Fix incorrect thread summaries when the latest event is edited. (#11992)

If the latest event in a thread was edited than the original
event content was included in bundled aggregation for
threads instead of the edited event content.

1 files changed, 45 insertions, 24 deletions

diff --git a/synapse/events/utils.py b/synapse/events/utils.py

index 243696b357..9386fa29dd 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -425,6 +425,33 @@ class EventClientSerializer:
 
         return serialized_event
 
+    def _apply_edit(
+        self, orig_event: EventBase, serialized_event: JsonDict, edit: EventBase
+    ) -> None:
+        """Replace the content, preserving existing relations of the serialized event.
+
+        Args:
+            orig_event: The original event.
+            serialized_event: The original event, serialized. This is modified.
+            edit: The event which edits the above.
+        """
+
+        # Ensure we take copies of the edit content, otherwise we risk modifying
+        # the original event.
+        edit_content = edit.content.copy()
+
+        # Unfreeze the event content if necessary, so that we may modify it below
+        edit_content = unfreeze(edit_content)
+        serialized_event["content"] = edit_content.get("m.new_content", {})
+
+        # Check for existing relations
+        relates_to = orig_event.content.get("m.relates_to")
+        if relates_to:
+            # Keep the relations, ensuring we use a dict copy of the original
+            serialized_event["content"]["m.relates_to"] = relates_to.copy()
+        else:
+            serialized_event["content"].pop("m.relates_to", None)
+
     def _inject_bundled_aggregations(
         self,
         event: EventBase,
@@ -450,26 +477,11 @@ class EventClientSerializer:
             serialized_aggregations[RelationTypes.REFERENCE] = aggregations.references
 
         if aggregations.replace:
-            # If there is an edit replace the content, preserving existing
-            # relations.
+            # If there is an edit, apply it to the event.
             edit = aggregations.replace
+            self._apply_edit(event, serialized_event, edit)
 
-            # Ensure we take copies of the edit content, otherwise we risk modifying
-            # the original event.
-            edit_content = edit.content.copy()
-
-            # Unfreeze the event content if necessary, so that we may modify it below
-            edit_content = unfreeze(edit_content)
-            serialized_event["content"] = edit_content.get("m.new_content", {})
-
-            # Check for existing relations
-            relates_to = event.content.get("m.relates_to")
-            if relates_to:
-                # Keep the relations, ensuring we use a dict copy of the original
-                serialized_event["content"]["m.relates_to"] = relates_to.copy()
-            else:
-                serialized_event["content"].pop("m.relates_to", None)
-
+            # Include information about it in the relations dict.
             serialized_aggregations[RelationTypes.REPLACE] = {
                 "event_id": edit.event_id,
                 "origin_server_ts": edit.origin_server_ts,
@@ -478,13 +490,22 @@ class EventClientSerializer:
 
         # If this event is the start of a thread, include a summary of the replies.
         if aggregations.thread:
+            thread = aggregations.thread
+
+            # Don't bundle aggregations as this could recurse forever.
+            serialized_latest_event = self.serialize_event(
+                thread.latest_event, time_now, bundle_aggregations=None
+            )
+            # Manually apply an edit, if one exists.
+            if thread.latest_edit:
+                self._apply_edit(
+                    thread.latest_event, serialized_latest_event, thread.latest_edit
+                )
+
             serialized_aggregations[RelationTypes.THREAD] = {
-                # Don't bundle aggregations as this could recurse forever.
-                "latest_event": self.serialize_event(
-                    aggregations.thread.latest_event, time_now, bundle_aggregations=None
-                ),
-                "count": aggregations.thread.count,
-                "current_user_participated": aggregations.thread.current_user_participated,
+                "latest_event": serialized_latest_event,
+                "count": thread.count,
+                "current_user_participated": thread.current_user_participated,
             }
 
         # Include the bundled aggregations in the event.