Don't drop user dir deltas when server leaves room (#10982)

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.

* Pull out `wait_for_background_update` in tests

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>
Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

2 files changed, 42 insertions, 18 deletions

diff --git a/tests/handlers/test_stats.py b/tests/handlers/test_stats.py
index 24b7ef6efc..56207f4db6 100644
--- a/tests/handlers/test_stats.py
+++ b/tests/handlers/test_stats.py
@@ -103,12 +103,7 @@ class StatsRoomTests(unittest.HomeserverTestCase):
         # Do the initial population of the stats via the background update
         self._add_background_updates()
 
-        while not self.get_success(
-            self.store.db_pool.updates.has_completed_background_updates()
-        ):
-            self.get_success(
-                self.store.db_pool.updates.do_next_background_update(100), by=0.1
-            )
+        self.wait_for_background_updates()
 
     def test_initial_room(self):
         """
@@ -140,12 +135,7 @@ class StatsRoomTests(unittest.HomeserverTestCase):
         # Do the initial population of the user directory via the background update
         self._add_background_updates()
 
-        while not self.get_success(
-            self.store.db_pool.updates.has_completed_background_updates()
-        ):
-            self.get_success(
-                self.store.db_pool.updates.do_next_background_update(100), by=0.1
-            )
+        self.wait_for_background_updates()
 
         r = self.get_success(self.get_all_room_state())
 
@@ -568,12 +558,7 @@ class StatsRoomTests(unittest.HomeserverTestCase):
             )
         )
 
-        while not self.get_success(
-            self.store.db_pool.updates.has_completed_background_updates()
-        ):
-            self.get_success(
-                self.store.db_pool.updates.do_next_background_update(100), by=0.1
-            )
+        self.wait_for_background_updates()
 
         r1stats_complete = self._get_current_stats("room", r1)
         u1stats_complete = self._get_current_stats("user", u1)
diff --git a/tests/handlers/test_user_directory.py b/tests/handlers/test_user_directory.py
index b3c3af113b..03fd5a3e2c 100644
--- a/tests/handlers/test_user_directory.py
+++ b/tests/handlers/test_user_directory.py
@@ -363,6 +363,45 @@ class UserDirectoryTestCase(unittest.HomeserverTestCase):
         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