# Phase 185 Completion Report: Body-local Pattern2 Integration (Partial)

**Date**: 2025-12-09
**Status**: ⚠️ **Partially Complete** - Infrastructure integrated, init lowering blocked
**Duration**: ~2 hours

---

## Executive Summary

Phase 185 successfully integrated Phase 184's body-local infrastructure into Pattern2's API and code structure, but discovered that **body-local initialization lowering** was never implemented in Phase 184. The integration skeleton is complete and builds successfully, but tests fail due to undefined ValueIds from uninitialized body-local variables.

**Key outcome**: Identified Phase 186 scope (body-local init lowering) as prerequisite for functional body-local variable support.

---

## Completed Work

### ✅ Task 185-1: Design Document

**File**: `docs/development/current/main/phase185-body-local-integration.md`

- Comprehensive architecture design
- Integration approach documented
- Test strategy defined
- Scope and constraints clarified

### ✅ Task 185-2: Pattern2 Integration Skeleton

**Modified files**:
1. `src/mir/builder/control_flow/joinir/patterns/pattern2_with_break.rs`:
   - Added `collect_body_local_variables()` helper function
   - Created LoopBodyLocalEnv from collected locals
   - Pass body_local_env to lower_loop_with_break_minimal

2. `src/mir/join_ir/lowering/loop_with_break_minimal.rs`:
   - Added `body_local_env: Option<&LoopBodyLocalEnv>` parameter
   - Added imports for LoopBodyLocalEnv, UpdateEnv, emit_carrier_update_with_env
   - Modified carrier update emission to use UpdateEnv when body_local_env present
   - Backward compatibility: existing callers pass None

**Build status**: ✅ `cargo build --release` SUCCESS (0 errors)

**Code quality**:
- Clean separation of concerns
- Backward compatible API
- Box-first design principles followed

### ✅ Task 185-3: Pattern4 Deferred

**Decision**: Pattern4 uses different architecture (inline lowering, no emit_carrier_update).

**Rationale**:
- Pattern4 has custom inline update logic
- Variable resolution is hardcoded
- "Minimal" scope constraint
- Would require significant refactoring

**Documentation**: Clearly marked as future work in design doc.

### ✅ Task 185-4: Test Created, Blocker Identified

**Test file**: `apps/tests/phase185_p2_body_local_int_min.hako`

**Test content**: JsonParser-style loop with body-local integer calculation (`local digit_pos = pos - start`).

**Test result**: ❌ BLOCKED

**Error**:
```
[ERROR] use of undefined value ValueId(11)
```

**Root cause identified**: Body-local variables are **collected but not initialized**.

**What works**:
- ✅ Variable name collection: `[pattern2/body-local] Collected local 'digit_pos' → ValueId(2)`
- ✅ LoopBodyLocalEnv creation: `Phase 185-2: Collected 1 body-local variables`
- ✅ Pattern2 routing: Correctly detected and lowered to JoinIR

**What doesn't work**:
- ❌ Init expression lowering: `local digit_pos = pos - start` never lowered to JoinIR
- ❌ ValueId definition: ValueId(11) allocated but never assigned a value
- ❌ Runtime execution: VM error on use of undefined value

### ✅ Task 185-5: Documentation Updated

**Updated files**:
1. `phase185-body-local-integration.md`: Status section with detailed analysis
2. `phase185-completion-report.md`: This file
3. `CURRENT_TASK.md`: (will be updated after this report)

**Documentation quality**:
- Root cause clearly explained
- Phase 186 scope defined
- Alternative approaches provided
- Lessons learned documented

---

## Technical Analysis

### What Was Assumed (Incorrectly)

**Phase 184 was assumed to include**:
- ✅ LoopBodyLocalEnv (storage) - **Actually implemented**
- ✅ UpdateEnv (resolution) - **Actually implemented**
- ✅ emit_carrier_update_with_env() - **Actually implemented**
- ❌ Body-local init lowering - **NOT implemented**

### What Phase 184 Actually Delivered

**Infrastructure only**:
- Data structures (LoopBodyLocalEnv, UpdateEnv)
- API extensions (emit_carrier_update_with_env)
- Variable resolution priority logic
- Unit tests for storage and resolution

**Missing piece**:
- AST expression → JoinIR instruction lowering for body-local init
- Integration of init instructions into loop body
- Full E2E test (would have caught this)

### What Phase 185 Accomplished

**API integration**:
- Pattern2 now accepts body_local_env parameter
- lower_loop_with_break_minimal ready to use UpdateEnv
- Backward compatibility maintained

**Discovered gap**:
- Identified init lowering as blocking issue
- Defined Phase 186 scope clearly
- Provided implementation roadmap

---

## Phase 186 Requirements

### Goal

Implement body-local variable initialization lowering to make Phase 185 integration functional.

### Scope

1. **Expression lowering** (`local digit_pos = pos - start`):
   - Lower AST BinOp nodes to JoinIR BinOp instructions
   - Lower AST Variable nodes to ValueId lookups in ConditionEnv
   - Handle nested expressions recursively

2. **Init instruction insertion**:
   - Emit init instructions at start of loop_step function
   - Before break condition, after parameter allocation
   - Update LoopBodyLocalEnv with resulting ValueIds

3. **Helper refactoring**:
   - Replace `collect_body_local_variables()` with `collect_and_lower_body_locals()`
   - Add `lower_expr_to_joinir()` helper function
   - Pass instruction vector to enable emission

### Estimate

**Full implementation**: 6-7 hours
- Expression lowerer: 2-3 hours
- Integration: 2 hours
- Testing: 2 hours

**Simplified (variables only)**: 2-3 hours
- Only support `local temp = var` (no binops)
- Defer complex expressions to Phase 187

---

## Files Modified

### Source Code (3 files)

1. `src/mir/builder/control_flow/joinir/patterns/pattern2_with_break.rs`
   - Lines added: ~35 (helper function + integration)
   - Changes: collect_body_local_variables(), LoopBodyLocalEnv creation, lower call update

2. `src/mir/join_ir/lowering/loop_with_break_minimal.rs`
   - Lines added: ~20 (imports + parameter + conditional emission)
   - Changes: body_local_env parameter, UpdateEnv usage, emit_carrier_update_with_env call

### Documentation (3 files)

3. `docs/development/current/main/phase185-body-local-integration.md`
   - Lines: ~680 (comprehensive design + status update)

4. `docs/development/current/main/phase185-completion-report.md`
   - Lines: ~350 (this file)

### Tests (1 file, non-functional)

5. `apps/tests/phase185_p2_body_local_int_min.hako`
   - Lines: ~25 (test blocked by init lowering)

---

## Build & Test Results

### Build Status

```bash
$ cargo build --release
Compiling nyash-rust v0.1.0
Finished `release` profile [optimized] target(s) in 1m 07s
```

✅ **SUCCESS** - No compilation errors, no warnings in modified files

### Test Execution

```bash
$ NYASH_JOINIR_CORE=1 ./target/release/hakorune apps/tests/phase185_p2_body_local_int_min.hako
[pattern2/body-local] Collected local 'digit_pos' → ValueId(2)
[pattern2/body-local] Phase 185-2: Collected 1 body-local variables
[pattern2/before_lowerer] About to call lower_loop_with_break_minimal with carrier_info.loop_var_name='pos'
[ERROR] use of undefined value ValueId(11)
```

❌ **BLOCKED** - Runtime error due to uninitialized body-local variable

---

## Validation Checklist

- [x] Design document created
- [x] Pattern2 integration skeleton implemented
- [x] Build succeeds with no errors
- [x] Backward compatibility maintained (existing tests pass)
- [x] Pattern4 scope decision documented
- [x] Test file created
- [ ] Test execution successful ❌ (blocked by init lowering)
- [ ] Representative test outputs correct value ❌ (blocked)
- [x] Documentation updated with status and next steps
- [x] Root cause analysis completed
- [x] Phase 186 requirements defined

**7/10 completed** (3 blocked by missing init lowering)

---

## Lessons Learned

### 1. Infrastructure ≠ Implementation

**Issue**: Phase 184 delivered "infrastructure" but left core functionality (init lowering) unimplemented.

**Impact**: Phase 185 integration appeared complete (builds successfully) but fails at runtime.

**Lesson**: "Infrastructure" phases must include E2E test to validate full functionality, not just API structure.

### 2. Test Early, Test Often

**Issue**: Phase 184 had unit tests but no E2E test showing body-local variables actually working.

**Impact**: Missing init lowering wasn't discovered until Phase 185 integration testing.

**Lesson**: Even "infrastructure-only" phases need at least one E2E test demonstrating the feature works end-to-end.

### 3. Scope Boundaries Must Be Clear

**Issue**: Phase 184/185 scope boundary was unclear - where does "infrastructure" end and "implementation" begin?

**Impact**: Phase 185 assumed init lowering was done, wasted time on integration before discovering blocker.

**Lesson**: Explicitly document what IS and IS NOT in scope for each phase. Use "In Scope" / "Out of Scope" sections.

### 4. Pattern4 Architecture Differences

**Issue**: Pattern4 uses inline lowering (no emit_carrier_update), different from Pattern2.

**Decision**: Deferred Pattern4 integration to avoid scope creep.

**Lesson**: "Minimal" integration for Phase 185 was correct - Pattern4 needs its own refactoring phase.

---

## Next Steps

### Immediate (Phase 186)

1. **Implement body-local init lowering**:
   - Add `lower_expr_to_joinir()` helper
   - Refactor `collect_body_local_variables()` to `collect_and_lower_body_locals()`
   - Emit init instructions in loop_step function

2. **Test Phase 185 integration**:
   - Run phase185_p2_body_local_int_min.hako
   - Verify output: `123`
   - Confirm no [joinir/freeze] or SSA-undef errors

3. **Document Phase 186 completion**:
   - Update CURRENT_TASK.md
   - Mark Phase 185 as fully complete
   - Provide Phase 187 preview

### Future (Phase 187+)

1. **Phase 187**: String UpdateKind support (careful, gradual)
2. **Phase 188**: Pattern4 body-local integration (refactor inline lowering)
3. **Phase 189**: JsonParser full loop coverage (_parse_number, _atoi, etc.)

---

## Conclusion

Phase 185 successfully prepared the API and code structure for body-local variable support in Pattern2, but revealed that the core initialization lowering was never implemented in Phase 184. This is a valuable discovery that clarifies the scope for Phase 186 and provides a clear implementation roadmap.

**Value delivered**:
- ✅ API integration skeleton (builds successfully)
- ✅ Root cause analysis (init lowering missing)
- ✅ Phase 186 requirements defined
- ✅ Test infrastructure in place

**Phase 185 status**: Partially complete - integration skeleton done, awaiting Phase 186 for functional completion.

**Next phase**: Phase 186 - Body-local Init Lowering (2-3 hours simplified, 6-7 hours full)