backport-to-branch.yml

name: Backport on Comment

# Example use: /backport llvm_release_190
on:
  issue_comment:
    types: [created]

permissions:
  contents: write
  pull-requests: write
  issues: read

jobs:
  backport:
    if: >
      github.event.issue.pull_request != null &&
      startsWith(github.event.comment.body, '/backport ')
    runs-on: ubuntu-latest

    steps:
      - name: Checkout repository
        uses: actions/checkout@v5
        with:
          fetch-depth: 0

      - name: Configure Git
        run: |
          git config user.name "${{ github.actor }}"
          git config user.email "${{ github.actor }}@users.noreply.github.com"

      - name: Ensure PR is merged
        uses: actions/github-script@v7
        with:
          script: |
            const pr = await github.rest.pulls.get({
              owner: context.repo.owner,
              repo: context.repo.repo,
              pull_number: context.issue.number
            });
            if (!pr.data.merged) {
              core.setFailed('PR #' + context.issue.number + ' is not merged.');
            }

      - name: Parse backport command
        uses: actions/github-script@v7
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          result-encoding: string
          script: |
            const body = context.payload.comment.body.trim();
            const msg = body.match(/^\/backport\s+(llvm_release_[0-9]+)$/);
            if (!msg) {
              await github.rest.issues.createComment({
                owner: context.repo.owner,
                repo:  context.repo.repo,
                issue_number: context.issue.number,
                body: 'Invalid backport command. Expected `/backport llvm_release_<digits>`'
              });
              throw new Error('Invalid backport command.');
            }
            core.exportVariable('TARGET', msg[1]);

      - name: Notify attempt
        uses: actions/github-script@v7
        with:
          script: |
            const target = process.env.TARGET;
            await github.rest.issues.createComment({
              owner: context.repo.owner,
              repo: context.repo.repo,
              issue_number: context.issue.number,
              body: `Attempting to create backport to \`${target}\`...`
            });

      - name: Create backport branch
        run: |
          git fetch origin ${{ env.TARGET }}:${{ env.TARGET }}
          git checkout -b backport/pr-${{ github.event.issue.number }}-to-${{ env.TARGET }} origin/${{ env.TARGET }}

      - name: Get commit sha
        id: merge_sha
        uses: actions/github-script@v7
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          result-encoding: string
          script: |
            const pr = await github.rest.pulls.get({
              owner: context.repo.owner,
              repo: context.repo.repo,
              pull_number: context.issue.number
            });
            // FIXME: handle PRs that are merged with "Rebase and Merge" strategy
            const sha = pr.data.merge_commit_sha;
            if (!sha) {
              throw new Error(`No merge_commit_sha found.`);
            }
            return sha;

      - name: Cherry-pick commit
        id: cherry
        run: |
          conflict=false
          SHA="${{ steps.merge_sha.outputs.result }}"
          echo "Cherry-picking squash-merge commit $SHA"
          if git cherry-pick "$SHA"; then
            echo "Cherry-picked $SHA"
          else
            echo "Conflict on $SHA"
            conflict=true
            echo "CONFLICT_SHA=$SHA" >> $GITHUB_ENV
          fi
          echo "CONFLICT=$conflict" >> $GITHUB_ENV

      - name: Notify conflict
        if: env.CONFLICT == 'true'
        uses: actions/github-script@v7
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          script: |
            const sha = process.env.CONFLICT_SHA;
            const target = process.env.TARGET;
            await github.rest.issues.createComment({
              owner: context.repo.owner,
              repo: context.repo.repo,
              issue_number: context.issue.number,
              body: `Backport to \`${target}\` failed due to conflicts on commit \`${sha}\`. Please backport manually.`
            });

      - name: Stop on conflict
        if: env.CONFLICT == 'true'
        run: exit 0

      - name: Push backport branch
        if: env.CONFLICT == 'false'
        run: git push --set-upstream origin HEAD

      - name: Prepare PR
        if: env.CONFLICT == 'false'
        id: prinfo
        run: |
          echo "BODY<<EOF" >> $GITHUB_ENV
          echo "Backport of PR #${{ github.event.issue.number }} into \`${{ env.TARGET }}\`." >> $GITHUB_ENV
          echo "" >> $GITHUB_ENV
          echo "All commits applied cleanly." >> $GITHUB_ENV
          echo "EOF" >> $GITHUB_ENV
          echo "LABELS=backport" >> $GITHUB_ENV

      - name: Create Pull Request
        if: env.CONFLICT == 'false'
        id: create_pr
        uses: actions/github-script@v7
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          result-encoding: string
          script: |
            const {data: pr} = await github.rest.pulls.create({
              owner: context.repo.owner,
              repo: context.repo.repo,
              head: `backport/pr-${context.issue.number}-to-${process.env.TARGET}`,
              base: process.env.TARGET,
              title: `[Backport to ${process.env.TARGET}] ${context.payload.issue.title}`,
              body: process.env.BODY
            });
            return pr.html_url;

      - name: Notify success
        if: env.CONFLICT == 'false'
        uses: actions/github-script@v7
        env:
          PR_URL: ${{ steps.create_pr.outputs.result }}
        with:
          script: |
            const target = process.env.TARGET;
            await github.rest.issues.createComment({
              owner: context.repo.owner,
              repo: context.repo.repo,
              issue_number: context.issue.number,
              body: `Success. Backport PR created: ${process.env.PR_URL}`
            });

      - name: Notify workflows
        if: env.CONFLICT == 'false'
        uses: peter-evans/repository-dispatch@v3
        with:
          token: ${{ secrets.GITHUB_TOKEN }}
          event-type: backport-complete