model [nfc]: Make displayRecipient nullable.

We want to only allow it to be nullable after deserialization, because
the nullability does not belong to the API, and it exists only for later
implementing invalidation of the field when a stream message is moved to
a different stream.

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

Author: PIG208

lib/api/model/model.dart

@@ -576,7 +576,11 @@ class StreamMessage extends Message {
   @JsonKey(includeToJson: true)
   String get type => 'stream';
 
-  final String displayRecipient;
+  // This is not nullable API-wise, but if the message moves across channels,
+  // [displayRecipient] still refers to the original channel and it has to be
+  // invalidated.
+  @JsonKey(required: true, disallowNullValue: true)
+  String? displayRecipient;
   final int streamId;
 
   StreamMessage({

lib/api/model/model.g.dart

@@ -978,7 +978,9 @@ class StreamMessageRecipientHeader extends StatelessWidget {
       streamWidget = const SizedBox(width: 16);
     } else {
       final stream = store.streams[message.streamId];
-      final streamName = stream?.name ?? message.displayRecipient; // TODO(log) if missing
+      final streamName = stream?.name
+        ?? message.displayRecipient
+        ?? '(unknown channel)'; // TODO(log)
 
       streamWidget = GestureDetector(
         onTap: () => Navigator.push(context,

lib/widgets/message_list.dart

@@ -49,6 +49,10 @@ extension MessageChecks on Subject<Message> {
   Subject<String?> get matchTopic => has((e) => e.matchTopic, 'matchTopic');
 }
 
+extension StreamMessageChecks on Subject<StreamMessage> {
+  Subject<String?> get displayRecipient => has((e) => e.displayRecipient, 'displayRecipient');
+}
+
 extension ReactionsChecks on Subject<Reactions> {
   Subject<int> get total => has((e) => e.total, 'total');
   Subject<List<ReactionWithVotes>> get aggregated => has((e) => e.aggregated, 'aggregated');

test/api/model/model_checks.dart

@@ -1,6 +1,7 @@
 import 'dart:convert';
 
 import 'package:checks/checks.dart';
+import 'package:json_annotation/json_annotation.dart';
 import 'package:test/scaffolding.dart';
 import 'package:zulip/api/model/model.dart';
 
@@ -149,6 +150,14 @@ void main() {
       check(m2).flags.deepEquals([MessageFlag.read, MessageFlag.unknown]);
     });
 
+    test('require displayRecipient on parse', () {
+      check(() => StreamMessage.fromJson(baseStreamJson()..['display_recipient'] = null))
+        .throws<DisallowedNullValueException>();
+
+      check(() => StreamMessage.fromJson(baseStreamJson()..remove('display_recipient')))
+        .throws<MissingRequiredKeysException>();
+    });
+
     // Code relevant to messageEditState is tested separately in the
     // MessageEditState group.
   });