Don't apply retention policy based filtering on state events

As per MSC1763, 'Retention is only considered for non-state events.', so don't filter out state events based on the room's retention policy.

synapse/visibility.py

@@ -111,14 +111,17 @@ def filter_events_for_client(
         if not event.is_state() and event.sender in ignore_list:
             return None
 
-        retention_policy = retention_policies[event.room_id]
-        max_lifetime = retention_policy.get("max_lifetime")
+        # Don't try to apply the room's retention policy if the event is a state event, as
+        # MSC1763 states that retention is only considered for non-state events.
+        if not event.is_state():
+            retention_policy = retention_policies[event.room_id]
+            max_lifetime = retention_policy.get("max_lifetime")
 
-        if max_lifetime is not None:
-            oldest_allowed_ts = storage.main.clock.time_msec() - max_lifetime
+            if max_lifetime is not None:
+                oldest_allowed_ts = storage.main.clock.time_msec() - max_lifetime
 
-            if event.origin_server_ts < oldest_allowed_ts:
-                return None
+                if event.origin_server_ts < oldest_allowed_ts:
+                    return None
 
         if event.event_id in always_include_ids:
             return event

tests/rest/client/test_retention.py

@@ -164,6 +164,12 @@ class RetentionTestCase(unittest.HomeserverTestCase):
         self.assertEqual(filtered_events[0].event_id, valid_event_id, filtered_events)
 
     def _test_retention_event_purged(self, room_id, increment):
+        # Get the create event to, later, check that we can still access it.
+        message_handler = self.hs.get_message_handler()
+        create_event = self.get_success(
+            message_handler.get_room_data(self.user_id, room_id, EventTypes.Create)
+        )
+
         # Send a first event to the room. This is the event we'll want to be purged at the
         # end of the test.
         resp = self.helper.send(
@@ -202,6 +208,10 @@ class RetentionTestCase(unittest.HomeserverTestCase):
         valid_event = self.get_event(room_id, valid_event_id)
         self.assertEqual(valid_event.get("content", {}).get("body"), "2", valid_event)
 
+        # Check that we can still access state events that were sent before the event that
+        # has been purged.
+        self.get_event(room_id, create_event.event_id)
+
     def get_event(self, room_id, event_id, expected_code=200):
         url = "/_matrix/client/r0/rooms/%s/event/%s" % (room_id, event_id)