[H] Tabs (#27477)

* Crash when a TabBar is put in a BottomAppBar.

* Tabs bugs (e.g. crash on transparent material)

- Tabs would crash when placed on transparent Materials
- Tabs would fail to render the child if an icon was specified

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

@@ -95,7 +95,7 @@ class Tab extends StatelessWidget {
     if (icon == null) {
       height = _kTabHeight;
       label = _buildLabelText();
-    } else if (text == null) {
+    } else if (text == null && child == null) {
       height = _kTabHeight;
       label = icon;
     } else {
@@ -730,7 +730,10 @@ class _TabBarState extends State<TabBar> {
     // When that happens, automatic transitions of the theme will likely look
     // ugly as the indicator color suddenly snaps to white at one end, but it's
     // not clear how to avoid that any further.
-    if (color.value == Material.of(context).color.value)
+    //
+    // The material's color might be null (if it's a transparency). In that case
+    // there's no good way for us to find out what the color is so we don't.
+    if (color.value == Material.of(context).color?.value)
       color = Colors.white;
 
     return UnderlineTabIndicator(

packages/flutter/test/material/tabs_test.dart

@@ -186,6 +186,68 @@ void main() {
     debugResetSemanticsIdCounter();
   });
 
+  testWidgets('Tab sizing - icon', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const MaterialApp(home: Center(child: Material(child: Tab(icon: SizedBox(width: 10.0, height: 10.0))))),
+    );
+    expect(tester.getSize(find.byType(Tab)), const Size(10.0, 46.0));
+  });
+
+  testWidgets('Tab sizing - child', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const MaterialApp(home: Center(child: Material(child: Tab(child: SizedBox(width: 10.0, height: 10.0))))),
+    );
+    expect(tester.getSize(find.byType(Tab)), const Size(10.0, 46.0));
+  });
+
+  testWidgets('Tab sizing - text', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      MaterialApp(theme: ThemeData(fontFamily: 'Ahem'), home: const Center(child: Material(child: Tab(text: 'x')))),
+    );
+    expect(tester.renderObject<RenderParagraph>(find.byType(RichText)).text.style.fontFamily, 'Ahem');
+    expect(tester.getSize(find.byType(Tab)), const Size(14.0, 46.0));
+  });
+
+  testWidgets('Tab sizing - icon and text', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      MaterialApp(theme: ThemeData(fontFamily: 'Ahem'), home: const Center(child: Material(child: Tab(icon: SizedBox(width: 10.0, height: 10.0), text: 'x')))),
+    );
+    expect(tester.renderObject<RenderParagraph>(find.byType(RichText)).text.style.fontFamily, 'Ahem');
+    expect(tester.getSize(find.byType(Tab)), const Size(14.0, 72.0));
+  });
+
+  testWidgets('Tab sizing - icon and child', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      MaterialApp(theme: ThemeData(fontFamily: 'Ahem'), home: const Center(child: Material(child: Tab(icon: SizedBox(width: 10.0, height: 10.0), child: Text('x'))))),
+    );
+    expect(tester.renderObject<RenderParagraph>(find.byType(RichText)).text.style.fontFamily, 'Ahem');
+    expect(tester.getSize(find.byType(Tab)), const Size(14.0, 72.0));
+  });
+
+  testWidgets('Tab color - normal', (WidgetTester tester) async {
+    final Widget tabBar = TabBar(tabs: const <Widget>[SizedBox.shrink()], controller: TabController(length: 1, vsync: tester));
+    await tester.pumpWidget(
+      MaterialApp(home: Material(child: tabBar)),
+    );
+    expect(find.byType(TabBar), paints..line(color: Colors.blue[500]));
+  });
+
+  testWidgets('Tab color - match', (WidgetTester tester) async {
+    final Widget tabBar = TabBar(tabs: const <Widget>[SizedBox.shrink()], controller: TabController(length: 1, vsync: tester));
+    await tester.pumpWidget(
+      MaterialApp(home: Material(color: const Color(0xff2196f3), child: tabBar)),
+    );
+    expect(find.byType(TabBar), paints..line(color: Colors.white));
+  });
+
+  testWidgets('Tab color - transparency', (WidgetTester tester) async {
+    final Widget tabBar = TabBar(tabs: const <Widget>[SizedBox.shrink()], controller: TabController(length: 1, vsync: tester));
+    await tester.pumpWidget(
+      MaterialApp(home: Material(type: MaterialType.transparency, child: tabBar)),
+    );
+    expect(find.byType(TabBar), paints..line(color: Colors.blue[500]));
+  });
+
   testWidgets('TabBar tap selects tab', (WidgetTester tester) async {
     final List<String> tabs = <String>['A', 'B', 'C'];