2c71881f50
fixes [Material 3 `TabBar` does not take full width when `isScrollable: true`](https://github.com/flutter/flutter/issues/117722) ### Description 1. Fixed the divider doesn't stretch to take all the available width in the scrollable tab bar in M3 2. Added `dividerHeight` property. ### Code sample <details> <summary>expand to view the code sample</summary> ```dart import 'package:flutter/material.dart'; /// Flutter code sample for [TabBar]. void main() => runApp(const TabBarApp()); class TabBarApp extends StatelessWidget { const TabBarApp({super.key}); @override Widget build(BuildContext context) { return const MaterialApp( debugShowCheckedModeBanner: false, home: TabBarExample(), ); } } class TabBarExample extends StatefulWidget { const TabBarExample({super.key}); @override State<TabBarExample> createState() => _TabBarExampleState(); } class _TabBarExampleState extends State<TabBarExample> { bool rtl = false; bool customColors = false; bool removeDivider = false; Color dividerColor = Colors.amber; Color indicatorColor = Colors.red; @override Widget build(BuildContext context) { return DefaultTabController( initialIndex: 1, length: 3, child: Directionality( textDirection: rtl ? TextDirection.rtl : TextDirection.ltr, child: Scaffold( appBar: AppBar( title: const Text('TabBar Sample'), actions: <Widget>[ IconButton.filledTonal( tooltip: 'Switch direction', icon: const Icon(Icons.swap_horiz), onPressed: () { setState(() { rtl = !rtl; }); }, ), IconButton.filledTonal( tooltip: 'Use custom colors', icon: const Icon(Icons.color_lens), onPressed: () { setState(() { customColors = !customColors; }); }, ), IconButton.filledTonal( tooltip: 'Show/hide divider', icon: const Icon(Icons.remove_rounded), onPressed: () { setState(() { removeDivider = !removeDivider; }); }, ), ], ), body: Column( children: <Widget>[ const Spacer(), const Text('Scrollable - TabAlignment.start'), TabBar( isScrollable: true, tabAlignment: TabAlignment.start, dividerColor: customColors ? dividerColor : null, indicatorColor: customColors ? indicatorColor : null, dividerHeight: removeDivider ? 0 : null, tabs: const <Widget>[ Tab( icon: Icon(Icons.cloud_outlined), ), Tab( icon: Icon(Icons.beach_access_sharp), ), Tab( icon: Icon(Icons.brightness_5_sharp), ), ], ), const Text('Scrollable - TabAlignment.startOffset'), TabBar( isScrollable: true, tabAlignment: TabAlignment.startOffset, dividerColor: customColors ? dividerColor : null, indicatorColor: customColors ? indicatorColor : null, dividerHeight: removeDivider ? 0 : null, tabs: const <Widget>[ Tab( icon: Icon(Icons.cloud_outlined), ), Tab( icon: Icon(Icons.beach_access_sharp), ), Tab( icon: Icon(Icons.brightness_5_sharp), ), ], ), const Text('Scrollable - TabAlignment.center'), TabBar( isScrollable: true, tabAlignment: TabAlignment.center, dividerColor: customColors ? dividerColor : null, indicatorColor: customColors ? indicatorColor : null, dividerHeight: removeDivider ? 0 : null, tabs: const <Widget>[ Tab( icon: Icon(Icons.cloud_outlined), ), Tab( icon: Icon(Icons.beach_access_sharp), ), Tab( icon: Icon(Icons.brightness_5_sharp), ), ], ), const Spacer(), const Text('Non-scrollable - TabAlignment.fill'), TabBar( tabAlignment: TabAlignment.fill, dividerColor: customColors ? dividerColor : null, indicatorColor: customColors ? indicatorColor : null, dividerHeight: removeDivider ? 0 : null, tabs: const <Widget>[ Tab( icon: Icon(Icons.cloud_outlined), ), Tab( icon: Icon(Icons.beach_access_sharp), ), Tab( icon: Icon(Icons.brightness_5_sharp), ), ], ), const Text('Non-scrollable - TabAlignment.center'), TabBar( tabAlignment: TabAlignment.center, dividerColor: customColors ? dividerColor : null, indicatorColor: customColors ? indicatorColor : null, dividerHeight: removeDivider ? 0 : null, tabs: const <Widget>[ Tab( icon: Icon(Icons.cloud_outlined), ), Tab( icon: Icon(Icons.beach_access_sharp), ), Tab( icon: Icon(Icons.brightness_5_sharp), ), ], ), const Spacer(), const Text('Secondary - TabAlignment.fill'), TabBar.secondary( tabAlignment: TabAlignment.fill, dividerColor: customColors ? dividerColor : null, indicatorColor: customColors ? indicatorColor : null, dividerHeight: removeDivider ? 0 : null, tabs: const <Widget>[ Tab( icon: Icon(Icons.cloud_outlined), ), Tab( icon: Icon(Icons.beach_access_sharp), ), Tab( icon: Icon(Icons.brightness_5_sharp), ), ], ), const Text('Secondary - TabAlignment.center'), TabBar.secondary( tabAlignment: TabAlignment.center, dividerColor: customColors ? dividerColor : null, indicatorColor: customColors ? indicatorColor : null, dividerHeight: removeDivider ? 0 : null, tabs: const <Widget>[ Tab( icon: Icon(Icons.cloud_outlined), ), Tab( icon: Icon(Icons.beach_access_sharp), ), Tab( icon: Icon(Icons.brightness_5_sharp), ), ], ), const Spacer(), ], ), ), ), ); } } ``` </details> ### Before  ### After  This also contains regression test for https://github.com/flutter/flutter/pull/125974#discussion_r1239089151 ```dart // This is a regression test for https://github.com/flutter/flutter/pull/125974#discussion_r1239089151. testWidgets('Divider can be constrained', (WidgetTester tester) async { ``` 
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