Fix widgets with built-in scrollbars (#83828)

packages/flutter/lib/src/cupertino/dialog.dart

@@ -365,44 +365,48 @@ class CupertinoAlertDialog extends StatelessWidget {
           // iOS does not shrink dialog content below a 1.0 scale factor
           textScaleFactor: math.max(textScaleFactor, 1.0),
         ),
-        child: LayoutBuilder(
-          builder: (BuildContext context, BoxConstraints constraints) {
-            return AnimatedPadding(
-              padding: MediaQuery.of(context).viewInsets +
-                  const EdgeInsets.symmetric(horizontal: 40.0, vertical: 24.0),
-              duration: insetAnimationDuration,
-              curve: insetAnimationCurve,
-              child: MediaQuery.removeViewInsets(
-                removeLeft: true,
-                removeTop: true,
-                removeRight: true,
-                removeBottom: true,
-                context: context,
-                child: Center(
-                  child: Container(
-                    margin: const EdgeInsets.symmetric(vertical: _kDialogEdgePadding),
-                    width: isInAccessibilityMode
-                        ? _kAccessibilityCupertinoDialogWidth
-                        : _kCupertinoDialogWidth,
-                    child: CupertinoPopupSurface(
-                      isSurfacePainted: false,
-                      child: Semantics(
-                        namesRoute: true,
-                        scopesRoute: true,
-                        explicitChildNodes: true,
-                        label: localizations.alertDialogLabel,
-                        child: _CupertinoDialogRenderWidget(
-                          contentSection: _buildContent(context),
-                          actionsSection: _buildActions(),
-                          dividerColor: CupertinoColors.separator,
+        child: ScrollConfiguration(
+          // A CupertinoScrollbar is built-in below.
+          behavior: ScrollConfiguration.of(context).copyWith(scrollbars: false),
+          child: LayoutBuilder(
+            builder: (BuildContext context, BoxConstraints constraints) {
+              return AnimatedPadding(
+                padding: MediaQuery.of(context).viewInsets +
+                    const EdgeInsets.symmetric(horizontal: 40.0, vertical: 24.0),
+                duration: insetAnimationDuration,
+                curve: insetAnimationCurve,
+                child: MediaQuery.removeViewInsets(
+                  removeLeft: true,
+                  removeTop: true,
+                  removeRight: true,
+                  removeBottom: true,
+                  context: context,
+                  child: Center(
+                    child: Container(
+                      margin: const EdgeInsets.symmetric(vertical: _kDialogEdgePadding),
+                      width: isInAccessibilityMode
+                          ? _kAccessibilityCupertinoDialogWidth
+                          : _kCupertinoDialogWidth,
+                      child: CupertinoPopupSurface(
+                        isSurfacePainted: false,
+                        child: Semantics(
+                          namesRoute: true,
+                          scopesRoute: true,
+                          explicitChildNodes: true,
+                          label: localizations.alertDialogLabel,
+                          child: _CupertinoDialogRenderWidget(
+                            contentSection: _buildContent(context),
+                            actionsSection: _buildActions(),
+                            dividerColor: CupertinoColors.separator,
+                          ),
                         ),
                       ),
                     ),
                   ),
                 ),
-              ),
-            );
-          },
+              );
+            },
+          ),
         ),
       ),
     );
@@ -694,23 +698,27 @@ class CupertinoActionSheet extends StatelessWidget {
     }
 
     return SafeArea(
-      child: Semantics(
-        namesRoute: true,
-        scopesRoute: true,
-        explicitChildNodes: true,
-        label: 'Alert',
-        child: CupertinoUserInterfaceLevel(
-          data: CupertinoUserInterfaceLevelData.elevated,
-          child: Container(
-            width: actionSheetWidth,
-            margin: const EdgeInsets.symmetric(
-              horizontal: _kActionSheetEdgeHorizontalPadding,
-              vertical: _kActionSheetEdgeVerticalPadding,
-            ),
-            child: Column(
-              mainAxisSize: MainAxisSize.min,
-              crossAxisAlignment: CrossAxisAlignment.stretch,
-              children: children,
+      child: ScrollConfiguration(
+        // A CupertinoScrollbar is built-in below
+        behavior: ScrollConfiguration.of(context).copyWith(scrollbars: false),
+        child: Semantics(
+          namesRoute: true,
+          scopesRoute: true,
+          explicitChildNodes: true,
+          label: 'Alert',
+          child: CupertinoUserInterfaceLevel(
+            data: CupertinoUserInterfaceLevelData.elevated,
+            child: Container(
+              width: actionSheetWidth,
+              margin: const EdgeInsets.symmetric(
+                horizontal: _kActionSheetEdgeHorizontalPadding,
+                vertical: _kActionSheetEdgeVerticalPadding,
+              ),
+              child: Column(
+                mainAxisSize: MainAxisSize.min,
+                crossAxisAlignment: CrossAxisAlignment.stretch,
+                children: children,
+              ),
             ),
           ),
         ),

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

@@ -925,8 +925,12 @@ class _PackageLicensePageState extends State<_PackageLicensePage> {
               child: Localizations.override(
                 locale: const Locale('en', 'US'),
                 context: context,
-                child: Scrollbar(
-                  child: ListView(padding: padding, children: listWidgets),
+                child: ScrollConfiguration(
+                  // A Scrollbar is built-in below.
+                  behavior: ScrollConfiguration.of(context).copyWith(scrollbars: false),
+                  child: Scrollbar(
+                    child: ListView(padding: padding, children: listWidgets),
+                  ),
                 ),
               ),
             ),

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

@@ -285,9 +285,10 @@ class _DropdownMenuState<T> extends State<_DropdownMenu<T>> {
             textStyle: route.style,
             child: ScrollConfiguration(
               // Dropdown menus should never overscroll or display an overscroll indicator.
-              // The default scrollbar platforms will apply.
+              // Scrollbars are built-in below.
               // Platform must use Theme and ScrollPhysics must be Clamping.
               behavior: ScrollConfiguration.of(context).copyWith(
+                scrollbars: false,
                 overscroll: false,
                 physics: const ClampingScrollPhysics(),
                 platform: Theme.of(context).platform,

packages/flutter/test/cupertino/action_sheet_test.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
 
 import 'package:flutter_test/flutter_test.dart';
 
@@ -993,6 +994,46 @@ void main() {
 
     semantics.dispose();
   });
+
+  testWidgets('Conflicting scrollbars are not applied by ScrollBehavior to CupertinoActionSheet', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/83819
+    final ScrollController actionScrollController = ScrollController();
+    await tester.pumpWidget(
+      createAppWithButtonThatLaunchesActionSheet(
+        Builder(builder: (BuildContext context) {
+          return MediaQuery(
+            data: MediaQuery.of(context).copyWith(textScaleFactor: 3.0),
+            child: CupertinoActionSheet(
+              title: const Text('The title'),
+              message: const Text('The message.'),
+              actions: <Widget>[
+                CupertinoActionSheetAction(
+                  child: const Text('One'),
+                  onPressed: () { },
+                ),
+                CupertinoActionSheetAction(
+                  child: const Text('Two'),
+                  onPressed: () { },
+                ),
+              ],
+              actionScrollController: actionScrollController,
+            ),
+          );
+        }),
+      ),
+    );
+
+    await tester.tap(find.text('Go'));
+    await tester.pump();
+
+    // The inherited ScrollBehavior should not apply Scrollbars since they are
+    // already built in to the widget.
+    expect(find.byType(Scrollbar), findsNothing);
+    expect(find.byType(RawScrollbar), findsNothing);
+    // Built in CupertinoScrollbars should only number 2: one for the actions,
+    // one for the content.
+    expect(find.byType(CupertinoScrollbar), findsNWidgets(2));
+  }, variant: TargetPlatformVariant.all());
 }
 
 RenderBox findScrollableActionsSectionRenderBox(WidgetTester tester) {

packages/flutter/test/cupertino/dialog_test.dart

@@ -5,6 +5,7 @@
 import 'dart:math';
 
 import 'package:flutter/cupertino.dart';
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -1247,6 +1248,45 @@ void main() {
     await tester.restoreFrom(restorationData);
     expect(find.byType(CupertinoAlertDialog), findsOneWidget);
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/33615
+
+  testWidgets('Conflicting scrollbars are not applied by ScrollBehavior to CupertinoAlertDialog', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/83819
+    const double textScaleFactor = 1.0;
+    final ScrollController actionScrollController = ScrollController();
+    await tester.pumpWidget(
+      createAppWithButtonThatLaunchesDialog(
+        dialogBuilder: (BuildContext context) {
+          return MediaQuery(
+            data: MediaQuery.of(context).copyWith(textScaleFactor: textScaleFactor),
+            child: CupertinoAlertDialog(
+              title: const Text('Test Title'),
+              content: const Text('Test Content'),
+              actions: const <Widget>[
+                CupertinoDialogAction(
+                  child: Text('One'),
+                ),
+                CupertinoDialogAction(
+                  child: Text('Two'),
+                ),
+              ],
+              actionScrollController: actionScrollController,
+            ),
+          );
+        },
+      ),
+    );
+
+    await tester.tap(find.text('Go'));
+    await tester.pump();
+
+    // The inherited ScrollBehavior should not apply Scrollbars since they are
+    // already built in to the widget.
+    expect(find.byType(Scrollbar), findsNothing);
+    expect(find.byType(RawScrollbar), findsNothing);
+    // Built in CupertinoScrollbars should only number 2: one for the actions,
+    // one for the content.
+    expect(find.byType(CupertinoScrollbar), findsNWidgets(2));
+  }, variant: TargetPlatformVariant.all());
 }
 
 RenderBox findActionButtonRenderBoxByTitle(WidgetTester tester, String title) {

packages/flutter/test/material/about_test.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:flutter/cupertino.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -705,6 +706,50 @@ void main() {
     expect(materialDones[0].color, scaffoldColor);
     expect(materialDones[1].color, cardColor);
   });
+
+  testWidgets('Conflicting scrollbars are not applied by ScrollBehavior to _PackageLicensePage', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/83819
+    LicenseRegistry.addLicense(() {
+      return Stream<LicenseEntry>.fromIterable(<LicenseEntry>[
+        const LicenseEntryWithLineBreaks(<String>['AAA'], 'BBB'),
+      ]);
+    });
+
+    await tester.pumpWidget(
+      const MaterialApp(
+        home: Center(
+          child: LicensePage(),
+        ),
+      ),
+    );
+    await tester.pumpAndSettle();
+
+    // Check for packages.
+    expect(find.text('AAA'), findsOneWidget);
+    // Check license is displayed after entering into license page for 'AAA'.
+    await tester.tap(find.text('AAA'));
+    await tester.pumpAndSettle(const Duration(milliseconds: 100));
+
+    // The inherited ScrollBehavior should not apply Scrollbars since they are
+    // already built in to the widget.
+    switch (debugDefaultTargetPlatformOverride) {
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+      case TargetPlatform.linux:
+      case TargetPlatform.macOS:
+      case TargetPlatform.windows:
+        expect(find.byType(CupertinoScrollbar), findsNothing);
+        break;
+      case TargetPlatform.iOS:
+        expect(find.byType(CupertinoScrollbar), findsOneWidget);
+        break;
+      case null:
+        break;
+    }
+    expect(find.byType(Scrollbar), findsOneWidget);
+    expect(find.byType(RawScrollbar), findsNothing);
+
+  }, variant: TargetPlatformVariant.all());
 }
 
 class FakeLicenseEntry extends LicenseEntry {

packages/flutter/test/material/dropdown_test.dart

@@ -5,6 +5,7 @@
 import 'dart:math' as math;
 import 'dart:ui' show window;
 
+import 'package:flutter/cupertino.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
@@ -3449,4 +3450,26 @@ void main() {
     await gesture.moveTo(offDropdownButton);
     expect(RendererBinding.instance!.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.basic);
   });
+
+  testWidgets('Conflicting scrollbars are not applied by ScrollBehavior to Dropdown', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/83819
+    // Open the dropdown menu
+    final Key buttonKey = UniqueKey();
+    await tester.pumpWidget(buildFrame(
+      buttonKey: buttonKey,
+      value: null, // nothing selected
+      items: List<String>.generate(100, (int index) => index.toString()),
+      onChanged: onChanged,
+    ));
+    await tester.tap(find.byKey(buttonKey));
+    await tester.pump();
+    await tester.pumpAndSettle(); // finish the menu animation
+
+    // The inherited ScrollBehavior should not apply Scrollbars since they are
+    // already built in to the widget.
+    expect(find.byType(CupertinoScrollbar), findsNothing);
+    expect(find.byType(Scrollbar), findsOneWidget);
+    expect(find.byType(RawScrollbar), findsNothing);
+
+  }, variant: TargetPlatformVariant.all());
 }