action.yml

name: 'Commit range'
description: 'Determine commit range'
outputs:
  commit-range:
    description: 'Range of commits in this run'
    value: ${{ steps.commit-range.outputs.commit-range }}
runs:
  using: "composite"
  steps:
    - name: Commit range
      id: commit-range
      env:
        commit_list: ${{ toJson(github.event.commits) }} # Doing this inside run doesn't work because of piping
      run: |
        if [ "${GITHUB_EVENT_NAME}" == "push" ]
        then
          NUMBER_COMMITS=$(echo "${commit_list}" | jq 'length')
          if [ ${NUMBER_COMMITS} -le 1 ]
          then
            COMMIT_RANGE=""
          else
            OLDEST=$(echo "${commit_list}" | jq 'first.id' | tr -d '"')
            NEWEST=$(echo "${commit_list}" | jq 'last.id' | tr -d '"')
            OLDEST_PARENTS=($(git show --no-patch --format="%P" ${OLDEST}))
            NUMBER_OLDEST_PARENTS=${#OLDEST_PARENTS[@]}
            COMMIT_RANGE="${OLDEST}^${NUMBER_OLDEST_PARENTS}...${NEWEST}" # Take second parent if possible, see https://stackoverflow.com/a/2222920
          fi
        elif [ "${GITHUB_EVENT_NAME}" == "pull_request" ]
        then
          OLDEST=${{ github.event.pull_request.base.sha }}
          NEWEST=${{ github.event.pull_request.head.sha }}
          COMMIT_RANGE="${OLDEST}...${NEWEST}"
        fi
        echo -e "\e[35;1m COMMIT_RANGE = ${COMMIT_RANGE} \e[0m"
        echo "commit-range=${COMMIT_RANGE}" >> $GITHUB_OUTPUT
      shell: bash