Merge pull request #9405 from bluetech/ci-backport

ci: add a workflow for backporting to other branches

Author: bluetech

.github/workflows/backport.yml

@@ -0,0 +1,45 @@
+name: backport
+
+on:
+  pull_request:
+    types: [labeled]
+
+# Set permissions at the job level.
+permissions: {}
+
+jobs:
+  backport:
+    if: ${{ startsWith(github.event.label.name, 'backport ') }}
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
+
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
+        persist-credentials: true
+
+    - name: Create backport PR
+      run: |
+        set -eux
+
+        git config --global user.name "pytest bot"
+        git config --global user.email "[email protected]"
+
+        label='${{ github.event.label.name }}'
+        target_branch="${label#backport }"
+        backport_branch=backport-${{ github.event.number }}-to-"${target_branch}"
+        subject="[$target_branch] $(gh pr view --json title -q .title ${{ github.event.number }})"
+
+        git checkout origin/"${target_branch}" -b "${backport_branch}"
+        git cherry-pick -x --mainline 1 ${{ github.event.pull_request.merge_commit_sha }}
+        git commit --amend --message "$subject"
+        git push --set-upstream origin --force-with-lease "${backport_branch}"
+        gh pr create \
+          --base "${target_branch}" \
+          --title "${subject}" \
+          --body "Backport of PR #${{ github.event.number }} to $target_branch branch. PR created by backport workflow."
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

CONTRIBUTING.rst

@@ -391,6 +391,13 @@ actual latest release). The procedure for this is:
    request, as described above. An exception to this is if the bug fix is not
    applicable to ``main`` anymore.
 
+Automatic method:
+
+Add a ``backport 1.2.x`` label to the PR you want to backport. This will create
+a backport PR against the ``1.2.x`` branch.
+
+Manual method:
+
 #. ``git checkout origin/1.2.x -b backport-XXXX`` # use the main PR number here
 
 #. Locate the merge commit on the PR, in the *merged* message, for example: