hakorune/docs/development/current/main/PHASE_75_SUMMARY.md

Phase 75: BindingId Pilot Integration - Completion Summary

Status: ✅ COMPLETE Date: 2025-12-13 Feature: normalized_dev (dev-only) Impact: Zero production impact

Executive Summary

Phase 75 successfully implemented a pilot integration of BindingId-based variable lookup in ConditionEnv, demonstrating the "BindingId priority → name fallback" strategy with zero production impact. This completes the second step of the Phase 73-77 migration roadmap.

Objectives Met

✅ Primary Goal: Implement BindingId-based lookup in 1 isolation point (ConditionEnv) ✅ Secondary Goal: Demonstrate 3-tier fallback (BindingId → name → None) ✅ Safety Goal: Maintain zero production impact (feature-gated) ✅ Quality Goal: Comprehensive test coverage (3 new unit tests)

Implementation Details

Files Modified (3 files, +170 lines net)

1. src/mir/join_ir/lowering/scope_manager.rs (+50 lines)

   • Added lookup_with_binding() trait method with default implementation
   • Feature-gated BindingId import

2. src/mir/join_ir/lowering/condition_env.rs (+120 lines)

   • Added binding_id_map: BTreeMap<BindingId, ValueId> field (feature-gated)
   • Implemented resolve_var_with_binding() method
   • Added 3 unit tests (priority/fallback/legacy)
   • Dev logging support (NYASH_JOINIR_DEBUG=1)

3. docs/development/current/main/phase75-bindingid-pilot.md (new file, ~200 lines)

   • Complete design documentation
   • API reference
   • Test strategy
   • Next steps (Phase 76)

Key Design Decisions

1. Pilot Integration Point: ConditionEnv

Rationale:

• Isolated Component: Clear responsibility (condition variable resolution)
• Well-Tested: Existing test coverage from Phase 171-fix
• Simple API: Single lookup method to extend
• Representative: Typical use case for ScopeManager trait

2. 3-Tier Fallback Strategy

pub fn resolve_var_with_binding(
    &self,
    binding_id: Option<BindingId>,
    name: &str,
) -> Option<ValueId> {
    if let Some(bid) = binding_id {
        // Tier 1: BindingId priority lookup
        if let Some(&value_id) = self.binding_id_map.get(&bid) {
            return Some(value_id);  // [binding_pilot/hit]
        } else {
            // Tier 2: BindingId miss → name fallback
            return self.get(name);  // [binding_pilot/fallback]
        }
    } else {
        // Tier 3: Legacy (no BindingId)
        return self.get(name);      // [binding_pilot/legacy]
    }
}

Benefits:

• Incremental Migration: Legacy code continues to work (Tier 3)
• Graceful Degradation: BindingId miss doesn't break (Tier 2)
• Future-Ready: BindingId hit path ready for Phase 76+ (Tier 1)

3. ScopeManager Trait Extension

#[cfg(feature = "normalized_dev")]
fn lookup_with_binding(
    &self,
    binding_id: Option<BindingId>,
    name: &str
) -> Option<ValueId> {
    // Default: BindingId not supported, fall back to name
    let _ = binding_id;
    self.lookup(name)
}

Benefits:

• Zero Impact: Default implementation → existing implementors unaffected
• Opt-In: Pattern2ScopeManager can override when ready (Phase 76+)
• Type Safety: Trait contract ensures consistent API

Test Results

Unit Tests (3 new tests, all PASS)

✅ test_condition_env_binding_id_priority  - BindingId hit path
✅ test_condition_env_binding_id_fallback  - BindingId miss → name fallback
✅ test_condition_env_binding_id_none      - Legacy (no BindingId)

Regression Tests

✅ cargo test --release --lib
   958/958 PASS (0 failures, 56 ignored)

✅ cargo test --release --lib --features normalized_dev condition_env
   15/15 PASS (including 3 new tests)

Build Verification

✅ cargo build --release --lib
   Finished in 48.75s (0 errors, 0 warnings)

Observability

Dev Logging (NYASH_JOINIR_DEBUG=1)

When BindingId lookup is used (future Phase 76+ integration):

# BindingId hit
[binding_pilot/hit] BindingId(5) -> ValueId(100) for 'x'

# BindingId miss → fallback
[binding_pilot/fallback] BindingId(99) miss, name 'x' -> Some(ValueId(100))

# Legacy path
[binding_pilot/legacy] No BindingId, name 'x' -> Some(ValueId(100))

Safety Guarantees

Production Impact: ZERO

1. Feature Gate: All BindingId code is #[cfg(feature = "normalized_dev")]
2. Default Behavior: ScopeManager trait default impl uses name lookup only
3. Additive Only: Existing APIs (lookup(), get()) completely unchanged
4. No Callers Yet: resolve_var_with_binding() only called from tests (Phase 76+ will add production callers)

Type Safety

• BindingId: Opaque newtype (u32) with overflow checks
• Option: Explicit handling of "no BindingId" case
• BTreeMap: Deterministic iteration (Phase 222.5-D consistency)

Next Steps: Phase 76

Phase 76: Promoted Bindings Migration

Objective: Remove digit_pos → is_digit_pos naming hack, use promoted_bindings map

Prerequisites (DONE):

• ✅ BindingId infrastructure (Phase 74)
• ✅ ConditionEnv pilot integration (Phase 75)

Phase 76 Tasks:

1. Add promoted_bindings: BTreeMap<BindingId, BindingId> to CarrierInfo
2. Extend resolve_var_with_binding() to check promoted_bindings first
3. Populate promoted_bindings in Pattern2 lowering
4. Remove naming convention hack from CarrierInfo::resolve_promoted_join_id()

Estimated Effort: 2-3 hours

Benefits:

• Structural: Promoted variables tracked by BindingId, not naming convention
• Type-Safe: Promoted mapping explicit in CarrierInfo
• Testable: Promoted bindings can be verified independently

Lessons Learned

What Worked Well

1. Incremental Approach: Pilot integration in 1 component validated design without risk
2. 3-Tier Fallback: Clear strategy for gradual migration (BindingId → name → None)
3. Feature Gate: normalized_dev kept production code pristine
4. Test-First: 3 unit tests ensured correct behavior before lowering integration

Design Validation

✅ BindingId Infrastructure (Phase 74) is solid:

• binding_map correctly populated
• allocate_binding_id() works as expected
• Shadowing test evidence gives confidence

✅ Fallback Strategy is sound:

• BindingId miss doesn't break (graceful degradation)
• Legacy path (None) preserves existing behavior
• Logging helps diagnose which path was taken

✅ ScopeManager Extension is flexible:

• Default impl keeps existing implementors working
• Opt-in override allows gradual adoption
• Trait contract ensures API consistency

References

• Phase 73: phase73-scope-manager-design.md - Design + PoC
• Phase 74: CURRENT_TASK.md - Infrastructure
• Phase 75: phase75-bindingid-pilot.md - This implementation
• Migration Roadmap: Phase 76-77 (next 4-6 hours)

Metrics

Metric	Value
Files Modified	3
Lines Added	+170
New Tests	3
Test Pass Rate	100% (961/961)
Production Impact	0 (feature-gated)
Implementation Time	~1.5 hours
Documentation	Complete

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Phase 75 Complete: BindingId pilot integration successfully demonstrated in ConditionEnv with 3-tier fallback, zero production impact, and comprehensive test coverage. Ready for Phase 76 (promoted_bindings migration).