name: Prettier

# Check-only: reports formatting issues without modifying the branch.
# Runs on pull_request (so fork PRs are checked too) and only checks the
# files the PR actually changed, so a PR can never go red for unformatted
# files it did not touch. Developers run `npx prettier@3 --write <files>`
# locally to fix the reported files.

on:
  pull_request:

jobs:
  format:
    runs-on: ubuntu-latest
    permissions:
      contents: read
    steps:
      - uses: actions/checkout@v4
        with:
          # Full history so the merge-base with the PR base branch exists.
          fetch-depth: 0

      - name: Check formatting of changed files with Prettier
        run: |
          git diff --name-only -z --diff-filter=d \
            "origin/${{ github.base_ref }}...HEAD" \
            | xargs -0 --no-run-if-empty npx --yes prettier@3 --check --ignore-unknown