Don't drop user dir deltas when server leaves room

Fix a long-standing bug where a batch of user directory changes would be
silently dropped if the server left a room early in the batch.

Author: David Robertson

synapse/handlers/user_directory.py

@@ -220,7 +220,7 @@ async def _handle_deltas(self, deltas: List[Dict[str, Any]]) -> None:
 
                         for user_id in user_ids:
                             await self._handle_remove_user(room_id, user_id)
-                        return
+                        continue
                     else:
                         logger.debug("Server is still in room: %r", room_id)
 

tests/handlers/test_user_directory.py

@@ -363,6 +363,45 @@ def test_reactivation_makes_regular_user_searchable(self) -> None:
         self.assertEqual(len(s["results"]), 1)
         self.assertEqual(s["results"][0]["user_id"], user)
 
+    def test_process_join_after_server_leaves_room(self) -> None:
+        alice = self.register_user("alice", "pass")
+        alice_token = self.login(alice, "pass")
+        bob = self.register_user("bob", "pass")
+        bob_token = self.login(bob, "pass")
+
+        # Alice makes two rooms. Bob joins one of them.
+        room1 = self.helper.create_room_as(alice, tok=alice_token)
+        room2 = self.helper.create_room_as(alice, tok=alice_token)
+        print("room1=", room1)
+        print("room2=", room2)
+        self.helper.join(room1, bob, tok=bob_token)
+
+        # The user sharing tables should have been updated.
+        public1 = self.get_success(self.user_dir_helper.get_users_in_public_rooms())
+        self.assertEqual(set(public1), {(alice, room1), (alice, room2), (bob, room1)})
+
+        # Alice leaves room1. The user sharing tables should be updated.
+        self.helper.leave(room1, alice, tok=alice_token)
+        public2 = self.get_success(self.user_dir_helper.get_users_in_public_rooms())
+        self.assertEqual(set(public2), {(alice, room2), (bob, room1)})
+
+        # Pause the processing of new events.
+        dir_handler = self.hs.get_user_directory_handler()
+        dir_handler.update_user_directory = False
+
+        # Bob leaves one room and joins the other.
+        self.helper.leave(room1, bob, tok=bob_token)
+        self.helper.join(room2, bob, tok=bob_token)
+
+        # Process the leave and join in one go.
+        dir_handler.update_user_directory = True
+        dir_handler.notify_new_event()
+        self.wait_for_background_updates()
+
+        # The user sharing tables should have been updated.
+        public3 = self.get_success(self.user_dir_helper.get_users_in_public_rooms())
+        self.assertEqual(set(public3), {(alice, room2), (bob, room2)})
+
     def test_private_room(self) -> None:
         """
         A user can be searched for only by people that are either in a public