Adds splashBorderRadius property to TabBarTheme (flutter#160046)

Adds splashBorderRadius property to TabBarTheme

Fix flutter#159845 


## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

---------

Co-authored-by: Qun Cheng <[email protected]>

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

@@ -327,6 +327,7 @@ class TabBarThemeData with Diagnosticable {
     this.tabAlignment,
     this.textScaler,
     this.indicatorAnimation,
+    this.splashBorderRadius
   });
 
   /// Overrides the default value for [TabBar.indicator].
@@ -389,6 +390,9 @@ class TabBarThemeData with Diagnosticable {
   /// Overrides the default value for [TabBar.indicatorAnimation].
   final TabIndicatorAnimation? indicatorAnimation;
 
+  /// Defines the clipping radius of splashes that extend outside the bounds of the tab.
+  final BorderRadius? splashBorderRadius;
+
   /// Creates a copy of this object but with the given fields replaced with the
   /// new values.
   TabBarThemeData copyWith({
@@ -408,6 +412,7 @@ class TabBarThemeData with Diagnosticable {
     TabAlignment? tabAlignment,
     TextScaler? textScaler,
     TabIndicatorAnimation? indicatorAnimation,
+    BorderRadius? splashBorderRadius,
   }) {
     return TabBarThemeData(
       indicator: indicator ?? this.indicator,
@@ -426,6 +431,7 @@ class TabBarThemeData with Diagnosticable {
       tabAlignment: tabAlignment ?? this.tabAlignment,
       textScaler: textScaler ?? this.textScaler,
       indicatorAnimation: indicatorAnimation ?? this.indicatorAnimation,
+      splashBorderRadius: splashBorderRadius ?? this.splashBorderRadius,
     );
   }
 
@@ -453,6 +459,7 @@ class TabBarThemeData with Diagnosticable {
       tabAlignment: t < 0.5 ? a.tabAlignment : b.tabAlignment,
       textScaler: t < 0.5 ? a.textScaler : b.textScaler,
       indicatorAnimation: t < 0.5 ? a.indicatorAnimation : b.indicatorAnimation,
+      splashBorderRadius: BorderRadius.lerp(a.splashBorderRadius, a.splashBorderRadius, t)
     );
   }
 
@@ -474,6 +481,7 @@ class TabBarThemeData with Diagnosticable {
     tabAlignment,
     textScaler,
     indicatorAnimation,
+    splashBorderRadius,
   );
 
   @override
@@ -500,7 +508,8 @@ class TabBarThemeData with Diagnosticable {
         && other.mouseCursor == mouseCursor
         && other.tabAlignment == tabAlignment
         && other.textScaler == textScaler
-        && other.indicatorAnimation == indicatorAnimation;
+        && other.indicatorAnimation == indicatorAnimation
+        && other.splashBorderRadius == splashBorderRadius;
   }
 
   @override
@@ -522,5 +531,6 @@ class TabBarThemeData with Diagnosticable {
     properties.add(DiagnosticsProperty<TabAlignment?>('tabAlignment', tabAlignment, defaultValue: null));
     properties.add(DiagnosticsProperty<TextScaler?>('textScaler', textScaler, defaultValue: null));
     properties.add(DiagnosticsProperty<TabIndicatorAnimation?>('indicatorAnimation', indicatorAnimation, defaultValue: null));
+    properties.add(DiagnosticsProperty<BorderRadius?>('splashBorderRadius', splashBorderRadius, defaultValue: null));
   }
 }

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

@@ -1813,7 +1813,7 @@ class _TabBarState extends State<TabBar> {
         enableFeedback: widget.enableFeedback ?? true,
         overlayColor: widget.overlayColor ?? tabBarTheme.overlayColor ?? defaultOverlay,
         splashFactory: widget.splashFactory ?? tabBarTheme.splashFactory ?? _defaults.splashFactory,
-        borderRadius: widget.splashBorderRadius,
+        borderRadius: widget.splashBorderRadius ?? tabBarTheme.splashBorderRadius ?? _defaults.splashBorderRadius,
         child: Padding(
           padding: EdgeInsets.only(bottom: widget.indicatorWeight),
           child: Stack(

packages/flutter/test/material/tab_bar_theme_test.dart

@@ -1791,4 +1791,58 @@ void main() {
     targetRect = const Rect.fromLTRB(275.0, 0.0, 325.0, 48.0);
     expectIndicatorAttrs(tabBarBox, rect: rect, targetRect: targetRect);
   });
+
+  testWidgets('TabBar inherits splashBorderRadius from theme', (WidgetTester tester) async {
+    const Color hoverColor = Color(0xfff44336);
+    const double radius = 20;
+    await tester.pumpWidget(
+      Material(
+        child: Localizations(
+          locale: const Locale('en', 'US'),
+          delegates: const <LocalizationsDelegate<dynamic>>[
+            DefaultMaterialLocalizations.delegate,
+            DefaultWidgetsLocalizations.delegate,
+          ],
+          child: DefaultTabController(
+            length: 1,
+            child: TabBarTheme(
+              data: TabBarThemeData(
+                 splashBorderRadius: BorderRadius.circular(radius),
+              ),
+              child: const TabBar(
+                overlayColor: WidgetStateMapper<Color>(
+                  <WidgetStatesConstraint, Color>{
+                    WidgetState.hovered: hoverColor,
+                    WidgetState.any: Colors.black54,
+                  },
+                ),
+                tabs: <Widget>[
+                  Tab(
+                    child: Text(''),
+                  ),
+                ],
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+    final TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse, pointer: 1);
+    await gesture.moveTo(tester.getCenter(find.byType(Tab)));
+    await tester.pumpAndSettle();
+    final Finder findInkWell = find.byType(InkWell);
+
+    final BuildContext context = tester.element(findInkWell);
+    expect(
+      Material.of(context),
+      paints..rrect(
+        color: hoverColor,
+        rrect: RRect.fromRectAndRadius(
+          tester.getRect(findInkWell),
+          const Radius.circular(radius),
+        ),
+      ),
+    );
+    gesture.removePointer();
+  });
 }