72 lines
2.1 KiB
Markdown
72 lines
2.1 KiB
Markdown
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# Phase 178: LoopUpdateAnalyzer String Detection
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## Summary
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Phase 178 extends `LoopUpdateAnalyzer` to detect string/complex carrier updates,
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enabling Fail-Fast behavior for unsupported patterns.
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## Changes
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### 1. UpdateRhs Enum Extension (`loop_update_analyzer.rs`)
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Added two new variants:
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- `StringLiteral(String)` - for `result = result + "x"` patterns
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- `Other` - for method calls and complex expressions
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### 2. analyze_rhs Extension
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Extended to detect:
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- String literals: `ASTNode::Literal { value: LiteralValue::String(_) }`
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- Method calls: `ASTNode::MethodCall { .. }`
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- Other complex expressions: `ASTNode::Call`, `ASTNode::BinaryOp`, etc.
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### 3. Pattern 2/4 can_lower Updates
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Both `pattern2_with_break.rs` and `pattern4_with_continue.rs` now check for
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string/complex updates in `can_lower()` and return `false` if detected.
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This triggers a clear error message instead of silent incorrect behavior.
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### 4. Legacy Fallback Comment Fixes
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Updated misleading comments about "legacy fallback" - LoopBuilder was removed
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in Phase 187-2 and all loops must use JoinIR.
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## Behavior
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When a loop contains string concatenation like:
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```nyash
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loop(i < limit) {
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result = result + "x" // String update
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i = i + 1
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}
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```
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Phase 178 now produces a clear error:
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```
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[pattern2/can_lower] Phase 178: String/complex update detected, rejecting Pattern 2 (unsupported)
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[ERROR] MIR compilation error: [joinir/freeze] Loop lowering failed:
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JoinIR does not support this pattern, and LoopBuilder has been removed.
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```
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## Test Results
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- P1 (simple while): OK
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- P2 (break + int carriers): OK
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- P4 (continue + multi-carrier): OK
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- String loops: Fail-Fast with clear error
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## Known Issues
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- **79 global test failures**: Pre-existing issue, NOT caused by Phase 178
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- Confirmed by `git stash` test - failures exist in HEAD~1
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- Tracked separately from Phase 178
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## Future Work
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To support string loops, either:
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1. Add JoinIR instructions for string concatenation (Option A)
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2. Process loop body statements in MIR alongside JoinIR control flow (Option B)
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Phase 178 provides the detection foundation for future string support.
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