work around const lints (#14416)

* work around const lints

* update nonconst doc

dev/tools/lib/archive_publisher.dart

@@ -143,7 +143,7 @@ class ArchivePublisher {
     jsonData['releases'][revision] = metadata;
     final Directory localTempDir = tempDir ?? Directory.systemTemp.createTempSync('flutter_');
     final File tempFile = new File(path.join(localTempDir.absolute.path, 'releases.json'));
-    final JsonEncoder encoder = const JsonEncoder.withIndent('  ');
+    const JsonEncoder encoder = const JsonEncoder.withIndent('  ');
     tempFile.writeAsStringSync(encoder.convert(jsonData));
     _cloudCopy(tempFile.absolute.path, metadataGsPath);
     if (tempDir == null) {

packages/flutter/test/material/tabs_test.dart

@@ -1503,8 +1503,7 @@ void main() {
   });
 
   test('illegal constructor combinations', () {
-    final Widget $null = null;
+    expect(() => new Tab(icon: nonconst(null)), throwsAssertionError);
-    expect(() => new Tab(icon: $null), throwsAssertionError);
     expect(() => new Tab(icon: new Container(), text: 'foo', child: new Container()), throwsAssertionError);
     expect(() => new Tab(text: 'foo', child: new Container()), throwsAssertionError);
   });

packages/flutter/test/painting/alignment_test.dart

@@ -92,8 +92,7 @@ void main() {
     expect(const AlignmentDirectional(0.0, 0.0).resolve(TextDirection.rtl), const Alignment(0.0, 0.0));
     expect(const AlignmentDirectional(1.0, 1.0).resolve(TextDirection.ltr), const Alignment(1.0, 1.0));
     expect(const AlignmentDirectional(1.0, 1.0).resolve(TextDirection.rtl), const Alignment(-1.0, 1.0));
-    final double $1 = 1.0; // we want these instances to be separate instances so that we're not just checking with a single object
+    expect(new AlignmentDirectional(nonconst(1.0), 2.0), new AlignmentDirectional(nonconst(1.0), 2.0));
-    expect(new AlignmentDirectional($1, 2.0), new AlignmentDirectional($1, 2.0));
     expect(const AlignmentDirectional(1.0, 2.0), isNot(const AlignmentDirectional(2.0, 1.0)));
     expect(const AlignmentDirectional(-1.0, 0.0).resolve(TextDirection.ltr),
            const AlignmentDirectional(1.0, 0.0).resolve(TextDirection.rtl));

packages/flutter/test/painting/border_rtl_test.dart

@@ -317,11 +317,10 @@ void main() {
   });
 
   test('BorderDirectional constructor', () {
-    final Null $null = null;
+    expect(() => new BorderDirectional(top: nonconst(null)), throwsAssertionError);
-    expect(() => new BorderDirectional(top: $null), throwsAssertionError);
+    expect(() => new BorderDirectional(start: nonconst(null)), throwsAssertionError);
-    expect(() => new BorderDirectional(start: $null), throwsAssertionError);
+    expect(() => new BorderDirectional(end: nonconst(null)), throwsAssertionError);
-    expect(() => new BorderDirectional(end: $null), throwsAssertionError);
+    expect(() => new BorderDirectional(bottom: nonconst(null)), throwsAssertionError);
-    expect(() => new BorderDirectional(bottom: $null), throwsAssertionError);
   });
 
   test('BorderDirectional.merge', () {
@@ -622,7 +621,7 @@ void main() {
   });
 
   test('BorderDirectional hashCode', () {
-    final BorderSide side = const BorderSide(width: 2.0);
+    final BorderSide side = new BorderSide(width: nonconst(2.0));
     expect(new BorderDirectional(top: side).hashCode, new BorderDirectional(top: side).hashCode);
     expect(new BorderDirectional(top: side).hashCode, isNot(new BorderDirectional(bottom: side).hashCode));
   });

packages/flutter/test/painting/border_side_test.dart

@@ -15,13 +15,10 @@ void main() {
         style: BorderStyle.solid,
       ),
     );
-    // so that we can use `new` below, we use these:
+    expect(() => new BorderSide(color: nonconst(null)), throwsAssertionError);
-    final Null $null = null;
+    expect(() => new BorderSide(width: nonconst(null)), throwsAssertionError);
-    final double $minus1 = -1.0;
+    expect(() => new BorderSide(style: nonconst(null)), throwsAssertionError);
-    expect(() => new BorderSide(color: $null), throwsAssertionError);
+    expect(() => new BorderSide(width: nonconst(-1.0)), throwsAssertionError);
-    expect(() => new BorderSide(width: $null), throwsAssertionError);
-    expect(() => new BorderSide(style: $null), throwsAssertionError);
-    expect(() => new BorderSide(width: $minus1), throwsAssertionError);
     expect(
       const BorderSide(width: -0.0),
       const BorderSide(

packages/flutter/test/painting/border_test.dart

@@ -7,11 +7,10 @@ import 'package:flutter_test/flutter_test.dart';
 
 void main() {
   test('Border constructor', () {
-    final Null $null = null;
+    expect(() => new Border(left: nonconst(null)), throwsAssertionError);
-    expect(() => new Border(left: $null), throwsAssertionError);
+    expect(() => new Border(top: nonconst(null)), throwsAssertionError);
-    expect(() => new Border(top: $null), throwsAssertionError);
+    expect(() => new Border(right: nonconst(null)), throwsAssertionError);
-    expect(() => new Border(right: $null), throwsAssertionError);
+    expect(() => new Border(bottom: nonconst(null)), throwsAssertionError);
-    expect(() => new Border(bottom: $null), throwsAssertionError);
   });
 
   test('Border.merge', () {

packages/flutter/test/painting/colors_test.dart

@@ -40,7 +40,7 @@ void main() {
   });
 
   test('ColorSwatch test', () {
-    final int color = 0xFF027223;
+    final int color = nonconst(0xFF027223);
     final ColorSwatch<String> greens1 = new ColorSwatch<String>(
       color, const <String, Color>{
         '2259 C': const Color(0xFF027223),

packages/flutter/test/painting/edge_insets_test.dart

@@ -73,7 +73,7 @@ void main() {
   });
 
   test('EdgeInsets equality', () {
-    final double $5 = 5.0; // we want these instances to be separate instances so that we're not just checking with a single object
+    final double $5 = nonconst(5.0);
     expect(new EdgeInsetsDirectional.only(top: $5, bottom: 7.0), new EdgeInsetsDirectional.only(top: $5, bottom: 7.0));
     expect(new EdgeInsets.only(top: $5, bottom: 7.0), new EdgeInsetsDirectional.only(top: $5, bottom: 7.0));
     expect(new EdgeInsetsDirectional.only(top: $5, bottom: 7.0), new EdgeInsets.only(top: $5, bottom: 7.0));

packages/flutter/test/painting/image_provider_test.dart

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

packages/flutter/test/painting/text_span_test.dart

@@ -3,19 +3,17 @@
 // found in the LICENSE file.
 
 import 'package:flutter/painting.dart';
-
+import 'package:flutter_test/flutter_test.dart' show nonconst;
 import 'package:test/test.dart';
 
 void main() {
   test('TextSpan equals', () {
-    final String text = 'a'; // we want these instances to be separate instances so that we're not just checking with a single object
+    final TextSpan a1 = new TextSpan(text: nonconst('a'));
-    final TextSpan a1 = new TextSpan(text: text);
+    final TextSpan a2 = new TextSpan(text: nonconst('a'));
-    final TextSpan a2 = new TextSpan(text: text);
     final TextSpan b1 = new TextSpan(children: <TextSpan>[ a1 ]);
     final TextSpan b2 = new TextSpan(children: <TextSpan>[ a2 ]);
-    final String nullText = null; // we want these instances to be separate instances so that we're not just checking with a single object
+    final TextSpan c1 = new TextSpan(text: nonconst(null));
-    final TextSpan c1 = new TextSpan(text: nullText);
+    final TextSpan c2 = new TextSpan(text: nonconst(null));
-    final TextSpan c2 = new TextSpan(text: nullText);
 
     expect(a1 == a2, isTrue);
     expect(b1 == b2, isTrue);

packages/flutter/test/widgets/directionality_test.dart

@@ -65,8 +65,7 @@ void main() {
 
   testWidgets('Directionality can\'t be null', (WidgetTester tester) async {
     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: nonconst(null), child: const Placeholder());
-      new Directionality(textDirection: textDirection, child: const Placeholder());
     }, throwsAssertionError);
   });
 }

packages/flutter/test/widgets/key_test.dart

@@ -19,21 +19,18 @@ class NotEquals {
 
 void main() {
   testWidgets('Keys', (WidgetTester tester) async {
-    final int int3 = 3; // we want these instances to be separate instances so that we're not just checking with a single object
+    expect(new ValueKey<int>(nonconst(3)) == new ValueKey<int>(nonconst(3)), isTrue);
-    expect(new ValueKey<int>(int3) == new ValueKey<int>(int3), isTrue);
+    expect(new ValueKey<num>(nonconst(3)) == new ValueKey<int>(nonconst(3)), isFalse);
-    expect(new ValueKey<num>(int3) == new ValueKey<int>(int3), isFalse);
+    expect(new ValueKey<int>(nonconst(3)) == new ValueKey<int>(nonconst(2)), isFalse);
-    final int int2 = 2; // we want these instances to be separate instances so that we're not just checking with a single object
-    expect(new ValueKey<int>(int3) == new ValueKey<int>(int2), isFalse);
     expect(const ValueKey<double>(double.NAN) == const ValueKey<double>(double.NAN), isFalse);
 
-    final String empty = ''; // we want these instances to be separate instances so that we're not just checking with a single object
+    expect(new Key(nonconst('')) == new ValueKey<String>(nonconst('')), isTrue);
-    expect(new Key(empty) == new ValueKey<String>(empty), isTrue);
+    expect(new ValueKey<String>(nonconst('')) == new ValueKey<String>(nonconst('')), isTrue);
-    expect(new ValueKey<String>(empty) == new ValueKey<String>(empty), isTrue);
+    expect(new TestValueKey<String>(nonconst('')) == new ValueKey<String>(nonconst('')), isFalse);
-    expect(new TestValueKey<String>(empty) == new ValueKey<String>(empty), isFalse);
+    expect(new TestValueKey<String>(nonconst('')) == new TestValueKey<String>(nonconst('')), isTrue);
-    expect(new TestValueKey<String>(empty) == new TestValueKey<String>(empty), isTrue);
 
-    expect(new ValueKey<String>(empty) == new ValueKey<dynamic>(empty), isFalse);
+    expect(new ValueKey<String>(nonconst('')) == new ValueKey<dynamic>(nonconst('')), isFalse);
-    expect(new TestValueKey<String>(empty) == new TestValueKey<dynamic>(empty), isFalse);
+    expect(new TestValueKey<String>(nonconst('')) == new TestValueKey<dynamic>(nonconst('')), isFalse);
 
     expect(new UniqueKey() == new UniqueKey(), isFalse);
     final LocalKey k = new UniqueKey();
@@ -44,11 +41,11 @@ void main() {
     expect(new ValueKey<LocalKey>(k) == new ValueKey<UniqueKey>(k), isFalse);
     expect(new ObjectKey(k) == new ObjectKey(k), isTrue);
 
-    final NotEquals constNotEquals = const NotEquals(); // we want these instances to be separate instances so that we're not just checking with a single object
+    final NotEquals constNotEquals = nonconst(const NotEquals());
     expect(new ValueKey<NotEquals>(constNotEquals) == new ValueKey<NotEquals>(constNotEquals), isFalse);
     expect(new ObjectKey(constNotEquals) == new ObjectKey(constNotEquals), isTrue);
 
-    final Object constObject = const Object(); // we want these instances to be separate instances so that we're not just checking with a single object
+    final Object constObject = nonconst(const Object());
     expect(new ObjectKey(constObject) == new ObjectKey(constObject), isTrue);
     expect(new ObjectKey(new Object()) == new ObjectKey(new Object()), isFalse);
 

packages/flutter/test/widgets/render_object_widget_test.dart

@@ -6,10 +6,9 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
-final Border nullBorder = null; // we want these instances to be separate instances so that we're not just checking with a single object
+final BoxDecoration kBoxDecorationA = new BoxDecoration(border: nonconst(null));
-final BoxDecoration kBoxDecorationA = new BoxDecoration(border: nullBorder);
+final BoxDecoration kBoxDecorationB = new BoxDecoration(border: nonconst(null));
-final BoxDecoration kBoxDecorationB = new BoxDecoration(border: nullBorder);
+final BoxDecoration kBoxDecorationC = new BoxDecoration(border: nonconst(null));
-final BoxDecoration kBoxDecorationC = new BoxDecoration(border: nullBorder);
 
 class TestWidget extends StatelessWidget {
   const TestWidget({ this.child });

packages/flutter_test/lib/flutter_test.dart

@@ -12,6 +12,7 @@ export 'src/binding.dart';
 export 'src/controller.dart';
 export 'src/finders.dart';
 export 'src/matchers.dart';
+export 'src/nonconst.dart';
 export 'src/stack_manipulation.dart';
 export 'src/test_async_utils.dart';
 export 'src/test_pointer.dart';

packages/flutter_test/lib/src/nonconst.dart

@@ -0,0 +1,23 @@
+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/// This function can be used to call a const constructor in such a way as to
+/// create a new instance rather than creating the common const instance.
+///
+/// ```dart
+/// class A {
+///   const A(this.i);
+///   int i;
+/// }
+///
+/// main () {
+///   // prevent prefer_const_constructors lint
+///   new A(nonconst(null));
+///
+///   // prevent prefer_const_declarations lint
+///   final int $null = nonconst(null);
+///   final A a = nonconst(const A(null));
+/// }
+/// ```
+T nonconst<T>(T t) => t;