Fix a bug that corrupted the cache of federated space hierarchies (#11775)

`FederationClient.get_room_hierarchy()` caches its return values, so
refactor the code to avoid modifying the returned room summary.

1 files changed, 2 insertions, 1 deletions

diff --git a/synapse/handlers/room_summary.py b/synapse/handlers/room_summary.py

index 7c60cb0bdd..4844b69a03 100644
--- a/synapse/handlers/room_summary.py
+++ b/synapse/handlers/room_summary.py
@@ -780,6 +780,7 @@ class RoomSummaryHandler:
         try:
             (
                 room_response,
+                children_state_events,
                 children,
                 inaccessible_children,
             ) = await self._federation_client.get_room_hierarchy(
@@ -804,7 +805,7 @@ class RoomSummaryHandler:
         }
 
         return (
-            _RoomEntry(room_id, room_response, room_response.pop("children_state", ())),
+            _RoomEntry(room_id, room_response, children_state_events),
             children_by_room_id,
             set(inaccessible_children),
         )