ln-742-precommit-setup Skill

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ln-742-precommit-setup

Type: L3 Worker Category: 7XX Project Bootstrap Parent: ln-740-quality-setup

Sets up Git hooks for automated code quality enforcement before commits.

Purpose & Scope

Does:

Installs hook management tools (Husky or pre-commit)
Configures staged file linting (lint-staged or pre-commit hooks)
Sets up commit message validation (commitlint)
Verifies hooks trigger correctly

Does NOT:

Configure linters themselves (ln-741 does this)
Set up test infrastructure (ln-743 does this)
Modify source code

Supported Stacks

| Technology | Hook Manager | Staged Linting | Commit Validation | |------------|--------------|----------------|-------------------| | Node.js | Husky | lint-staged | commitlint | | Python | pre-commit | pre-commit hooks | pre-commit hook | | Mixed | Both (if needed) | Stack-specific | commitlint |

Phase 1: Check Existing Hooks

Before installing, check for existing hook configurations.

Files to Check:

| Tool | Indicators | |------|------------| | Husky | .husky/ directory, husky in package.json | | pre-commit | .pre-commit-config.yaml | | lint-staged | lint-staged in package.json or .lintstagedrc* | | commitlint | commitlint.config.*, .commitlintrc* |

Decision Logic:

If hooks exist and working: SKIP (inform user)
If partial setup: ASK user to complete or replace
If no hooks: CREATE from templates

Phase 2: Install Hook Manager

Node.js Projects (Husky)

npm install -D husky
npx husky init

This creates:

.husky/ directory
.husky/pre-commit hook file
Adds prepare script to package.json

Python Projects (pre-commit)

pip install pre-commit
# OR with uv:
uv add --dev pre-commit

pre-commit install

This creates:

.git/hooks/pre-commit (managed by pre-commit)
Requires .pre-commit-config.yaml for configuration

Phase 3: Configure Staged Linting

Node.js (lint-staged)

npm install -D lint-staged

Create configuration (.lintstagedrc.mjs or in package.json):

Key Rules:

TypeScript files: ESLint + Prettier
JSON/MD/CSS: Prettier only
C# files: dotnet format (if mixed project)

CRITICAL FIX: For .NET files, use correct syntax: "*.cs": "dotnet format --include" is WRONG Use: "*.cs": "dotnet format whitespace --include" or run dotnet format separately

Python (pre-commit hooks)

Configuration in .pre-commit-config.yaml:

repos:
  - repo: https://github.com/astral-sh/ruff-pre-commit
    rev: v0.8.0
    hooks:
      - id: ruff
        args: [--fix]
      - id: ruff-format

Phase 4: Configure Commit Message Validation

Node.js (commitlint)

npm install -D @commitlint/cli @commitlint/config-conventional

Create commitlint.config.mjs with:

Conventional Commits format
Allowed types: feat, fix, docs, style, refactor, test, chore, ci
Max header length: 100 characters

Update Husky hook

Add commit-msg hook:

echo 'npx --no -- commitlint --edit "$1"' > .husky/commit-msg

Python (pre-commit hook for commit message)

Add to .pre-commit-config.yaml:

  - repo: https://github.com/compilerla/conventional-pre-commit
    rev: v3.4.0
    hooks:
      - id: conventional-pre-commit
        stages: [commit-msg]

Phase 5: Test Hooks

Verify hooks work correctly.

Test 1: Lint-staged triggers

# Create a file with lint issues
echo "const x=1" > test-file.ts
git add test-file.ts
git commit -m "test: verify hooks"
# Expected: lint-staged runs, either fixes or blocks

Test 2: Commit message validation

git commit --allow-empty -m "bad message"
# Expected: commitlint rejects

git commit --allow-empty -m "test: valid message format"
# Expected: commit succeeds

Cleanup:

rm test-file.ts
git reset HEAD~1  # If test commit was made

Critical Rules

RULE 1: Husky requires Git repository (git init first).

RULE 2: lint-staged MUST have linters configured first (run ln-741 before ln-742).

RULE 3: Document --no-verify escape hatch for emergency commits.

RULE 4: pre-commit hooks should auto-fix when possible (--fix flag).

Definition of Done

[ ] Hook manager installed (Husky or pre-commit)
[ ] Staged linting configured and working
[ ] Commit message validation configured
[ ] Test commit triggers hooks correctly
[ ] User informed of:
- How hooks work
- How to skip hooks in emergency (git commit --no-verify)
- Commit message format required

Reference Files

| File | Purpose | |------|---------| | husky_precommit_template.sh | Husky pre-commit hook | | husky_commitmsg_template.sh | Husky commit-msg hook | | lintstaged_template.mjs | lint-staged configuration | | commitlint_template.mjs | commitlint configuration | | precommit_config_template.yaml | Python pre-commit config | | hooks_guide.md | Detailed hooks guide |

Error Handling

| Error | Cause | Resolution | |-------|-------|------------| | Husky not running | Missing prepare script | Run npx husky init again | | lint-staged fails | Missing linter | Run ln-741 first | | pre-commit not found | Not in PATH | pip install pre-commit | | Hooks not triggering | Git hooks disabled | Check .git/hooks/ permissions | | Windows path issues | Shell script format | Use cross-platform syntax |

Emergency Bypass

Document for users:

# Skip all hooks (use sparingly!)
git commit --no-verify -m "emergency: bypass hooks"

# Skip only pre-commit (keeps commit-msg)
HUSKY=0 git commit -m "fix: urgent hotfix"

Version: 2.0.0 Last Updated: 2026-01-10

Agent Skills: ln-742-precommit-setup

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