Reland "Implement the type Never"

This reverts commit 78e50a5f9b.

Change-Id: I2ec4cdcfda4a6d199308a3b25a2ed0792e9d9a26
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/101621
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

pkg/analysis_server/test/protocol_server_test.dart

@@ -183,6 +183,7 @@ class EnumTest {
       engine.ElementKind.GENERIC_FUNCTION_TYPE: ElementKind.FUNCTION_TYPE_ALIAS,
       engine.ElementKind.IMPORT: ElementKind.UNKNOWN,
       engine.ElementKind.NAME: ElementKind.UNKNOWN,
+      engine.ElementKind.NEVER: ElementKind.UNKNOWN,
       engine.ElementKind.UNIVERSE: ElementKind.UNKNOWN
     });
   }

pkg/analyzer/lib/dart/element/element.dart

@@ -843,25 +843,27 @@ class ElementKind implements Comparable<ElementKind> {
 
   static const ElementKind NAME = const ElementKind('NAME', 15, "<name>");
 
+  static const ElementKind NEVER = const ElementKind('NEVER', 16, "<never>");
+
   static const ElementKind PARAMETER =
-      const ElementKind('PARAMETER', 16, "parameter");
+      const ElementKind('PARAMETER', 17, "parameter");
 
   static const ElementKind PREFIX =
-      const ElementKind('PREFIX', 17, "import prefix");
+      const ElementKind('PREFIX', 18, "import prefix");
 
-  static const ElementKind SETTER = const ElementKind('SETTER', 18, "setter");
+  static const ElementKind SETTER = const ElementKind('SETTER', 19, "setter");
 
   static const ElementKind TOP_LEVEL_VARIABLE =
-      const ElementKind('TOP_LEVEL_VARIABLE', 19, "top level variable");
+      const ElementKind('TOP_LEVEL_VARIABLE', 20, "top level variable");
 
   static const ElementKind FUNCTION_TYPE_ALIAS =
-      const ElementKind('FUNCTION_TYPE_ALIAS', 20, "function type alias");
+      const ElementKind('FUNCTION_TYPE_ALIAS', 21, "function type alias");
 
   static const ElementKind TYPE_PARAMETER =
-      const ElementKind('TYPE_PARAMETER', 21, "type parameter");
+      const ElementKind('TYPE_PARAMETER', 22, "type parameter");
 
   static const ElementKind UNIVERSE =
-      const ElementKind('UNIVERSE', 22, "<universe>");
+      const ElementKind('UNIVERSE', 23, "<universe>");
 
   static const List<ElementKind> values = const [
     CLASS,
@@ -880,6 +882,7 @@ class ElementKind implements Comparable<ElementKind> {
     LOCAL_VARIABLE,
     METHOD,
     NAME,
+    NEVER,
     PARAMETER,
     PREFIX,
     SETTER,

pkg/analyzer/lib/error/error.dart

@@ -350,6 +350,7 @@ const List<ErrorCode> errorCodeValues = const [
   HintCode.SDK_VERSION_EQ_EQ_OPERATOR_IN_CONST_CONTEXT,
   HintCode.SDK_VERSION_GT_GT_GT_OPERATOR,
   HintCode.SDK_VERSION_IS_EXPRESSION_IN_CONST_CONTEXT,
+  HintCode.SDK_VERSION_NEVER,
   HintCode.SDK_VERSION_SET_LITERAL,
   HintCode.SDK_VERSION_UI_AS_CODE,
   HintCode.STRICT_RAW_TYPE,

pkg/analyzer/lib/src/dart/analysis/dependency/reference_collector.dart

@@ -631,7 +631,10 @@ class ReferenceCollector {
     if (node.isSynthetic) return;
 
     var name = node.name;
-    if (_localScopes.contains(name) || name == 'void' || name == 'dynamic') {
+    if (_localScopes.contains(name) ||
+        name == 'void' ||
+        name == 'dynamic' ||
+        name == 'Never') {
       return;
     }
 

pkg/analyzer/lib/src/dart/analysis/library_context.dart

@@ -289,6 +289,8 @@ class LibraryContext {
     var rootReference = Reference.root();
     rootReference.getChild('dart:core').getChild('dynamic').element =
         DynamicElementImpl.instance;
+    rootReference.getChild('dart:core').getChild('Never').element =
+        NeverElementImpl.instance;
 
     elementFactory = LinkedElementFactory(
       analysisContext,

pkg/analyzer/lib/src/dart/element/element.dart

@@ -7815,6 +7815,30 @@ class MultiplyInheritedPropertyAccessorElementImpl
   }
 }
 
+/// The synthetic element representing the declaration of the type `Never`.
+class NeverElementImpl extends ElementImpl implements TypeDefiningElement {
+  /// Return the unique instance of this class.
+  static NeverElementImpl get instance =>
+      BottomTypeImpl.instance.element as NeverElementImpl;
+
+  @override
+  BottomTypeImpl type;
+
+  /// Initialize a newly created instance of this class. Instances of this class
+  /// should <b>not</b> be created except as part of creating the type
+  /// associated with this element. The single instance of this class should be
+  /// accessed through the method [instance].
+  NeverElementImpl() : super('Never', -1) {
+    setModifier(Modifier.SYNTHETIC, true);
+  }
+
+  @override
+  ElementKind get kind => ElementKind.NEVER;
+
+  @override
+  T accept<T>(ElementVisitor<T> visitor) => null;
+}
+
 /// A [VariableElementImpl], which is not a parameter.
 abstract class NonParameterVariableElementImpl extends VariableElementImpl {
   /// The unlinked representation of the variable in the summary.

pkg/analyzer/lib/src/dart/element/type.dart

@@ -63,7 +63,9 @@ class BottomTypeImpl extends TypeImpl {
   /**
    * Prevent the creation of instances of this class.
    */
-  BottomTypeImpl._() : super(null, "<bottom>");
+  BottomTypeImpl._() : super(new NeverElementImpl(), "Never") {
+    (element as NeverElementImpl).type = this;
+  }
 
   @override
   int get hashCode => 0;

pkg/analyzer/lib/src/dart/error/hint_codes.dart

@@ -627,6 +627,13 @@ class HintCode extends ErrorCode {
           "but this code is required to be able to run on earlier versions.",
       correction: "Try updating the SDK constraints.");
 
+  /**
+   * The type Never is being used in code that is expected to run on versions of
+   * the SDK that did not support it.
+   */
+  static const HintCode SDK_VERSION_NEVER = const HintCode(
+      'SDK_VERSION_NEVER', "The type Never is not yet supported.");
+
   /**
    * The for, if or spread element is being used in code that is expected to run
    * on versions of the SDK that did not support them.

pkg/analyzer/lib/src/dart/resolver/scope.dart

@@ -7,6 +7,7 @@ import 'dart:collection';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/element.dart';
+import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/generated/source.dart';
@@ -526,7 +527,7 @@ class LibraryImportScope extends Scope {
       for (int i = 0; i < _importedNamespaces.length; i++) {
         Element element = lookup(_importedNamespaces[i]);
         if (element != null) {
-          if (element.library.isInSdk) {
+          if (element is NeverElementImpl || element.library.isInSdk) {
             sdkElements.add(element);
           } else {
             nonSdkElements.add(element);
@@ -725,6 +726,7 @@ class NamespaceBuilder {
     // which is not possible for `dynamic`.
     if (library.isDartCore) {
       definedNames['dynamic'] = DynamicElementImpl.instance;
+      definedNames['Never'] = BottomTypeImpl.instance.element;
     }
 
     return new Namespace(definedNames);

pkg/analyzer/lib/src/generated/resolver.dart

@@ -6553,6 +6553,9 @@ class TypeNameResolver {
     if (element == DynamicElementImpl.instance) {
       _setElement(typeName, element);
       type = DynamicTypeImpl.instance;
+    } else if (element is NeverElementImpl) {
+      _setElement(typeName, element);
+      type = element.type;
     } else if (element is FunctionTypeAliasElement) {
       _setElement(typeName, element);
       type = element.type as TypeImpl;
@@ -7231,7 +7234,7 @@ abstract class TypeProvider {
   InterfaceType get mapType;
 
   /// Return the type representing the built-in type 'Never'.
-  InterfaceType get neverType;
+  DartType get neverType;
 
   /// Return a list containing all of the types that cannot be either extended
   /// or implemented.
@@ -7288,11 +7291,11 @@ abstract class TypeProvider {
 abstract class TypeProviderBase implements TypeProvider {
   @override
   List<InterfaceType> get nonSubtypableTypes => <InterfaceType>[
+        boolType,
+        doubleType,
+        intType,
         nullType,
         numType,
-        intType,
-        doubleType,
-        boolType,
         stringType
       ];
 
@@ -7321,18 +7324,12 @@ class TypeProviderImpl extends TypeProviderBase {
   /// The type representing the built-in type 'bool'.
   InterfaceType _boolType;
 
-  /// The type representing the type 'bottom'.
-  DartType _bottomType;
-
   /// The type representing the built-in type 'double'.
   InterfaceType _doubleType;
 
   /// The type representing the built-in type 'Deprecated'.
   InterfaceType _deprecatedType;
 
-  /// The type representing the built-in type 'dynamic'.
-  DartType _dynamicType;
-
   /// The type representing the built-in type 'Function'.
   InterfaceType _functionType;
 
@@ -7375,9 +7372,6 @@ class TypeProviderImpl extends TypeProviderBase {
   /// An shared object representing the value 'null'.
   DartObjectImpl _nullObject;
 
-  /// The type representing the type 'Never'.
-  InterfaceType _neverType;
-
   /// The type representing the type 'Null'.
   InterfaceType _nullType;
 
@@ -7418,7 +7412,7 @@ class TypeProviderImpl extends TypeProviderBase {
   InterfaceType get boolType => _boolType;
 
   @override
-  DartType get bottomType => _bottomType;
+  DartType get bottomType => BottomTypeImpl.instance;
 
   @override
   InterfaceType get deprecatedType => _deprecatedType;
@@ -7427,7 +7421,7 @@ class TypeProviderImpl extends TypeProviderBase {
   InterfaceType get doubleType => _doubleType;
 
   @override
-  DartType get dynamicType => _dynamicType;
+  DartType get dynamicType => DynamicTypeImpl.instance;
 
   @override
   InterfaceType get functionType => _functionType;
@@ -7469,7 +7463,7 @@ class TypeProviderImpl extends TypeProviderBase {
   InterfaceType get mapType => _mapType;
 
   @override
-  InterfaceType get neverType => _neverType;
+  DartType get neverType => BottomTypeImpl.instance;
 
   @override
   DartObjectImpl get nullObject {
@@ -7509,16 +7503,6 @@ class TypeProviderImpl extends TypeProviderBase {
   @override
   InterfaceType get typeType => _typeType;
 
-  InterfaceType _createNever(Namespace namespace) {
-    // TODO(brianwilkerson) Remove this method when the class is defined in the
-    //  SDK.
-    CompilationUnitElement compilationUnit =
-        boolType.element.getAncestor((e) => e is CompilationUnitElement);
-    ClassElementImpl element = ElementFactory.classElement('Never', objectType);
-    element.enclosingElement = compilationUnit;
-    return element.type;
-  }
-
   /// Return the type with the given [typeName] from the given [namespace], or
   /// `null` if there is no class with the given name.
   InterfaceType _getType(Namespace namespace, String typeName) {
@@ -7541,10 +7525,8 @@ class TypeProviderImpl extends TypeProviderBase {
         new NamespaceBuilder().createPublicNamespaceForLibrary(asyncLibrary);
 
     _boolType = _getType(coreNamespace, 'bool');
-    _bottomType = BottomTypeImpl.instance;
     _deprecatedType = _getType(coreNamespace, 'Deprecated');
     _doubleType = _getType(coreNamespace, 'double');
-    _dynamicType = DynamicTypeImpl.instance;
     _functionType = _getType(coreNamespace, 'Function');
     _futureOrType = _getType(asyncNamespace, 'FutureOr');
     _futureType = _getType(asyncNamespace, 'Future');
@@ -7552,8 +7534,6 @@ class TypeProviderImpl extends TypeProviderBase {
     _iterableType = _getType(coreNamespace, 'Iterable');
     _listType = _getType(coreNamespace, 'List');
     _mapType = _getType(coreNamespace, 'Map');
-    _neverType =
-        _getType(coreNamespace, 'Never') ?? _createNever(coreNamespace);
     _nullType = _getType(coreNamespace, 'Null');
     _numType = _getType(coreNamespace, 'num');
     _objectType = _getType(coreNamespace, 'Object');
@@ -7563,13 +7543,13 @@ class TypeProviderImpl extends TypeProviderBase {
     _stringType = _getType(coreNamespace, 'String');
     _symbolType = _getType(coreNamespace, 'Symbol');
     _typeType = _getType(coreNamespace, 'Type');
-    _futureDynamicType = _futureType.instantiate(<DartType>[_dynamicType]);
+    _futureDynamicType = _futureType.instantiate(<DartType>[dynamicType]);
     _futureNullType = _futureType.instantiate(<DartType>[_nullType]);
-    _iterableDynamicType = _iterableType.instantiate(<DartType>[_dynamicType]);
+    _iterableDynamicType = _iterableType.instantiate(<DartType>[dynamicType]);
     _iterableObjectType = _iterableType.instantiate(<DartType>[_objectType]);
     _mapObjectObjectType =
         _mapType.instantiate(<DartType>[_objectType, _objectType]);
-    _streamDynamicType = _streamType.instantiate(<DartType>[_dynamicType]);
+    _streamDynamicType = _streamType.instantiate(<DartType>[dynamicType]);
     // FutureOr<T> is still fairly new, so if we're analyzing an SDK that
     // doesn't have it yet, create an element for it.
     _futureOrType ??= createPlaceholderFutureOr(_futureType, _objectType);

pkg/analyzer/lib/src/hint/sdk_constraint_verifier.dart

@@ -81,6 +81,12 @@ class SdkConstraintVerifier extends RecursiveAstVisitor<void> {
   bool get checkFutureAndStream => _checkFutureAndStream ??=
       !before_2_1_0.intersect(_versionConstraint).isEmpty;
 
+  /// Return `true` if references to the non-nullable features need to be
+  /// checked.
+  // TODO(brianwilkerson) Implement this as a version check when a version has
+  //  been selected.
+  bool get checkNnbd => true;
+
   /// Return `true` if references to set literals need to be checked.
   bool get checkSetLiterals =>
       _checkSetLiterals ??= !before_2_2_0.intersect(_versionConstraint).isEmpty;
@@ -214,6 +220,8 @@ class SdkConstraintVerifier extends RecursiveAstVisitor<void> {
       }
       _errorReporter.reportErrorForNode(
           HintCode.SDK_VERSION_ASYNC_EXPORTED_FROM_CORE, node, [element.name]);
+    } else if (checkNnbd && element == _typeProvider.neverType.element) {
+      _errorReporter.reportErrorForNode(HintCode.SDK_VERSION_NEVER, node);
     }
   }
 

pkg/analyzer/lib/src/summary/link.dart

@@ -5390,7 +5390,6 @@ class TypeProviderForLink extends TypeProviderBase {
   InterfaceType _listType;
   InterfaceType _mapType;
   InterfaceType _mapObjectObjectType;
-  InterfaceType _neverType;
   InterfaceType _nullType;
   InterfaceType _numType;
   InterfaceType _objectType;
@@ -5475,8 +5474,7 @@ class TypeProviderForLink extends TypeProviderBase {
       _mapType ??= _buildInterfaceType(_linker.coreLibrary, 'Map');
 
   @override
-  InterfaceType get neverType =>
-      _neverType ??= _buildInterfaceType(_linker.coreLibrary, 'Never');
+  DartType get neverType => BottomTypeImpl.instance;
 
   @override
   DartObjectImpl get nullObject {

pkg/analyzer/lib/src/summary/summary_sdk.dart

@@ -128,7 +128,6 @@ class SummaryTypeProvider extends TypeProviderBase {
   InterfaceType _listType;
   InterfaceType _mapType;
   InterfaceType _mapObjectObjectType;
-  InterfaceType _neverType;
   DartObjectImpl _nullObject;
   InterfaceType _nullType;
   InterfaceType _numType;
@@ -267,10 +266,7 @@ class SummaryTypeProvider extends TypeProviderBase {
   }
 
   @override
-  InterfaceType get neverType {
-    assert(_coreLibrary != null);
-    return _neverType ??= _getType(_coreLibrary, 'Never');
-  }
+  DartType get neverType => BottomTypeImpl.instance;
 
   @override
   DartObjectImpl get nullObject {

pkg/analyzer/lib/src/summary2/builder/source_library_builder.dart

@@ -169,6 +169,7 @@ class SourceLibraryBuilder {
     }
     if ('$uri' == 'dart:core') {
       localScope.declare('dynamic', reference.getChild('dynamic'));
+      localScope.declare('Never', reference.getChild('Never'));
     }
   }
 

pkg/analyzer/lib/src/summary2/link.dart

@@ -64,6 +64,8 @@ class Linker {
   ) {
     var dynamicRef = rootReference.getChild('dart:core').getChild('dynamic');
     dynamicRef.element = DynamicElementImpl.instance;
+    var neverRef = rootReference.getChild('dart:core').getChild('Never');
+    neverRef.element = NeverElementImpl.instance;
 
     linkingBundleContext = LinkingBundleContext(dynamicRef);
 

pkg/analyzer/test/src/dart/element/type_algebra_test.dart

@@ -92,7 +92,7 @@ typedef F<T> = T Function(T);
       {t: intType},
       {t: BottomTypeImpl.instance},
     ).substituteType(type);
-    assertElementTypeString(result, '(<bottom>) → int');
+    assertElementTypeString(result, '(Never) → int');
   }
 }
 

pkg/analyzer/test/src/dart/resolution/namespace_test.dart

@@ -0,0 +1,38 @@
+// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:analyzer/dart/analysis/features.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import 'driver_resolution.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(ImportResolutionTest);
+    defineReflectiveTests(ImportResolutionWithNnbdTest);
+  });
+}
+
+@reflectiveTest
+class ImportResolutionTest extends DriverResolutionTest {
+  test_overrideCoreType_Never() async {
+    newFile('/test/lib/declares_never.dart', content: '''
+class Never {}
+''');
+    assertNoErrorsInCode(r'''
+import 'declares_never.dart';
+
+Never f() => throw 'foo';
+''');
+  }
+}
+
+@reflectiveTest
+class ImportResolutionWithNnbdTest extends ImportResolutionTest {
+  @override
+  AnalysisOptionsImpl get analysisOptions => AnalysisOptionsImpl()
+    ..contextFeatures = new FeatureSet.forTesting(
+        sdkVersion: '2.3.0', additionalFeatures: [Feature.non_nullable]);
+}

pkg/analyzer/test/src/dart/resolution/test_all.dart

@@ -26,6 +26,7 @@ import 'instance_member_inference_mixin_test.dart'
     as instance_member_inference_mixin;
 import 'method_invocation_test.dart' as method_invocation;
 import 'mixin_test.dart' as mixin_resolution;
+import 'namespace_test.dart' as namespace;
 import 'non_nullable_test.dart' as non_nullable;
 import 'optional_const_test.dart' as optional_const;
 import 'property_access_test.dart' as property_access;
@@ -53,6 +54,7 @@ main() {
     instance_member_inference_mixin.main();
     method_invocation.main();
     mixin_resolution.main();
+    namespace.main();
     non_nullable.main();
     optional_const.main();
     property_access.main();

pkg/analyzer/test/src/diagnostics/extends_non_class_test.dart

@@ -0,0 +1,36 @@
+// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:analyzer/dart/analysis/features.dart';
+import 'package:analyzer/src/error/codes.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import '../dart/resolution/driver_resolution.dart';
+
+main() {
+  defineReflectiveSuite(() {
+//    defineReflectiveTests(ExtendsNonClassTest);
+    defineReflectiveTests(ExtendsNonClassWithNnbdTest);
+  });
+}
+
+@reflectiveTest
+class ExtendsNonClassTest extends DriverResolutionTest {}
+
+@reflectiveTest
+class ExtendsNonClassWithNnbdTest extends ExtendsNonClassTest {
+  @override
+  AnalysisOptionsImpl get analysisOptions => AnalysisOptionsImpl()
+    ..contextFeatures = new FeatureSet.forTesting(
+        sdkVersion: '2.3.0', additionalFeatures: [Feature.non_nullable]);
+
+  test_Never() async {
+    await assertErrorsInCode('''
+class A extends Never {}
+''', [
+      error(CompileTimeErrorCode.EXTENDS_NON_CLASS, 16, 5),
+    ]);
+  }
+}

pkg/analyzer/test/src/diagnostics/implements_non_class_test.dart

@@ -0,0 +1,36 @@
+// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:analyzer/dart/analysis/features.dart';
+import 'package:analyzer/src/error/codes.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import '../dart/resolution/driver_resolution.dart';
+
+main() {
+  defineReflectiveSuite(() {
+//    defineReflectiveTests(ImplementsNonClassTest);
+    defineReflectiveTests(ImplementsNonClassWithNnbdTest);
+  });
+}
+
+@reflectiveTest
+class ImplementsNonClassTest extends DriverResolutionTest {}
+
+@reflectiveTest
+class ImplementsNonClassWithNnbdTest extends ImplementsNonClassTest {
+  @override
+  AnalysisOptionsImpl get analysisOptions => AnalysisOptionsImpl()
+    ..contextFeatures = new FeatureSet.forTesting(
+        sdkVersion: '2.3.0', additionalFeatures: [Feature.non_nullable]);
+
+  test_Never() async {
+    await assertErrorsInCode('''
+class A implements Never {}
+''', [
+      error(CompileTimeErrorCode.IMPLEMENTS_NON_CLASS, 19, 5),
+    ]);
+  }
+}

pkg/analyzer/test/src/diagnostics/mixin_of_non_class_test.dart

@@ -0,0 +1,36 @@
+// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:analyzer/dart/analysis/features.dart';
+import 'package:analyzer/src/error/codes.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import '../dart/resolution/driver_resolution.dart';
+
+main() {
+  defineReflectiveSuite(() {
+//    defineReflectiveTests(MixinOfNonClassTest);
+    defineReflectiveTests(MixinOfNonClassWithNnbdTest);
+  });
+}
+
+@reflectiveTest
+class MixinOfNonClassTest extends DriverResolutionTest {}
+
+@reflectiveTest
+class MixinOfNonClassWithNnbdTest extends MixinOfNonClassTest {
+  @override
+  AnalysisOptionsImpl get analysisOptions => AnalysisOptionsImpl()
+    ..contextFeatures = new FeatureSet.forTesting(
+        sdkVersion: '2.3.0', additionalFeatures: [Feature.non_nullable]);
+
+  test_Never() async {
+    await assertErrorsInCode('''
+class A with Never {}
+''', [
+      error(CompileTimeErrorCode.MIXIN_OF_NON_CLASS, 13, 5),
+    ]);
+  }
+}

pkg/analyzer/test/src/diagnostics/mixin_super_class_constraint_non_interface_test.dart

@@ -27,7 +27,6 @@ class MixinSuperClassConstraintNonInterfaceWithNnbdTest
     ..contextFeatures = new FeatureSet.forTesting(
         sdkVersion: '2.3.0', additionalFeatures: [Feature.non_nullable]);
 
-  @failingTest
   test_Never() async {
     await assertErrorsInCode('''
 mixin M on Never {}

pkg/analyzer/test/src/diagnostics/sdk_version_never_test.dart

@@ -0,0 +1,48 @@
+// Copyright (c) 2018, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:analyzer/dart/analysis/features.dart';
+import 'package:analyzer/src/dart/error/hint_codes.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import 'sdk_constraint_verifier_support.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(SdkVersionNeverTest);
+  });
+}
+
+@reflectiveTest
+class SdkVersionNeverTest extends SdkConstraintVerifierTest {
+  @override
+  AnalysisOptionsImpl get analysisOptions => AnalysisOptionsImpl()
+    ..contextFeatures = new FeatureSet.forTesting(
+        sdkVersion: '2.3.0', additionalFeatures: [Feature.non_nullable]);
+
+  @failingTest
+  test_equals() async {
+    // This test cannot pass because there is no version number that is equal to
+    // when non-nullable was enabled.
+    await verifyVersion('2.1.0', '''
+Never sink;
+''');
+  }
+
+  @failingTest
+  test_greaterThan() async {
+    // This test cannot pass because there is no version number that is equal to
+    // when non-nullable was enabled.
+    await verifyVersion('2.1.0', '''
+Never sink;
+''');
+  }
+
+  test_lessThan() async {
+    await verifyVersion('2.3.0', '''
+Never sink;
+''', errorCodes: [HintCode.SDK_VERSION_NEVER]);
+  }
+}

pkg/analyzer/test/src/diagnostics/test_all.dart

@@ -32,7 +32,9 @@ import 'duplicate_import_test.dart' as duplicate_import;
 import 'equal_elements_in_const_set_test.dart' as equal_elements_in_const_set;
 import 'equal_keys_in_const_map_test.dart' as equal_keys_in_const_map;
 import 'expression_in_map_test.dart' as expression_in_map;
+import 'extends_non_class_test.dart' as extends_non_class;
 import 'final_not_initialized_test.dart' as final_not_initialized;
+import 'implements_non_class_test.dart' as implements_non_class;
 import 'implicit_this_reference_in_initializer_test.dart'
     as implicit_this_reference_in_initializer;
 import 'import_deferred_library_with_load_function_test.dart'
@@ -69,6 +71,7 @@ import 'missing_default_value_for_parameter_test.dart'
     as missing_default_value_for_paramter;
 import 'missing_required_param_test.dart' as missing_required_param;
 import 'missing_return_test.dart' as missing_return;
+import 'mixin_of_non_class_test.dart' as mixin_of_non_class;
 import 'mixin_on_sealed_class_test.dart' as mixin_on_sealed_class;
 import 'mixin_super_class_constraint_non_interface_test.dart'
     as mixin_super_class_constraint_non_interface;
@@ -128,6 +131,7 @@ import 'sdk_version_gt_gt_gt_operator_test.dart'
     as sdk_version_gt_gt_gt_operator;
 import 'sdk_version_is_expression_in_const_context_test.dart'
     as sdk_version_is_expression_in_const_context;
+import 'sdk_version_never_test.dart' as sdk_version_never;
 import 'sdk_version_set_literal_test.dart' as sdk_version_set_literal;
 import 'sdk_version_ui_as_code_test.dart' as sdk_version_ui_as_code;
 import 'set_element_type_not_assignable_test.dart'
@@ -184,7 +188,9 @@ main() {
     equal_elements_in_const_set.main();
     equal_keys_in_const_map.main();
     expression_in_map.main();
+    extends_non_class.main();
     final_not_initialized.main();
+    implements_non_class.main();
     implicit_this_reference_in_initializer.main();
     import_deferred_library_with_load_function.main();
     invalid_assignment.main();
@@ -209,6 +215,7 @@ main() {
     missing_default_value_for_paramter.main();
     missing_required_param.main();
     missing_return.main();
+    mixin_of_non_class.main();
     mixin_on_sealed_class.main();
     mixin_super_class_constraint_non_interface.main();
     must_be_immutable.main();
@@ -248,6 +255,7 @@ main() {
     sdk_version_eq_eq_operator.main();
     sdk_version_gt_gt_gt_operator.main();
     sdk_version_is_expression_in_const_context.main();
+    sdk_version_never.main();
     sdk_version_set_literal.main();
     sdk_version_ui_as_code.main();
     set_element_type_not_assignable.main();

pkg/analyzer/test/src/summary/linker_test.dart

@@ -327,7 +327,7 @@ class C {
     ClassElementForLink_Class cls = library.getContainedName('C');
     expect(cls.fields, hasLength(1));
     var field = cls.fields[0];
-    expect(field.type.toString(), '(<bottom>) → int');
+    expect(field.type.toString(), '(Never) → int');
   }
 
   void test_inferredType_instanceField_dynamic() {

pkg/analyzer/test/src/summary/resynthesize_ast2_test.dart

@@ -83,6 +83,8 @@ class ResynthesizeAst2Test extends ResynthesizeTestStrategyTwoPhase
     var rootReference = Reference.root();
     rootReference.getChild('dart:core').getChild('dynamic').element =
         DynamicElementImpl.instance;
+    rootReference.getChild('dart:core').getChild('Never').element =
+        NeverElementImpl.instance;
 
     var elementFactory = LinkedElementFactory(
       analysisContext,

pkg/analyzer/test/src/summary/resynthesize_common.dart

@@ -8969,7 +8969,7 @@ final v = f() ? <T>(T t) => 0 : <T>(T t) => 1;
 bool f() => true;
 ''');
     checkElementText(library, r'''
-final int Function(<bottom>) v;
+final int Function(Never) v;
 bool f() {}
 ''');
   }

pkg/analyzer/test/src/summary/summary_common.dart

@@ -9504,7 +9504,7 @@ var v = extract(f);
     UnlinkedVariable variable = serializeVariableText('int v = null;');
     expect(variable.initializer.returnType, isNull);
     checkInferredTypeSlot(
-        variable.initializer.inferredReturnTypeSlot, null, '*bottom*',
+        variable.initializer.inferredReturnTypeSlot, null, 'Never',
         onlyInStrongMode: false);
   }
 
@@ -10827,7 +10827,7 @@ bool f() => true;
     EntityRef inferredType = getTypeRefForSlot(variable.inferredTypeSlot);
     checkLinkedTypeRef(inferredType.syntheticReturnType, 'dart:core', 'int');
     expect(inferredType.syntheticParams, hasLength(1));
-    checkLinkedTypeRef(inferredType.syntheticParams[0].type, null, '*bottom*');
+    checkLinkedTypeRef(inferredType.syntheticParams[0].type, null, 'Never');
   }
 
   test_syntheticFunctionType_inGenericClass() {

pkg/analyzer_plugin/lib/src/utilities/change_builder/dart/import_library_element.dart

@@ -27,7 +27,7 @@ ImportLibraryRequest importLibraryElementImpl({
   }
 
   var requestedElements = requestedLibrary.exportNamespace.definedNames;
-  _removeEntryForDynamic(requestedElements);
+  _removeEntriesForDynamicAndNever(requestedElements);
 
   // Find URIs of all libraries that import the requested name into the target.
   var unprefixedNameUriSet = Set<Uri>();
@@ -145,11 +145,13 @@ ImportLibraryRequest importLibraryElementImpl({
   return ImportLibraryRequest(requestedLibraryUri, prefix);
 }
 
-/// The type `dynamic` is part of 'dart:core', but has no library.
-void _removeEntryForDynamic(Map<String, Element> requestedElements) {
+/// The types `dynamic` and `Never` are part of 'dart:core', but have no
+/// library.
+void _removeEntriesForDynamicAndNever(Map<String, Element> requestedElements) {
   requestedElements.removeWhere((_, element) {
     if (element.librarySource == null) {
-      assert(element.displayName == 'dynamic');
+      assert(
+          element.displayName == 'dynamic' || element.displayName == 'Never');
       return true;
     }
     return false;