[material_ui] Avoid InheritedCupertinoTheme lookup in Theme.of and preserve MaterialBasedCupertinoThemeData

packages/material_ui/lib/src/theme.dart

@@ -141,14 +141,17 @@ class Theme extends StatelessWidget {
       MaterialLocalizations,
     );
     final ScriptCategory category = localizations?.scriptCategory ?? ScriptCategory.englishLike;
-    final InheritedCupertinoTheme? inheritedCupertinoTheme = context
-        .dependOnInheritedWidgetOfExactType<InheritedCupertinoTheme>();
-    final ThemeData theme =
-        inheritedTheme?.theme.data ??
-        (inheritedCupertinoTheme != null
-            ? CupertinoBasedMaterialThemeData(themeData: inheritedCupertinoTheme.theme.data)
-                  .materialTheme
-            : _fallbackTheme);
+    final ThemeData theme;
+    if (inheritedTheme != null) {
+      theme = inheritedTheme.theme.data;
+    } else {
+      final InheritedCupertinoTheme? inheritedCupertinoTheme = context
+          .dependOnInheritedWidgetOfExactType<InheritedCupertinoTheme>();
+      theme = inheritedCupertinoTheme != null
+          ? CupertinoBasedMaterialThemeData(themeData: inheritedCupertinoTheme.theme.data)
+                .materialTheme
+          : _fallbackTheme;
+    }
     return ThemeData.localize(theme, theme.typography.geometryThemeFor(category));
   }
 

packages/material_ui/lib/src/theme_data.dart

@@ -3092,7 +3092,7 @@ class MaterialBasedCupertinoThemeData extends CupertinoThemeData {
   MaterialBasedCupertinoThemeData({required ThemeData materialTheme})
     : this._(
         materialTheme,
-        (materialTheme.cupertinoOverrideTheme ?? const CupertinoThemeData()).noDefault(),
+        materialTheme.cupertinoOverrideTheme?.noDefault() ?? const NoDefaultCupertinoThemeData(),
       );
 
   MaterialBasedCupertinoThemeData._(this._materialTheme, this._cupertinoOverrideTheme)
@@ -3192,14 +3192,17 @@ class CupertinoBasedMaterialThemeData {
   /// Creates a Material theme with a color scheme based off of the colors from
   /// a [CupertinoThemeData].
   CupertinoBasedMaterialThemeData({required CupertinoThemeData themeData})
-    : materialTheme = ThemeData(
-        colorScheme: ColorScheme.fromSeed(
-          seedColor: themeData.primaryColor,
-          brightness: themeData.brightness ?? Brightness.light,
-          primary: themeData.primaryColor,
-          onPrimary: themeData.primaryContrastingColor,
+    : materialTheme = switch (themeData) {
+        MaterialBasedCupertinoThemeData() => themeData._materialTheme,
+        _ => ThemeData(
+          colorScheme: ColorScheme.fromSeed(
+            seedColor: themeData.primaryColor,
+            brightness: themeData.brightness ?? Brightness.light,
+            primary: themeData.primaryColor,
+            onPrimary: themeData.primaryContrastingColor,
+          ),
         ),
-      );
+      };
 
   /// The Material theme data with colors based on an existing [CupertinoThemeData].
   final ThemeData materialTheme;

packages/material_ui/pending_changelogs/change_2026_10_31_theme_of_cupertino_treeshake.yaml

@@ -0,0 +1,3 @@
+changelog: |
+  - Avoids looking up `InheritedCupertinoTheme` in `Theme.of` when a Material `Theme` ancestor is present and preserves `MaterialBasedCupertinoThemeData` in `CupertinoBasedMaterialThemeData`, allowing unused `ColorScheme.fromSeed` and `material_color_utilities` code to be tree-shaken.
+version: patch

packages/material_ui/test/theme_test.dart

@@ -1174,6 +1174,40 @@ void main() {
       expect(theme.primaryColor, Colors.blue);
       expect(theme.primaryContrastingColor, CupertinoColors.destructiveRed);
     });
+
+    testWidgets(
+      'Theme.of does not depend on InheritedCupertinoTheme when Theme ancestor is present',
+      (WidgetTester tester) async {
+        testBuildCalled = 0;
+        final themeData = ThemeData(primaryColor: const Color(0xFF000000));
+
+        Widget buildTree(CupertinoThemeData cupertinoTheme) {
+          return Theme(
+            data: themeData,
+            child: CupertinoTheme(data: cupertinoTheme, child: const Test()),
+          );
+        }
+
+        await tester.pumpWidget(
+          buildTree(const CupertinoThemeData(primaryColor: CupertinoColors.activeBlue)),
+        );
+        expect(testBuildCalled, 1);
+
+        await tester.pumpWidget(
+          buildTree(const CupertinoThemeData(primaryColor: CupertinoColors.activeGreen)),
+        );
+        expect(testBuildCalled, 1);
+      },
+    );
+
+    test('CupertinoBasedMaterialThemeData returns underlying ThemeData for MaterialBasedCupertinoThemeData', () {
+      final materialTheme = ThemeData(colorScheme: const ColorScheme.light(primary: Colors.purple));
+      final cupertinoTheme = MaterialBasedCupertinoThemeData(materialTheme: materialTheme);
+      expect(
+        CupertinoBasedMaterialThemeData(themeData: cupertinoTheme).materialTheme,
+        same(materialTheme),
+      );
+    });
   });
 }