---
description: impact-analysis
allowed-tools: Bash, Read, Edit, Write, Glob, Grep
---

# impact-analysis

Analyze the impact of code changes on other parts of the codebase.

## Prompt

ROLE: Impact Analyzer

OBJECTIVE
Identify which files, tests, and features are affected by code changes to prevent regressions.

INPUTS (optional)
- FILES=<comma-separated paths> (default: auto-detect from git diff)
- BASE=<base branch> (default: main/master)
- RUN_TESTS=yes|no (default: yes, if tests found)

DETECTION
1. Get changed files:
   ```bash
   git diff <BASE>...HEAD --name-only
   ```

2. For each changed file, find:
   - **Direct imports**: Files that import this file
   - **Indirect imports**: Files that import files that import this file (2 levels)
   - **Test files**: Corresponding test files (*\.test\*, *\.spec\*)
   - **Related stories**: Stories mentioning this file in docs/06-stories/

ANALYSIS METHODS

### Static Analysis (AST parsing)
- Parse import/require statements
- Build dependency graph
- Identify circular dependencies
- Find dead code (exported but never imported)

### Test Coverage Mapping
- Read coverage reports (coverage/lcov.info, coverage.json)
- Map changed lines to test files
- Identify uncovered changes

### Pattern Matching
- API routes → API tests
- Components → Component tests + Storybook stories
- Services → Service tests + Integration tests
- Database models → Migration tests

IMPACT REPORT
```markdown
# Impact Analysis Report

**Branch**: <BRANCH>
**Base**: <BASE>
**Changed Files**: 5
**Potentially Affected Files**: 23
**Tests to Run**: 12

## Direct Impacts

### src/api/auth/login.ts (MODIFIED)
**Type**: API endpoint
**Changes**: 23 lines modified

**Direct dependents** (3):
- src/api/auth/index.ts (exports this endpoint)
- src/middleware/auth.ts (uses login logic)
- tests/api/auth/login.test.ts (tests this file)

**Indirect dependents** (8):
- src/app.ts → src/api/auth/index.ts → login.ts
- src/routes.ts → src/api/auth/index.ts → login.ts
- [6 more...]

**Related tests**:
- ✅ tests/api/auth/login.test.ts (exists)
- ⚠️ tests/integration/auth-flow.test.ts (may need updates)
- ❌ Missing: E2E test for login flow

**Related stories**:
- US-0042: Implement JWT authentication (IN-REVIEW)

**Coverage**: 87% (lines 45-52 uncovered)

---

### src/components/LoginForm.tsx (MODIFIED)
**Type**: UI component
**Changes**: 15 lines modified

**Direct dependents** (2):
- src/pages/Login.tsx
- src/components/AuthModal.tsx

**Related tests**:
- ✅ tests/components/LoginForm.test.tsx (exists)
- ⚠️ Accessibility tests not found

**Related stories**:
- US-0041: Create login form UI (IN-REVIEW)

**Coverage**: 92%
```

## Breaking Changes Detection

Analyze function signatures and types:
```
⚠️ BREAKING CHANGE DETECTED

File: src/api/auth/login.ts
Function: login()

Before:
  login(email: string, password: string): Promise<Token>

After:
  login(credentials: LoginRequest): Promise<AuthResponse>

Affected callers (3):
- src/middleware/auth.ts:45
- tests/api/auth/login.test.ts:23
- tests/integration/auth-flow.test.ts:67
```

## Test Recommendations

Based on changes, suggest tests to run:

**Critical** (always run):
- tests/api/auth/login.test.ts (direct test)
- tests/integration/auth-flow.test.ts (integration)

**Recommended** (affected indirectly):
- tests/api/users/*.test.ts (uses auth)
- tests/e2e/login.spec.ts (E2E)

**Optional** (low risk):
- tests/components/Header.test.tsx (displays user from auth)

ACTIONS (after user review)

1. Show impact summary
2. Ask: "Run affected tests? (YES/NO)"
3. If YES:
   ```bash
   # Run only affected tests
   npm test -- tests/api/auth/login.test.ts tests/integration/auth-flow.test.ts
   ```
4. If tests fail:
   - Show failures
   - Suggest creating story: "US-XXXX: Fix regressions from <change>"

5. If breaking changes detected:
   - Warn user
   - Suggest creating ADR if architectural change
   - Create stories for updating affected callers

INTEGRATION

### CI Optimization
Suggest optimized CI that only runs affected tests:
```yaml
- name: Impact analysis
  run: npx claude-code /AgileFlow:impact-analysis BASE=main

- name: Run affected tests
  run: npm test -- $(cat affected-tests.txt)
```

### Story Updates
- Update related stories with impact notes
- Create new stories for regressions or breaking changes
- Append to bus/log.jsonl: {"type":"impact","affected":23,"tests":12}

VISUALIZATION (optional)
Generate dependency graph:
```
src/api/auth/login.ts
├── src/api/auth/index.ts
│   ├── src/app.ts
│   └── src/routes.ts
├── src/middleware/auth.ts
│   └── src/app.ts
└── tests/api/auth/login.test.ts
```

RULES
- Use static analysis when possible (faster than running tests)
- Prioritize tests by risk (critical path first)
- Never skip tests for modified files
- Warn about uncovered changes
- Suggest creating tests for uncovered code
- Diff-first for any file modifications

OUTPUT
- Impact analysis report (markdown)
- List of affected files and tests
- Test recommendations (critical/recommended/optional)
- Optional: Run tests and report results