Let material ThemeData dictate brightness if cupertinoOverrideTheme.brightness is null (#47249)

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

@@ -847,7 +847,7 @@ class _CupertinoTextFieldState extends State<CupertinoTextField> with AutomaticK
 
     final TextStyle placeholderStyle = textStyle.merge(resolvedPlaceholderStyle);
 
-    final Brightness keyboardAppearance = widget.keyboardAppearance ?? themeData.brightness;
+    final Brightness keyboardAppearance = widget.keyboardAppearance ?? CupertinoTheme.brightnessOf(context);
     final Color cursorColor = CupertinoDynamicColor.resolve(widget.cursorColor, context) ?? themeData.primaryColor;
     final Color disabledColor = CupertinoDynamicColor.resolve(_kDisabledBackground, context);
 

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

@@ -71,17 +71,22 @@ class CupertinoTheme extends StatelessWidget {
     return (inheritedTheme?.theme?.data ?? const CupertinoThemeData()).resolveFrom(context, nullOk: true);
   }
 
-  /// Retrieves the [Brightness] value from the closest ancestor [CupertinoTheme]
-  /// widget.
+  /// Retrieves the [Brightness] to use for descendant Cupertino widgets, based
+  /// on the value of [CupertinoThemeData.brightness] in the given [context].
   ///
-  /// If no [CupertinoTheme] ancestor with an explicit brightness value could be
-  /// found, this method will resort to the closest ancestor [MediaQuery] widget.
+  /// If no [CupertinoTheme] can be found in the given [context], or its `brightness`
+  /// is null, it will fall back to [MediaQueryData.brightness].
   ///
-  /// Throws an exception if no such [CupertinoTheme] or [MediaQuery] widgets exist
-  /// in the ancestry tree, unless [nullOk] is set to true.
+  /// Throws an exception if no valid [CupertinoTheme] or [MediaQuery] widgets
+  /// exist in the ancestry tree, unless [nullOk] is set to true.
+  ///
+  /// See also:
+  ///
+  /// * [CupertinoThemeData.brightness], the property takes precedence over
+  ///   [MediaQueryData.platformBrightness] for descendant Cupertino widgets.
   static Brightness brightnessOf(BuildContext context, { bool nullOk = false }) {
     final _InheritedCupertinoTheme inheritedTheme = context.dependOnInheritedWidgetOfExactType<_InheritedCupertinoTheme>();
-    return inheritedTheme?.theme?.data?._brightness ?? MediaQuery.of(context, nullOk: nullOk)?.platformBrightness;
+    return inheritedTheme?.theme?.data?.brightness ?? MediaQuery.of(context, nullOk: nullOk)?.platformBrightness;
   }
 
   /// The widget below this widget in the tree.
@@ -181,7 +186,7 @@ class CupertinoThemeData extends Diagnosticable {
   );
 
   const CupertinoThemeData._rawWithDefaults(
-    this._brightness,
+    this.brightness,
     this._primaryColor,
     this._primaryContrastingColor,
     this._textTheme,
@@ -192,10 +197,11 @@ class CupertinoThemeData extends Diagnosticable {
 
   final _CupertinoThemeDefaults _defaults;
 
-  /// The general brightness theme of the [CupertinoThemeData].
+  /// The brightness override for Cupertino descendants.
   ///
-  /// Overrides the ambient [MediaQueryData.platformBrightness] when specified.
-  /// Defaults to [Brightness.light].
+  /// Defaults to null. If a non-null [Brightness] is specified, the value will
+  /// take precedence over the ambient [MediaQueryData.platformBrightness], when
+  /// determining the brightness of descendant Cupertino widgets.
   ///
   /// If coming from a Material [Theme] and unspecified, [brightness] will be
   /// derived from the Material [ThemeData]'s `brightness`.
@@ -204,8 +210,10 @@ class CupertinoThemeData extends Diagnosticable {
   ///
   ///  * [MaterialBasedCupertinoThemeData], a [CupertinoThemeData] that defers
   ///    [brightness] to its Material [Theme] parent if it's unspecified.
-  Brightness get brightness => _brightness ?? Brightness.light;
-  final Brightness _brightness;
+  ///
+  ///  * [CupertinoTheme.brightnessOf], a method used to retrieve the overall
+  ///    [Brightness] from a [BuildContext], for Cupertino widgets.
+  final Brightness brightness;
 
   /// A color used on interactive elements of the theme.
   ///
@@ -268,7 +276,7 @@ class CupertinoThemeData extends Diagnosticable {
   /// theme properties instead of iOS defaults.
   CupertinoThemeData noDefault() {
     return _NoDefaultCupertinoThemeData(
-      _brightness,
+      brightness,
       _primaryColor,
       _primaryContrastingColor,
       _textTheme,
@@ -287,7 +295,7 @@ class CupertinoThemeData extends Diagnosticable {
     Color convertColor(Color color) => CupertinoDynamicColor.resolve(color, context, nullOk: nullOk);
 
     return CupertinoThemeData._rawWithDefaults(
-      _brightness,
+      brightness,
       convertColor(_primaryColor),
       convertColor(_primaryContrastingColor),
       _textTheme?.resolveFrom(context, nullOk: nullOk),
@@ -313,7 +321,7 @@ class CupertinoThemeData extends Diagnosticable {
     Color scaffoldBackgroundColor,
   }) {
     return CupertinoThemeData._rawWithDefaults(
-      brightness ?? _brightness,
+      brightness ?? this.brightness,
       primaryColor ?? _primaryColor,
       primaryContrastingColor ?? _primaryContrastingColor,
       textTheme ?? _textTheme,
@@ -327,7 +335,7 @@ class CupertinoThemeData extends Diagnosticable {
   void debugFillProperties(DiagnosticPropertiesBuilder properties) {
     super.debugFillProperties(properties);
     const CupertinoThemeData defaultData = CupertinoThemeData();
-    properties.add(EnumProperty<Brightness>('brightness', brightness, defaultValue: defaultData.brightness));
+    properties.add(EnumProperty<Brightness>('brightness', brightness, defaultValue: null));
     properties.add(createCupertinoColorProperty('primaryColor', primaryColor, defaultValue: defaultData.primaryColor));
     properties.add(createCupertinoColorProperty('primaryContrastingColor', primaryContrastingColor, defaultValue: defaultData.primaryContrastingColor));
     properties.add(createCupertinoColorProperty('barBackgroundColor', barBackgroundColor, defaultValue: defaultData.barBackgroundColor));
@@ -338,7 +346,7 @@ class CupertinoThemeData extends Diagnosticable {
 
 class _NoDefaultCupertinoThemeData extends CupertinoThemeData {
   const _NoDefaultCupertinoThemeData(
-    this.brightness,
+    Brightness brightness,
     this.primaryColor,
     this.primaryContrastingColor,
     this.textTheme,
@@ -354,8 +362,6 @@ class _NoDefaultCupertinoThemeData extends CupertinoThemeData {
         null,
       );
 
-  @override
-  final Brightness brightness;
   @override
   final Color primaryColor;
   @override

packages/flutter/test/cupertino/theme_test.dart

@@ -52,7 +52,7 @@ void main() {
   testWidgets('Default theme has defaults', (WidgetTester tester) async {
     final CupertinoThemeData theme = await testTheme(tester, const CupertinoThemeData());
 
-    expect(theme.brightness, Brightness.light);
+    expect(theme.brightness, isNull);
     expect(theme.primaryColor, CupertinoColors.activeBlue);
     expect(theme.textTheme.textStyle.fontSize, 17.0);
   });

packages/flutter/test/material/theme_test.dart

@@ -418,12 +418,14 @@ void main() {
     int buildCount;
     CupertinoThemeData actualTheme;
     IconThemeData actualIconTheme;
+    BuildContext context;
 
     final Widget singletonThemeSubtree = Builder(
-      builder: (BuildContext context) {
+      builder: (BuildContext localContext) {
         buildCount++;
-        actualTheme = CupertinoTheme.of(context);
-        actualIconTheme = IconTheme.of(context);
+        actualTheme = CupertinoTheme.of(localContext);
+        actualIconTheme = IconTheme.of(localContext);
+        context = localContext;
         return const Placeholder();
       },
     );
@@ -437,6 +439,7 @@ void main() {
       buildCount = 0;
       actualTheme = null;
       actualIconTheme = null;
+      context = null;
     });
 
     testWidgets('Default theme has defaults', (WidgetTester tester) async {
@@ -461,6 +464,27 @@ void main() {
       expect(theme.textTheme.textStyle.fontSize, 17.0);
     });
 
+    testWidgets('MaterialTheme overrides the brightness', (WidgetTester tester) async {
+      await testTheme(tester, ThemeData.dark());
+      expect(CupertinoTheme.brightnessOf(context), Brightness.dark);
+
+      await testTheme(tester, ThemeData.light());
+      expect(CupertinoTheme.brightnessOf(context), Brightness.light);
+
+      // Overridable by cupertinoOverrideTheme.
+      await testTheme(tester, ThemeData(
+        brightness: Brightness.light,
+        cupertinoOverrideTheme: const CupertinoThemeData(brightness: Brightness.dark),
+      ));
+      expect(CupertinoTheme.brightnessOf(context), Brightness.dark);
+
+      await testTheme(tester, ThemeData(
+        brightness: Brightness.dark,
+        cupertinoOverrideTheme: const CupertinoThemeData(brightness: Brightness.light),
+      ));
+      expect(CupertinoTheme.brightnessOf(context), Brightness.light);
+    });
+
     testWidgets('Can override material theme', (WidgetTester tester) async {
       final CupertinoThemeData theme = await testTheme(tester, ThemeData(
         cupertinoOverrideTheme: const CupertinoThemeData(