Add `clipBehavior` to `Snackbar` (#98252)

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

@@ -204,6 +204,7 @@ class SnackBar extends StatefulWidget {
     this.animation,
     this.onVisible,
     this.dismissDirection = DismissDirection.down,
+    this.clipBehavior = Clip.hardEdge,
   }) : assert(elevation == null || elevation >= 0.0),
        assert(content != null),
        assert(
@@ -211,6 +212,7 @@ class SnackBar extends StatefulWidget {
          'Width and margin can not be used together',
        ),
        assert(duration != null),
+       assert(clipBehavior != null),
        super(key: key);
 
   /// The primary content of the snack bar.
@@ -336,6 +338,11 @@ class SnackBar extends StatefulWidget {
   /// Cannot be null, defaults to [DismissDirection.down].
   final DismissDirection dismissDirection;
 
+  /// {@macro flutter.material.Material.clipBehavior}
+  ///
+  /// Defaults to [Clip.hardEdge], and must not be null.
+  final Clip clipBehavior;
+
   // API for ScaffoldMessengerState.showSnackBar():
 
   /// Creates an animation controller useful for driving a snack bar's entrance and exit animation.
@@ -367,6 +374,7 @@ class SnackBar extends StatefulWidget {
       animation: newAnimation,
       onVisible: onVisible,
       dismissDirection: dismissDirection,
+      clipBehavior: clipBehavior,
     );
   }
 
@@ -612,7 +620,10 @@ class _SnackBarState extends State<SnackBar> {
 
     return Hero(
       tag: '<SnackBar Hero tag - ${widget.content}>',
-      child: snackBarTransition,
+      child: ClipRect(
+        clipBehavior: widget.clipBehavior,
+        child: snackBarTransition,
+      ),
     );
   }
 }

packages/flutter/test/material/snack_bar_test.dart

@@ -6,6 +6,8 @@
 // machines.
 @Tags(<String>['reduced-test-set'])
 
+import 'dart:ui';
+
 import 'package:flutter/foundation.dart' show FlutterExceptionHandler;
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
@@ -2558,6 +2560,38 @@ void main() {
       'was set by default.',
     );
   });
+
+  testWidgets('Snackbar by default clips BackdropFilter', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/98205
+    await tester.pumpWidget(MaterialApp(
+      home: Scaffold(
+        body: const Scaffold(),
+        floatingActionButton: FloatingActionButton(onPressed: () {}),
+      ),
+    ));
+
+    final ScaffoldMessengerState scaffoldMessengerState = tester.state<ScaffoldMessengerState>(
+      find.byType(ScaffoldMessenger),
+    );
+    scaffoldMessengerState.showSnackBar(SnackBar(
+      backgroundColor: Colors.transparent,
+      content: BackdropFilter(
+        filter: ImageFilter.blur(
+          sigmaX: 20.0,
+          sigmaY: 20.0,
+        ),
+        child: const Text('I am a snack bar.'),
+      ),
+      duration: const Duration(seconds: 2),
+      action: SnackBarAction(label: 'ACTION', onPressed: () {}),
+      behavior: SnackBarBehavior.fixed,
+    ));
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('I am a snack bar.'));
+    await tester.pump(); // start animation
+    await tester.pump(const Duration(milliseconds: 750));
+    await expectLater(find.byType(MaterialApp), matchesGoldenFile('snack_bar.goldenTest.backdropFilter.png'));
+  });
 }
 
 /// Start test for "SnackBar dismiss test".