[llvm] [GitHub][workflows] Ask reviewers to merge PRs when author can not (PR #81142)

[Tom Stellard via llvm-commits]

================
@@ -298,6 +299,76 @@ def run(self) -> bool:
         return True
 
 
+class PRMergeOnBehalfInformation:
+    COMMENT_TAG = "<!--LLVM MERGE ON BEHALF INFORMATION COMMENT-->\n"
+
+    def __init__(self, token: str, repo: str, pr_number: int, author: str):
+        repo = github.Github(token).get_repo(repo)
+        self.pr = repo.get_issue(pr_number).as_pull_request()
+        self.author = author
+        self.repo = repo
+        self.token = token
+
+    def author_has_push_permission(self):
+        # https://docs.github.com/en/rest/collaborators/collaborators?apiVersion=2022-11-28#get-repository-permissions-for-a-user
+        response = requests.get(
+            # Where repo is "owner/repo-name".
+            f"https://api.github.com/repos/{self.repo}/collaborators/{self.author}/permission",
+            headers={
+                "Accept": "application/vnd.github+json",
+                "Authorization": f"Bearer {self.token}",
+                "X-GitHub-Api-Version": "2022-11-28",
+            },
+        )
+
+        # 404 means this user is not a collaborator.
+        if response.status_code == 404:
+            # Does not have push permission if not a collaborator.
+            return False
+        # User is a collaborator.
+        elif response.status_code == 200:
+            user_details = json.loads(response.text)
+            user = user_details["user"]
+
+            # We may have a list of permissions.
+            if permissions := user.get("permissions"):
+                return permissions["pull"]
+            else:
+                # Otherwise we can always fall back to the permission
+                # on the top level object. The other permissions "read" and
+                # "none" cannot push changes.
+                return user_details["permisson"] in ["admin", "write"]
+        else:
+            # Something went wrong, log and carry on.
+            print("Unexpected response code", response.status_code)
+            # Assume they do have push permissions, so that we don't spam
+            # PRs with comments if there are API problems.
+            return True
+
+    def run(self) -> bool:
+        # A review can be approved more than once, only comment the first time.
+        # Doing this check first as I'm assuming we get the comment data "free" in
+        # terms of API cost.
----------------
tstellar wrote:

If it's not free, then the `self.author_has_push_permission()` check should be first.

https://github.com/llvm/llvm-project/pull/81142