Fix widgets with built-in scrollbars (#83828)

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

@@ -365,6 +365,9 @@ class CupertinoAlertDialog extends StatelessWidget {
           // iOS does not shrink dialog content below a 1.0 scale factor
           textScaleFactor: math.max(textScaleFactor, 1.0),
         ),
+        child: ScrollConfiguration(
+          // A CupertinoScrollbar is built-in below.
+          behavior: ScrollConfiguration.of(context).copyWith(scrollbars: false),
           child: LayoutBuilder(
             builder: (BuildContext context, BoxConstraints constraints) {
               return AnimatedPadding(
@@ -405,6 +408,7 @@ class CupertinoAlertDialog extends StatelessWidget {
             },
           ),
         ),
+      ),
     );
   }
 }
@@ -694,6 +698,9 @@ class CupertinoActionSheet extends StatelessWidget {
     }
 
     return SafeArea(
+      child: ScrollConfiguration(
+        // A CupertinoScrollbar is built-in below
+        behavior: ScrollConfiguration.of(context).copyWith(scrollbars: false),
         child: Semantics(
           namesRoute: true,
           scopesRoute: true,
@@ -715,6 +722,7 @@ class CupertinoActionSheet extends StatelessWidget {
             ),
           ),
         ),
+      ),
     );
   }
 }

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

@@ -925,6 +925,9 @@ class _PackageLicensePageState extends State<_PackageLicensePage> {
               child: Localizations.override(
                 locale: const Locale('en', 'US'),
                 context: context,
+                child: ScrollConfiguration(
+                  // A Scrollbar is built-in below.
+                  behavior: ScrollConfiguration.of(context).copyWith(scrollbars: false),
                   child: Scrollbar(
                     child: ListView(padding: padding, children: listWidgets),
                   ),
@@ -932,6 +935,7 @@ class _PackageLicensePageState extends State<_PackageLicensePage> {
               ),
             ),
           ),
+        ),
       );
     } else {
       page = CustomScrollView(

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());
 }