compose_box: Send typing notifications on scroll

When selecting from the list of autocompletion, the user is still
considered to be actively composing.

Fixes: #666

Author: PIG208

lib/widgets/compose_box.dart

@@ -339,6 +339,12 @@ class _ContentInputState extends State<_ContentInput> with WidgetsBindingObserve
     store.typingNotifier.stoppedComposing();
   }
 
+  bool _handleScroll(ScrollNotification notification) {
+    final store = PerAccountStoreWidget.of(context);
+    store.typingNotifier.keystroke(widget.destination);
+    return false;
+  }
+
   @override
   void didChangeAppLifecycleState(AppLifecycleState state) {
     switch (state) {
@@ -377,21 +383,23 @@ class _ContentInputState extends State<_ContentInput> with WidgetsBindingObserve
           // TODO constrain this adaptively (i.e. not hard-coded 200)
           maxHeight: 200,
         ),
-        child: ComposeAutocomplete(
-          narrow: widget.narrow,
-          controller: widget.controller,
-          focusNode: widget.focusNode,
-          fieldViewBuilder: (context) {
-            return TextField(
-              controller: widget.controller,
-              focusNode: widget.focusNode,
-              style: TextStyle(color: colorScheme.onSurface),
-              decoration: InputDecoration.collapsed(hintText: widget.hintText),
-              maxLines: null,
-              textCapitalization: TextCapitalization.sentences,
-            );
-          }),
-        ));
+        child: NotificationListener<ScrollNotification>(
+          onNotification: _handleScroll,
+          child: ComposeAutocomplete(
+            narrow: widget.narrow,
+            controller: widget.controller,
+            focusNode: widget.focusNode,
+            fieldViewBuilder: (context) {
+              return TextField(
+                controller: widget.controller,
+                focusNode: widget.focusNode,
+                style: TextStyle(color: colorScheme.onSurface),
+                decoration: InputDecoration.collapsed(hintText: widget.hintText),
+                maxLines: null,
+                textCapitalization: TextCapitalization.sentences,
+              );
+            }),
+        )));
   }
 }
 

test/widgets/compose_box_test.dart

@@ -423,6 +423,35 @@ void main() {
       await tester.pump(store.typingNotifier.typingStoppedWaitPeriod);
       checkTypingRequest(TypingOp.stop, narrow);
     });
+
+    testWidgets('scrolling autocompletion sends "typing started" notice', (tester) async {
+      final users = List.generate(10, (i) => eg.user(fullName: 'User $i'));
+      final narrow = DmNarrow.withUser(
+        users[0].userId, selfUserId: eg.selfUser.userId);
+      await prepareComposeBox(tester,
+        narrow: narrow, users: [eg.otherUser, ...users]);
+
+      connection.prepare(json: {});
+      // TODO(#226): Remove this extra edit when this bug is fixed.
+      await tester.enterText(contentInputFinder, '@Use');
+      await tester.enterText(contentInputFinder, '@User');
+      await tester.pumpAndSettle(); // async computation; options appear
+      checkTypingRequest(TypingOp.start, narrow);
+
+      connection.prepare(json: {});
+      await tester.pump(store.typingNotifier.typingStoppedWaitPeriod);
+      checkTypingRequest(TypingOp.stop, narrow);
+
+      connection.prepare(json: {});
+      await tester.drag(find.text(users[0].fullName), const Offset(0, 5));
+      await tester.pump(Duration.zero);
+      checkTypingRequest(TypingOp.start, narrow);
+
+      // Ensures that a "typing stopped" notice is sent when the test ends.
+      connection.prepare(json: {});
+      await tester.pump(store.typingNotifier.typingStoppedWaitPeriod);
+      checkTypingRequest(TypingOp.stop, narrow);
+    });
   });
 
   group('message-send request response', () {