Add garbage collection for WASM linear memory (#51)#202
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…#51) Implement a conservative mark-sweep GC entirely in WASM (no host-side logic). Programs that allocate heavily now survive beyond the initial 64 KiB page through automatic memory reclamation and memory.grow fallback. Key changes: - Object headers: 4-byte header (mark bit + payload size) prepended by $alloc - Shadow stack: explicit root tracking in linear memory (4096 bytes) - Mark worklist: iterative marking with conservative pointer scanning (4096 bytes) - $gc_collect: clear marks, mark from shadow stack roots, sweep to free list - $alloc: free-list first-fit before bump allocation, GC trigger on OOM - Function prologue/epilogue: save/restore $gc_sp, push pointer params/returns - Lifted closure functions: same GC instrumentation as regular functions - to_string/strip: allocate exact-size result buffers (no interior pointers) Co-Authored-By: Claude <noreply@anthropic.invalid>
Document GC architecture in vera/README.md: memory layout, allocator, collector phases, shadow stack, and zero-overhead guarantee. Update module line counts to reflect GC implementation growth. Co-Authored-By: Claude <noreply@anthropic.invalid>
Collapse C8 into a <details> block (matching C6/C6.5/C7 pattern), update roadmap table with version range v0.0.40-v0.0.65, mark C8.5 as "In progress" and make it the active "Working on" section. Co-Authored-By: Claude <noreply@anthropic.invalid>
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Summary
memory.growfallbackChanges
Core GC implementation:
vera/codegen/assembly.py— GC globals, rewritten$alloc(header + free-list + GC trigger),$gc_collect(clear/mark/sweep)vera/codegen/functions.py— GC prologue/epilogue in_compile_fn(save/restore$gc_sp, push pointer params/returns)vera/codegen/closures.py— Same prologue/epilogue for lifted closure functionsvera/wasm/helpers.py—gc_shadow_push()helper (7 WAT instructions)vera/wasm/data.py— Shadow stack push after constructor/array allocationsvera/wasm/closures.py— Shadow stack push after closure allocation +needs_allocflagvera/wasm/calls.py— Fixto_string/stripinterior pointers; shadow stack pushes in string operationsTests:
TestGarbageCollectionclass (WAT-level + behavioral)Example:
examples/gc_pressure.vera— builds and discards 100-element linked lists 30 timesDocumentation:
spec/12-runtime.mdTest plan
pytest tests/ -q)mypy vera/)python scripts/check_examples.py)python scripts/check_version_sync.py)python scripts/check_readme_examples.py)python scripts/check_skill_examples.py)vera run examples/gc_pressure.verareturns 151500Closes #51
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