chore: add husky pre-commit hook with lint-staged

[hydrosquall]

Motivation

This PR adds pre-commit hooks to catch formatting issues locally before CI, reduce wasted CI minutes, and ensure consistent code style across the codebase (related to vega/vega#4237).

Changes

• Adds husky@^9.1.7 for git hooks management
• Adds lint-staged@^16.2.7 to run linters only on staged files
• Configures pre-commit hook to run npx lint-staged
• Adds "prepare": "husky" script to auto-initialize hooks on npm install
• Configures lint-staged to run Python linting and formatting with ruff:
  • uv run ruff check --fix - auto-fixes linting issues
  • uv run ruff format - formats code to project standards
• Uses uv run to ensure correct tool versions from uv.lock (per project standards)
• Updates .gitignore to exclude .claude/ directory

Note: Taplo is excluded from pre-commit hooks due to maintainer stepping away and ARM Linux compatibility concerns, though it remains in CI.

Why Python/ruff instead of eslint format?

As noted in review feedback, this repository has a small TypeScript surface (4 files, 2 auto-generated) but significant Python development (11+ scripts). Recent CI failures have been in the "Format and lint (python)" step, not TypeScript.

Testing

Expand for local testing instructions

1. Verify husky initialization:

   npm install
   # Should see husky install hooks

2. Test the pre-commit hook with formatting issues:

   # Create a test file with bad formatting
   cat > test_formatting.py << 'PYEOF'
   def badly_formatted(x,y,z):
       result=x+y+z
       return result
   PYEOF
   
   # Try to commit it
   git add test_formatting.py
   git commit -m "test: formatting"
   
   # Should see ruff auto-fix the formatting issues
   # Check the file was reformatted:
   cat test_formatting.py
   
   # Clean up
   git rm test_formatting.py

[dsmedia]

Hi @hydrosquall — am very supportive of pre-commit hooks. I wonder though if vega-datasets might need a different approach?

The TypeScript surface in this repo is very small (4 files in src/, two of which are auto-generated). The primary development here consists of Python scripts and TOML config. In fact, looking at recent CI failures, the bottleneck is the "Format and lint (python)" step, not TypeScript:

Run 21546775137 (ruff failure)

Run 21695659624 (ruff failure)

Also, just wanted to check about running tsc on specific staged files (which lint-staged does). This forces tsc to ignore tsconfig.json, losing the full project context.

I'd suggest somehow targeting ruff instead. Maybe like this.

"lint-staged": {
  "*.py": ["ruff check --fix", "ruff format"]
}

A note on Taplo: We might want to leave it out of the hook for now. The original maintainer stepped away from the project in December 2024. While v0.10.0 includes a Linux aarch64 binary, it was never published to PyPI. The latest PyPI version (0.9.3) lacks a Linux ARM wheel, which would break the pre-commit hook for developers on that platform. I'm hopeful v0.10.0 can get published to PyPI soon and if so that would hold us for a while.

All this said, I'm very much in favor of finding a suitable way to add pre-commit hooks for this repo.

[hydrosquall]

@dsmedia thanks for the feedback and looking up the recent issues in CI that were specific to this repo.

Even though we could opt to run both, I agree ruff is probably the more useful formatter here and it might be enough to just run one given there are only 2 non-auto-generated TS files in this repo! I've adjusted the PR based on your comments.