Fix MSC4222 returning full state (#17915)

There was a bug that meant we would return the full state of the room on
incremental syncs when using lazy loaded members and there were no
entries in the timeline.

This was due to trying to use `state_filter or state_filter.all()` as a
short hand for handling `None` case, however `state_filter` implements
`__bool__` so if the state filter was empty it would be set to full.

c.f. MSC4222 and #17888

1 files changed, 4 insertions, 4 deletions

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

index 42b3638e1c..788f7d1e32 100644
--- a/synapse/storage/databases/main/state.py
+++ b/synapse/storage/databases/main/state.py
@@ -572,10 +572,10 @@ class StateGroupWorkerStore(EventsWorkerStore, SQLBaseStore):
         Returns:
             Map from type/state_key to event ID.
         """
+        if state_filter is None:
+            state_filter = StateFilter.all()
 
-        where_clause, where_args = (
-            state_filter or StateFilter.all()
-        ).make_sql_filter_clause()
+        where_clause, where_args = (state_filter).make_sql_filter_clause()
 
         if not where_clause:
             # We delegate to the cached version
@@ -584,7 +584,7 @@ class StateGroupWorkerStore(EventsWorkerStore, SQLBaseStore):
         def _get_filtered_current_state_ids_txn(
             txn: LoggingTransaction,
         ) -> StateMap[str]:
-            results = StateMapWrapper(state_filter=state_filter or StateFilter.all())
+            results = StateMapWrapper(state_filter=state_filter)
 
             sql = """
                 SELECT type, state_key, event_id FROM current_state_events