GitHub Actions workflow to rewrite cherry-picked commit messages, preserving original authors and referencing the source repository.

backport-rewrite.yml

name: Reference backported commits

on:
  push:
    branches:
      - backport-*
  pull_request:

jobs:
  rewrite-messages:
    runs-on: ubuntu-latest
    environment: dev
    env:
      ORIGINAL_REPO: ${{ vars.ORIGINAL_REPO }}  # Configurable repo name

    steps:
      - name: Checkout the current repository
        uses: actions/checkout@v4
        with:
          fetch-depth: 0  # Ensure full commit history

      - name: Checkout original repository
        uses: actions/checkout@v4
        with:
          repository: ${{ env.ORIGINAL_REPO }}
          path: original_repo
          fetch-depth: 0  # Ensure full history for commit lookup
          ref: main

      - name: Find All New Commits
        id: find_commits
        run: |
          BEFORE_COMMIT="${{ github.event.before }}"

          # Check if BEFORE_COMMIT exists in local history
          if ! git cat-file -e "$BEFORE_COMMIT^{commit}" 2>/dev/null; then
            echo "WARNING: BEFORE_COMMIT ($BEFORE_COMMIT) not found locally."
            echo "Fetching full history for BEFORE_COMMIT from origin..."
          
            # Fetch full history for BEFORE_COMMIT
            git fetch origin "$BEFORE_COMMIT" || true
          fi

          # Check again after fetch
          if git cat-file -e "$BEFORE_COMMIT^{commit}" 2>/dev/null; then
            echo "Successfully fetched BEFORE_COMMIT."
          
            if git merge-base --is-ancestor "$BEFORE_COMMIT" HEAD; then
              BASE_COMMIT=$BEFORE_COMMIT
              echo "Detected normal push. Using BEFORE_COMMIT as BASE_COMMIT."
            else
              BASE_COMMIT=$(git merge-base HEAD "$BEFORE_COMMIT")
              echo "Detected force push. Using nearest merge-base as BASE_COMMIT."
            fi
          else
            echo "ERROR: BEFORE_COMMIT ($BEFORE_COMMIT) is missing even after fetch."
            echo "Falling back to origin/main."
          
            # Use a fallback base commit
            BASE_COMMIT=$(git merge-base HEAD origin/main)
          fi

          echo "Using BASE_COMMIT: $BASE_COMMIT"

          git rev-list --reverse "$BASE_COMMIT"..HEAD > new_commits.txt

      - name: Process Each Commit
        run: |
          if [ ! -s new_commits.txt ]; then
            echo "No new commits to process. Skipping."
            exit 0
          fi

          while IFS= read -r COMMIT; do
            COMMIT_MSG=$(git log -1 --format='%B' "$COMMIT")

            echo "Processing commit: $COMMIT"
            echo "Message: $COMMIT_MSG"
          
            CHERRY_PICKED_COMMIT=$(echo "$COMMIT_MSG" | sed -nE 's/.*\(cherry picked from commit ([0-9a-f]+)\).*/\1/p')

            if [ -n "$CHERRY_PICKED_COMMIT" ]; then
              echo "Processing cherry-picked commit: $CHERRY_PICKED_COMMIT"

              if git -C original_repo cat-file -e "$CHERRY_PICKED_COMMIT^{commit}" 2>/dev/null; then
                echo "Commit exists in $ORIGINAL_REPO. Rewriting message and author."
          
                ORIGINAL_AUTHOR_NAME=$(git -C original_repo log -1 --format="%an" "$CHERRY_PICKED_COMMIT")
                ORIGINAL_AUTHOR_EMAIL=$(git -C original_repo log -1 --format="%ae" "$CHERRY_PICKED_COMMIT")
          
                echo "Original Author: $ORIGINAL_AUTHOR_NAME <$ORIGINAL_AUTHOR_EMAIL>"
          
                NEW_MSG=$(echo "$COMMIT_MSG" | sed -E "s/\(cherry picked from commit ([0-9a-f]+)\)/\(Backported from $ORIGINAL_REPO@\1\)/")
          
                git commit --amend --author="$ORIGINAL_AUTHOR_NAME <$ORIGINAL_AUTHOR_EMAIL>" -m "$NEW_MSG" --no-edit
              else
                echo "Skipping: Commit $CHERRY_PICKED_COMMIT not found in $ORIGINAL_REPO."
              fi
            fi
          done < new_commits.txt

      - name: Force Push Changes
        run: |
          if git diff --quiet HEAD@{1} HEAD; then
            echo "No commits were changed. Skipping force push."
          else
            echo "Commits were modified. Force pushing..."
            git push origin HEAD --force
          fi