subscription_list: Show @-mention indicator when it applies

Fixes: #747

Author: Khader-1

lib/model/unreads.dart

@@ -219,6 +219,17 @@ class Unreads extends ChangeNotifier {
     }
   }
 
+  Set<int> get channelsWithUnreadMentions {
+    final channels = <int>{};
+    for (var messageId in mentions) {
+      final streamId = _reverseStreamsLookup[messageId]?.streamId;
+      if (streamId != null) {
+        channels.add(streamId);
+      }
+    }
+    return channels;
+  }
+
   void handleMessageEvent(MessageEvent event) {
     final message = event.message;
     if (message.flags.contains(MessageFlag.read)) {

lib/widgets/subscription_list.dart

@@ -185,16 +185,19 @@ class _SubscriptionList extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final channelsWithMentions = unreadsModel!.channelsWithUnreadMentions;
     return SliverList.builder(
       itemCount: subscriptions.length,
       itemBuilder: (BuildContext context, int index) {
         final subscription = subscriptions[index];
         final unreadCount = unreadsModel!.countInChannel(subscription.streamId);
         final showMutedUnreadBadge = unreadCount == 0
           && unreadsModel!.countInChannelNarrow(subscription.streamId) > 0;
+        final hasMentions = channelsWithMentions.contains(subscription.streamId);
         return SubscriptionItem(subscription: subscription,
           unreadCount: unreadCount,
-          showMutedUnreadBadge: showMutedUnreadBadge);
+          showMutedUnreadBadge: showMutedUnreadBadge,
+          hasMentions: hasMentions);
     });
   }
 }
@@ -206,11 +209,13 @@ class SubscriptionItem extends StatelessWidget {
     required this.subscription,
     required this.unreadCount,
     required this.showMutedUnreadBadge,
+    required this.hasMentions,
   });
 
   final Subscription subscription;
   final int unreadCount;
   final bool showMutedUnreadBadge;
+  final bool hasMentions;
 
   @override
   Widget build(BuildContext context) {
@@ -258,7 +263,7 @@ class SubscriptionItem extends StatelessWidget {
                   subscription.name)))),
           if (hasUnreads) ...[
             const SizedBox(width: 12),
-            // TODO(#747) show @-mention indicator when it applies
+            if (hasMentions) const AtMentionMarker(),
             Opacity(
               opacity: opacity,
               child: UnreadCountBadge(
@@ -267,7 +272,7 @@ class SubscriptionItem extends StatelessWidget {
                 bold: true)),
           ] else if (showMutedUnreadBadge) ...[
             const SizedBox(width: 12),
-            // TODO(#747) show @-mention indicator when it applies
+            if (hasMentions) const AtMentionMarker(),
             const MutedUnreadBadge(),
           ],
           const SizedBox(width: 16),

test/model/unreads_test.dart

@@ -298,6 +298,20 @@ void main() {
           });
         }
       });
+
+      test('channelsWithUnreadMentions', () {
+        final stream1 = eg.stream();
+        final stream2 = eg.stream();
+
+        prepare();
+        fillWithMessages([
+          eg.streamMessage(stream: stream1, flags: [MessageFlag.mentioned]),
+          eg.streamMessage(stream: stream1, flags: []),
+          eg.streamMessage(stream: stream2, flags: []),
+        ]);
+
+        check(model.channelsWithUnreadMentions.single).equals(stream1.streamId);
+      });
     });
 
     group('DM messages', () {

test/widgets/subscription_list_test.dart

@@ -315,4 +315,32 @@ void main() {
     checkStreamNameWght(mutedStreamWithUnmutedUnreads.name,     400);
     checkStreamNameWght(mutedStreamWithNoUnmutedUnreads.name,   400);
   });
+
+  testWidgets('@-mention indicator is shown when subscription has unread mentions', (tester) async {
+    void checkMentionIndicatorsCount(int expectedCount) {
+      check(find.byIcon(ZulipIcons.at_sign).evaluate().length).equals(expectedCount);
+    }
+
+    final streamWithMentions =   eg.stream();
+    final streamWithNoMentions = eg.stream();
+
+    await setupStreamListPage(tester,
+      subscriptions: [
+        eg.subscription(streamWithMentions),
+        eg.subscription(streamWithNoMentions),
+      ],
+      userTopics: [
+        eg.userTopicItem(streamWithMentions,   'a', UserTopicVisibilityPolicy.unmuted),
+        eg.userTopicItem(streamWithNoMentions, 'b', UserTopicVisibilityPolicy.muted),
+      ],
+      unreadMsgs: eg.unreadMsgs(
+        mentions: [1],
+        channels: [
+          UnreadChannelSnapshot(streamId: streamWithMentions.streamId,   topic: 'a', unreadMessageIds: [1]),
+          UnreadChannelSnapshot(streamId: streamWithNoMentions.streamId, topic: 'b', unreadMessageIds: [2]),
+        ]),
+    );
+
+    checkMentionIndicatorsCount(1);
+  });
 }