add key to constructors of public widgets (#47884)

* add key to constructors of public widgets

* fix a test

* fix a test

packages/flutter/lib/src/cupertino/action_sheet.dart

@@ -265,12 +265,14 @@ class CupertinoActionSheetAction extends StatelessWidget {
   ///
   /// The [child] and [onPressed] arguments must not be null.
   const CupertinoActionSheetAction({
+    Key key,
     @required this.onPressed,
     this.isDefaultAction = false,
     this.isDestructiveAction = false,
     @required this.child,
   }) : assert(child != null),
-       assert(onPressed != null);
+       assert(onPressed != null),
+       super(key: key);
 
   /// The callback that is called when the button is tapped.
   ///

packages/flutter/lib/src/cupertino/date_picker.dart

@@ -230,6 +230,7 @@ class CupertinoDatePicker extends StatefulWidget {
   ///
   /// [use24hFormat] decides whether 24 hour format is used. Defaults to false.
   CupertinoDatePicker({
+    Key key,
     this.mode = CupertinoDatePickerMode.dateAndTime,
     @required this.onDateTimeChanged,
     DateTime initialDateTime,
@@ -247,7 +248,8 @@ class CupertinoDatePicker extends StatefulWidget {
        assert(
          minuteInterval > 0 && 60 % minuteInterval == 0,
          'minute interval is not a positive integer factor of 60',
-       ) {
+       ),
+       super(key: key) {
     assert(this.initialDateTime != null);
     assert(
       mode != CupertinoDatePickerMode.dateAndTime || minimumDate == null || !this.initialDateTime.isBefore(minimumDate),

packages/flutter/lib/src/cupertino/nav_bar.dart

@@ -1270,11 +1270,13 @@ class CupertinoNavigationBarBackButton extends StatelessWidget {
   ///
   /// The [color] parameter must not be null.
   const CupertinoNavigationBarBackButton({
+    Key key,
     this.color,
     this.previousPageTitle,
     this.onPressed,
   }) : _backChevron = null,
-       _backLabel = null;
+       _backLabel = null,
+       super(key: key);
 
   // Allow the back chevron and label to be separately created (and keyed)
   // because they animate separately during page transitions.

packages/flutter/lib/src/cupertino/page_scaffold.dart

@@ -200,7 +200,7 @@ class _CupertinoPageScaffoldState extends State<CupertinoPageScaffold> {
 ///
 /// Used by [CupertinoPageScaffold] to either shift away fully obstructed content
 /// or provide a padding guide to partially obstructed content.
-abstract class ObstructingPreferredSizeWidget extends PreferredSizeWidget {
+abstract class ObstructingPreferredSizeWidget implements PreferredSizeWidget {
   /// If true, this widget fully obstructs widgets behind it by the specified
   /// size.
   ///

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

@@ -58,6 +58,7 @@ class ReorderableListView extends StatefulWidget {
 
   /// Creates a reorderable list.
   ReorderableListView({
+    Key key,
     this.header,
     @required this.children,
     @required this.onReorder,
@@ -70,7 +71,8 @@ class ReorderableListView extends StatefulWidget {
        assert(
          children.every((Widget w) => w.key != null),
          'All children of this widget must have a key.',
-       );
+       ),
+       super(key: key);
 
   /// A non-reorderable header widget to show before the list.
   ///

packages/flutter/lib/src/widgets/platform_view.dart

@@ -922,12 +922,14 @@ class PlatformViewSurface extends LeafRenderObjectWidget {
   ///
   /// The [controller] must not be null.
   const PlatformViewSurface({
+    Key key,
     @required this.controller,
     @required this.hitTestBehavior,
     @required this.gestureRecognizers,
   }) : assert(controller != null),
        assert(hitTestBehavior != null),
-       assert(gestureRecognizers != null);
+       assert(gestureRecognizers != null),
+       super(key: key);
 
   /// The controller for the platform view integrated by this [PlatformViewSurface].
   ///

packages/flutter/lib/src/widgets/text.dart

@@ -58,13 +58,14 @@ class DefaultTextStyle extends InheritedTheme {
   ///
   /// This constructor creates a [DefaultTextStyle] that lacks a [child], which
   /// means the constructed value cannot be incorporated into the tree.
-  const DefaultTextStyle.fallback()
+  const DefaultTextStyle.fallback({ Key key })
     : style = const TextStyle(),
       textAlign = null,
       softWrap = true,
       maxLines = null,
       overflow = TextOverflow.clip,
-      textWidthBasis = TextWidthBasis.parent;
+      textWidthBasis = TextWidthBasis.parent,
+      super(key: key, child: null);
 
   /// Creates a default text style that overrides the text styles in scope at
   /// this point in the widget tree.

packages/flutter/lib/src/widgets/value_listenable_builder.dart

@@ -115,11 +115,13 @@ class ValueListenableBuilder<T> extends StatefulWidget {
   /// The [child] is optional but is good practice to use if part of the widget
   /// subtree does not depend on the value of the [valueListenable].
   const ValueListenableBuilder({
+    Key key,
     @required this.valueListenable,
     @required this.builder,
     this.child,
   }) : assert(valueListenable != null),
-       assert(builder != null);
+       assert(builder != null),
+       super(key: key);
 
   /// The [ValueListenable] whose value you depend on in order to build.
   ///

packages/flutter/test/material/bottom_app_bar_test.dart

@@ -419,7 +419,7 @@ class ClipCachePainter extends CustomPainter {
 }
 
 class ShapeListener extends StatefulWidget {
-  const ShapeListener(this.child);
+  const ShapeListener(this.child, { Key key }) : super(key: key);
 
   final Widget child;
 

packages/flutter/test/material/dropdown_form_field_test.dart

@@ -107,10 +107,17 @@ class _TestAppState extends State<TestApp> {
 }
 
 class TestApp extends StatefulWidget {
-  const TestApp({ this.textDirection, this.child, this.mediaSize });
+  const TestApp({
+    Key key,
+    this.textDirection,
+    this.child,
+    this.mediaSize,
+  }) : super(key: key);
+
   final TextDirection textDirection;
   final Widget child;
   final Size mediaSize;
+
   @override
   _TestAppState createState() => _TestAppState();
 }

packages/flutter/test/material/dropdown_test.dart

@@ -93,10 +93,17 @@ Widget buildFrame({
 }
 
 class TestApp extends StatefulWidget {
-  const TestApp({ this.textDirection, this.child, this.mediaSize });
+  const TestApp({
+    Key key,
+    this.textDirection,
+    this.child,
+    this.mediaSize,
+  }) : super(key: key);
+
   final TextDirection textDirection;
   final Widget child;
   final Size mediaSize;
+
   @override
   _TestAppState createState() => _TestAppState();
 }

packages/flutter/test/material/expansion_panel_test.dart

@@ -55,7 +55,7 @@ class _SimpleExpansionPanelListTestWidgetState extends State<SimpleExpansionPane
 }
 
 class ExpansionPanelListSemanticsTest extends StatefulWidget {
-  const ExpansionPanelListSemanticsTest({this.headerKey});
+  const ExpansionPanelListSemanticsTest({ Key key, this.headerKey }) : super(key: key);
 
   final Key headerKey;
 

packages/flutter/test/material/feedback_test.dart

@@ -201,11 +201,11 @@ void main () {
 }
 
 class TestWidget extends StatelessWidget {
-
   const TestWidget({
+    Key key,
     this.tapHandler = nullHandler,
     this.longPressHandler = nullHandler,
-  });
+  }) : super(key: key);
 
   final HandlerCreator tapHandler;
   final HandlerCreator longPressHandler;

packages/flutter/test/material/material_test.dart

@@ -11,6 +11,7 @@ import '../rendering/mock_canvas.dart';
 import '../widgets/test_border.dart' show TestBorder;
 
 class NotifyMaterial extends StatelessWidget {
+  const NotifyMaterial({ Key key }) : super(key: key);
   @override
   Widget build(BuildContext context) {
     LayoutChangedNotification().dispatch(context);
@@ -101,7 +102,7 @@ void main() {
 
   testWidgets('LayoutChangedNotification test', (WidgetTester tester) async {
     await tester.pumpWidget(
-      Material(
+      const Material(
         child: NotifyMaterial(),
       ),
     );

packages/flutter/test/material/popup_menu_test.dart

@@ -1194,9 +1194,15 @@ void main() {
 }
 
 class TestApp extends StatefulWidget {
-  const TestApp({ this.textDirection, this.child });
+  const TestApp({
+    Key key,
+    this.textDirection,
+    this.child,
+  }) : super(key: key);
+
   final TextDirection textDirection;
   final Widget child;
+
   @override
   _TestAppState createState() => _TestAppState();
 }

packages/flutter/test/material/search_test.dart

@@ -644,11 +644,12 @@ void main() {
 
 class TestHomePage extends StatelessWidget {
   const TestHomePage({
+    Key key,
     this.results,
     this.delegate,
     this.passInInitialQuery = false,
     this.initialQuery,
-  });
+  }) : super(key: key);
 
   final List<String> results;
   final SearchDelegate<String> delegate;

packages/flutter/test/material/tabbed_scrollview_warp_test.dart

@@ -24,6 +24,8 @@ class MySliverPersistentHeaderDelegate extends SliverPersistentHeaderDelegate {
 }
 
 class MyHomePage extends StatefulWidget {
+  const MyHomePage({ Key key }) : super(key: key);
+
   @override
   _MyHomePageState createState() => _MyHomePageState();
 }
@@ -73,7 +75,7 @@ class _MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
 
 void main() {
   testWidgets('Tabbed CustomScrollViews, warp from tab 1 to 3', (WidgetTester tester) async {
-    await tester.pumpWidget(MaterialApp(home: MyHomePage()));
+    await tester.pumpWidget(const MaterialApp(home: MyHomePage()));
 
     // should not crash.
     await tester.tap(find.text('Tab 2'));

packages/flutter/test/material/tabs_test.dart

@@ -127,7 +127,12 @@ Widget buildFrame({
 typedef TabControllerFrameBuilder = Widget Function(BuildContext context, TabController controller);
 
 class TabControllerFrame extends StatefulWidget {
-  const TabControllerFrame({ this.length, this.initialIndex = 0, this.builder });
+  const TabControllerFrame({
+    Key key,
+    this.length,
+    this.initialIndex = 0,
+    this.builder,
+  }) : super(key: key);
 
   final int length;
   final int initialIndex;

packages/flutter/test/material/theme_test.dart

@@ -650,7 +650,7 @@ void main() {
 
 int testBuildCalled;
 class Test extends StatefulWidget {
-  const Test();
+  const Test({ Key key }) : super(key: key);
 
   @override
   _TestState createState() => _TestState();

packages/flutter/test/material/will_pop_test.dart

@@ -8,6 +8,7 @@ import 'package:flutter/material.dart';
 bool willPopValue = false;
 
 class SamplePage extends StatefulWidget {
+  const SamplePage({ Key key }) : super(key: key);
   @override
   SamplePageState createState() => SamplePageState();
 }
@@ -86,7 +87,7 @@ void main() {
                   onPressed: () {
                     showDialog<void>(
                       context: context,
-                      builder: (BuildContext context) => SamplePage(),
+                      builder: (BuildContext context) => const SamplePage(),
                     );
                   },
                 ),

packages/flutter/test/widgets/baseline_test.dart

@@ -94,7 +94,7 @@ void main() {
 }
 
 class BaselineDetector extends LeafRenderObjectWidget {
-  const BaselineDetector(this.callback);
+  const BaselineDetector(this.callback, { Key key }) : super(key: key);
 
   final VoidCallback callback;
 

packages/flutter/test/widgets/build_scope_test.dart

@@ -8,6 +8,7 @@ import 'package:flutter/widgets.dart';
 import 'test_widgets.dart';
 
 class ProbeWidget extends StatefulWidget {
+  const ProbeWidget({ Key key }) : super(key: key);
   @override
   ProbeWidgetState createState() => ProbeWidgetState();
 }
@@ -36,7 +37,7 @@ class ProbeWidgetState extends State<ProbeWidget> {
 }
 
 class BadWidget extends StatelessWidget {
-  const BadWidget(this.parentState);
+  const BadWidget(this.parentState, { Key key }) : super(key: key);
 
   final BadWidgetParentState parentState;
 
@@ -48,6 +49,7 @@ class BadWidget extends StatelessWidget {
 }
 
 class BadWidgetParent extends StatefulWidget {
+  const BadWidgetParent({ Key key }) : super(key: key);
   @override
   BadWidgetParentState createState() => BadWidgetParentState();
 }
@@ -67,6 +69,7 @@ class BadWidgetParentState extends State<BadWidgetParent> {
 }
 
 class BadDisposeWidget extends StatefulWidget {
+  const BadDisposeWidget({ Key key }) : super(key: key);
   @override
   BadDisposeWidgetState createState() => BadDisposeWidgetState();
 }
@@ -133,14 +136,14 @@ void main() {
   testWidgets('Legal times for setState', (WidgetTester tester) async {
     final GlobalKey flipKey = GlobalKey();
     expect(ProbeWidgetState.buildCount, equals(0));
-    await tester.pumpWidget(ProbeWidget());
+    await tester.pumpWidget(const ProbeWidget(key: Key('a')));
     expect(ProbeWidgetState.buildCount, equals(1));
-    await tester.pumpWidget(ProbeWidget());
+    await tester.pumpWidget(const ProbeWidget(key: Key('b')));
     expect(ProbeWidgetState.buildCount, equals(2));
     await tester.pumpWidget(FlipWidget(
       key: flipKey,
       left: Container(),
-      right: ProbeWidget(),
+      right: const ProbeWidget(key: Key('c')),
     ));
     expect(ProbeWidgetState.buildCount, equals(2));
     final FlipWidgetState flipState1 = flipKey.currentState as FlipWidgetState;
@@ -156,13 +159,13 @@ void main() {
   });
 
   testWidgets('Setting parent state during build is forbidden', (WidgetTester tester) async {
-    await tester.pumpWidget(BadWidgetParent());
+    await tester.pumpWidget(const BadWidgetParent());
     expect(tester.takeException(), isFlutterError);
     await tester.pumpWidget(Container());
   });
 
   testWidgets('Setting state during dispose is forbidden', (WidgetTester tester) async {
-    await tester.pumpWidget(BadDisposeWidget());
+    await tester.pumpWidget(const BadDisposeWidget());
     expect(tester.takeException(), isNull);
     await tester.pumpWidget(Container());
     expect(tester.takeException(), isNotNull);

packages/flutter/test/widgets/dismissible_test.dart

@@ -208,7 +208,7 @@ Future<void> rollbackElement(WidgetTester tester, Finder finder, { @required Axi
 }
 
 class Test1215DismissibleWidget extends StatelessWidget {
-  const Test1215DismissibleWidget(this.text);
+  const Test1215DismissibleWidget(this.text, { Key key }) : super(key: key);
 
   final String text;
 

packages/flutter/test/widgets/dispose_ancestor_lookup_test.dart

@@ -8,7 +8,7 @@ import 'package:flutter/widgets.dart';
 typedef TestCallback = void Function(BuildContext context);
 
 class TestWidget extends StatefulWidget {
-  const TestWidget(this.callback);
+  const TestWidget(this.callback, { Key key }) : super(key: key);
 
   final TestCallback callback;