action.yml

# Copyright 2024 Craig Motlin
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

name: 'Forbid Merge Commits'
description: 'A composite action to forbid merge commits in pull requests.'
branding:
  icon: 'git-merge'
  color: 'purple'

runs:
  using: "composite"
  steps:
    - name: Check for Pull Request event
      if: ${{ github.event_name != 'pull_request' }}
      shell: bash
      run: |
        echo "::warning::This action is intended to be used in pull_request events only. The event type was '${{ github.event_name }}'. See: https://github.com/motlin/forbid-merge-commits-action#how-to-add-this-action-to-your-repository."
        echo "## This action is intended to be used in pull_request events only. The event type was '${{ github.event_name }}'." >> $GITHUB_STEP_SUMMARY
        echo "See: [How to add this action to your repository](https://github.com/motlin/forbid-merge-commits-action#how-to-add-this-action-to-your-repository)." >> $GITHUB_STEP_SUMMARY
        exit 1

    - name: Checkout code
      uses: actions/checkout@v4
      with:
        fetch-depth: 0

    - name: Check for merge commits
      shell: bash
      run: |
        set -Eeuo pipefail

        MERGE_COMMITS=$(git log --merges --format=%H origin/${{github.base_ref}}..refs/remotes/pull/${{github.event.pull_request.number}}/merge^2 --)
        if [ -n "$MERGE_COMMITS" ]; then

          echo '::error title=Found merge commits::Found merge commits. Refer to https://github.com/motlin/forbid-merge-commits-action#handling-failure-messages for guidance.'

          echo -e '## Found merge commits.\n\nRefer to [handling failure messages](https://github.com/motlin/forbid-merge-commits-action#handling-failure-messages) for guidance.\n' >> $GITHUB_STEP_SUMMARY

          for COMMIT_HASH in $MERGE_COMMITS; do
            echo "::warning::Merge commit: $COMMIT_HASH"
            echo "::group::git show $COMMIT_HASH"
            git show $COMMIT_HASH
            echo '::endgroup::'

            echo ''                                       >> $GITHUB_STEP_SUMMARY
            echo '```console'                             >> $GITHUB_STEP_SUMMARY
            git show $COMMIT_HASH                         >> $GITHUB_STEP_SUMMARY
            echo '```'                                    >> $GITHUB_STEP_SUMMARY
          done

          exit 1
        else
          echo 'Success: No merge commits found'
        fi