msglist: When initial message fetch comes up empty, auto-focus compose box

lib/widgets/compose_box.dart

@@ -1546,6 +1546,15 @@ sealed class ComposeBoxController {
   final content = ComposeContentController();
   final contentFocusNode = FocusNode();
 
+  /// If no input is focused, requests focus on the appropriate input.
+  ///
+  /// A convenience method to encapsulate choosing the topic or content input
+  /// when both exist (see [StreamComposeBoxController.requestFocusIfUnfocused]).
+  void requestFocusIfUnfocused() {
+    if (contentFocusNode.hasFocus) return;
+    contentFocusNode.requestFocus();
+  }
+
   @mustCallSuper
   void dispose() {
     content.dispose();
@@ -1609,6 +1618,15 @@ class StreamComposeBoxController extends ComposeBoxController {
   final ValueNotifier<ComposeTopicInteractionStatus> topicInteractionStatus =
     ValueNotifier(ComposeTopicInteractionStatus.notEditingNotChosen);
 
+  @override void requestFocusIfUnfocused() {
+    if (topicFocusNode.hasFocus || contentFocusNode.hasFocus) return;
+    if (topicInteractionStatus.value == ComposeTopicInteractionStatus.notEditingNotChosen) {
+      topicFocusNode.requestFocus();
+    } else {
+      contentFocusNode.requestFocus();
+    }
+  }
+
   @override
   void dispose() {
     topic.dispose();

lib/widgets/message_list.dart

@@ -522,6 +522,8 @@ class _MessageListState extends State<MessageList> with PerAccountStoreAwareStat
     model.fetchInitial();
   }
 
+  bool _prevFetched = false;
+
   void _modelChanged() {
     if (model.narrow != widget.narrow) {
       // Either:
@@ -535,6 +537,15 @@ class _MessageListState extends State<MessageList> with PerAccountStoreAwareStat
       // The actual state lives in the [MessageListView] model.
       // This method was called because that just changed.
     });
+
+    if (!_prevFetched && model.fetched && model.messages.isEmpty) {
+      // If the fetch came up empty, there's nothing to read,
+      // so opening the keyboard won't be bothersome and could be helpful.
+      // It's definitely helpful if we got here from the new-DM page.
+      MessageListPage.ancestorOf(context)
+        .composeBoxState?.controller.requestFocusIfUnfocused();
+    }
+    _prevFetched = model.fetched;
   }
 
   void _handleScrollMetrics(ScrollMetrics scrollMetrics) {

test/widgets/compose_box_checks.dart

@@ -11,6 +11,11 @@ extension ComposeBoxControllerChecks on Subject<ComposeBoxController> {
   Subject<FocusNode> get contentFocusNode => has((c) => c.contentFocusNode, 'contentFocusNode');
 }
 
+extension StreamComposeBoxControllerChecks on Subject<StreamComposeBoxController> {
+  Subject<ComposeTopicController> get topic => has((c) => c.topic, 'topic');
+  Subject<FocusNode> get topicFocusNode => has((c) => c.topicFocusNode, 'topicFocusNode');
+}
+
 extension EditMessageComposeBoxControllerChecks on Subject<EditMessageComposeBoxController> {
   Subject<int> get messageId => has((c) => c.messageId, 'messageId');
   Subject<String?> get originalRawContent => has((c) => c.originalRawContent, 'originalRawContent');

test/widgets/compose_box_test.dart

@@ -3,6 +3,7 @@ import 'dart:convert';
 import 'dart:io';
 
 import 'package:checks/checks.dart';
+import 'package:collection/collection.dart';
 import 'package:crypto/crypto.dart';
 import 'package:file_picker/file_picker.dart';
 import 'package:flutter_checks/flutter_checks.dart';
@@ -56,14 +57,23 @@ void main() {
     User? selfUser,
     List<User> otherUsers = const [],
     List<ZulipStream> streams = const [],
+    List<Message>? messages,
     bool? mandatoryTopics,
     int? zulipFeatureLevel,
   }) async {
     if (narrow case ChannelNarrow(:var streamId) || TopicNarrow(: var streamId)) {
-      assert(streams.any((stream) => stream.streamId == streamId),
+      final channel = streams.firstWhereOrNull((s) => s.streamId == streamId);
+      assert(channel != null,
         'Add a channel with "streamId" the same as of $narrow.streamId to the store.');
+      if (narrow is ChannelNarrow) {
+        // By default, bypass the complexity where the topic input is autofocused
+        // on an empty fetch, by making the fetch not empty. (In particular that
+        // complexity includes a getStreamTopics fetch for topic autocomplete.)
+        messages ??= [eg.streamMessage(stream: channel)];
+      }
     }
     addTearDown(testBinding.reset);
+    messages ??= [];
     selfUser ??= eg.selfUser;
     zulipFeatureLevel ??= eg.futureZulipFeatureLevel;
     final selfAccount = eg.account(user: selfUser, zulipFeatureLevel: zulipFeatureLevel);
@@ -81,7 +91,11 @@ void main() {
     connection = store.connection as FakeApiConnection;
 
     connection.prepare(json:
-      eg.newestGetMessagesResult(foundOldest: true, messages: []).toJson());
+      eg.newestGetMessagesResult(foundOldest: true, messages: messages).toJson());
+    if (narrow is ChannelNarrow && messages.isEmpty) {
+      // The topic input will autofocus, triggering a getStreamTopics request.
+      connection.prepare(json: GetStreamTopicsResult(topics: []).toJson());
+    }
     await tester.pumpWidget(TestZulipApp(accountId: selfAccount.id,
       child: MessageListPage(initNarrow: narrow)));
     await tester.pumpAndSettle();
@@ -134,6 +148,61 @@ void main() {
     await tester.pump(Duration.zero);
   }
 
+  group('auto focus', () {
+    testWidgets('ChannelNarrow, non-empty fetch', (tester) async {
+      final channel = eg.stream();
+      await prepareComposeBox(tester,
+        narrow: ChannelNarrow(channel.streamId),
+        streams: [channel],
+        messages: [eg.streamMessage(stream: channel)]);
+      check(controller).isA<StreamComposeBoxController>()
+        .topicFocusNode.hasFocus.isFalse();
+    });
+
+    testWidgets('ChannelNarrow, empty fetch', (tester) async {
+      final channel = eg.stream();
+      await prepareComposeBox(tester,
+        narrow: ChannelNarrow(channel.streamId),
+        streams: [channel],
+        messages: []);
+      check(controller).isA<StreamComposeBoxController>()
+        .topicFocusNode.hasFocus.isTrue();
+    });
+
+    testWidgets('TopicNarrow, non-empty fetch', (tester) async {
+      final channel = eg.stream();
+      await prepareComposeBox(tester,
+        narrow: TopicNarrow(channel.streamId, eg.t('topic')),
+        streams: [channel],
+        messages: [eg.streamMessage(stream: channel, topic: 'topic')]);
+      check(controller).isNotNull().contentFocusNode.hasFocus.isFalse();
+    });
+
+    testWidgets('TopicNarrow, empty fetch', (tester) async {
+      final channel = eg.stream();
+      await prepareComposeBox(tester,
+        narrow: TopicNarrow(channel.streamId, eg.t('topic')),
+        streams: [channel],
+        messages: []);
+      check(controller).isNotNull().contentFocusNode.hasFocus.isTrue();
+    });
+
+    testWidgets('DmNarrow, non-empty fetch', (tester) async {
+      final user = eg.user();
+      await prepareComposeBox(tester,
+        narrow: DmNarrow.withUser(user.userId, selfUserId: store.selfUserId),
+        messages: [eg.dmMessage(from: user, to: [store.selfUser])]);
+      check(controller).isNotNull().contentFocusNode.hasFocus.isFalse();
+    });
+
+    testWidgets('DmNarrow, empty fetch', (tester) async {
+      await prepareComposeBox(tester,
+        narrow: DmNarrow.withUser(eg.user().userId, selfUserId: store.selfUserId),
+        messages: []);
+      check(controller).isNotNull().contentFocusNode.hasFocus.isTrue();
+    });
+  });
+
   group('ComposeBoxTheme', () {
     test('lerp light to dark, no crash', () {
       final a = ComposeBoxTheme.light;