63 lines
2.4 KiB
Markdown
63 lines
2.4 KiB
Markdown
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# Phase 140: NormalizedExprLowererBox (pure expressions)
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Status: DONE ✅
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Scope: Normalized shadow の expression lowering を AST walker で一般化し、パターン爆発を避ける（pure のみ）。
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Related:
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- `docs/development/current/main/design/normalized-expr-lowering.md`
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- `docs/development/current/main/30-Backlog.md`
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- `docs/development/current/main/phases/phase-139/README.md`
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- `src/mir/control_tree/normalized_shadow/common/expr_lowerer_box.rs`
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- `src/mir/control_tree/normalized_shadow/common/return_value_lowerer_box.rs`
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---
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## Goal
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- `NormalizedExprLowererBox` を導入し、pure expression を JoinIR（Normalized dialect）へ lowering できるようにする。
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- return lowering は `ReturnValueLowererBox` → `ExprLowererBox` 委譲へ寄せ、return の形追加を “総当たり” にしない。
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## Scope (Phase 140 P0)
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### ✅ In scope: pure expression
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- `Variable`
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- `Literal`（Integer/Bool から開始）
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- `UnaryOp`（not, -）
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- `BinaryOp`（+ - * /）
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- `Compare`（==, <, <=, >, >=）
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### ❌ Out of scope
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- Call/MethodCall（Phase 141+）
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- Short-circuit（&&/||）の制御フローを伴う lowering
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- 例外/throw/try/catch
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- NormalizationPlan の粒度変更（suffix→statement などの再設計は Phase 141+ の検討に回す）
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## Contract
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`NormalizedExprLowererBox::lower_expr(...) -> Result<Option<ValueId>, String>`
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- `Ok(Some(vid))`: lowering 成功
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- `Ok(None)`: out-of-scope（既存経路へフォールバック、既定挙動不変）
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- `Err(_)`: 内部不整合のみ（strict では fail-fast）
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## Implementation Notes
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- 既存の `ReturnValueLowererBox` は “return 構文” の薄い箱に縮退し、expr lowering の実体は `ExprLowererBox` に置く。
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- 型は過剰に推論しない。Const/Compare/BinOp の最小ヒントのみ（必要なら段階投入）。
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## Tests
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- Unit tests:
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- `cargo test -p nyash-rust --lib mir::control_tree::normalized_shadow::common`
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- Smokes (regressions):
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- Phase 139（VM/LLVM EXE）
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- Phase 136/137/138（return 系）
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- Phase 97（フォールバック）
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## Implementation (DONE)
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- Added pure expression SSOT: `src/mir/control_tree/normalized_shadow/common/expr_lowerer_box.rs`
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- `ReturnValueLowererBox` shrunk to return-syntax only and delegates to `NormalizedExprLowererBox`
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- Explicitly keeps out-of-scope = `Ok(None)` (fallback) and avoids fail-fast expansion
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