[M3] Update checkbox shape value (#120976)

* update m3 values

* update test formatting

* update crswap

* update test

* update token value

* update tests

dev/tools/gen_defaults/lib/checkbox_template.dart

@@ -110,6 +110,11 @@ class _${blockName}DefaultsM3 extends CheckboxThemeData {
 
   @override
   VisualDensity get visualDensity => _theme.visualDensity;
+
+  @override
+  OutlinedBorder get shape => RoundedRectangleBorder(
+    borderRadius: BorderRadius.circular(${tokens['md.comp.checkbox.unselected.outline.width']}),
+  );
 }
 ''';
 }

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

@@ -305,7 +305,7 @@ class Checkbox extends StatefulWidget {
   ///
   /// If this property is null then [CheckboxThemeData.shape] of [ThemeData.checkboxTheme]
   /// is used. If that's null then the shape will be a [RoundedRectangleBorder]
-  /// with a circular corner radius of 1.0.
+  /// with a circular corner radius of 1.0 in Material 2, and 2.0 in Material 3.
   final OutlinedBorder? shape;
 
   /// {@template flutter.material.checkbox.side}
@@ -522,9 +522,7 @@ class _CheckboxState extends State<Checkbox> with TickerProviderStateMixin, Togg
           ..checkColor = effectiveCheckColor
           ..value = value
           ..previousValue = _previousValue
-          ..shape = widget.shape ?? checkboxTheme.shape ?? const RoundedRectangleBorder(
+          ..shape = widget.shape ?? checkboxTheme.shape ?? defaults.shape!
-              borderRadius: BorderRadius.all(Radius.circular(1.0)),
-          )
           ..side = _resolveSide(widget.side) ?? _resolveSide(checkboxTheme.side),
       ),
     );
@@ -759,6 +757,11 @@ class _CheckboxDefaultsM2 extends CheckboxThemeData {
 
   @override
   VisualDensity get visualDensity => _theme.visualDensity;
+
+  @override
+  OutlinedBorder get shape => const RoundedRectangleBorder(
+    borderRadius: BorderRadius.all(Radius.circular(1.0)),
+  );
 }
 
 // BEGIN GENERATED TOKEN PROPERTIES - Checkbox
@@ -869,6 +872,11 @@ class _CheckboxDefaultsM3 extends CheckboxThemeData {
 
   @override
   VisualDensity get visualDensity => _theme.visualDensity;
+
+  @override
+  OutlinedBorder get shape => RoundedRectangleBorder(
+    borderRadius: BorderRadius.circular(2.0),
+  );
 }
 
 // END GENERATED TOKEN PROPERTIES - Checkbox

packages/flutter/test/material/checkbox_test.dart

@@ -1698,7 +1698,7 @@ void main() {
         paints
         ..drrect(
           color: borderColor,
-          outer: RRect.fromLTRBR(15, 15, 33, 33, const Radius.circular(1)),
+          outer: RRect.fromLTRBR(15, 15, 33, 33, const Radius.circular(2)),
           inner: RRect.fromLTRBR(19, 19, 29, 29, Radius.zero),
         ),
       );
@@ -1735,6 +1735,41 @@ void main() {
     await gestureLongPress.up();
     await tester.pump();
   });
+
+  testWidgets('Checkbox has correct default shape - M3', (WidgetTester tester) async {
+    final ThemeData themeData = ThemeData(useMaterial3: true);
+
+    Widget buildApp() {
+      return MaterialApp(
+        theme: themeData,
+        home: Material(
+          child: Center(
+            child: StatefulBuilder(builder: (BuildContext context, StateSetter setState) {
+              return Checkbox(
+                value: false,
+                onChanged: (bool? newValue) {},
+
+              );
+            }),
+          ),
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildApp());
+    await tester.pumpAndSettle();
+
+    final OutlinedBorder? expectedShape = themeData.checkboxTheme.shape;
+    expect(tester.widget<Checkbox>(find.byType(Checkbox)).shape, expectedShape);
+    expect(
+      Material.of(tester.element(find.byType(Checkbox))),
+      paints
+        ..drrect(
+          outer: RRect.fromLTRBR(15.0, 15.0, 33.0, 33.0, const Radius.circular(2)),
+          inner: RRect.fromLTRBR(17.0, 17.0, 31.0, 31.0, Radius.zero),
+        ),
+    );
+  });
 }
 
 class _SelectedGrabMouseCursor extends MaterialStateMouseCursor {