msglist: In single-conversation view, make recipient headers not tappable.

Updated onTap for recipient headers in single-conversation view.
Adjusted GestureDetector logic to conditionally enable navigation.
Simplified ColoredBox structure for non-tappable recipient headers.
Improves user experience by removing unnecessary tap interactions.

Fixes: zulip#1171

Author: lakshya1goel

lib/widgets/message_list.dart

@@ -896,11 +896,14 @@ class RecipientHeader extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final isTopicNarrow = narrow is TopicNarrow;
+    final isDmNarrow = narrow is DmNarrow;
     final message = this.message;
     return switch (message) {
       StreamMessage() => StreamMessageRecipientHeader(message: message,
-        showStream: _containsDifferentChannels(narrow)),
-      DmMessage() => DmRecipientHeader(message: message),
+        showStream: _containsDifferentChannels(narrow),
+        isTopicNarrow: isTopicNarrow),
+      DmMessage() => DmRecipientHeader(message: message, isDmNarrow: isDmNarrow),
     };
   }
 }
@@ -1015,10 +1018,12 @@ class StreamMessageRecipientHeader extends StatelessWidget {
     super.key,
     required this.message,
     required this.showStream,
+    required this.isTopicNarrow,
   });
 
   final StreamMessage message;
   final bool showStream;
+  final bool isTopicNarrow;
 
   @override
   Widget build(BuildContext context) {
@@ -1105,9 +1110,9 @@ class StreamMessageRecipientHeader extends StatelessWidget {
         ]));
 
     return GestureDetector(
-      onTap: () => Navigator.push(context,
+      onTap: () => !isTopicNarrow? Navigator.push(context,
         MessageListPage.buildRoute(context: context,
-          narrow: TopicNarrow.ofMessage(message))),
+          narrow: TopicNarrow.ofMessage(message))): null,
       onLongPress: () => showTopicActionSheet(context,
         channelId: message.streamId, topic: topic),
       child: ColoredBox(
@@ -1126,9 +1131,10 @@ class StreamMessageRecipientHeader extends StatelessWidget {
 }
 
 class DmRecipientHeader extends StatelessWidget {
-  const DmRecipientHeader({super.key, required this.message});
+  const DmRecipientHeader({super.key, required this.message, required this.isDmNarrow});
 
   final DmMessage message;
+  final bool isDmNarrow;
 
   @override
   Widget build(BuildContext context) {
@@ -1149,9 +1155,9 @@ class DmRecipientHeader extends StatelessWidget {
     final messageListTheme = MessageListTheme.of(context);
 
     return GestureDetector(
-      onTap: () => Navigator.push(context,
+      onTap: () => !isDmNarrow? Navigator.push(context,
         MessageListPage.buildRoute(context: context,
-          narrow: DmNarrow.ofMessage(message, selfUserId: store.selfUserId))),
+          narrow: DmNarrow.ofMessage(message, selfUserId: store.selfUserId))): null,
       child: ColoredBox(
         color: messageListTheme.dmRecipientHeaderBg,
         child: Padding(

test/widgets/message_list_test.dart

@@ -922,6 +922,37 @@ void main() {
         await tester.pump();
         tester.widget(find.text('new stream name'));
       });
+
+      testWidgets('does not navigate on tapping topic in TopicNarrow', (tester) async {
+        final pushedRoutes = <Route<void>>[];
+        final navObserver = TestNavigatorObserver()
+          ..onPushed = (route, prevRoute) => pushedRoutes.add(route);
+
+        final channel = eg.stream(name: 'stream name');
+        final msg = eg.streamMessage(stream: channel, topic: 'topic name');
+
+        await setupMessageListPage(
+          tester,
+          narrow: TopicNarrow(channel.streamId, 'topic name'),
+          navObservers: [navObserver],
+          streams: [channel],
+          messages: [msg],
+        );
+
+        assert(pushedRoutes.length == 1);
+        pushedRoutes.clear();
+
+        final topicFinder = find.descendant(
+          of: find.byType(StreamMessageRecipientHeader),
+          matching: find.text('topic name'),
+        );
+
+        expect(topicFinder.evaluate().length, equals(1));
+        await tester.tap(topicFinder);
+        await tester.pumpAndSettle();
+
+        expect(pushedRoutes.length, equals(0));
+      });
     });
 
     group('DmRecipientHeader', () {
@@ -987,6 +1018,34 @@ void main() {
       tester.widget(find.textContaining(RegExp("Dec 1[89], 2022")));
       tester.widget(find.textContaining(RegExp("Aug 2[23], 2022")));
     });
+
+    testWidgets('does not navigate on tapping recipient header in DmNarrow', (tester) async {
+      final pushedRoutes = <Route<void>>[];
+      final navObserver = TestNavigatorObserver()
+        ..onPushed = (route, prevRoute) => pushedRoutes.add(route);
+
+      final dmMessage = eg.dmMessage(from: eg.selfUser, to: [eg.otherUser]);
+
+      await setupMessageListPage(
+        tester,
+        narrow: DmNarrow.withUser(eg.otherUser.userId, selfUserId: eg.selfUser.userId),
+        navObservers: [navObserver],
+        messages: [dmMessage],
+      );
+
+      assert(pushedRoutes.length == 1);
+
+      pushedRoutes.clear();
+
+      final recipientHeaderFinder = find.byType(DmRecipientHeader);
+
+      expect(recipientHeaderFinder.evaluate().length, equals(1));
+
+      await tester.tap(recipientHeaderFinder);
+      await tester.pumpAndSettle();
+
+      expect(pushedRoutes.length, equals(0));
+    });
   });
 
   group('formatHeaderDate', () {