Fix oops, add simple test

syncapi/synctypes/clientevent.go

@@ -145,7 +145,7 @@ func ToClientEvent(se gomatrixserverlib.PDU, format ClientEventFormat, userIDFor
 	// For compatibility with older clients, we keep the "redacts" top-level field.
 	// TODO: At which point do we remove "redacts" from the top-level?
 	if se.Type() == spec.MRoomRedaction && se.Version() == gomatrixserverlib.RoomVersionV11 && ce.Redacts != "" {
-		v11content, err := sjson.SetBytes(ce.Content, "content.redacts", ce.Redacts)
+		v11content, err := sjson.SetBytes(ce.Content, "redacts", ce.Redacts)
 		if err != nil {
 			logrus.WithError(err).Warn("failed to set content.redacts")
 		} else {

syncapi/synctypes/clientevent_test.go

@@ -154,6 +154,50 @@ func TestToClientEvent(t *testing.T) { // nolint: gocyclo
 	}
 }
 
+// Merely tests that the top-level "redacts" is copied to "content.redacts" and keeps the top-level
+// one as is
+func TestToClientEventRedactionV11(t *testing.T) { // nolint: gocyclo
+	ev, err := gomatrixserverlib.MustGetRoomVersion(gomatrixserverlib.RoomVersionV11).NewEventFromTrustedJSON([]byte(`{
+		"type": "m.room.redaction",
+		"state_key": "",
+		"event_id": "$test",
+		"room_id": "!test:localhost",
+		"sender": "@test:localhost",
+		"content": {
+			"reason": "Hello World"
+		},
+		"origin_server_ts": 123456,
+		"unsigned": {
+			"prev_content": {
+				"name": "Goodbye World"
+			}
+		},
+		"redacts": "$abc"
+	}`), false)
+	if err != nil {
+		t.Fatalf("failed to create Event: %s", err)
+	}
+
+	ce, err := ToClientEvent(ev, FormatAll, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+		return queryUserIDForSender(senderID)
+	})
+	if err != nil {
+		t.Fatalf("failed to create ClientEvent: %s", err)
+	}
+
+	j, err := json.Marshal(ce)
+	if err != nil {
+		t.Fatalf("failed to Marshal ClientEvent: %s", err)
+	}
+	// Marshal sorts keys in structs by the order they are defined in the struct, which is alphabetical
+	out := `{"content":{"reason":"Hello World","redacts":"$abc"},"event_id":"$test","origin_server_ts":123456,` +
+		`"room_id":"!test:localhost","sender":"@test:localhost","state_key":"","type":"m.room.redaction",` +
+		`"unsigned":{"prev_content":{"name":"Goodbye World"}},"redacts":"$abc"}`
+	if !bytes.Equal([]byte(out), j) {
+		t.Errorf("ClientEvent marshalled to wrong bytes: wanted \n%s, got \n%s", out, string(j))
+	}
+}
+
 func TestToClientFormatSync(t *testing.T) {
 	ev, err := gomatrixserverlib.MustGetRoomVersion(gomatrixserverlib.RoomVersionV1).NewEventFromTrustedJSON([]byte(`{
 		"type": "m.room.name",