Fix scrollbar config for hover events (#72833)

packages/flutter/lib/src/material/scrollbar.dart

@@ -98,9 +98,6 @@ class _ScrollbarState extends RawScrollbarState<Scrollbar> {
   late ColorScheme _colorScheme;
   // On Android, scrollbars should match native appearance.
   late bool _useAndroidScrollbar;
-  // Hover events should be ignored on mobile, the exit event cannot be
-  // triggered, but the enter event can on tap.
-  late bool _isMobile;
 
   Set<MaterialState> get _states => <MaterialState>{
     if (_dragIsActive) MaterialState.dragged,
@@ -174,7 +171,7 @@ class _ScrollbarState extends RawScrollbarState<Scrollbar> {
       if (states.contains(MaterialState.hovered) && widget.showTrackOnHover)
         return widget.hoverThickness ?? _kScrollbarThicknessWithTrack;
       // The default scrollbar thickness is smaller on mobile.
-      return widget.thickness ?? (_kScrollbarThickness / (_isMobile ? 2 : 1));
+      return widget.thickness ?? (_kScrollbarThickness / (_useAndroidScrollbar ? 2 : 1));
     });
   }
 
@@ -196,18 +193,13 @@ class _ScrollbarState extends RawScrollbarState<Scrollbar> {
     switch (theme.platform) {
       case TargetPlatform.android:
         _useAndroidScrollbar = true;
-        _isMobile = true;
         break;
       case TargetPlatform.iOS:
-        _useAndroidScrollbar = false;
-        _isMobile = true;
-        break;
       case TargetPlatform.linux:
       case TargetPlatform.fuchsia:
       case TargetPlatform.macOS:
       case TargetPlatform.windows:
         _useAndroidScrollbar = false;
-        _isMobile = false;
         break;
     }
     super.didChangeDependencies();
@@ -242,8 +234,6 @@ class _ScrollbarState extends RawScrollbarState<Scrollbar> {
 
   @override
   void handleHover(PointerHoverEvent event) {
-    // Hover events should not be triggered on mobile.
-    assert(!_isMobile);
     super.handleHover(event);
     // Check if the position of the pointer falls over the painted scrollbar
     if (isPointerOverScrollbar(event.position)) {
@@ -259,8 +249,6 @@ class _ScrollbarState extends RawScrollbarState<Scrollbar> {
 
   @override
   void handleHoverExit(PointerExitEvent event) {
-    // Hover events should not be triggered on mobile.
-    assert(!_isMobile);
     super.handleHoverExit(event);
     setState(() { _hoverIsActive = false; });
     _hoverAnimationController.reverse();

packages/flutter/lib/src/widgets/scrollbar.dart

@@ -782,7 +782,6 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
   late Animation<double> _fadeoutOpacityAnimation;
   final GlobalKey  _scrollbarPainterKey = GlobalKey();
   bool _hoverIsActive = false;
-  late bool _isMobile;
 
 
   /// Used to paint the scrollbar.
@@ -813,18 +812,6 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
-    switch (defaultTargetPlatform) {
-      case TargetPlatform.android:
-      case TargetPlatform.iOS:
-        _isMobile = true;
-        break;
-      case TargetPlatform.fuchsia:
-      case TargetPlatform.linux:
-      case TargetPlatform.macOS:
-      case TargetPlatform.windows:
-        _isMobile = false;
-        break;
-    }
     _maybeTriggerScrollbar();
   }
 
@@ -1165,27 +1152,42 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
   Widget build(BuildContext context) {
     updateScrollbarPainter();
 
-    Widget child = CustomPaint(
-      key: _scrollbarPainterKey,
-      foregroundPainter: scrollbarPainter,
-      child: RepaintBoundary(child: widget.child),
-    );
-
-    if (!_isMobile) {
-      // Hover events not supported on mobile.
-      child = MouseRegion(
-        onExit: handleHoverExit,
-        onHover: handleHover,
-        child: child
-      );
-    }
-
     return NotificationListener<ScrollNotification>(
       onNotification: _handleScrollNotification,
       child: RepaintBoundary(
         child: RawGestureDetector(
           gestures: _gestures,
-          child: child,
+          child: MouseRegion(
+            onExit: (PointerExitEvent event) {
+              switch(event.kind) {
+                case PointerDeviceKind.mouse:
+                  handleHoverExit(event);
+                  break;
+                case PointerDeviceKind.stylus:
+                case PointerDeviceKind.invertedStylus:
+                case PointerDeviceKind.unknown:
+                case PointerDeviceKind.touch:
+                  break;
+              }
+            },
+            onHover: (PointerHoverEvent event) {
+              switch(event.kind) {
+                case PointerDeviceKind.mouse:
+                  handleHover(event);
+                  break;
+                case PointerDeviceKind.stylus:
+                case PointerDeviceKind.invertedStylus:
+                case PointerDeviceKind.unknown:
+                case PointerDeviceKind.touch:
+                  break;
+              }
+            },
+            child: CustomPaint(
+              key: _scrollbarPainterKey,
+              foregroundPainter: scrollbarPainter,
+              child: RepaintBoundary(child: widget.child),
+            )
+          ),
         ),
       ),
     );

packages/flutter/test/material/scrollbar_test.dart

@@ -842,7 +842,7 @@ void main() {
     }),
   );
 
-  testWidgets('Hover animation is not triggered on mobile', (WidgetTester tester) async {
+  testWidgets('Hover animation is not triggered by tap gestures', (WidgetTester tester) async {
     final ScrollController scrollController = ScrollController();
     await tester.pumpWidget(
       MaterialApp(
@@ -864,7 +864,7 @@ void main() {
       find.byType(Scrollbar),
       paints..rrect(
         rrect: RRect.fromRectAndRadius(
-          const Rect.fromLTRB(794.0, 0.0, 798.0, 90.0),
+          const Rect.fromLTRB(790.0, 0.0, 798.0, 90.0),
           const Radius.circular(8.0),
         ),
         color: const Color(0x1a000000),
@@ -873,18 +873,50 @@ void main() {
     await tester.tapAt(const Offset(794.0, 5.0));
     await tester.pumpAndSettle();
 
-    // Tapping on mobile triggers a hover enter event. In this case, the
+    // Tapping triggers a hover enter event. In this case, the Scrollbar should
-    // Scrollbar should be unchanged since it ignores hover events on mobile.
+    // be unchanged since it ignores hover events that aren't from a mouse.
     expect(
       find.byType(Scrollbar),
       paints..rrect(
         rrect: RRect.fromRectAndRadius(
-          const Rect.fromLTRB(794.0, 0.0, 798.0, 90.0),
+          const Rect.fromLTRB(790.0, 0.0, 798.0, 90.0),
           const Radius.circular(8.0),
         ),
         color: const Color(0x1a000000),
       ),
     );
+
+    // Now trigger hover with a mouse.
+    final TestGesture gesture = await tester.createGesture(kind: ui.PointerDeviceKind.mouse);
+    await gesture.addPointer();
+    addTearDown(gesture.removePointer);
+    await gesture.moveTo(const Offset(794.0, 5.0));
+    await tester.pump();
+
+    expect(
+      find.byType(Scrollbar),
+      paints
+        ..rect(
+          rect: const Rect.fromLTRB(784.0, 0.0, 800.0, 600.0),
+          color: const Color(0x08000000),
+        )
+        ..line(
+          p1: const Offset(784.0, 0.0),
+          p2: const Offset(784.0, 600.0),
+          strokeWidth: 1.0,
+          color: const Color(0x1a000000),
+        )
+        ..rrect(
+          rrect: RRect.fromRectAndRadius(
+            // Scrollbar thumb is larger
+            const Rect.fromLTRB(786.0, 0.0, 798.0, 90.0),
+            const Radius.circular(8.0),
+          ),
+          // Hover color
+          color: const Color(0x80000000),
+        ),
+    );
+
   },
     variant: const TargetPlatformVariant(<TargetPlatform>{
       TargetPlatform.iOS,