auto-rebase.yml

# This workflow automatically rebases pull requests targeting the base branch
# and when a comment containing '/rebase' is created or edited.
name: Automatic rebase strategy

on:
  pull_request:
    types:
      - opened
      - synchronize
      - reopened
    branches:
      - main
  issue_comment:
    types:
      - created
      - edited

env:
  # Change `secrets.GH_TOKEN` to your own secret name if you want to use a different one
  GITHUB_TOKEN: ${{ secrets.GH_TOKEN }}
  GH_BRANCH_BASE: ${{ github.event.pull_request.base.ref }}
  GH_BRANCH: ${{ github.event.pull_request.head.ref }}
  GH_BRANCH_SHA: ${{ github.event.pull_request.head.sha }}

jobs:
  rebase:
    name: Rebase
    runs-on: ubuntu-latest
    if: github.event_name == 'pull_request' || contains(github.event.comment.body, '/rebase')
    permissions:
      pull-requests: write
    steps:
      - name: Checkout
        uses: actions/checkout@v2
        with:
          token: ${{ env.GITHUB_TOKEN }}
          fetch-depth: 0
          ref: ${{ env.GH_BRANCH }}

      - name: Configure git
        run: |
          # Use the author of the last commit as the committer
          git config user.name $(git log -1 --pretty=format:'%an')
          git config user.email $(git log -1 --pretty=format:'%ae')

          # Keep the original author date
          git config rebase.instructionFormat '%s%nexec GIT_COMMITTER_DATE="%cD" git commit --amend --no-edit --reset-author --date="%cD"'
        shell: bash

      - id: branch_status
        name: Check if branch is up-to-date
        run: |
          git fetch origin ${{ env.GH_BRANCH_BASE }}

          if git merge-base --is-ancestor origin/${{ env.GH_BRANCH_BASE }} ${{ env.GH_BRANCH_SHA }}; then
            echo "up_to_date=true" >> $GITHUB_OUTPUT
          else
            echo "up_to_date=false" >> $GITHUB_OUTPUT
          fi
        shell: bash

      - name: Try to rebase
        if: steps.branch_status.outputs.up_to_date == 'false'
        run: |
          git fetch origin ${{ env.GH_BRANCH_BASE }}
          # Rebase with the `--rebase-merges` flag to preserve merge commits
          git rebase --rebase-merges origin/${{ env.GH_BRANCH_BASE }}

          # Edit last commit message to include [skip ci] and avoid triggering subsequent workflows
          git commit --amend -m "$(git log -1 --pretty=%B) [skip ci]"

          git push origin ${{ env.GH_BRANCH }} --force-with-lease

      - name: Comment on pull request if rebase was successful
        if: success() && steps.branch_status.outputs.up_to_date == 'false'
        uses: thollander/actions-comment-pull-request@v2
        with:
          message: |
            Branch is up-to-date :tada:
          pr_number: ${{ github.event.pull_request.number }}

      - name: Comment on pull request if rebase failed
        if: failure()
        uses: thollander/actions-comment-pull-request@v2
        with:
          message: |
            :stop_sign::raised_hand: Cannot rebase automatically.

            Please rebase manually and push again.

            If you don't familiar with git rebase, please check out [this guide](https://docs.github.com/en/get-started/using-git/resolving-merge-conflicts-after-a-git-rebase).
          pr_number: ${{ github.event.pull_request.number }}