[feat] Add automatic backport workflow (#4778)

Author: christian-byrne

.github/workflows/backport.yaml

@@ -0,0 +1,165 @@
+name: Auto Backport
+
+on:
+  pull_request_target:
+    types: [closed]
+    branches: [main]
+
+jobs:
+  backport:
+    if: github.event.pull_request.merged == true && contains(github.event.pull_request.labels.*.name, 'needs-backport')
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
+      issues: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Configure git
+        run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+
+      - name: Extract version labels
+        id: versions
+        run: |
+          # Extract version labels (e.g., "1.24", "1.22")
+          VERSIONS=""
+          LABELS='${{ toJSON(github.event.pull_request.labels) }}'
+          for label in $(echo "$LABELS" | jq -r '.[].name'); do
+            # Match version labels like "1.24" (major.minor only)
+            if [[ "$label" =~ ^[0-9]+\.[0-9]+$ ]]; then
+              # Validate the branch exists before adding to list
+              if git ls-remote --exit-code origin "core/${label}" >/dev/null 2>&1; then
+                VERSIONS="${VERSIONS}${label} "
+              else
+                echo "::warning::Label '${label}' found but branch 'core/${label}' does not exist"
+              fi
+            fi
+          done
+
+          if [ -z "$VERSIONS" ]; then
+            echo "::error::No version labels found (e.g., 1.24, 1.22)"
+            exit 1
+          fi
+
+          echo "versions=${VERSIONS}" >> $GITHUB_OUTPUT
+          echo "Found version labels: ${VERSIONS}"
+
+      - name: Backport commits
+        id: backport
+        env:
+          PR_NUMBER: ${{ github.event.pull_request.number }}
+          PR_TITLE: ${{ github.event.pull_request.title }}
+          MERGE_COMMIT: ${{ github.event.pull_request.merge_commit_sha }}
+        run: |
+          FAILED=""
+          SUCCESS=""
+
+          for version in ${{ steps.versions.outputs.versions }}; do
+            echo "::group::Backporting to core/${version}"
+
+            TARGET_BRANCH="core/${version}"
+            BACKPORT_BRANCH="backport-${PR_NUMBER}-to-${version}"
+
+            # Fetch target branch (fail if doesn't exist)
+            if ! git fetch origin "${TARGET_BRANCH}"; then
+              echo "::error::Target branch ${TARGET_BRANCH} does not exist"
+              FAILED="${FAILED}${version}:branch-missing "
+              echo "::endgroup::"
+              continue
+            fi
+
+            # Create backport branch
+            git checkout -b "${BACKPORT_BRANCH}" "origin/${TARGET_BRANCH}"
+
+            # Try cherry-pick
+            if git cherry-pick "${MERGE_COMMIT}"; then
+              git push origin "${BACKPORT_BRANCH}"
+              SUCCESS="${SUCCESS}${version}:${BACKPORT_BRANCH} "
+              echo "Successfully created backport branch: ${BACKPORT_BRANCH}"
+              # Return to main (keep the branch, we need it for PR)
+              git checkout main
+            else
+              # Get conflict info
+              CONFLICTS=$(git diff --name-only --diff-filter=U | tr '\n' ',')
+              git cherry-pick --abort
+
+              echo "::error::Cherry-pick failed due to conflicts"
+              FAILED="${FAILED}${version}:conflicts:${CONFLICTS} "
+
+              # Clean up the failed branch
+              git checkout main
+              git branch -D "${BACKPORT_BRANCH}"
+            fi
+
+            echo "::endgroup::"
+          done
+
+          echo "success=${SUCCESS}" >> $GITHUB_OUTPUT
+          echo "failed=${FAILED}" >> $GITHUB_OUTPUT
+
+          if [ -n "${FAILED}" ]; then
+            exit 1
+          fi
+
+      - name: Create PR for each successful backport
+        if: steps.backport.outputs.success
+        env:
+          GH_TOKEN: ${{ secrets.PR_GH_TOKEN }}
+        run: |
+          PR_TITLE="${{ github.event.pull_request.title }}"
+          PR_NUMBER="${{ github.event.pull_request.number }}"
+          PR_AUTHOR="${{ github.event.pull_request.user.login }}"
+
+          for backport in ${{ steps.backport.outputs.success }}; do
+            IFS=':' read -r version branch <<< "${backport}"
+
+            if PR_URL=$(gh pr create \
+              --base "core/${version}" \
+              --head "${branch}" \
+              --title "[backport ${version}] ${PR_TITLE}" \
+              --body "Backport of #${PR_NUMBER} to \`core/${version}\`"$'\n\n'"Automatically created by backport workflow." \
+              --label "backport" 2>&1); then
+
+              # Extract PR number from URL
+              PR_NUM=$(echo "${PR_URL}" | grep -o '[0-9]*$')
+
+              if [ -n "${PR_NUM}" ]; then
+                gh pr comment "${PR_NUMBER}" --body "@${PR_AUTHOR} Successfully backported to #${PR_NUM}"
+              fi
+            else
+              echo "::error::Failed to create PR for ${version}: ${PR_URL}"
+              # Still try to comment on the original PR about the failure
+              gh pr comment "${PR_NUMBER}" --body "@${PR_AUTHOR} Backport branch created but PR creation failed for \`core/${version}\`. Please create the PR manually from branch \`${branch}\`"
+            fi
+          done
+
+      - name: Comment on failures
+        if: failure() && steps.backport.outputs.failed
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          PR_NUMBER="${{ github.event.pull_request.number }}"
+          PR_AUTHOR="${{ github.event.pull_request.user.login }}"
+          MERGE_COMMIT="${{ github.event.pull_request.merge_commit_sha }}"
+
+          for failure in ${{ steps.backport.outputs.failed }}; do
+            IFS=':' read -r version reason conflicts <<< "${failure}"
+
+            if [ "${reason}" = "branch-missing" ]; then
+              gh pr comment "${PR_NUMBER}" --body "@${PR_AUTHOR} Backport failed: Branch \`core/${version}\` does not exist"
+
+            elif [ "${reason}" = "conflicts" ]; then
+              # Convert comma-separated conflicts back to newlines for display
+              CONFLICTS_LIST=$(echo "${conflicts}" | tr ',' '\n' | sed 's/^/- /')
+
+              COMMENT_BODY="@${PR_AUTHOR} Backport to \`core/${version}\` failed: Merge conflicts detected."$'\n\n'"Please manually cherry-pick commit \`${MERGE_COMMIT}\` to the \`core/${version}\` branch."$'\n\n'"<details><summary>Conflicting files</summary>"$'\n\n'"${CONFLICTS_LIST}"$'\n\n'"</details>"
+              gh pr comment "${PR_NUMBER}" --body "${COMMENT_BODY}"
+            fi
+          done