name: missing-commits

on:
  push:
    branches:
      # Only check that the branches are up to date when updating the
      # relevant branches.
      - develop
      - release

jobs:
  up_to_date:
    runs-on: ubuntu-24.04
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0
      - name: Check for missing commits
        id: commits
        env:
          SUGGESTION: |

            If you are reading this, then the commits indicated above are
            missing from "develop" and/or "release". Do a reverse-merge
            as soon as possible. See CONTRIBUTING.md for instructions.
        run: |
          set -o pipefail
          # Branches ordered by how "canonical" they are. Every commit in
          # one branch should be in all the branches behind it
          order=( master release develop )
          branches=()
          for branch in "${order[@]}"
          do
            # Check that the branches exist so that this job will work on
            # forked repos, which don't necessarily have master and
            # release branches.
            if git ls-remote --exit-code --heads origin \
              refs/heads/${branch} > /dev/null
            then
              branches+=( origin/${branch} )
            fi
          done

          prior=()
          for branch in "${branches[@]}"
          do
            if [[ ${#prior[@]} -ne 0 ]]
            then
              echo "Checking ${prior[@]} for commits missing from ${branch}"
              git log --oneline --no-merges "${prior[@]}" \
                ^$branch | tee -a "missing-commits.txt"
              echo
            fi
            prior+=( "${branch}" )
          done
          if [[ $( cat missing-commits.txt | wc -l ) -ne 0 ]]
          then
            echo "${SUGGESTION}"
            exit 1
          fi