Add 'Backport Pending' label whenever a PR merges with master

.github/scripts/backport-pending.py

@@ -0,0 +1,128 @@
+import json
+import os
+import re
+import sys
+import urllib.error
+import urllib.request
+from dataclasses import dataclass
+from typing import List
+
+VERSION_LABEL_RE = re.compile(r"^v\d{1,2}$|(^v\d{1,2}\.\d{1,2}$)")
+PENDING_LABEL = "backport pending"
+PENDING_LABEL_COLOR = "fff2bf"
+
+
+@dataclass
+class PRInfo:
+    number: int
+    labels: List[str]
+
+
+def load_event() -> dict:
+    path = os.environ.get("GITHUB_EVENT_PATH")
+    if not path or not os.path.exists(path):
+        print("::warning::GITHUB_EVENT_PATH not set or file missing; nothing to do", file=sys.stderr)
+        return {}
+    with open(path, "r", encoding="utf-8") as f:
+        return json.load(f)
+
+
+def extract_pr(event: dict) -> PRInfo | None:
+    pr = event.get("pull_request")
+    if not pr:
+        return None
+    labels = [lbl.get("name", "") for lbl in pr.get("labels", [])]
+    return PRInfo(number=pr["number"], labels=labels)
+
+
+def needs_pending_label(info: PRInfo) -> bool:
+    has_version_label = any(VERSION_LABEL_RE.match(l) for l in info.labels)
+    has_pending = PENDING_LABEL in info.labels
+    return not (has_version_label and has_pending)
+
+
+def add_label(pr_number: int, label: str) -> None:
+    repo = os.environ.get("GITHUB_REPOSITORY")
+    token = os.environ.get("BACKPORT_TOKEN")
+    if not repo or not token:
+        print("::error::Missing GITHUB_REPOSITORY or BACKPORT_TOKEN", file=sys.stderr)
+        sys.exit(1)
+    owner, repo_name = repo.split("/", 1)
+    # First ensure the label exists (create or update color/description)
+    ensure_label(owner, repo_name, token)
+    url = f"https://api.github.com/repos/{owner}/{repo_name}/issues/{pr_number}/labels"
+    body = json.dumps({"labels": [label]}).encode()
+    # POST adds label(s) keeping old ones
+    req = urllib.request.Request(url, data=body, method="POST")
+    req.add_header("Authorization", f"Bearer {token}")
+    req.add_header("Accept", "application/vnd.github+json")
+    try:
+        with urllib.request.urlopen(req) as resp:
+            if resp.status not in (200, 201):
+                print(f"::error::Failed to add label: HTTP {resp.status}", file=sys.stderr)
+                sys.exit(1)
+            print(f"Added label '{label}' to PR #{pr_number}")
+    except urllib.error.HTTPError as e:
+        print(f"::error::HTTP error adding label: {e.code} {e.reason}", file=sys.stderr)
+        sys.exit(1)
+    except Exception as e:
+        print(f"::error::Unexpected error adding label: {e}", file=sys.stderr)
+        sys.exit(1)
+
+
+def ensure_label(owner: str, repo_name: str, token: str) -> None:
+    """Create the Backport Pending label if it does not already exist."""
+    label_api = f"https://api.github.com/repos/{owner}/{repo_name}/labels/{PENDING_LABEL.replace(' ', '%20')}"
+    get_req = urllib.request.Request(label_api, method="GET")
+    get_req.add_header("Authorization", f"Bearer {token}")
+    get_req.add_header("Accept", "application/vnd.github+json")
+    try:
+        with urllib.request.urlopen(get_req) as resp:
+            if resp.status == 200:
+                return
+    except urllib.error.HTTPError as e:
+        print(f"::warning::Failed to check label existence ({e.code})")
+        return
+    create_api = f"https://api.github.com/repos/{owner}/{repo_name}/labels"
+    body = json.dumps({"name": PENDING_LABEL, "color": PENDING_LABEL_COLOR}).encode()
+    req = urllib.request.Request(create_api, data=body, method="POST")
+    req.add_header("Authorization", f"Bearer {token}")
+    req.add_header("Accept", "application/vnd.github+json")
+    try:
+        with urllib.request.urlopen(req) as resp:
+            if resp.status not in (200, 201):
+                print(f"::warning::Failed to create label (status {resp.status})")
+    except Exception as e:
+        print(f"::warning::Error creating label: {e}")
+
+
+"""
+Label a PR with 'Backport pending' if it has no version label.
+
+Expected environment:
+  GITHUB_EVENT_PATH: Path to the event JSON (GitHub sets this automatically)
+  GITHUB_REPOSITORY: owner/repo
+  BACKPORT_TOKEN: token with repo:issues scope (use BACKPORT_TOKEN or a PAT)
+
+This script is idempotent: if the PR already has a version label (vX.Y) or already
+has the 'Backport Pending' label, it exits without error.
+"""
+
+
+def main() -> int:
+    event = load_event()
+    if not event:
+        return 0
+    info = extract_pr(event)
+    if not info:
+        print("No pull_request object in event; skipping")
+        return 0
+    if needs_pending_label(info):
+        add_label(info.number, PENDING_LABEL)
+    else:
+        print("No label needed (either PR has version label or already pending)")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

.github/workflows/backport.yml

@@ -5,6 +5,9 @@ on:
     branches: ['master']
     types: ["labeled", "closed"]
 
+env:
+  BACKPORT_TOKEN: ${{ secrets.BACKPORT_TOKEN }}
+
 jobs:
   backport:
     name: Backport PR
@@ -17,7 +20,11 @@ jobs:
         uses: sorenlouv/backport-github-action@ad888e978060bc1b2798690dd9d03c4036560947  # v9.5.1
         continue-on-error: true
         with:
-          github_token: ${{ secrets.BACKPORT_TOKEN }}
+          github_token: $BACKPORT_TOKEN
+
+      - uses: actions/checkout@v4
+      - name: Label PR if needed
+        run: python .github/scripts/backport-pending.py
 
       - name: Info log
         if: ${{ success() }}