prettify_code.yml

name: Prettify Code
on:
  pull_request:
  push:
    branches:
      - main

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

      - name: Fetch base branch
        if: github.event_name == 'pull_request'
        run: git fetch origin ${{ github.event.pull_request.base.ref }}

      - name: Get changed files
        id: changed-files
        run: |
          if [ "${{ github.event_name }}" == "pull_request" ]; then
            BASE_SHA="origin/${{ github.event.pull_request.base.ref }}"
          else
            BASE_SHA="${{ github.event.before }}"
          fi
          
          # Get files and store as space-separated string
          CHANGED_FILES=$(git diff --name-only --diff-filter=ACMR -z $BASE_SHA HEAD | \
            grep -zE '\.(js|md)$' | \
            xargs -0 -r)
          
          if [ -n "$CHANGED_FILES" ]; then
            echo "files=$CHANGED_FILES" >> $GITHUB_OUTPUT
            echo "has_files=true" >> $GITHUB_OUTPUT
            echo "Changed files: $CHANGED_FILES"
          else
            echo "has_files=false" >> $GITHUB_OUTPUT
          fi

      # Prettier is invoked directly rather than through
      # creyD/prettier_action@v4.6, which accepts a prettier_version input but
      # does not honour it: with 2.8.8 declared, the action installed 3.9.6
      # ("The following package was not found and will be installed:
      # prettier@3.9.6"). So CI silently enforced a different formatting
      # contract than CONTRIBUTING and .prettierrc.json describe, and the two
      # could drift apart without anyone noticing — a file formatted by hand to
      # match the documented version could fail here, and vice versa.
      #
      # `npx prettier@<version>` pins what actually runs, so the version in this
      # file is the version that checks the code. 2.8.8 is kept because it is
      # what the repository is formatted with; 3.x reflows markdown differently
      # and moving to it is a deliberate migration, not a CI detail.
      - name: Check code formatting
        if: steps.changed-files.outputs.has_files == 'true'
        run: npx --yes prettier@2.8.8 --check ${{ steps.changed-files.outputs.files }}