blathers-backport.yml

name: Blathers Backport

on:
  repository_dispatch:
    types: [backport]

jobs:
  backport:
    runs-on: ubuntu-latest
    timeout-minutes: 30
    permissions:
      contents: write
      pull-requests: write
      issues: write

    steps:
      - name: Generate GitHub App token
        id: app-token
        uses: actions/create-github-app-token@v1
        with:
          app-id: ${{ secrets.BLATHERS_APP_ID }}
          private-key: ${{ secrets.BLATHERS_PRIVATE_KEY }}

      - uses: actions/checkout@v4
        with:
          fetch-depth: 0
          token: ${{ steps.app-token.outputs.token }}

      - name: Configure git identity
        run: |
          git config user.name "blathers-crl[bot]"
          git config user.email "blathers-crl[bot]@users.noreply.github.com"

      - name: Backport PR
        env:
          GH_TOKEN: ${{ steps.app-token.outputs.token }}
          PR_NUMBER: ${{ github.event.client_payload.pr_number }}
          BRANCHES: ${{ github.event.client_payload.branches }}
          PR_AUTHOR: ${{ github.event.client_payload.pr_author }}
          RUN_URL: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}
        run: |
          set -euo pipefail

          # Fetch PR title and body for use in backport PRs.
          PR_TITLE=$(gh pr view "$PR_NUMBER" --json title --jq '.title')
          PR_BODY=$(gh pr view "$PR_NUMBER" --json body --jq '.body')

          # Get commit SHAs from the merged PR.
          COMMIT_SHAS=$(gh pr view "$PR_NUMBER" --json commits --jq '.commits[].oid')
          COMMIT_COUNT=$(echo "$COMMIT_SHAS" | wc -l | tr -d ' ')

          # Collect reviewers from the original PR.
          REVIEWERS=$(gh pr view "$PR_NUMBER" --json reviews --jq '[.reviews[].author.login] | unique | join(",")')

          FAILED_BRANCHES=""
          SUCCEEDED_BRANCHES=""

          for BRANCH in $BRANCHES; do
            echo "=== Backporting to $BRANCH ==="

            # Normalize branch name: try as-is first, then with release- prefix.
            # Also strip .x suffix (backport labels use e.g. "24.1.x").
            TARGET_BRANCH="${BRANCH%.x}"
            if ! git rev-parse --verify "origin/$TARGET_BRANCH" >/dev/null 2>&1; then
              TARGET_BRANCH="release-$TARGET_BRANCH"
              if ! git rev-parse --verify "origin/$TARGET_BRANCH" >/dev/null 2>&1; then
                echo "::error::Branch $BRANCH not found (tried $BRANCH and release-${BRANCH%.x})"
                FAILED_BRANCHES="$FAILED_BRANCHES $BRANCH"
                continue
              fi
            fi

            BACKPORT_BRANCH="blathers/backport-${TARGET_BRANCH}-${PR_NUMBER}"

            # Clean up any existing backport branch.
            git branch -D "$BACKPORT_BRANCH" 2>/dev/null || true
            git push origin --delete "$BACKPORT_BRANCH" 2>/dev/null || true

            # Create backport branch from target.
            git checkout -b "$BACKPORT_BRANCH" "origin/$TARGET_BRANCH"

            # Cherry-pick all commits from the PR.
            CHERRY_PICK_FAILED=false
            for SHA in $COMMIT_SHAS; do
              if ! git cherry-pick "$SHA"; then
                echo "::error::Cherry-pick of $SHA failed on branch $TARGET_BRANCH"
                git cherry-pick --abort 2>/dev/null || true
                CHERRY_PICK_FAILED=true
                break
              fi
            done

            if [ "$CHERRY_PICK_FAILED" = "true" ]; then
              FAILED_BRANCHES="$FAILED_BRANCHES $BRANCH"
              git checkout -f HEAD 2>/dev/null || true
              continue
            fi

            # Push the backport branch.
            if ! git push origin "$BACKPORT_BRANCH"; then
              echo "::error::Failed to push branch $BACKPORT_BRANCH"
              FAILED_BRANCHES="$FAILED_BRANCHES $BRANCH"
              continue
            fi

            # Transform version-specific closing keywords.
            # e.g. "Fixes-26.1 #159676" -> "Fixes #159676" when targeting release-26.1.
            VERSION="${TARGET_BRANCH#release-}"
            ESCAPED_VERSION=$(echo "$VERSION" | sed 's/\./\\./g')
            TRANSFORMED_BODY=$(echo "$PR_BODY" | sed -E "s/(Fixes|Closes|Resolves|Addresses)-${ESCAPED_VERSION}:?[[:space:]]+/\1 /gi")

            # Create backport PR.
            BACKPORT_PR_URL=$(gh pr create \
              --base "$TARGET_BRANCH" \
              --head "$BACKPORT_BRANCH" \
              --title "${TARGET_BRANCH}: ${PR_TITLE}" \
              --body "$(cat <<EOF
          Backport ${COMMIT_COUNT}/${COMMIT_COUNT} commits from #${PR_NUMBER} on behalf of @${PR_AUTHOR}.

          ----

          ${TRANSFORMED_BODY}

          ----

          Release justification:
          EOF
          )")

            if [ -z "$BACKPORT_PR_URL" ]; then
              echo "::error::Failed to create PR for branch $TARGET_BRANCH"
              FAILED_BRANCHES="$FAILED_BRANCHES $BRANCH"
              continue
            fi

            BACKPORT_PR_NUMBER=$(echo "$BACKPORT_PR_URL" | grep -oE '[0-9]+$')

            # Add labels.
            gh pr edit "$BACKPORT_PR_NUMBER" --add-label "O-robot,blathers-backport"

            # Remove "backport-failed" label if it was previously added by a failed attempt.
            gh pr edit "$PR_NUMBER" --remove-label "backport-failed" || true

            # Add assignee (original PR author).
            gh pr edit "$BACKPORT_PR_NUMBER" --add-assignee "$PR_AUTHOR" || true

            # Request reviewers from the original PR.
            if [ -n "$REVIEWERS" ]; then
              gh pr edit "$BACKPORT_PR_NUMBER" --add-reviewer "$REVIEWERS" || true
            fi

            SUCCEEDED_BRANCHES="$SUCCEEDED_BRANCHES $BRANCH"
            echo "=== Successfully created backport PR: $BACKPORT_PR_URL ==="
          done

          # Post results on the original PR.
          if [ -n "$(echo "$SUCCEEDED_BRANCHES" | xargs)" ]; then
            SUCCESS_MSG="Successfully created backport PRs for:$SUCCEEDED_BRANCHES"
            if [ -n "$(echo "$FAILED_BRANCHES" | xargs)" ]; then
              SUCCESS_MSG="$SUCCESS_MSG

          Failed to backport to:$FAILED_BRANCHES
          Please create these backports manually using the [backport tool](https://github.com/cockroachdb/backport).

          [See action run for details]($RUN_URL)."
            fi
            gh pr comment "$PR_NUMBER" --body "$SUCCESS_MSG"
          fi

          if [ -n "$(echo "$FAILED_BRANCHES" | xargs)" ]; then
            if [ -z "$(echo "$SUCCEEDED_BRANCHES" | xargs)" ]; then
              gh pr comment "$PR_NUMBER" --body "$(cat <<EOF
          Encountered an error creating backports. Some common things that can go wrong:
          1. The backport branch might have already existed.
          2. There was a merge conflict.
          3. The backport branch contained merge commits.

          You might need to create your backport manually using the [backport](https://github.com/cockroachdb/backport) tool.

          [See action run for details]($RUN_URL).

          ----

          Failed branches:$FAILED_BRANCHES
          EOF
          )"
            fi
            gh issue edit "$PR_NUMBER" --add-label "backport-failed" || true
            exit 1
          fi