msglist: Add channel-feed action from topic narrows

Fixes: zulip#1040

assets/l10n/app_en.arb

@@ -545,6 +545,10 @@
   "@starredMessagesPageTitle": {
     "description": "Title for the page of starred messages."
   },
+  "channelFeedButtonTooltip": "Channel feed",
+  "@channelFeedButtonTooltip": {
+    "description": "Tooltip for button to navigate to a given channel's feed"
+  },
   "notifGroupDmConversationLabel": "{senderFullName} to you and {numOthers, plural, =1{1 other} other{{numOthers} others}}",
   "@notifGroupDmConversationLabel": {
     "description": "Label for a group DM conversation notification.",

lib/generated/l10n/zulip_localizations.dart

@@ -823,6 +823,12 @@ abstract class ZulipLocalizations {
   /// **'Starred messages'**
   String get starredMessagesPageTitle;
 
+  /// Tooltip for button to navigate to a given channel's feed
+  ///
+  /// In en, this message translates to:
+  /// **'Channel feed'**
+  String get channelFeedButtonTooltip;
+
   /// Label for a group DM conversation notification.
   ///
   /// In en, this message translates to:

lib/generated/l10n/zulip_localizations_ar.dart

@@ -431,6 +431,9 @@ class ZulipLocalizationsAr extends ZulipLocalizations {
   @override
   String get starredMessagesPageTitle => 'Starred messages';
 
+  @override
+  String get channelFeedButtonTooltip => 'Channel feed';
+
   @override
   String notifGroupDmConversationLabel(String senderFullName, int numOthers) {
     String _temp0 = intl.Intl.pluralLogic(

lib/generated/l10n/zulip_localizations_en.dart

@@ -431,6 +431,9 @@ class ZulipLocalizationsEn extends ZulipLocalizations {
   @override
   String get starredMessagesPageTitle => 'Starred messages';
 
+  @override
+  String get channelFeedButtonTooltip => 'Channel feed';
+
   @override
   String notifGroupDmConversationLabel(String senderFullName, int numOthers) {
     String _temp0 = intl.Intl.pluralLogic(

lib/generated/l10n/zulip_localizations_ja.dart

@@ -431,6 +431,9 @@ class ZulipLocalizationsJa extends ZulipLocalizations {
   @override
   String get starredMessagesPageTitle => 'Starred messages';
 
+  @override
+  String get channelFeedButtonTooltip => 'Channel feed';
+
   @override
   String notifGroupDmConversationLabel(String senderFullName, int numOthers) {
     String _temp0 = intl.Intl.pluralLogic(

lib/widgets/message_list.dart

@@ -233,6 +233,7 @@ class _MessageListPageState extends State<MessageListPage> implements MessageLis
   Widget build(BuildContext context) {
     final store = PerAccountStoreWidget.of(context);
     final messageListTheme = MessageListTheme.of(context);
+    final zulipLocalizations = ZulipLocalizations.of(context);
 
     final Color? appBarBackgroundColor;
     bool removeAppBarBottomBorder = false;
@@ -259,9 +260,20 @@ class _MessageListPageState extends State<MessageListPage> implements MessageLis
         removeAppBarBottomBorder = true;
     }
 
+    List<Widget>? actions;
+    if (narrow case TopicNarrow(:final streamId)) {
+      (actions ??= []).add(IconButton(
+        icon: const Icon(ZulipIcons.message_feed),
+        tooltip: zulipLocalizations.channelFeedButtonTooltip,
+        onPressed: () => Navigator.push(context,
+          MessageListPage.buildRoute(context: context,
+            narrow: ChannelNarrow(streamId)))));
+    }
+
     return Scaffold(
       appBar: ZulipAppBar(
         title: MessageListAppBarTitle(narrow: narrow),
+        actions: actions,
         backgroundColor: appBarBackgroundColor,
         shape: removeAppBarBottomBorder
           ? const Border()

test/widgets/message_list_test.dart

@@ -21,6 +21,7 @@ import 'package:zulip/widgets/color.dart';
 import 'package:zulip/widgets/content.dart';
 import 'package:zulip/widgets/icons.dart';
 import 'package:zulip/widgets/message_list.dart';
+import 'package:zulip/widgets/page.dart';
 import 'package:zulip/widgets/store.dart';
 import 'package:zulip/widgets/channel_colors.dart';
 
@@ -32,8 +33,11 @@ import '../model/test_store.dart';
 import '../flutter_checks.dart';
 import '../stdlib_checks.dart';
 import '../test_images.dart';
+import '../test_navigation.dart';
 import 'content_checks.dart';
 import 'dialog_checks.dart';
+import 'message_list_checks.dart';
+import 'page_checks.dart';
 import 'test_app.dart';
 
 void main() {
@@ -51,6 +55,7 @@ void main() {
     List<User>? users,
     List<Subscription>? subscriptions,
     UnreadMessagesSnapshot? unreadMsgs,
+    List<NavigatorObserver> navObservers = const [],
   }) async {
     TypingNotifier.debugEnable = false;
     addTearDown(TypingNotifier.debugReset);
@@ -72,6 +77,7 @@ void main() {
       eg.newestGetMessagesResult(foundOldest: foundOldest, messages: messages).toJson());
 
     await tester.pumpWidget(TestZulipApp(accountId: eg.selfAccount.id,
+      navigatorObservers: navObservers,
       child: MessageListPage(initNarrow: narrow)));
 
     // global store, per-account store, and message list get loaded
@@ -126,6 +132,28 @@ void main() {
     });
   });
 
+  group('app bar', () {
+    testWidgets('has channel-feed action for topic narrows', (tester) async {
+      final pushedRoutes = <Route<void>>[];
+      final navObserver = TestNavigatorObserver()
+        ..onPushed = (route, prevRoute) => pushedRoutes.add(route);
+      final channel = eg.stream();
+      await setupMessageListPage(tester, narrow: TopicNarrow(channel.streamId, 'hi'),
+        navObservers: [navObserver],
+        streams: [channel], messageCount: 1);
+
+      // Clear out initial route.
+      assert(pushedRoutes.length == 1);
+      pushedRoutes.clear();
+
+      // Tap button; it works.
+      await tester.tap(find.byIcon(ZulipIcons.message_feed));
+      check(pushedRoutes).single.isA<WidgetRoute>()
+        .page.isA<MessageListPage>().initNarrow
+          .equals(ChannelNarrow(channel.streamId));
+    });
+  });
+
   group('presents message content appropriately', () {
     testWidgets('content not asked to consume insets (including bottom), even without compose box', (tester) async {
       // Regression test for: https://github.com/zulip/zulip-flutter/issues/736