[.github/scripts/auto-backport.py] improve label logic

In this commit there few improvments to the backport automation process
based on the work done in scylladb/scylla-pkg#4340

1. Create new parameter `--commit` to be use only when `--pull-request`
   is provided
2. Trigger workflow when label is `backport/x.y` only, rather then
   `backport/` as it was defined before. This way we will not trigger to
flow when `backport/x.y-done` was added
3. when running on specific PR with `--pull-request` make sure we don't
   pass an empty commit
4. fix `get_prs_from_commits()` while trying to do `get_commit` on the
   wrong sha1 value

.github/scripts/auto-backport.py

@@ -3,6 +3,7 @@
 import argparse
 import os
 import re
+import sys
 import tempfile
 import logging
 
@@ -12,12 +13,17 @@
 logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(levelname)s - %(message)s')
 
 
+def is_pull_request():
+    return '--pull-request' in sys.argv[1:]
+
+
 def parse_args():
     parser = argparse.ArgumentParser()
     parser.add_argument('--repo', type=str, required=True, help='Github repository name')
     parser.add_argument('--base-branch', type=str, default='refs/heads/next', help='Base branch')
     parser.add_argument('--commits', default=None, type=str, help='Range of promoted commits.')
     parser.add_argument('--pull-request', type=int, help='Pull request number to be backported')
+    parser.add_argument('--head-commit', type=str, required=is_pull_request(), help='The HEAD of target branch after the pull request specified by --pull-request is merged')
     return parser.parse_args()
 
 
@@ -66,6 +72,8 @@ def get_pr_commits(repo, pr, stable_branch, start_commit=None):
                     # So here, we are validating the correct SHA for each commit so we can cherry-pick
                     if promoted_commit.commit.message.startswith(commit_title):
                         commits.append(promoted_commit.sha)
+                else:
+                    commits.append(start_commit)
 
     elif pr.state == 'closed':
         events = pr.get_issue_events()
@@ -104,7 +112,7 @@ def backport(repo, pr, version, commits, backport_base_branch):
 
 def get_prs_from_commits(repo, commits):
     for sha1 in commits:
-        commit = repo.get_commit(sha1)
+        commit = repo.get_commit(sha1.sha)
         for parent in commit.parents:
             prs = repo.get_pulls(state="closed", head=parent.sha)
             if prs:
@@ -143,7 +151,7 @@ def main():
         prs = get_prs_from_commits(repo, commits)
         closed_prs = list(prs)
     if args.pull_request:
-        start_commit = args.commits
+        start_commit = args.head_commit
         pr = repo.get_pull(args.pull_request)
         closed_prs = [pr]
 

.github/workflows/add-label-when-promoted.yaml

@@ -42,8 +42,19 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.AUTO_BACKPORT_TOKEN }}
         run: python .github/scripts/auto-backport.py --repo ${{ github.repository }} --base-branch ${{ github.ref }} --commits ${{ github.event.before }}..${{ github.sha }}
+      - name: Check if label starts with 'backport/' and contains digits
+        id: check_label
+        run: |
+          label_name="${{ github.event.label.name }}"
+          if [[ "$label_name" =~ ^backport/[0-9]+\.[0-9]+$ ]]; then
+            echo "Label matches backport/X.X pattern."
+            echo "backport_label=true" >> $GITHUB_OUTPUT
+          else
+            echo "Label does not match the required pattern."
+            echo "backport_label=false" >> $GITHUB_OUTPUT
+          fi
       - name: Run auto-backport.py when label was added
-        if: github.event_name == 'pull_request_target' && startsWith(github.event.label.name, 'backport/') && (github.event.pull_request.state == 'closed' && github.event.pull_request.merged == true)
+        if: github.event_name == 'pull_request_target' && steps.check_label.outputs.backport_label == 'true' && (github.event.pull_request.state == 'closed' && github.event.pull_request.merged == true)
         env:
           GITHUB_TOKEN: ${{ secrets.AUTO_BACKPORT_TOKEN }}
-        run: python .github/scripts/auto-backport.py --repo ${{ github.repository }} --base-branch ${{ github.ref }} --pull-request ${{ github.event.pull_request.number }} --commits ${{ github.sha }}
+        run: python .github/scripts/auto-backport.py --repo ${{ github.repository }} --base-branch ${{ github.ref }} --pull-request ${{ github.event.pull_request.number }} --head-commit ${{ github.sha }}