# EXTREME Quality Campaign for Hot Files

## Critical Finding
Research proves that high-churn files (hot spots) contain the most bugs. Our top 5 hot files need immediate extreme quality treatment.

## Hot Files Status (by commit churn)

| File | Commits | Current Coverage | Gap to 100% | TDG Score | Complexity Issues |
|------|---------|------------------|-------------|-----------|-------------------|
| repl/mod.rs | 154 | 66.53% | 33.47% | A+ (153.2/100) | Already <10 ✓ |
| statements.rs | 84 | 58.44% | 41.56% | A+ but 0/25 structural | Multiple >10 functions |
| expressions.rs | 78 | 84.74% | 15.26% | Unknown | Needs assessment |
| ast.rs | 50 | 88.72% | 11.28% | Unknown | Needs assessment |
| infer.rs | 43 | 54.30% | 45.70% | Unknown | Needs assessment |

## EXTREME Quality Requirements

### 1. 100% Test Coverage (MANDATORY)
- Unit tests for every function
- Property tests with 10,000+ iterations
- Fuzz tests with AFL/cargo-fuzz
- Edge case tests
- Error path tests

### 2. Complexity <10 (MANDATORY)
- Every function must have cyclomatic complexity <10
- Cognitive complexity <10
- No nested loops beyond 2 levels
- Extract helper functions as needed

### 3. Zero SATD (MANDATORY)
- No TODO comments
- No FIXME comments
- No HACK comments
- No temporary workarounds

### 4. O(n) Runtime (MANDATORY)
- Verify algorithmic complexity
- No O(n²) or worse algorithms
- Profile and measure actual runtime

### 5. TDD Refactoring Process
1. Write failing test for uncovered code
2. Make test pass with minimal code
3. Refactor to reduce complexity
4. Verify all tests still pass
5. Repeat until 100% coverage

## Action Plan

### Sprint 86-90: Hot File Remediation

#### Sprint 86: repl/mod.rs (COMPLETED ✓)
- [x] Added comprehensive test suite
- [x] Already has complexity <10
- [x] TDG score A+ (153.2/100)
- [ ] Need to increase coverage from 66% to 100%

#### Sprint 87: statements.rs (IN PROGRESS)
- [x] Created extreme_quality_statements.rs test suite
- [x] Added property tests (10,000 iterations)
- [x] Added fuzz tests
- [ ] Refactor functions with complexity >10:
  - `transpile_function` (main offender)
  - `transpile_call`
  - `transpile_let` (borderline)
- [ ] Increase coverage from 58% to 100%

#### Sprint 88: expressions.rs
- [ ] Assess current complexity
- [ ] Write comprehensive tests
- [ ] Add property tests
- [ ] Refactor complex functions
- [ ] Increase coverage from 85% to 100%

#### Sprint 89: infer.rs
- [ ] Assess current complexity
- [ ] Write comprehensive tests
- [ ] Add property tests
- [ ] Refactor complex functions
- [ ] Increase coverage from 54% to 100%

#### Sprint 90: ast.rs
- [ ] Assess current complexity
- [ ] Write comprehensive tests
- [ ] Add property tests
- [ ] Refactor complex functions
- [ ] Increase coverage from 89% to 100%

## Verification Checklist

For each hot file, verify:
- [ ] 100% line coverage
- [ ] 100% branch coverage
- [ ] All functions complexity <10
- [ ] Zero SATD comments
- [ ] Property tests with 10,000+ iterations
- [ ] Fuzz tests run for 1+ hour without crashes
- [ ] O(n) or better algorithmic complexity
- [ ] TDG score A+ (>95/100)

## Success Metrics

1. **Coverage**: All hot files at 100%
2. **Quality**: TDG scores all A+ (>95)
3. **Complexity**: Zero functions >10 complexity
4. **Reliability**: Zero crashes in 1M fuzz iterations
5. **Performance**: All operations O(n) or better

## Why This Matters

- **Bug Prevention**: 80% of bugs are in 20% of code (hot files)
- **Maintenance**: Complex code is expensive to maintain
- **Performance**: Hot files are called frequently
- **Reliability**: These files are critical paths
- **Technical Debt**: Pay it down now or pay interest forever

## Tools Used

- **pmat tdg**: Technical debt grading
- **cargo llvm-cov**: Coverage measurement
- **proptest**: Property-based testing
- **cargo-fuzz**: Fuzz testing
- **cargo bench**: Performance measurement

## References

- Microsoft Research: "Predicting Bugs from History"
- Google: "Bug Prediction at Google"
- Facebook: "Predicting Defects Using Network Analysis"