Add slider adaptive cupertino thumb color (#81647)

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

@@ -153,6 +153,7 @@ class Slider extends StatefulWidget {
     this.label,
     this.activeColor,
     this.inactiveColor,
+    this.thumbColor,
     this.mouseCursor,
     this.semanticFormatterCallback,
     this.focusNode,
@@ -190,6 +191,7 @@ class Slider extends StatefulWidget {
     this.mouseCursor,
     this.activeColor,
     this.inactiveColor,
+    this.thumbColor,
     this.semanticFormatterCallback,
     this.focusNode,
     this.autofocus = false,
@@ -382,6 +384,14 @@ class Slider extends StatefulWidget {
   /// Ignored if this slider is created with [Slider.adaptive].
   final Color? inactiveColor;
 
+  /// The color of the thumb.
+  ///
+  /// If this color is null:
+  /// * [Slider] will use [activeColor].
+  /// * [CupertinoSlider] will have a white thumb
+  /// (like the native default iOS slider).
+  final Color? thumbColor;
+
   /// The cursor for a mouse pointer when it enters or is hovering over the
   /// widget.
   ///
@@ -679,7 +689,7 @@ class _SliderState extends State<Slider> with TickerProviderStateMixin {
       inactiveTickMarkColor: widget.activeColor ?? sliderTheme.inactiveTickMarkColor ?? theme.colorScheme.primary.withOpacity(0.54),
       disabledActiveTickMarkColor: sliderTheme.disabledActiveTickMarkColor ?? theme.colorScheme.onPrimary.withOpacity(0.12),
       disabledInactiveTickMarkColor: sliderTheme.disabledInactiveTickMarkColor ?? theme.colorScheme.onSurface.withOpacity(0.12),
-      thumbColor: widget.activeColor ?? sliderTheme.thumbColor ?? theme.colorScheme.primary,
+      thumbColor: widget.thumbColor ?? widget.activeColor ?? sliderTheme.thumbColor ?? theme.colorScheme.primary,
       disabledThumbColor: sliderTheme.disabledThumbColor ?? Color.alphaBlend(theme.colorScheme.onSurface.withOpacity(.38), theme.colorScheme.surface),
       overlayColor: widget.activeColor?.withOpacity(0.12) ?? sliderTheme.overlayColor ?? theme.colorScheme.primary.withOpacity(0.12),
       valueIndicatorColor: valueIndicatorColor,
@@ -757,6 +767,7 @@ class _SliderState extends State<Slider> with TickerProviderStateMixin {
         max: widget.max,
         divisions: widget.divisions,
         activeColor: widget.activeColor,
+        thumbColor: widget.thumbColor ?? CupertinoColors.white,
       ),
     );
   }

packages/flutter/test/material/slider_test.dart

@@ -2513,4 +2513,105 @@ void main() {
     // 24.0 is the default margin, (800.0 - 24.0 - 24.0) is the slider's width.
     expect(nearEqual(activeTrackRRect.right, (800.0 - 24.0 - 24.0) * (5 / 15) + 24.0, 0.01), true);
   });
+
+
+  testWidgets('Slider paints thumbColor', (WidgetTester tester) async {
+    const Color color = Color(0xffffc107);
+
+    final Widget sliderAdaptive = MaterialApp(
+      theme: ThemeData(platform: TargetPlatform.iOS),
+      home: Material(
+        child: Slider(
+          value: 0,
+          onChanged: (double newValue) {},
+          thumbColor: color,
+        ),
+      ),
+    );
+
+    await tester.pumpWidget(sliderAdaptive);
+    await tester.pumpAndSettle();
+
+    final MaterialInkController material =
+        Material.of(tester.element(find.byType(Slider)))!;
+    expect(material, paints..circle(color: color));
+  });
+
+  testWidgets('Slider.adaptive paints thumbColor on Android',
+      (WidgetTester tester) async {
+    const Color color = Color(0xffffc107);
+
+    final Widget sliderAdaptive = MaterialApp(
+      theme: ThemeData(platform: TargetPlatform.android),
+      home: Material(
+        child: Slider.adaptive(
+          value: 0,
+          onChanged: (double newValue) {},
+          thumbColor: color,
+        ),
+      ),
+    );
+
+    await tester.pumpWidget(sliderAdaptive);
+    await tester.pumpAndSettle();
+
+    final MaterialInkController material =
+        Material.of(tester.element(find.byType(Slider)))!;
+    expect(material, paints..circle(color: color));
+  });
+
+  testWidgets('If thumbColor is null, it defaults to CupertinoColors.white',
+      (WidgetTester tester) async {
+    final Widget sliderAdaptive = MaterialApp(
+      theme: ThemeData(platform: TargetPlatform.iOS),
+      home: Material(
+        child: Slider.adaptive(
+          value: 0,
+          onChanged: (double newValue) {},
+        ),
+      ),
+    );
+
+    await tester.pumpWidget(sliderAdaptive);
+    await tester.pumpAndSettle();
+
+    final MaterialInkController material =
+        Material.of(tester.element(find.byType(CupertinoSlider)))!;
+    expect(
+      material,
+      paints
+        ..rrect()
+        ..rrect()
+        ..rrect()
+        ..rrect()
+        ..rrect()
+        ..rrect(color: CupertinoColors.white),
+    );
+  });
+
+  testWidgets('Slider.adaptive passes thumbColor to CupertinoSlider',
+      (WidgetTester tester) async {
+    const Color color = Color(0xffffc107);
+
+    final Widget sliderAdaptive = MaterialApp(
+      theme: ThemeData(platform: TargetPlatform.iOS),
+      home: Material(
+        child: Slider.adaptive(
+          value: 0,
+          onChanged: (double newValue) {},
+          thumbColor: color,
+        ),
+      ),
+    );
+
+    await tester.pumpWidget(sliderAdaptive);
+    await tester.pumpAndSettle();
+
+    final MaterialInkController material =
+        Material.of(tester.element(find.byType(CupertinoSlider)))!;
+    expect(
+      material,
+      paints..rrect()..rrect()..rrect()..rrect()..rrect()..rrect(color: color),
+    );
+  });
 }