[Medium] Stringly-typed context selector is brittle

[coderabbitai]

Description

PatternContext::new branches on string literals ("match pattern", "for-loop pattern"), making the context selector brittle and prone to errors.

Details

Location:

• src/parser/expression/pattern_collection.rs:51

Current implementation:
PatternContext::new uses string literal matching to determine context type:

• "match pattern"
• "for-loop pattern"

Problems:

• String literals are error-prone (typos, case sensitivity)
• No compile-time exhaustiveness checking
• Unreachable string branches can slip through
• Difficult to refactor or extend with new context types

Impact

• Type safety: No compiler guarantees for valid context types
• Maintainability: Adding new contexts requires string coordination across call sites
• Reliability: Typos in string literals lead to runtime failures
• Refactoring: IDE refactoring tools cannot help with string-based dispatch

Actionable Fix

Replace the string-based context selector with an enum:

1. Introduce PatternContextKind enum with variants:
   • MatchPattern
   • ForLoopPattern
2. Replace PatternContext::new string parameter with PatternContextKind
3. Use match over enum variants instead of string comparisons
4. Remove unreachable string branch

Benefits:

• Compile-time exhaustiveness checking
• Type-safe context selection
• Better IDE support and refactoring
• Self-documenting code

Priority

Medium – Type safety and maintainability issue, but not blocking current functionality.

References

• PR: Add ADR: parser crate split for multi-consumer use #212
• Requested by @leynos

Requested by

@leynos

[traycerai]

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