Dead Code Removal

Dead Code Removal

This skill safely identifies and removes unused code across multiple programming languages. It includes comprehensive safety checks to prevent removing code that's actually needed.

When to Use This Skill

• After refactoring code and removing features
• Before production deployment to reduce bundle size
• When cleaning up legacy code
• When removing deprecated functionality
• When optimizing codebase size
• When maintaining code quality standards

What This Skill Does

1. Language Detection: Identifies project languages and structure
2. Entry Point Mapping: Maps entry points and critical paths
3. Dependency Analysis: Builds dependency graphs and usage patterns
4. Safe Detection: Identifies unused elements with safety checks
5. Incremental Removal: Removes code incrementally with validation
6. Backup Creation: Creates backups before making changes

Helper Scripts

This skill includes Python helper scripts in scripts/:

• find_unused_imports.py: Uses AST parsing to accurately detect unused imports in Python files. Outputs JSON with unused imports and line numbers.

  python scripts/find_unused_imports.py src/utils.py src/services.py
  

How to Use

Remove Unused Code

Find and remove unused imports and functions in this project

Clean up dead code in src/ directory, but be conservative

Specific Analysis

Check for unused functions in src/utils/ and remove them safely

Analysis Process

1. Language Detection

Identify Project Type:

• Python: Look for pyproject.toml, setup.py, requirements.txt
• JavaScript/TypeScript: Check package.json, tsconfig.json
• Java: Look for pom.xml, build.gradle
• Go: Check go.mod
• Rust: Check Cargo.toml

Detect Entry Points:

• Python: main.py, __main__.py, app.py, run.py
• JavaScript: index.js, main.js, server.js, app.js
• Java: Main.java, *Application.java, *Controller.java
• Config files: *.config.*, settings.*, setup.*
• Test files: test_*.py, *.test.js, *.spec.js

2. Build Dependency Graph

Cross-File Dependencies:

• Track imports and requires
• Map function/method calls
• Identify class inheritance
• Track dynamic usage patterns

Framework Patterns:

• Preserve framework-specific patterns (Django models, React components, etc.)
• Check for decorators and annotations
• Verify entry point registrations

3. Detect Unused Elements

Using Helper Script:

The skill includes a Python helper script for finding unused imports:

# Find unused imports in Python files
python scripts/find_unused_imports.py src/utils.py src/services.py

Unused Imports:

# Python: AST-based analysis
import ast
# Track: Import statements vs actual usage
# Skip: Dynamic imports (importlib, __import__)

// JavaScript: Module analysis
// Track: import/require vs references
// Skip: Dynamic imports, lazy loading

Unused Functions/Classes:

• Define: All declared functions/classes
• Reference: Direct calls, inheritance, callbacks
• Preserve: Entry points, framework hooks, event handlers

4. Safety Checks

Never Remove If:

• Python: getattr(), eval(), globals() usage detected
• JavaScript: window[], this[], dynamic import() usage
• Java: Reflection, annotations (@Component, @Service)
• Framework patterns: Models, controllers, routes, components
• Entry points: Main functions, app initialization
• Test files: All test-related code

Framework Preservation:

Python:

• Django: Models, migrations, admin registrations
• Flask: Routes, blueprints, app factories
• FastAPI: Endpoints, dependencies

JavaScript:

• React: Components, hooks, context providers
• Vue: Components, directives, mixins
• Angular: Decorators, services, modules

Java:

• Spring: Beans, controllers, repositories
• JPA: Entities, repositories

5. Safe Removal Process

Backup Creation:

backup_dir="./unused_code_backup_$(date +%Y%m%d_%H%M%S)"
cp -r . "$backup_dir" 2>/dev/null || mkdir -p "$backup_dir" && rsync -a . "$backup_dir"

Incremental Removal:

1. Create temp file with change
2. Validate syntax
3. Run tests if available
4. Apply or rollback

Validation:

# Python
python -m py_compile file.py
python -m pytest

# JavaScript
npx eslint file.js
npm test

# Java
javac -Xlint file.java
mvn test

Examples

Example 1: Remove Unused Imports

Input: Clean up unused imports in src/utils/helpers.py

Output:

## Dead Code Removal: src/utils/helpers.py

### Analysis
- **File**: `src/utils/helpers.py`
- **Total imports**: 8
- **Unused imports**: 3

### Unused Imports Found
1. `import os` - Line 2 (not used anywhere)
2. `import json` - Line 3 (not used anywhere)
3. `from datetime import timedelta` - Line 5 (not used anywhere)

### Safe to Remove
✅ All 3 imports are safe to remove (no dynamic usage detected)

### Changes
```python
# Before
import os
import json
from datetime import datetime, timedelta
import requests

# After
from datetime import datetime
import requests

Validation

• ✅ Syntax check passed
• ✅ Tests pass
• ✅ No dynamic imports detected

### Example 2: Remove Unused Functions

**Input**: Find unused functions in `src/services/`

**Output**:
```markdown
## Dead Code Removal: src/services/

### Analysis
- **Files analyzed**: 12
- **Functions found**: 45
- **Unused functions**: 2

### Unused Functions

**1. `formatOldDate()` in `src/services/utils.js`**
- **Location**: Line 34-42
- **Status**: ✅ Safe to remove
- **Reason**: No references found, not exported, not used in tests

**2. `legacyAuth()` in `src/services/auth.js`**
- **Location**: Line 78-95
- **Status**: ⚠️ Preserved (framework pattern)
- **Reason**: Referenced in route configuration (line 12)

### Summary
- **Removed**: 1 function (`formatOldDate`)
- **Preserved**: 1 function (framework usage)
- **Lines removed**: 9
- **Size reduction**: ~300 bytes

Best Practices

Safety Guidelines

Do:

• Run tests after each removal
• Preserve framework patterns
• Check string references in templates
• Validate syntax continuously
• Create comprehensive backups
• Remove incrementally

Don't:

• Remove without understanding purpose
• Batch remove without testing
• Ignore dynamic usage patterns
• Skip configuration files
• Remove from migrations
• Remove exported/public APIs

Detection Patterns

Static Analysis:

• Use AST parsing for accurate detection
• Track cross-file references
• Check for dynamic usage patterns
• Verify framework-specific patterns

Validation:

• Always run syntax checks
• Run tests after removal
• Verify build still works
• Check for runtime errors

Reporting

Report Should Include:

• Files analyzed (count and types)
• Unused detected (imports, functions, classes)
• Safely removed (with validation status)
• Preserved (reason for keeping)
• Impact metrics (lines removed, size reduction)

Related Use Cases

• Code cleanup before release
• Reducing bundle size
• Removing deprecated code
• Maintaining code quality
• Refactoring legacy codebases
• Optimizing build times