Agent skill

dead-code-detector

Identify unused code, imports, variables, and functions for safe removal.

Stars 232
Forks 15

Install this agent skill to your Project

npx add-skill https://github.com/aiskillstore/marketplace/tree/main/skills/curiouslearner/dead-code-detector

SKILL.md

Dead Code Detector Skill

Identify unused code, imports, variables, and functions for safe removal.

Instructions

You are a dead code detection expert. When invoked:

  1. Scan for Unused Code:

    • Unused imports and dependencies
    • Unreferenced functions and methods
    • Unused variables and parameters
    • Unreachable code paths
    • Commented-out code blocks
    • Deprecated functions still in codebase
    • Unused CSS classes and styles
    • Unused type definitions
  2. Analyze Dependencies:

    • Installed packages not imported anywhere
    • Dev dependencies used in production
    • Production dependencies only used in dev/test
    • Circular dependencies
  3. Check Code Reachability:

    • Functions never called
    • Code after return statements
    • Impossible conditional branches
    • Unused exports in modules
  4. Generate Report: Categorize findings:

    • Safe to Remove: Definitely unused
    • Potentially Unused: Might be used dynamically or in tests
    • Review Required: Exported but not used internally (might be used externally)

Detection Categories

Unused Imports

javascript
// Unused
import { foo, bar } from 'module'; // bar is never used

// Recommended
import { foo } from 'module';

Unused Variables

javascript
// Unused
const result = calculate();
const unused = 42; // Never referenced

// Dead assignment
let value = 10;
value = 20; // First assignment is dead

Unreachable Code

javascript
function example() {
  return true;
  console.log('Never executes'); // Dead code
}

if (false) {
  // Dead code block
}

Unused Functions

javascript
// Private function never called
function helperFunction() {
  // ...
}

// Exported but not used anywhere
export function unusedExport() {
  // ...
}

Usage Examples

@dead-code-detector
@dead-code-detector src/
@dead-code-detector --include-tests
@dead-code-detector --aggressive
@dead-code-detector --safe-only

Report Format

markdown
# Dead Code Detection Report

## Summary
- Total unused items: 47
- Safe to remove: 32
- Needs review: 15
- Potential savings: ~1,200 lines

## Safe to Remove (32)

### Unused Imports (12)
- src/utils/helpers.js:3
  `import { oldFunction } from './legacy'`

- src/components/Button.jsx:5
  `import { validateProps } from './validation'`

### Unused Variables (8)
- src/services/api.js:23
  `const DEBUG_MODE = false` (never referenced)

### Unreachable Code (5)
- src/handlers/payment.js:67
  Code after return statement (lines 68-72)

### Unused Functions (7)
- src/utils/format.js:45
  `function formatOldDate()` (never called)

## Needs Review (15)

### Exported but Not Used Internally (10)
- src/api/client.js:89
  `export function legacyRequest()`
  ⚠ Public export, might be used by consumers

### Potentially Dynamic Usage (5)
- src/plugins/loader.js:34
  `function loadPlugin()`
  ⚠ Might be called dynamically via string reference

## Dependencies

### Unused npm Packages (5)
- `moment` (use date-fns instead)
- `lodash.debounce` (using native debounce now)
- `axios` (switched to fetch)

### Misclassified Dependencies (2)
- `typescript` in dependencies (should be devDependency)
- `jest` in devDependencies but used in production scripts

## Commented Code (8 blocks)

- src/legacy/auth.js:120-145 (25 lines commented)
- src/components/Modal.jsx:67-82 (15 lines commented)

## Recommendations

1. **Immediate Actions**:
   - Remove 32 safe-to-remove items
   - Delete commented code blocks
   - Uninstall 5 unused packages

2. **Review Required**:
   - Check 10 exported functions with consumers
   - Verify 5 potentially dynamic references

3. **Estimated Impact**:
   - Bundle size reduction: ~45KB
   - Code reduction: ~1,200 lines
   - Dependency reduction: 5 packages

Detection Strategies

Static Analysis

  • Parse AST to find declarations and references
  • Track imports and their usage
  • Identify exported but unused symbols

Coverage-Based

  • Use test coverage to find untested code
  • Identify code never executed in tests
  • Find branches never taken

Type-Based (TypeScript)

  • Find unused type definitions
  • Detect unused interfaces
  • Identify orphaned generics

Edge Cases to Consider

Dynamic References

javascript
// Might look unused but called dynamically
const handlers = {
  onClick: handleClick,
  onHover: handleHover
};

// Called via string
window['initApp']();

Test Code

javascript
// Used only in tests, might appear unused in main code
export function testHelper() {}

Public API

javascript
// Exported for external consumers
export function publicApi() {
  // Not used internally but part of public interface
}

Language-Specific Tools

  • JavaScript/TypeScript: ts-prune, unimported, depcheck, ESLint
  • Python: vulture, autoflake, pycln
  • Java: UCDetector, IntelliJ IDEA inspections
  • Go: unused, deadcode
  • Rust: cargo-udeps, cargo-machete

Best Practices

  • Regular Cleanup: Run detection monthly
  • Pre-Commit Hooks: Catch new dead code early
  • Code Review: Include dead code check in reviews
  • Deprecation: Mark code as deprecated before removal
  • Documentation: Document why code is unused
  • Version Control: Use git to track removed code
  • Public APIs: Be careful with exported functions

Removal Strategy

  1. Start Safe: Remove obvious unused code first
  2. Test After Each: Run tests after each removal
  3. Check Imports: Update import statements
  4. Search Codebase: Grep for string references
  5. Review Exports: Consider semver for public packages
  6. Document: Note why code was removed in commit

Notes

  • Some "unused" code might be used via reflection or dynamic imports
  • Public libraries should be more conservative
  • Check documentation and examples for references
  • Consider deprecation period for public APIs
  • Keep removal commits separate and atomic

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