Improvements to bundling aggregations. (#11815)

This is some odds and ends found during the review of #11791
and while continuing to work in this code:

* Return attrs classes instead of dictionaries from some methods
  to improve type safety.
* Call `get_bundled_aggregations` fewer times.
* Adds a missing assertion in the tests.
* Do not return empty bundled aggregations for an event (preferring
  to not include the bundle at all, as the docstring states).

1 files changed, 24 insertions, 15 deletions

diff --git a/synapse/rest/client/room.py b/synapse/rest/client/room.py
index 90bb9142a0..90355e44b2 100644
--- a/synapse/rest/client/room.py
+++ b/synapse/rest/client/room.py
@@ -706,27 +706,36 @@ class RoomEventContextServlet(RestServlet):
         else:
             event_filter = None
 
-        results = await self.room_context_handler.get_event_context(
+        event_context = await self.room_context_handler.get_event_context(
             requester, room_id, event_id, limit, event_filter
         )
 
-        if not results:
+        if not event_context:
             raise SynapseError(404, "Event not found.", errcode=Codes.NOT_FOUND)
 
         time_now = self.clock.time_msec()
-        aggregations = results.pop("aggregations", None)
-        results["events_before"] = self._event_serializer.serialize_events(
-            results["events_before"], time_now, bundle_aggregations=aggregations
-        )
-        results["event"] = self._event_serializer.serialize_event(
-            results["event"], time_now, bundle_aggregations=aggregations
-        )
-        results["events_after"] = self._event_serializer.serialize_events(
-            results["events_after"], time_now, bundle_aggregations=aggregations
-        )
-        results["state"] = self._event_serializer.serialize_events(
-            results["state"], time_now
-        )
+        results = {
+            "events_before": self._event_serializer.serialize_events(
+                event_context.events_before,
+                time_now,
+                bundle_aggregations=event_context.aggregations,
+            ),
+            "event": self._event_serializer.serialize_event(
+                event_context.event,
+                time_now,
+                bundle_aggregations=event_context.aggregations,
+            ),
+            "events_after": self._event_serializer.serialize_events(
+                event_context.events_after,
+                time_now,
+                bundle_aggregations=event_context.aggregations,
+            ),
+            "state": self._event_serializer.serialize_events(
+                event_context.state, time_now
+            ),
+            "start": event_context.start,
+            "end": event_context.end,
+        }
 
         return 200, results