Provide a default IconTheme in CupertinoTheme (#30521)

-* Inserted an `IconTheme` widget under `CupertinoTheme` to provide a default icon color when using `CupertinoTheme`.
* Changed `CupertinoTheme` to a `StatelessWidget`, to match the implementation of `Theme`
* Changed the nesting order of `Theme`'s sub widgets, to let `Theme.iconTheme` take precedence, so that `Theme`'s behavior is kept as is.

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

@@ -24,38 +24,68 @@ const Color _kDefaultBarDarkBackgroundColor = Color(0xB7212121);
 /// [CupertinoTheme.of]. An [InheritedWidget] dependency is created when
 /// an ancestor [CupertinoThemeData] is retrieved via [CupertinoTheme.of].
 ///
+/// The [CupertinoTheme] widget implies an [IconTheme] widget, whose
+/// [IconTheme.data] has the same color as [CupertinoThemeData.primaryColor]
+///
 /// See also:
 ///
 ///  * [CupertinoThemeData], specifies the theme's visual styling.
 ///  * [CupertinoApp], which will automatically add a [CupertinoTheme].
 ///  * [Theme], a Material theme which will automatically add a [CupertinoTheme]
 ///    with a [CupertinoThemeData] derived from the Material [ThemeData].
-class CupertinoTheme extends InheritedWidget {
+class CupertinoTheme extends StatelessWidget {
   /// Creates a [CupertinoTheme] to change descendant Cupertino widgets' styling.
   ///
   /// The [data] and [child] parameters must not be null.
   const CupertinoTheme({
     Key key,
     @required this.data,
-    @required Widget child,
+    @required this.child,
   }) : assert(child != null),
        assert(data != null),
-       super(key: key, child: child);
+       super(key: key);
 
   /// The [CupertinoThemeData] styling for this theme.
   final CupertinoThemeData data;
 
-  @override
-  bool updateShouldNotify(CupertinoTheme oldWidget) => data != oldWidget.data;
-
   /// Retrieve the [CupertinoThemeData] from an ancestor [CupertinoTheme] widget.
   ///
   /// Returns a default [CupertinoThemeData] if no [CupertinoTheme] widgets
   /// exist in the ancestry tree.
   static CupertinoThemeData of(BuildContext context) {
-    final CupertinoTheme theme = context.inheritFromWidgetOfExactType(CupertinoTheme);
-    return theme?.data ?? const CupertinoThemeData();
+    final _InheritedCupertinoTheme inheritedTheme = context.inheritFromWidgetOfExactType(_InheritedCupertinoTheme);
+    return inheritedTheme?.theme?.data ?? const CupertinoThemeData();
   }
+
+  /// The widget below this widget in the tree.
+  ///
+  /// {@macro flutter.widgets.child}
+  final Widget child;
+
+  @override
+  Widget build(BuildContext context) {
+    return  _InheritedCupertinoTheme(
+      theme: this,
+      child: IconTheme(
+        data: IconThemeData(color: data.primaryColor),
+        child: child,
+      )
+    );
+  }
+}
+
+class _InheritedCupertinoTheme extends InheritedWidget {
+  const _InheritedCupertinoTheme({
+    Key key,
+    @required this.theme,
+    @required Widget child,
+  }) : assert(theme != null),
+       super(key: key, child: child);
+
+  final CupertinoTheme theme;
+
+  @override
+  bool updateShouldNotify(_InheritedCupertinoTheme old) => theme.data != old.theme.data;
 }
 
 /// Styling specifications for a [CupertinoTheme].

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

@@ -142,8 +142,6 @@ class Theme extends StatelessWidget {
   Widget build(BuildContext context) {
     return _InheritedTheme(
       theme: this,
-      child: IconTheme(
-        data: data.iconTheme,
       child: CupertinoTheme(
         // We're using a MaterialBasedCupertinoThemeData here instead of a
         // CupertinoThemeData because it defers some properties to the Material
@@ -151,9 +149,11 @@ class Theme extends StatelessWidget {
         data: MaterialBasedCupertinoThemeData(
           materialTheme: data,
         ),
+        child: IconTheme(
+          data: data.iconTheme,
           child: child,
         ),
-      ),
+      )
     );
   }
 

packages/flutter/test/cupertino/segmented_control_test.dart

@@ -247,20 +247,20 @@ void main() {
       );
 
       DefaultTextStyle textStyle = tester.widget(find.widgetWithText(DefaultTextStyle, 'Child 1').first);
-      IconTheme iconTheme = tester.widget(find.widgetWithIcon(IconTheme, const IconData(1)));
+      IconThemeData iconTheme = IconTheme.of(tester.element(find.byIcon(const IconData(1))));
 
       expect(textStyle.style.color, CupertinoColors.black);
-      expect(iconTheme.data.color, CupertinoColors.activeOrange);
+      expect(iconTheme.color, CupertinoColors.activeOrange);
 
-      await tester.tap(find.widgetWithIcon(IconTheme, const IconData(1)));
+      await tester.tap(find.byIcon(const IconData(1)));
       await tester.pump();
       await tester.pump(const Duration(milliseconds: 500));
 
       textStyle = tester.widget(find.widgetWithText(DefaultTextStyle, 'Child 1').first);
-      iconTheme = tester.widget(find.widgetWithIcon(IconTheme, const IconData(1)));
+      iconTheme = IconTheme.of(tester.element(find.byIcon(const IconData(1))));
 
       expect(textStyle.style.color, CupertinoColors.activeOrange);
-      expect(iconTheme.data.color, CupertinoColors.black);
+      expect(iconTheme.color, CupertinoColors.black);
     },
   );
 

packages/flutter/test/cupertino/theme_test.dart

@@ -9,11 +9,13 @@ import 'package:flutter_test/flutter_test.dart';
 
 int buildCount;
 CupertinoThemeData actualTheme;
+IconThemeData actualIconTheme;
 
 final Widget singletonThemeSubtree = Builder(
   builder: (BuildContext context) {
     buildCount++;
     actualTheme = CupertinoTheme.of(context);
+    actualIconTheme = IconTheme.of(context);
     return const Placeholder();
   },
 );
@@ -28,6 +30,16 @@ Future<CupertinoThemeData> testTheme(WidgetTester tester, CupertinoThemeData the
   return actualTheme;
 }
 
+Future<IconThemeData> testIconTheme(WidgetTester tester, CupertinoThemeData theme) async {
+  await tester.pumpWidget(
+    CupertinoTheme(
+      data: theme,
+      child: singletonThemeSubtree,
+    ),
+  );
+  return actualIconTheme;
+}
+
 void main() {
   setUp(() {
     buildCount = 0;
@@ -123,4 +135,24 @@ void main() {
       expect(theme.scaffoldBackgroundColor, CupertinoColors.black);
     },
   );
+
+  testWidgets("Theme has default IconThemeData, which is derived from the theme's primary color", (WidgetTester tester) async {
+      const Color primaryColor = CupertinoColors.destructiveRed;
+      const CupertinoThemeData themeData = CupertinoThemeData(primaryColor: primaryColor);
+
+      final IconThemeData resultingIconTheme = await testIconTheme(tester, themeData);
+
+      expect(resultingIconTheme.color, themeData.primaryColor);
+  });
+
+  testWidgets('IconTheme.of creates a dependency on iconTheme', (WidgetTester tester) async {
+      IconThemeData iconTheme = await testIconTheme(tester, const CupertinoThemeData(primaryColor: CupertinoColors.destructiveRed));
+
+      expect(buildCount, 1);
+      expect(iconTheme.color, CupertinoColors.destructiveRed);
+
+      iconTheme = await testIconTheme(tester, const CupertinoThemeData(primaryColor: CupertinoColors.activeOrange));
+      expect(buildCount, 2);
+      expect(iconTheme.color, CupertinoColors.activeOrange);
+  });
 }

packages/flutter/test/material/theme_test.dart

@@ -417,28 +417,26 @@ void main() {
   group('Cupertino theme', () {
     int buildCount;
     CupertinoThemeData actualTheme;
+    IconThemeData actualIconTheme;
 
     final Widget singletonThemeSubtree = Builder(
       builder: (BuildContext context) {
         buildCount++;
         actualTheme = CupertinoTheme.of(context);
+        actualIconTheme = IconTheme.of(context);
         return const Placeholder();
       },
     );
 
     Future<CupertinoThemeData> testTheme(WidgetTester tester, ThemeData theme) async {
-      await tester.pumpWidget(
-        Theme(
-          data: theme,
-          child: singletonThemeSubtree,
-        ),
-      );
+      await tester.pumpWidget(Theme(data: theme, child: singletonThemeSubtree));
       return actualTheme;
     }
 
     setUp(() {
       buildCount = 0;
       actualTheme = null;
+      actualIconTheme = null;
     });
 
     testWidgets('Default theme has defaults', (WidgetTester tester) async {
@@ -509,6 +507,20 @@ void main() {
       expect(theme.primaryColor, Colors.orange);
     });
 
+    testWidgets("CupertinoThemeData does not override material theme's icon theme",
+      (WidgetTester tester) async {
+        const Color materialIconColor = Colors.blue;
+        const Color cupertinoIconColor = Colors.black;
+
+        await testTheme(tester, ThemeData(
+            iconTheme: const IconThemeData(color: materialIconColor),
+            cupertinoOverrideTheme: const CupertinoThemeData(primaryColor: cupertinoIconColor)
+        ));
+
+        expect(buildCount, 1);
+        expect(actualIconTheme.color, materialIconColor);
+    });
+
     testWidgets(
       'Changing cupertino theme override triggers rebuilds',
       (WidgetTester tester) async {