Structure validation algorithms

When implementing or modifying parsing and validation algorithms, carefully consider both the correctness and user experience aspects:

1. Preserve structural ordering in data structures like ASTs when order impacts semantics. As noted in discussion #1, “In some cases, like in macro scoping, the order is actually important,” so field reordering can introduce subtle bugs that are difficult to track down.

2. Implement intelligent error recovery for mismatched delimiters by analyzing the context. For different mismatched delimiters scenarios, determine the most likely error:

// When suggesting missing delimiters, analyze the surrounding context
// BAD: Generic message for all cases
if 1 < 2 {
    let _a = vec!]; // Just showing "mismatched closing delimiter"
}

// GOOD: Context-aware message
if 1 < 2 {
    let _a = vec!]; // "mismatched closing delimiter, may be missing open `[`"
}

1. Avoid over-suggesting fixes when multiple interpretations are possible. As mentioned in discussion #8, for constructs like #![w,), the fix could be either [w,] or (w,) depending on context, so the diagnostic algorithm should avoid suggesting a specific solution when ambiguous.

2. Track related delimiter errors by collecting information about unmatched opening delimiters to provide more comprehensive diagnostics, as suggested in discussion #7.

These validation algorithms should prioritize correctness while providing meaningful guidance to developers when errors occur.