Include bundled aggregations for the latest event in a thread. (#12273)

The `latest_event` field of the bundled aggregations for `m.thread` relations
did not include bundled aggregations itself. This resulted in clients needing to
immediately request the event from the server (and thus making it useless that
the latest event itself was serialized instead of just including an event ID).

1 files changed, 33 insertions, 22 deletions

diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index a6c48308b3..026dcde8d8 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -426,13 +426,12 @@ class EventClientSerializer:
 
         # Check if there are any bundled aggregations to include with the event.
         if bundle_aggregations:
-            event_aggregations = bundle_aggregations.get(event.event_id)
-            if event_aggregations:
+            if event.event_id in bundle_aggregations:
                 self._inject_bundled_aggregations(
                     event,
                     time_now,
                     config,
-                    event_aggregations,
+                    bundle_aggregations,
                     serialized_event,
                     apply_edits=apply_edits,
                 )
@@ -471,7 +470,7 @@ class EventClientSerializer:
         event: EventBase,
         time_now: int,
         config: SerializeEventConfig,
-        aggregations: "BundledAggregations",
+        bundled_aggregations: Dict[str, "BundledAggregations"],
         serialized_event: JsonDict,
         apply_edits: bool,
     ) -> None:
@@ -481,22 +480,37 @@ class EventClientSerializer:
             event: The event being serialized.
             time_now: The current time in milliseconds
             config: Event serialization config
-            aggregations: The bundled aggregation to serialize.
+            bundled_aggregations: Bundled aggregations to be injected.
+                A map from event_id to aggregation data. Must contain at least an
+                entry for `event`.
+
+                While serializing the bundled aggregations this map may be searched
+                again for additional events in a recursive manner.
             serialized_event: The serialized event which may be modified.
             apply_edits: Whether the content of the event should be modified to reflect
                any replacement in `aggregations.replace`.
         """
+
+        # We have already checked that aggregations exist for this event.
+        event_aggregations = bundled_aggregations[event.event_id]
+
+        # The JSON dictionary to be added under the unsigned property of the event
+        # being serialized.
         serialized_aggregations = {}
 
-        if aggregations.annotations:
-            serialized_aggregations[RelationTypes.ANNOTATION] = aggregations.annotations
+        if event_aggregations.annotations:
+            serialized_aggregations[
+                RelationTypes.ANNOTATION
+            ] = event_aggregations.annotations
 
-        if aggregations.references:
-            serialized_aggregations[RelationTypes.REFERENCE] = aggregations.references
+        if event_aggregations.references:
+            serialized_aggregations[
+                RelationTypes.REFERENCE
+            ] = event_aggregations.references
 
-        if aggregations.replace:
+        if event_aggregations.replace:
             # If there is an edit, optionally apply it to the event.
-            edit = aggregations.replace
+            edit = event_aggregations.replace
             if apply_edits:
                 self._apply_edit(event, serialized_event, edit)
 
@@ -507,19 +521,16 @@ class EventClientSerializer:
                 "sender": edit.sender,
             }
 
-        # If this event is the start of a thread, include a summary of the replies.
-        if aggregations.thread:
-            thread = aggregations.thread
+        # Include any threaded replies to this event.
+        if event_aggregations.thread:
+            thread = event_aggregations.thread
 
-            # Don't bundle aggregations as this could recurse forever.
-            serialized_latest_event = serialize_event(
-                thread.latest_event, time_now, config=config
+            serialized_latest_event = self.serialize_event(
+                thread.latest_event,
+                time_now,
+                config=config,
+                bundle_aggregations=bundled_aggregations,
             )
-            # Manually apply an edit, if one exists.
-            if thread.latest_edit:
-                self._apply_edit(
-                    thread.latest_event, serialized_latest_event, thread.latest_edit
-                )
 
             thread_summary = {
                 "latest_event": serialized_latest_event,