandler: (input: string, meta: Meta) => void

Better alternatives:

export function useInput(
	inputHandler: (input: string, metadata: InputMetadata) => void
	// or
	inputHandler: (input: string, key: KeyInfo) => void

The name meta is ambiguous because it could be confused with “meta keys” (a different keyboard concept), while metadata or key clearly indicate what the parameter contains.

---

Stable observability components

Always use stable, production-ready versions of observability components (libraries, dependencies, and documentation references) in your applications. Monitoring and observability systems are critical infrastructure that should prioritize stability over cutting-edge features.

For libraries:

• Avoid alpha, beta, or milestone releases in production code
• Test compatibility with your entire observability stack before upgrading
• Consider downstream dependencies that might be affected

For documentation and references:

• Link to specific stable versions (tags or SHAs) rather than main branches

Example of what to avoid:

library("OpenTelemetry", "1.23.1-alpha") {  // Problematic: alpha version
    group("io.opentelemetry") {
        imports = [
            "opentelemetry-bom-alpha"       // Indicates unstable release
        ]
    }
}

Instead, use stable versions:

library("OpenTelemetry", "1.19.0") {  // Stable version
    group("io.opentelemetry") {
        imports = [
            "opentelemetry-bom"            // Standard stable artifact
        ]
    }
}

This approach helps ensure your monitoring systems remain reliable and don’t introduce unexpected behavior when capturing critical operational data.

---

Package null-safety annotations

All package-info.java files must include both @NonNullApi and @NonNullFields annotations to establish null-safety at the package level. These annotations must each be on a single line for proper detection by static analysis tools. This practice makes null-handling behavior explicit, reduces NullPointerExceptions, and enforces consistent null-safety conventions across the codebase.

Example:

/**
 * Package documentation here.
 */
@NonNullApi
@NonNullFields
package com.example.mypackage;

import org.springframework.lang.NonNullApi;
import org.springframework.lang.NonNullFields;

---

API input validation

When working with APIs, always validate inputs beyond basic format checking to ensure semantic correctness and handle edge cases properly. Simple constructor calls or basic format validation may accept invalid or unexpected inputs that could cause issues downstream.

For URL validation, don’t rely solely on constructor success - verify the parsed components meet your requirements:

const isValidURL = (url: string) => {
  try {
    const parsedUrl = new URL(url)
    return parsedUrl.host && ['http:', 'https:'].includes(parsedUrl.protocol)
  } catch {
    return false
  }
}

Similarly, when choosing API methods, understand their behavior and constraints rather than assuming functionality. Test different approaches empirically when stability is critical, and be prepared to revert changes if they break expected behavior. Always validate that your API usage works as intended across different scenarios and edge cases.

---

Configuration file precision

Ensure configuration files are precisely maintained with correct syntax and compatible version declarations. This includes:

1. Version compatibility: When using language features, ensure the declared version in configuration files (e.g., go.mod) is compatible. For example, if using Go 1.20 features like unsafe.StringData(), ensure go.mod specifies the correct version:

// Correct
go 1.20

// Incorrect if using Go 1.20 features
go 1.18

1. Correct ignore patterns: When configuring file exclusions, use precise path patterns and correctly structure exceptions. For example, when working with nested directories:

# Correct pattern for files in subdirectories
Godeps/*
!Godeps/Godeps.json

# Incorrect pattern
Godeps/*
!Godep.json

1. Project-focused configurations: Only include configurations that are directly relevant to the project itself, avoiding IDE-specific or personal environment settings unless absolutely necessary for project functionality.

Following these practices ensures consistent behavior across different development environments and prevents configuration-related errors.

---

Graph-based dependency management

When managing module dependencies in a system, treat the dependencies as a directed graph and apply appropriate graph algorithms to ensure proper initialization order and prevent errors.

Key considerations:

1. Implement topological sorting for dependencies to ensure modules are initialized in the correct order (modules should be initialized after their dependencies)
2. Handle circular dependencies explicitly - they can cause infinite recursion in graph traversal algorithms
3. Calculate proper distance metrics when modules have multiple import paths

Example of calculating proper distance in a module graph:

// When adding a related module, calculate the correct distance 
// by considering all possible paths
public addRelatedModule(module: Module) {
  this._imports.add(module);
  // Take the maximum distance to ensure all dependencies are resolved
  module.distance = this._distance + 1 > module._distance 
    ? this._distance + 1 
    : module._distance;
}

For circular dependencies, consider implementing cycle detection as part of your topological sort or applying algorithms like Tarjan’s strongly connected components algorithm to identify and manage cycles appropriately.

Failing to use proper graph algorithms for dependency management can lead to subtle runtime errors where modules are initialized in an incorrect order, resulting in undefined references or incomplete configurations.

---

Use topological sorting

When managing dependencies between modules or components, implement a topological sorting algorithm to ensure correct initialization order. This prevents cascading errors and ensures that dependencies are properly initialized before they’re used.

Key implementation guidelines:

1. Detect and handle circular dependencies
2. When calculating distances between modules, preserve maximum distance when a module is imported by multiple parents
3. Sort modules by dependency order before initialization

Example implementation for updating module distances:

// When a module is imported by multiple parents
// always use the maximum possible distance
addRelatedModule(module: Module) {
  this._imports.add(module);
  // Use max to prevent distance regression
  module.distance = Math.max(
    module.distance || 0, 
    this._distance + 1
  );
}

This approach ensures stable dependency ordering and prevents initialization issues when components depend on each other. It’s particularly important for frameworks where proper initialization sequence directly affects functionality, such as when providers from one module need to be registered before dependent modules can access them.

---

Package.json configuration standards

Ensure package.json follows modern standards and maintains consistency across configuration fields. Use structured exports instead of simple main field, align dependency versions with engine requirements, prefer configuration properties over CLI flags, and avoid accidental version locking.

Key practices:

• Use structured exports with explicit types and default fields:

  "exports": {
  "types": "./build/index.d.ts", 
  "default": "./build/index.js"
  }
  

• Align @types/node version with engines field (e.g., if engines specifies “node”: “>=10”, use “@types/node”: “^10.17.26”)
• Place build tool configuration in package.json properties rather than CLI flags where possible
• Use caret (^) prefixes for dependencies unless intentionally locking versions
• Ensure consistency between related fields like main/exports and engines/type dependencies

---

Fix linting root causes

Address underlying code issues rather than disabling linting rules or working around auto-formatter conflicts. When linting tools flag legitimate problems, fix the root cause instead of suppressing the warning. When auto-formatters conflict with intentional code patterns, adjust project-wide configuration rather than using local disables.

For example, instead of:

// eslint-disable-next-line @typescript-eslint/ban-ts-comment
// @ts-ignore
internal_static

Fix the underlying TypeScript issue that requires the ignore comment.

When auto-formatters incorrectly modify intentional test patterns like A{'B'} to AB, configure the formatter globally rather than disabling rules on individual lines. This maintains code quality while preserving intentional code structure.

---

Secure hash algorithms

Always use cryptographically secure hash algorithms for sensitive operations instead of weak or broken ones. Weak algorithms can compromise security and make your application vulnerable. Prefer modern algorithms like SHA-256 over older or non-cryptographic hash functions.

When selecting a hashing algorithm, consider both security requirements and performance implications. As demonstrated in the benchmarks, sometimes the more secure option may also offer better performance:

// Avoid using weak hashing algorithms
// AVOID: return xxh32(value).toString();

// PREFER: Use cryptographically secure algorithms
return createHash('sha256').update(value).digest('hex');

Note that non-cryptographic hash functions (like xxhash) are designed for speed and collision resistance in data structures, but not for security purposes where resistance to attacks is required.

---

Use secure hash algorithms

Always use strong, modern cryptographic hash algorithms for security-sensitive operations. Avoid deprecated or weak algorithms that might be vulnerable to attacks. When selecting hash algorithms, consider both security requirements and performance characteristics.

For general hashing needs, prefer SHA-256 over older algorithms like SHA-1 or MD5, which have known vulnerabilities. As demonstrated in the benchmark, SHA-256 often offers better performance alongside stronger security:

// Avoid weak algorithms
// BAD:
return xxh32(value).toString();

// GOOD:
return createHash('sha256').update(value).digest('hex');

This change not only improves security by using a cryptographically stronger algorithm but can also improve performance. Security scanning tools often flag the use of deprecated cryptographic functions, so following this practice helps prevent security vulnerabilities while maintaining or enhancing application performance.

---

Use consistent curly braces

Always use curly braces for conditional statements and loops, even for single-line bodies. This maintains consistency throughout the codebase and improves readability. Avoid inline conditionals.

Instead of:

if (areThereNoFileIn && this.fileIsRequired) return;
if (this.moduleTokenCache.has(key)) return this.moduleTokenCache.get(key);

Use:

if (areThereNoFileIn && this.fileIsRequired) {
  return;
}
if (this.moduleTokenCache.has(key)) {
  return this.moduleTokenCache.get(key);
}

This style:

• Maintains consistent formatting across the codebase
• Makes code more readable and maintainable
• Reduces the risk of errors when modifying conditions
• Makes it easier to add additional statements later without restructuring

---

Use consistent control structures

Always use curly braces for control structures (if, for, while, etc.), even for single-line statements. This improves code readability and maintainability by making the code structure explicit and consistent.

Example:

// Incorrect
if (areThereNoFileIn && this.fileIsRequired) return;

// Correct
if (areThereNoFileIn && this.fileIsRequired) {
  return;
}

// Incorrect
if (this.flushLogsOnOverride) this.flushLogs();

// Correct
if (this.flushLogsOnOverride) {
  this.flushLogs();
}

This style:

• Prevents errors when adding more statements later
• Makes code structure immediately clear
• Maintains consistency across the codebase
• Makes code reviews more efficient by eliminating style discussions
• Reduces cognitive load when reading code

---

Optimize critical path iterations

Use appropriate iteration techniques in performance-critical code paths to minimize overhead and maximize execution speed:

1. Use raw for loops with early termination instead of array methods like map and filter for maximum performance:

// Less performant
return methods
  .map(methodKey => this.exploreMethodMetadata(instance, instancePrototype, methodKey))
  .filter(route => route !== undefined);

// More performant
const routes = [];
for (const methodKey of methods) {
  const route = this.exploreMethodMetadata(instance, instancePrototype, methodKey);
  if (!route) continue;
  routes.push(route);
}
return routes;

1. Consider reduce as a middle ground between readability and performance when appropriate.

2. Move invariant calculations outside loops and callbacks to prevent redundant executions:

// Less performant
function callback() {
  const isTreeDurable = wrapper.isDependencyTreeDurable(); // Executed on each call
  // ...
}

// More performant
const isTreeDurable = wrapper.isDependencyTreeDurable(); // Executed once
function callback() {
  // ...
}

1. Break loops early when the goal has been achieved:

// Less performant (processes all items)
return this.getAll(metadataKey, targets).find(item => item !== undefined);

// More performant (stops at first match)
for (const target of targets) {
  const result = this.get(metadataKey, target);
  if (result !== undefined) {
    return result;
  }
}
return undefined;

For critical code paths, benchmark different approaches with realistic data volumes to confirm performance benefits before sacrificing readability.

---

Proper asynchronous error handling

Ensure errors in asynchronous operations and event-based systems are handled consistently to prevent unexpected behavior. Always maintain Promise integrity by never resolving and rejecting the same Promise, and use appropriate error event handlers.

When working with Promises:

// INCORRECT: Could both reject and resolve the same promise
if (err instanceof KafkaRetriableException && !isPromiseResolved) {
  reject(err);
}

// CORRECT: Ensure mutual exclusivity
if (err instanceof KafkaRetriableException && !isPromiseResolved) {
  reject(err);
} else {
  // other code
}

For event streams and emitters:

// INCORRECT: Using .on() may trigger multiple error handling instances
body.getStream().on('error', (err: Error) => {
  // This could be called multiple times, causing "headers already sent" errors
});

// CORRECT: Use .once() for one-time error events
body.getStream().once('error', (err: Error) => {
  // This will only be called once
});

For reactive streams, handle errors properly with catchError:

result$.pipe(
  takeUntil(fromEvent(call, CANCEL_EVENT)),
  catchError(err => {
    const data = err instanceof Error ? err.message : err;
    stream.writeMessage({ type: 'error', data }, handleWriteError);
    return EMPTY; // or of(fallbackValue) depending on your recovery strategy
  })
)

Always ensure error handling preserves system consistency and properly releases resources. For critical errors, implement graceful shutdown mechanisms to prevent resource leaks and data corruption.

---

Simplify naming conventions

Prioritize simple, enforceable naming conventions over complex guidelines that are difficult to follow consistently. When establishing naming standards, focus on what serves a clear purpose and can be realistically maintained by the team.

Rather than creating detailed, multi-part naming schemes that require constant enforcement, identify the most critical naming points and make those standards clear and simple. For example, instead of complex commit message formats, focus on descriptive pull request titles that serve the changelog.

Key principles:

• Choose fewer, more important naming rules over many detailed ones
• Document naming conventions explicitly to avoid reliance on “tribal knowledge”
• Tailor naming standards to their specific use case and audience
• Recognize that “naming things is hard, the less the better”

Example: Instead of enforcing detailed commit message conventions that aren’t consistently followed, establish clear PR title guidelines since those titles will be used in changelogs and need to be descriptive for end users.

This approach leads to better compliance and more consistent naming across the codebase, as team members can actually follow and remember simpler standards.

---

CSS comment standards

Always use proper CSS comment syntax (/* */) instead of inline comments (//) for better cross-browser compatibility and code consistency. Additionally, rely on autoprefixer configuration for vendor prefixes rather than manually adding them, which reduces code duplication and maintenance overhead.

Example of proper CSS commenting:

/* Good: Proper CSS comment syntax */
right: 10px; /* Allows clicking on the scrollbar */

/* Avoid: Inline comment syntax */
right: 10px; // Allows clicking on the scrollbar

For vendor prefixes, configure autoprefixer at the project level instead of manually adding prefixes:

/* Good: Let autoprefixer handle this */
user-select: none;

/* Avoid: Manual vendor prefixes when autoprefixer is available */
-webkit-user-select: none;
-khtml-user-select: none;
-moz-user-select: none;
-ms-user-select: none;
user-select: none;

This approach ensures consistent formatting, reduces maintenance burden, and leverages build tools effectively for better code organization.

---

Extract reusable hooks

When you identify React logic that handles complex state management or event handling patterns that could be reused across multiple components, extract it into a custom hook. This promotes code reusability, reduces duplication, and makes components more focused on their primary responsibilities.

For example, IME (Input Method Editor) composition handling is a common pattern that should be extracted:

(defn use-ime-composition []
  (let [*composing? (rum/use-ref false)]
    {:composing? (rum/deref *composing?)
     :on-composition-start #(rum/set-ref! *composing? true)
     :on-composition-end #(rum/set-ref! *composing? false)}))

;; Usage in component:
(rum/defc search-input [q matches]
  (let [{:keys [composing? on-composition-start on-composition-end]} (use-ime-composition)
        on-change-fn (fn [e]
                       (let [value (util/evalue e)
                             e-type (gobj/getValueByKeys e "type")]
                         (cond (= e-type "compositionstart") (on-composition-start)
                               (= e-type "compositionend") (on-composition-end))
                         (when-not composing?
                           (debounced-search))))]
    ;; component JSX...
    ))

This approach also helps identify and eliminate redundant local state when the same functionality is already handled by other mechanisms like global state updates or component properties.

---

Respect existing formatting

When modifying existing files, maintain the formatting and style conventions already established in those files rather than imposing new formatting standards. This includes respecting existing whitespace patterns, indentation styles, and structural formatting choices.

For documentation files, ensure consistency with existing patterns such as proper spacing between headers and content. For code files, follow the existing whitespace and indentation conventions of the file being modified.

Example:

## Auto-formatting

[cljfmt](https://cljdoc.org/d/cljfmt/cljfmt/0.9.0/doc/readme) is a common formatter...

The principle is that contributions should harmonize with the existing codebase style rather than introduce formatting inconsistencies, even if the new formatting might be considered “better” in isolation.

---

Prevent command injection vulnerabilities

When implementing shell command execution or CLI features, prioritize security by avoiding direct shell execution and implementing robust input validation. Simple allow/deny lists for dangerous commands may not provide sufficient protection against command injection attacks.

Consider using established security libraries like shellquote for proper input sanitization, or avoid shell execution entirely when possible. Before exposing command execution capabilities to plugins or user input, thoroughly research and test the security implications.

Example of insufficient protection:

(def dangerous-commands
  ["rm" "sudo" "chmod"]) ; This list-based approach may not be comprehensive enough

Instead, prefer safer alternatives like:

• Using specific APIs rather than shell commands
• Implementing strict input validation and escaping
• Leveraging security-focused libraries for command sanitization
• Deferring shell execution features until proper security measures are established

The goal is to prevent attackers from injecting malicious commands through user input or plugin interfaces.

---

Check undefined before use

Always verify that values are not undefined before accessing or using them, whether they are object properties or function parameters. This prevents TypeScript compilation errors and potential runtime issues.

When accessing object properties that may not exist, use conditional checks or optional chaining. When dealing with function parameters that could be undefined, ensure proper type handling and validation.

Example from the codebase:

// Before: Direct property access (causes TS error)
<TablerIcon name="text" />

// After: Check existence before use
<TablerIcon name={shape.props.label || shape.props.text ? "forms" : "text"} />

// For function parameters, ensure types handle undefined:
// Instead of assuming 'color' exists, fix types in ColorInput to handle undefined values

This practice ensures type safety and prevents unexpected behavior when values might be missing or undefined.

---

Structure behavior-driven tests properly

Organize tests using behavior-driven development (BDD) patterns to improve clarity and maintainability. Group related tests using descriptive describe blocks for methods/scenarios, and write clear test cases that focus on testing behavior rather than implementation details.

Key principles:

1. Use nested describe blocks to group related tests
2. Write descriptive test cases that explain the expected behavior
3. Test public interfaces instead of implementation details
4. Avoid redundant test calls
5. Focus assertions on behavior verification

Example:

describe('CatsService', () => {
  describe('findAll', () => {
    it('should return an array of cats', async () => {
      // Test the actual service behavior, don't mock what you're testing
      const result = await catsService.findAll();
      await expect(result).resolves.toEqual(expectedCats);
    });
  });

  describe('create', () => {
    describe('when provided valid cat data', () => {
      it('should successfully create a new cat', async () => {
        const newCat = { name: 'Whiskers', age: 2 };
        const result = await catsService.create(newCat);
        expect(result).toMatchObject(newCat);
      });
    });
  });
});

---

Avoid testing anti-patterns

Ensure your tests actually validate functionality by avoiding common testing anti-patterns:

1. Don’t mock what you’re testing - When testing a method, don’t mock its implementation as this tests nothing meaningful:

// WRONG - mocking the method under test
it('should find all cats', async () => {
  jest.spyOn(catsService, 'findAll').mockImplementation(() => result);
  expect(await catsService.findAll()).toEqual(result);
});

// RIGHT - setting up the state to test the actual implementation
it('should find all cats', async () => {
  // @ts-ignore - access internal state for test setup
  catsService.cats = result;
  expect(await catsService.findAll()).toEqual(result);
});

1. Test public interfaces, not private functions - Private methods should be tested through public methods. If a private method is complex, consider extracting it to a separate class:

// WRONG - testing private methods directly
describe('getPaths', () => { // private method
  it('should return paths', () => {
    expect(middlewareModule['getPaths'](routes)).toEqual(['path1', 'path2']);
  });
});

// RIGHT - test via public interface or extract to a testable class
describe('register', () => { // public method
  it('should configure paths correctly', () => {
    middlewareModule.register(routes);
    // assert the expected behavior
  });
});

1. Don’t make redundant test calls - Call the method once and make all assertions on that single call:

// WRONG - calling the method multiple times
it('should create a user', () => {
  usersController.create(createUserDto); // unnecessary call
  expect(usersController.create(createUserDto)).resolves.toEqual({
    id: 'a id',
    ...createUserDto,
  });
});

// RIGHT - single call with multiple assertions
it('should create a user', () => {
  expect(usersController.create(createUserDto)).resolves.toEqual({
    id: 'a id',
    ...createUserDto,
  });
  expect(usersService.create).toHaveBeenCalledWith(createUserDto);
});

1. Test the actual behavior - Ensure your tests verify functionality, not just that methods were called:

// WRONG - only checking if a method was called
it('should remove a user', async () => {
  const removeUserSpy = jest.spyOn(service, 'remove');
  service.remove('anyid');
  expect(removeUserSpy).toHaveBeenCalledWith('anyid');
});

// RIGHT - checking the actual behavior
it('should remove a user', async () => {
  const repositorySpy = jest.spyOn(repository, 'delete');
  await service.remove('anyid');
  expect(repositorySpy).toHaveBeenCalledWith('anyid');
  // and possibly check that the user is actually gone
});

---

## Prevent race conditions

<!-- source: nestjs/nest | topic: Concurrency | language: TypeScript | updated: 2022-11-09 -->

When handling concurrent operations in asynchronous environments, avoid mutating shared state that could lead to race conditions. Instead, create operation-specific state or use immutable patterns to ensure each request path has isolated context.

**Problem example:**
```typescript
// PROBLEMATIC: Mutating shared socket instance can cause race conditions
Object.assign(socket, {
  getPattern: () => this.reflectCallbackPattern(currentCallback),
});

If multiple messages arrive nearly simultaneously, they could overwrite each other’s metadata before processing completes.

Better approach:

// Create request-specific context instead of modifying shared objects
class WsArgumentHost {
  constructor(private client: any, private callback: MessageHandler) {}
  
  getClient() {
    return this.client;
  }
  
  getPattern() {
    return this.reflectCallbackPattern(this.callback);
  }
}

Other best practices:

1. Use flags to check cancellation before performing resource allocation
2. Use Set or Map data structures to track execution state without side effects
3. Create local copies of data instead of modifying shared objects
4. Consider using immutable data structures for shared state

---

Define Equality Semantics

Ensure algorithmic helpers that use data structures (e.g., deep equality, key intersections) have an explicit correctness contract and are implemented with runtime-compatible structures.

• For deep equality: verify the algorithm enforces all required invariants (e.g., same keys present in both objects, not just equal lengths). Clearly decide whether special values follow native === semantics or “collection” semantics (e.g., treating NaN as equal like Set).
• For intersections/maps/sets: don’t assume Set/custom map types are available or supported across all target runtimes. Prefer native Map when broadly supported, or implement a fallback/intersection that avoids Set when legacy environments matter.

Example (avoid Set for key intersection):

// Compatible intersection without Set
function sharedKeys(a: Record<string, unknown>, b: Record<string, unknown>) {
  const out: string[] = [];
  for (const key in a) {
    if (Object.prototype.hasOwnProperty.call(b, key)) out.push(key);
  }
  return out;
}

Apply this by (1) writing down the intended semantics (especially for equality) and (2) choosing the simplest compatible data structure/approach for the supported JavaScript environments.

---

Follow protocol standards

When implementing networking features, strictly adhere to protocol specifications and standards to ensure proper interoperability. This applies to HTTP headers, status codes, and protocol-specific connection handling.

For HTTP responses:

1. Only use standardized status codes (avoid non-standard codes like 499) to ensure consistent client behavior
2. When setting default headers, respect existing values by checking with !== undefined rather than truthy checks:

// Good practice - only set default if undefined
if (!response.getHeader('Content-Type')) {
  response.setHeader('Content-Type', 'application/octet-stream');
}

// For redirects, use standard status codes with proper defaults
const code = statusCode ? statusCode : HttpStatus.FOUND; // 302

1. For specialized protocols like Server-Sent Events (SSE), include all required headers for compatibility with browsers and proxies:

response.writeHead(200, {
  'Content-Type': 'text/event-stream; charset=utf-8',
  'Cache-Control': 'no-cache',
  'X-Accel-Buffering': 'no'
  // Server will set Transfer-Encoding automatically
});

1. Implement proper connection cleanup during service shutdown to prevent resource leaks:

// Close open connections on server shutdown
this.openConnections.forEach(socket => {
  socket.destroy();
});

Consistent adherence to protocol standards improves interoperability, simplifies debugging, and prevents subtle edge cases in network communications.

---

Strategic dependency versioning

Use strategic versioning approaches for dependencies based on their impact and maintenance status. Pin exact versions for dependencies that inject global styles, configurations, or behaviors to prevent unintended breaking changes during automatic updates. For unmaintained dependencies, evaluate alternatives or consider forking if there are useful pending PRs that benefit your project.

Example from package.json:

{
  "dependencies": {
    // Pin exact versions for global-affecting dependencies
    "@tailwindcss/forms": "0.5.3",
    "@tailwindcss/typography": "0.5.7",
    
    // Use semantic versioning for stable, well-maintained packages
    "@playwright/test": "^1.24.2",
    
    // Consider forking or alternatives for stale dependencies
    "remove-accents": "0.4.2" // Last updated 4 years ago - evaluate alternatives
  }
}

This approach balances stability with maintainability, ensuring that configuration changes are intentional while avoiding technical debt from abandoned dependencies.

---

Tailwind configuration patterns

Follow Tailwind CSS’s recommended configuration patterns to ensure proper functionality and JIT mode compatibility. Use the theme.extend object for custom values like font sizes, implement plugin functions for advanced customizations like CSS variable exposure, and explicitly safelist dynamic classes when regex patterns are incompatible with JIT mode.

Example configuration structure:

module.exports = {
  mode: 'jit',
  purge: {
    content: ['./src/**/*.js'],
    safelist: [
      "bg-red-500", "bg-blue-500", // explicit listing for JIT
    ]
  },
  plugins: [
    exposeColorsToCssVars, // custom plugin function
  ],
  theme: {
    extend: {
      fontSize: {
        '2xs': ['0.625rem', '0.875rem'] // proper extension
      },
    }
  }
}

This approach ensures dynamic classes aren’t purged, custom functionality works correctly, and the configuration remains maintainable and compatible with Tailwind’s optimization features.

---

Proper HTTP status codes

When implementing authentication and authorization systems, use semantically correct HTTP status codes to accurately convey the nature of security-related failures. This improves API security by providing accurate information to clients without exposing unnecessary details.

Specifically:

• Use 403 Forbidden when a user is authenticated but lacks authorization (e.g., inactive user, insufficient permissions)
• Use 401 Unauthorized for authentication failures (invalid or missing credentials)
• Use 400 Bad Request only for malformed client requests

Example implementation:

async def get_current_active_user(current_user: User = Depends(get_current_user)):
    if current_user.disabled:
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN, detail="Inactive user"
        )
    return current_user

This approach follows REST principles and improves security by providing consistent and accurate status codes that properly communicate authorization states without revealing implementation details.

---

Clear intention in names

Choose names that clearly communicate intention and follow established conventions. This applies to variables, functions, methods, and architectural components.

Key practices:

1. Follow architectural naming patterns (e.g., Controller-Service-Repository)

   // Instead of:
   function NotesUseCase(notesRepository) { ... }
      
   // Prefer:
   function NotesService(notesRepository) { ... }
   

2. Use explicit function names rather than anonymous expressions

   // Instead of:
   var proto = module.exports = function(options) { ... }
      
   // Prefer:
   function router(options) { ... }
   module.exports = router;
   

3. Choose distinct names for properties and methods to prevent confusion

   // Confusing - same name used for different purposes:
   app.router = function() { ... }  // Method
   this.router = new Router();      // Property
      
   // Better - clearly distinguished names:
   app.createRouter = function() { ... }  // Method
   this._router = new Router();           // Property
   

4. Use prefixes (like underscore) to indicate private members

   // No visibility indication:
   this.cache = Object.create(null);
      
   // With visibility indication:
   this._cache = Object.create(null);
   

5. Avoid names that could be misinterpreted for other common patterns

   // Potentially confusing:
   app.dispatch = function(res, event, args) { ... }
      
   // More descriptive of actual purpose:
   app.dispatchEvent = function(res, event, args) { ... }
   

6. Choose descriptive names over abbreviated ones

   // Unclear abbreviation:
   res.addTmplVars(options);
      
   // More descriptive:
   res.addTemplateVariables(options);
   

Consistently following these naming conventions improves code readability, maintainability, and helps prevent confusion among team members.

---

comprehensive error handling

Ensure error handling mechanisms are comprehensive and graceful rather than limited or forceful. Use persistent event listeners (process.on()) instead of one-time listeners (process.once()) for critical error scenarios to handle all occurrences, not just the first one. Similarly, prefer graceful shutdown methods that allow proper cleanup over forceful process termination.

For signal and exception handling:

// Preferred: Handles all occurrences
process.on('SIGINT', this.kill)
process.on('SIGTERM', this.kill)
process.on('uncaughtException', (error) => {
  // Handle error
})

// Avoid: Only handles first occurrence
process.once('SIGINT', this.kill)

For application shutdown:

// Preferred: Graceful shutdown with cleanup
await this.application.shutdown()

// Avoid: Forceful termination
await this.exit()

This approach ensures that all error scenarios are properly handled and allows applications to clean up resources gracefully, preventing issues like interrupted stdout or incomplete cleanup operations.

---

Modern null safety patterns

Leverage modern JavaScript features and utility functions for safer null/undefined handling. This reduces code verbosity while improving reliability.

Key practices:

1. Use optional chaining for nested property access: ```typescript // Instead of if (pattern && pattern.test(str)) { }

// Use if (pattern?.test(str)) { }

2. Apply nullish coalescing for default values:
```typescript
// Instead of
const ttl = value || defaultValue;

// Use
const ttl = value ?? defaultValue;

1. Utilize isNil() utility for explicit null/undefined checks: ```typescript // Instead of if (value === null || value === undefined) { }

// Use import { isNil } from ‘@nestjs/common/utils/shared.utils’; if (isNil(value)) { }

These patterns make code more concise while maintaining clear intent and proper null safety. They help prevent null reference errors and make null handling more consistent across the codebase.

---

## Standardize null safety patterns

<!-- source: nestjs/nest | topic: Null Handling | language: TypeScript | updated: 2022-03-07 -->

Use modern JavaScript features and utility functions consistently for null/undefined checks. Prefer optional chaining (?.), nullish coalescing (??), and dedicated utility functions like isNil() over direct null checks or OR (||) operators.

Key practices:
1. Use optional chaining for potentially null properties:
```typescript
// Instead of
if (pattern && pattern.test(str))

// Use
if (pattern?.test(str))

1. Use nullish coalescing for default values: ```typescript // Instead of const ttlValueOrFactory = ttlMetadata || null;

// Use const ttlValueOrFactory = ttlMetadata ?? null;

3. Use utility functions for explicit null/undefined checks:
```typescript
// Instead of
if (value === null || value === undefined)

// Use
import { isNil } from '@nestjs/common/utils';
if (isNil(value))

This approach improves code readability, reduces potential null reference errors, and maintains consistency across the codebase. It leverages TypeScript’s type system and modern JavaScript features for better null safety.

---

Clear array operations

When working with arrays, prioritize clarity and explicitness over terse or clever constructs. For array membership checks, use array.indexOf(item) === -1 rather than less obvious expressions like !~array.indexOf(item) or array.indexOf(item) < 0. This improves readability and makes code intent immediately clear to other developers.

Be cautious with array manipulation methods that can cause unexpected behavior. The .concat() method can flatten arrays in unexpected ways:

// Potentially problematic:
[key].concat(fns)  // Will flatten if fns contains arrays

// More predictable alternatives:
[key, ...fns]      // ES6 spread syntax preserves structure
[].concat([key], fns)  // More explicit nesting

These practices ensure that array operations behave predictably and their intention is clear to anyone reading the code, which is especially important for search and manipulation algorithms.

---

optimize computational complexity

When implementing algorithms, especially in runtime or performance-critical code, prioritize computational efficiency by minimizing redundant operations and simplifying mathematical expressions. Look for opportunities to reduce the number of multiplications, divisions, and variable assignments.

For example, instead of performing multiple redundant calculations:

const scale = {
    x: to.width / node.clientWidth,
    y: to.height / node.clientHeight
};
const dx = ((from.left / scale.x) + (from.width / scale.x) * ox / (to.width / scale.x)) - ((to.left / scale.x) + ox);

Simplify to reduce operations:

const dx = ((from.left - to.left) * node.clientWidth + from.width * ox) / to.width - ox;

Similarly, consolidate variable declarations and operations:

// Instead of multiple variables and assignments
export function createSlot(slots) {
    const root_slots = {};
    for (const slot_name in slots) {
        let elements = slots[slot_name];
        if (!Array.isArray(elements)) {
            elements = [elements];
        }
        root_slots[slot_name] = [create_root_slot_fn(elements)];
    }
    return root_slots;
}

// Optimize to fewer operations
export function createSlot(input) {
    var key, tmp, slots={};
    for (key in input) {
        tmp = input[key];
        slots[key] = [create_root_slot_fn(Array.isArray(tmp) ? tmp : [tmp])];
    }
    return slots;
}

This approach is particularly important in runtime code where efficiency is paramount, as it directly impacts user experience and application performance.

---

Preserve unset field values

When implementing partial updates in FastAPI, use the exclude_unset parameter in Pydantic’s .dict() or .model_dump() method to avoid overriding existing values with defaults. This ensures that only fields explicitly set by the client are updated, while preserving any existing values for fields not included in the request. This pattern is particularly useful for PATCH operations.

@app.patch("/items/{item_id}")
def update_item(item_id: str, item: Item):
    # Retrieve the existing item from storage
    stored_item = get_stored_item(item_id)
    stored_item_model = Item(**stored_item)
    
    # Get only the fields that were set in the request
    update_data = item.dict(exclude_unset=True)  # or .model_dump(exclude_unset=True) in Pydantic v2
    
    # Update the stored model, preserving fields not explicitly set
    updated_item = stored_item_model.copy(update=update_data)
    
    # Convert the updated model to a format suitable for storage
    return updated_item

By using exclude_unset=True, you prevent accidentally resetting fields to default values when they weren’t included in the request body. This approach respects null handling principles by distinguishing between fields that were explicitly set to null and fields that were simply not included in the request.

---

Documentation code quality

Ensure documentation code blocks use appropriate syntax highlighting and provide comprehensive, functional examples. For shell commands in markdown, use sh syntax highlighting rather than console for better highlighting accuracy and copy functionality. When documenting APIs or components, provide multiple complete examples that demonstrate different usage patterns rather than incomplete snippets.

Example of proper shell command formatting:

$ npm install ink@next react

Example of comprehensive API documentation:

import { Text } from "ink"

// Basic usage
<Text color="red">Error message</Text>

// Background color
<Text bgRed>Alert</Text>

// RGB colors
<Text rgb={[255, 255, 255]}>Custom color</Text>

This approach improves code readability in documentation and helps developers understand the full scope of available options through practical, working examples.

---

Consistent code formatting

Maintain consistent formatting and alignment throughout the codebase to improve readability and maintainability. This includes proper indentation for multi-line constructs, consistent spacing in documentation, and clear structural organization.

Key formatting practices:

• Use consistent indentation for multi-line type intersections and complex structures
• Align related elements properly for visual clarity
• Format JSDoc comments with proper spacing and include relevant tags like @default
• Prefer simpler conditional structures (separate if statements over else if chains when conditions are mutually exclusive)

Example of proper multi-line type formatting:

export type Styles = PaddingStyles &
	MarginStyles &
	FlexStyles &
	DimensionStyles &
	PositionStyles &
	WrapTextStyles;

Example of proper JSDoc formatting:

/**
 * Set this property to `hidden` to hide content overflowing the box.
 *
 * @default 'visible'
 */

This approach ensures code is visually consistent, easier to scan, and more maintainable across the entire codebase.

---

Use unique password salts

When implementing password hashing, always use unique, randomly generated salts for each user. Using constant or shared salts significantly reduces security by allowing identical passwords to produce identical hashes, making them vulnerable to rainbow table attacks.

Modern hashing libraries like bcrypt handle salt generation automatically. Instead of manually managing salts:

// AVOID: Using fixed salt values
var encryPassword = bcrypt.hashSync('foobar', 10); // '10' is not a salt but work factor

// RECOMMENDED: Let bcrypt generate and manage unique salts
const hashedPassword = bcrypt.hashSync('foobar', bcrypt.genSaltSync(10));
// Or with promises
const hashedPassword = await bcrypt.hash('foobar', 10);

When verifying passwords, bcrypt automatically handles salt extraction from the stored hash, so no separate salt storage is needed:

// Verification is simple
const isMatch = bcrypt.compareSync('foobar', hashedPassword);
// Or with promises
const isMatch = await bcrypt.compare('foobar', hashedPassword);

The work factor (10 in the examples) determines the computational complexity and should be adjusted based on your server’s performance capabilities.

---

Pin dependency versions

Always specify exact versions of tools and dependencies in CI/CD workflows rather than using ‘latest’ or floating versions. This ensures build reproducibility, prevents unexpected failures when upstream dependencies change, and makes debugging easier.

Example:

# Instead of this (unstable):
- name: Setup golangci-lint
  uses: golangci/golangci-lint-action@v2
  with:
    version: latest

# Do this (stable):
- name: Setup golangci-lint
  uses: golangci/golangci-lint-action@v2
  with:
    version: v1.41.1
    args: --verbose

Similarly, when defining test matrices, explicitly specify all supported versions to ensure comprehensive coverage across environments.

---

HTTP header management

When working with HTTP responses, follow these principles for proper header management:

1. Only set default headers when undefined, not when falsy:

   if (!response.getHeader('Content-Type')) {
     response.setHeader('Content-Type', 'application/octet-stream');
   }
   

   This preserves intentionally set falsy values while ensuring compatibility between different HTTP adapters like Express and Fastify.

2. For specialized protocols like Server-Sent Events (SSE), include all necessary headers for proxy compatibility:

   response.writeHead(200, {
     'Content-Type': 'text/event-stream; charset=utf-8',
     'Cache-Control': 'private, no-cache, no-store, must-revalidate, max-age=0, no-transform',
     'X-Accel-Buffering': 'no'
   });
   

   Avoid setting headers that should be determined by the server, such as Transfer-Encoding.

3. For redirects, use standard HTTP status codes with 302 (FOUND) as the default:

   public redirect(response: any, statusCode: number, url: string) {
     const code = statusCode ? statusCode : HttpStatus.FOUND;
     // implementation
   }
   

4. Maintain consistency between different HTTP adapters to ensure predictable behavior across platforms.

---

Use descriptive variable names

Avoid single-character variables and abbreviations in favor of descriptive, full-word names that clearly communicate the variable’s purpose or content. This improves code readability and makes the codebase more maintainable for other developers.

Examples of improvements:

• Change x to children in function parameters
• Change str to string for string parameters
• Change e to focusable when iterating over focusable elements

Descriptive names act as inline documentation, making code self-explanatory and reducing the cognitive load for developers reading or maintaining the code.

---

React interface clarity

Ensure React interfaces have descriptive names and accurate documentation that clearly communicate their purpose and usage. Interface names should be specific to their context (e.g., StdoutContextProps instead of StdoutProps for Context-related interfaces), and API documentation should accurately reflect how methods are called (e.g., distinguishing between instance methods and callback functions returned from hooks).

Example of good naming:

// Good: Context-specific naming
export interface StdoutContextProps {
  // ...
}

// Good: Clear hook documentation
/**
 * Assign an ID to this component, so it can be programmatically focused with `focus(id)`.
 * Note: `focus` is a callback returned from `useFocus`, not an instance method.
 */

This practice helps developers quickly understand the purpose and correct usage of React components, hooks, and Context APIs, reducing confusion and implementation errors.

---

Use appropriate documentation formats

Choose the most suitable documentation format based on context to maximize readability and information value.

For Pydantic models:

• Use class-level docstrings for comprehensive documentation that supports rich formatting including newlines and emphasis
• Use Field descriptions for specific field-level details
• Include line breaks in longer descriptions to improve readability

Example:

class Item(BaseModel):
    """Description of the model.
    
    This allows more formatting than field descriptions like
    
    newlines, *emphasis*.
    """
    id: str = Field(
        title="Short title of the field",
        description="Longer description what the field is used for.\n\nUse line breaks for readability.",
    )

This approach provides consistent and well-structured documentation that’s readable both in source code and in generated API documentation.

---

Ensure documentation usability

Documentation should be practical and serve its intended audience effectively. Examples must be runnable out-of-the-box or include clear setup instructions, while API documentation should focus on public interfaces that users actually need.

For code examples, ensure they can be executed without complex setup. If dependencies are required, either make examples self-contained or provide clear integration guidance in appropriate documentation sections.

For API documentation, document public methods and parameters that users will interact with, but avoid exposing internal implementation details that could confuse or mislead developers.

Example of good practice:

// Good: Clear public API documentation
/**
 * Unmounts the component instance
 * @returns {void}
 */
unmount() {
  // Internal error handling hidden from public API
  this.internalUnmount(error);
}

Rather than documenting internal parameters like unmount(error) that users shouldn’t use, keep the public interface clean and move complex examples to dedicated recipe documentation where proper context can be provided.

---

prefer idiomatic patterns

Choose language-native methods and control structures that make code more readable and maintainable. Use built-in functions instead of manual implementations, select appropriate control flow structures, and write explicit code that clearly communicates intent.

Examples of preferred patterns:

• Use char.repeat(max) instead of manual string concatenation loops
• Use switch statements instead of multiple if-else chains when handling discrete values
• Use explicit return statements in cleanup functions: return () => { cleanup(); }; rather than return () => cleanup(); when you don’t want to return the cleanup function’s result
• Use cleaner import paths that leverage package.json configuration

This approach reduces cognitive load, leverages language features effectively, and makes code intentions clearer to other developers.

---

Use descriptive names

Choose variable, function, and export names that clearly communicate their purpose and content. Avoid abbreviations and ambiguous terms that could mislead other developers about what the identifier represents.

Key principles:

• Variable names should accurately reflect what they contain, not just their general category
• Avoid abbreviations when full words improve clarity (e.g., previousCounter instead of prevCounter)
• Export names should be specific enough to understand their purpose (e.g., ProgressBar instead of Bar)

Example of unclear naming:

const subProcess = childProcess.spawn('ping', ['8.8.8.8']).stdout;
// Misleading: subProcess actually contains stdout, not the process

exports.Bar = Bar; // Too ambiguous

Example of clear naming:

const subProcess = childProcess.spawn('ping', ['8.8.8.8']);
const stdout = subProcess.stdout;
// Clear: each variable accurately represents what it contains

exports.ProgressBar = ProgressBar; // Specific and clear

This practice prevents confusion during code reviews and maintenance, making the codebase more self-documenting and easier to understand.

---

semantic names with counters

When generating unique identifiers that may have multiple instances, combine semantic base names with counters or indices to ensure both readability and uniqueness. Use meaningful component names, scope IDs, or descriptive strings as the base, then append a counter to distinguish multiple instances.

Use clear separators (like ‘:’ or ‘-‘) between the semantic part and the counter to improve readability and parsing:

// Good: semantic base + separator + counter
const defaultKey = this.$options._scopeId || this.$options.name || ''
this._fetchKey = key + ':' + getCounter(key)

// Results in readable keys like:
// 'MyComponent:0', 'MyComponent:1'
// 'UserProfile-0', 'UserProfile-1'

This pattern prevents identifier collisions while maintaining semantic meaning, making debugging and state inspection much easier than using purely numeric or random identifiers.

---

Manage testing dependencies

Properly manage testing-related dependencies by placing them in devDependencies and regularly auditing them to remove redundant tools. Test-only packages should never appear in regular dependencies, and outdated testing libraries should be removed when newer alternatives are already present in the project.

Examples:

• Add testing frameworks like nunjucks in devDependencies: ```diff “mysql”: “2.18.1”, “nats”: “1.4.9”, “nodemon”: “2.0.4”,
  • “nunjucks”: “^3.2.1”, ```
• Remove redundant testing tools: ```diff “imports-loader”: “^0.7.0”,
  • “istanbul”: “^0.4.5”, ``` (When using nyc which already depends on istanbul-lib-coverage)

Keep your testing infrastructure lean by regularly reviewing dependencies to ensure they’re necessary, properly placed, and up-to-date.

---

Test dependency management

Testing tools and libraries should be placed in devDependencies rather than regular dependencies in package.json. Regularly review testing dependencies to identify and remove outdated or redundant packages. For example, if a newer testing tool now includes functionality previously provided by a separate package (like ‘nyc’ now depending on ‘istanbul-lib-coverage’ instead of ‘istanbul’), remove the redundant dependency.

// Good practice:
"devDependencies": {
  "nunjucks": "^3.2.1",  // For integration tests
  "nyc": "^15.0.0"       // Uses istanbul-lib-coverage internally
}

// Avoid:
"dependencies": {
  "nunjucks": "^3.2.1"   // Wrong place for testing tools
},
"devDependencies": {
  "istanbul": "^0.4.5",  // Redundant with nyc
}

---

Use standard API constants

Always use standard library constants for HTTP methods and status codes rather than string literals or numeric values. This improves code readability, prevents typos, and makes it easier to maintain API consistency.

For HTTP methods:

// Incorrect
switch method {
  case "GET":
    return blue
  case "POST":
    return cyan
  case "DELETE":
    return red
  // ...
}

// Correct
switch method {
  case http.MethodGet:
    return blue
  case http.MethodPost:
    return cyan
  case http.MethodDelete:
    return red
  // ...
}

For status codes:

// Incorrect
c.ProtoBuf(201, data)

// Correct
c.ProtoBuf(http.StatusCreated, data)

Similarly, keep references to standards (like RFCs) current in code comments and documentation. For example, update content negotiation references from RFC 2616 to the more current RFC 7231 section 5.3.2.

This practice improves code maintainability, leverages compiler checking, provides better IDE support, and ensures your API follows widely accepted conventions.

---

Provide clear documentation context

Documentation should include practical context, clear explanations, and appropriate examples to help users understand both what functionality does and when to use it. Avoid confusing technical jargon and provide concrete use cases.

When documenting APIs or features:

• Include use-case examples that show when and why someone would use the functionality
• Replace confusing technical descriptions with clear, practical explanations
• Add visual aids like screenshots or GIFs when showcasing functionality
• Provide code examples that demonstrate real-world usage

For example, instead of writing “This function is useful when your component needs to know the amount of available space it has before it can start rendering”, write “This function is useful when your component needs to know the amount of available space it has. You could use it, for example, when you need to change layout based on the length of its content.”

The goal is to make documentation immediately useful to developers by providing the context they need to understand not just how something works, but when and why they should use it.

---

Use appropriate collections

Choose the right collection implementation for each algorithmic task to optimize both performance and readability. Use Sets for operations requiring uniqueness, TreeMap for maintaining sorted keys, and leverage built-in collection methods rather than implementing operations manually.

Key practices:

• Use HashSet instead of List+contains checks when eliminating duplicates
• Prefer Map.computeIfAbsent over get-check-put patterns
• Use specialized collection methods like Collections.addAll or direct List.sort instead of chained operations
• Select TreeMap when sorted key access is required

Example of improvement:

// Less efficient approach
List<String> items = new ArrayList<>();
items.addAll(Arrays.asList(array1));
for (String item : array2) {
    if (!items.contains(item)) {  // O(n) operation for each check
        items.add(item);
    }
}

// More efficient approach
Set<String> uniqueItems = new LinkedHashSet<>();
Collections.addAll(uniqueItems, array1);
Collections.addAll(uniqueItems, array2);  // Duplicates automatically handled

Another optimization example:

// Less efficient sorting
Collections.sort(advisors, new OrderComparator());

// More efficient sorting
advisors.sort(OrderComparator.INSTANCE);  // Or OrderComparator.sort(advisors)

This approach improves algorithmic efficiency by selecting data structures with appropriate time complexity for the required operations.

---

Short-Circuit for Performance

In performance-sensitive code paths, minimize unnecessary work by ordering conditions to short-circuit early, and avoid redundant async wrappers.

Apply these rules:

1. Guard with cheap predicates first (e.g., enabled/boolean flags) so later conditions/callbacks are never evaluated when they can’t change the outcome.
2. Don’t call expensive checkers unless needed: ensure threshold/count/boolean conditions gate any retryChecker(...)-style functions.
3. In async functions, return values directly—don’t wrap them with Promise.resolve, and avoid unnecessary else after a return.

Example patterns:

// 1) Guard before evaluating other conditions
const shouldRefetch = query.instances.some(instance =>
  instance.config.enabled && instance.config.refetchIntervalInBackground
);

// 2) Gate expensive retryChecker with cheaper conditions
const canRetryByCount = query.state.failureCount <= query.config.retry;
const shouldRetry =
  query.config.retry === true ||
  (canRetryByCount && query.config.retryChecker(error, query.state.failureCount));

// 3) Avoid redundant Promise.resolve in async functions
async function getData() {
  // ...
  return query.state.data; // no Promise.resolve, no redundant else
}

This reduces wasted evaluations and prevents unnecessary function calls, improving execution speed and resource utilization.

---

useEffect for measurements

When using functions that depend on rendered layout or DOM measurements, call them within useEffect hooks to ensure they execute after the component has rendered and layout calculations are complete.

Functions like measureElement() return incorrect results (typically zero values) when called during the initial render phase, before the browser has calculated the actual layout. This timing issue can lead to incorrect component behavior or layout calculations.

import { useEffect, useRef, useState } from 'react';

const MyComponent = () => {
  const boxRef = useRef();
  const [dimensions, setDimensions] = useState({ width: 0, height: 0 });

  useEffect(() => {
    // Call measurement functions after render
    const { width, height } = measureElement(boxRef);
    setDimensions({ width, height });
  }, []);

  return <Box ref={boxRef}>Content</Box>;
};

This pattern ensures accurate measurements and prevents layout-dependent operations from executing prematurely, leading to more reliable component behavior.

---

Prefer explicit RTL assertions

In React Testing Library tests, keep assertions outside components, and rely on proper global teardown.

• Teardown/cleanup: Since RTL v9, cleanup() is automatic when RTL is configured normally. Only call cleanup() manually if your test setup does not provide an afterEach.
• Assertion placement: Do not use expect(...) inside a React component. Instead, render the value to the DOM (or expose it via an element) and assert after render using RTL queries.
• Snapshot restraint: Prefer explicit assertions on specific text/values. Use snapshots only when they meaningfully reduce effort without obscuring intent.

Example (asserting after render, without component-level expect):

function Page() {
  const { canFetchMore } = useInfiniteQuery(
    'items',
    (key, nextId = 0) => fetchItems(nextId),
    { initialData: [/* ... */] }
  )

  return <div data-testid="can-fetch-more">{String(canFetchMore)}</div>
}

const { getByTestId } = render(<Page />)
expect(getByTestId('can-fetch-more').textContent).toBe('true')

---

Active Cache & Config Safety

When implementing caching layers/providers and cache-driven handlers:

• Assume multiple cache instances may exist. Avoid single “default cache” globals for runtime behaviors (e.g., focus handlers). Track all active caches and update/notify each.
• Create cache instances exactly once. If a cache prop isn’t provided, ensure the provider creates a single cache instance (not a new one per render).
• Define cleanup semantics for created vs injected caches. If the provider created a cache, clean it up on unmount and when it’s replaced; if a cache was injected by the parent, do not dispose it inside the provider.
• Never mutate shared config objects stored in cached entries. When applying per-query/per-hook config, avoid mutating a config object referenced by another query instance. Prefer replacing with a new merged object.

Example: safe config merge (avoid mutating a shared reference)

// BAD: mutates shared object reference
// Object.assign(query.config, config)

// GOOD: replace with a new merged object
query.config = { ...query.config, ...config }

Example: multi-cache handling pattern (conceptual)

// Instead of using a single default cache ref for focus events,
// maintain a registry/list of active caches and notify all.
activeCaches.forEach((cache) => {
  if (/* visible + online */) {
    cache.refetchAllOnWindowFocus?.()
  }
})

These rules prevent hard-to-debug cross-query/cross-cache state leaks and make behavior correct under multi-cache usage.

---

Use React.FC consistently

Use React.FC (or React.FunctionComponent) for typing functional components instead of verbose function type definitions. React.FC provides built-in typing for common props like children, key, and ref, reducing boilerplate and ensuring consistency across the codebase.

Instead of verbose function signatures:

const UserInput: (props: { test: string }) => JSX.Element | null = ({test}) => {
  // component logic
};

Use React.FC for cleaner, more maintainable type definitions:

const UserInput: React.FC<{ test: string }> = ({test}) => {
  // component logic
};

When children are required (not optional), include them explicitly in your props interface rather than relying on React.FC’s optional children:

interface ColorProps {
  color: string;
  children: ReactNode; // explicit when required
}

const Color: React.FC<ColorProps> = ({color, children}) => {
  // component logic
};

This approach provides better TypeScript integration, clearer component contracts, and leverages React’s built-in type definitions effectively.

---

Propagate and Test Errors

Handle errors at the right boundary, keep failure state consistent, and ensure tests validate the real semantics.

Apply these rules: 1) Don’t swallow errors inside reusable helpers.

• If a helper is part of your public API (e.g., a function consumers can intentionally call), catching and only logging can hide failures from the caller.
• Prefer catching at the specific fetch boundary you’re trying to protect (e.g., automatic/refetch flows), and either rethrow or return a rejected promise so callers can detect failures.

Example (pattern):

export async function refetchAllQueries({ queryCache }) {
  return Promise.all(
    queryCache.getAll().map(query =>
      query.fetch({ force: true })
    )
  );
}

// In the caller/boundary where automatic fetching should not crash:
refetchAllQueries({ queryCache }).catch(err => {
  console.error(err?.message ?? err);
  // keep error observable to the boundary’s own logic
});

2) Make failure metrics deterministic.

• If you track failureCount, reset it in the same place you mark a request as successful (e.g., in actionSuccess), rather than relying on an extra action that may not be wired through correctly.

3) Ensure tests genuinely exercise error-handling behavior.

• For retry logic, don’t write assertions that would pass accidentally due to incorrect assumptions (e.g., treating retry as a boolean when it can be a function).
• Structure tests so they would fail if retry semantics (like retry: (failureCount, error) => ...) aren’t implemented.

Result: callers can detect failures, internal failure state doesn’t drift, and tests accurately guard the intended error-handling semantics.

---

Null-Safe Optional Handling

When dealing with possibly missing or nullable values (especially globals and config), make null/undefined handling explicit and never call a value unless you’ve verified its type.

Apply this standard:

• Use explicit checks for undefined: x === undefined (or x !== undefined) rather than relying on implicit truthiness.
• Guard optional callbacks: before calling maybeFn(...), ensure typeof maybeFn === 'function'.
• If refactoring boolean logic around undefined/missing values, add/adjust unit tests to confirm behavior is unchanged.

Example:

function isDocumentVisible(document) {
  return (
    document.visibilityState === undefined ||
    document.visibilityState === 'visible' ||
    document.visibilityState === 'prerender'
  );
}

function shouldRetry(query, error) {
  const retry = query.config.retry;

  if (retry === true) return true;
  if (typeof retry === 'number') return query.state.failureCount <= retry;
  if (typeof retry === 'function') {
    return retry(query.state.failureCount, error);
  }
  return false;
}

---

avoid any type usage

Replace any type annotations with more specific types to improve type safety and null handling. The any type disables TypeScript’s type checking, including null safety checks, making code prone to runtime errors.

Use unknown as a safer alternative when the type is truly unknown, as it requires type checking before use. When possible, use specific types like ReactNode, interfaces, or union types that accurately describe the expected values.

Example progression from unsafe to safe typing:

// Avoid: Disables all type checking
let resolve: (value?: any) => void;

// Better: Requires type checking before use  
let resolve: (value?: unknown) => void;

// Best: Use specific types when known
let resolve: (value?: void) => void;

// For React components, use specific types
readonly unstable__transformChildren?: (children: ReactNode) => ReactNode;

This approach prevents null reference errors by ensuring TypeScript can properly track nullable and undefined values through the type system.

---

Clear API interfaces

Ensure API interfaces are clearly defined with proper formatting and comprehensive documentation. Type definitions should use consistent formatting with appropriate line breaks for complex objects, and documentation should precisely explain callback behavior, timing, and parameters.

For type definitions, format complex objects with proper indentation:

const renderToString: (
	node: ReactNode,
	options?: {
		columns?: number
	}
) => string;

For API documentation, be specific about when and how callbacks are invoked:

/**
 * Hook that calls the `inputHandler` callback with the input that the program received.
 * Called on each keypress and when text is pasted.
 */

This ensures APIs are self-documenting and reduces confusion about interface contracts and expected behavior.

---

Deterministic Async Lifecycle

Ensure async features that depend on a query/promise’s lifecycle (e.g., cancellation hooks, query function availability) are wired using a deterministic initialization order. Don’t write code paths that assume query/query.promise already exists; either (a) centralize initialization (e.g., reuse a prefetch-like path) or (b) explicitly create/transition query state before starting concurrent work. This prevents unreachable cancellation handles and race conditions where different callers observe different lifecycle states.

Example pattern (conceptual):

async function ensureQueryInitialized({ queryHash, queryFn, client, variables }) {
  let query = client.queries.find(d => d.queryHash === queryHash)
  if (!query) {
    // Create/initialize via the single shared initialization path
    query = await client.prefetchQuery({ queryHash, queryFn, variables })
  }
  return query
}

function wireCancelAtCreation({ query, pageVariables }) {
  // Wire cancel when promises are created (when the handle is available)
  const promises = pageVariables.map(v => {
    const p = query.queryFn(v)
    // store cancel handle immediately in a dedicated field
    query._cancel = p.cancel
    return p
  })
  return Promise.all(promises)
}

Standard checklist:

• Define the allowed lifecycle states for query and query.promise (e.g., uninitialized → initialized → running).
• Any code needing cancellation must capture the cancel handle at the moment the promise (or equivalent control object) is created.
• Any API (like setQueryData) that might run before initialization must either (1) wait for a shared initialization path or (2) create the query using the same logic as other entry points.
• Add concurrency-focused tests that simulate interleavings (set before prefetch finishes, cancel before promise assignment, etc.).

---

Verify package.json accuracy

Ensure that package.json configuration entries accurately reflect the actual project structure and include complete, working settings. Incorrect or incomplete package.json configuration can cause runtime failures and deployment issues.

Key practices:

• Verify that the main field points to the correct entry file path
• Include complete configuration objects rather than shortcuts (e.g., full Babel preset configurations with targets)
• Test package configuration in a clean environment before publishing
• Maintain consistent formatting throughout configuration files

Example of problematic vs. correct configuration:

// Problematic - main points to wrong file
{
  "main": "index.js",  // but actual file is dist/index.js
  "babel": {
    "presets": ["@babel/preset-react"]  // incomplete, missing targets
  }
}

// Correct - accurate paths and complete configuration
{
  "main": "dist/index.js",
  "babel": {
    "presets": [
      "@babel/preset-react",
      [
        "@babel/preset-env",
        {
          "targets": {
            "node": "current"
          }
        }
      ]
    ]
  }
}

Always validate that configuration entries work as intended in the target environment before committing or publishing.

---

Close resource handles properly

Always close file resources and other system handles after use to prevent resource leaks. Resource leaks can cause system instability, memory issues, and limit scalability, especially in long-running services handling many requests.

For example, when working with files or similar resources:

// BAD: Resource leak
func handleUpload(c *gin.Context) {
    file, _ := c.Request.FormFile("upload")
    // file is never closed
    // process file...
}

// GOOD: Properly closed resource
func handleUpload(c *gin.Context) {
    file, err := c.Request.FormFile("upload")
    if err != nil {
        // Handle error
        return
    }
    defer file.Close() // Always close the file
    
    // process file...
}

For more complex scenarios, ensure resources are closed even when errors occur. The defer statement in Go is particularly useful for this purpose as it guarantees execution even if the function returns early due to an error. When managing multiple resources, close them in the reverse order of acquisition to avoid dependency issues.

---

Document API behavior

Thoroughly document how your API endpoints handle data binding and processing, especially non-obvious behaviors that affect how client data is mapped to server-side structures. This includes:

1. Clearly document form tag behaviors and special syntax (like form:"-")
2. Explain how different HTTP methods affect binding logic
3. Document content-type specific behaviors

For example, when implementing binding in a web framework like Gin, include explanatory comments:

// Person represents data received from API clients
type Person struct {
  Name    string `form:"name"`
  Address string `form:"address"`
  InternalID string `form:"-"` // This field won't be populated from form data
}

func handleRequest(c *gin.Context) {
  var person Person
  
  // Document binding behavior:
  // If `GET`, only `Form` binding engine (`query`) used.
  // If `POST`, first checks the `content-type` for `JSON` or `XML`, then uses `Form` (`form-data`).
  if c.Bind(&person) == nil {
    // Process the data
  }
}

Clear API behavior documentation reduces friction for API consumers, minimizes unexpected behaviors, and reduces support burden for your team.

---

Minimize configuration complexity

Keep configuration files clean and maintainable by regularly reviewing and removing unnecessary settings and outdated version support. This includes:

1. Remove environment variables that are no longer required in newer versions of tools or languages
2. Drop support for legacy versions that require special configuration or lack compatibility with modern tooling

Example from Go configuration:

# Good practice - only set environment variables when needed
matrix:
  - go: 1.12.x
    env: GO111MODULE=on
  - go: 1.13.x
    # No GO111MODULE needed for 1.13+ as it's the default behavior

When evaluating which configurations to keep, consider:

• Is this setting still required for the latest versions?
• Does maintaining support for older versions add unnecessary complexity?
• Are there newer conventions or defaults that make explicit configuration redundant?

Regular audits of configuration files prevent accumulation of outdated settings and help maintain a cleaner, more understandable development environment.

---

Validate configuration interdependencies

When configuration options have logical dependencies or constraints, implement both smart defaults and validation checks to ensure consistent behavior. Set dependent options to appropriate default values based on other configuration values, and validate that the final combination of options represents a valid state.

For interdependent options, derive defaults from related settings:

options = assign({ 
  generate: 'dom', 
  dev: false, 
  shadowDom: options.customElement  // Default based on another option
}, options);

Then validate the final configuration to catch invalid combinations:

if (!customElement && shadowDom) {
  throw new Error(`options.shadowDom cannot be true if options.customElement is false`);
}

This approach prevents invalid configuration states while maintaining backwards compatibility and providing clear error messages when constraints are violated.

---

Follow StandardJS when modifying

When modifying existing code, update the touched lines to follow StandardJS conventions while preserving the style of untouched code. This ensures gradual, consistent adoption of StandardJS formatting.

Key StandardJS rules to apply:

• Use multiple const declarations instead of comma-separated ones
• Omit semicolons
• Add space after function keyword
• Don’t indent chained method calls

Example of updating code to StandardJS:

// Before
var express = require('../..'),
    bodyParser = require('body-parser'),
    session = require('express-session');

app.get('/', function(req, res){
  res.send('Hello form root route.');
});

// After
const express = require('../..')
const bodyParser = require('body-parser')
const session = require('express-session')

app.get('/', function (req, res) {
  res.send('Hello from root route.')
})

Only update lines you’re actively modifying - don’t reformat entire files just for style consistency. This enables gradual adoption while maintaining codebase stability.

---

Use standard HTTP constants

Always use the standard HTTP status constants from the http package instead of raw numeric values in your networking code. This practice improves code readability, maintainability, and helps prevent errors when working with HTTP responses.

For example, instead of:

writer.WriteHeader(500)
c.AsciiJSON(204, []string{"lang", "Go语言"})

Use the semantic constants:

writer.WriteHeader(http.StatusInternalServerError)
c.AsciiJSON(http.StatusNoContent, []string{"lang", "Go语言"})

This approach makes your code more descriptive and self-documenting. It also ensures consistency across the codebase and makes it easier for other developers to understand the HTTP status codes being used without having to memorize numeric values.

---

Accurate JSDoc documentation

Always ensure JSDoc comments accurately reflect the actual code implementation. Parameter types, optionality, and function behavior must be precisely documented to prevent confusion and bugs.

When documenting parameters:

• Match the exact types accepted by the function
• Indicate optional parameters appropriately
• Verify documentation when code changes

For example, if a function accepts multiple types or optional parameters:

/**
 * Process user input
 *
 * @param {String|Array} input - The input to process
 * @param {Object} [options] - Optional configuration object
 * @return {Boolean} Whether processing succeeded
 */
function process(input, options) {
  // implementation
}

Incorrect or outdated JSDoc can mislead developers and lead to runtime errors. Always review JSDoc comments when changing function signatures or behavior to ensure documentation and implementation remain synchronized.

---

Declare .PHONY targets

Always explicitly declare all Makefile targets that don’t create files as .PHONY. This prevents conflicts with potential files of the same name, makes build intentions clear, and increases reliability in CI/CD pipelines.

For better readability and maintenance, place the .PHONY declaration directly above the corresponding target:

.PHONY: deps
deps:
    go get -d -v github.com/dustin/go-broadcast/...

.PHONY: build
build: deps
    go build -o realtime-chat main.go rooms.go template.go

Rather than grouping all .PHONY declarations at the end or beginning of the Makefile, this pattern makes the relationship between declarations and targets obvious at a glance, reducing the chance of forgetting to update declarations when adding new targets.

---

ESLint configuration alignment

Ensure your ESLint configuration matches the JavaScript language features used in your codebase to prevent false warnings and maintain consistent code quality checks. When using ES6+ features like let, const, object shorthand notation, or other modern JavaScript syntax, update your ESLint configuration to recognize these features.

Common symptoms of misaligned configuration include warnings like “‘let’ is available in ES6 (use esnext option)” or “‘const’ is available in ES6” when these features are intentionally used in the code.

Example configuration fix:

// .eslintrc.js
module.exports = {
  "parserOptions": {
    "ecmaVersion": 6, // or higher for newer features
    "sourceType": "module"
  },
  "env": {
    "es6": true,
    "node": true
  }
};

This prevents the need for eslint-disable comments and ensures your linting rules accurately reflect your coding standards rather than generating noise from outdated configuration settings.

---

Enforce null safety patterns

Implement comprehensive null safety patterns to prevent runtime errors and ensure predictable behavior. Follow these guidelines:

1. Use explicit null/undefined checks instead of loose comparisons: ```javascript // Good if (value === undefined || value === null) { // handle null case }

// Avoid if (!value) // Could match 0, ‘’, false if (typeof value === ‘undefined’) // Doesn’t catch null

2. Never mutate input parameters or objects:
```javascript
// Good
function process(options) {
  const opts = { ...options }; // Create new object
  opts.value = opts.value || defaultValue;
  return opts;
}

// Avoid
function process(options) {
  options.value = options.value || defaultValue; // Mutates input
  return options;
}

1. Use Object.create(null) for clean object instances without prototype chain: ```javascript // Good const cleanObject = Object.create(null);

// Avoid const dirtyObject = {}; // Inherits from Object.prototype

4. Implement strict type checking for boolean options:
```javascript
// Good
if (typeof options.flag !== 'boolean') {
  throw new TypeError('flag must be boolean');
}

// Avoid
if (options.flag) // Allows non-boolean values

This pattern prevents common null-related bugs, ensures type safety, and maintains immutability principles.

---

Optimize CI environment configuration

When configuring CI environments, carefully evaluate whether default dependency versions are sufficient for your project needs before adding custom installation steps. Default configurations (like Travis CI’s JDK version) often provide adequate support while maintaining optimal build times. Only include additional installation commands when specific project requirements demand newer or different versions.

Example in Travis CI configuration:

language: groovy
jdk:
  - oraclejdk8  # Default JDK 8 may be sufficient (e.g., JDK 8u65)

# Only add custom installation steps when default versions are inadequate:
# before_install:
#   - sudo apt-get update && sudo apt-get install oracle-java8-installer

This approach ensures your CI pipeline remains efficient while still meeting all project requirements. Document any custom configuration decisions to help team members understand why defaults were overridden.

---

Access settings properly

Always use the provided settings accessor methods (app.get(), app.set(), app.enabled(), app.disabled()) to access application configuration instead of directly accessing the settings object. Direct access to the settings object was deprecated and may lead to inconsistent behavior or errors.

When checking configuration values:

// Incorrect
if (app.settings.etag == false) {
  opts.etag = app.settings.etag;
}

// Correct
if (app.disabled('etag')) {
  opts.etag = app.get('etag');
}

Similarly, when referencing environment settings:

// Incorrect
var space = 2 * process.env.NODE_ENV == 'development';

// Correct
var space = 2 * app.get('env') == 'development';

This approach ensures your code respects the configuration system’s internal logic, handles default values correctly, and remains compatible with future framework versions. It also makes your code more maintainable as all configuration access follows a consistent pattern.

---

Method chaining for clarity

Design API methods that favor chaining over multiple parameters to improve readability and maintainability. When implementing methods that require both a resource and configuration options (like status codes), prefer method chaining patterns that clearly separate concerns and make the purpose of each parameter explicit.

Example - Avoid:

// Unclear parameter order and purpose
res.json(obj, status);
res.send(body, status);

Example - Prefer:

// Clear separation of concerns through method chaining
res.status(status).json(obj);
res.status(status).send(body);

This pattern improves API usability by making method calls self-documenting, reducing the need to remember parameter order, and creating more intuitive interfaces for developers. It also allows for more flexible extension of the API in the future without breaking changes to parameter signatures.

---

Structured release workflows

Implement a clearly defined release strategy that distinguishes between different types of changes. Create separate workflows for patch releases (typo fixes, safe dependency updates, low-risk fixes) and non-patch releases (features, breaking changes):

For patch releases:

• Use direct commits to the main branch for simple, low-risk changes
• Verify with appropriate tests before releasing
• Document changes in a consistent format

For non-patch releases:

• Create dedicated feature branches (e.g., 4.13, 5.0)
• Track changes through a release pull request that documents all included changes
• Implement proper access controls for release automation
• Consider using shared credentials stored securely for release publishing

Example workflow for non-patch release:

# Create a new branch for the release
git checkout -b 5.0

# Make and commit your changes
...

# Open a release PR tracking all changes
# Example: https://github.com/expressjs/express/pull/2682

# After review and approval, merge and publish
npm version minor  # or major for breaking changes
git push origin --tags
npm publish

This structured approach ensures changes are properly tracked, reviewed, and deployed according to their risk level, making the release process more predictable and maintainable.

---

Comprehensive documentation standards

Create clear, well-structured API documentation following these practices:

1. Use proper formatting:
   • Separate distinct thoughts with blank lines
   • Ensure consistent paragraph structure
   • Add proper spacing after section headers

/// Create a multipart form to be used in API responses.
///
/// This struct implements [`IntoResponse`], and so it can be returned from a handler.

1. Use correct references:
   • Place code elements in backticks with proper linking: [Type] not Type or Type
   • Use intra-doc links for internal references: [order-of-extractors]: crate::extract#the-order-of-extractors
   • Specify version requirements when applicable: “This macro is only available with Rust >= 1.80”
2. Write informative examples:
   • Implement documentation tests where possible: #[doc(test)]
   • Include complete, runnable code examples
   • Add explanatory comments for complex operations
   • Format examples consistently with proper spacing
3. Ensure completeness:
   • Document security implications of sensitive operations
   • Clarify parameter constraints and return value behaviors
   • Use precise language: “This allows sharing state with IntoResponse implementations” not “This allows sharing state with IntoResponse implementations”
   • Add trailing periods to documentation sentences

Documentation should be treated as a first-class feature - it’s often the first interaction users have with your API.

---

Use specific assertion methods

Choose the appropriate assertion method based on the data type being tested. This improves test readability and provides clearer error messages when tests fail.

For scalar values (numbers, strings, booleans), use strictEqual instead of equal or deepStrictEqual:

// ❌ Not ideal - less specific assertion
t.assert.equal(response.statusCode, 200)
t.assert.deepStrictEqual(fastify.hasRoute({ }), false)

// ✅ Better - correct assertion for scalar types
t.assert.strictEqual(response.statusCode, 200)
t.assert.strictEqual(fastify.hasRoute({ }), false)

For objects and arrays, use deepStrictEqual rather than deepEqual or same:

// ❌ Not ideal - can miss type differences
t.assert.deepEqual(body.toString(), JSON.stringify({ hello: 'world' }))

// ✅ Better - ensures exact object equality
t.assert.deepStrictEqual(body.toString(), JSON.stringify({ hello: 'world' }))

When possible, combine assertions directly with awaited methods to reduce code verbosity:

// ❌ Not ideal - unnecessary intermediate variable
const body = await response.text()
t.assert.deepStrictEqual(body, 'this was not found')

// ✅ Better - direct assertion
t.assert.deepStrictEqual(await response.text(), 'this was not found')

Ensure proper resource cleanup using t.after() hooks rather than closing resources at the end of tests:

// ❌ Not ideal - may not run if test fails
fastify.close()

// ✅ Better - ensures cleanup even if test fails
t.after(() => fastify.close())

---

Type-safe flexible APIs

Design APIs that favor both type safety and flexibility. Use strongly typed wrappers instead of primitive types, but accept generic parameters where flexibility is beneficial.

For headers and content types, use typed wrappers rather than strings:

// Instead of:
fn get_page(app: Router, path: &str) -> (StatusCode, String, String) // String for content-type
    
// Prefer:
fn get_page(app: Router, path: &str) -> (StatusCode, headers::ContentType, Vec<u8>)

Accept more general trait bounds instead of specific types for parameters:

// Instead of:
pub async fn from_path(path: PathBuf) -> io::Result<FileStream<AsyncReaderStream>>

// Prefer:
pub async fn from_path(path: impl AsRef<Path>) -> io::Result<FileStream<AsyncReaderStream>>

Use more general parameter types when possible:

// Instead of:
pub fn from_bytes(bytes: &Bytes) -> Result<Self, JsonRejection>

// Prefer:
pub fn from_bytes(bytes: &[u8]) -> Result<Self, JsonRejection>

Leverage existing conversion mechanisms rather than duplicating types, allowing users to map between your API and domain types:

// Instead of copying a CloseCode enum, expose a u16 and let users convert
socket.send(Message::Close(Some(CloseFrame {
    code: axum::extract::ws::close_code::NORMAL, // Use constants instead of magic numbers
    // ...
})))

Provide ergonomic builder methods, but also implement standard traits like FromIterator to support more idiomatic usage patterns:

// Support both explicit additions and collection-based construction
let form1 = MultipartForm::new().add_part(part1).add_part(part2);
let form2 = MultipartForm::from_iter([part1, part2]);

For constructors, follow consistent patterns across related types, making both empty initialization and conversion from domain objects simple:

// Empty jar: CookieJar::new(), SignedCookieJar::new(key)
// With headers: CookieJar::from_headers(headers), SignedCookieJar::from_headers(headers, key)

When documenting your API, explicitly mention behaviors like content-type handling to avoid surprises: “The Protocol Buffer extractor does not check the content-type header.”

---

Axum Code Review: Interaction Patterns

When implementing Axum-based applications, it is crucial to ensure that the interaction patterns between components are well-designed and clearly documented. This includes understanding edge cases, limitations, and best practices around state sharing, router nesting, and extractor ordering.

For nested routers, be sure to explicitly document how fallbacks work between the nested components. Provide clear examples showing the order in which fallbacks are handled for different paths.

When using extractors, clearly specify the ordering constraints and provide complete, working examples to demonstrate the correct usage. Extractors that consume the request body must be ordered last.

Carefully consider state sharing mechanisms between routers. Explain how states are merged or propagated, and explicitly note any limitations. This will help other developers avoid common pitfalls when integrating your Axum-based components.

By providing this level of detail and guidance, you can help ensure that developers working with your Axum-based code can understand critical interactions and implement them correctly, avoiding common issues and improving the overall quality and maintainability of the application.

---

Write clear documentation

Documentation should be clear, precise, and self-contained while following established style conventions. When writing technical documentation:

1. Use precise language: Clearly describe how APIs work, including any restrictions or requirements.

   // Good
   // The function must be synchronous, and must not throw an error.
   fastify.setGenReqId(function (rawReq) { return 'request-id' })
      
   // Bad
   // This function can be used to set a request ID.
   fastify.setGenReqId(function (rawReq) { return 'request-id' })
   

2. Make documentation self-contained: Include all necessary context within the document itself rather than relying on external links.

   // Good
   // The `preHandler` hook allows you to specify a function that is executed before
   // routes' handler.
      
   // Bad
   // See Issue #1234 for more details on the preHandler hook.
   

3. Follow style conventions:
   • Avoid using “you” in reference documentation
   • Avoid contractions in formal documentation
   • Use proper formatting for headers, lists, and code blocks

   // Good
   // When request logging is enabled, request logs can be customized by
   // supplying a createRequestLogMessage() function.
      
   // Bad
   // You can customize your request logs by using a createRequestLogMessage() function.
   

4. Create accessible links: Provide meaningful context in link text rather than using generic phrases.

   <!-- Good -->
   [TypeScript no-floating-promises configuration](https://typescript-eslint.io/rules/no-floating-promises/)
      
   <!-- Bad -->
   Click [here](https://typescript-eslint.io/rules/no-floating-promises/) for more information.
   

---

Effective Cache Management in Next.js Applications

When implementing caching in Next.js applications, it is crucial to be intentional about the caching behavior for each component and function. Apply caching directives consistently and consider their implications:

1. Specify Caching Behavior: Explicitly indicate whether values should be cached or evaluated fresh for each request:

export async function getCachedRandomOrder() {
  'use cache'
  // This random value will be cached and reused for all users
  return Math.random();
}

export async function getUniqueRandomPerRequest() {
  // No cache directive - will be evaluated fresh for each request
  return Math.random();
}

1. Understand Cache Keys: Cache entries are determined by function arguments, so document parameter effects on caching:

export async function getPosts(slug) {
  'use cache'
  // This function's result will be cached based on the slug parameter
  // Different slug values = different cache entries
  const data = await fetch(`/api/posts/${slug}`)
  return data.json()
}

1. Implement Proper Invalidation: Define explicit cache invalidation strategies rather than relying on default periods:

import { cacheTag, cacheLife } from 'next/cache'

export async function getPosts(slug) {
  'use cache'
  cacheTag('posts')           // Tag this cache entry for targeted invalidation
  cacheLife(60 * 60 * 1000)   // Cache for 1 hour instead of default period
  
  const data = await fetch(`/api/posts/${slug}`)
  return data.json()
}

1. Enable Debugging: During development, configure cache logging to verify that caching behaves as expected and to identify cache hits and misses.

Adopting a strategic approach to cache configuration in Next.js applications can significantly improve performance while ensuring data consistency and freshness.

---

Secure Data Handling in Next.js Applications

When building Next.js applications that handle sensitive data, it’s crucial to implement robust security measures to prevent data leakage and injection attacks. This reviewer provides guidance on best practices for securely handling data in Next.js:

1. Sanitize User Input: When rendering user-provided data in your Next.js components, always sanitize the input to prevent Cross-Site Scripting (XSS) attacks. Use specialized libraries like serialize-javascript or the JsonLd component from react-schemaorg instead of relying on JSON.stringify() alone.

2. Taint Sensitive Data: Leverage React’s experimental taintObjectReference API to mark sensitive data objects. This will help you identify and extract only the necessary fields in your Server Components, preventing the entire sensitive object from being passed to the client.

3. Set Appropriate Security Headers: Ensure that security headers like Content Security Policy (CSP) are set on the response, not the request. This will ensure the headers are properly applied and effective in protecting your Next.js application.

4. Model Data Defensively: Design your data models to exclude sensitive fields by default, reducing the risk of accidentally exposing sensitive information to the client.

By following these guidelines, you can build Next.js applications that securely handle sensitive data and protect against common security vulnerabilities.

---

Technical documentation precision

Ensure technical documentation is precise, accurate, and correctly formatted to prevent confusion and improve developer experience. Focus on these key aspects:

1. Fix broken links and references: Update outdated paths and ensure all links point to the correct documentation sections. ```diff
   • memoized
   • memoized ```
2. Correct syntax and formatting errors: Verify code blocks have proper closing tags, backticks, and XML elements match correctly. ```diff
   • A provider using useSearchParams() without `, triggering CSR bailout
   • A provider using useSearchParams() without <Suspense>, triggering CSR bailout diff
   • </urlset>
   • </sitemapindex> ```
3. Fix grammatical issues and missing words: Review for missing words in comparisons and incorrect grammatical constructions. ```diff
   • This limits prefetching to routes the user is more likely to visit, rather all links
   • This limits prefetching to routes the user is more likely to visit, rather than all links diff
   • With PPR is enabled, a page is divided into…
   • When PPR is enabled, a page is divided into… ```
4. Clarify technical behavior and limitations: Explicitly state when features have specific constraints or behaviors. ```diff
   • Next.js will automatically determine the intrinsic width and height of your image
   • When using local images, Next.js will automatically determine the intrinsic width and height of your image ```
5. Remove artifacts from documentation drafting: Check for URLs or references from documentation creation tools. ```diff
   • Disabled Prefetch
   • Disabled Prefetch ```
6. Add explanations for complex concepts: Include sufficient explanations for technical concepts like caching behavior and component relationships.

Following these practices ensures documentation remains a reliable and frustration-free resource for developers.

---

Prefer simpler code constructs

Always opt for simpler, more idiomatic code constructs over complex or verbose alternatives. This includes:

1. Using built-in Rust patterns instead of manual implementations: ```rust // Instead of .for_each(|(name, value)| { // … implementation });

// Prefer for (name, value) in items { // … implementation }

2. Leveraging pattern matching for cleaner control flow:
```rust
// Instead of
let content_length = req.method().clone();
if content_length > N { ... }

// Prefer
match (content_length, req.method()) {
    (content_length, &(Method::GET | Method::HEAD)) => { ... }
}

1. Using method chaining when it improves readability: ```rust // Instead of cmd.arg(“–body”); cmd.arg(body);

// Prefer cmd.args(&[”–body”, body])

4. Maintaining consistent formatting:
- Group related imports together
- Avoid mixing inline and non-inline arguments
- Use consistent line wrapping in documentation

The goal is to write code that is easier to read, maintain, and reason about by leveraging Rust's built-in constructs and following consistent patterns.

---

## Concurrent operations completion management

<!-- source: fastify/fastify | topic: Concurrency | language: JavaScript | updated:  -->

When running concurrent operations in tests, ensure all operations complete before concluding the test. Race conditions occur when your test calls `done()` or resolves before all async operations finish, leading to flaky tests or missed assertions.

**For multiple concurrent HTTP/API calls:**
```javascript
// AVOID: Race condition - test might complete before all operations finish
test('API calls', (t, testDone) => {
  sget(url1, (err, res) => {
    t.assert.ifError(err)
    t.assert.strictEqual(res.statusCode, 200)
    testDone() // BAD: Other calls might still be running!
  })
  sget(url2, (err, res) => { /* assertions */ })
})

// BETTER: Use Promise.all for truly concurrent operations
test('API calls', async (t) => {
  const results = await Promise.all([
    fetch(url1),
    fetch(url2),
    fetch(url3)
  ])
  
  // All operations are complete before assertions run
  t.assert.strictEqual(results[0].status, 200)
  t.assert.strictEqual(results[1].status, 200)
})

// ALTERNATIVE: Use completion counter for callback style
test('API calls', (t, testDone) => {
  let pending = 3
  function completed() {
    if (--pending === 0) {
      testDone()
    }
  }
  
  sget(url1, (err, res) => {
    t.assert.ifError(err)
    t.assert.strictEqual(res.statusCode, 200)
    completed()
  })
  sget(url2, (err, res) => {
    t.assert.ifError(err)
    completed()
  })
  sget(url3, (err, res) => {
    t.assert.ifError(err)
    completed()
  })
})

// UTILITY APPROACH: Use waitForCb or similar utilities
test('API calls', (t, testDone) => {
  const completion = waitForCb({ steps: 3 })
  
  sget(url1, (err, res) => {
    t.assert.ifError(err)
    t.assert.strictEqual(res.statusCode, 200)
    completion.stepIn()
  })
  sget(url2, (err, res) => {
    // assertions
    completion.stepIn()
  })
  sget(url3, (err, res) => {
    // assertions
    completion.stepIn()
  })
  
  completion.patience.then(testDone)
})

---

Consistent test code style

Maintain consistent and clear testing patterns by following these guidelines:

1. Use strict equality assertions: ```javascript // Incorrect t.assert.equal(response.statusCode, 200) t.same(JSON.parse(body), expectedValue)

// Correct t.assert.strictEqual(response.statusCode, 200) t.assert.deepStrictEqual(JSON.parse(body), expectedValue)

2. For multiple sequential requests, prefer variable reassignment over block scoping:
```javascript
// Avoid
{
  const response = await fastify.inject('/first')
  t.assert.strictEqual(response.statusCode, 200)
}
{
  const response = await fastify.inject('/second')
  t.assert.strictEqual(response.statusCode, 200)
}

// Prefer
let response = await fastify.inject('/first')
t.assert.strictEqual(response.statusCode, 200)

response = await fastify.inject('/second')
t.assert.strictEqual(response.statusCode, 200)

This approach improves code readability, reduces unnecessary indentation, and makes test flow easier to follow while maintaining variable scope control.

---

Handling Dynamic Content in Next.js Components

When implementing Next.js components that rely on dynamic content (e.g. random values, current time), it is crucial to use proper boundary handling to avoid hydration errors and performance issues. Components that use non-serializable values like Math.random(), Date.now(), or crypto APIs must be wrapped in a Suspense boundary to ensure correct client-server rendering. Alternatively, for values only needed in the browser, you can use the useState and useEffect hooks to initialize and update the dynamic content safely. Remember that props passed between Server and Client Components must be serializable to prevent rendering mismatches.

---

Complete error handling chain

Implement comprehensive error handling throughout the codebase by ensuring all error scenarios are properly caught, typed, and propagated. This includes:

1. Always include catch blocks for async operations
2. Properly type and propagate error information
3. Use standardized error codes for consistent error handling
4. Ensure error callbacks receive and handle error parameters

Example:

// Bad
import(modulePath)
  .then(module => {
    module.default(req, res);
  });

// Good
import(modulePath)
  .then(module => {
    module.default(req, res);
  })
  .catch(error => {
    // Properly typed error with standardized code
    const err = new Error('Module load failed');
    err.code = 'EMODLOAD';
    err.cause = error;
    errorHandler(err);
  });

// For error callbacks
service.use(
  (config) => { /* ... */ },
  (error) => {
    // Properly handle error parameter
    errorLogger(error);
    throw error; // Propagate if needed
  }
);

---

Consistent method behaviors

Design API methods with predictable behavior patterns that follow common conventions. Methods that modify objects directly (setSth()) should not return values unless supporting method chaining. Methods that retrieve or transform data (getSth()) should return new objects without modifying inputs. Public class interfaces should maintain backward compatibility even if not all functionality is used internally. Ensure method signatures clearly indicate whether they accept request bodies:

// Good - clear behavior from naming and return type
function setHeaders(config, headers) {
  config.headers = headers;
  // No return, modifies object directly
}

function getHeaders(config) {
  // Returns new object, doesn't modify input
  return {...config.headers};
}

// Support method chaining explicitly
function addHeader(config, key, value) {
  config.headers[key] = value;
  return this; // Explicitly returns for chaining
}

When adding features to public APIs, ensure all methods have consistent signatures, behavior, and documentation, even if some functionality isn’t used in your codebase yet.

---

Documentation reflects reality

Always ensure documentation accurately represents the actual code behavior and implementation details. Include important contextual information such as:

1. Platform-specific limitations (e.g., “Node only” features)
2. Explanations for deprecated features with recommended alternatives
3. Precise descriptions of function parameters and behaviors
4. Concise, merged code examples to demonstrate functionality

When documenting APIs, verify that your descriptions match the actual implementation rather than the intended design. For example, if a function behaves differently than originally designed, update the documentation to reflect the actual behavior:

// INCORRECT DOCUMENTATION
// `validateStatus` defines whether to resolve or reject the promise for a given
// HTTP response status code. If `validateStatus` returns `true` (or is set to `null`
// or `undefined`), the promise will be resolved; otherwise, the promise will be rejected.

// CORRECT DOCUMENTATION
// `validateStatus` defines whether to resolve or reject the promise for a given
// HTTP response status code. If `validateStatus` returns `true` (or is set to `null`), 
// the promise will be resolved; otherwise, the promise will be rejected.

For deprecated features, clearly indicate:

~~Concurrency~~
Deprecated. Use `Promise.all` to replace them.

Keep documentation concise by consolidating related code examples when possible.

---

Proxy protocol handling

When implementing HTTP clients with proxy support, ensure the connection to the proxy uses the protocol specified in the proxy configuration (not the request protocol). This is crucial for scenarios like accessing HTTPS resources through an HTTP proxy.

Key implementation guidelines:

• Use the proxy’s protocol for the connection to the proxy server
• Implement HTTP CONNECT tunneling for HTTPS destinations through proxies
• Parse proxy URLs correctly using the hostname property (not host)
• Support common proxy environment variables including fallbacks

function configureProxy(options, config) {
  // Check for explicitly configured proxy
  let proxy = config.proxy;
  
  if (!proxy) {
    // Check for environment variables
    const proxyEnv = parsed.protocol.slice(0, -1) + '_proxy';
    const proxyUrl = process.env[proxyEnv] || 
                     process.env[proxyEnv.toUpperCase()] ||
                     process.env.all_proxy || 
                     process.env.ALL_PROXY;
    
    if (proxyUrl) {
      const parsedProxyUrl = url.parse(proxyUrl);
      proxy = {
        host: parsedProxyUrl.hostname,  // Use hostname, not host (which includes port)
        port: parsedProxyUrl.port,
        protocol: parsedProxyUrl.protocol
      };
      
      // Handle proxy authentication if present
      if (parsedProxyUrl.auth) {
        // Configure proxy authentication
      }
    }
  }
  
  if (proxy) {
    // Use proxy's protocol for connection to proxy
    // Set up tunneling for HTTPS requests through HTTP proxy
    const usesTunnel = proxy.protocol === "http:" && options.protocol === "https:";
    if (usesTunnel) {
      // Configure HTTP CONNECT tunneling
    }
  }
  
  return options;
}

---

Specific test assertions

When writing tests, explicitly assert specific conditions and expected values rather than relying on general success/failure checks. This prevents tests from silently passing when they should fail and ensures tests verify exactly what they’re intended to verify.

Three key practices to follow:

1. Handle promise rejections explicitly - Always include catch clauses in promise chains and pass errors to the done callback:

   axios.get('http://localhost:4444/')
     .then(function(res) {
    // assertions here
    done();
     }).catch(done); // This ensures test fails if promise rejects
   

2. Assert specific error conditions - When testing error cases, verify specific error details rather than just that an error occurred:

   axios.get('http://localhost:4444/')
     .catch(function(error) {
    assert.equal(error.code, 'ERR_FR_TOO_MANY_REDIRECTS');
    // Test specific error conditions, not just that an error happened
    done();
     });
   

3. Include explicit expected values - Use literal expected values in assertions rather than relying on functions with unclear output: ```javascript // Bad: Hard to see expected value expect(buildURL(‘/foo’, {date: date})).toEqual(‘/foo?date=’ + date.toISOString());

// Better: Shows exact expected output expect(buildURL(‘/foo’, {date: date})).toEqual(‘/foo?date=’ + encodeURIComponent(date.toISOString()));

Following these practices makes tests more reliable indicators of correct behavior and easier to debug when they fail.

---

## Standardize null value checks

<!-- source: axios/axios | topic: Null Handling | language: JavaScript | updated:  -->

Always use consistent patterns and utility functions for handling null and undefined values. This improves code reliability and maintainability while preventing common errors.

Key guidelines:
1. Use utility functions (like isUndefined, isNull) instead of direct comparisons
2. Prefer empty collections over null for container types
3. Use explicit null checks when dealing with potentially undefined objects

Example:
```javascript
// ❌ Avoid direct null/undefined checks
if (typeof value === 'undefined' || value === null) {
  // ...
}

// ✅ Use utility functions
if (utils.isUndefined(value) || utils.isNull(value)) {
  // ...
}

// ❌ Avoid setting null for collections
this.handlers = null;

// ✅ Use empty collections instead
this.handlers = [];

// ❌ Avoid unsafe property access
if (payload && payload.isAxiosError) {
  // ...
}

// ✅ Use comprehensive null checks
if (!!payload && typeof payload === 'object' && payload.isAxiosError) {
  // ...
}

---

Type-safe API interfaces design

Design API interfaces with strong type safety while maintaining excellent developer experience. Prefer explicit types over loose ones to enable better IDE support and catch errors at compile time.

Key principles:

1. Use explicit generic parameters with meaningful names
2. Prefer unknown over any for better type safety
3. Use intersection types when combining interface properties
4. Avoid string literals when specific types are available

Example:

// ❌ Avoid
interface ApiConfig {
  headers?: Record<string, any>;
  data?: any;
}

// ✅ Better
interface ApiConfig<ResponseData = unknown, RequestData = unknown> {
  headers?: HeadersDefaults & RequestHeaders;
  data?: RequestData;
  response?: AxiosResponse<ResponseData>;
}

This approach provides better IDE autocompletion, makes the code more maintainable, and catches potential type errors during development rather than at runtime.

---

Consistent axum Usage in TypeScript

When implementing TypeScript code that uses the axum package, maintain consistent and idiomatic usage:

1. Always use the lowercase “axum” when referring to the framework, not “Axum”.
2. Leverage axum’s built-in types and utilities correctly, such as Router, Middleware, and RequestBody.
3. Follow best practices for handling state and dependencies in axum applications, such as using task_local to pass state between middleware and handlers.
4. Ensure error handling is properly implemented, with clear and informative error messages returned to clients.
5. Use axum’s routing and middleware features effectively to structure your application, avoiding overly complex or nested routing.

Example of correct axum usage in TypeScript:

import { Router, RequestBody } from '@awslabs/aws-lambda-typescript-runtime';

const router = new Router();

router.get('/', (req) => {
  return { message: 'Hello, axum!' };
});

router.post('/users', async (req: RequestBody<{ name: string }>) => {
  const { name } = req.body;
  // Handle user creation logic here
  return { id: 1, name };
});

export default router;

---

## Documentation consistency standards

<!-- source: tokio-rs/axum | topic: Documentation | language: Markdown | updated:  -->

Maintain consistent documentation formatting standards across all project files, especially in changelogs, code examples, and technical documentation. This ensures readability and prevents confusion when documentation is viewed in different contexts.

Key practices to follow:
1. Use consistent formatting for PR references in changelogs - always use parentheses for PR references `([#123])` and include reference links at the bottom of the file
2. Format code elements with backticks in markdown text (e.g., `IntoResponse`, `FromRequest`)
3. Format code examples to clearly demonstrate the intended API usage:
```rust
// GOOD: Clear method chaining that shows which method calls apply to which objects
let app = Router::new().route(
    "/foo",
    get(|| async {})
        .route_layer(ValidateRequestHeaderLayer::bearer("password"))
);

// BAD: Confusing formatting that obscures the method call hierarchy
let app = Router::new()
    .route("/foo", get(|| async {})
    .route_layer(ValidateRequestHeaderLayer::bearer("password"))
);

1. Use proper Markdown link syntax consistently - either inline links [text](url) or reference-style links [text][reference] with the reference defined elsewhere, but not mixed approaches
2. Remember that documentation may be viewed outside GitHub (in editors, package documentation sites), where automatic linking doesn’t work

Consistent documentation makes the codebase more approachable and reduces confusion for both contributors and users.

---

Prefer descriptive over brief

Choose clear, descriptive names over abbreviated or shortened versions. Names should be self-documenting and follow Rust conventions. While brevity can be tempting, the clarity and maintainability benefits of descriptive names outweigh the extra characters.

Good practices:

• Use full, meaningful names instead of abbreviations
• Follow Rust naming conventions (snake_case for variables/functions, PascalCase for types)
• Use semantic names that describe the purpose
• If external conventions conflict with Rust’s, use attributes to maintain both

Example:

// Instead of:
use axum::http::StatusCode as SC;
const HTML: &str = "text/html";
struct User { _id: u32 }

// Prefer:
use axum::http::StatusCode;
const CONTENT_TYPE_HTML: &str = "text/html";
struct User {
    #[serde(rename = "_id")]  // maintains MongoDB convention while using Rust style
    id: u32
}

---

Adhere to Fastify Coding Conventions

When implementing code that uses the Fastify package in TypeScript, ensure the following conventions are followed:

1. Avoid Contractions: Use full words instead of contractions in code and comments. For example, use “it is” instead of “it’s”.

// Incorrect
// app.get('/hello', (req, res) => res.send("it's working!"));

// Correct 
app.get('/hello', (req, res) => res.send("it is working!"));

1. Use Oxford Commas: Include an Oxford comma (serial comma) when listing three or more items in function parameters, middleware, or plugin configurations.

// Incorrect
app.use(helmet, compression, morgan);

// Correct
app.use(helmet, compression, and morgan);

1. Maintain Consistent Formatting: Keep formatting consistent throughout the codebase, including:
   • Avoid emojis in function/variable names or comments unless used consistently
   • Use relative paths for internal Fastify plugin imports
   • Maintain consistent capitalization in function and variable names

Adhering to these conventions ensures the Fastify codebase remains readable, maintainable, and cohesive across different developers and components.

---

Consistent JSDoc standards

Document all public APIs and significant internal functions with comprehensive JSDoc comments that include accurate descriptions, parameter and return types, and any notable side effects. Follow standard JSDoc format conventions consistently across the codebase.

When documenting functions:

• Include clear descriptions of purpose and behavior: ```js /**
• Leverage light-my-request package to injects a fake HTTP request/response
• into Fastify for simulating server logic, writing tests, or debugging. *
• Warning: if the server is not yet “ready,” this utility will force
• the server into the ready state. *

• @see {@link https://github.com/fastify/light-my-request} */ fastify.inject = setupInject(fastify, { ```

• Use proper JSDoc tag formats with types and descriptions: ```js /**
• @param {object} serverOptions the fastify server options
• @returns {object} New logger instance, inheriting all parent bindings,

• with child bindings added. */ ```

• For utility functions, especially those used in tests, include explanation of parameters and execution flow: ```js /**
• Executes an array of asynchronous steps in sequence. Each step is a function
• that takes a next callback as its argument. The next callback must be
• called to proceed to the next step. *
• @param {Function[]} steps - An array of functions representing the steps to execute. */ ```

Maintain consistent formatting across all JSDoc comments. This improves code readability, makes API documentation generation more effective, and helps new developers understand the codebase more quickly.

---

Explicit Configuration Usage in Fastify

When using the Fastify framework in TypeScript, ensure that all configuration options are explicitly declared and properly documented. This includes:

1. Clearly defining all required configuration parameters, including their data types and default values (with units where applicable).
2. Explicitly specifying any configuration constraints or mutually exclusive options.
3. Providing comprehensive examples that demonstrate the correct usage of Fastify configuration settings.

Example - Poor Usage:

// Unclear timeout setting with no units
const fastify = Fastify({
  http2SessionTimeout: 72000 
});

// Incomplete schema definition
fastify.get('/route', {
  schema: {
    querystring: { name: { type: 'string' } }
  }
});

Example - Recommended Usage:

// Clear timeout setting with units
const fastify = Fastify({
  http2SessionTimeout: 72000 // Timeout in milliseconds for HTTP/2 sessions
});

// Fully defined schema requirements
fastify.get('/route', {
  schema: {
    querystring: {
      type: 'object',
      properties: {
        name: { type: 'string' }
      },
      required: ['name']
    }
  }
});

By following these guidelines, you can ensure that your Fastify-based applications are properly configured and documented, reducing the risk of user confusion and configuration errors.

---

Null safe patterns

Use concise null checking patterns to prevent runtime errors and improve code readability when handling potentially undefined values.

When checking if a value is neither null nor undefined:

// Preferred: Concise null check
if (err != null) {
  // err is neither null nor undefined
}

// Instead of verbose explicit checks
if (err !== undefined && err !== null) {
  // Same result but more typing
}

Before accessing properties of objects that might be null/undefined:

// Check before access to prevent "cannot read property of undefined" errors
if (reply.request.socket != null && !reply.request.socket.destroyed) {
  // Safe to use socket property
}

For default values, leverage nullish coalescing:

// Assign default value if property is null or undefined
reply[kReplyHeaders]['content-type'] = reply[kReplyHeaders]['content-type'] ?? 'application/json; charset=utf-8'

// Or with fallback chains when appropriate
this[kRequestOriginalUrl] = this.raw.originalUrl || this.raw.url

These patterns ensure your code handles null and undefined values safely while remaining concise and readable.

---

Preserve error context

When handling errors, always ensure the original error context is preserved and properly surfaced. Error information should never be silently swallowed in try/catch blocks, as this makes debugging extremely difficult and can lead to unexpected system behavior.

There are two recommended approaches to preserving error context:

1. Use the standard error.cause property to maintain error chains:

try {
  // Original operation
  const result = func(error, reply.request, reply);
  // Process result...
} catch (err) {
  // Preserve original error context
  if (!Object.prototype.hasOwnProperty.call(err, 'cause')) {
    err.cause = error; // Link the original error as the cause
  } else {
    // Log when unable to set cause to avoid losing context
    logger.warn({
      err: error,
      parentError: err,
      message: 'Original error cannot be linked as cause'
    });
  }
  
  // Propagate the error with context preserved
  throw err;
}

1. In asynchronous code, ensure proper promise rejection handling:

// BAD: Double resolution if error occurs
sget(options, (err, response, body) => {
  if (err) reject(err)
  resolve({ response, body }) // Still runs after reject!
})

// GOOD: Return after rejection to prevent double resolution
sget(options, (err, response, body) => {
  if (err) {
    reject(err)
    return // Important! Prevents executing the resolve
  }
  resolve({ response, body })
})

Remember that proper error handling includes validation of your error conditions themselves. Be careful with falsy checks that might incorrectly handle empty strings or zero values as error conditions.

---

Properly Handle Errors in Fastify Applications

When implementing error handling in Fastify applications, it is important to always throw instances of the Error class rather than primitive values or non-Error objects. This ensures that errors are properly propagated through the Fastify error handling chain.

If a Fastify plugin’s error handler re-throws a non-Error value (such as a string or number), it will not propagate to parent context error handlers and instead will be caught by the default error handler. This can lead to unexpected behavior and make it difficult to debug issues.

For example, instead of:

fastify.setErrorHandler((error, request, reply) => {
  // This will NOT propagate correctly to parent error handlers
  throw 'foo';
});

You should use:

fastify.setErrorHandler((error, request, reply) => {
  // This will properly propagate through the error handling chain
  throw new Error('foo');
});

By consistently throwing Error instances, you can ensure that errors are properly handled and propagated throughout your Fastify application, leading to more robust and maintainable error handling.

---

Type-safe API designs

Design APIs with strong type safety to improve developer experience and catch errors at compile time. Avoid using any types when possible, carefully order generic parameters to support type inference, and ensure return types accurately reflect API behavior.

When designing APIs with generic parameters:

1. Consider how type inference will work for users of your API
2. Place automatically inferable parameters last in generic lists
3. Ensure return types accurately reflect response possibilities

For example, when defining route handlers that can return different response types:

// Good: Strong typing for status codes and responses
server.get<{
  Reply: {
    200: string | { msg: string }
    400: number
    '5xx': { error: string }
  }
}>(
  '/',
  async (_, res) => {
    const option = 1 as 1 | 2 | 3 | 4
    switch (option) {
      case 1: return 'hello'               // typed as 200 response
      case 2: return { msg: 'hello' }      // typed as 200 response
      case 3: return 400                   // typed as 400 response
      case 4: return { error: 'error' }    // typed as 5xx response
    }
  }
)

// Bad: Using 'any' types or improper generic ordering that breaks type inference
function badExample<T = any>(req: any): any {
  // Types are lost, errors not caught until runtime
  return req.data;
}

When testing types, verify that constraints work as expected by explicitly checking the type constraints with test assertions.

---

Optimize Next.js Resource Utilization

As a code reviewer, I recommend the following practices to optimize resource utilization when implementing Next.js applications:

1. Leverage Server Components for Direct Data Fetching: Fetch data directly from the database or other sources in Server Components, rather than routing through API endpoints. This eliminates unnecessary HTTP roundtrips and improves performance.

Example:

// DON'T: Fetch through API Route
export default async function Component() {
  const data = await fetch('/api/data'); // Creates unnecessary HTTP roundtrip
  return <div>{data}</div>;
}

// DO: Fetch directly in Server Component
export default async function Component() {
  const data = await db.query('SELECT * FROM data'); // Direct database access
  return <div>{data}</div>;
}

1. Optimize Module Preloading: For memory-intensive applications, consider controlling module preloading by setting preloadEntriesOnStart to false in your next.config.js. This will load modules on-demand instead of at startup, helping to balance the initial memory footprint with runtime performance.

// next.config.js
module.exports = {
  preloadEntriesOnStart: false, // Load modules on-demand instead of at startup
};

1. Manage Memory-Intensive Operations: Carefully monitor and optimize memory-intensive operations in your Next.js application to ensure efficient resource utilization across the entire system.

By following these practices, you can improve the performance and scalability of your Next.js applications while maintaining a low memory footprint.

---

Write robust assertions

When writing tests, ensure assertions can handle non-deterministic content while providing clear failure context:

1. For non-deterministic content (like absolute paths in error outputs):
   • Use targeted assertions (toContain(), toInclude()) instead of full snapshots
   • Add explanatory comments about why standard approaches aren’t being used

   // GOOD
   // rspack returns error content that contains absolute paths which are non deterministic
   await session.assertHasRedbox();
   expect(redboxContent).toContain("Module not found: Can't resolve 'dns'");
   expect(redboxLabel).toContain('Build Error');
      
   // AVOID
   await expect(browser).toDisplayRedbox(`
     "error": {
       "message": "[absolute path that will change]",
     }
   `);
   

2. For DOM testing:
   • Use specialized tools like cheerio instead of string manipulation
   • Add identifiers to tested elements to make assertions more reliable

   // GOOD
   const $ = await next.render$('/');
   expect($('#server-value').text()).toBe('Server value: foobar');
      
   // AVOID
   const html = (await res.text()).replaceAll(/<!-- -->/g, '');
   expect(html).toContain('Server value: foobar');
   

3. For diagnostic tests:
   • Include contextual information (e.g., filenames) in assertions
   • Use declarative assertion patterns over iterative approaches

   // GOOD
   expect(diagnosedFiles).toEqual({
     'page.tsx': { code: NEXT_TS_ERRORS.INVALID_METADATA_EXPORT, /*...*/ },
     'layout.tsx': { code: NEXT_TS_ERRORS.INVALID_METADATA_EXPORT, /*...*/ }
   });
      
   // AVOID
   for (const tsFile of tsFiles) {
     const diagnostics = languageService.getSemanticDiagnostics(tsFile);
     expect(diagnostics.length).toBe(1);
     // No context about which file failed if assertion fails
   }
   

---

Extract for better readability

Complex expressions and repeated code should be extracted into well-named variables to improve readability and maintainability. This applies to:

• Repeated string/value combinations
• Complex conditional logic
• Array transformations
• URL or path constructions

Example - Instead of:

if ([options.path, responseDetails.headers.location].every(item => item === '/foo')) {
  // ...
}

Better approach:

const isPathMatching = options.path === '/foo';
const isLocationMatching = responseDetails.headers.location === '/foo';
if (isPathMatching && isLocationMatching) {
  // ...
}

This practice:

• Makes code self-documenting through meaningful variable names
• Reduces cognitive load when reading complex logic
• Makes debugging easier by providing clear intermediate values
• Prevents duplicate calculations

---

Proper Error Handling in Axios TypeScript Code

As a code reviewer, it is important to ensure that Axios-based TypeScript code properly handles and propagates errors. Key recommendations:

1. Use console.error() instead of console.log() when logging errors to maintain complete error context.
2. When handling Axios promise rejections, always preserve the full error object rather than just the error message. This provides downstream error handlers with the necessary information for debugging.
3. Follow established Axios error handling patterns, such as using .catch() blocks in promise chains to centralize error logging and potential recovery logic.
4. Ensure consistent error handling approaches are used throughout the codebase, such as always including the full error object when logging or rejecting promises.

Example of proper Axios error handling in TypeScript:

// In Axios interceptors, preserve the full error object
axios.interceptors.response.use(
  (response) => response,
  (error) => {
    console.error(error);
    return Promise.reject(error);
  }
);

// In promise chains, use consistent error handling
axios.get('/user?ID=12345')
  .then((response) => {
    // handle success
    console.log(response.data);
  })
  .catch((error) => {
    console.error(error);
    // Consider error recovery or propagation needs
  })
  .finally(() => {
    // always executed
  });

This approach enables better debugging, maintains backward compatibility, and follows established Axios error handling conventions.

---

Robust Axios Usage in TypeScript

This review focuses on ensuring robust and type-safe usage of the Axios library in TypeScript codebases. Key recommendations:

1. Leverage Axios’ built-in type-checking utilities rather than relying on error-prone instanceof checks. Use axios.isCancel() to detect canceled requests instead of manual type checking.

2. Properly handle Content-Type headers when sending data. Document how Axios automatically manages Content-Type for different data types (e.g. JSON, form data, URL-encoded). Provide clear examples of correct data transformation before sending, such as using URLSearchParams for URL-encoded form data.

3. Standardize serialization patterns for complex data types like FormData and nested objects to ensure consistent data handling across the codebase.

Following these practices will help ensure your Axios-based APIs remain robust and maintainable when used in applications with varying dependency versions, environments (browser/Node.js), and data formats.

---

Validate security-critical inputs

Always validate and sanitize user-supplied inputs before using them in security-sensitive operations. This helps prevent multiple types of vulnerabilities including Server-Side Request Forgery (SSRF), prototype pollution, and command injection.

For URL validation to prevent SSRF attacks:

// When handling user input that affects URLs
try {
  const ssrfAxios = axios.create({
    baseURL: 'http://localhost:' + String(GOOD_PORT),
  });
  
  // Validate user input before using in URL paths
  const userId = validateInput(userSuppliedId);
  
  // If validation fails, throw specific error
  if (!isValidUserId(userId)) {
    throw new Error('Invalid URL:' + userId);
  }
  
  const response = await ssrfAxios.get(`/users/${userId}`);
} catch (error) {
  // Handle error appropriately
}

For object property validation to prevent prototype pollution:

function isPrototypePollutionAttempt(key) {
  // Check for common prototype pollution patterns
  return ['__proto__', 'constructor', 'prototype'].some(
    term => key === term || key.includes('.' + term)
  );
}

// Use when processing user inputs into objects
function safeAddProperty(obj, key, value) {
  if (isPrototypePollutionAttempt(key)) {
    throw new Error('Potential prototype pollution detected');
  }
  obj[key] = value;
}

When using user input in command execution contexts, always use parameterized approaches instead of string concatenation to prevent command injection.

---

Handle protocol headers properly

When implementing network services, especially proxies and protocol handlers, proper HTTP header management is critical for correct functionality, compatibility, and diagnostics.

For proxy services:

• Remove or replace the HOST header when forwarding requests to avoid conflicts
• Include standard forwarded headers to maintain origin information:

  // Add standard proxy headers
  req.headers_mut().insert(
      "X-Forwarded-Host", 
      original_host.clone()
  );
  req.headers_mut().insert(
      "X-Forwarded-Proto",
      HeaderValue::from_static(original_scheme)
  );
  req.headers_mut().insert(
      "X-Forwarded-For",
      client_ip.to_string().parse().unwrap()
  );
  

For protocol upgrades (like WebSockets):

• Validate required headers with specific error messages

  let sec_websocket_key = req
      .headers_mut()
      .remove(header::SEC_WEBSOCKET_KEY)
      .ok_or(WebSocketKeyHeaderMissing)?;
  

• Be aware of protocol version differences (HTTP/1.0 doesn’t support upgrades, HTTP/1.1 uses GET for WebSockets, later versions use CONNECT)
• Document the last points where protocol-specific data is available:

  /// This is the last point where we can extract TCP/IP metadata such as 
  /// IP address of the client as well as things from HTTP headers
  

Proper header handling improves interoperability, makes debugging easier, and creates more robust network applications.

---

Lock carefully in async

When using locks in async code, follow these critical guidelines:

1. Never hold std::sync::Mutex locks across .await points as this can cause deadlocks even in single-threaded runtimes. Use tokio::sync::Mutex when the lock needs to be held across await points.

2. Consider lock granularity carefully - avoid overly fine-grained locking that could increase complexity and potential deadlocks.

Example of proper mutex usage in async context:

#[derive(Clone)]
struct AppState {
    // Coarse-grained locking - entire data structure under one lock
    data: Arc<tokio::sync::Mutex<ComplexData>>,
    
    // Fine-grained locking - only when specifically needed
    // Note: Choose granularity based on your specific use case
    counters: Arc<std::sync::Mutex<Counters>>,
}

async fn handle_request(state: AppState) {
    // OK: std::sync::Mutex for quick operations without .await
    let count = state.counters.lock().unwrap().get_count();
    
    // OK: tokio::sync::Mutex for operations involving .await
    let mut data = state.data.lock().await;
    data.update_with_async_operation().await;
} // locks are automatically released at end of scope

Remember: The choice between std::sync::Mutex and tokio::sync::Mutex isn’t about thread safety, but about async compatibility. std::sync::Mutex is thread-safe but can deadlock if held across .await points.

---

Minimize memory allocation overhead

Optimize performance by minimizing unnecessary memory allocations and using allocation-efficient APIs. Key practices:

1. Use static data when possible instead of dynamic allocations
2. Leverage specialized types and methods that minimize copies
3. Consider allocation patterns in data transformations

Example - Before:

// Unnecessary allocation
.send(Message::Ping("Hello, Server!".into()))

// Multiple potential allocations
let string = std::str::from_utf8(&bytes)
    .map_err(InvalidUtf8::from_err)?
    .to_owned();

Example - After:

// Using static data
.send(Message::Ping(Payload::Shared(
    "Hello, Server!".as_bytes().into()
)))

// Direct conversion avoiding copies
let string = String::from_utf8(bytes.into())
    .map_err(InvalidUtf8::from_err)?;

For serialization/encoding operations, prefer methods that write directly to pre-allocated buffers rather than creating intermediate allocations. Consider using specialized types like BytesMut when working with byte buffers.

---

Structure errors for safety

Create specific error types with appropriate status codes while ensuring sensitive details are logged but not exposed to clients. Follow these guidelines:

1. Define specific error types instead of using generic ones
2. Implement proper status codes for each error variant
3. Log detailed errors internally
4. Return sanitized error messages to clients

Example:

#[derive(Debug, Error)]
pub enum ApiError {
    #[error("Invalid input provided")]
    ValidationError(#[from] JsonRejection),
    #[error("Internal server error")]
    InternalError(#[source] anyhow::Error),
}

impl IntoResponse for ApiError {
    fn into_response(self) -> Response {
        let status = match &self {
            Self::ValidationError(_) => StatusCode::UNPROCESSABLE_ENTITY,
            Self::InternalError(_) => StatusCode::INTERNAL_SERVER_ERROR,
        };
        
        // Log detailed error internally
        tracing::error!("{:#}", self);
        
        // Return sanitized response to client
        let body = Json(json!({
            "error": self.to_string()  // Uses the #[error] messages
        }));
        
        (status, body).into_response()
    }
}

---

Use Option combinators

Instead of verbose conditional logic, prefer Rust’s Option combinators like map, and_then, and filter for handling potentially null values. This creates more concise, readable code that expresses intent clearly and reduces the chance of null-related bugs.

For example, replace:

let result = if let Some(value) = optional_value {
    Some(process(value))
} else {
    None
};

With:

let result = optional_value.map(process);

Similarly, when handling multiple optional values, use and_then instead of nested if-lets:

// Instead of this
let session_cookie =
    if let Ok(TypedHeader(cookie)) = TypedHeader::<Cookie>::from_request(req).await {
        cookie.get(AXUM_SESSION_COOKIE_NAME).map(|x| x.to_owned())
    } else {
        None
    };

// Prefer this
let session_cookie = Option::<TypedHeader<Cookie>>::from_request(req).await
    .and_then(|cookie| Some(cookie.get(AXUM_SESSION_COOKIE_NAME)?.to_owned()));

When validating values that might fail, explicitly set to None on failure:

self.filename = if let Ok(filename) = value.try_into() {
    Some(filename)
} else {
    trace!("Attachment filename contains invalid characters");
    None
};

Using Option combinators not only makes code more concise but also makes the intent clearer and reduces the chance of null-handling mistakes.

---

Benchmark before choosing methods

Always benchmark different implementation approaches for performance-critical operations before selecting a method. Different approaches (like array operations, string parsing, or data iteration) can have significant performance implications that may not be intuitive.

Example comparing array operations:

const Benchmark = require('benchmark')
const suite = new Benchmark.Suite()

suite
  .add('concat', function() {
    return ['cookie'].concat(['cookie2', 'cookie3'])
  })
  .add('push', function() {
    return Array.prototype.push.apply(['cookie'], ['cookie2', 'cookie3'])
  })
  .on('cycle', function(event) {
    console.log(String(event.target))
  })
  .on('complete', function() {
    console.log('Fastest is ' + this.filter('fastest').map('name'))
  })
  .run()

Key considerations:

• Use appropriate sample sizes and realistic test data
• Test in your target environment
• Consider memory implications alongside pure speed
• Document benchmark results to justify implementation choices

---

Consistent descriptive naming

Use precise, consistent, and descriptive naming conventions throughout your code to enhance readability and maintainability. This includes:

1. Use past participle (adjective form) for variables storing processed data: ```javascript // ✅ Good const normalizedMethod = options.method?.toUpperCase() ?? ‘’

// ❌ Bad const normalizeMethod = options.method?.toUpperCase() ?? ‘’

2. Choose function names that clearly describe their purpose without ambiguity:
```javascript
// ✅ Good
function addHTTPMethod(method, { acceptBody = true } = {}) {
  // Implementation
}

// ❌ Bad (confusing with HTTP Accept header)
function acceptHTTPMethod(method, { hasBody = false } = {}) {
  // Implementation
}

1. Use consistent naming patterns for related parameters and properties: ```javascript // ✅ Good - consistent terminology contentTypeSchemas[contentType] = compile({ schema: contentSchema, method, url, httpPart: ‘body’, contentType })

// ❌ Bad - inconsistent terminology contentTypeSchemas[mediaName] = compile({ schema: contentSchema, method, url, httpPart: ‘body’ })

4. Name properties to clearly indicate their relationships:
```javascript
// ✅ Good - clear relationship between host and hostname
host: {
  get() { return this.raw.headers.host || this.raw.headers[':authority'] }
},
hostname: {
  get() { return this.host.split(':')[0] }
},
port: {
  get() { return this.host.split(':')[1] }
}

These conventions improve code understandability and reduce cognitive load for developers working in the codebase.

---

Content negotiation design

When building APIs, implement proper content negotiation to handle various media types in both requests and responses. This ensures your API can work with different client requirements and maintain compatibility with diverse ecosystems.

Key practices include:

1. Explicitly define and check content types for requests
2. Implement content type-specific validation schemas
3. Handle different response formats appropriately (JSON, streams, buffers)
4. Support both native and polyfill implementations of web standards

For example, when defining route schemas with content-specific validation:

fastify.post('/', {
  schema: {
    body: {
      content: {
        'application/json': {
          schema: jsonSchema
        },
        'application/octet-stream': {
          schema: binarySchema
        }
      }
    }
  }
})

When handling response objects, avoid tight coupling to specific implementations:

// Instead of:
if (payload instanceof Response) {
  // handle response
}

// Prefer more flexible detection:
if (
  // node:stream
  typeof payload.pipe === 'function' ||
  // node:stream/web
  typeof payload.getReader === 'function' ||
  // Response (works with polyfills too)
  Object.prototype.toString.call(payload) === '[object Response]'
) {
  // handle response
}

This approach enables your API to work correctly with various clients and frameworks while maintaining a clean, standards-compliant design.

---

Proper Handling of Promises in Fastify Implementations

When implementing Fastify applications in TypeScript, it is important to follow consistent patterns for handling promises and respecting the framework’s specific constraints. Avoid mixing async/await with callback styles, especially when registering routes, plugins, or parsers. Be aware that some Fastify methods are designed as thenables and do not require explicit awaiting.

For example, when registering content type parsers, do not use await as this can cause issues in Fastify:

// INCORRECT: Mixing await with registration methods
await fastify.addContentTypeParser('application/json', async (req, body) => {
  // This causes issues in Fastify
});

// CORRECT: Don't use await when registering content type parsers
fastify.addContentTypeParser('application/json', async (req, body) => {
  // Proper usage without await
});

When decorating reply methods, ensure they return values for proper chaining:

// INCORRECT: Missing return value
fastify.decorateReply('sendSuccess', function (data) {
  this.send({ success: true })
})

// CORRECT: Return this for chaining
fastify.decorateReply('sendSuccess', function (data) {
  return this.send({ success: true })
})

If using ESLint with no-floating-promises, configure exceptions for Fastify-specific promise patterns to avoid unnecessary warnings.

---

Maintain Consistent Naming Conventions in Next.js Code

As a code reviewer for Next.js projects, ensure that all code artifacts, including component names, file names, and configuration keys, adhere to consistent naming conventions. This helps improve code readability, maintainability, and alignment with the Next.js framework’s best practices.

Key guidelines:

1. Use consistent file extensions for Next.js components: .jsx for React components and .js for non-React JavaScript files.
2. Maintain case sensitivity in Next.js configuration keys and API parameters, such as staticPageGenerationSourcemaps instead of staticPageGenerationSourceMaps.
3. Choose clear, concise, and consistent terminology for Next.js-specific concepts, such as “pages”, “components”, “middleware”, and “API routes”.

Example of inconsistent Next.js code:

// Inconsistent file extensions
pages/search.js   // Should be search.jsx for a React component
pages/utils.ts   // Should be utils.js for a non-React JavaScript file

// Inconsistent configuration keys
next.config.js:
{
  staticPageGenerationSourceMaps: false, // Documentation
  staticPageGenerationSourcemaps: false // Implementation
}

Corrected version:

// Consistent file extensions
pages/search.jsx  // React component
pages/utils.js    // Non-React JavaScript file

// Consistent configuration keys
next.config.js:
{
  staticPageGenerationSourcemaps: false, // Matches implementation
}

---

Proper Error Handling in Next.js API Routes

This review focuses on ensuring proper error handling in Next.js API routes. Key principles:

1. Validate incoming request data before processing to catch and handle errors early.
2. Use a consistent error response structure, including appropriate HTTP status codes.
3. Sanitize error messages to avoid exposing sensitive information.
4. Handle errors securely using try/catch blocks and avoid leaking internal details.
5. Return only necessary error details in responses to provide useful feedback to clients.

Example of correct error handling in a Next.js API route:

export async function POST(request: Request) {
  try {
    // 1. Validate incoming data
    const data = await request.json();
    const validationResult = await validateInputs(data);
    
    if (!validationResult.success) {
      return Response.json(
        { 
          error: 'Validation failed',
          message: validationResult.message 
        }, 
        { status: 400 }
      );
    }

    // 2. Process the request
    const result = await processData(data);
    
    // 3. Return success response
    return Response.json({ data: result });
    
  } catch (error) {
    // 4. Handle errors securely
    const safeMessage = error instanceof Error 
      ? sanitizeErrorMessage(error.message)  // Remove sensitive details
      : 'An unexpected error occurred';
      
    return Response.json(
      { 
        error: true,
        message: safeMessage
      },
      { status: 500 }
    );
  }
}

Developers should follow these guidelines to ensure robust and secure error handling in their Next.js API implementations.

---

Proper Use of Suspense in Next.js Components

When building Next.js applications that leverage server-side rendering (SSR) or Partial Prerendering (PPR), it is essential to wrap components that access dynamic or non-deterministic values (e.g. random values, current time, request-specific data) in Suspense boundaries with appropriate fallbacks. This ensures proper handling of components that cannot be statically prerendered, preventing hydration mismatches and improving performance.

Specifically, developers should:

1. Identify components in their Next.js application that rely on dynamic or non-deterministic data.
2. Wrap these components in a Suspense boundary, providing a fallback UI to display while the dynamic content is being fetched.
3. Ensure that the fallback UI is visually consistent with the final rendered component, to maintain a seamless user experience.

Here is an example of the correct usage of Suspense in a Next.js component:

import { Suspense } from 'react'

export default function Page() {
  return (
    <section>
      <h1>This will be prerendered</h1>
      <Suspense fallback={<FallbackComponent />}>
        <DynamicComponent />
      </Suspense>
    </section>
  )
}

By following this pattern, developers can leverage the benefits of Next.js’s SSR and PPR capabilities while ensuring a robust and consistent user experience, even for components that rely on dynamic data.

---

Verify documentation references

When writing or updating documentation, ensure all code examples, installation commands, and project references accurately reflect the current codebase. This includes:

1. Double-check that example names in installation commands match the actual project being documented: ```bash

   INCORRECT

   npx create-next-app –example hello-world my-etag-test-app

CORRECT

npx create-next-app –example etag-test etag-test-app

2. Verify that all command examples are up-to-date with the latest CLI parameters and syntax.

3. Include clear explanations of the purpose and functionality of examples rather than generic descriptions:
```markdown
# INSUFFICIENT
This is the most minimal starter for your Next.js project.

# BETTER
This example demonstrates the differences in ETag behavior between Next.js 14 and 15 for static pre-rendered pages.

1. When copy-pasting documentation templates, carefully review and update all project-specific references to prevent inaccuracies that could confuse users.

Keeping references accurate prevents user frustration and maintains trust in the documentation.

---

Balance constraints with flexibility

When designing APIs, carefully evaluate constraints imposed on consumers. Each limitation should serve a clear purpose; otherwise, favor flexibility. Instead of rigid enforcement, consider more adaptable interfaces with documentation about recommended usage patterns.

For example, in discussion #4, an initial API design restricted objects to a single observer:

if (this._observer !== null && this._observer !== observer) {
  throw new Error(
    'You are attaching an observer to a fragment instance that already has one. Fragment instances ' +
      'can only have one observer. Use multiple fragment instances or first call unobserveUsing() to ' +
      'remove the previous observer.',
  );
}

After review, this constraint was questioned: “What’s the reason for this limitation?” The developer decided to “extend it to handle multiple and drop this error” since it “doesn’t really take away anything to make it more flexible.”

Similarly, in discussion #5, assumptions about mouse events were challenged with a suggestion to handle more edge cases:

case 'mousedown': {
  if (((nativeEvent: any): MouseEvent).button === 0) {
    isMouseDown = true;
  }
  break;
}
case 'mouseup':
case 'dragend': {
  if (((nativeEvent: any): MouseEvent).button === 0) {
    isMouseDown = false;
  }
  break;
}

When designing APIs that must work across different versions or environments, use fallback patterns rather than rigid requirements. As seen in discussion #1, compatibility can be preserved with approaches like:

const sourceCode = context.sourceCode ?? context.getSourceCode();

This approach enables your API to adapt to varying contexts while maintaining a consistent interface for consumers.

---

Optimize hot paths

In performance-critical code paths that execute frequently, optimize to reduce unnecessary operations that can impact runtime performance:

1. Minimize repeated type checks - Cache type information or restructure code to avoid redundant typeof calls, especially in loops or frequently called functions

2. Avoid unnecessary allocations - Don’t create new arrays, Sets, or objects when you can work with existing data structures directly

3. Use direct traversal - When operating on DOM nodes or other hierarchical structures, prefer inline traversal over building intermediate collections:

// Avoid this in hot paths
const children = new Set(); // Unnecessary allocation
elements.forEach(el => children.add(el));
children.forEach(child => child.addEventListener(type, listener));

// Prefer this approach
elements.forEach(el => el.addEventListener(type, listener));

1. Be aware of thresholds - Understand the impact of operations based on execution frequency:
   • <1ms: Optimal for very frequent operations
   • <10ms: Good for maintaining 60fps animations
   • <100ms: Maximum for responsive interactions

Operations that take more time should be candidates for optimization when they appear in hot paths.

---

Configuration property standards

Always define configuration properties with sensible defaults and consistent naming conventions. When adding new configurable features, establish clear defaults that follow platform conventions and document their purpose.

Guidelines:

• Group related configuration properties together in a structured object
• Use descriptive names that clearly indicate the property’s purpose
• Provide sensible defaults that work in most common scenarios
• Document the expected values and behavior of each configuration option

Example:

const defaults = {
  // HTTP request defaults
  headers: {
    common: {
      'Accept': 'application/json, text/plain, */*'
    }
  },
  
  // Fetch-related configurations
  fetcher: null,
  fetchOptions: {
    cache: 'default',
    redirect: 'follow'
  },
  
  // Character encoding settings
  charset: 'utf-8',
  
  // Feature flags
  experimental_http2: false
};

For experimental features, use clearly named boolean flags (like experimental_http2). For encoding or format settings, follow platform conventions and provide fallbacks where appropriate (e.g., config.charset || 'utf-8'). This approach ensures configurations are discoverable, maintainable, and properly understood by all developers.

---

Consistent Naming Conventions for Axios Requests and Responses

When using the Axios library in TypeScript, it is important to follow consistent naming conventions to improve code readability and maintainability. Specifically:

1. Use the “on” prefix for Axios event handlers and callbacks, such as onUploadProgress and onDownloadProgress.
2. Use domain-specific prefixes like “response” to clarify the scope of Axios-related functionality, such as responseEncoding and responseType.
3. Maintain consistent naming patterns for similar Axios-related functionality, such as using the same parameter structure for authentication-related properties.
4. Align Axios-specific naming with established conventions in the TypeScript ecosystem, such as using camelCase for properties and methods.

Following these practices will help developers working on your Axios-based code understand the purpose and usage of your API more intuitively. Provide clear, well-named Axios-related functionality to improve the developer experience.

Example:

// ✅ Good - Clear event handler naming with "on" prefix
const config: AxiosRequestConfig = {
  onUploadProgress: (progressEvent: ProgressEvent) => { /* ... */ },
  onDownloadProgress: (progressEvent: ProgressEvent) => { /* ... */ }
}

// ❌ Bad - Unclear purpose of the function
const config: AxiosRequestConfig = {
  uploadProgress: (progressEvent: ProgressEvent) => { /* ... */ },
  downloadProgress: (progressEvent: ProgressEvent) => { /* ... */ }
}

// ✅ Good - Consistent parameter structure and clear scope
const config: AxiosRequestConfig = {
  responseEncoding: 'utf-8',
  proxy: {
    auth: { username: 'mikeymike', password: 'rapunz3l' } // Matches other auth patterns
  }
}

---

Proper Axios Configuration and Usage

When implementing code that uses the Axios library in TypeScript, it is important to follow best practices for configuring and accessing Axios instances and settings. Ensure that:

1. Axios instances are properly configured with appropriate defaults, such as timeout values and custom properties.
2. Configuration properties are accessed correctly, using the proper namespacing and access paths.
3. Request-specific configuration overrides instance-level defaults in a predictable manner.

For example, when creating an Axios instance:

// GOOD: Clearly document Axios instance configuration
// Configuration precedence order:
// 1. Library defaults
// 2. Instance defaults
// 3. Request-specific config (overrides instance defaults for url, method, params, data)

const instance = axios.create({
  timeout: 5000,
  customConfig: { retryOnError: true } // Custom properties in their own namespace
});

// Access custom config properly
if (config && instance.customConfig.retryOnError) {
  // Handle retry logic
}

This ensures that developers working on the codebase understand how Axios configuration is resolved, preventing unexpected behavior from improperly merged settings and maintaining clear separation between standard and custom configuration properties.

---

Document feature flags

When configuring feature flags in Cargo.toml, ensure they are properly structured and documented:

1. Chain feature dependencies correctly - Features that depend on other features should explicitly list those dependencies: ```toml

   Incorrect:

   cookie-signed = [“cookie-lib/signed”]

Correct:

cookie-signed = [“cookie”, “cookie-lib/signed”]

2. **Document non-obvious configuration choices** with comments to help other developers understand your reasoning:
```toml
# `default-features = false` to not depend on tokio which doesn't support compiling to wasm
axum = { path = "../../axum", default-features = false }

1. Use appropriate syntax for conditional feature activation, understanding special operators like ? for optional dependencies:

   async-read-body = ["dep:tokio-util", "tokio-util?/io"]
   

These practices ensure that your configuration is both functionally correct and easier for other developers to understand and maintain.

---

Consistent Fastify Integration Patterns

When implementing integrations and plugins using the Fastify framework, maintain consistent coding patterns and conventions:

1. Follow Fastify’s recommended package naming conventions, using the @fastify scope for all Fastify-specific packages (e.g. @fastify/kafka instead of fastify-kafka).
2. Ensure integrations provide clear and comprehensive documentation of the specific protocol, system or service being integrated (e.g. “Plugin to interact with Apache Kafka message broker”).
3. Use Fastify’s built-in type definitions and decorators consistently across all plugins and integrations.
4. When referencing external protocol standards, include the full RFC reference with a period at the end of the description (e.g. “Plugin to add HTTP 103 Early Hints based on RFC 8297.”).

Example Fastify integration:

import fastify, { FastifyInstance } from 'fastify';
import { FastifyKafka } from '@fastify/kafka';

const server: FastifyInstance = fastify();

server.register(FastifyKafka, {
  brokers: ['kafka1:9092', 'kafka2:9092'],
  topic: 'my-topic'
});

server.get('/messages', async (request, reply) => {
  const messages = await server.kafka.consume();
  return messages;
});

Consistent implementation of Fastify integrations and plugins improves maintainability, makes resources easier to discover, and ensures developers can quickly understand the purpose and usage of network-related features in Fastify applications.

---

Consistent variable style patterns

Maintain consistent patterns for variable declarations and naming conventions:

1. Use const by default for variable declarations, only use let when the variable needs to be reassigned
2. Use clear, complete words in variable names instead of abbreviations
3. For truthiness checks, prefer simple boolean conditions unless explicit null/undefined checks are required

Example:

// ❌ Inconsistent patterns
let lockFile = findRootLockFile(cwd)
const normChunkPath = '/path'
if (testWasmDir != null) {
  // ...
}

// ✅ Consistent patterns
const lockFile = findRootLockFile(cwd)
const normalizedChunkPath = '/path'
if (testWasmDir) {
  // ...
}

This promotes code readability and reduces cognitive load by establishing predictable patterns across the codebase.

---

Optimize data structure selection

Choose data structures that match your specific access patterns and performance requirements. The right data structure can significantly improve performance without requiring algorithm changes.

For concurrent access patterns, consider specialized concurrent data structures:

// Instead of this
subscribers: Arc<Mutex<HashMap<String, Vec<mpsc::Sender<Arc<dyn CompilationEvent>>>>>>,

// Consider this for better concurrent performance
subscribers: DashMap<String, Vec<mpsc::Sender<Arc<dyn CompilationEvent>>>>,

For data storage, evaluate compression benefits with appropriate thresholds:

// Consider compression only when beneficial
if bytes.len() > MIN_COMPRESSION_SIZE && compressed.len() < bytes.len() {
    Compressed(compressed)
} else {
    Local(bytes)
}

For serialization/deserialization, minimize allocations using stack allocation for small values:

// Instead of always allocating on the heap
struct Data(Vec<u8>, IndexSet<RcStr, FxBuildHasher>);

// Consider stack allocation for small values
struct SerData(SmallVec<[u8; 16]>, FxIndexSet<RcStr>);

Always measure the performance impact of your choices with benchmarks to confirm expected improvements. As seen in real examples, the right data structure can yield performance improvements of 3x or more in high-throughput scenarios.

---

Prefer Existence Checks in Next.js Components

When working with props, state, or other values in Next.js components that may be null, undefined, or contain error states, use existence checks rather than direct property access or value comparisons. This helps prevent runtime exceptions and improves the reliability of your Next.js application.

For conditional rendering or operations in Next.js components:

// ❌ Problematic - assumes 'previous' prop is a number
{previous > 0 ? <button onClick={previous}>Previous</button> : null}

// ✅ Better - checks if 'previous' prop exists at all
{previous ? <button onClick={previous}>Previous</button> : null}

When working with optional or error-prone properties in Next.js components:

// ✅ Check for property existence before proceeding
export default function RemoteMdxPage({ mdxSource }) {
  if ("error" in mdxSource) {
    // Handle error state
    return <ErrorComponent error={mdxSource.error} />;
  }
  return <MDXClient {...mdxSource} />;
}

This approach applies to any value that could be null, undefined, or contain an error state in your Next.js components. Using the appropriate existence check pattern improves code safety, reliability, and readability.

---

Verify workflow configuration integrity

Carefully review GitHub Actions workflow configurations to prevent subtle errors that can cause CI/CD pipeline failures or unexpected behavior:

1. Ensure correct syntax in workflow triggers, especially avoiding nested quotes in branch names: ```yaml

   Incorrect

   branches:

   • ‘“canary”’

Correct

branches:

• “canary” ```

1. Always provide explicit IDs for steps that will be referenced by subsequent steps: ```yaml

   Missing ID that will cause reference failure

   • name: ‘Deploy to Cloud Run’ uses: ‘google-github-actions/deploy-cloudrun@v2’

Correct with ID

• name: ‘Deploy to Cloud Run’ id: deploy uses: ‘google-github-actions/deploy-cloudrun@v2’ ```

1. Use appropriate conditions for workflow execution, considering job skip scenarios: ```yaml

   May cause issues when dependency is skipped

   if: ${{ always() && needs.deploy-target.outputs.value != ‘’ }}

More robust handling of skipped jobs

if: ${{ always() && needs.deploy-target.result != ‘skipped’ }}

---

## Write concise idiomatic code

<!-- source: vercel/next.js | topic: Code Style | language: Rust | updated:  -->

Favor concise and idiomatic expressions in your Rust code to improve readability and maintainability. Specifically:

1. Use Rust's expressive methods instead of verbose alternatives
   ```rust
   // Prefer this
   ident_ref.query.owned().await?
   
   // Instead of this
   (*ident_ref.query.await?).clone()

1. Avoid redundant .to_string() calls in format! arguments when the type already implements Display

   // Prefer this
   format!("Check {} and {}", this.page, this.other_page)
      
   // Instead of this
   format!("Check {} and {}", this.page.to_string(), this.other_page.to_string())
   

2. Only derive the traits you actually need, removing unnecessary derives like serde::Serialize and serde::Deserialize when they’re not used

   // Prefer this
   #[derive(Debug, Clone, Eq, PartialEq, Hash)]
      
   // Instead of this when serialization isn't needed
   #[derive(Debug, Clone, Eq, PartialEq, Hash, serde::Serialize, serde::Deserialize)]
   

These practices reduce visual noise and make the intent of your code clearer.

---

Check property existence first

Always verify that an object and its properties exist before accessing them to prevent “cannot read property of undefined/null” errors. This is especially important when dealing with objects that might come from different build environments (dev vs. production) or third-party libraries.

There are two common approaches:

1. Using a falsy check when null and undefined are both invalid: if (!obj) or if (!obj.property)
2. Using explicit checks when you need to distinguish between different falsy values: if (obj === undefined) or if (obj.property === null)

Example - Before:

// Risky code that might fail
clonedElement._store.validated = oldElement._store.validated;

Example - After:

// Safe code that checks existence first
if (oldElement._store && clonedElement._store) {
  clonedElement._store.validated = oldElement._store.validated;
}

This is particularly important in codebases where:

1. Components might be rendered in both development and production environments
2. You’re integrating with third-party libraries that might have different property structures
3. Properties might be conditionally added to objects

Being proactive about property existence checks leads to more robust code and prevents unexpected runtime errors.

---

Complete hook dependencies

Always specify complete dependency arrays in React hooks to prevent bugs from stale closures and avoid unnecessary rerenders. When using hooks like useEffect, useMemo, or useCallback, include all values from the component scope that are referenced inside the hook’s callback function.

For custom hooks that wrap React’s built-in hooks:

1. Pass through dependency arrays correctly rather than hardcoding them
2. Avoid type assertions (like as any) that bypass dependency checking
3. Remember that global variables and constants defined outside the component don’t need to be dependencies

// ❌ Incorrect: Missing dependencies
function Component({foo, bar}) {
  useEffect(() => {
    console.log(foo, bar);
  }, []); // Missing foo and bar

  // ❌ Incorrect: Bypassing dependency checks
  useCustomCallback(callback, [] as any);
}

// ✅ Correct: All dependencies included
function Component({foo, bar}) {
  const nonreactive = 0; // Local constant
  
  useEffect(() => {
    console.log(foo, bar, nonreactive);
  }, [foo, bar]); // nonreactive is a constant, doesn't need to be a dependency
  
  // ✅ Correct: Properly passing dependencies through
  useCustomCallback(callback, [callback]);
}

ESLint’s exhaustive-deps rule can help identify missing dependencies automatically, preventing subtle bugs caused by stale closures.

---

Match errors to context

Choose error handling mechanisms based on the error’s severity and context. For critical issues that should prevent further execution, throw explicit exceptions. For non-critical issues, use logging with sufficient detail to aid debugging without interrupting execution.

When throwing exceptions for critical validation errors:

if (reference.resolved === null) {
  throw new Error('Unexpected undefined reference.resolved');
}

When logging non-critical issues, include precise location information and use visual indicators to distinguish error types:

const { reason, severity, loc } = compilation.detail;
const lnNo = loc.start?.line;
const colNo = loc.start?.column;
const isTodo = severity === ErrorSeverity.Todo;

console.log(
  chalk[isTodo ? 'yellow' : 'red'](
    `Failed to compile ${filename}${lnNo !== undefined ? `:${lnNo}${colNo !== undefined ? `:${colNo}` : ""}` : ""}`
  ),
  reason ? `\n  Reason: ${isTodo ? 'Unimplemented' : reason}` : ""
);

This approach helps identify bugs early in the development process for critical issues while providing informative, actionable feedback for less severe problems without unnecessarily halting execution.

---

Optimize React Component Dependencies

When implementing React components, ensure that dependencies between component state, props, and side effects are accurately tracked to prevent missed updates and unnecessary re-renders. This is crucial for maintaining efficient and responsive React applications.

Key practices:

1. Carefully analyze component state and derived values to identify all true dependencies for useEffect and other hooks.
2. Properly handle conditional rendering and dynamic dependencies in your use of hooks like useEffect.
3. Consider object identity and reference semantics when determining dependencies, especially for props and state.
4. Separate control flow dependencies from data dependencies when possible, using techniques like memoization.

Example:

// Problematic - missing dependency in useEffect
function ProcessData({ inputData }: { inputData: any }) {
  const derived = condition ? sourceA : sourceB;
  
  // Later operations use 'derived' but don't track its dependencies
  useEffect(() => {
    process(derived.value);
  }, []); // Missing dependency on 'derived'
}

// Improved - proper dependency tracking in useEffect
function ProcessData({ inputData }: { inputData: any }) {
  const derived = condition ? sourceA : sourceB;

  // Correctly tracks the dependency on 'derived'
  useEffect(() => {
    process(derived.value);
  }, [derived]); // Properly includes derived as dependency
}

By carefully managing component dependencies, you can create more maintainable React code and improve the efficiency of your application, avoiding both unnecessary re-renders and missed updates.

---

Separate conditional paths

When working with concurrent operations, separate conditional logic from potentially expensive or suspenseful execution paths. This improves performance, prevents race conditions, and makes concurrent code more predictable and maintainable.

Why it matters:

• Prevents unnecessary work in hot paths
• Reduces the risk of duplicate invocations and race conditions
• Makes concurrent code easier to reason about

How to apply it:

1. Hoist conditional checks higher in the call stack
2. Only invoke complex operations when necessary
3. Structure tests to properly simulate real concurrency patterns

Example - Before:

function preloadInstanceAndSuspendIfNeeded(type, props, workInProgress, renderLanes) {
  // This check happens on every call, even when it's not needed
  if (!maySuspendCommit(type, props)) {
    // Regular path...
  } else {
    // Suspending path...
  }
}

Example - After:

// In the calling function (e.g., completeWork):
const maySuspend = checkInstanceMaySuspend(type, props);
if (maySuspend) {
  preloadInstanceAndSuspendIfNeeded(type, props, workInProgress, renderLanes);
}

// Then the function only handles suspension cases
function preloadInstanceAndSuspendIfNeeded(type, props, workInProgress, renderLanes) {
  // Only suspension logic here
}

For testing concurrent operations, model tests to match real-world behavior using appropriate timing mechanisms:

await act(async () => {
  submitButton.current.click();
  await waitForMicrotasks(); // Allow natural processing cycles
  submitButton.current.click(); // Second interaction
});

---

Use appropriate testing methods

When writing tests, use the appropriate testing utilities and ensure proper test isolation.

For testing warning behaviors:

• Use assertConsoleErrorDev or toErrorDev instead of gating tests with environment flags like @gate __DEV__
• Assert both the warning and the expected behavior outcomes

For testing sequential or asynchronous actions:

• Use logging utilities like Scheduler.log() with corresponding assertions like assertLog(['Action', 'Action'])

Always clean up after tests that use mocks:

// Bad: No cleanup after mocking
console.error = jest.fn();
// Test code...
// Missing cleanup!

// Good: Proper cleanup
const originalConsoleError = console.error;
console.error = jest.fn();
// Test code...
console.error = originalConsoleError; // Or use console.error.mockRestore();

// Better: Use afterEach for guaranteed cleanup
beforeEach(() => {
  jest.spyOn(console, 'error').mockImplementation(() => {});
});

afterEach(() => {
  console.error.mockRestore();
});

Failing to clean up mocks can silently break subsequent tests by interfering with their assertions, making test failures difficult to debug.

---

Verify performance empirically

Always validate performance optimizations through measurement rather than assumptions. Run multiple iterations of performance tests to ensure statistical significance and reduce noise in your metrics.

When proposing performance-related changes:

1. Establish baseline measurements before making changes
2. Implement your optimization
3. Run the same tests multiple times (at least 5 iterations)
4. Calculate average metrics to verify actual improvement

// Example: Multiple iterations for reliable performance testing
const iterations = 5;
let totalRenderTime = 0;

// Collect performance data across multiple runs
for (let i = 0; i < iterations; i++) {
  const performance = await measurePerformance(component);
  totalRenderTime += performance.renderTime;
}

// Calculate and report the average
const averageRenderTime = totalRenderTime / iterations;
console.log(`Average render time: ${averageRenderTime.toFixed(2)}ms`);

This approach prevents changes that might appear beneficial in a single test run but actually have neutral or negative impacts in production environments. Increasing the number of iterations provides higher confidence in your performance results.

---

Consistent Axios Usage Patterns

Maintain consistent usage of the Axios library throughout your TypeScript codebase. Pay special attention to the following:

1. Consistent Error Handling: Ensure all Axios requests have proper error handling, such as using try/catch blocks to handle network errors, timeouts, and invalid responses. Provide clear and actionable error messages to aid debugging.

2. Axios Configuration Options: Leverage Axios configuration options like timeout, headers, and baseURL to ensure consistent behavior across your application. Avoid hardcoding these values in multiple places.

3. Axios Request Patterns: Use the appropriate Axios request methods (e.g. get, post, put, delete) consistently based on the HTTP verb required by the API. Avoid mixing request types for the same endpoint.

4. Axios Response Handling: Extract and handle the response data consistently, whether it’s accessing the data property or parsing the response body. Ensure error responses are also handled appropriately.

Provide code examples demonstrating best practices for the above Axios usage patterns to help developers write maintainable and robust Axios-based code.

---

Consistent semicolon usage

Always terminate statements with explicit semicolons to maintain consistency with the existing codebase style. Avoid relying on JavaScript’s automatic semicolon insertion (ASI) feature, as this can lead to inconsistent code appearance and potential subtle bugs. Project convention shows that 99% of statements already use explicit semicolons.

Example (incorrect):

const headers = new AxiosHeaders({foo: "bar"})

Example (correct):

const headers = new AxiosHeaders({foo: "bar"});

---

Flexible configuration design

Design configuration interfaces to be flexible and extensible rather than overly specific. When creating configuration objects:

1. Make configuration parameters optional when possible with sensible defaults
2. Allow for arbitrary additional properties rather than creating specific fields for custom configurations

Example - Instead of this:

export interface AxiosRequestConfig<D = any> {
  // other properties...
  customConfig?: Record<string, any>;
}

// Required configuration parameter
getUri(config: AxiosRequestConfig): string;

Do this:

export interface AxiosRequestConfig<D = any> {
  // other properties...
  [key: string]: any; // Allow arbitrary properties
}

// Optional configuration parameter
getUri(config?: AxiosRequestConfig): string;

This approach allows consumers to extend configurations naturally without requiring interface changes for each new use case, while maintaining backward compatibility through sensible defaults.

---

User-friendly error messages

Error messages should be concise and clearly communicate what went wrong without unnecessary verbosity. When implementing error handling, maintain consistent code style and organize related operations logically within appropriate blocks.

Example:

// Instead of this:
try {
    data = JSON.parse(data);
} catch (e) {
    output.innerHTML = "Error : Is blank or not JSON string type. Please check your data.";
    data = null;
}

// Do this:
try {
    data = JSON.parse(data);
    
    // Keep related operations in the try block
    axios.post('/post/server', data)
        .then(function (res) {
            output.className = 'container';
            output.innerHTML = res.data;
        })
        .catch(function (err) {
            output.className = 'container text-danger';
            output.innerHTML = err.message;
        });
} catch (e) {
    // Use concise, clear error messages
    output.innerHTML = "Error: empty string or invalid JSON";
    output.className = 'container text-danger';
}

This approach improves user experience by providing clear feedback while maintaining clean, logically structured code with consistent styling.

---

Implement Distributed Tracing in Axum Applications

As an Axum code reviewer, I recommend implementing proper distributed tracing in your Axum-based web applications to ensure observability across service boundaries. Use Axum’s built-in middleware layers to consistently instrument your code:

1. Propagate Request IDs: Use the tower_http::request_id middleware to generate and propagate unique request IDs across service calls. This allows you to correlate requests and trace their flow through your distributed system.

import { Router } from '@awslabs/aws-lambda-typescript-runtime';
import { RequestIdLayer } from '@awslabs/aws-lambda-typescript-runtime/middleware';

const app = Router.create()
  .use(RequestIdLayer.create({
    headerName: 'x-request-id',
    generateRequestId: () => crypto.randomUUID()
  }));

1. Implement Structured Logging with Trace Context: Leverage the tower_http::trace middleware to add detailed tracing information to your application logs. This allows you to correlate log entries with specific requests and understand the flow of execution.

import { Router } from '@awslabs/aws-lambda-typescript-runtime';
import { TraceLayer } from '@awslabs/aws-lambda-typescript-runtime/middleware';

const app = Router.create()
  .use(TraceLayer.create({
    makeSpan: (req) => {
      return tracing.info('request', {
        requestId: req.headers.get('x-request-id') || 'unknown',
        method: req.method,
        uri: req.url.pathname
      });
    }
  }));

1. Integrate with OpenTelemetry: Consider using the @opentelemetry/api and @opentelemetry/sdk-node packages to connect your Axum application to a standardized observability backend, such as Jaeger, Zipkin, or a cloud-native monitoring platform. This allows you to export traces and metrics for deeper analysis and debugging.

By implementing these patterns, you can effectively debug production issues, understand service dependencies, and measure performance across your distributed Axum-based system.

---

Use Appropriate Concurrency Patterns with Axum

When building asynchronous Axum applications that share mutable state, it’s important to select the right concurrency mechanisms:

1. For general shared state:
   • Use Axum’s built-in Mutex or RwLock to protect access to in-memory data structures
   • Only use asynchronous Mutex or RwLock when the lock must be held across .await points
2. For shared I/O resources (like database connections):
   • Avoid wrapping individual connections in Axum’s Mutex or RwLock, which can lead to deadlocks
   • Prefer using Axum’s built-in connection pool (PoolOptions) to handle concurrency internally
   • Consider the actor pattern (e.g. using Axum’s Service and State) for complex shared I/O operations

Example:

// GOOD: Using Axum's Mutex to protect in-memory state
const counter = new Mutex<number>(0);

// GOOD: Using Axum's connection pool to handle concurrency
const db = await createPool({
  connectionString: 'postgres://...',
  maxConnections: 10,
});

// AVOID: Wrapping I/O resource in Axum's Mutex
// const db = new Mutex(await createConnection('postgres://...'));

Choosing the right concurrency pattern in Axum prevents deadlocks, improves performance, and makes your code more maintainable. Always consider what happens when your Axum handler yields while holding a lock.

---

Consistent Fastify Package Naming and References

When implementing code using the Fastify package in TypeScript, it is important to use consistent and accurate naming conventions for Fastify-related references:

• Always use the actual Fastify package name (fastify) rather than referring to the Fastify repository or other informal names.
• When referencing Fastify types, plugins, or other Fastify-specific concepts, use the correct Fastify terminology and casing (e.g. FastifyInstance, fastify.get()).
• Organize Fastify-related imports and references alphabetically to maintain consistency and make the code easier to navigate.

Example:

// Preferred: Using the correct Fastify package name and terminology
import fastify, { FastifyInstance, FastifyReply, FastifyRequest } from 'fastify';

// Instead of informal references
import { createFastifyApp } from 'my-fastify-utils';

// Preferred: Alphabetized Fastify imports
import { FastifyPluginAsync } from 'fastify';
import fastifyAuth from '@fastify/auth';
import fastifyCors from '@fastify/cors';

Following these conventions will improve the maintainability of your Fastify-based codebase and make it easier for other developers to understand and work with the Fastify package correctly.

---

Ensure Proper Null Handling When Using Fastify Decorators

When working with Fastify decorators, always perform explicit null checks before accessing potentially undefined properties. Relying on implicit null handling can lead to subtle bugs and unexpected behavior. Instead, leverage Fastify’s type-safe decorator APIs and type guards to ensure null safety at compile-time.

Why? Fastify decorators provide a powerful way to extend the functionality of your application, but they can also introduce the risk of accessing undefined values. Explicit null checks help make your code’s intent clear and prevent cascading errors caused by missing dependencies.

Example:

// ❌ Problematic - unclear if user decorator is missing
const user = request.user;
if (user && user.isAdmin) {
  // Execute admin tasks
}

// ✅ Better - use Fastify's type-safe decorator API
try {
  const user = request.getDecorator<User>('user');
  if (user.isAdmin) {
    // Execute admin tasks
  }
} catch (err) {
  // Handle missing decorator case explicitly
}

// ✅ Also good - use type guards to ensure null safety
request.raw.on('close', () => {
  if (isRequestDestroyed(request.raw)) {
    // Handle aborted request
  }
});

function isRequestDestroyed(raw: FastifyRawRequest): raw is FastifyRawRequest & { destroyed: true } {
  return raw.destroyed;
}

By following these practices, you can write more robust and maintainable Fastify applications that are less prone to null-related errors.

---

Proper IPv6 address formatting

When constructing URLs with IP addresses, ensure IPv6 addresses are properly formatted according to RFC standards by wrapping them in square brackets. This applies to all IPv6 addresses, not just specific cases like localhost (::1). Additionally, use appropriate event handlers (once instead of on) for network events that should only be handled once per connection.

Code example for IPv6 address handling:

// Incorrect - only handles a specific IPv6 address
const host = address.address === '::1' ? '[::1]' : address.address

// Correct - handles all IPv6 addresses according to RFC standards
const host = address.family === 'IPv6' ? `[${address.address}]` : address.address

Code example for proper event handling:

// Incorrect - may cause multiple handlers to be registered
session.on('connect', function () {
  http2Sessions.add(session)
})

// Correct - ensures the handler is registered exactly once
session.once('connect', function () {
  http2Sessions.add(session)
})

Following these practices ensures compliance with RFC 3986 and RFC 2732 for URL formatting and prevents potential issues with network connection management.

---

Secure Fastify Code Implementation

This review focuses on secure implementation patterns when using the Fastify web framework in TypeScript:

1. Prevent Prototype Pollution Attacks: Avoid direct property access on untrusted objects. Instead, use Object.prototype methods to safely access object properties:

// Vulnerable approach
fastify.get('/route', (req, reply) => {
  console.log(req.params.hasOwnProperty('name')); // Potential prototype pollution vulnerability
  return { hello: req.params.name };
});

// Secure approach
fastify.get('/route', (req, reply) => {
  console.log(Object.prototype.hasOwnProperty.call(req.params, 'name')); // Safe property access
  return { hello: req.params.name };
}); 

1. Protect Against Denial-of-Service Attacks: Configure appropriate request timeouts, especially when deploying Fastify without a reverse proxy:

const fastify = Fastify({
  requestTimeout: 120000 // Set a non-zero timeout (e.g., 120 seconds)
});

These security measures help mitigate common web application vulnerabilities when using the Fastify framework.

---

Support flexible logging

When designing logging interfaces, create flexible APIs that accommodate both standard and custom logging needs. This includes:

1. Support custom log levels: Don’t assume only standard levels (trace, debug, info, warn, error, fatal) will be used. Always check against logger.levels which includes any custom levels.

2. Allow message format customization: Provide hooks that let users customize log message content.

3. Enable level selection based on context: Let users determine the appropriate log level dynamically based on runtime properties.

Example of a flexible logging interface:

// Instead of this limited approach:
childLogger.info({ req: request }, 'incoming request')

// Provide a customization hook that gives control over both level and message:
function createRequestLogMessage(childLogger, req) {
  // User can choose log level based on request properties
  const level = req.headers['x-debug'] ? 'debug' : 'info'
  
  // User can customize the message content
  const message = `Incoming ${req.method} request to ${req.url}`
  
  // User controls both level and formatting
  childLogger[level]({ req: req, custom: true }, message)
}

// Usage
if (createRequestLogMessage) {
  createRequestLogMessage(childLogger, req)
} else {
  childLogger.info({ req: request }, 'incoming request')
}

This approach increases flexibility without sacrificing simplicity for common use cases.

---

Use bot identity

When configuring Git operations in GitHub Actions workflows, especially for automated commits, use the GitHub Actions bot identity instead of personal user accounts. This clearly distinguishes automated actions from manual ones, provides better audit trails, and avoids personal attribution for system-generated changes.

Implementation:

- name: Git Config
  run: |
    git config --global user.email "41898282+github-actions[bot]@users.noreply.github.com"
    git config --global user.name "github-actions[bot]"

This approach ensures that commit history properly reflects which changes were made through automation versus direct developer intervention, making repository history more transparent and accurate. It also prevents confusion that might arise when commits appear to come from individuals but are actually from automated processes.

---

Verify types in tests

Use explicit type assertions in TypeScript tests to verify that types behave as expected across various scenarios. Include assertions for inheritance relationships, property types, and different response status codes. This helps catch type-related regressions early and ensures the type system correctly models your application’s behavior.

Example:

instance.register(childInstance => {
  // Verify inherited properties maintain correct types
  expectType<void>(childInstance.testPropSync)
  expectType<string>(childInstance.testValueSync)
  expectType<number>(childInstance.testFnSync())
})

// Verify response types with different status codes
expectType<(payload?: string) => typeof res>(res.code(200).send)
// Add assertions for other status codes

---

Choose optimal data structures

Select data structures based on their performance characteristics and actual usage patterns. When implementing algorithms:

1. Consider usage patterns: Analyze how data will be accessed and modified. For collections that might contain duplicates where duplicates add no value (like in discussion 3), prefer Sets over Lists/Arrays:

// Less efficient: Using Vec when duplicates don't matter
let mut used_exports = Vec::new();
used_exports.push(Export::Named("React"));  // This might be added many times

// More efficient: Using a Set to automatically handle duplicates
let mut used_exports = FxHashSet::default();
used_exports.insert(Export::Named("React"));  // Will only be stored once

1. Understand API differences: Data structures with similar purposes may have different method behaviors. For example, in discussion 1, changing from HashSet to HashMap required adjusting logic because:

// HashSet.insert() returns a boolean indicating if the element was newly inserted
if !set.insert(key) {
    return;  // Element was already present
}

// HashMap.insert() returns Option<V> with the previous value, if any
if map.insert(key, value).is_some() {
    return;  // Key was already present (previous value returned)
}

1. Match data structures to access patterns: Use hashmaps for fast lookups, vectors for sequential access, sets for uniqueness enforcement, and specialized structures for specific needs.

Choosing the right data structure is often the difference between an efficient algorithm and one that performs poorly at scale.

---

Complete data structures

When implementing data structures such as tries, trees, or graphs, ensure all critical operations (insertion, deletion, traversal) are fully implemented with proper cleanup logic. Incomplete implementations can lead to memory leaks, stale data, and incorrect application behavior.

For example, in a trie implementation, the remove operation should:

1. Traverse the structure to locate the target node
2. Clear the node’s value
3. Clean up orphaned parent nodes when appropriate
4. Update any dependent systems

function remove(value: Value) {
  const key = getKey(value)
  if (!key) return

  let current = root
  const parts = key.split('/')
  const path: Node[] = [current]

  // Traverse the trie to find the node
  for (const part of parts) {
    if (!current.children[part]) {
      return // Node doesn't exist
    }
    current = current.children[part]
    path.push(current)
  }

  // Clear the node's value
  current.value = undefined

  // Clean up empty parent nodes
  for (let i = path.length - 1; i > 0; i--) {
    const node = path[i]
    if (!node.value && Object.keys(node.children).length === 0) {
      const parent = path[i - 1]
      const nodeName = parts[i - 1]
      delete parent.children[nodeName]
    } else {
      break // Stop if we find a non-empty node
    }
  }

  // Notify listeners or update UI if needed
  markUpdated()
}

When designing data structures, also consider using generics to make them reusable across different value types, increasing their utility throughout your application.

---

Complete error handling flows

Implement robust error handling patterns that ensure both proper resource cleanup and error context preservation.

Resource cleanup: Always clean up resources such as timeouts, connections, and file handles using finally blocks or promise .finally() handlers to prevent memory leaks:

const timeoutId = setTimeout(() => {
  processLookupController.abort(`Operation timed out after ${timeoutMs}ms`);
}, timeoutMs);

try {
  // Main operation code
  return await someAsyncOperation();
} catch (error) {
  // Error handling
} finally {
  // Cleanup runs regardless of success or failure
  clearTimeout(timeoutId);
}

Error context preservation: When catching and rethrowing errors, preserve the original error context using the cause property instead of modifying error messages directly:

try {
  await instrumentationModule.register();
} catch (err) {
  // Preserve the original error while adding context
  throw new Error("An error occurred while loading instrumentation hook", { cause: err });
}

This approach maintains the original stack trace and error details while allowing you to add meaningful context for debugging.

---

Dependency conscious APIs

Design APIs with dependency implications in mind. Carefully consider how your API design choices might force dependencies on consumers, which can lead to dependency bloat or tight coupling between components.

When designing APIs that bridge between different modules or layers:

1. Structure interfaces to minimize unnecessary dependencies across your codebase
2. Balance between using convenient abstractions and maintaining clean dependency isolation
3. Consider alternative designs that maintain functionality without adding dependencies

Example: Instead of forcing all components to depend on a specific implementation:

// Avoid: Forces napi dependency on all consumers
#[napi(object)]
struct EventObject {
    type_name: String,
    severity: String,
    message: String
}

// Better: Uses generic interfaces without dependency leakage
pub fn emit_compilation_event<T: CompilationEvent>(event: T) {
    turbo_tasks().emit_compilation_event(Arc::new(event));
}

This approach allows functionality to be used without requiring direct dependencies on implementation details, keeping your architecture more flexible and maintainable.

---

Document configuration sources

When providing configuration instructions, document the exact location and method to obtain required values. Include specific paths, URLs, or UI navigation steps needed to find configuration settings. For tool-specific configurations, explain the reasoning behind non-standard settings.

Examples:

# Good - Clear and specific
# Update these with your Supabase details from the Connect modal via your project's project header
# https://supabase.com/dashboard/project/_?showConnect=true

# Good - Explains non-standard configuration
# Uses --watch=always instead of --watch because Turborepo doesn't wire stdin correctly
"tw-watch": "pnpm tw-build --watch=always"

# Bad - Vague and potentially outdated
# Update these with your Supabase details from your project settings

Including precise configuration source information reduces setup time, prevents errors, and ensures developers can efficiently update configuration values when needed.

---

Non-blocking observability mechanisms

When implementing observability mechanisms like telemetry or status monitoring, ensure they don’t block or interfere with critical application operations. Use background processes for telemetry submissions and dedicated endpoints for status checks.

For telemetry during shutdown operations:

// Incorrect: Blocking on telemetry before shutdown
await telemetry.flush();
process.exit(RESTART_EXIT_CODE);

// Better: Use detached processes for telemetry
telemetry.flushDetached();
process.exit(RESTART_EXIT_CODE);

For service status monitoring:

// Reliable approach: Query dedicated status endpoints
await fetchWithTimeout('/__nextjs_server_status');
// Then proceed with operations that may affect service

// Unreliable approach: Depending on functional endpoints that might be interrupted
await fetch('/__nextjs_restart_dev');
// Don't rely on response from endpoints that might be affected by the operation itself

This pattern ensures that observability data is collected reliably while maintaining system performance and responsiveness, particularly during critical lifecycle events like server restarts.

---

Proper panic chains

When implementing panic handlers, follow these critical practices to ensure robust error handling:

1. Register panic handlers as early as possible in your program to avoid race conditions in multi-threaded environments
2. Always chain new panic handlers with existing ones to preserve important error context
3. Use appropriate error type downcasting methods to extract meaningful error information

Example of correct panic hook chaining:

use std::panic::{set_hook, take_hook};

// Capture previous hook and chain it with your custom handler
let prev_hook = take_hook();
set_hook(Box::new(move |info| {
    // Your custom panic handling logic here
    handle_panic(info);
    
    // Call the previous hook to maintain the chain
    prev_hook(info);
}));

When handling error types in panic recovery:

// Prefer this approach for downcasting errors
.downcast_ref::<dyn Display>()

// Instead of this, which expects Box<Box<_>>
.downcast_ref::<Box<dyn Error + 'static>>()

Use Any::downcast_ref for borrowed references and Any::downcast when you need ownership of the error value. Implementing comprehensive panic handling helps create more resilient applications with better error reporting.

---

Robust Error Handling in Next.js Components

When building Next.js components, it is crucial to implement robust error handling to ensure the stability and predictability of your application. Always explicitly check for error conditions before proceeding with normal execution flow.

For operations that may throw exceptions, such as API calls or data parsing, use try/catch blocks to handle errors gracefully and provide appropriate fallbacks. Avoid implicit error handling, as it can lead to unpredictable behavior and make debugging more difficult.

Here’s an example of how to handle errors in a Next.js component that processes data from an API:

import ErrorDisplay from './ErrorDisplay';

function MyNextJSComponent({ data }) {
  try {
    // Check for errors in the API response
    if ('error' in data) {
      // Handle the error case appropriately
      return <ErrorDisplay error={data.error} />;
    }

    // Only proceed with normal processing if no error exists
    return (
      <div>
        <h1>{data.title}</h1>
        <p>{data.content}</p>
      </div>
    );
  } catch (error) {
    // Handle any unexpected exceptions
    return <ErrorDisplay error={error.message} />;
  }
}

By following this pattern, you can ensure that your Next.js components are resilient to errors and provide a better user experience for your application.

---

Validate Next.js Configuration Usage

When implementing Next.js in your application, ensure that you are correctly using the framework’s documented configuration options and patterns. Configuration in Next.js is handled in specific ways, and improper usage can lead to runtime errors or unexpected behavior.

Verify the following:

1. Use Documented Configuration Options: Only use configuration options that are officially supported by Next.js. Refer to the Next.js documentation to identify the correct options for your use case, such as compiler.define, devServer, i18n, etc. Avoid using undocumented or non-existent options, as these may not be processed correctly.

2. Properly Format Configuration Values: Ensure that the data types of your configuration values match the expected types in the Next.js documentation. For example, boolean, number, and string values should be provided in the correct format, as shown in the example below:

```js filename=”next.config.js” module.exports = { compiler: { define: { BOOLEAN_VALUE: false, NUMBER_VALUE: 123, STRING_VALUE: “hello world” } } }

3. **Test Configurations in Development**: Always test your Next.js configurations in a development environment before deploying to production. This will help you catch any configuration errors or unexpected behavior early in the development process.

By following these guidelines, you can ensure that your Next.js implementation adheres to the framework's best practices and avoids common configuration-related issues.

---

## Defensive Handling of Nullable React Components

<!-- source: facebook/react | topic: React | language: TypeScript | updated:  -->

When working with React components that may return null or undefined values, implement defensive coding patterns to prevent runtime errors and improve code reliability.

- Consume iterables that may contain null values into an intermediate array before spreading them into React components:

```typescript
// Potentially problematic - may cause runtime errors if items contains null
const items = [0, 1, 2, null, 4, false, 6];
return <MyComponent items={items} />;

// Safer approach - create intermediate array and then spread
const items = [0, 1, 2, null, 4, false, 6];
const itemValues = items.filter(item => item !== null); 
return <MyComponent items={itemValues} />;

• When accessing properties of React component props or state, verify the prop/state exists first or use defensive access patterns like optional chaining and nullish coalescing:

// Risky - assumes arr1[0] exists and has a value property
const MyComponent = ({ arr1 }) => <div>{arr1[0].value}</div>;

// Safer with optional chaining and nullish coalescing
const MyComponent = ({ arr1 }) => <div>{arr1?.[0]?.value ?? 0}</div>;

Following these practices will improve the robustness of your React code and help static analysis tools correctly infer nullability.

---

Document code intent

Add clear comments that explain the intent and behavior of code that might not be immediately obvious to other developers. Meaningful comments should provide context about why the code exists and how it works, especially for:

1. Complex test cases: ```javascript await waitForAll([ ‘Suspend! [Hi]’, ‘Loading…’,

// pre-warming ‘Suspend! [Hi]’ ]);

2. Configuration options with special status:
```javascript
/**
 * 'recommended' is currently aliased to the legacy / rc recommended config to maintain backwards compatibility.
 * This is deprecated and in v6, it will switch to alias the flat recommended config.
 */
recommended: legacyRecommendedConfig,

Good comments focus on explaining the “why” behind code decisions rather than merely restating what the code does. They serve as documentation that remains valuable even as implementations change, helping future maintainers understand design intent and important constraints.

---

Dry configuration patterns

Apply DRY (Don’t Repeat Yourself) principles to all configuration files to improve maintainability. Extract shared configuration options into reusable constants, especially for values used across multiple environments or settings. This pattern reduces errors when configurations need updating and makes your codebase more maintainable.

For example, instead of duplicating the same rule definitions across different configuration variants:

// Instead of repeated configuration:
export const configs = {
  recommended: {
    rules: {
      'react-hooks/rules-of-hooks': 'error',
      'react-hooks/exhaustive-deps': 'warn',
    },
  },
  'flat/recommended': {
    rules: {
      'react-hooks/rules-of-hooks': 'error',
      'react-hooks/exhaustive-deps': 'warn',
    },
  }
};

// Extract common configuration to constants:
const sharedRules = {
  'react-hooks/rules-of-hooks': 'error',
  'react-hooks/exhaustive-deps': 'warn',
};

export const configs = {
  recommended: { rules: sharedRules },
  'flat/recommended': { rules: sharedRules }
};

This approach also makes it easier to see at a glance which configurations are shared vs. environment-specific, improving code readability and making configuration changes less error-prone.

---

Explicit CSP nonce management

When implementing Content Security Policy (CSP) protections, always explicitly pass nonce values to components rather than auto-applying them. This gives developers more control over security aspects and prevents potential security bypasses when integrating components from different sources.

Key implementation guidelines:

• Pass nonces explicitly to components that need them (like style and script elements)
• Be aware that different content types may require different nonce values (style-src and script-src directives)
• Ensure elements with different nonces aren’t inappropriately merged
• Handle nonces consistently across your application

Example in React:

// Correct: Explicitly passing nonce to style elements
<style
  href="foo"
  precedence="default"
  nonce={CSPnonce}>{`.foo { color: hotpink; }`}</style>

// When rendering on server, pass nonce to the renderer
renderToPipeableStream(
  <App />,
  { nonce: CSPnonce }
);

// For preinitialized styles, ensure nonces are added consistently
// to maintain security guarantees
const preinitOptions = {
  precedence: 'default',
  nonce: CSPnonce // Explicitly add nonce here too
};

Properly implemented CSP with nonces is one of the strongest defenses against cross-site scripting (XSS) attacks, but only if nonces are managed correctly and consistently throughout your application.

---

Multi-stack config settings

When creating configuration files for development environments that use multiple technology stacks, ensure settings are properly scoped to accommodate different file types and tools within the same project. This prevents validation errors and improves developer productivity.

For example, in a workspace with both Flow and TypeScript files, customize editor settings by file type:

{
  "settings": {
    // General settings
    "editor.formatOnSave": true,
    
    // Tool-specific paths
    "flow.pathToFlow": "${workspaceFolder}/node_modules/.bin/flow",
    
    // Search optimization
    "search.exclude": {
      "**/dist/**": true,
      "**/build/**": true,
      "**/out/**": true
    },
    
    // File-type specific settings
    "prettier.configPath": "",
    "prettier.ignorePath": ""
  }
}

These scoped configurations ensure that the proper validation rules and formatting settings are applied to different parts of the codebase, making it easier for developers to work with mixed technology projects.

---

Proper Scoping and Usage of React Variables

When implementing React components, it is important to ensure that variables are properly scoped and used throughout the component lifecycle. This reviewer provides guidance on best practices for managing variable declarations and usage in React code:

• Group related variable declarations together to improve code organization and readability.
• When using variables within React hooks like useEffect, explicitly list all dependencies to prevent subtle bugs related to variable capturing.
• For loop variables used in closures (e.g. event handlers), prefer block scoping to ensure the intent of the variable usage is clear.
• Ensure that the scope and purpose of variables used across different contexts (hooks, closures, JSX) is obvious to readers of the code.

Proper variable management is crucial for writing maintainable and bug-free React components. The provided code examples demonstrate correct usage patterns that align with these principles.

---

Proper Usage of React Hooks

When using the React library in TypeScript, ensure that you are correctly implementing the recommended React hooks based on the version of ESLint being used in your project.

For projects using ESLint 9.0.0 and above, use the recommended-latest configuration for the react-hooks plugin. This will enforce the latest best practices for React hook usage.

For projects using ESLint versions below 9.0.0, use the recommended-legacy configuration for the react-hooks plugin. This will ensure compatibility with older versions of React and ESLint.

Example of correct usage:

// For ESLint 9.0.0+
{
  "extends": [
    // ...
    "plugin:react-hooks/recommended-latest"
  ]
}

// For ESLint below 9.0.0 
{
  "extends": [
    // ...
    "plugin:react-hooks/recommended-legacy"
  ]
}

Avoid using deprecated configuration names like the plain recommended, even if they are still supported for backward compatibility. Always use the version-specific configurations to ensure your React code follows the latest best practices and remains compatible with the ESLint version in use.

---

Standardize URL handling

When working with URLs in networking code, always use the standard URL constructor to properly resolve relative URLs against a base URL instead of manual string concatenation or ad-hoc replacements. This ensures proper path resolution according to the URL specification and handles edge cases correctly.

For example, instead of:

// Problematic: Doesn't properly resolve relative paths
const sourceMap = await fetchFileWithCaching(sourceMapURL).catch(() => null);

// Or hacky string replacements
const normalizedURL = url.replace('/./', '/');

Use the URL constructor:

// Properly resolves relative URLs against the base URL
const sourceMap = await fetchFileWithCaching(
  new URL(sourceMapURL, sourceURL).toString()
).catch(() => null);

For complex URL normalization needs, consider extracting the logic to a dedicated function that can be maintained centrally and handle different URL formats, including those with custom protocols used by bundlers. This approach prevents networking errors caused by malformed URLs and improves code maintainability.

---

Write readable conditionals

Structure conditionals for maximum clarity and comprehension. Avoid unnecessary negation in boolean expressions, use else clauses appropriately, and organize compound conditions to reduce cognitive load.

For JSX conditionals, prefer positive conditions with natural reading order:

// Instead of:
<h1>{!show ? 'A' + counter : 'B' + counter}</h1>

// Prefer:
<h1>{show ? 'B' + counter : 'A' + counter}</h1>

For branching logic, use complete if/else structures rather than separate conditional blocks when checking for mutually exclusive conditions:

// Instead of:
if (enableUnifiedSyncLane && (renderLane & SyncUpdateLanes) !== NoLane) {
  lane = SyncHydrationLane;
}
if (!lane) {
  // ...more code
}

// Prefer:
if (enableUnifiedSyncLane && (renderLane & SyncUpdateLanes) !== NoLane) {
  lane = SyncHydrationLane;
} else {
  // ...more code
}

These practices make code easier to scan, understand, and maintain, while reducing the potential for logical errors.

---

Secure cookie configuration

Always set appropriate security flags on cookies, especially those used for authentication or session management. At minimum, include:

1. HttpOnly - Prevents JavaScript access to the cookie, protecting against XSS attacks
2. Secure - Ensures the cookie is only sent over HTTPS connections
3. SameSite - Use Lax for cookies needed after redirects (like OAuth flows), or Strict for maximum protection when redirects aren’t needed

Example of properly configured cookie in an OAuth flow:

// Attach the session cookie to the response header with security flags
let cookie = format!(
    "{COOKIE_NAME}={cookie}; SameSite=Lax; Path=/; HttpOnly; Secure"
);

These settings significantly reduce the risk of cookie theft, session hijacking, and cross-site request forgery attacks.

---

Secure Content-Type validation

When implementing Content-Type validation, ensure regular expressions start with ‘^’ or include ‘;?’ to properly detect the essence MIME type. Improper validation patterns may create vulnerabilities to CORS attacks.

For example, instead of using a pattern like:

const contentTypeRegex = /json/;

Use one of these more secure approaches:

const contentTypeRegex = /^application\/json/; // Anchoring with ^ ensures exact matches
// OR
const contentTypeRegex = /application\/json;?/; // Including ;? handles parameters properly

This ensures that malicious Content-Types like “faketype+json” cannot bypass your security validation mechanisms.

---

Decode before validation

Always decode URL paths before performing security validations to prevent bypass attacks using URL encoding. Security mechanisms that rely on string pattern matching (like includes(), startsWith(), or regular expressions) can be circumvented when attackers use URL-encoded characters.

For example, instead of:

function isSecurePath(url) {
  // VULNERABLE: Can be bypassed with encoding
  return !url.includes('/admin') && !url.includes('/internal');
}

Use decoded URLs for validation:

function isSecurePath(url) {
  // SECURE: Handles encoded paths
  const decodedUrl = decodeURIComponent(url);
  return !decodedUrl.includes('/admin') && !decodedUrl.includes('/internal');
}

This pattern prevents attacks where /%61dmin (encoded ‘a’) would bypass a check for ‘/admin’. Always normalize URL inputs before security-critical validations to maintain consistent security controls across your application.

---

Document security attributes

When handling security-related attributes (like nonces, integrity hashes, or CSP directives), always document the logic and prioritize explicitly passed values over automatically provided ones. This ensures that security intentions are clear and that developers can override default security configurations when necessary.

Example:

// Get default security attributes from context
let { nonce } = useContext(SecurityContext)

// If a nonce is explicitly passed to the component, favor that over the automatic handling
nonce = props.nonce || nonce

This pattern makes security behaviors predictable and allows for custom security requirements while maintaining a secure default implementation.

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