iOS context menu shadow (#122429)

Update the visuals of the iOS context menu to match iOS 16.3.1 more closely.

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

@@ -37,19 +37,6 @@ const CupertinoDynamicColor _kToolbarDividerColor = CupertinoDynamicColor.withBr
   darkColor: Color(0xFF808080),
 );
 
-// These values were extracted from a screenshot of iOS 16.0.3, as light mode
-// didn't appear in the Apple design resources assets linked above.
-final BoxDecoration _kToolbarShadow = BoxDecoration(
-  borderRadius: const BorderRadius.all(_kToolbarBorderRadius),
-  boxShadow: <BoxShadow>[
-    BoxShadow(
-      color: CupertinoColors.black.withOpacity(0.1),
-      blurRadius: 16.0,
-      offset: Offset(0, _kToolbarArrowSize.height / 2),
-    ),
-  ],
-);
-
 /// The type for a Function that builds a toolbar's container with the given
 /// child.
 ///
@@ -160,7 +147,22 @@ class CupertinoTextSelectionToolbar extends StatelessWidget {
       return outputChild;
     }
     return DecoratedBox(
-      decoration: _kToolbarShadow,
+      // These shadow values were eyeballed from a screenshot of iOS 16.3.1, as
+      // light mode didn't appear in the Apple design resources assets linked at
+      // the top of this file.
+      decoration: BoxDecoration(
+        borderRadius: const BorderRadius.all(_kToolbarBorderRadius),
+        boxShadow: <BoxShadow>[
+          BoxShadow(
+            color: CupertinoColors.black.withOpacity(0.2),
+            blurRadius: 15.0,
+            offset: Offset(
+              0.0,
+              isAbove ? 0.0 : _kToolbarArrowSize.height,
+            ),
+          ),
+        ],
+      ),
       child: outputChild,
     );
   }

packages/flutter/test/cupertino/text_selection_toolbar_test.dart

@@ -371,4 +371,75 @@ void main() {
       }, skip: kIsWeb); // [intended] We do not use Flutter-rendered context menu on the Web.
     }
   }
+
+  testWidgets('draws a shadow below the toolbar in light mode', (WidgetTester tester) async {
+    late StateSetter setState;
+    const double height = _kToolbarHeight;
+    double anchorAboveY = 0.0;
+
+    await tester.pumpWidget(
+      CupertinoApp(
+        theme: const CupertinoThemeData(
+          brightness: Brightness.light,
+        ),
+        home: Center(
+          child: StatefulBuilder(
+            builder: (BuildContext context, StateSetter setter) {
+              setState = setter;
+              final MediaQueryData data = MediaQuery.of(context);
+              // Add some custom vertical padding to make this test more strict.
+              // By default in the testing environment, _kToolbarContentDistance
+              // and the built-in padding from CupertinoApp can end up canceling
+              // each other out.
+              return MediaQuery(
+                data: data.copyWith(
+                  padding: data.viewPadding.copyWith(
+                    top: 12.0,
+                  ),
+                ),
+                child: CupertinoTextSelectionToolbar(
+                  anchorAbove: Offset(50.0, anchorAboveY),
+                  anchorBelow: const Offset(50.0, 500.0),
+                  children: <Widget>[
+                    Container(color: const Color(0xffff0000), width: 50.0, height: height),
+                    Container(color: const Color(0xff00ff00), width: 50.0, height: height),
+                    Container(color: const Color(0xff0000ff), width: 50.0, height: height),
+                  ],
+                ),
+              );
+            },
+          ),
+        ),
+      ),
+    );
+
+    // When the toolbar is below the content, the shadow hangs below the entire
+    // toolbar.
+    final Finder finder = find.descendant(
+      of: find.byType(CupertinoTextSelectionToolbar),
+      matching: find.byType(DecoratedBox),
+    );
+    expect(finder, findsNWidgets(2));
+    DecoratedBox decoratedBox = tester.widget(finder.first);
+    BoxDecoration boxDecoration = decoratedBox.decoration as BoxDecoration;
+    List<BoxShadow>? shadows = boxDecoration.boxShadow;
+    expect(shadows, isNotNull);
+    expect(shadows, hasLength(1));
+    BoxShadow shadow = boxDecoration.boxShadow!.first;
+    expect(shadow.offset.dy, equals(7.0));
+
+    // When the toolbar is above the content, the shadow sits around the arrow
+    // with no offset.
+    setState(() {
+      anchorAboveY = 80.0;
+    });
+    await tester.pump();
+    decoratedBox = tester.widget(finder.first);
+    boxDecoration = decoratedBox.decoration as BoxDecoration;
+    shadows = boxDecoration.boxShadow;
+    expect(shadows, isNotNull);
+    expect(shadows, hasLength(1));
+    shadow = boxDecoration.boxShadow!.first;
+    expect(shadow.offset.dy, equals(0.0));
+  }, skip: kIsWeb); // [intended] We do not use Flutter-rendered context menu on the Web.
 }