hakorune/docs/development/current/main/phase73-completion-summary.md

Phase 73: Completion Summary

Date: 2025-12-13 Status: ✅ Complete (Design Phase) Scope: JoinIR ScopeManager → BindingId-Based Design

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Deliverables

1. Design Document (SSOT)

File: docs/development/current/main/phase73-scope-manager-design.md

Contents:

• ✅ Current state analysis (MIR + JoinIR scope systems)
• ✅ Problem identification (name-based vs BindingId mismatch)
• ✅ Proposed architecture (Option A: Parallel BindingId Layer)
• ✅ Integration with MIR Builder (binding_map additions)
• ✅ Migration path (Phases 74-77 roadmap)
• ✅ Example scenarios (shadowing, promoted variables)

Key Insights:

• MIR builder uses BindingId for lexical scope tracking (Phase 68-69)
• JoinIR lowering uses name-based lookup (fragile for shadowing)
• Naming convention hacks (is_digit_pos, is_ch_match) can be replaced with BindingId maps
• Gradual migration strategy minimizes risk

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2. Proof-of-Concept Implementation

File: src/mir/join_ir/lowering/scope_manager_bindingid_poc/mod.rs

Status: ✅ All tests passing (6/6) Feature Gate: #[cfg(feature = "normalized_dev")] (dev-only)

Implemented Structures:

• BindingId type wrapper
• ConditionEnvV2 (parallel name + BindingId lookup)
• CarrierInfoV2 (BindingId-based promotion tracking)
• ScopeManagerV2 trait + Pattern2ScopeManagerV2 implementation

Test Coverage:

test mir::join_ir::lowering::scope_manager_bindingid_poc::tests::test_condition_env_v2_basic ... ok
test mir::join_ir::lowering::scope_manager_bindingid_poc::tests::test_shadowing_simulation ... ok
test mir::join_ir::lowering::scope_manager_bindingid_poc::tests::test_promoted_binding_resolution ... ok
test mir::join_ir::lowering::scope_manager_bindingid_poc::tests::test_scope_manager_v2_binding_lookup ... ok
test mir::join_ir::lowering::scope_manager_bindingid_poc::tests::test_scope_manager_v2_promoted_lookup ... ok
test mir::join_ir::lowering::scope_manager_bindingid_poc::tests::test_unified_lookup_fallback ... ok

Key Validations:

• ✅ Parallel lookup (BindingId + name fallback) works
• ✅ Shadowing simulation (multiple bindings for same name)
• ✅ Promoted variable resolution (BindingId → BindingId mapping)
• ✅ Unified lookup with graceful fallback

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Design Highlights

Problem Statement

Before (Current):

// JoinIR lowering (name-based)
env.get("digit_pos") → searches for "is_digit_pos" via naming convention
                    → fragile, breaks if naming convention changes

After (Phase 76+):

// JoinIR lowering (BindingId-based)
env.get_by_binding(BindingId(5)) → resolves promoted_bindings[BindingId(5)] = BindingId(10)
                                 → type-safe, no string matching

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Proposed Architecture (Option A)

Gradual Migration Strategy:

1. Phase 74: Add BindingId infrastructure (binding_map, binding_to_join)
2. Phase 75: Migrate Pattern 1 (simple, no carriers)
3. Phase 76: Migrate Pattern 2 (carrier promotion)
4. Phase 77: Migrate Pattern 3-4, remove legacy code

Backward Compatibility:

• New fields added alongside existing name-based maps
• Legacy code continues to work during transition
• Fallback mechanism ensures no breakage

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Integration Points

MirBuilder Changes (Phase 74)

pub struct MirBuilder {
    pub variable_map: HashMap<String, ValueId>,  // Existing (SSA conversion)
    pub binding_map: HashMap<String, BindingId>, // NEW (lexical scope)
    next_binding_id: u32,                        // NEW (allocator)
}

ConditionEnv Changes (Phase 74)

pub struct ConditionEnv {
    name_to_join: BTreeMap<String, ValueId>,      // Legacy (keep)
    binding_to_join: BTreeMap<BindingId, ValueId>, // NEW (Phase 74+)
    name_to_binding: BTreeMap<String, BindingId>,  // NEW (shadowing)
}

CarrierInfo Changes (Phase 76)

pub struct CarrierInfo {
    promoted_loopbodylocals: Vec<String>,           // Legacy (Phase 224)
    promoted_bindings: BTreeMap<BindingId, BindingId>, // NEW (Phase 76+)
}

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No Production Code Changes

Confirmation:

• ✅ No changes to src/mir/builder.rs
• ✅ No changes to src/mir/join_ir/lowering/*.rs (except mod.rs for PoC)
• ✅ PoC is feature-gated (normalized_dev only)
• ✅ All existing tests still pass

Modified Files:

1. docs/development/current/main/phase73-scope-manager-design.md (new)
2. docs/development/current/main/phase73-completion-summary.md (new)
3. src/mir/join_ir/lowering/scope_manager_bindingid_poc/mod.rs (new, dev-only)
4. src/mir/join_ir/lowering/mod.rs (1 line added for PoC module)

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Migration Roadmap

Phase 74: Infrastructure (Estimated 2-3 hours)

Goal: Add BindingId tracking without breaking existing code

Tasks:

• Add binding_map to MirBuilder
• Add binding_to_join to ConditionEnv
• Update declare_local_in_current_scope to return BindingId
• Add BindingId allocator tests

Acceptance: All existing tests pass, BindingId populated

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Phase 75: Pattern 1 Pilot (Estimated 1-2 hours)

Goal: Prove BindingId integration with simplest pattern

Tasks:

• Update CarrierInfo::from_variable_map to accept binding_map
• Migrate Pattern 1 lowering to use BindingId
• Add E2E test with BindingId

Acceptance: Pattern 1 uses BindingId, legacy fallback works

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Phase 76: Pattern 2 Carrier Promotion (Estimated 2-3 hours)

Goal: Eliminate naming convention hacks

Tasks:

• Add promoted_bindings: BTreeMap<BindingId, BindingId> to CarrierInfo
• Update resolve_promoted_join_id to use BindingId
• Migrate Pattern 2 lowering

Acceptance: DigitPos pattern works without string matching

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Phase 77: Pattern 3-4 + Cleanup (Estimated 2-3 hours)

Goal: Complete migration, remove legacy code

Tasks:

• Migrate Pattern 3 (multi-carrier)
• Migrate Pattern 4 (generic case A)
• Remove name_to_join, promoted_loopbodylocals (legacy fields)

Acceptance: All patterns BindingId-only, full test suite passes

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Open Questions (for Future Phases)

Q1: BindingId Scope (Per-Function vs Global)

Current Assumption: Per-function (like ValueId)

Reasoning:

• Each function has independent binding scope
• No cross-function binding references
• Simpler allocation (no global state)

Alternative: Global BindingId pool (for Phase 63 ownership analysis integration)

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Q2: Captured Variable Handling

Proposed: Add binding_id to CapturedVar

pub struct CapturedVar {
    name: String,
    host_id: ValueId,
    host_binding: BindingId,  // Phase 73+ (NEW)
    is_immutable: bool,
}

Impact: Requires updating function_scope_capture module

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Q3: Performance Impact

Concern: Dual maps (binding_to_join + name_to_join) double memory

Mitigation:

• Phase 74-76: Both maps active (transition period)
• Phase 77: Remove name_to_join after migration
• BTreeMap overhead minimal (<10 variables per loop typically)

Measurement: Profile after Phase 74 implementation

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Success Criteria (Phase 73)

Design Document ✅

• Current state analysis (MIR + JoinIR)
• Proposed architecture (Option A)
• Integration points (MirBuilder changes)
• Migration path (Phases 74-77)
• Example scenarios

Proof-of-Concept ✅

• BindingId type + structures
• Parallel lookup (BindingId + name)
• Shadowing simulation test
• Promoted variable resolution test
• All tests passing (6/6)

No Production Impact ✅

• Feature-gated (normalized_dev)
• No production code changes
• Existing tests unaffected

Documentation ✅

• SSOT design document
• Completion summary (this document)
• PoC code comments

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References

Related Phases

• Phase 68-69: MIR lexical scope + shadowing (existing)
• Phase 63: Ownership analysis (dev-only, uses BindingId)
• Phase 231: ScopeManager trait (current implementation)
• Phase 224: Promoted LoopBodyLocal (naming convention hacks)

Key Files

• docs/development/current/main/phase73-scope-manager-design.md (SSOT)
• src/mir/join_ir/lowering/scope_manager_bindingid_poc/mod.rs (PoC)
• src/mir/builder/vars/lexical_scope.rs (MIR lexical scope)
• src/mir/join_ir/lowering/scope_manager.rs (current ScopeManager)
• src/mir/join_ir/lowering/carrier_info.rs (current CarrierInfo)

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Estimated Total Effort (Phases 74-77)

Phase	Task	Hours
74	Infrastructure	2-3
75	Pattern 1 Pilot	1-2
76	Pattern 2 Promotion	2-3
77	Pattern 3-4 + Cleanup	2-3
Total	Full Migration	8-12

Risk Level: Low (gradual migration, backward compatible)

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Next Steps

1. User Review: Confirm design makes sense
2. Phase 74 Start: Implement BindingId infrastructure
3. Iterative Migration: Phases 75-77 (one pattern at a time)

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Conclusion

Phase 73 Success: ✅ Design + PoC Complete

Key Achievements:

• Comprehensive design document (SSOT for BindingId migration)
• Working proof-of-concept (6 tests passing)
• Clear migration path (Phases 74-77 roadmap)
• No production code impact (feature-gated)

Ready for Phase 74: Infrastructure implementation can begin immediately.