34 lines
1.7 KiB
Markdown
34 lines
1.7 KiB
Markdown
Title: MIR Builder — Declaration Indexing (Two‑Phase) Design Note
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Summary
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- Purpose: eliminate order‑sensitivity for forward references during AST→MIR lowering without changing language semantics.
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- Approach: run a lightweight “Phase A: declaration indexing” over the AST to collect symbols, then perform normal lowering as “Phase B”.
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Scope
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- Internal compiler detail (builder). No changes to syntax/semantics/flags.
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- Applies to: user‑defined boxes (instance types) and static methods lookup for bare calls.
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Why
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- Previous behavior processed AST in appearance order. Forward references (e.g., new JsonParser() before its box declaration) required ad‑hoc preindex_* helpers.
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- Centralizing indexing avoids proliferation (preindex_user_boxes, preindex_static_methods, …) and keeps lowering simple.
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Design
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- Phase A (index_declarations):
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- user_defined_boxes: collect non‑static Box names to decide constructor behavior (skip birth() for user types).
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- static_method_index: map method name → [(BoxName, arity)] to resolve bare calls in using‑merged sources.
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- Phase B (lowering): unchanged logic uses the above indices.
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Invariants
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- No behavior change. Only ordering robustness improves.
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- Indexing walks AST once (O(N)). Data kept in MirBuilder fields already present.
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Implementation Notes
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- Function: MirBuilder::index_declarations(&ASTNode)
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- Called once at lower_root() entry. Existing ad‑hoc preindex_* replaced by this single pass.
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- Keep deltas small and localized to builder lifecycle.
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Testing
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- Existing smokes cover forward references (using/JSON). No new flags required.
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- Acceptance: no stray unresolved calls due to order, no change in MIR output types for the same sources.
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