home: Sort leading emoji first in channel names

Update the channel sorting logic to match the channels order
of web by putting emoji-prefixed channels first.

Fixes: zulip#1202

Author: lakshya1goel

lib/widgets/subscription_list.dart

@@ -41,10 +41,22 @@ class _SubscriptionListPageBodyState extends State<SubscriptionListPageBody> wit
     });
   }
 
+  final _startsWithEmojiRegex = RegExp(r'^\p{Emoji}', unicode: true);
+
   void _sortSubs(List<Subscription> list) {
     list.sort((a, b) {
       if (a.isMuted && !b.isMuted) return 1;
       if (!a.isMuted && b.isMuted) return -1;
+
+      // A user gave feedback wanting zulip-flutter to match web in putting
+      // emoji-prefixed channels first; see #1202.
+      // For matching web's ordering completely, see:
+      //   https://github.com/zulip/zulip-flutter/issues/1165
+      final aStartsWithEmoji = _startsWithEmojiRegex.hasMatch(a.name);
+      final bStartsWithEmoji = _startsWithEmojiRegex.hasMatch(b.name);
+      if (aStartsWithEmoji && !bStartsWithEmoji) return -1;
+      if (!aStartsWithEmoji && bStartsWithEmoji) return 1;
+
       // TODO(i18n): add locale-aware sorting
       return a.name.toLowerCase().compareTo(b.name.toLowerCase());
     });

test/widgets/subscription_list_test.dart

@@ -150,6 +150,32 @@ void main() {
       ]);
       check(listedStreamIds(tester)).deepEquals([2, 1, 3, 4, 6, 5]);
     });
+
+    testWidgets('channels with emoji in name are listed above non-emoji names', (tester) async {
+      await setupStreamListPage(tester, subscriptions: [
+        eg.subscription(eg.stream(streamId: 1, name: 'Happy 😊 Stream')),
+        eg.subscription(eg.stream(streamId: 2, name: 'Alpha Stream')),
+        eg.subscription(eg.stream(streamId: 3, name: '🚀 Rocket Stream')),
+        eg.subscription(eg.stream(streamId: 4, name: 'Beta Stream')),
+      ]);
+
+      check(listedStreamIds(tester)).deepEquals([3, 2, 4, 1]);
+    });
+
+    testWidgets('channels with emoji in name, pinned, unpinned, muted, and unmuted are sorted correctly', (tester) async {
+      await setupStreamListPage(tester, subscriptions: [
+        eg.subscription(eg.stream(streamId: 1, name: '😊 Happy Stream'), pinToTop: true, isMuted: false),
+        eg.subscription(eg.stream(streamId: 2, name: '🚀 Rocket Stream'), pinToTop: true, isMuted: true),
+        eg.subscription(eg.stream(streamId: 3, name: 'Alpha Stream'), pinToTop: true, isMuted: false),
+        eg.subscription(eg.stream(streamId: 4, name: 'Beta Stream'), pinToTop: true, isMuted: true),
+        eg.subscription(eg.stream(streamId: 5, name: '🌟 Star Stream'), pinToTop: false, isMuted: false),
+        eg.subscription(eg.stream(streamId: 6, name: '🔥 Fire Stream'), pinToTop: false, isMuted: true),
+        eg.subscription(eg.stream(streamId: 7, name: 'Gamma Stream'), pinToTop: false, isMuted: false),
+        eg.subscription(eg.stream(streamId: 8, name: 'Delta Stream'), pinToTop: false, isMuted: true),
+      ]);
+
+      check(listedStreamIds(tester)).deepEquals([1, 3, 2, 4, 5, 7, 6, 8]);
+    });
   });
 
   testWidgets('unread badge shows with unreads', (tester) async {