---

name: clean-codebase description: > Remove dead code, unused imports, fix lint warnings, and normalize formatting across a codebase without changing business logic or architecture. Use when lint warnings have piled up during rapid development, unused imports and variables clutter files, dead code paths were never removed, formatting is inconsistent, or static analysis tools report fixable hygiene issues. license: MIT allowed-tools: Read Write Edit Bash Grep Glob metadata: author: Philipp Thoss version: "1.0" domain: maintenance complexity: intermediate language: multi tags: maintenance, cleanup, lint, dead-code, formatting locale: ja source_locale: en source_commit: 75ded7a1 fence_basis_commit: 75ded7a1 translator: claude translation_date: "2026-03-17"

コードベースのクリーンアップ

使用タイミング

Use this skill when a codebase has accumulated hygiene debt:

• Lint warnings have piled up during rapid development
• Unused imports and variables clutter files
• Dead code paths exist but were never removed
• Formatting is inconsistent across files
• Static analysis tools report fixable issues

Do NOT use for architectural refactoring, bug fixes, or business logic changes. This skill focuses purely on hygiene and automated cleanup.

入力

Parameter	Type	Required	Description
codebase_path	string	Yes	Absolute path to codebase root
language	string	Yes	Primary language (js, python, r, rust, etc.)
cleanup_mode	enum	No	safe (default) or aggressive
run_tests	boolean	No	Run test suite after cleanup (default: true)
backup	boolean	No	Create backup before deletion (default: true)

手順

ステップ1: Pre-Cleanup Assessment

Measure the current state to quantify improvements later.

# Count lint warnings by severity
lint_tool --format json > lint_before.json

# Count lines of code
cloc . --json > cloc_before.json

# List unused symbols (language-dependent)
# JavaScript/TypeScript: ts-prune or depcheck
# Python: vulture
# R: lintr unused function checks

期待結果: Baseline metrics saved to lint_before.json and cloc_before.json

失敗時: If lint tool not found, skip automated fixes and focus on manual review

ステップ2: Fix Automated Lint Warnings

Apply safe automated fixes (spacing, quotes, semicolons, trailing whitespace).

JavaScript/TypeScript:

eslint --fix .
prettier --write .

Python:

black .
isort .
ruff check --fix .

R:

Rscript -e "styler::style_dir('.')"

Rust:

cargo fmt
cargo clippy --fix --allow-dirty

期待結果: All safe lint warnings resolved; files formatted consistently

失敗時: If automated fixes introduce test failures, revert changes and escalate

ステップ3: Identify Dead Code Paths

Use static analysis to find unreferenced functions, unused variables, and orphaned files.

JavaScript/TypeScript:

ts-prune | tee dead_code.txt
depcheck | tee unused_deps.txt

Python:

vulture . | tee dead_code.txt

R:

Rscript -e "lintr::lint_dir('.', linters = lintr::unused_function_linter())"

General approach:

1. Grep for function definitions
2. Grep for function calls
3. Report functions defined but never called

期待結果: dead_code.txt lists unused functions, variables, and files

失敗時: If static analysis tool unavailable, manually review recent commit history for orphaned code

ステップ4: Remove Unused Imports

Clean up import blocks by removing references to packages never used.

JavaScript:

eslint --fix --rule 'no-unused-vars: error'

Python:

autoflake --remove-all-unused-imports --in-place --recursive .

R:

# Manual review: grep for library() calls, check if package used
grep -r "library(" . | cut -d: -f2 | sort | uniq

期待結果: All unused import statements removed

失敗時: If removing imports breaks build, they were used indirectly — restore and document

ステップ5: Remove Dead Code (Mode-Dependent)

Safe Mode (default):

• Only remove code explicitly marked as deprecated
• Remove commented-out code blocks (if >10 lines and >6 months old)
• Remove TODO comments referencing completed issues

Aggressive Mode (opt-in):

• Remove all functions identified as unused in Step 3
• Remove private methods with zero references
• Remove feature flags for deprecated features

For each candidate deletion:

1. Verify zero references in codebase
2. Check git history for recent activity (skip if modified in last 30 days)
3. Remove code and add entry to CLEANUP_LOG.md

期待結果: Dead code removed; CLEANUP_LOG.md documents all deletions

失敗時: If uncertain whether code is truly dead, move to archive/ directory instead

ステップ6: Normalize Formatting

Ensure consistent formatting across all files (even if not caught by linters).

1. Normalize line endings (LF vs CRLF)
2. Ensure single newline at end of file
3. Remove trailing whitespace
4. Normalize indentation (spaces vs tabs, indent width)

# Example: Fix line endings and trailing whitespace
find . -type f -name "*.js" -exec sed -i 's/\r$//' {} +
find . -type f -name "*.js" -exec sed -i 's/[[:space:]]*$//' {} +

期待結果: All files follow consistent formatting conventions

失敗時: If sed breaks binary files, skip and document

ステップ7: Run Tests

Validate that cleanup didn't break functionality.

# Language-specific test command
npm test              # JavaScript
pytest                # Python
R CMD check           # R
cargo test            # Rust

期待結果: All tests pass (or same failures as before cleanup)

失敗時: Revert changes incrementally to identify breaking change, then escalate

ステップ8: Generate Cleanup Report

Document all changes for review.

# Codebase Cleanup Report

**Date**: YYYY-MM-DD
**Mode**: safe | aggressive
**Language**: <language>

## Metrics

| Metric | Before | After | Change |
|--------|--------|-------|--------|
| Lint warnings | X | Y | -Z |
| Lines of code | A | B | -C |
| Unused imports | D | 0 | -D |
| Dead functions | E | F | -G |

## Changes Applied

1. Fixed X lint warnings (automated)
2. Removed Y unused imports
3. Deleted Z lines of dead code (see CLEANUP_LOG.md)
4. Normalized formatting across W files

## Escalations

- [Issue description requiring human review]
- [Uncertain deletion moved to archive/]

## Validation

- [x] All tests pass
- [x] Backup created: backup_YYYYMMDD/
- [x] CLEANUP_LOG.md updated

期待結果: Report saved to CLEANUP_REPORT.md in project root

失敗時: (N/A — generate report regardless of outcome)

バリデーション Checklist

After cleanup:

• All tests pass (or same failures as before)
• No new lint warnings introduced
• Backup created before any deletions
• CLEANUP_LOG.md documents all removed code
• Cleanup report generated with metrics
• Git diff reviewed for unexpected changes
• CI pipeline passes

よくある落とし穴

1. Removing Code Still Used via Reflection: Static analysis misses dynamic calls (e.g., eval(), metaprogramming). Always check git history.

2. Breaking Implicit Dependencies: Removing imports that were used by dependencies. Run tests after every import removal.

3. Deleting Feature Flags for Active Features: Even if unused in current branch, feature flags may be active in other environments. Check deployment configs.

4. Over-Aggressive Formatting: Tools like black or prettier may reformat code in ways that trigger unnecessary diffs. Configure tools to match project style.

5. Ignoring Test Coverage: Cannot safely clean codebases without tests. If coverage is low, escalate for test additions first.

6. Not Backing Up: Always create backup_YYYYMMDD/ directory before deleting anything, even if using git.

7. Wrong R binary on hybrid systems: On WSL or Docker, Rscript may resolve to a cross-platform wrapper instead of native R. Check with which Rscript && Rscript --version. Prefer the native R binary (e.g., /usr/local/bin/Rscript on Linux/WSL) for reliability. See Setting Up Your Environment for R path configuration.

関連スキル

• tidy-project-structure — Organize directory layout, update READMEs
• repair-broken-references — Fix dead links and imports
• escalate-issues — Route complex problems to specialists
• r-packages/run-r-cmd-check — Run full R package checks
• devops/dependency-audit — Check for outdated dependencies