msglist: Show list of topics in channel

assets/l10n/app_ar.arb

@@ -7,5 +7,13 @@
   "wildcardMentionChannelDescription": "إخطار القناة",
   "wildcardMentionStreamDescription": "إخطار الدفق",
   "wildcardMentionAllDmDescription": "إخطار المستلمين",
-  "wildcardMentionTopicDescription": "إخطار الموضوع"
+  "wildcardMentionTopicDescription": "إخطار الموضوع",
+  "topicListButtonTooltip": "عرض المواضيع",
+  "@topicListButtonTooltip": {
+    "description": "Tooltip for button to navigate to a given channel's topic list"
+  },
+  "searchTopicsPlaceholder": "بحث المواضيع",
+  "@searchTopicsPlaceholder": {
+    "description": "Placeholder text for the search field in the topic list page"
+  }
 }

assets/l10n/app_en.arb

@@ -830,5 +830,13 @@
   "zulipAppTitle": "Zulip",
   "@zulipAppTitle": {
     "description": "The name of Zulip. This should be either 'Zulip' or a transliteration."
+  },
+  "topicListButtonTooltip": "Show topics",
+  "@topicListButtonTooltip": {
+    "description": "Tooltip for button to navigate to a given channel's topic list"
+  },
+  "searchTopicsPlaceholder": "Search topics",
+  "@searchTopicsPlaceholder": {
+    "description": "Placeholder text for the search field in the topic list page"
   }
 }

assets/l10n/app_ja.arb

@@ -16,5 +16,13 @@
   "userRoleGuest": "ゲスト",
   "@userRoleGuest": {},
   "userRoleUnknown": "不明",
-  "@userRoleUnknown": {}
+  "@userRoleUnknown": {},
+  "topicListButtonTooltip": "トピックを表示",
+  "@topicListButtonTooltip": {
+    "description": "Tooltip for button to navigate to a given channel's topic list"
+  },
+  "searchTopicsPlaceholder": "トピックを検索",
+  "@searchTopicsPlaceholder": {
+    "description": "Placeholder text for the search field in the topic list page"
+  }
 }

assets/l10n/app_nb.arb

@@ -10,5 +10,13 @@
   "aboutPageOpenSourceLicenses": "Lisenser for åpen kildekode",
   "@aboutPageOpenSourceLicenses": {
     "description": "Item title in About Zulip page to navigate to Licenses page"
+  },
+  "topicListButtonTooltip": "Vis emner",
+  "@topicListButtonTooltip": {
+    "description": "Tooltip for button to navigate to a given channel's topic list"
+  },
+  "searchTopicsPlaceholder": "Søk emner",
+  "@searchTopicsPlaceholder": {
+    "description": "Placeholder text for the search field in the topic list page"
   }
 }

assets/l10n/app_pl.arb

@@ -886,5 +886,13 @@
   "unpinnedSubscriptionsLabel": "Odpięte",
   "@unpinnedSubscriptionsLabel": {
     "description": "Label for the list of unpinned subscribed channels."
+  },
+  "topicListButtonTooltip": "Pokaż tematy",
+  "@topicListButtonTooltip": {
+    "description": "Tooltip for button to navigate to a given channel's topic list"
+  },
+  "searchTopicsPlaceholder": "Szukaj tematów",
+  "@searchTopicsPlaceholder": {
+    "description": "Placeholder text for the search field in the topic list page"
   }
 }

assets/l10n/app_ru.arb

@@ -758,5 +758,13 @@
   "errorMessageNotSent": "Сообщение не отправлено",
   "@errorMessageNotSent": {
     "description": "Error message for compose box when a message could not be sent."
+  },
+  "topicListButtonTooltip": "Показать темы",
+  "@topicListButtonTooltip": {
+    "description": "Tooltip for button to navigate to a given channel's topic list"
+  },
+  "searchTopicsPlaceholder": "Поиск тем",
+  "@searchTopicsPlaceholder": {
+    "description": "Placeholder text for the search field in the topic list page"
   }
 }

assets/l10n/app_sk.arb

@@ -546,5 +546,13 @@
   "errorNotificationOpenTitle": "Nepodarilo sa otvoriť oznámenie",
   "@errorNotificationOpenTitle": {
     "description": "Error title when notification opening fails"
+  },
+  "topicListButtonTooltip": "Zobraziť témy",
+  "@topicListButtonTooltip": {
+    "description": "Tooltip for button to navigate to a given channel's topic list"
+  },
+  "searchTopicsPlaceholder": "Hľadať témy",
+  "@searchTopicsPlaceholder": {
+    "description": "Placeholder text for the search field in the topic list page"
   }
 }

lib/generated/l10n/zulip_localizations.dart

@@ -1214,6 +1214,18 @@ abstract class ZulipLocalizations {
   /// In en, this message translates to:
   /// **'Zulip'**
   String get zulipAppTitle;
+
+  /// Tooltip for button to navigate to a given channel's topic list
+  ///
+  /// In en, this message translates to:
+  /// **'Show topics'**
+  String get topicListButtonTooltip;
+
+  /// Placeholder text for the search field in the topic list page
+  ///
+  /// In en, this message translates to:
+  /// **'Search topics'**
+  String get searchTopicsPlaceholder;
 }
 
 class _ZulipLocalizationsDelegate extends LocalizationsDelegate<ZulipLocalizations> {

lib/generated/l10n/zulip_localizations_ar.dart

@@ -648,4 +648,10 @@ class ZulipLocalizationsAr extends ZulipLocalizations {
 
   @override
   String get zulipAppTitle => 'Zulip';
+
+  @override
+  String get topicListButtonTooltip => 'عرض المواضيع';
+
+  @override
+  String get searchTopicsPlaceholder => 'بحث المواضيع';
 }

lib/generated/l10n/zulip_localizations_en.dart

@@ -648,4 +648,10 @@ class ZulipLocalizationsEn extends ZulipLocalizations {
 
   @override
   String get zulipAppTitle => 'Zulip';
+
+  @override
+  String get topicListButtonTooltip => 'Show topics';
+
+  @override
+  String get searchTopicsPlaceholder => 'Search topics';
 }

lib/generated/l10n/zulip_localizations_ja.dart

@@ -648,4 +648,10 @@ class ZulipLocalizationsJa extends ZulipLocalizations {
 
   @override
   String get zulipAppTitle => 'Zulip';
+
+  @override
+  String get topicListButtonTooltip => 'トピックを表示';
+
+  @override
+  String get searchTopicsPlaceholder => 'トピックを検索';
 }

lib/generated/l10n/zulip_localizations_nb.dart

@@ -648,4 +648,10 @@ class ZulipLocalizationsNb extends ZulipLocalizations {
 
   @override
   String get zulipAppTitle => 'Zulip';
+
+  @override
+  String get topicListButtonTooltip => 'Vis emner';
+
+  @override
+  String get searchTopicsPlaceholder => 'Søk emner';
 }

lib/generated/l10n/zulip_localizations_pl.dart

@@ -648,4 +648,10 @@ class ZulipLocalizationsPl extends ZulipLocalizations {
 
   @override
   String get zulipAppTitle => 'Zulip';
+
+  @override
+  String get topicListButtonTooltip => 'Pokaż tematy';
+
+  @override
+  String get searchTopicsPlaceholder => 'Szukaj tematów';
 }

lib/generated/l10n/zulip_localizations_ru.dart

@@ -648,4 +648,10 @@ class ZulipLocalizationsRu extends ZulipLocalizations {
 
   @override
   String get zulipAppTitle => 'Zulip';
+
+  @override
+  String get topicListButtonTooltip => 'Показать темы';
+
+  @override
+  String get searchTopicsPlaceholder => 'Поиск тем';
 }

lib/generated/l10n/zulip_localizations_sk.dart

@@ -648,4 +648,10 @@ class ZulipLocalizationsSk extends ZulipLocalizations {
 
   @override
   String get zulipAppTitle => 'Zulip';
+
+  @override
+  String get topicListButtonTooltip => 'Zobraziť témy';
+
+  @override
+  String get searchTopicsPlaceholder => 'Hľadať témy';
 }

lib/widgets/message_list.dart

@@ -24,6 +24,7 @@ import 'sticky_header.dart';
 import 'store.dart';
 import 'text.dart';
 import 'theme.dart';
+import 'topic_list.dart';
 
 /// Message-list styles that differ between light and dark themes.
 class MessageListTheme extends ThemeExtension<MessageListTheme> {
@@ -275,6 +276,13 @@ class _MessageListPageState extends State<MessageListPage> implements MessageLis
         onPressed: () => Navigator.push(context,
           MessageListPage.buildRoute(context: context,
             narrow: ChannelNarrow(streamId)))));
+    } else if (narrow case ChannelNarrow(:final streamId)) {
+      (actions ??= []).add(IconButton(
+        icon: const Icon(ZulipIcons.topic),
+        tooltip: zulipLocalizations.topicListButtonTooltip,
+        onPressed: () => Navigator.push(context,
+          TopicListPage.buildRoute(context: context, streamId: streamId, messageListView: model!)),
+      ));
     }
 
     // Insert a PageRoot here, to provide a context that can be used for