Stop applying edits to event contents (MSC3925). (#15193)

Enables MSC3925 support by default, which:

* Includes the full edit event in the bundled aggregations of an
  edited event.
* Stops modifying the original event's content to return the new
  content from the edit event.

This is a backwards-incompatible change that is considered to be
"correct" by the spec.

6 files changed, 15 insertions, 109 deletions

diff --git a/changelog.d/15193.bugfix b/changelog.d/15193.bugfix
new file mode 100644
index 0000000000..ca781e9631
--- /dev/null
+++ b/changelog.d/15193.bugfix
@@ -0,0 +1 @@
+Stop applying edits when bundling aggregations, per [MSC3925](https://github.com/matrix-org/matrix-spec-proposals/pull/3925).
diff --git a/synapse/config/experimental.py b/synapse/config/experimental.py
index 9c58cee2c8..489f2601ac 100644
--- a/synapse/config/experimental.py
+++ b/synapse/config/experimental.py
@@ -166,9 +166,6 @@ class ExperimentalConfig(Config):
         # MSC3391: Removing account data.
         self.msc3391_enabled = experimental.get("msc3391_enabled", False)
 
-        # MSC3925: do not replace events with their edits
-        self.msc3925_inhibit_edit = experimental.get("msc3925_inhibit_edit", False)
-
         # MSC3873: Disambiguate event_match keys.
         self.msc3873_escape_event_match_key = experimental.get(
             "msc3873_escape_event_match_key", False
diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index eaa6cad4af..45f46949a1 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -39,7 +39,6 @@ from synapse.api.constants import (
 from synapse.api.errors import Codes, SynapseError
 from synapse.api.room_versions import RoomVersion
 from synapse.types import JsonDict
-from synapse.util.frozenutils import unfreeze
 
 from . import EventBase
 
@@ -403,14 +402,6 @@ class EventClientSerializer:
     clients.
     """
 
-    def __init__(self, inhibit_replacement_via_edits: bool = False):
-        """
-        Args:
-            inhibit_replacement_via_edits: If this is set to True, then events are
-               never replaced by their edits.
-        """
-        self._inhibit_replacement_via_edits = inhibit_replacement_via_edits
-
     def serialize_event(
         self,
         event: Union[JsonDict, EventBase],
@@ -418,7 +409,6 @@ class EventClientSerializer:
         *,
         config: SerializeEventConfig = _DEFAULT_SERIALIZE_EVENT_CONFIG,
         bundle_aggregations: Optional[Dict[str, "BundledAggregations"]] = None,
-        apply_edits: bool = True,
     ) -> JsonDict:
         """Serializes a single event.
 
@@ -428,10 +418,7 @@ class EventClientSerializer:
             config: Event serialization config
             bundle_aggregations: A map from event_id to the aggregations to be bundled
                into the event.
-            apply_edits: Whether the content of the event should be modified to reflect
-               any replacement in `bundle_aggregations[<event_id>].replace`.
-               See also the `inhibit_replacement_via_edits` constructor arg: if that is
-               set to True, then this argument is ignored.
+
         Returns:
             The serialized event
         """
@@ -450,38 +437,10 @@ class EventClientSerializer:
                     config,
                     bundle_aggregations,
                     serialized_event,
-                    apply_edits=apply_edits,
                 )
 
         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,
@@ -489,7 +448,6 @@ class EventClientSerializer:
         config: SerializeEventConfig,
         bundled_aggregations: Dict[str, "BundledAggregations"],
         serialized_event: JsonDict,
-        apply_edits: bool,
     ) -> None:
         """Potentially injects bundled aggregations into the unsigned portion of the serialized event.
 
@@ -504,9 +462,6 @@ class EventClientSerializer:
                 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` (subject to the
-               `inhibit_replacement_via_edits` constructor arg).
         """
 
         # We have already checked that aggregations exist for this event.
@@ -522,11 +477,6 @@ class EventClientSerializer:
             ] = event_aggregations.references
 
         if event_aggregations.replace:
-            # If there is an edit, optionally apply it to the event.
-            edit = event_aggregations.replace
-            if apply_edits and not self._inhibit_replacement_via_edits:
-                self._apply_edit(event, serialized_event, edit)
-
             # Include information about it in the relations dict.
             #
             # Matrix spec v1.5 (https://spec.matrix.org/v1.5/client-server-api/#server-side-aggregation-of-mreplace-relationships)
@@ -534,10 +484,7 @@ class EventClientSerializer:
             # `sender` of the edit; however MSC3925 proposes extending it to the whole
             # of the edit, which is what we do here.
             serialized_aggregations[RelationTypes.REPLACE] = self.serialize_event(
-                edit,
-                time_now,
-                config=config,
-                apply_edits=False,
+                event_aggregations.replace, time_now, config=config
             )
 
         # Include any threaded replies to this event.
diff --git a/synapse/rest/client/room.py b/synapse/rest/client/room.py
index 45aee3d3fe..c5af07816a 100644
--- a/synapse/rest/client/room.py
+++ b/synapse/rest/client/room.py
@@ -818,7 +818,7 @@ class RoomEventServlet(RestServlet):
             # per MSC2676, /rooms/{roomId}/event/{eventId}, should return the
             # *original* event, rather than the edited version
             event_dict = self._event_serializer.serialize_event(
-                event, time_now, bundle_aggregations=aggregations, apply_edits=False
+                event, time_now, bundle_aggregations=aggregations
             )
             return 200, event_dict
 
diff --git a/synapse/server.py b/synapse/server.py
index a7c32e9a60..df80fc1beb 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -743,7 +743,7 @@ class HomeServer(metaclass=abc.ABCMeta):
 
     @cache_in_self
     def get_event_client_serializer(self) -> EventClientSerializer:
-        return EventClientSerializer(self.config.experimental.msc3925_inhibit_edit)
+        return EventClientSerializer()
 
     @cache_in_self
     def get_password_policy_handler(self) -> PasswordPolicyHandler:
diff --git a/tests/rest/client/test_relations.py b/tests/rest/client/test_relations.py
index a8a0a16141..fbbbcb23f1 100644
--- a/tests/rest/client/test_relations.py
+++ b/tests/rest/client/test_relations.py
@@ -30,7 +30,6 @@ from tests import unittest
 from tests.server import FakeChannel
 from tests.test_utils import make_awaitable
 from tests.test_utils.event_injection import inject_event
-from tests.unittest import override_config
 
 
 class BaseRelationsTestCase(unittest.HomeserverTestCase):
@@ -403,7 +402,7 @@ class RelationsTestCase(BaseRelationsTestCase):
 
     def test_edit(self) -> None:
         """Test that a simple edit works."""
-
+        orig_body = {"body": "Hi!", "msgtype": "m.text"}
         new_body = {"msgtype": "m.text", "body": "I've been edited!"}
         edit_event_content = {
             "msgtype": "m.text",
@@ -424,9 +423,7 @@ class RelationsTestCase(BaseRelationsTestCase):
             access_token=self.user_token,
         )
         self.assertEqual(200, channel.code, channel.json_body)
-        self.assertEqual(
-            channel.json_body["content"], {"body": "Hi!", "msgtype": "m.text"}
-        )
+        self.assertEqual(channel.json_body["content"], orig_body)
         self._assert_edit_bundle(channel.json_body, edit_event_id, edit_event_content)
 
         # Request the room messages.
@@ -443,7 +440,7 @@ class RelationsTestCase(BaseRelationsTestCase):
         )
 
         # Request the room context.
-        # /context should return the edited event.
+        # /context should return the event.
         channel = self.make_request(
             "GET",
             f"/rooms/{self.room}/context/{self.parent_id}",
@@ -453,7 +450,7 @@ class RelationsTestCase(BaseRelationsTestCase):
         self._assert_edit_bundle(
             channel.json_body["event"], edit_event_id, edit_event_content
         )
-        self.assertEqual(channel.json_body["event"]["content"], new_body)
+        self.assertEqual(channel.json_body["event"]["content"], orig_body)
 
         # Request sync, but limit the timeline so it becomes limited (and includes
         # bundled aggregations).
@@ -491,45 +488,11 @@ class RelationsTestCase(BaseRelationsTestCase):
             edit_event_content,
         )
 
-    @override_config({"experimental_features": {"msc3925_inhibit_edit": True}})
-    def test_edit_inhibit_replace(self) -> None:
-        """
-        If msc3925_inhibit_edit is enabled, then the original event should not be
-        replaced.
-        """
-
-        new_body = {"msgtype": "m.text", "body": "I've been edited!"}
-        edit_event_content = {
-            "msgtype": "m.text",
-            "body": "foo",
-            "m.new_content": new_body,
-        }
-        channel = self._send_relation(
-            RelationTypes.REPLACE,
-            "m.room.message",
-            content=edit_event_content,
-        )
-        edit_event_id = channel.json_body["event_id"]
-
-        # /context should return the *original* event.
-        channel = self.make_request(
-            "GET",
-            f"/rooms/{self.room}/context/{self.parent_id}",
-            access_token=self.user_token,
-        )
-        self.assertEqual(200, channel.code, channel.json_body)
-        self.assertEqual(
-            channel.json_body["event"]["content"], {"body": "Hi!", "msgtype": "m.text"}
-        )
-        self._assert_edit_bundle(
-            channel.json_body["event"], edit_event_id, edit_event_content
-        )
-
     def test_multi_edit(self) -> None:
         """Test that multiple edits, including attempts by people who
         shouldn't be allowed, are correctly handled.
         """
-
+        orig_body = orig_body = {"body": "Hi!", "msgtype": "m.text"}
         self._send_relation(
             RelationTypes.REPLACE,
             "m.room.message",
@@ -570,7 +533,7 @@ class RelationsTestCase(BaseRelationsTestCase):
         )
         self.assertEqual(200, channel.code, channel.json_body)
 
-        self.assertEqual(channel.json_body["event"]["content"], new_body)
+        self.assertEqual(channel.json_body["event"]["content"], orig_body)
         self._assert_edit_bundle(
             channel.json_body["event"], edit_event_id, edit_event_content
         )
@@ -642,6 +605,7 @@ class RelationsTestCase(BaseRelationsTestCase):
 
     def test_edit_edit(self) -> None:
         """Test that an edit cannot be edited."""
+        orig_body = {"body": "Hi!", "msgtype": "m.text"}
         new_body = {"msgtype": "m.text", "body": "Initial edit"}
         edit_event_content = {
             "msgtype": "m.text",
@@ -675,14 +639,12 @@ class RelationsTestCase(BaseRelationsTestCase):
             access_token=self.user_token,
         )
         self.assertEqual(200, channel.code, channel.json_body)
-        self.assertEqual(
-            channel.json_body["content"], {"body": "Hi!", "msgtype": "m.text"}
-        )
+        self.assertEqual(channel.json_body["content"], orig_body)
 
         # The relations information should not include the edit to the edit.
         self._assert_edit_bundle(channel.json_body, edit_event_id, edit_event_content)
 
-        # /context should return the event updated for the *first* edit
+        # /context should return the bundled edit for the *first* edit
         # (The edit to the edit should be ignored.)
         channel = self.make_request(
             "GET",
@@ -690,7 +652,7 @@ class RelationsTestCase(BaseRelationsTestCase):
             access_token=self.user_token,
         )
         self.assertEqual(200, channel.code, channel.json_body)
-        self.assertEqual(channel.json_body["event"]["content"], new_body)
+        self.assertEqual(channel.json_body["event"]["content"], orig_body)
         self._assert_edit_bundle(
             channel.json_body["event"], edit_event_id, edit_event_content
         )
@@ -1287,7 +1249,6 @@ class BundledAggregationsTestCase(BaseRelationsTestCase):
         thread_summary = relations_dict[RelationTypes.THREAD]
         self.assertIn("latest_event", thread_summary)
         latest_event_in_thread = thread_summary["latest_event"]
-        self.assertEqual(latest_event_in_thread["content"]["body"], "I've been edited!")
         # The latest event in the thread should have the edit appear under the
         # bundled aggregations.
         self.assertDictContainsSubset(