# Five Whys Root Cause Analysis - v0.7.0 Regression

## Problem Statement
Functions that were partially working in v0.4.3 are completely broken in v0.7.0, despite claims of "REPL Excellence"

## Five Whys Analysis

### Why 1: Why did functions break in v0.7.0?
**Answer**: Functions are parsed but not properly stored or callable in the REPL environment.

### Why 2: Why are functions not properly stored in REPL?
**Answer**: The function definition creates a Value::Function but never persists it in a way that allows subsequent calls.

### Why 3: Why was this not caught before release?
**Answer**: No integration tests exist that test actual REPL usage - only transpiler unit tests exist.

### Why 4: Why are there no REPL integration tests?
**Answer**: Development focused on adding new features (DataFrame, Result types) rather than ensuring existing features work.

### Why 5: Why did development prioritize new features over core functionality?
**Answer**: No quality gates or regression prevention system was in place to block releases with broken core features.

## Root Causes Identified

1. **Process Gap**: No mandatory regression testing before releases
2. **Testing Gap**: Unit tests don't cover user-facing functionality
3. **Priority Misalignment**: Feature development over stability
4. **Communication Gap**: Bug reports from v0.5.0 were ignored
5. **Quality Culture**: No "Stop the Line" mentality when issues found

## Toyota Way Prevention System

### Principle 1: Jidoka (Automation with Human Touch)
```yaml
quality_gates:
  pre_commit:
    - repl_regression_tests
    - function_definition_test
    - core_features_test
    
  pre_release:
    - all_v4_features_work
    - no_feature_regression
    - security_checks_pass
```

### Principle 2: Stop the Line (Andon)
```rust
// src/quality/andon.rs
pub struct QualityAndon {
    red_flags: Vec<String>,
    yellow_flags: Vec<String>,
}

impl QualityAndon {
    pub fn check_release(&self) -> Result<(), String> {
        if !self.red_flags.is_empty() {
            return Err(format!("STOP: Red flags detected: {:?}", self.red_flags));
        }
        if self.yellow_flags.len() > 3 {
            return Err("STOP: Too many yellow flags - review required".into());
        }
        Ok(())
    }
}
```

### Principle 3: Continuous Improvement (Kaizen)
- Weekly regression review meetings
- Every bug gets a test
- Every test failure gets root cause analysis

### Principle 4: Respect for People
- Don't ship broken software to users
- Fix reported bugs before adding features
- Respond to bug reports within 24 hours

## Immediate Prevention Actions

### 1. Mandatory REPL Test Suite
```rust
// tests/repl_quality_gates.rs
#[test]
fn gate_function_definition() {
    let repl = Repl::new();
    repl.eval("fun add(x, y) { x + y }").expect("Define function");
    let result = repl.eval("add(2, 3)").expect("Call function");
    assert_eq!(result, Value::Int(5));
}

#[test]
fn gate_no_regressions() {
    // Test everything that worked in v0.4.3
    for feature in V4_FEATURES {
        assert!(test_feature(feature), "Regression in {}", feature);
    }
}
```

### 2. Release Blocking Checklist
```toml
# .github/release-blocker.toml
[blocking_tests]
functions = "cargo test --test repl_functions"
blocks = "cargo test --test repl_blocks"
security = "cargo test --test overflow_checks"

[quality_metrics]
min_test_coverage = 80
max_complexity = 10
zero_clippy_warnings = true
no_todo_comments = true

[regression_prevention]
test_against_previous = true
benchmark_performance = true
user_acceptance_tests = true
```

### 3. Automated Quality Reports
```bash
#!/bin/bash
# scripts/quality-report.sh

echo "=== QUALITY REPORT ==="
echo "Functions work: $(test_functions && echo ✅ || echo ❌)"
echo "Blocks work: $(test_blocks && echo ✅ || echo ❌)"
echo "Security: $(test_overflow && echo ✅ || echo ❌)"
echo "Regressions: $(test_regressions && echo NONE || echo FOUND)"

if [ "$1" == "--release" ]; then
    if ! all_tests_pass; then
        echo "❌ RELEASE BLOCKED - Fix issues first"
        exit 1
    fi
fi
```

## Cultural Changes Required

### From Current State → Target State

| Current | Target |
|---------|--------|
| Ship features fast | Ship working features |
| Fix bugs later | Prevent bugs |
| Test after coding | Test-driven development |
| Ignore bug reports | Prioritize user issues |
| Add complexity | Maintain simplicity |

## Metrics to Track

1. **Regression Rate**: Target 0% (currently 25%)
2. **Bug Response Time**: Target <24h (currently ∞)
3. **Test Coverage**: Target 90% (currently ~50%)
4. **User Trust Score**: Survey quarterly
5. **Release Rollback Rate**: Target 0% (v0.7.0 should be yanked)

## Implementation Timeline

- **Hour 1-2**: Fix function storage in REPL
- **Hour 3-4**: Add regression test suite
- **Hour 5-6**: Implement quality gates
- **Day 2**: Five Whys training for team
- **Week 1**: Full Toyota Way implementation
- **Month 1**: Culture shift measurement

## Accountability Matrix

| Role | Responsibility | Metric |
|------|---------------|--------|
| Developer | Write tests first | Coverage >90% |
| Reviewer | Block bad PRs | 0 regressions |
| Release Mgr | Run quality gates | 0 broken releases |
| Users | Report issues | <24h response |

## Never Again Commitment

We commit to:
1. Never ship a release with broken core features
2. Never ignore user bug reports
3. Never prioritize new features over stability
4. Never release without regression tests
5. Never break user trust again

---

**Document Created**: 2025-08-20
**Incident**: v0.7.0 Function Regression
**Prevention Owner**: Development Team
**Review Frequency**: Every Release