Git rebase reminder for CircleCI

rebase-reminder-circleci-job.yml

rebase-reminder:
    docker:
      # specify the version you desire here
       - image: circleci/ruby:2.4.1-node-browsers
         environment:
           RAILS_ENV: test
           PGHOST: 127.0.0.1
           PGUSER: root
           PUBLIC_HOST: https://example.org

    working_directory: ~/repo

    steps:
      - checkout
      - run:
          name: Check if rebase is required
          command: |
            mkdir -p /tmp/test-results/rebase-status

            PR_NUMBER=${CI_PULL_REQUEST//*pull\//}
            CI_HEAD_BRANCH=${CI_HEAD_BRANCH-"master"}
            err=0

            # Set git identity
            git config user.email "circleci@wework.com"
            git config user.name "circleci"

            if [ -z "$PR_NUMBER" ]; then
                echo --> Not merging with master
                exit
            fi

            # Update the CI_HEAD_BRANCH (ie. master/develop)
            (set -x && git fetch -f origin $CI_HEAD_BRANCH) || err=$?

            # Find current head from the HEAD_BRANCH
            # Thanks to this: https://stackoverflow.com/questions/30177047/how-to-pragmatically-check-with-bash-script-if-a-branch-in-git-needs-to-be-rebas
            hash1=$(git show-ref --heads -s $CI_HEAD_BRANCH)
            hash2=$(git merge-base $CI_HEAD_BRANCH $CIRCLE_BRANCH)

            if [[ "${hash1}" = "${hash2}" ]]; then
              echo "OK: Already rebased" > /tmp/test-results/rebase-status/rebase-status.txt
            else
              echo "FAIL: Rebase is required" > /tmp/test-results/rebase-status/rebase-status.txt
              exit 1
            fi

      # collect reports
      - store_test_results:
          path: /tmp/test-results
      - store_artifacts:
          path: /tmp/test-results