msglist [nfc]: Display realmEmptyTopicDisplayName where empty topic appears

While this appears to be a user facing change, it's not visible yet, not
until TopicName.displayName becomes nullable.  This is a part of a
series of changes to handle empty topics.

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

Author: PIG208

lib/widgets/message_list.dart

@@ -339,8 +339,11 @@ class MessageListAppBarTitle extends StatelessWidget {
     return Row(
       mainAxisSize: MainAxisSize.min,
       children: [
-        Flexible(child: Text(topic.displayName, style: const TextStyle(
+        // ignore: dead_null_aware_expression // null topic names soon to be enabled
+        Flexible(child: Text(topic.displayName ?? store.realmEmptyTopicDisplayName, style: TextStyle(
           fontSize: 13,
+          // ignore: unnecessary_null_comparison // null topic names soon to be enabled
+          fontStyle: topic.displayName == null ? FontStyle.italic : null,
         ).merge(weightVariableTextStyle(context)))),
         if (icon != null)
           Padding(
@@ -1092,11 +1095,15 @@ class StreamMessageRecipientHeader extends StatelessWidget {
       child: Row(
         children: [
           Flexible(
-            child: Text(topic.displayName,
+            // ignore: dead_null_aware_expression // null topic names soon to be enabled
+            child: Text(topic.displayName ?? store.realmEmptyTopicDisplayName,
               // TODO: Give a way to see the whole topic (maybe a
               //   long-press interaction?)
               overflow: TextOverflow.ellipsis,
-              style: recipientHeaderTextStyle(context))),
+              style: recipientHeaderTextStyle(context,
+                // ignore: unnecessary_null_comparison // null topic names soon to be enabled
+                fontStyle: topic.displayName == null ? FontStyle.italic : null,
+              ))),
           const SizedBox(width: 4),
           Icon(size: 14, color: designVariables.title.withFadedAlpha(0.5),
             // A null [Icon.icon] makes a blank space.
@@ -1191,12 +1198,13 @@ class DmRecipientHeader extends StatelessWidget {
   }
 }
 
-TextStyle recipientHeaderTextStyle(BuildContext context) {
+TextStyle recipientHeaderTextStyle(BuildContext context, {FontStyle? fontStyle}) {
   return TextStyle(
     color: DesignVariables.of(context).title,
     fontSize: 16,
     letterSpacing: proportionalLetterSpacing(context, 0.02, baseFontSize: 16),
     height: (18 / 16),
+    fontStyle: fontStyle,
   ).merge(weightVariableTextStyle(context, wght: 600));
 }
 

test/widgets/message_list_test.dart

@@ -194,6 +194,16 @@ void main() {
   group('app bar', () {
     // Tests for the topic action sheet are in test/widgets/action_sheet_test.dart.
 
+    testWidgets('handle empty topics', (tester) async {
+      final channel = eg.stream();
+      await setupMessageListPage(tester,
+        narrow: eg.topicNarrow(channel.streamId, ''),
+        streams: [channel],
+        messageCount: 1);
+      checkAppBarChannelTopic(
+        channel.name, eg.defaultRealmEmptyTopicDisplayName);
+    }, skip: true); // null topic names soon to be enabled
+
     testWidgets('has channel-feed action for topic narrows', (tester) async {
       final pushedRoutes = <Route<void>>[];
       final navObserver = TestNavigatorObserver()
@@ -934,6 +944,26 @@ void main() {
         check(findInMessageList('topic name')).length.equals(1);
       });
 
+      final messageEmptyTopic = eg.streamMessage(stream: stream, topic: '');
+
+      testWidgets('show general chat for empty topics with channel name', (tester) async {
+        await setupMessageListPage(tester,
+          narrow: const CombinedFeedNarrow(),
+          messages: [messageEmptyTopic], subscriptions: [eg.subscription(stream)]);
+        await tester.pump();
+        check(findInMessageList('stream name')).single;
+        check(findInMessageList(eg.defaultRealmEmptyTopicDisplayName)).single;
+      }, skip: true); // null topic names soon to be enabled
+
+      testWidgets('show general chat for empty topics without channel name', (tester) async {
+        await setupMessageListPage(tester,
+          narrow: TopicNarrow.ofMessage(messageEmptyTopic),
+          messages: [messageEmptyTopic]);
+        await tester.pump();
+        check(findInMessageList('stream name')).isEmpty();
+        check(findInMessageList(eg.defaultRealmEmptyTopicDisplayName)).single;
+      }, skip: true); // null topic names soon to be enabled
+
       testWidgets('show topic visibility icon when followed', (tester) async {
         await setupMessageListPage(tester,
           narrow: const CombinedFeedNarrow(),