Don't merge PR unless it has "awaiting merge" label (#112)

Change the behavior for when deciding when miss-islington
should merge the PR.

Previously it checks if the PR has one core dev who approved the PR.
But that is unreliable because the review may be dismissed later,
or another core dev might decide not to backport the PR anymore.

The "awaiting merge" label is a better indicator that the PR
is ready for merge.

Adjust tests.

Fixes python/miss-islington#62

miss_islington/status_change.py

@@ -22,13 +22,11 @@ async def check_status(event, gh, *args, **kwargs):
         await check_ci_status_and_approval(gh, sha, leave_comment=True)
 
 
-@router.register("pull_request_review", action="submitted")
+@router.register("pull_request", action="labeled")
 async def pr_reviewed(event, gh, *args, **kwargs):
     if event.data["pull_request"]["user"]["login"] == "miss-islington":
-        reviewer = event.data["review"]["user"]["login"]
-        approved = event.data["review"]["state"] == "approved"
-        if approved and await util.is_core_dev(gh, reviewer):
-            sha = event.data["review"]["commit_id"]
+        if util.pr_is_awaiting_merge(event.data["pull_request"]["labels"]):
+            sha = event.data["pull_request"]["head"]["sha"]
             await check_ci_status_and_approval(gh, sha)
 
 
@@ -75,14 +73,12 @@ async def check_ci_status_and_approval(gh, sha, leave_comment=False):
                             )
 
                         if result["state"] == "success":
-                            async for review in gh.getiter(
-                                f"/repos/python/cpython/pulls/{pr_number}/reviews"
-                            ):
-                                reviewer = review["user"]["login"]
-                                approved = review["state"].lower() == "approved"
-                                if approved and await util.is_core_dev(gh, reviewer):
-                                    await merge_pr(gh, pr_number, sha)
-                                    break
+                            pr = await gh.getitem(
+                                f"/repos/python/cpython/pulls/{pr_number}"
+                            )
+                            if util.pr_is_awaiting_merge(pr["labels"]):
+                                await merge_pr(gh, pr_number, sha)
+                                break
 
 
 async def merge_pr(gh, pr_number, sha):

miss_islington/util.py

@@ -104,3 +104,10 @@ async def is_core_dev(gh, username):
         raise
     else:
         return True
+
+
+def pr_is_awaiting_merge(pr_labels):
+    for label in pr_labels:
+        if label["name"] == "awaiting merge":
+            return True
+    return False

tests/test_delete_branch.py

@@ -7,10 +7,6 @@ class FakeGH:
     def __init__(self):
         self.post_data = None
 
-    async def post(self, url, *, data):
-        self.post_url = url
-        self.post_data = data
-
     async def delete(self, url):
         self.delete_url = url