Add origin_server_ts and sender fields to m.replace (#5613)

Riot team would like some extra fields as part of m.replace, so here you go.

Fixes: #5598

changelog.d/5613.feature

+Add `sender` and `origin_server_ts` fields to `m.replace`.

synapse/events/utils.py

@@ -392,7 +392,11 @@ class EventClientSerializer(object):
                     serialized_event["content"].pop("m.relates_to", None)
 
                 r = serialized_event["unsigned"].setdefault("m.relations", {})
-                r[RelationTypes.REPLACE] = {"event_id": edit.event_id}
+                r[RelationTypes.REPLACE] = {
+                    "event_id": edit.event_id,
+                    "origin_server_ts": edit.origin_server_ts,
+                    "sender": edit.sender,
+                }
 
         defer.returnValue(serialized_event)
 

tests/rest/client/v2_alpha/test_relations.py

@@ -466,9 +466,15 @@ class RelationsTestCase(unittest.HomeserverTestCase):
 
         self.assertEquals(channel.json_body["content"], new_body)
 
-        self.assertEquals(
-            channel.json_body["unsigned"].get("m.relations"),
-            {RelationTypes.REPLACE: {"event_id": edit_event_id}},
+        relations_dict = channel.json_body["unsigned"].get("m.relations")
+        self.assertIn(RelationTypes.REPLACE, relations_dict)
+
+        m_replace_dict = relations_dict[RelationTypes.REPLACE]
+        for key in ["event_id", "sender", "origin_server_ts"]:
+            self.assertIn(key, m_replace_dict)
+
+        self.assert_dict(
+            {"event_id": edit_event_id, "sender": self.user_id}, m_replace_dict
         )
 
     def test_multi_edit(self):
@@ -518,9 +524,15 @@ class RelationsTestCase(unittest.HomeserverTestCase):
 
         self.assertEquals(channel.json_body["content"], new_body)
 
-        self.assertEquals(
-            channel.json_body["unsigned"].get("m.relations"),
-            {RelationTypes.REPLACE: {"event_id": edit_event_id}},
+        relations_dict = channel.json_body["unsigned"].get("m.relations")
+        self.assertIn(RelationTypes.REPLACE, relations_dict)
+
+        m_replace_dict = relations_dict[RelationTypes.REPLACE]
+        for key in ["event_id", "sender", "origin_server_ts"]:
+            self.assertIn(key, m_replace_dict)
+
+        self.assert_dict(
+            {"event_id": edit_event_id, "sender": self.user_id}, m_replace_dict
         )
 
     def _send_relation(