general chat #2: support sending to empty topic from channel narrow, hide resolve/unresolve conditionally

lib/widgets/action_sheet.dart

@@ -300,7 +300,11 @@ void showTopicActionSheet(BuildContext context, {
       pageContext: pageContext);
   }));
 
-  if (someMessageIdInTopic != null) {
+  // TODO: check for other cases that may disallow this action (e.g.: time
+  //   limit for editing topics).
+  if (someMessageIdInTopic != null
+      // ignore: unnecessary_null_comparison // null topic names soon to be enabled
+      && topic.displayName != null) {
     optionButtons.add(ResolveUnresolveButton(pageContext: pageContext,
       topic: topic,
       someMessageIdInTopic: someMessageIdInTopic));

lib/widgets/compose_box.dart

@@ -157,15 +157,33 @@ class ComposeTopicController extends ComposeController<TopicValidationError> {
   @override
   String _computeTextNormalized() {
     String trimmed = text.trim();
-    return trimmed.isEmpty ? kNoTopicTopic : trimmed;
+    // TODO(server-10): simplify
+    if (store.zulipFeatureLevel < 334) {
+      return trimmed.isEmpty ? kNoTopicTopic : trimmed;
+    }
+
+    return trimmed;
   }
 
   /// Whether [textNormalized] would fail a mandatory-topics check
   /// (see [mandatory]).
   ///
   /// The term "Vacuous" draws distinction from [String.isEmpty], in the sense
   /// that certain strings are not empty but also indicate the absence of a topic.
-  bool get isTopicVacuous => textNormalized == kNoTopicTopic;
+  ///
+  /// See also: https://zulip.com/api/send-message#parameter-topic
+  bool get isTopicVacuous {
+    if (textNormalized.isEmpty) return true;
+
+    if (textNormalized == kNoTopicTopic) return true;
+
+    // TODO(server-10): simplify
+    if (store.zulipFeatureLevel >= 334) {
+      return textNormalized == store.realmEmptyTopicDisplayName;
+    }
+
+    return false;
+  }
 
   @override
   List<TopicValidationError> _computeValidationErrors() {
@@ -558,10 +576,17 @@ class _StreamContentInputState extends State<_StreamContentInput> {
     });
   }
 
+  void _contentFocusChanged() {
+    setState(() {
+      // The relevant state lives on widget.controller.contentFocusNode itself.
+    });
+  }
+
   @override
   void initState() {
     super.initState();
     widget.controller.topic.addListener(_topicChanged);
+    widget.controller.contentFocusNode.addListener(_contentFocusChanged);
   }
 
   @override
@@ -571,31 +596,61 @@ class _StreamContentInputState extends State<_StreamContentInput> {
       oldWidget.controller.topic.removeListener(_topicChanged);
       widget.controller.topic.addListener(_topicChanged);
     }
+    if (widget.controller.contentFocusNode != oldWidget.controller.contentFocusNode) {
+      oldWidget.controller.contentFocusNode.removeListener(_contentFocusChanged);
+      widget.controller.contentFocusNode.addListener(_contentFocusChanged);
+    }
   }
 
   @override
   void dispose() {
     widget.controller.topic.removeListener(_topicChanged);
+    widget.controller.contentFocusNode.removeListener(_contentFocusChanged);
     super.dispose();
   }
 
+  /// The topic name to show in the hint text, or null to show no topic.
+  TopicName? _hintTopic() {
+    if (widget.controller.topic.isTopicVacuous) {
+      if (widget.controller.topic.mandatory) {
+        // The chosen topic can't be sent to, so don't show it.
+        return null;
+      }
+      if (!widget.controller.contentFocusNode.hasFocus) {
+        // Do not fall back to a vacuous topic unless the user explicitly chooses
+        // to do so (by skipping topic input and moving focus to content input),
+        // so that the user is not encouraged to use vacuous topic when they
+        // have not interacted with the inputs at all.
+        return null;
+      }
+    }
+
+    return TopicName(widget.controller.topic.textNormalized);
+  }
+
   @override
   Widget build(BuildContext context) {
     final store = PerAccountStoreWidget.of(context);
     final zulipLocalizations = ZulipLocalizations.of(context);
+
     final streamName = store.streams[widget.narrow.streamId]?.name
       ?? zulipLocalizations.unknownChannelName;
-    final topic = TopicName(widget.controller.topic.textNormalized);
+    final hintTopic = _hintTopic();
+    final hintDestination = hintTopic == null
+      // No i18n of this use of "#" and ">" string; those are part of how
+      // Zulip expresses channels and topics, not any normal English punctuation,
+      // so don't make sense to translate. See:
+      //   https://github.com/zulip/zulip-flutter/pull/1148#discussion_r1941990585
+      ? '#$streamName'
+      // ignore: dead_null_aware_expression // null topic names soon to be enabled
+      : '#$streamName > ${hintTopic.displayName ?? store.realmEmptyTopicDisplayName}';
+
     return _ContentInput(
       narrow: widget.narrow,
-      destination: TopicNarrow(widget.narrow.streamId, topic),
+      destination: TopicNarrow(widget.narrow.streamId,
+        TopicName(widget.controller.topic.textNormalized)),
       controller: widget.controller,
-      hintText: zulipLocalizations.composeBoxChannelContentHint(
-        // No i18n of this use of "#" and ">" string; those are part of how
-        // Zulip expresses channels and topics, not any normal English punctuation,
-        // so don't make sense to translate. See:
-        //   https://github.com/zulip/zulip-flutter/pull/1148#discussion_r1941990585
-        '#$streamName > ${topic.displayName}'));
+      hintText: zulipLocalizations.composeBoxChannelContentHint(hintDestination));
   }
 }
 
@@ -658,7 +713,8 @@ class _FixedDestinationContentInput extends StatelessWidget {
           // Zulip expresses channels and topics, not any normal English punctuation,
           // so don't make sense to translate. See:
           //   https://github.com/zulip/zulip-flutter/pull/1148#discussion_r1941990585
-          '#$streamName > ${topic.displayName}');
+          // ignore: dead_null_aware_expression // null topic names soon to be enabled
+          '#$streamName > ${topic.displayName ?? store.realmEmptyTopicDisplayName}');
 
       case DmNarrow(otherRecipientIds: []): // The self-1:1 thread.
         return zulipLocalizations.composeBoxSelfDmContentHint;

test/widgets/action_sheet_test.dart

@@ -353,24 +353,27 @@ void main() {
 
     Future<void> showFromAppBar(WidgetTester tester, {
       ZulipStream? channel,
-      String topic = someTopic,
+      TopicName? topic,
       List<StreamMessage>? messages,
     }) async {
       final effectiveChannel = channel ?? someChannel;
+      final effectiveTopic = topic ?? TopicName(someTopic);
       final effectiveMessages = messages ?? [someMessage];
-      assert(effectiveMessages.every((m) => m.topic.apiName == topic));
+      assert(effectiveMessages.every((m) => m.topic.apiName == effectiveTopic.apiName));
 
       connection.prepare(json: eg.newestGetMessagesResult(
         foundOldest: true, messages: effectiveMessages).toJson());
       await tester.pumpWidget(TestZulipApp(accountId: eg.selfAccount.id,
         child: MessageListPage(
-          initNarrow: eg.topicNarrow(effectiveChannel.streamId, topic))));
+          initNarrow: TopicNarrow(effectiveChannel.streamId, effectiveTopic))));
       // global store, per-account store, and message list get loaded
       await tester.pumpAndSettle();
 
       final topicRow = find.descendant(
         of: find.byType(ZulipAppBar),
-        matching: find.text(topic));
+        matching: find.text(
+          // ignore: dead_null_aware_expression // null topic names soon to be enabled
+          effectiveTopic.displayName ?? eg.defaultRealmEmptyTopicDisplayName));
       await tester.longPress(topicRow);
       // sheet appears onscreen; default duration of bottom-sheet enter animation
       await tester.pump(const Duration(milliseconds: 250));
@@ -446,6 +449,16 @@ void main() {
         check(findButtonForLabel('Mark as unresolved')).findsNothing();
       });
 
+      testWidgets('show from app bar: resolve/unresolve not offered when topic is empty', (tester) async {
+        await prepare();
+        final message = eg.streamMessage(stream: someChannel, topic: '');
+        await showFromAppBar(tester,
+          topic: TopicName(''),
+          messages: [message]);
+        check(findButtonForLabel('Mark as resolved')).findsNothing();
+        check(findButtonForLabel('Mark as unresolved')).findsNothing();
+      }, skip: true); // null topic names soon to be enabled
+
       testWidgets('show from recipient header', (tester) async {
         await prepare();
         await showFromRecipientHeader(tester);
@@ -485,7 +498,7 @@ void main() {
         final message = eg.streamMessage(
           stream: someChannel, topic: topic, sender: eg.otherUser);
         await showFromAppBar(tester,
-          channel: someChannel, topic: topic, messages: [message]);
+          channel: someChannel, topic: TopicName(topic), messages: [message]);
       }
 
       void checkButtons(List<Finder> expectedButtonFinders) {
@@ -697,7 +710,8 @@ void main() {
       testWidgets('unresolve: happy path', (tester) async {
         final message = eg.streamMessage(stream: someChannel, topic: '✔ zulip');
         await prepare(topic: '✔ zulip');
-        await showFromAppBar(tester, topic: '✔ zulip', messages: [message]);
+        await showFromAppBar(tester,
+          topic: TopicName('✔ zulip'), messages: [message]);
         connection.takeRequests();
         connection.prepare(json: UpdateMessageResult().toJson());
         await tester.tap(findButtonForLabel('Mark as unresolved'));
@@ -710,7 +724,8 @@ void main() {
       testWidgets('unresolve: weird prefix', (tester) async {
         final message = eg.streamMessage(stream: someChannel, topic: '✔ ✔ zulip');
         await prepare(topic: '✔ ✔ zulip');
-        await showFromAppBar(tester, topic: '✔ ✔ zulip', messages: [message]);
+        await showFromAppBar(tester,
+          topic: TopicName('✔ ✔ zulip'), messages: [message]);
         connection.takeRequests();
         connection.prepare(json: UpdateMessageResult().toJson());
         await tester.tap(findButtonForLabel('Mark as unresolved'));