Add TODO to handle state resets

See https://github.com/element-hq/synapse/pull/17320#discussion_r1656548733

synapse/handlers/sliding_sync.py

@@ -1002,6 +1002,12 @@ class SlidingSyncHandler:
 
             stripped_state.append(strip_event(invite_or_knock_event))
 
+        # TODO: Handle state resets. For example, if we see
+        # `rooms_membership_for_user_at_to_token.membership = Membership.LEAVE` but
+        # `required_state` doesn't include it, we should indicate to the client that a
+        # state reset happened. Perhaps we should indicate this by setting `initial:
+        # True` and empty `required_state`.
+
         return SlidingSyncResult.RoomResult(
             # TODO: Dummy value
             name=None,

tests/rest/client/test_sync.py

@@ -1624,7 +1624,7 @@ class SlidingSyncTestCase(unittest.HomeserverTestCase):
         user1_id = self.register_user("user1", "pass")
         user1_tok = self.login(user1_id, "pass")
 
-        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+        _room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
         room_id2 = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
         room_id3 = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
 

tests/storage/test_stream.py

@@ -46,7 +46,7 @@ from synapse.types import (
 from synapse.util import Clock
 
 from tests.test_utils.event_injection import create_event
-from tests.unittest import FederatingHomeserverTestCase, HomeserverTestCase, skip_unless
+from tests.unittest import FederatingHomeserverTestCase, HomeserverTestCase
 
 logger = logging.getLogger(__name__)
 
@@ -1012,115 +1012,6 @@ class GetCurrentStateDeltaMembershipChangesForUserTestCase(HomeserverTestCase):
             ],
         )
 
-    @skip_unless(
-        False,
-        "persist code does not support multiple membership events for the same user in the same batch",
-    )
-    def test_membership_persisted_in_same_batch(self) -> None:
-        """
-        Test batch of membership events for the same user being processed at once.
-
-        This *should* (doesn't happen currently) result in all of the memberships being
-        stored in the `current_state_delta_stream` table with the same `stream_ordering`
-        even though the individual events have different `stream_ordering`s.
-
-        FIXME: Currently, only the `join_event` is recorded in the `current_state_delta_stream`
-        table.
-        """
-        user1_id = self.register_user("user1", "pass")
-        _user1_tok = self.login(user1_id, "pass")
-        user2_id = self.register_user("user2", "pass")
-        user2_tok = self.login(user2_id, "pass")
-
-        before_room1_token = self.event_sources.get_current_token()
-
-        # User2 is just the designated person to create the room (we do this across the
-        # tests to be consistent)
-        room_id1 = self.helper.create_room_as(user2_id, tok=user2_tok)
-
-        # Persist a timeline event sandwiched between two membership events so they end
-        # up in the `current_state_delta_stream` table with the same `stream_id`.
-        join_event, join_event_context = self.get_success(
-            create_event(
-                self.hs,
-                sender=user1_id,
-                type=EventTypes.Member,
-                state_key=user1_id,
-                content={"membership": "join"},
-                room_id=room_id1,
-            )
-        )
-        timeline_event, timeline_event_context = self.get_success(
-            create_event(
-                self.hs,
-                sender=user1_id,
-                type=EventTypes.Message,
-                state_key=user1_id,
-                content={"body": "foo bar", "msgtype": "m.text"},
-                room_id=room_id1,
-            )
-        )
-        leave_event, leave_event_context = self.get_success(
-            create_event(
-                self.hs,
-                sender=user1_id,
-                type=EventTypes.Member,
-                state_key=user1_id,
-                content={"membership": "leave"},
-                room_id=room_id1,
-            )
-        )
-        self.get_success(
-            self.persistence.persist_events(
-                [
-                    (join_event, join_event_context),
-                    (timeline_event, timeline_event_context),
-                    (leave_event, leave_event_context),
-                ]
-            )
-        )
-
-        after_room1_token = self.event_sources.get_current_token()
-
-        # Get the membership changes for the user.
-        #
-        # At this point, the `current_state_delta_stream` table should look like (notice
-        # those three memberships at the end with `stream_id=7` because we persisted
-        # them in the same batch):
-        #
-        # TODO: DB rows to better see what's going on.
-        membership_changes = self.get_success(
-            self.store.get_current_state_delta_membership_changes_for_user(
-                user1_id,
-                from_key=before_room1_token.room_key,
-                to_key=after_room1_token.room_key,
-            )
-        )
-
-        join_pos = self.get_success(
-            self.store.get_position_for_event(join_event.event_id)
-        )
-
-        # Let the whole diff show on failure
-        self.maxDiff = None
-        self.assertEqual(
-            membership_changes,
-            [
-                CurrentStateDeltaMembership(
-                    event_id=leave_event.event_id,
-                    # Ideally, this would be `leave_pos` (to match the `event_id`) but
-                    # when events are persisted in a batch, they are all stored in the
-                    # `current_state_delta_stream` table with the minimum
-                    # `stream_ordering` from the batch.
-                    event_pos=join_pos,  # leave_pos,
-                    prev_event_id=None,
-                    room_id=room_id1,
-                    membership="leave",
-                    sender=user1_id,
-                ),
-            ],
-        )
-
     def test_state_reset(self) -> None:
         """
         Test a state reset scenario where the user gets removed from the room (when