Prefer const constructors (#11853)

* upgrade to linter-0.1.35

* re-enable lint prefer_const_constructors

* address review comments

analysis_options.yaml

@@ -71,6 +71,7 @@ linter:
     # === style rules ===
     - always_declare_return_types
     - always_put_control_body_on_new_line
+    # - always_put_required_named_parameters_first # we prefer having parameters in the same order as fields https://github.com/flutter/flutter/issues/10219
     - always_require_non_null_named_parameters
     - always_specify_types
     - annotate_overrides
@@ -108,9 +109,11 @@ linter:
     - package_prefixed_library_names
     # - parameter_assignments # we do this commonly
     - prefer_adjacent_string_concatenation
+    # - prefer_asserts_in_initializer_lists # not yet tested
     - prefer_collection_literals
     # - prefer_conditional_assignment # not yet tested
-    # - prefer_const_constructors # https://github.com/dart-lang/linter/issues/752
+    - prefer_const_constructors
+    # - prefer_const_constructors_in_immutables # not yet tested
     # - prefer_constructors_over_static_methods # not yet tested
     - prefer_contains
     # - prefer_expression_function_bodies # conflicts with https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo#consider-using--for-short-functions-and-methods
@@ -122,6 +125,7 @@ linter:
     # - prefer_interpolation_to_compose_strings # not yet tested
     - prefer_is_empty
     - prefer_is_not_empty
+    # - prefer_single_quote_strings # not yet tested
     # - public_member_api_docs # this is the only difference from analysis_options_repo.yaml
     # - recursive_getters # https://github.com/dart-lang/linter/issues/452
     - slash_for_doc_comments

analysis_options_repo.yaml

@@ -65,6 +65,7 @@ linter:
     # === style rules ===
     - always_declare_return_types
     - always_put_control_body_on_new_line
+    # - always_put_required_named_parameters_first # we prefer having parameters in the same order as fields https://github.com/flutter/flutter/issues/10219
     - always_require_non_null_named_parameters
     - always_specify_types
     - annotate_overrides
@@ -102,9 +103,11 @@ linter:
     - package_prefixed_library_names
     # - parameter_assignments # we do this commonly
     - prefer_adjacent_string_concatenation
+    # - prefer_asserts_in_initializer_lists # not yet tested
     - prefer_collection_literals
     # - prefer_conditional_assignment # not yet tested
-    # - prefer_const_constructors # https://github.com/dart-lang/linter/issues/752
+    - prefer_const_constructors
+    # - prefer_const_constructors_in_immutables # not yet tested
     # - prefer_constructors_over_static_methods # not yet tested
     - prefer_contains
     # - prefer_expression_function_bodies # conflicts with https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo#consider-using--for-short-functions-and-methods
@@ -116,6 +119,7 @@ linter:
     # - prefer_interpolation_to_compose_strings # not yet tested
     - prefer_is_empty
     - prefer_is_not_empty
+    # - prefer_single_quote_strings # not yet tested
     - public_member_api_docs # this is the only difference from analysis_options_repo.yaml
     # - recursive_getters # https://github.com/dart-lang/linter/issues/452
     - slash_for_doc_comments

dev/devicelab/bin/tasks/commands_test.dart

@@ -98,7 +98,7 @@ void main() {
       if (result != 0)
         throw 'Received unexpected exit code $result from run process.';
       print('test: validating that the app has in fact closed...');
-      await client.done.timeout(new Duration(seconds: 5));
+      await client.done.timeout(const Duration(seconds: 5));
     });
     return new TaskResult.success(null);
   });

dev/integration_tests/flavors/lib/main.dart

@@ -18,7 +18,7 @@ class _FlavorState extends State<Flavor> {
   @override
   void initState() {
     super.initState();
-    new MethodChannel('flavor').invokeMethod('getFlavor').then((String flavor) {
+    const MethodChannel('flavor').invokeMethod('getFlavor').then((String flavor) {
       setState(() {
         _flavor = flavor;
       });
@@ -28,7 +28,7 @@ class _FlavorState extends State<Flavor> {
   @override
   Widget build(BuildContext context) {
     return _flavor == null
-      ? new Text('Awaiting flavor...')
+      ? const Text('Awaiting flavor...')
       : new Text(_flavor, key: const ValueKey<String>('flavor'));
   }
 }

dev/integration_tests/platform_interaction/lib/src/system_navigation.dart

@@ -16,7 +16,7 @@ Future<TestStepResult> systemNavigatorPop() {
 
   channel.setMessageHandler((String message) async {
     completer.complete(
-        new TestStepResult('System navigation pop', '', TestStatus.ok));
+        const TestStepResult('System navigation pop', '', TestStatus.ok));
     return '';
   });
   SystemNavigator.pop();

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

@@ -318,7 +318,7 @@ class _RenderInspectorOverlay extends RenderBox {
 
   @override
   void performResize() {
-    size = constraints.constrain(new Size(double.INFINITY, double.INFINITY));
+    size = constraints.constrain(const Size(double.INFINITY, double.INFINITY));
   }
 
   @override

packages/flutter/test/cupertino/slider_test.dart

@@ -181,9 +181,9 @@ void main() {
     ));
 
     // Disable slider
-    await tester.pumpWidget(new Directionality(
+    await tester.pumpWidget(const Directionality(
       textDirection: TextDirection.ltr,
-      child: new CupertinoSlider(
+      child: const CupertinoSlider(
         value: 0.5,
         onChanged: null,
       ),

packages/flutter/test/gestures/drag_test.dart

@@ -253,7 +253,7 @@ void main() {
     tester.route(pointer.move(const Offset(30.0, 25.0), timeStamp: const Duration(milliseconds: 30)));
     tester.route(pointer.move(const Offset(40.0, 25.0), timeStamp: const Duration(milliseconds: 40)));
     tester.route(pointer.move(const Offset(50.0, 25.0), timeStamp: const Duration(milliseconds: 50)));
-    tester.route(new PointerMoveEvent(
+    tester.route(const PointerMoveEvent(
       pointer: 1,
       // Simulate a small synthesized wobble which would have slowed down the
       // horizontal velocity from 1 px/ms and introduced a slight vertical velocity.

packages/flutter/test/material/button_bar_test.dart

@@ -8,7 +8,7 @@ import 'package:flutter_test/flutter_test.dart';
 void main() {
   testWidgets('ButtonBar default control smoketest', (WidgetTester tester) async {
     await tester.pumpWidget(
-      new Directionality(
+      const Directionality(
         textDirection: TextDirection.ltr,
         child: const ButtonBar(),
       ),

packages/flutter/test/material/chip_test.dart

@@ -178,13 +178,13 @@ void main() {
   });
 
   testWidgets('Chip in row works ok', (WidgetTester tester) async {
-    final TextStyle style = new TextStyle(fontFamily: 'Ahem', fontSize: 10.0);
+    final TextStyle style = const TextStyle(fontFamily: 'Ahem', fontSize: 10.0);
     await tester.pumpWidget(
       new MaterialApp(
         home: new Material(
           child: new Row(
             children: <Widget>[
-              new Chip(label: new Text('Test'), labelStyle: style),
+              new Chip(label: const Text('Test'), labelStyle: style),
             ],
           ),
         ),
@@ -197,7 +197,7 @@ void main() {
         home: new Material(
           child: new Row(
             children: <Widget>[
-              new Flexible(child: new Chip(label: new Text('Test'), labelStyle: style)),
+              new Flexible(child: new Chip(label: const Text('Test'), labelStyle: style)),
             ],
           ),
         ),
@@ -210,7 +210,7 @@ void main() {
         home: new Material(
           child: new Row(
             children: <Widget>[
-              new Expanded(child: new Chip(label: new Text('Test'), labelStyle: style)),
+              new Expanded(child: new Chip(label: const Text('Test'), labelStyle: style)),
             ],
           ),
         ),
@@ -228,7 +228,7 @@ void main() {
               child: new Center(
                 child: new Chip(
                   onDeleted: () { },
-                  label: new Text('ABC'),
+                  label: const Text('ABC'),
                 ),
               ),
             );

packages/flutter/test/material/page_test.dart

@@ -276,11 +276,11 @@ void main() {
     final Map<String, WidgetBuilder> routes = <String, WidgetBuilder>{
       '/': (BuildContext context) => new Material(
         child: new FlatButton(
-          child: new Text('PUSH'),
+          child: const Text('PUSH'),
           onPressed: () { Navigator.of(context).pushNamed('/b'); },
         ),
       ),
-      '/b': (BuildContext context) => new Container(child: new Text('HELLO')),
+      '/b': (BuildContext context) => new Container(child: const Text('HELLO')),
     };
     await tester.pumpWidget(
       new MaterialApp(

packages/flutter/test/material/popup_menu_test.dart

@@ -110,7 +110,7 @@ void main() {
             icon: const Icon(Icons.view_carousel),
             itemBuilder: simplePopupMenuItemBuilder,
         );
-      }, throwsA(new isInstanceOf<AssertionError>()));
+      }, throwsA(const isInstanceOf<AssertionError>()));
     });
 
     testWidgets('PopupMenuButton creates IconButton when given an icon', (WidgetTester tester) async {

packages/flutter/test/material/scaffold_test.dart

@@ -148,11 +148,11 @@ void main() {
     Widget build(TextDirection textDirection) {
       return new Directionality(
         textDirection: textDirection,
-        child: new MediaQuery(
+        child: const MediaQuery(
           data: const MediaQueryData(
             padding: const EdgeInsets.only(bottom: 200.0),
           ),
-          child: new Scaffold(
+          child: const Scaffold(
             floatingActionButton: const FloatingActionButton(
               onPressed: null,
               child: const Text('1'),

packages/flutter/test/material/slider_test.dart

@@ -472,10 +472,10 @@ void main() {
     ));
 
     // Disable slider
-    await tester.pumpWidget(new Directionality(
+    await tester.pumpWidget(const Directionality(
       textDirection: TextDirection.ltr,
-      child: new Material(
-        child: new Slider(
+      child: const Material(
+        child: const Slider(
           value: 0.5,
           onChanged: null,
         ),

packages/flutter/test/rendering/flex_test.dart

@@ -358,7 +358,7 @@ void main() {
     expect(exceptions, isEmpty);
     layout(parent);
     expect(exceptions, isNotEmpty);
-    expect(exceptions.first, new isInstanceOf<FlutterError>());
+    expect(exceptions.first, const isInstanceOf<FlutterError>());
   });
 
   test('MainAxisSize.min inside unconstrained', () {
@@ -388,7 +388,7 @@ void main() {
     expect(exceptions, isEmpty);
     layout(parent);
     expect(exceptions, isNotEmpty);
-    expect(exceptions.first, new isInstanceOf<FlutterError>());
+    expect(exceptions.first, const isInstanceOf<FlutterError>());
   });
 
   test('Flex RTL', () {

packages/flutter/test/services/image_provider_test.dart

@@ -8,7 +8,8 @@ import 'package:flutter_test/flutter_test.dart';
 void main() {
   test('NetworkImage non-null url test', () {
     expect(() {
-      new NetworkImage(null); // ignore: prefer_const_constructors
+      final String url = null; // we don't want this instance to be const because otherwise it would throw at compile time.
+      new NetworkImage(url);
     }, throwsAssertionError);
   });
 }

packages/flutter/test/widgets/directionality_test.dart

@@ -11,7 +11,7 @@ void main() {
     final Widget inner = new Builder(
       builder: (BuildContext context) {
         log.add(Directionality.of(context));
-        return new Placeholder();
+        return const Placeholder();
       }
     );
     await tester.pumpWidget(
@@ -57,13 +57,16 @@ void main() {
       builder: (BuildContext context) {
         expect(Directionality.of(context), isNull);
         good = true;
-        return new Placeholder();
+        return const Placeholder();
       },
     ));
     expect(good, isTrue);
   });
 
   testWidgets('Directionality can\'t be null', (WidgetTester tester) async {
-    expect(() { new Directionality(textDirection: null, child: new Placeholder()); }, throwsAssertionError);
+    expect(() {
+      final TextDirection textDirection = null; // we don't want this instance to be const because otherwise it would throw at compile time.
+      new Directionality(textDirection: textDirection, child: const Placeholder());
+    }, throwsAssertionError);
   });
 }

packages/flutter/test/widgets/localizations_test.dart

@@ -130,7 +130,7 @@ void main() {
       buildFrame(
         buildContent: (BuildContext context) {
           pageContext = context;
-          return new Text('Hello World');
+          return const Text('Hello World');
         }
       )
     );
@@ -153,7 +153,7 @@ void main() {
         locale: locale,
         buildContent: (BuildContext context) {
           pageContext = context;
-          return new Text('Hello World');
+          return const Text('Hello World');
         },
       )
     );
@@ -295,7 +295,7 @@ void main() {
                 locale: const Locale('en', 'GB'),
                 delegates: <LocalizationsDelegate<dynamic>>[
                   new SyncTestLocalizationsDelegate(),
-                  new DefaultWidgetsLocalizationsDelegate(),
+                  const DefaultWidgetsLocalizationsDelegate(),
                 ],
                 // Create a new context within the en_GB Localization
                 child: new Builder(

packages/flutter/test/widgets/rtl_test.dart

@@ -7,9 +7,9 @@ import 'package:flutter/widgets.dart';
 
 void main() {
   testWidgets('Padding RTL', (WidgetTester tester) async {
-    final Widget child = new Padding(
-      padding: new EdgeInsetsDirectional.only(start: 10.0),
-      child: new Placeholder(),
+    final Widget child = const Padding(
+      padding: const EdgeInsetsDirectional.only(start: 10.0),
+      child: const Placeholder(),
     );
     await tester.pumpWidget(new Directionality(
       textDirection: TextDirection.ltr,
@@ -25,9 +25,9 @@ void main() {
 
   testWidgets('Container padding/margin RTL', (WidgetTester tester) async {
     final Widget child = new Container(
-      padding: new EdgeInsetsDirectional.only(start: 6.0),
-      margin: new EdgeInsetsDirectional.only(end: 20.0, start: 4.0),
-      child: new Placeholder(),
+      padding: const EdgeInsetsDirectional.only(start: 6.0),
+      margin: const EdgeInsetsDirectional.only(end: 20.0, start: 4.0),
+      child: const Placeholder(),
     );
     await tester.pumpWidget(new Directionality(
       textDirection: TextDirection.ltr,
@@ -45,9 +45,9 @@ void main() {
 
   testWidgets('Container padding/margin mixed RTL/absolute', (WidgetTester tester) async {
     final Widget child = new Container(
-      padding: new EdgeInsets.only(left: 6.0),
-      margin: new EdgeInsetsDirectional.only(end: 20.0, start: 4.0),
-      child: new Placeholder(),
+      padding: const EdgeInsets.only(left: 6.0),
+      margin: const EdgeInsetsDirectional.only(end: 20.0, start: 4.0),
+      child: const Placeholder(),
     );
     await tester.pumpWidget(new Directionality(
       textDirection: TextDirection.ltr,
@@ -64,7 +64,7 @@ void main() {
   });
 
   testWidgets('EdgeInsetsDirectional without Directionality', (WidgetTester tester) async {
-    await tester.pumpWidget(new Padding(padding: new EdgeInsetsDirectional.only()));
+    await tester.pumpWidget(const Padding(padding: const EdgeInsetsDirectional.only()));
     expect(tester.takeException(), isAssertionError);
   });
 }

packages/flutter/test/widgets/semantics_10_test.dart

@@ -51,10 +51,10 @@ Widget buildTestWidgets({bool excludeSemantics, String label, bool isSemanticsBo
         isSemanticBoundary: isSemanticsBoundary,
         child: new Column(
           children: <Widget>[
-            new Semantics(
+            const Semantics(
               label: 'child1',
             ),
-            new Semantics(
+            const Semantics(
               label: 'child2',
             ),
           ],

packages/flutter/test/widgets/semantics_11_test.dart

@@ -13,7 +13,7 @@ void main() {
   testWidgets('markNeedsSemanticsUpdate allways resets node', (WidgetTester tester) async {
     final SemanticsTester semantics = new SemanticsTester(tester);
 
-    await tester.pumpWidget(new TestWidget());
+    await tester.pumpWidget(const TestWidget());
     final RenderTest renderObj = tester.renderObject(find.byType(TestWidget));
     expect(renderObj.labelWasReset, hasLength(1));
     expect(renderObj.labelWasReset.last, true);

packages/flutter/test/widgets/sliver_semantics_test.dart

@@ -29,7 +29,7 @@ void main() {
         child: new CustomScrollView(
           controller: scrollController,
           slivers: <Widget>[
-            new SliverAppBar(
+            const SliverAppBar(
               pinned: true,
               expandedHeight: appBarExpandedHeight,
               title: const Text('Semantics Test with Slivers'),
@@ -295,10 +295,10 @@ void main() {
     final ScrollController controller = new ScrollController(initialScrollOffset: 280.0);
     await tester.pumpWidget(
       new MediaQuery(
-        data: new MediaQueryData(),
+        data: const MediaQueryData(),
         child: new CustomScrollView(
           slivers: <Widget>[
-            new SliverAppBar(
+            const SliverAppBar(
               pinned: true,
               expandedHeight: 100.0,
             ),
@@ -377,11 +377,11 @@ void main() {
     });
     await tester.pumpWidget(
       new MediaQuery(
-        data: new MediaQueryData(),
+        data: const MediaQueryData(),
         child: new CustomScrollView(
           controller: controller,
           slivers: <Widget>[
-            new SliverAppBar(
+            const SliverAppBar(
               pinned: true,
               expandedHeight: 100.0,
             ),
@@ -454,11 +454,11 @@ void main() {
     final ScrollController controller = new ScrollController(initialScrollOffset: 280.0);
     await tester.pumpWidget(
       new MediaQuery(
-        data: new MediaQueryData(),
+        data: const MediaQueryData(),
         child: new CustomScrollView(
           reverse: true,  // This is the important setting for this test.
           slivers: <Widget>[
-            new SliverAppBar(
+            const SliverAppBar(
               pinned: true,
               expandedHeight: 100.0,
             ),
@@ -538,12 +538,12 @@ void main() {
     });
     await tester.pumpWidget(
       new MediaQuery(
-        data: new MediaQueryData(),
+        data: const MediaQueryData(),
         child: new CustomScrollView(
           reverse: true,  // This is the important setting for this test.
           controller: controller,
           slivers: <Widget>[
-            new SliverAppBar(
+            const SliverAppBar(
               pinned: true,
               expandedHeight: 100.0,
             ),
@@ -624,7 +624,7 @@ void main() {
     });
     await tester.pumpWidget(
       new MediaQuery(
-        data: new MediaQueryData(),
+        data: const MediaQueryData(),
         child: new Scrollable(
           controller: controller,
           viewportBuilder: (BuildContext context, ViewportOffset offset) {
@@ -635,7 +635,7 @@ void main() {
                 new SliverList(
                   delegate: new SliverChildListDelegate(backwardChildren),
                 ),
-                new SliverAppBar(
+                const SliverAppBar(
                   pinned: true,
                   expandedHeight: 100.0,
                   flexibleSpace: const FlexibleSpaceBar(

packages/flutter_tools/test/ios/devices_test.dart

@@ -90,7 +90,7 @@ iPhone SE (11.0) [667E8DCD-5DCD-4C80-93A9-60D1D995206F] (Simulator)
   Runner(libsystem_asl.dylib)[297] <Notice>: libMobileGestalt MobileGestalt.c:550: no access to InverseDeviceID (see <rdar://problem/11744455>)
   Runner(libsystem_asl.dylib)[297] <Notice>: I is for ichigo
   '''.codeUnits]));
-        when(mockProcess.stderr).thenReturn(new Stream<List<int>>.empty());
+        when(mockProcess.stderr).thenReturn(const Stream<List<int>>.empty());
         // Delay return of exitCode until after stdout stream data, since it terminates the logger.
         when(mockProcess.exitCode).thenReturn(new Future<int>.delayed(Duration.ZERO, () => 0));
         return new Future<Process>.value(mockProcess);