msglist: Normalize topic name when opening message list

Fixes: #1717

Author: rajveermalviya

lib/widgets/message_list.dart

@@ -2,6 +2,7 @@ import 'dart:async';
 
 import 'package:collection/collection.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter/scheduler.dart';
 import 'package:flutter_color_models/flutter_color_models.dart';
 import 'package:intl/intl.dart' hide TextDirection;
 
@@ -772,8 +773,17 @@ class _MessageListState extends State<MessageList> with PerAccountStoreAwareStat
   }
 
   void _initModel(PerAccountStore store, Anchor anchor) {
+    // Normalize topic name if this is a TopicNarrow. See #1717.
+    var narrow = widget.narrow;
+    if (narrow is TopicNarrow) {
+      narrow = narrow.processTopicLikeServer(
+        zulipFeatureLevel: store.zulipFeatureLevel,
+        realmEmptyTopicDisplayName: store.zulipFeatureLevel > 334
+          ? store.realmEmptyTopicDisplayName
+          : null);
+    }
     _model = MessageListView.init(store: store,
-      narrow: widget.narrow, anchor: anchor);
+      narrow: narrow, anchor: anchor);
     model.addListener(_modelChanged);
     model.fetchInitial();
   }
@@ -794,6 +804,7 @@ class _MessageListState extends State<MessageList> with PerAccountStoreAwareStat
 
     if (model.narrow != widget.narrow) {
       // Either:
+      // - We normalized the topic name in `_initModel` above.
       // - A message move event occurred, where propagate mode is
       //   [PropagateMode.changeAll] or [PropagateMode.changeLater]. Or:
       // - We fetched a "with" / topic-permalink narrow, and the response

test/widgets/message_list_test.dart

@@ -158,6 +158,17 @@ void main() {
       check(state.narrow).equals(ChannelNarrow(stream.streamId));
     });
 
+    testWidgets('MessageListPageState.narrow (general chat)', (tester) async {
+      final stream = eg.stream();
+      final topic = eg.defaultRealmEmptyTopicDisplayName;
+      final topicNarrow = eg.topicNarrow(stream.streamId, topic);
+      await setupMessageListPage(tester, narrow: topicNarrow,
+        streams: [stream],
+        messages: [eg.streamMessage(stream: stream, topic: topic, content: "<p>a message</p>")]);
+      final state = MessageListPage.ancestorOf(tester.element(find.text("a message")));
+      check(state.narrow).equals(eg.topicNarrow(stream.streamId, ''));
+    });
+
     testWidgets('composeBoxState finds compose box', (tester) async {
       final stream = eg.stream();
       await setupMessageListPage(tester, narrow: ChannelNarrow(stream.streamId),