Fix incorrect `get_rooms_for_user` for remote user (#11999)

When the server leaves a room the `get_rooms_for_user` cache is not
correctly invalidated for the remote users in the room. This means that
subsequent calls to `get_rooms_for_user` for the remote users would
incorrectly include the room (it shouldn't be included because the
server no longer knows anything about the room).

1 files changed, 16 insertions, 11 deletions

diff --git a/synapse/storage/databases/main/events.py b/synapse/storage/databases/main/events.py

index 5246fccad5..a1d7a9b413 100644
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -975,6 +975,17 @@ class PersistEventsStore:
             to_delete = delta_state.to_delete
             to_insert = delta_state.to_insert
 
+            # Figure out the changes of membership to invalidate the
+            # `get_rooms_for_user` cache.
+            # We find out which membership events we may have deleted
+            # and which we have added, then we invalidate the caches for all
+            # those users.
+            members_changed = {
+                state_key
+                for ev_type, state_key in itertools.chain(to_delete, to_insert)
+                if ev_type == EventTypes.Member
+            }
+
             if delta_state.no_longer_in_room:
                 # Server is no longer in the room so we delete the room from
                 # current_state_events, being careful we've already updated the
@@ -993,6 +1004,11 @@ class PersistEventsStore:
                 """
                 txn.execute(sql, (stream_id, self._instance_name, room_id))
 
+                # We also want to invalidate the membership caches for users
+                # that were in the room.
+                users_in_room = self.store.get_users_in_room_txn(txn, room_id)
+                members_changed.update(users_in_room)
+
                 self.db_pool.simple_delete_txn(
                     txn,
                     table="current_state_events",
@@ -1102,17 +1118,6 @@ class PersistEventsStore:
 
             # Invalidate the various caches
 
-            # Figure out the changes of membership to invalidate the
-            # `get_rooms_for_user` cache.
-            # We find out which membership events we may have deleted
-            # and which we have added, then we invalidate the caches for all
-            # those users.
-            members_changed = {
-                state_key
-                for ev_type, state_key in itertools.chain(to_delete, to_insert)
-                if ev_type == EventTypes.Member
-            }
-
             for member in members_changed:
                 txn.call_after(
                     self.store.get_rooms_for_user_with_stream_ordering.invalidate,