precommit

name	precommit
description	Use when running quality checks before commits, validating code passes compilation/formatting/linting/tests, or when user invokes /precommit

Precommit Skill

Executes the production-ready precommit workflow to ensure code quality before commits.

When to Use

Invoke with /precommit when:

• Preparing code for commit
• Validating code quality after completing a feature
• Running the full quality check suite
• Checking if code meets production standards

Skip this skill when:

• Doing rapid prototyping (use /spike instead)
• Only need to run tests (use mix test or cargo test directly)
• Reviewing code for design issues (use /review instead)

Usage

/precommit          # Run all checks
/precommit --fix    # Run checks and auto-fix formatting issues

Tools Used

This skill typically uses:

• Bash - Run language-specific commands (mix, cargo, npm, pytest)
• Read - Check configuration files and dependencies
• Edit - Auto-fix formatting issues (with --fix flag)

What It Does

Runs four quality checks in sequence (language-aware):

1. Compilation/Type Check with warnings as errors
2. Code formatting verification
3. Static analysis/Linting
4. Test suite execution

Implementation

Step 1: Detect Language and Check Dependencies

First detect project language and verify required tools.

Language Detection:

Load the language-detection skill for canonical detection logic and tooling commands.

Check Language-Specific Dependencies:

Elixir:

# Check if credo is in mix.exs
if ! grep -q ':credo' mix.exs; then
  echo "Missing dependency: credo"
  echo "Add to mix.exs:"
  echo '  {:credo, "~> 1.7", only: [:dev, :test], runtime: false}'
  exit 1
fi

Rust:

# Check rustfmt and clippy installed
if ! command -v cargo-fmt &> /dev/null; then
  echo "rustfmt not installed"
  echo "Run: rustup component add rustfmt"
  exit 1
fi

Python:

# Check for quality tools
if ! command -v mypy &> /dev/null; then
  echo "mypy not installed"
  echo "Run: pip install mypy"
fi

TypeScript:

# Check for eslint
if ! npm list eslint &> /dev/null; then
  echo "eslint not installed"
  echo "Run: npm install --save-dev eslint"
fi

Step 2: Run Checks

Execute checks based on detected language:

Language-Specific Commands:

Step	Elixir	Rust	Python	TypeScript
1. Compile/Check	mix compile --warnings-as-errors	cargo check	mypy src/	tsc --noEmit
2. Format	mix format --check-formatted	cargo fmt -- --check	ruff format --check .	prettier --check .
3. Lint	mix credo --strict	cargo clippy -- -D warnings	ruff check .	eslint .
4. Test	mix test	cargo test	pytest	npm test

Elixir Example:

echo "Running precommit checks..."
echo ""

# 1. Compile with warnings as errors
echo "1/4 Compiling..."
if mix compile --warnings-as-errors; then
  echo "Compilation passed"
else
  echo "Compilation failed with warnings"
  exit 1
fi

# 2. Format code
echo "2/4 Formatting..."
if mix format --check-formatted; then
  echo "Formatting correct"
else
  echo "Code needs formatting. Run: mix format"
  exit 1
fi

# 3. Run credo
echo "3/4 Static analysis..."
if mix credo --strict; then
  echo "Credo passed"
else
  echo "Credo found issues"
  exit 1
fi

# 4. Run tests
echo "4/4 Running tests..."
if mix test; then
  echo "All tests passed"
else
  echo "Tests failed"
  exit 1
fi

echo "All precommit checks passed!"

Rust Example:

echo "Running precommit checks..."

# 1. Check compilation
echo "1/4 Checking..."
cargo check || exit 1

# 2. Check formatting
echo "2/4 Formatting..."
cargo fmt -- --check || exit 1

# 3. Run clippy
echo "3/4 Linting..."
cargo clippy -- -D warnings || exit 1

# 4. Run tests
echo "4/4 Testing..."
cargo test || exit 1

echo "All precommit checks passed!"

Step 3: Report Results

If all checks pass:

Precommit Checks Complete

All checks passed:
- Compilation (0 warnings)
- Formatting (all files formatted)
- Linting (strict mode)
- Tests (X tests, 0 failures)

Ready to commit!

If any check fails:

Precommit Checks Failed

Results:
- Compilation: passed
- Formatting: 3 files need formatting

Next steps:
1. Run formatter (see language-detection skill for command)
2. Review changes
3. Run /precommit again

Auto-Fix Mode

With --fix flag:

Precommit with Auto-Fix

1/4 Compilation... passed
2/4 Formatting... Fixed 3 files
3/4 Static analysis... passed
4/4 Tests... passed

Auto-fixed:
- Formatted 3 files
- Run git diff to review changes

All checks passed!

Error Handling

Missing Dependencies

Elixir:

Required dependencies not found

Missing:
- credo: Add {:credo, "~> 1.7", only: [:dev, :test], runtime: false}

After adding to mix.exs, run: mix deps.get

Rust:

Clippy not installed

Run: rustup component add clippy

Compilation Errors

Elixir:

Compilation Failed

Errors found:
  lib/my_app/accounts.ex:42: warning: variable "user" is unused

Fix: Remove unused variables or prefix with underscore: _user
Run: mix compile --warnings-as-errors

Rust:

Compilation Failed

error[E0382]: borrow of moved value: `data`

Fix: Review ownership and borrowing
Run: cargo check

Test Failures

Elixir:

Tests Failed

Failed tests:
  1) test create_user/1 creates user (MyApp.AccountsTest)
     test/my_app/accounts_test.exs:42

Fix: Review test failure, fix implementation or update tests
Run: mix test test/my_app/accounts_test.exs:42

Rust:

Tests Failed

---- tests::test_create_user stdout ----
thread 'tests::test_create_user' panicked

Fix: Review test failure and fix implementation
Run: cargo test test_create_user

Configuration

Configure behavior per language via environment variables or project config:

Environment Variables:

• PRECOMMIT_SKIP_TESTS=1 - Skip test step
• PRECOMMIT_FIX=1 - Auto-fix formatting issues

Language-Specific Configuration:

Elixir: .credo.exs for Credo rules Rust: clippy.toml for Clippy settings Python: pyproject.toml for tool configuration TypeScript: .eslintrc.js for ESLint rules

Integration with Git Hooks

To run automatically before each commit, add to .git/hooks/pre-commit:

#!/bin/bash
set -e

echo "Running precommit checks..."
claude-code /precommit

if [ $? -ne 0 ]; then
  echo ""
  echo "Precommit checks failed. Commit aborted."
  echo "Fix issues and try again, or use --no-verify to skip (not recommended)."
  exit 1
fi

Make executable:

chmod +x .git/hooks/pre-commit

Tips

1. Run frequently: Don't wait until commit time
2. Fix as you go: Address warnings immediately
3. Use --fix: Auto-fix formatting issues
4. Focus on tests first: If tests fail, fix before other checks
5. Batch formatting: Run formatter on entire codebase periodically

Success Criteria

Precommit succeeds when:

• All code compiles without warnings
• All files properly formatted
• Linter passes in strict mode
• All tests pass
• No flaky tests (consistent pass/fail)

Related Skills

• /review - Comprehensive code review beyond precommit checks
• /spike - Fast prototyping mode (skips some checks)
• /spike-migrate - Upgrade SPIKE code to pass precommit
• production-quality - Knowledge about quality standards (not a workflow)