commits.yml

# Checks all commits in a PR follow the repo rules:
#
#   1. conventional commit messages
#   2. used `git commit --signoff`
#   3. no extra merge commits
name: Commits

on:
  workflow_dispatch:
  # Perform these checks on PRs into *any* branch.
  #
  # Motivation:
  #   Commits which are not --signoff but merged into other branches
  #   will likely make their way into PRs for master. At which
  #   point it will be difficult to get the original author to --signoff.
  pull_request:

jobs:
  commit-checks:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
        with:
          fetch-depth: 0

      - name: Set commit range variables
        # Finding the commit range is not as trivial as it may seem.
        #
        # At this stage git's HEAD does not refer to the latest commit in the PR,
        # but rather to the merge commit inserted by the PR. So instead we have
        # to get 'HEAD' from the PR event.
        #
        # One cannot use the number of commits (github.event.pull_request.commits)
        # to find the start commit i.e. HEAD~N does not work, this breaks if there
        # are merge commits.
        run: |
          echo "PR_HEAD=${{ github.event.pull_request.head.sha }}" >> $GITHUB_ENV
          echo "PR_BASE=${{ github.event.pull_request.base.sha }}" >> $GITHUB_ENV

      - name: Install conventional-commit linter
        run: |
          # Intall the linter and the conventional commits config
          npm install @commitlint/config-conventional @commitlint/cli

          # Extend the conventional commits config with the `--signoff`
          # requirement.
          echo "module.exports = {
            extends: ['@commitlint/config-conventional'],
            rules: {
              'signed-off-by': [2, 'always', 'Signed-off-by:'],
            }
          }" > commitlint.config.js

      - name: Conventional commit check
        run: |
          npx commitlint --from $PR_BASE --to $PR_HEAD

      - name: No merge commits
        run: |
          # This will list any merge commits in the PR commit path
          MERGE=$(git log --merges --ancestry-path $PR_BASE..$PR_HEAD)

          # The merge list should be empty
          [[ ! -z "$MERGE" ]] && {
            echo "PR contains merge commits:";
            echo $MERGE;
            exit 1;
          }
          exit 0;