# Sprint 7 Phase 4: Mutation Testing - BLOCKED

## Status: ⛔ BLOCKED

**Blocking Issue**: Value type migration breaking all integration tests

## Problem Summary

Sprint 7 Phase 4 (Mutation Testing) is blocked by a widespread compilation failure in integration tests caused by a Value enum type migration that occurred earlier in the project.

### Root Cause

The `Value` enum was refactored from:
- **Old**: `Array(Rc<Vec<Value>>)` and `String(Rc<String>)`
- **New**: `Array(Rc<[Value]>)` and `String(Rc<str>)`

This change improved memory efficiency by using slice types instead of heap-allocated vectors, but **all integration test files** were not updated to match the new API.

### Impact

**Affected Test Files** (compilation errors):
- `tests/builtin_registry_integration_tdd.rs`
- `tests/tab_completion_mathematical_proof.rs`
- `tests/runtime_value_tdd.rs`
- `tests/minimal_builtin_debug_tdd.rs`
- `tests/binary_ops_coverage_tdd.rs`
- `tests/sprint71_runtime_tests.rs`
- Many more...

**Blocking Scenario**:
1. cargo-mutants runs `cargo test --no-run` for baseline verification
2. Baseline compilation fails due to Value type mismatches in tests
3. Mutation testing cannot proceed without successful baseline

**Working Tests**:
- ✅ Lib tests: 3,383 passing
- ✅ Bin tests: All passing
- ❌ Integration tests: Compilation failures

## Attempted Solutions

### Attempt 1: Manual .into() Conversion
- Used `sed` and `perl` to replace `Rc::new(vec![...])` with `vec![...].into()`
- **Result**: Syntax errors due to multiline patterns and incomplete replacements

### Attempt 2: From Trait Implementation
- Added `impl From<Vec<T>> for Value` and `impl From<Rc<Vec<Value>>> for Value`
- **Result**: Type conflicts - cannot convert `Rc<Vec<T>>` to `Rc<[T]>` without cloning

### Attempt 3: Configure cargo-mutants to Skip Integration Tests
- Set `additional_cargo_test_args = ["--lib", "--bins"]`
- **Result**: Config only affects test execution, not compilation - baseline still fails

### Attempt 4: Git Restore and Retry
- Reverted all manual changes and tried different approaches
- **Result**: Same fundamental issue remains

## Technical Details

### Required Migration Pattern

**Old Code** (broken):
```rust
let arr = Value::Array(Rc::new(vec![Value::Integer(1), Value::Integer(2)]));
let s = Value::String(Rc::new("test".to_string()));
```

**New Code** (correct):
```rust
let arr = Value::Array(vec![Value::Integer(1), Value::Integer(2)].into());
let s = Value::String(Rc::from("test"));
```

### Why .into() Works
- `Vec<T>` has `impl From<Vec<T>> for Rc<[T]>` in stdlib
- `&str` has `impl From<&str> for Rc<str>` in stdlib
- These conversions are zero-cost or minimal overhead

## Recommendation

### Option 1: Systematic Test File Migration (RECOMMENDED)
**Effort**: 2-4 hours
**Risk**: Low
**Benefit**: Fixes root cause permanently

1. Create migration script to update all test files
2. Use AST-based tool (rust-analyzer, syn) for accurate replacements
3. Run `cargo test` to verify all tests pass
4. Proceed with mutation testing

### Option 2: Temporary Test Exclusion
**Effort**: 1 hour
**Risk**: Medium (loses test coverage)
**Benefit**: Unblocks mutation testing immediately

1. Move broken test files to `tests_disabled/`
2. Run mutation tests on lib/bins only
3. File ticket to fix and re-enable tests later

### Option 3: Revert Value Type Change
**Effort**: 1-2 hours
**Risk**: High (loses performance improvements)
**Benefit**: Quick unblock but regression

1. Revert Value enum to old types
2. Verify all tests pass
3. Run mutation testing
4. Re-apply Value optimization with full test migration plan

## Next Steps

**Immediate**:
1. Create JIRA/GitHub ticket: "Value Type Migration - Fix Integration Tests"
2. Assign priority based on Sprint 7 timeline
3. Choose one of the three options above

**Follow-up**:
1. Implement chosen solution
2. Verify baseline: `cargo test --no-run` succeeds
3. Resume Phase 4: `cargo mutants --file src/frontend/parser/expressions.rs`
4. Continue with Sprint 7 roadmap

## Session Notes

- Spent 2+ hours debugging and attempting fixes
- Root cause identified: Value enum API breaking change
- Multiple solution approaches attempted and documented
- All lib/bin tests (3,383) passing - only integration tests affected
- cargo-mutants infrastructure ready, just blocked on baseline compilation

## Files Modified This Session

### Configuration:
- `.cargo/mutants.toml` - Added test configuration (additional_cargo_test_args)

### Source (attempted fix, reverted):
- `src/runtime/interpreter.rs` - Added/removed From implementations

### Documentation:
- This file: `docs/execution/SPRINT_7_PHASE_4_BLOCKED.md`
- `docs/execution/SPRINT_7_PHASE_4_APPROACH.md` (created earlier)

## References

- Value enum definition: `src/runtime/interpreter.rs:55-103`
- cargo-mutants config: `.cargo/mutants.toml`
- Phase 4 approach: `docs/execution/SPRINT_7_PHASE_4_APPROACH.md`
- Roadmap status: `docs/execution/roadmap.md`
