GitHub Action to merge commits > n-days from work branch to trunk

auto-merge.yml

# GitHub workflow to merge commits > n-days from a work branch to trunk.
#
# this is a low-overhead workflow implementing a time lock intended to
# allow people to rebase on a work branch but avoid rebases on trunk.
#
# the workflow is scheduled to fast-forward the target branch to the
# most recent commit in the source branch that is older than n-days.
#
# if there is a commit older than n-days common to both branches, the
# action will do nothing. the action will error in the case of commits
# in the source branch older than n-days that can't be fast forwarded.
#
# to use this workflow, one must create a secret named REPO_TOKEN
# on the repository in question, which itself contains a personal
# access token with repo write permissions.
#
# environment variables:
#
# - source_ref : source branch to merge from
# - target_ref : target branch to fast forward
# - date_spec  : date expression specifying the time period

name: Merge commits > n-days from work branch to trunk
on:
  schedule:
    - cron:  '5 12 * * *'
jobs:
  build:
    runs-on: ubuntu-latest
    env:
      source_ref: work
      target_ref: trunk
      date_spec: '-14 day'
    steps:
    - name: Checkout source branch
      uses: actions/checkout@v2
      with:
        ref: ${{ env.target_ref }}
        persist-credentials: false
    - name: Find recent commit
      run: |
        git fetch
        echo "commit_hash=$(git log -n1 --no-show-signature --format=format:%H \
            --before=$(date --date="$(date) ${{ env.date_spec }}" +%Y-%m-%d) \
             origin/${{ env.source_ref }})" >> $GITHUB_ENV
    - name: Merge recent commits
      run: |
        git merge --ff-only ${{ env.commit_hash }}
    - name: Push changes
      uses: ad-m/github-push-action@master
      with:
        github_token: ${{ secrets.REPO_TOKEN }}
        branch: ${{ env.target_ref }}