model: Set message.displayRecipient to null on stream move.

StreamMessage.displayRecipient no longer carries the up-to-date display
name of the stream when the message has been moved to another stream. We
invalidate it by setting it to null.

The only time StreamMessage.displayRecipient is useful is when we
don't have data on that stream. This is the reason why we don't go ahead
and lookup the stream store when such a stream move happen, because the
stream store likely will not have that information if we ever need to
use displayRecipient as the fallback.

Signed-off-by: Zixuan James Li <[email protected]>

Author: PIG208

lib/model/message.dart

@@ -192,8 +192,7 @@ class MessageStoreImpl with MessageStore {
 
       if (newStreamId != null) {
         message.streamId = newStreamId;
-        // TODO update [StreamMessage.displayRecipient]; doesn't usually
-        //   matter, because we only consult it when the stream is unknown
+        message.displayRecipient = null;
       }
 
       message.topic = newTopic;

test/model/message_test.dart

@@ -295,13 +295,17 @@ void main() {
       });
 
       test('message topic moved update', () async {
+        final originalDisplayRecipient = message.displayRecipient!;
         await sendEvent(message,
           eg.updateMessageMoveEvent([message, otherMessage],
             origTopic: 'old topic',
             newTopic:  'new topic'),
           notifiedCount: 2,
         );
-        check(store).messages.values.every(((message) => message.editState.equals(MessageEditState.moved)));
+        check(store).messages.values.every(((message) =>
+          message.isA<StreamMessage>()
+            ..editState.equals(MessageEditState.moved)
+            ..displayRecipient.equals(originalDisplayRecipient)));
       });
 
       test('message topic resolved update', () async {
@@ -352,7 +356,10 @@ void main() {
             newStreamId:  20),
           notifiedCount: 2,
         );
-        check(store).messages.values.every(((message) => message.editState.equals(MessageEditState.moved)));
+        check(store).messages.values.every(((message) =>
+          message.isA<StreamMessage>()
+            ..editState.equals(MessageEditState.moved)
+            ..displayRecipient.equals(null)));
       });
 
       test('message is both moved and updated', () async {