linter.yml

name: Linting

# Trigger each time HEAD branch is updated in a pull request
# see https://github.com/orgs/community/discussions/26366
on:
  pull_request:
    types: [synchronize]

jobs:

  # Resources:
  # number [1] being most important
  # [1] https://github.com/actions/checkout/issues/520#issuecomment-1167205721
  # [2] https://robertfaldo.medium.com/commands-to-run-rubocop-and-specs-you-changed-in-your-branch-e6d2f2e4110b
  # [3] https://community.atlassian.com/t5/Bitbucket-questions/Git-diff-show-different-files-than-PR-Pull-Request/qaq-p/2331786
  rubocop:
    name: RuboCop
    runs-on: ubuntu-latest
    steps:
      - name: 'Checkout PR branch (with test merge-commit)'
        uses: actions/checkout@v3
        with:
          fetch-depth: 2 # to also fetch parent of PR
      
      # Adapted from this great comment [1]. Git diff adapted from [2].
      # "|| test $? = 1;" is used to ignore the exit code of grep when no files
      # are found matching the pattern. For the "three dots" ... syntax, see [3].
      - name: Get changed files
        run: |
          files=$(git diff --name-only --diff-filter=ACMR -r HEAD^1...HEAD | grep '\.rb$' || test $? = 1;)
          printf "🎴 Changed ruby files: \n$files"
          echo "CHANGED_FILES=$(echo ${files} | xargs)" >> $GITHUB_ENV
      
      - name: Set up Ruby 3
        uses: ruby/setup-ruby@v1
        with:
          ruby-version: 3.1.4
          bundler-cache: true

      - name: Run RuboCop
        if: env.CHANGED_FILES != ''
        run: bundle exec rubocop $CHANGED_FILES