Code Migrator

⚡ UNIQUE FEATURE: Automated legacy code modernization with AI-powered migration paths, dependency resolution, test generation, and risk analysis. Migrate between languages, frameworks, or architectural patterns with confidence.

What This Skill Does

Intelligently migrates codebases with minimal manual intervention:

Language Migrations

• Python 2 → Python 3: Syntax, imports, unicode handling
• JavaScript → TypeScript: Type inference and definitions
• Java 8 → Java 17+: Modern language features
• Angular.js → React/Vue: Complete framework migration
• PHP 5 → PHP 8: Modernize deprecated features
• Ruby 2 → Ruby 3: Update syntax and gems

Framework Upgrades

• React Class → Hooks: Convert class components
• Vue 2 → Vue 3: Composition API migration
• Django 2 → Django 4: Settings and ORM updates
• Rails 5 → Rails 7: Modern Rails patterns
• Express 4 → Express 5: Route handlers, middleware

Architectural Migrations

• Monolith → Microservices: Service extraction
• REST → GraphQL: API transformation
• Callback Hell → Async/Await: Promise modernization
• MVC → Component-Based: Architecture refactoring

Why This Is Revolutionary

First migration skill with:

• AI-powered analysis: Understands code context and intent
• Risk assessment: Identifies high-risk changes
• Incremental migration: Migrate module by module
• Automated testing: Generates tests to verify migration
• Rollback support: Safe migration with undo capability
• Dependency resolution: Automatically updates imports and packages
• Pattern recognition: Identifies and modernizes anti-patterns

Instructions

Phase 1: Migration Discovery & Analysis

1. Identify Migration Type:

   Ask user:
   - What are you migrating FROM?
   - What are you migrating TO?
   - Full codebase or specific modules?
   - Any constraints or requirements?
   

2. Analyze Current State:

   # Discover project structure
   Use Glob to find all source files
   Use Grep to identify:
   - Framework versions
   - Import patterns
   - Deprecated APIs
   - Code smells
   

3. Generate Migration Plan:

   # Migration Plan: Python 2 → Python 3
   
   ## Scope
   - Files to migrate: 247
   - Estimated effort: 2-3 days
   - Risk level: Medium
   
   ## Changes Required
   
   ### High Priority (Breaking Changes)
   1. Print statements → print() function (187 occurrences)
   2. Unicode strings (u'') → default strings (423 occurrences)
   3. Dict.iteritems() → Dict.items() (89 occurrences)
   
   ### Medium Priority (Deprecated APIs)
   1. urllib → urllib.request (34 occurrences)
   2. ConfigParser → configparser (12 occurrences)
   
   ### Low Priority (Best Practices)
   1. Old-style classes → new-style classes
   2. % formatting → f-strings
   
   ## Dependencies to Update
   - Django 1.11 → Django 4.2
   - requests 2.9 → requests 2.31
   - pytest 3.0 → pytest 7.4
   
   ## Migration Strategy
   - Phase 1: Update dependencies (safe, reversible)
   - Phase 2: Automated syntax fixes (safe)
   - Phase 3: Manual code review (requires attention)
   - Phase 4: Test and validate
   
   ## Risk Assessment
   - **Critical**: Database migrations (manual review needed)
   - **High**: Third-party API calls (may have changed)
   - **Medium**: String encoding (test thoroughly)
   - **Low**: Print statements (auto-fixable)
   

Phase 2: Automated Migration

1. Create Migration Branch:

   git checkout -b migrate-to-python3
   

2. Backup Current State:

   # Create backup
   git tag pre-migration-backup
   

3. Execute Migration (module by module):

   For each file/module:

   a. Read current code:

   Use Read to load file contents
   

   b. Apply transformations:

   # Example: Python 2 → 3 print statements
   # Before
   print "Hello, World!"
   
   # After
   print("Hello, World!")
   
   # Example: Unicode strings
   # Before
   u"Hello, 世界"
   
   # After
   "Hello, 世界"
   
   # Example: Dict iteration
   # Before
   for key, value in my_dict.iteritems():
   
   # After
   for key, value in my_dict.items():
   

   c. Update imports:

   # Before
   import urllib
   import ConfigParser
   
   # After
   import urllib.request
   import configparser
   

   d. Modernize patterns:

   # Before: Old-style formatting
   "Hello, %s!" % name
   
   # After: f-strings
   f"Hello, {name}!"
   
   # Before: Manual file handling
   f = open('file.txt')
   content = f.read()
   f.close()
   
   # After: Context manager
   with open('file.txt') as f:
       content = f.read()
   

4. Use Edit tool to apply changes:

   For each transformation:
   - Use Edit with old_string/new_string
   - Preserve formatting and style
   - Add comments where behavior changes
   

Phase 3: Dependency Migration

1. Update package manager files:

   # requirements.txt migration
   # Before
   Django==1.11.29
   requests==2.9.1
   
   # After
   Django==4.2.0
   requests==2.31.0
   

   // package.json migration
   // Before
   {
     "dependencies": {
       "react": "^16.8.0"
     }
   }
   
   // After
   {
     "dependencies": {
       "react": "^18.2.0"
     }
   }
   

2. Install new dependencies:

   pip install -r requirements.txt
   # or
   npm install
   

Phase 4: Test Generation & Validation

1. Generate Migration Tests:

   # Use Task to launch test-generator agent
   Task: "Generate tests that verify migration correctness"
   
   For each migrated function:
   - Create test with Python 2/3 compatible inputs
   - Verify output is identical
   - Test edge cases
   

2. Run Existing Tests:

   # Run original test suite
   pytest tests/
   
   # Report:
   - Tests passing: 247/250
   - Tests failing: 3
   - New errors: 0
   

3. Run Migration Validation:

   # Custom validation checks
   - Import validation
   - Syntax check (python -m py_compile)
   - Linting (flake8, pylint)
   - Type checking (mypy for Python, tsc for TypeScript)
   

Phase 5: Manual Review Queue

For high-risk changes:

## Manual Review Required

### File: api/payments.py (Lines 45-67)
**Risk**: HIGH
**Reason**: External API call with changed response format

```python
# Original (Python 2)
response = urllib.urlopen(url)
data = json.loads(response.read())

# Migrated (Python 3)
response = urllib.request.urlopen(url)
data = json.loads(response.read().decode('utf-8'))

Action needed: Verify API still returns same data structure

File: database/models.py (Lines 102-115)

Risk: CRITICAL Reason: Database model migration

Action needed: Create and review Django migration files

### Phase 6: Documentation & Rollback Plan

1. **Generate Migration Report**:
   ```markdown
   # Migration Report: Python 2 → Python 3

   **Date**: 2025-01-13
   **Duration**: 3.2 hours
   **Status**: ✅ Complete (3 items need manual review)

   ## Statistics
   - Files modified: 247
   - Lines changed: 1,834
   - Dependencies updated: 12
   - Tests updated: 45
   - New tests added: 18

   ## Breaking Changes
   1. Unicode handling in API responses
   2. Dictionary iteration in processors
   3. Print output in CLI tools

   ## Rollback Instructions
   ```bash
   git checkout pre-migration-backup

Next Steps

1. Review 3 flagged items in review-queue.md
2. Run integration tests
3. Deploy to staging
4. Monitor for issues

2. **Create Migration Documentation**:
- What changed and why
- How to use new patterns
- Common gotchas
- Troubleshooting guide

## Example Migrations

### Example 1: React Class → Hooks

**User**: "Migrate this component to hooks"

**Input**:
```javascript
class UserProfile extends React.Component {
constructor(props) {
 super(props);
 this.state = { user: null, loading: true };
}

componentDidMount() {
 fetchUser(this.props.userId)
   .then(user => this.setState({ user, loading: false }));
}

render() {
 const { user, loading } = this.state;
 if (loading) return <div>Loading...</div>;
 return <div>{user.name}</div>;
}
}

Output:

import { useState, useEffect } from 'react';

function UserProfile({ userId }) {
  const [user, setUser] = useState(null);
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    fetchUser(userId)
      .then(user => {
        setUser(user);
        setLoading(false);
      });
  }, [userId]);

  if (loading) return <div>Loading...</div>;
  return <div>{user.name}</div>;
}

Example 2: Callback Hell → Async/Await

Before:

function processUser(userId, callback) {
  getUser(userId, (err, user) => {
    if (err) return callback(err);
    getOrders(user.id, (err, orders) => {
      if (err) return callback(err);
      calculateTotal(orders, (err, total) => {
        if (err) return callback(err);
        callback(null, { user, total });
      });
    });
  });
}

After:

async function processUser(userId) {
  const user = await getUser(userId);
  const orders = await getOrders(user.id);
  const total = await calculateTotal(orders);
  return { user, total };
}

Configuration

.code-migrator-config.yml

:

migration:
  backup_enabled: true
  incremental: true
  generate_tests: true
  risk_threshold: medium  # Require manual review for high/critical

patterns:
  # Custom pattern replacements
  - from: "old_api_call"
    to: "new_api_call"
    risk: high

exclusions:
  # Files to skip
  - "vendor/*"
  - "node_modules/*"
  - "*.min.js"

validation:
  run_tests: true
  run_linters: true
  type_check: true

Supported Migrations

Languages

• Python 2 → 3
• JavaScript ES5 → ES6+ → TypeScript
• Java 8 → 11 → 17
• PHP 5 → 7 → 8
• Ruby 2 → 3
• Go 1.x → 1.21+

Frameworks

• React (any version upgrade)
• Vue 2 → 3
• Angular any → any
• Django 1.x → 4.x
• Rails 5 → 7
• Express 4 → 5

Patterns

• Callbacks → Promises → Async/Await
• Class components → Functional + Hooks
• Options API → Composition API
• MVC → MVVM
• REST → GraphQL

Tool Requirements

• Read: Load source files
• Write: Create new files and reports
• Edit: Transform code in-place
• Glob: Find all files to migrate
• Grep: Search for patterns
• Bash: Run tests, install dependencies
• Task: Generate tests, analyze risks

Best Practices

1. Start small: Migrate one module at a time
2. Test continuously: Run tests after each module
3. Commit frequently: Easy rollback if needed
4. Review high-risk: Never auto-migrate critical code
5. Update docs: Keep documentation in sync
6. Monitor production: Watch for issues post-migration

Limitations

• Cannot migrate business logic (requires human understanding)
• Complex macros/metaprogramming may need manual work
• Performance characteristics may change
• Some migrations require iterative refinement

Related Skills

• unit-test-generator - Generate migration tests
• refactor-master - Further code improvements
• pr-reviewer - Review migrated code

Changelog

Version 1.0.0 (2025-01-13)

• Initial release
• Support for 6 languages
• 10+ framework migrations
• Risk assessment
• Automated testing
• Rollback support

Contributing

Help add migration paths:

• New language pairs
• Framework upgrades
• Pattern transformations
• Risk detection rules

License

Apache License 2.0 - See LICENSE

Author

GLINCKER Team

• GitHub: @GLINCKER
• Repository: claude-code-marketplace

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🌟 The most comprehensive code migration skill available - save weeks of manual work!