150 lines
2.8 KiB
Markdown
150 lines
2.8 KiB
Markdown
# PR-6.4 — GC Traversal for Closures (Model B)
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## Briefing
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Closures introduce heap-to-heap references through their captured environments.
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Under Model B, the closure object itself is passed at call time, but its environment remains stored in heap.
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GC must traverse:
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closure -> env -> inner HeapRefs
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---
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## Target
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Extend GC mark phase to handle `ObjectKind::Closure`:
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When marking a closure:
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* Iterate over env values.
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* If a value contains HeapRef → mark referenced object.
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No compaction. No relocation.
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---
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## Work Items
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1. Extend mark traversal switch.
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2. Ensure safe iteration over env payload.
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3. Add regression tests.
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---
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## Acceptance Checklist
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* [ ] Closure env scanned.
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* [ ] Nested closures retained.
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* [ ] No regression in existing GC tests.
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---
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## Tests
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1. Closure capturing another closure.
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2. Closure capturing heap object.
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3. Unreferenced closure collected.
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---
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## Junie Instructions
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You MAY:
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* Modify mark traversal.
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* Add tests.
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You MUST NOT:
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* Modify sweep policy.
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* Introduce compaction.
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If unsure whether Value variants can embed HeapRef, STOP and ask.
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---
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## Definition of Done
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GC correctly traverses closure environments under Model B semantics.
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---
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# PR-6.5 — Verifier Support for Closures (Model B)
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## Briefing
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The verifier must understand closure values and enforce safe invocation rules.
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Under Model B:
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* `CALL_CLOSURE` injects hidden `arg0`.
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* User-visible arg_count excludes hidden arg.
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* Captures are accessed via explicit instructions (future PR).
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## Target
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Extend verifier to:
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1. Introduce stack type: `ClosureValue`.
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2. Validate MAKE_CLOSURE effects.
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3. Validate CALL_CLOSURE semantics:
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* Ensure top of stack is ClosureValue.
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* Ensure sufficient args present.
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* Validate `arg_count` matches function signature expectations.
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* Account for hidden arg0 when checking callee arg arity.
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4. Validate ret_slots against function metadata.
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## Work Items
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1. Extend type lattice with ClosureValue.
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2. Define stack transitions for MAKE_CLOSURE.
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3. Define stack transitions for CALL_CLOSURE.
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4. Enforce strict failure on mismatch.
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---
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## Acceptance Checklist
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* [ ] ClosureValue type exists.
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* [ ] Invalid CALL_CLOSURE rejected.
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* [ ] Hidden arg0 accounted for.
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* [ ] ret_slots validated.
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* [ ] All verifier tests pass.
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---
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## Tests
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1. Valid closure call passes verification.
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2. CALL_CLOSURE with wrong arg_count fails.
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3. CALL_CLOSURE on non-closure fails verification.
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4. Nested closure calls verify correctly.
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---
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## Junie Instructions
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You MAY:
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* Extend verifier model.
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* Add tests.
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You MUST NOT:
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* Weaken verification rules.
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* Replace verifier checks with runtime-only traps.
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If function metadata (arg_slots/ret_slots) is insufficient, STOP and request clarification.
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---
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## Definition of Done
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Verifier fully supports closure creation and invocation under Model B semantics. |