Calculate the system overlay style based on the AppBar background color (#75091)

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

@@ -660,9 +660,11 @@ class AppBar extends StatefulWidget implements PreferredSizeWidget {
   /// {@template flutter.material.appbar.systemOverlayStyle}
   /// Specifies the style to use for the system overlays that overlap the AppBar.
   ///
-  /// If this property is null, then [SystemUiOverlayStyle.light] is used if the
-  /// overall theme is dark, [SystemUiOverlayStyle.dark] otherwise. Theme brightness
-  /// is defined by [ColorScheme.brightness] for [ThemeData.colorScheme].
+  /// This property is only used if [backwardsCompatibility] is set to false.
+  ///
+  /// If this property is null, then [AppBarTheme.systemOverlayStyle] of
+  /// [ThemeData.appBarTheme] is used. If that is also null, an appropriate
+  /// [SystemUiOverlayStyle] is calculated based on the [backgroundColor].
   ///
   /// The AppBar's descendants are built within a
   /// `AnnotatedRegion<SystemUiOverlayStyle>` widget, which causes
@@ -710,6 +712,10 @@ class _AppBarState extends State<AppBar> {
     Scaffold.of(context).openEndDrawer();
   }
 
+  SystemUiOverlayStyle _systemOverlayStyleForBrightness(Brightness brightness) {
+    return brightness == Brightness.dark ? SystemUiOverlayStyle.light : SystemUiOverlayStyle.dark;
+  }
+
   @override
   Widget build(BuildContext context) {
     assert(!widget.primary || debugCheckHasMediaQuery(context));
@@ -953,12 +959,15 @@ class _AppBarState extends State<AppBar> {
       );
     }
 
-    final Brightness overlayStyleBrightness = widget.brightness ?? appBarTheme.brightness ?? colorScheme.brightness;
     final SystemUiOverlayStyle overlayStyle = backwardsCompatibility
-      ? (overlayStyleBrightness == Brightness.dark ? SystemUiOverlayStyle.light : SystemUiOverlayStyle.dark)
+      ? _systemOverlayStyleForBrightness(
+          widget.brightness
+          ?? appBarTheme.brightness
+          ?? theme.primaryColorBrightness,
+        )
       : widget.systemOverlayStyle
         ?? appBarTheme.systemOverlayStyle
-        ?? (colorScheme.brightness == Brightness.dark ? SystemUiOverlayStyle.light : SystemUiOverlayStyle.dark);
+        ?? _systemOverlayStyleForBrightness(ThemeData.estimateBrightnessForColor(backgroundColor));
 
     return Semantics(
       container: true,

packages/flutter/test/material/app_bar_test.dart

@@ -1953,7 +1953,7 @@ void main() {
   });
 
   testWidgets('AppBar draws a dark system bar for a light background', (WidgetTester tester) async {
-    final ThemeData lightTheme = ThemeData(primaryColor: Colors.white);
+    final ThemeData lightTheme = ThemeData(primarySwatch: Colors.lightBlue);
     await tester.pumpWidget(
       MaterialApp(
         theme: lightTheme,
@@ -1974,6 +1974,48 @@ void main() {
     ));
   });
 
+  testWidgets('AppBar draws a light system bar for a light theme with a dark background', (WidgetTester tester) async {
+    final ThemeData lightTheme = ThemeData(primarySwatch: Colors.deepOrange);
+    await tester.pumpWidget(MaterialApp(
+      theme: lightTheme,
+      home: Scaffold(
+        appBar: AppBar(
+          backwardsCompatibility: false,
+          title: const Text('test')
+        ),
+      ),
+    ));
+
+    expect(lightTheme.primaryColorBrightness, Brightness.dark);
+    expect(lightTheme.colorScheme.brightness, Brightness.light);
+    expect(SystemChrome.latestStyle, const SystemUiOverlayStyle(
+      statusBarBrightness: Brightness.dark,
+      statusBarIconBrightness: Brightness.light,
+    ));
+  });
+
+  testWidgets('AppBar draws a dark system bar for a dark theme with a light background', (WidgetTester tester) async {
+    final ThemeData darkTheme = ThemeData(brightness: Brightness.dark, cardColor: Colors.white);
+    await tester.pumpWidget(
+      MaterialApp(
+        theme: darkTheme,
+        home: Scaffold(
+          appBar: AppBar(
+            backwardsCompatibility: false,
+            title: const Text('test')
+          ),
+        ),
+      ),
+    );
+
+    expect(darkTheme.primaryColorBrightness, Brightness.dark);
+    expect(darkTheme.colorScheme.brightness, Brightness.dark);
+    expect(SystemChrome.latestStyle, const SystemUiOverlayStyle(
+      statusBarBrightness: Brightness.light,
+      statusBarIconBrightness: Brightness.dark,
+    ));
+  });
+
   testWidgets('Changing SliverAppBar snap from true to false', (WidgetTester tester) async {
     // Regression test for https://github.com/flutter/flutter/issues/17598
     const double appBarHeight = 256.0;

packages/flutter/test/material/app_bar_theme_test.dart

@@ -30,7 +30,7 @@ void main() {
     final RichText actionIconText = _getAppBarIconRichText(tester);
     final DefaultTextStyle text = _getAppBarText(tester);
 
-    expect(SystemChrome.latestStyle!.statusBarBrightness, SystemUiOverlayStyle.dark.statusBarBrightness);
+    expect(SystemChrome.latestStyle!.statusBarBrightness, SystemUiOverlayStyle.light.statusBarBrightness);
     expect(widget.color, Colors.blue);
     expect(widget.elevation, 4.0);
     expect(widget.shadowColor, Colors.black);
@@ -249,7 +249,7 @@ void main() {
     // - background color: ColorScheme.primary
     // - foreground color: ColorScheme.onPrimary
     // - actions text: style bodyText2, foreground color
-    // - status bar brightness: dark (based on color scheme brightness)
+    // - status bar brightness: light (based on color scheme brightness)
     {
       await tester.pumpWidget(buildFrame(ThemeData.from(colorScheme: const ColorScheme.light())));
 
@@ -259,7 +259,7 @@ void main() {
       final RichText actionIconText = _getAppBarIconRichText(tester);
       final DefaultTextStyle text = _getAppBarText(tester);
 
-      expect(SystemChrome.latestStyle!.statusBarBrightness, SystemUiOverlayStyle.dark.statusBarBrightness);
+      expect(SystemChrome.latestStyle!.statusBarBrightness, SystemUiOverlayStyle.light.statusBarBrightness);
       expect(widget.color, theme.colorScheme.primary);
       expect(widget.elevation, 4.0);
       expect(widget.shadowColor, Colors.black);