Allow retrieving the relations of a redacted event. (#12130)

This is allowed per MSC2675, although the original implementation did
not allow for it and would return an empty chunk / not bundle aggregations.

The main thing to improve is that the various caches get cleared properly
when an event is redacted, and that edits must not leak if the original
event is redacted (as that would presumably leak something similar to
the original event content).

1 files changed, 6 insertions, 5 deletions

diff --git a/synapse/storage/databases/main/events.py b/synapse/storage/databases/main/events.py
index 1dc83aa5e3..1a322882bf 100644
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -1619,9 +1619,12 @@ class PersistEventsStore:
 
         txn.call_after(prefill)
 
-    def _store_redaction(self, txn, event):
-        # invalidate the cache for the redacted event
+    def _store_redaction(self, txn: LoggingTransaction, event: EventBase) -> None:
+        # Invalidate the caches for the redacted event, note that these caches
+        # are also cleared as part of event replication in _invalidate_caches_for_event.
         txn.call_after(self.store._invalidate_get_event_cache, event.redacts)
+        txn.call_after(self.store.get_relations_for_event.invalidate, (event.redacts,))
+        txn.call_after(self.store.get_applicable_edit.invalidate, (event.redacts,))
 
         self.db_pool.simple_upsert_txn(
             txn,
@@ -1812,9 +1815,7 @@ class PersistEventsStore:
             txn.call_after(self.store.get_applicable_edit.invalidate, (parent_id,))
 
         if rel_type == RelationTypes.THREAD:
-            txn.call_after(
-                self.store.get_thread_summary.invalidate, (parent_id, event.room_id)
-            )
+            txn.call_after(self.store.get_thread_summary.invalidate, (parent_id,))
             # It should be safe to only invalidate the cache if the user has not
             # previously participated in the thread, but that's difficult (and
             # potentially error-prone) so it is always invalidated.