Run Pre-commit Hooks Skill

This skill runs pre-commit hooks to validate code quality before committing.

When to Use

• User asks to run pre-commit (e.g., "run pre-commit hooks")
• Before committing code
• Testing if CI will pass
• After making code changes
• Troubleshooting commit failures

Pre-commit Hooks

Configured in .pre-commit-config.yaml:

1. Mojo Format

- id: mojo-format
  name: Mojo Format
  entry: mojo format
  language: system
  files: \.(mojo|🔥)$

2. Trailing Whitespace

- id: trailing-whitespace
  name: Trim Trailing Whitespace

3. End of File Fixer

- id: end-of-file-fixer
  name: Fix End of Files

4. YAML Check

- id: check-yaml
  name: Check YAML

5. Large Files Check

- id: check-added-large-files
  name: Check for Large Files
  args: ['--maxkb=1000']

6. Mixed Line Ending

- id: mixed-line-ending
  name: Fix Mixed Line Endings

7. Markdownlint (Disabled Currently)

# Will enable after fixing existing files
- id: markdownlint-cli2
  name: Markdown Lint

Usage

Run All Hooks

# Run all hooks on all files
pre-commit run --all-files

# Run all hooks on staged files only
pre-commit run

# Automatically runs on commit
git commit -m "message"

Run Specific Hook

# Run specific hook
pre-commit run trailing-whitespace --all-files

# Run on specific file
pre-commit run --files src/tensor.mojo

Install Hooks

# Install pre-commit hooks (one-time setup)
pre-commit install

# Now hooks run automatically on git commit

Hook Behavior

Auto-Fix Hooks

These hooks fix issues automatically:

• trailing-whitespace - Removes trailing spaces
• end-of-file-fixer - Adds final newline
• mixed-line-ending - Fixes line endings
• mojo-format - Formats Mojo code

Workflow when auto-fix runs:

git commit -m "message"
# Hooks run, fix files, commit aborts
# Files are fixed but not staged

git add .  # Stage the fixes
git commit -m "message"  # Commit again

Check-Only Hooks

These hooks check but don't fix:

• check-yaml - Reports YAML errors
• check-added-large-files - Reports large files

If these fail: Fix manually and re-commit

CI Integration

Pre-commit runs in CI:

name: Pre-commit Checks

on: [push, pull_request]

jobs:
  pre-commit:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-python@v5
      - run: pip install pre-commit
      - run: pre-commit run --all-files

Common Issues

Hooks Fail on Commit

$ git commit -m "message"
Trim Trailing Whitespace....Failed
- hook id: trailing-whitespace
- exit code: 1
- files were modified by this hook

Files were modified by this hook. Additional output:

Fixing file.md

Fix:

# Files were fixed, just stage and re-commit
git add .
git commit -m "message"

YAML Validation Fails

Check YAML...Failed
- hook id: check-yaml
- exit code: 1

Syntax error in .github/workflows/test.yml

Fix: Correct YAML syntax

Large File Detected

Check for Large Files...Failed
- hook id: check-added-large-files
- exit code: 1

large_file.bin (1500 KB) exceeds 1000 KB

Fix:

• Don't commit large files
• Use Git LFS if needed
• Add to .gitignore

Skipping Hooks

Only when necessary:

# Skip all hooks (not recommended)
git commit --no-verify -m "message"

# Skip specific hook
SKIP=trailing-whitespace git commit -m "message"

When to skip:

• Emergency hotfix
• Hook has bug
• False positive

Don't skip to bypass quality checks!

Examples

Run all hooks:

pre-commit run --all-files

Run before committing:

# Check if commit will pass
pre-commit run

# If passing, commit
git commit -m "message"

Install hooks:

pre-commit install

Update hooks:

pre-commit autoupdate

Scripts Available

• scripts/run_precommit.sh - Run all hooks
• scripts/install_precommit.sh - Install hooks
• scripts/update_precommit.sh - Update hook versions

Best Practices

1. Install hooks - Run pre-commit install once
2. Let hooks fix - Don't bypass, let them auto-fix
3. Run before push - Verify CI will pass
4. Don't skip - Only skip in emergencies
5. Keep updated - Run pre-commit autoupdate periodically

Workflow Integration

First Time Setup

# Install pre-commit
pip install pre-commit

# Install hooks
pre-commit install

# Test
pre-commit run --all-files

Daily Workflow

# Make changes
# ...

# Commit (hooks run automatically)
git commit -m "feat: new feature"

# If hooks fix files
git add .
git commit -m "feat: new feature"

Before PR

# Verify all files pass
pre-commit run --all-files

# If passing, create PR
gh pr create --issue 42

See .pre-commit-config.yaml for complete hook configuration.