update-pr-branch.yml

name: "Update PR Branch on PR Comment"
on:
  issue_comment:
    types: [created]
jobs:
  update_pr_branch:
    name: Update PR Branch on PR Comment
    if: github.event.issue.pull_request != '' && github.event.comment.body == '/update'
    runs-on: ubuntu-latest
    steps:
      - name: Fetch latest code
        uses: actions/checkout@v2
        with:
          token: ${{ secrets.ACTIONS_PAT }}
          fetch-depth: 0
          submodules: 'true'
      - name: Fetch PR and target branch names
        id: fetch_pr_and_target_branch
        uses: actions/github-script@v3
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          script: |
            const { issue, repository } = context.payload;
            const [ owner, repo ] = repository.full_name.split('/');
            const { data: pullRequest } = await github.pulls.get({
              owner,
              repo,
              pull_number: issue.number
            });
            const { ref: prBranch } = pullRequest.head;
            const { ref: baseBranch } = pullRequest.base;
            const { clone_url: prRemoteUrl } = pullRequest.head.repo;
            console.log(`##[set-output name=pr_branch;]${prBranch}`);
            console.log(`##[set-output name=pr_remote_url;]${prRemoteUrl}`);
            console.log(`##[set-output name=base_branch;]${baseBranch}`);
      - name: Update PR branch
        run: |
          git remote add pr_remote ${{ steps.fetch_pr_and_target_branch.outputs.pr_remote_url }}
          git fetch pr_remote
          git checkout ${{ steps.fetch_pr_and_target_branch.outputs.pr_branch }}
          git config user.name 'github-actions[bot]'
          git config user.email '41898282+github-actions[bot]@users.noreply.github.com'
          git merge ${{ steps.fetch_pr_and_target_branch.outputs.base_branch }} --no-edit
          git push