.github/workflows/pre-commit.yml

name: pre-commit

on:
  pull_request:
  push:

jobs:
  pre-commit:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Setup Python
        uses: actions/setup-python@v5
        with:
          python-version: "3.10"

      - name: Install tooling
        run: |
          python -m pip install --upgrade pip
          python -m pip install pre-commit

      - name: Run pre-commit on changed files
        env:
          EVENT_NAME: ${{ github.event_name }}
          BASE_SHA: ${{ github.event.pull_request.base.sha }}
          BEFORE_SHA: ${{ github.event.before }}
          HEAD_SHA: ${{ github.sha }}
        run: |
          set -euo pipefail

          if [ "$EVENT_NAME" = "pull_request" ]; then
            FROM_SHA="$BASE_SHA"
          else
            FROM_SHA="$BEFORE_SHA"
          fi

          if [ -z "${FROM_SHA:-}" ] || [ "$FROM_SHA" = "0000000000000000000000000000000000000000" ]; then
            echo "No valid base SHA found; running on all files."
            pre-commit run --all-files --show-diff-on-failure --color=always
          else
            pre-commit run --from-ref "$FROM_SHA" --to-ref "$HEAD_SHA" --show-diff-on-failure --color=always
          fi