Pre Commit Hooks

Pre-Commit Hooks

Core Principle

Automate quality gates - humans forget, machines don't.

When to Use This Skill

• Setting up new projects (MANDATORY)
• Onboarding team members
• Improving code quality
• Preventing bad commits
• Enforcing standards

The Iron Law

NO PROJECT WITHOUT PRE-COMMIT HOOKS.

Every repository MUST have automated quality checks before commits are allowed.

Why Pre-Commit Hooks Are Mandatory

Without hooks:

• ❌ Unformatted code enters repository
• ❌ Type errors slip through
• ❌ Tests broken by commits
• ❌ Secrets/credentials committed
• ❌ Linting errors ignored

With hooks:

• ✅ Automatic code formatting
• ✅ Type checking enforced
• ✅ Tests run before commit
• ✅ No secrets committed
• ✅ Consistent code quality

Authority: 95% of professional teams use pre-commit hooks. Not using them is unprofessional.

Setup by Language

JavaScript/TypeScript Projects

Install pre-commit framework:

npm install --save-dev husky lint-staged
npx husky install
npm set-script prepare "husky install"

Create .husky/pre-commit:

#!/bin/sh
. "$(dirname "$0")/_/husky.sh"

npx lint-staged

Configure package.json:

{
  "lint-staged": {
    "*.{js,jsx,ts,tsx}": [
      "eslint --fix",
      "prettier --write",
      "npm run test:related --bail"
    ],
    "*.{json,md,yml,yaml}": [
      "prettier --write"
    ]
  },
  "scripts": {
    "prepare": "husky install",
    "test:related": "jest --bail --findRelatedTests"
  }
}

Minimum hooks:

• ✅ ESLint (linting + auto-fix)
• ✅ Prettier (formatting)
• ✅ TypeScript check (tsc --noEmit)
• ✅ Jest (related tests)
• ✅ No secrets check

Python Projects

Install pre-commit:

pip install pre-commit

Create .pre-commit-config.yaml:

repos:
  # Code formatting
  - repo: https://github.com/psf/black
    rev: 23.12.1
    hooks:
      - id: black
        language_version: python3.11

  # Import sorting
  - repo: https://github.com/PyCQA/isort
    rev: 5.13.2
    hooks:
      - id: isort

  # Linting
  - repo: https://github.com/charliermarsh/ruff-pre-commit
    rev: v0.1.9
    hooks:
      - id: ruff
        args: [--fix, --exit-non-zero-on-fix]

  # Type checking
  - repo: https://github.com/pre-commit/mirrors-mypy
    rev: v1.8.0
    hooks:
      - id: mypy
        additional_dependencies: [types-requests]

  # Security checks
  - repo: https://github.com/PyCQA/bandit
    rev: 1.7.6
    hooks:
      - id: bandit
        args: ["-c", "pyproject.toml"]

  # Tests
  - repo: local
    hooks:
      - id: pytest
        name: pytest
        entry: pytest
        language: system
        pass_filenames: false
        always_run: true

Install hooks:

pre-commit install

Minimum hooks:

• ✅ Black (formatting)
• ✅ isort (import sorting)
• ✅ Ruff (linting)
• ✅ mypy (type checking)
• ✅ pytest (tests)
• ✅ bandit (security)

PHP/Laravel Projects

Install pre-commit tools:

composer require --dev friendsofphp/php-cs-fixer phpstan/phpstan

Create .husky/pre-commit (using Husky):

#!/bin/sh
. "$(dirname "$0")/_/husky.sh"

# Get staged PHP files
FILES=$(git diff --cached --name-only --diff-filter=ACMR | grep '\.php$')

if [ -n "$FILES" ]; then
  # Format code
  vendor/bin/php-cs-fixer fix $FILES --config=.php-cs-fixer.php

  # Static analysis
  vendor/bin/phpstan analyse $FILES

  # Run tests for changed files
  vendor/bin/paratest --filter=$(echo $FILES | tr '\n' '|')

  # Re-add formatted files
  git add $FILES
fi

Or use PHP pre-commit library:

composer require --dev brainmaestro/composer-git-hooks

Configure in composer.json:

{
  "extra": {
    "hooks": {
      "pre-commit": [
        "vendor/bin/php-cs-fixer fix --dry-run --diff",
        "vendor/bin/phpstan analyse",
        "vendor/bin/paratest"
      ]
    }
  }
}

Minimum hooks:

• ✅ PHP CS Fixer (formatting)
• ✅ PHPStan (static analysis)
• ✅ Psalm (type checking)
• ✅ Paratest (tests)
• ✅ No secrets check

Universal Hooks (All Projects)

Add these to every project:

1. No Secrets Check

# .pre-commit-config.yaml
repos:
  - repo: https://github.com/gitleaks/gitleaks
    rev: v8.18.1
    hooks:
      - id: gitleaks

2. Trailing Whitespace

- repo: https://github.com/pre-commit/pre-commit-hooks
  rev: v4.5.0
  hooks:
    - id: trailing-whitespace
    - id: end-of-file-fixer
    - id: check-yaml
    - id: check-json
    - id: check-added-large-files

3. Commit Message Validation

# .husky/commit-msg
#!/bin/sh
. "$(dirname "$0")/_/husky.sh"

npx --no -- commitlint --edit "$1"

Install commitlint:

npm install --save-dev @commitlint/cli @commitlint/config-conventional

Configure commitlint.config.js:

module.exports = {
  extends: ['@commitlint/config-conventional'],
  rules: {
    'type-enum': [2, 'always', [
      'feat', 'fix', 'docs', 'style', 'refactor',
      'perf', 'test', 'build', 'ci', 'chore'
    ]]
  }
};

Frontend + Backend Test Requirements

For projects with both frontend and backend:

# .husky/pre-commit
#!/bin/sh
. "$(dirname "$0")/_/husky.sh"

echo "🧪 Running pre-commit checks..."

# Check if backend files changed
BACKEND_CHANGED=$(git diff --cached --name-only | grep -E '\.(php|py|go|java)$')

# Check if frontend files changed
FRONTEND_CHANGED=$(git diff --cached --name-only | grep -E '\.(js|jsx|ts|tsx|vue)$')

# If backend changed, run backend tests
if [ -n "$BACKEND_CHANGED" ]; then
  echo "🔧 Backend files changed - running backend tests..."
  npm run test:backend || exit 1
fi

# If frontend changed, run frontend AND e2e tests
if [ -n "$FRONTEND_CHANGED" ]; then
  echo "🎨 Frontend files changed - running frontend tests..."
  npm run test:frontend || exit 1

  echo "🌐 Running e2e tests..."
  npm run test:e2e || exit 1
fi

# If both changed, ensure full test suite passes
if [ -n "$BACKEND_CHANGED" ] && [ -n "$FRONTEND_CHANGED" ]; then
  echo "🔄 Full stack changes detected - running complete test suite..."
  npm run test:all || exit 1
fi

echo "✅ All pre-commit checks passed!"

Bypassing Hooks (Emergency Only)

Never bypass hooks casually:

# WRONG - don't do this
git commit --no-verify

# ONLY use in true emergencies:
# - Hotfix for production outage
# - CI/CD system down, blocking critical deploy
# - After consulting team lead

If you bypass hooks:

1. Add TODO comment explaining why
2. Create follow-up task to fix properly
3. Inform team in commit message
4. Never bypass for "speed" or "convenience"

Verification

After setup, verify hooks work:

# Make a bad change (intentionally)
echo "const x = 1" > test.js  # Missing semicolon

# Try to commit
git add test.js
git commit -m "test"

# Should FAIL with linting error
# If it commits successfully, hooks aren't working!

Team Onboarding

When new developer joins:

# Clone repo
git clone <repo>
cd <repo>

# Install dependencies (includes hook setup)
npm install  # or pip install -r requirements.txt

# Verify hooks installed
ls .git/hooks/pre-commit

# Test hooks work
# (make intentional error, try to commit, should fail)

Common Issues

Issue: Hooks not running

Solution:

# Reinstall hooks
npm run prepare  # for Husky
# or
pre-commit install  # for Python

Issue: Hooks too slow

Solution:

# Run only on staged files (lint-staged)
# Skip slow tests in hooks, run in CI
# Use --bail flag to fail fast

Issue: Hooks block legitimate commits

Solution:

# Fix the actual issue (don't bypass)
# Update hook configuration if rule is wrong
# Discuss with team if standard should change

Integration with Skills

Pre-commit hooks enforce:

1. verification-before-completion - Tests must pass
2. git-workflow - Commit message format
3. database-backup - Prevent commits without backup (if DB changed)
4. code-review - Linting/formatting standards

Commitment Required

Before proceeding, acknowledge:

• I will set up pre-commit hooks on ALL projects
• I will NEVER bypass hooks without team discussion
• I understand hooks are quality gates, not obstacles
• I will help team members set up hooks correctly
• I will update hooks when new standards are adopted

The Iron Law (Repeated): NO PROJECT WITHOUT PRE-COMMIT HOOKS. This is not optional. This is professional software development.