compose: Omit "(no topic)" from hint when not allowed to send there

Previously, "Message #stream > (no topic)" would appear as the hint text
when the topic input is empty but mandatory.  Now, it is shown as
"Message #stream" instead, since the "(no topic)" isn't allowed when
topics are mandatory.

Co-authored-by: Zixuan James Li <[email protected]>

Author: gnprice

lib/widgets/compose_box.dart

@@ -579,8 +579,15 @@ class _StreamContentInputState extends State<_StreamContentInput> {
     super.dispose();
   }
 
-  /// The topic name to use in the hint text.
-  TopicName _hintTopic() {
+  /// 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;
+      }
+    }
+
     return TopicName(widget.controller.topic.textNormalized);
   }
 
@@ -591,12 +598,13 @@ class _StreamContentInputState extends State<_StreamContentInput> {
 
     final streamName = store.streams[widget.narrow.streamId]?.name
       ?? zulipLocalizations.unknownChannelName;
-    final hintDestination =
+    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 > ${_hintTopic().displayName}';
+      ? '#$streamName' : '#$streamName > ${hintTopic.displayName}';
 
     return _ContentInput(
       narrow: widget.narrow,

test/widgets/compose_box_test.dart

@@ -326,11 +326,13 @@ void main() {
 
     Future<void> prepare(WidgetTester tester, {
       required Narrow narrow,
+      bool? mandatoryTopics,
     }) async {
       await prepareComposeBox(tester,
         narrow: narrow,
         otherUsers: [eg.otherUser, eg.thirdUser],
-        streams: [channel]);
+        streams: [channel],
+        mandatoryTopics: mandatoryTopics);
     }
 
     /// This checks the input's configured hint text without regard to whether
@@ -351,17 +353,56 @@ void main() {
         .decoration.isNotNull().hintText.equals(contentHintText);
     }
 
-    group('to ChannelNarrow', () {
+    group('to ChannelNarrow, topics not mandatory', () {
+      final narrow = ChannelNarrow(channel.streamId);
+
       testWidgets('with empty topic', (tester) async {
-        await prepare(tester, narrow: ChannelNarrow(channel.streamId));
+        await prepare(tester, narrow: narrow, mandatoryTopics: false);
+        checkComposeBoxHintTexts(tester,
+          topicHintText: 'Topic',
+          contentHintText: 'Message #${channel.name} > (no topic)');
+      });
+
+      testWidgets('with non-empty but vacuous topic', (tester) async {
+        await prepare(tester, narrow: narrow, mandatoryTopics: false);
+        await enterTopic(tester, narrow: narrow, topic: '(no topic)');
+        await tester.pump();
         checkComposeBoxHintTexts(tester,
           topicHintText: 'Topic',
           contentHintText: 'Message #${channel.name} > (no topic)');
       });
 
       testWidgets('with non-empty topic', (tester) async {
-        final narrow = ChannelNarrow(channel.streamId);
-        await prepare(tester, narrow: narrow);
+        await prepare(tester, narrow: narrow, mandatoryTopics: false);
+        await enterTopic(tester, narrow: narrow, topic: 'new topic');
+        await tester.pump();
+        checkComposeBoxHintTexts(tester,
+          topicHintText: 'Topic',
+          contentHintText: 'Message #${channel.name} > new topic');
+      });
+    });
+
+    group('to ChannelNarrow, mandatory topics', () {
+      final narrow = ChannelNarrow(channel.streamId);
+
+      testWidgets('with empty topic', (tester) async {
+        await prepare(tester, narrow: narrow, mandatoryTopics: true);
+        checkComposeBoxHintTexts(tester,
+          topicHintText: 'Topic',
+          contentHintText: 'Message #${channel.name}');
+      });
+
+      testWidgets('with non-empty but vacuous topic', (tester) async {
+        await prepare(tester, narrow: narrow, mandatoryTopics: true);
+        await enterTopic(tester, narrow: narrow, topic: '(no topic)');
+        await tester.pump();
+        checkComposeBoxHintTexts(tester,
+          topicHintText: 'Topic',
+          contentHintText: 'Message #${channel.name}');
+      });
+
+      testWidgets('with non-empty topic', (tester) async {
+        await prepare(tester, narrow: narrow, mandatoryTopics: true);
         await enterTopic(tester, narrow: narrow, topic: 'new topic');
         await tester.pump();
         checkComposeBoxHintTexts(tester,