pkg/analyzer/lib/src/generated/error_verifier.dart - sdk.git - Git at Google

 // Copyright (c) 2014, 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.

 library engine.resolver.error_verifier;

 import 'dart:collection';
 import "dart:math" as math;

 import 'package:analyzer/src/generated/static_type_analyzer.dart';

 import 'ast.dart';
 import 'constant.dart';
 import 'element.dart';
 import 'element_resolver.dart';
 import 'error.dart';
 import 'java_engine.dart';
 import 'parser.dart' show Parser, ParserErrorCode;
 import 'resolver.dart';
 import 'scanner.dart' as sc;
 import 'sdk.dart' show DartSdk, SdkLibrary;
 import 'utilities_dart.dart';

 /**
  * A visitor used to traverse an AST structure looking for additional errors and
  * warnings not covered by the parser and resolver.
  */
 class ErrorVerifier extends RecursiveAstVisitor<Object> {
   /**
    * Static final string with value `"getter "` used in the construction of the
    * [StaticWarningCode.NON_ABSTRACT_CLASS_INHERITS_ABSTRACT_MEMBER_ONE], and
    * similar, error code messages.
    *
    * See [_checkForNonAbstractClassInheritsAbstractMember].
    */
   static String _GETTER_SPACE = "getter ";

   /**
    * Static final string with value `"setter "` used in the construction of the
    * [StaticWarningCode.NON_ABSTRACT_CLASS_INHERITS_ABSTRACT_MEMBER_ONE], and
    * similar, error code messages.
    *
    * See [_checkForNonAbstractClassInheritsAbstractMember].
    */
   static String _SETTER_SPACE = "setter ";

   /**
    * The error reporter by which errors will be reported.
    */
   final ErrorReporter _errorReporter;

   /**
    * The current library that is being analyzed.
    */
   final LibraryElement _currentLibrary;

   /**
    * The type representing the type 'bool'.
    */
   InterfaceType _boolType;

   /**
    * The type representing the type 'int'.
    */
   InterfaceType _intType;

   /**
    * The object providing access to the types defined by the language.
    */
   final TypeProvider _typeProvider;

   /**
    * The type system primitives
    */
   TypeSystem _typeSystem;

   /**
    * The manager for the inheritance mappings.
    */
   final InheritanceManager _inheritanceManager;

   /**
    * A flag indicating whether the visitor is currently within a constructor
    * declaration that is 'const'.
    *
    * See [visitConstructorDeclaration].
    */
   bool _isEnclosingConstructorConst = false;

   /**
    * A flag indicating whether we are currently within a function body marked as
    * being asynchronous.
    */
   bool _inAsync = false;

   /**
    * A flag indicating whether we are currently within a function body marked a
    *  being a generator.
    */
   bool _inGenerator = false;

   /**
    * A flag indicating whether the visitor is currently within a catch clause.
    *
    * See [visitCatchClause].
    */
   bool _isInCatchClause = false;

   /**
    * A flag indicating whether the visitor is currently within a comment.
    */
   bool _isInComment = false;

   /**
    * A flag indicating whether the visitor is currently within an instance
    * creation expression.
    */
   bool _isInConstInstanceCreation = false;

   /**
    * A flag indicating whether the visitor is currently within a native class
    * declaration.
    */
   bool _isInNativeClass = false;

   /**
    * A flag indicating whether the visitor is currently within a static variable
    * declaration.
    */
   bool _isInStaticVariableDeclaration = false;

   /**
    * A flag indicating whether the visitor is currently within an instance
    * variable declaration.
    */
   bool _isInInstanceVariableDeclaration = false;

   /**
    * A flag indicating whether the visitor is currently within an instance
    * variable initializer.
    */
   bool _isInInstanceVariableInitializer = false;

   /**
    * A flag indicating whether the visitor is currently within a constructor
    * initializer.
    */
   bool _isInConstructorInitializer = false;

   /**
    * This is set to `true` iff the visitor is currently within a function typed
    * formal parameter.
    */
   bool _isInFunctionTypedFormalParameter = false;

   /**
    * A flag indicating whether the visitor is currently within a static method.
    * By "method" here getter, setter and operator declarations are also implied
    * since they are all represented with a [MethodDeclaration] in the AST
    * structure.
    */
   bool _isInStaticMethod = false;

   /**
    * A flag indicating whether the visitor is currently within a factory
    * constructor.
    */
   bool _isInFactory = false;

   /**
    * A flag indicating whether the visitor is currently within code in the SDK.
    */
   bool _isInSystemLibrary = false;

   /**
    * A flag indicating whether the current library contains at least one import
    * directive with a URI that uses the "dart-ext" scheme.
    */
   bool _hasExtUri = false;

   /**
    * This is set to `false` on the entry of every [BlockFunctionBody], and is
    * restored to the enclosing value on exit. The value is used in
    * [_checkForMixedReturns] to prevent both
    * [StaticWarningCode.MIXED_RETURN_TYPES] and
    * [StaticWarningCode.RETURN_WITHOUT_VALUE] from being generated in the same
    * function body.
    */
   bool _hasReturnWithoutValue = false;

   /**
    * The class containing the AST nodes being visited, or `null` if we are not
    * in the scope of a class.
    */
   ClassElement _enclosingClass;

   /**
    * The method or function that we are currently visiting, or `null` if we are
    * not inside a method or function.
    */
   ExecutableElement _enclosingFunction;

   /**
    * The return statements found in the method or function that we are currently
    * visiting that have a return value.
    */
   List<ReturnStatement> _returnsWith = new List<ReturnStatement>();

   /**
    * The return statements found in the method or function that we are currently
    * visiting that do not have a return value.
    */
   List<ReturnStatement> _returnsWithout = new List<ReturnStatement>();

   /**
    * This map is initialized when visiting the contents of a class declaration.
    * If the visitor is not in an enclosing class declaration, then the map is
    * set to `null`.
    *
    * When set the map maps the set of [FieldElement]s in the class to an
    * [INIT_STATE.NOT_INIT] or [INIT_STATE.INIT_IN_DECLARATION]. The `checkFor*`
    * methods, specifically [_checkForAllFinalInitializedErrorCodes], can make a
    * copy of the map to compute error code states. The `checkFor*` methods
    * should only ever make a copy, or read from this map after it has been set
    * in [visitClassDeclaration].
    *
    * See [visitClassDeclaration], and [_checkForAllFinalInitializedErrorCodes].
    */
   HashMap<FieldElement, INIT_STATE> _initialFieldElementsMap;

   /**
    * A table mapping name of the library to the export directive which export
    * this library.
    */
   HashMap<String, LibraryElement> _nameToExportElement =
       new HashMap<String, LibraryElement>();

   /**
    * A table mapping name of the library to the import directive which import
    * this library.
    */
   HashMap<String, LibraryElement> _nameToImportElement =
       new HashMap<String, LibraryElement>();

   /**
    * A table mapping names to the exported elements.
    */
   HashMap<String, Element> _exportedElements = new HashMap<String, Element>();

   /**
    * A set of the names of the variable initializers we are visiting now.
    */
   HashSet<String> _namesForReferenceToDeclaredVariableInInitializer =
       new HashSet<String>();

   /**
    * A list of types used by the [CompileTimeErrorCode.EXTENDS_DISALLOWED_CLASS]
    * and [CompileTimeErrorCode.IMPLEMENTS_DISALLOWED_CLASS] error codes.
    */
   List<InterfaceType> _DISALLOWED_TYPES_TO_EXTEND_OR_IMPLEMENT;

   /**
    * If `true`, mixins are allowed to inherit from types other than Object, and
    * are allowed to reference `super`.
    */
   final bool enableSuperMixins;

   /**
    * Initialize a newly created error verifier.
    */
   ErrorVerifier(this._errorReporter, this._currentLibrary, this._typeProvider,
       this._inheritanceManager, this.enableSuperMixins) {
     this._isInSystemLibrary = _currentLibrary.source.isInSystemLibrary;
     this._hasExtUri = _currentLibrary.hasExtUri;
     _isEnclosingConstructorConst = false;
     _isInCatchClause = false;
     _isInStaticVariableDeclaration = false;
     _isInInstanceVariableDeclaration = false;
     _isInInstanceVariableInitializer = false;
     _isInConstructorInitializer = false;
     _isInStaticMethod = false;
     _boolType = _typeProvider.boolType;
     _intType = _typeProvider.intType;
     _DISALLOWED_TYPES_TO_EXTEND_OR_IMPLEMENT = _typeProvider.nonSubtypableTypes;
     _typeSystem = _currentLibrary.context.typeSystem;
   }

   @override
   Object visitAnnotation(Annotation node) {
     _checkForInvalidAnnotationFromDeferredLibrary(node);
     return super.visitAnnotation(node);
   }

   @override
   Object visitArgumentList(ArgumentList node) {
     _checkForArgumentTypesNotAssignableInList(node);
     return super.visitArgumentList(node);
   }

   @override
   Object visitAsExpression(AsExpression node) {
     _checkForTypeAnnotationDeferredClass(node.type);
     return super.visitAsExpression(node);
   }

   @override
   Object visitAssertStatement(AssertStatement node) {
     _checkForNonBoolExpression(node);
     return super.visitAssertStatement(node);
   }

   @override
   Object visitAssignmentExpression(AssignmentExpression node) {
     sc.TokenType operatorType = node.operator.type;
     Expression lhs = node.leftHandSide;
     Expression rhs = node.rightHandSide;
     if (operatorType == sc.TokenType.EQ ||
         operatorType == sc.TokenType.QUESTION_QUESTION_EQ) {
       _checkForInvalidAssignment(lhs, rhs);
     } else {
       _checkForInvalidCompoundAssignment(node, lhs, rhs);
       _checkForArgumentTypeNotAssignableForArgument(rhs);
     }
     _checkForAssignmentToFinal(lhs);
     return super.visitAssignmentExpression(node);
   }

   @override
   Object visitAwaitExpression(AwaitExpression node) {
     if (!_inAsync) {
       _errorReporter.reportErrorForToken(
           CompileTimeErrorCode.AWAIT_IN_WRONG_CONTEXT, node.awaitKeyword);
     }
     return super.visitAwaitExpression(node);
   }

   @override
   Object visitBinaryExpression(BinaryExpression node) {
     sc.Token operator = node.operator;
     sc.TokenType type = operator.type;
     if (type == sc.TokenType.AMPERSAND_AMPERSAND ||
         type == sc.TokenType.BAR_BAR) {
       String lexeme = operator.lexeme;
       _checkForAssignability(node.leftOperand, _boolType,
           StaticTypeWarningCode.NON_BOOL_OPERAND, [lexeme]);
       _checkForAssignability(node.rightOperand, _boolType,
           StaticTypeWarningCode.NON_BOOL_OPERAND, [lexeme]);
     } else {
       _checkForArgumentTypeNotAssignableForArgument(node.rightOperand);
     }
     return super.visitBinaryExpression(node);
   }

   @override
   Object visitBlockFunctionBody(BlockFunctionBody node) {
     bool wasInAsync = _inAsync;
     bool wasInGenerator = _inGenerator;
     bool previousHasReturnWithoutValue = _hasReturnWithoutValue;
     _hasReturnWithoutValue = false;
     List<ReturnStatement> previousReturnsWith = _returnsWith;
     List<ReturnStatement> previousReturnsWithout = _returnsWithout;
     try {
       _inAsync = node.isAsynchronous;
       _inGenerator = node.isGenerator;
       _returnsWith = new List<ReturnStatement>();
       _returnsWithout = new List<ReturnStatement>();
       super.visitBlockFunctionBody(node);
       _checkForMixedReturns(node);
     } finally {
       _inAsync = wasInAsync;
       _inGenerator = wasInGenerator;
       _returnsWith = previousReturnsWith;
       _returnsWithout = previousReturnsWithout;
       _hasReturnWithoutValue = previousHasReturnWithoutValue;
     }
     return null;
   }

   @override
   Object visitBreakStatement(BreakStatement node) {
     SimpleIdentifier labelNode = node.label;
     if (labelNode != null) {
       Element labelElement = labelNode.staticElement;
       if (labelElement is LabelElementImpl && labelElement.isOnSwitchMember) {
         _errorReporter.reportErrorForNode(
             ResolverErrorCode.BREAK_LABEL_ON_SWITCH_MEMBER, labelNode);
       }
     }
     return null;
   }

   @override
   Object visitCatchClause(CatchClause node) {
     bool previousIsInCatchClause = _isInCatchClause;
     try {
       _isInCatchClause = true;
       _checkForTypeAnnotationDeferredClass(node.exceptionType);
       return super.visitCatchClause(node);
     } finally {
       _isInCatchClause = previousIsInCatchClause;
     }
   }

   @override
   Object visitClassDeclaration(ClassDeclaration node) {
     ClassElement outerClass = _enclosingClass;
     try {
       _isInNativeClass = node.nativeClause != null;
       _enclosingClass = node.element;
       ExtendsClause extendsClause = node.extendsClause;
       ImplementsClause implementsClause = node.implementsClause;
       WithClause withClause = node.withClause;
       _checkForBuiltInIdentifierAsName(
           node.name, CompileTimeErrorCode.BUILT_IN_IDENTIFIER_AS_TYPE_NAME);
       _checkForMemberWithClassName();
       _checkForNoDefaultSuperConstructorImplicit(node);
       _checkForConflictingTypeVariableErrorCodes(node);
       // Only do error checks on the clause nodes if there is a non-null clause
       if (implementsClause != null ||
           extendsClause != null ||
           withClause != null) {
         // Only check for all of the inheritance logic around clauses if there
         // isn't an error code such as "Cannot extend double" already on the
         // class.
         if (!_checkForImplementsDisallowedClass(implementsClause) &&
             !_checkForExtendsDisallowedClass(extendsClause) &&
             !_checkForAllMixinErrorCodes(withClause)) {
           _checkForExtendsDeferredClass(extendsClause);
           _checkForImplementsDeferredClass(implementsClause);
           _checkForNonAbstractClassInheritsAbstractMember(node.name);
           _checkForInconsistentMethodInheritance();
           _checkForRecursiveInterfaceInheritance(_enclosingClass);
           _checkForConflictingGetterAndMethod();
           _checkForConflictingInstanceGetterAndSuperclassMember();
           _checkImplementsSuperClass(node);
           _checkImplementsFunctionWithoutCall(node);
           _checkForMixinHasNoConstructors(node);
         }
       }
       visitClassDeclarationIncrementally(node);
       _checkForFinalNotInitializedInClass(node);
       _checkForDuplicateDefinitionInheritance();
       _checkForConflictingInstanceMethodSetter(node);
       return super.visitClassDeclaration(node);
     } finally {
       _isInNativeClass = false;
       _initialFieldElementsMap = null;
       _enclosingClass = outerClass;
     }
   }

   /**
    * Implementation of this method should be synchronized with
    * [visitClassDeclaration].
    */
   void visitClassDeclarationIncrementally(ClassDeclaration node) {
     _isInNativeClass = node.nativeClause != null;
     _enclosingClass = node.element;
     // initialize initialFieldElementsMap
     if (_enclosingClass != null) {
       List<FieldElement> fieldElements = _enclosingClass.fields;
       _initialFieldElementsMap = new HashMap<FieldElement, INIT_STATE>();
       for (FieldElement fieldElement in fieldElements) {
         if (!fieldElement.isSynthetic) {
           _initialFieldElementsMap[fieldElement] = fieldElement.initializer ==
               null ? INIT_STATE.NOT_INIT : INIT_STATE.INIT_IN_DECLARATION;
         }
       }
     }
   }

   @override
   Object visitClassTypeAlias(ClassTypeAlias node) {
     _checkForBuiltInIdentifierAsName(
         node.name, CompileTimeErrorCode.BUILT_IN_IDENTIFIER_AS_TYPEDEF_NAME);
     ClassElement outerClassElement = _enclosingClass;
     try {
       _enclosingClass = node.element;
       ImplementsClause implementsClause = node.implementsClause;
       // Only check for all of the inheritance logic around clauses if there
       // isn't an error code such as "Cannot extend double" already on the
       // class.
       if (!_checkForExtendsDisallowedClassInTypeAlias(node) &&
           !_checkForImplementsDisallowedClass(implementsClause) &&
           !_checkForAllMixinErrorCodes(node.withClause)) {
         _checkForExtendsDeferredClassInTypeAlias(node);
         _checkForImplementsDeferredClass(implementsClause);
         _checkForRecursiveInterfaceInheritance(_enclosingClass);
         _checkForNonAbstractClassInheritsAbstractMember(node.name);
         _checkForMixinHasNoConstructors(node);
       }
     } finally {
       _enclosingClass = outerClassElement;
     }
     return super.visitClassTypeAlias(node);
   }

   @override
   Object visitComment(Comment node) {
     _isInComment = true;
     try {
       return super.visitComment(node);
     } finally {
       _isInComment = false;
     }
   }

   @override
   Object visitCompilationUnit(CompilationUnit node) {
     _checkForDeferredPrefixCollisions(node);
     return super.visitCompilationUnit(node);
   }

   @override
   Object visitConditionalExpression(ConditionalExpression node) {
     _checkForNonBoolCondition(node.condition);
     return super.visitConditionalExpression(node);
   }

   @override
   Object visitConstructorDeclaration(ConstructorDeclaration node) {
     ExecutableElement outerFunction = _enclosingFunction;
     try {
       ConstructorElement constructorElement = node.element;
       _enclosingFunction = constructorElement;
       _isEnclosingConstructorConst = node.constKeyword != null;
       _isInFactory = node.factoryKeyword != null;
       _checkForInvalidModifierOnBody(
           node.body, CompileTimeErrorCode.INVALID_MODIFIER_ON_CONSTRUCTOR);
       _checkForConstConstructorWithNonFinalField(node, constructorElement);
       _checkForConstConstructorWithNonConstSuper(node);
       _checkForConflictingConstructorNameAndMember(node, constructorElement);
       _checkForAllFinalInitializedErrorCodes(node);
       _checkForRedirectingConstructorErrorCodes(node);
       _checkForMultipleSuperInitializers(node);
       _checkForRecursiveConstructorRedirect(node, constructorElement);
       if (!_checkForRecursiveFactoryRedirect(node, constructorElement)) {
         _checkForAllRedirectConstructorErrorCodes(node);
       }
       _checkForUndefinedConstructorInInitializerImplicit(node);
       _checkForRedirectToNonConstConstructor(node, constructorElement);
       _checkForReturnInGenerativeConstructor(node);
       return super.visitConstructorDeclaration(node);
     } finally {
       _isEnclosingConstructorConst = false;
       _isInFactory = false;
       _enclosingFunction = outerFunction;
     }
   }

   @override
   Object visitConstructorFieldInitializer(ConstructorFieldInitializer node) {
     _isInConstructorInitializer = true;
     try {
       SimpleIdentifier fieldName = node.fieldName;
       Element staticElement = fieldName.staticElement;
       _checkForInvalidField(node, fieldName, staticElement);
       _checkForFieldInitializerNotAssignable(node, staticElement);
       return super.visitConstructorFieldInitializer(node);
     } finally {
       _isInConstructorInitializer = false;
     }
   }

   @override
   Object visitContinueStatement(ContinueStatement node) {
     SimpleIdentifier labelNode = node.label;
     if (labelNode != null) {
       Element labelElement = labelNode.staticElement;
       if (labelElement is LabelElementImpl &&
           labelElement.isOnSwitchStatement) {
         _errorReporter.reportErrorForNode(
             ResolverErrorCode.CONTINUE_LABEL_ON_SWITCH, labelNode);
       }
     }
     return null;
   }

   @override
   Object visitDefaultFormalParameter(DefaultFormalParameter node) {
     _checkForInvalidAssignment(node.identifier, node.defaultValue);
     _checkForDefaultValueInFunctionTypedParameter(node);
     return super.visitDefaultFormalParameter(node);
   }

   @override
   Object visitDoStatement(DoStatement node) {
     _checkForNonBoolCondition(node.condition);
     return super.visitDoStatement(node);
   }

   @override
   Object visitEnumDeclaration(EnumDeclaration node) {
     ClassElement outerClass = _enclosingClass;
     try {
       _isInNativeClass = false;
       _enclosingClass = node.element;
       return super.visitEnumDeclaration(node);
     } finally {
       _enclosingClass = outerClass;
     }
   }

   @override
   Object visitExportDirective(ExportDirective node) {
     ExportElement exportElement = node.element;
     if (exportElement != null) {
       LibraryElement exportedLibrary = exportElement.exportedLibrary;
       _checkForAmbiguousExport(node, exportElement, exportedLibrary);
       _checkForExportDuplicateLibraryName(node, exportElement, exportedLibrary);
       _checkForExportInternalLibrary(node, exportElement);
     }
     return super.visitExportDirective(node);
   }

   @override
   Object visitExpressionFunctionBody(ExpressionFunctionBody node) {
     bool wasInAsync = _inAsync;
     bool wasInGenerator = _inGenerator;
     try {
       _inAsync = node.isAsynchronous;
       _inGenerator = node.isGenerator;
       FunctionType functionType =
           _enclosingFunction == null ? null : _enclosingFunction.type;
       DartType expectedReturnType = functionType == null
           ? DynamicTypeImpl.instance
           : functionType.returnType;
       _checkForReturnOfInvalidType(node.expression, expectedReturnType);
       return super.visitExpressionFunctionBody(node);
     } finally {
       _inAsync = wasInAsync;
       _inGenerator = wasInGenerator;
     }
   }

   @override
   Object visitFieldDeclaration(FieldDeclaration node) {
     _isInStaticVariableDeclaration = node.isStatic;
     _isInInstanceVariableDeclaration = !_isInStaticVariableDeclaration;
     if (_isInInstanceVariableDeclaration) {
       VariableDeclarationList variables = node.fields;
       if (variables.isConst) {
         _errorReporter.reportErrorForToken(
             CompileTimeErrorCode.CONST_INSTANCE_FIELD, variables.keyword);
       }
     }
     try {
       _checkForAllInvalidOverrideErrorCodesForField(node);
       return super.visitFieldDeclaration(node);
     } finally {
       _isInStaticVariableDeclaration = false;
       _isInInstanceVariableDeclaration = false;
     }
   }

   @override
   Object visitFieldFormalParameter(FieldFormalParameter node) {
     _checkForValidField(node);
     _checkForConstFormalParameter(node);
     _checkForPrivateOptionalParameter(node);
     _checkForFieldInitializingFormalRedirectingConstructor(node);
     _checkForTypeAnnotationDeferredClass(node.type);
     return super.visitFieldFormalParameter(node);
   }

   @override
   Object visitFunctionDeclaration(FunctionDeclaration node) {
     ExecutableElement outerFunction = _enclosingFunction;
     try {
       SimpleIdentifier identifier = node.name;
       String methodName = "";
       if (identifier != null) {
         methodName = identifier.name;
       }
       _enclosingFunction = node.element;
       TypeName returnType = node.returnType;
       if (node.isSetter || node.isGetter) {
         _checkForMismatchedAccessorTypes(node, methodName);
         if (node.isSetter) {
           FunctionExpression functionExpression = node.functionExpression;
           if (functionExpression != null) {
             _checkForWrongNumberOfParametersForSetter(
                 identifier, functionExpression.parameters);
           }
           _checkForNonVoidReturnTypeForSetter(returnType);
         }
       }
       if (node.isSetter) {
         _checkForInvalidModifierOnBody(node.functionExpression.body,
             CompileTimeErrorCode.INVALID_MODIFIER_ON_SETTER);
       }
       _checkForTypeAnnotationDeferredClass(returnType);
       _checkForIllegalReturnType(returnType);
       return super.visitFunctionDeclaration(node);
     } finally {
       _enclosingFunction = outerFunction;
     }
   }

   @override
   Object visitFunctionExpression(FunctionExpression node) {
     // If this function expression is wrapped in a function declaration, don't
     // change the enclosingFunction field.
     if (node.parent is! FunctionDeclaration) {
       ExecutableElement outerFunction = _enclosingFunction;
       try {
         _enclosingFunction = node.element;
         return super.visitFunctionExpression(node);
       } finally {
         _enclosingFunction = outerFunction;
       }
     } else {
       return super.visitFunctionExpression(node);
     }
   }

   @override
   Object visitFunctionExpressionInvocation(FunctionExpressionInvocation node) {
     Expression functionExpression = node.function;
     DartType expressionType = functionExpression.staticType;
     if (!_isFunctionType(expressionType)) {
       _errorReporter.reportErrorForNode(
           StaticTypeWarningCode.INVOCATION_OF_NON_FUNCTION_EXPRESSION,
           functionExpression);
     }
     return super.visitFunctionExpressionInvocation(node);
   }

   @override
   Object visitFunctionTypeAlias(FunctionTypeAlias node) {
     _checkForBuiltInIdentifierAsName(
         node.name, CompileTimeErrorCode.BUILT_IN_IDENTIFIER_AS_TYPEDEF_NAME);
     _checkForDefaultValueInFunctionTypeAlias(node);
     _checkForTypeAliasCannotReferenceItself_function(node);
     return super.visitFunctionTypeAlias(node);
   }

   @override
   Object visitFunctionTypedFormalParameter(FunctionTypedFormalParameter node) {
     bool old = _isInFunctionTypedFormalParameter;
     _isInFunctionTypedFormalParameter = true;
     try {
       _checkForTypeAnnotationDeferredClass(node.returnType);
       return super.visitFunctionTypedFormalParameter(node);
     } finally {
       _isInFunctionTypedFormalParameter = old;
     }
   }

   @override
   Object visitIfStatement(IfStatement node) {
     _checkForNonBoolCondition(node.condition);
     return super.visitIfStatement(node);
   }

   @override
   Object visitImportDirective(ImportDirective node) {
     ImportElement importElement = node.element;
     if (importElement != null) {
       _checkForImportDuplicateLibraryName(node, importElement);
       _checkForImportInternalLibrary(node, importElement);
     }
     return super.visitImportDirective(node);
   }

   @override
   Object visitIndexExpression(IndexExpression node) {
     _checkForArgumentTypeNotAssignableForArgument(node.index);
     return super.visitIndexExpression(node);
   }

   @override
   Object visitInstanceCreationExpression(InstanceCreationExpression node) {
     bool wasInConstInstanceCreation = _isInConstInstanceCreation;
     _isInConstInstanceCreation = node.isConst;
     try {
       ConstructorName constructorName = node.constructorName;
       TypeName typeName = constructorName.type;
       DartType type = typeName.type;
       if (type is InterfaceType) {
         InterfaceType interfaceType = type;
         _checkForConstOrNewWithAbstractClass(node, typeName, interfaceType);
         _checkForConstOrNewWithEnum(node, typeName, interfaceType);
         if (_isInConstInstanceCreation) {
           _checkForConstWithNonConst(node);
           _checkForConstWithUndefinedConstructor(
               node, constructorName, typeName);
           _checkForConstWithTypeParameters(typeName);
           _checkForConstDeferredClass(node, constructorName, typeName);
         } else {
           _checkForNewWithUndefinedConstructor(node, constructorName, typeName);
         }
       }
       return super.visitInstanceCreationExpression(node);
     } finally {
       _isInConstInstanceCreation = wasInConstInstanceCreation;
     }
   }

   @override
   Object visitIsExpression(IsExpression node) {
     _checkForTypeAnnotationDeferredClass(node.type);
     return super.visitIsExpression(node);
   }

   @override
   Object visitListLiteral(ListLiteral node) {
     TypeArgumentList typeArguments = node.typeArguments;
     if (typeArguments != null) {
       if (node.constKeyword != null) {
         NodeList<TypeName> arguments = typeArguments.arguments;
         if (arguments.length != 0) {
           _checkForInvalidTypeArgumentInConstTypedLiteral(arguments,
               CompileTimeErrorCode.INVALID_TYPE_ARGUMENT_IN_CONST_LIST);
         }
       }
       _checkForExpectedOneListTypeArgument(node, typeArguments);
       _checkForListElementTypeNotAssignable(node, typeArguments);
     }
     return super.visitListLiteral(node);
   }

   @override
   Object visitMapLiteral(MapLiteral node) {
     TypeArgumentList typeArguments = node.typeArguments;
     if (typeArguments != null) {
       NodeList<TypeName> arguments = typeArguments.arguments;
       if (arguments.length != 0) {
         if (node.constKeyword != null) {
           _checkForInvalidTypeArgumentInConstTypedLiteral(arguments,
               CompileTimeErrorCode.INVALID_TYPE_ARGUMENT_IN_CONST_MAP);
         }
       }
       _checkExpectedTwoMapTypeArguments(typeArguments);
       _checkForMapTypeNotAssignable(node, typeArguments);
     }
     _checkForNonConstMapAsExpressionStatement(node);
     return super.visitMapLiteral(node);
   }

   @override
   Object visitMethodDeclaration(MethodDeclaration node) {
     ExecutableElement previousFunction = _enclosingFunction;
     try {
       _isInStaticMethod = node.isStatic;
       _enclosingFunction = node.element;
       SimpleIdentifier identifier = node.name;
       String methodName = "";
       if (identifier != null) {
         methodName = identifier.name;
       }
       TypeName returnTypeName = node.returnType;
       if (node.isSetter || node.isGetter) {
         _checkForMismatchedAccessorTypes(node, methodName);
       }
       if (node.isGetter) {
         _checkForVoidReturnType(node);
         _checkForConflictingStaticGetterAndInstanceSetter(node);
       } else if (node.isSetter) {
         _checkForInvalidModifierOnBody(
             node.body, CompileTimeErrorCode.INVALID_MODIFIER_ON_SETTER);
         _checkForWrongNumberOfParametersForSetter(node.name, node.parameters);
         _checkForNonVoidReturnTypeForSetter(returnTypeName);
         _checkForConflictingStaticSetterAndInstanceMember(node);
       } else if (node.isOperator) {
         _checkForOptionalParameterInOperator(node);
         _checkForWrongNumberOfParametersForOperator(node);
         _checkForNonVoidReturnTypeForOperator(node);
       }
       _checkForConcreteClassWithAbstractMember(node);
       _checkForAllInvalidOverrideErrorCodesForMethod(node);
       _checkForTypeAnnotationDeferredClass(returnTypeName);
       _checkForIllegalReturnType(returnTypeName);
       return super.visitMethodDeclaration(node);
     } finally {
       _enclosingFunction = previousFunction;
       _isInStaticMethod = false;
     }
   }

   @override
   Object visitMethodInvocation(MethodInvocation node) {
     Expression target = node.realTarget;
     SimpleIdentifier methodName = node.methodName;
     if (target != null) {
       ClassElement typeReference = ElementResolver.getTypeReference(target);
       _checkForStaticAccessToInstanceMember(typeReference, methodName);
       _checkForInstanceAccessToStaticMember(typeReference, methodName);
     } else {
       _checkForUnqualifiedReferenceToNonLocalStaticMember(methodName);
     }
     return super.visitMethodInvocation(node);
   }

   @override
   Object visitNativeClause(NativeClause node) {
     // TODO(brianwilkerson) Figure out the right rule for when 'native' is
     // allowed.
     if (!_isInSystemLibrary) {
       _errorReporter.reportErrorForNode(
           ParserErrorCode.NATIVE_CLAUSE_IN_NON_SDK_CODE, node);
     }
     return super.visitNativeClause(node);
   }

   @override
   Object visitNativeFunctionBody(NativeFunctionBody node) {
     _checkForNativeFunctionBodyInNonSDKCode(node);
     return super.visitNativeFunctionBody(node);
   }

   @override
   Object visitPostfixExpression(PostfixExpression node) {
     _checkForAssignmentToFinal(node.operand);
     _checkForIntNotAssignable(node.operand);
     return super.visitPostfixExpression(node);
   }

   @override
   Object visitPrefixedIdentifier(PrefixedIdentifier node) {
     if (node.parent is! Annotation) {
       ClassElement typeReference =
           ElementResolver.getTypeReference(node.prefix);
       SimpleIdentifier name = node.identifier;
       _checkForStaticAccessToInstanceMember(typeReference, name);
       _checkForInstanceAccessToStaticMember(typeReference, name);
     }
     return super.visitPrefixedIdentifier(node);
   }

   @override
   Object visitPrefixExpression(PrefixExpression node) {
     sc.TokenType operatorType = node.operator.type;
     Expression operand = node.operand;
     if (operatorType == sc.TokenType.BANG) {
       _checkForNonBoolNegationExpression(operand);
     } else if (operatorType.isIncrementOperator) {
       _checkForAssignmentToFinal(operand);
     }
     _checkForIntNotAssignable(operand);
     return super.visitPrefixExpression(node);
   }

   @override
   Object visitPropertyAccess(PropertyAccess node) {
     bool isConditional = node.operator.type == sc.TokenType.QUESTION_PERIOD;
     ClassElement typeReference =
         ElementResolver.getTypeReference(node.realTarget);
     SimpleIdentifier propertyName = node.propertyName;
     _checkForStaticAccessToInstanceMember(typeReference, propertyName);
     _checkForInstanceAccessToStaticMember(typeReference, propertyName);
     return super.visitPropertyAccess(node);
   }

   @override
   Object visitRedirectingConstructorInvocation(
       RedirectingConstructorInvocation node) {
     _isInConstructorInitializer = true;
     try {
       return super.visitRedirectingConstructorInvocation(node);
     } finally {
       _isInConstructorInitializer = false;
     }
   }

   @override
   Object visitRethrowExpression(RethrowExpression node) {
     _checkForRethrowOutsideCatch(node);
     return super.visitRethrowExpression(node);
   }

   @override
   Object visitReturnStatement(ReturnStatement node) {
     if (node.expression == null) {
       _returnsWithout.add(node);
     } else {
       _returnsWith.add(node);
     }
     _checkForAllReturnStatementErrorCodes(node);
     return super.visitReturnStatement(node);
   }

   @override
   Object visitSimpleFormalParameter(SimpleFormalParameter node) {
     _checkForConstFormalParameter(node);
     _checkForPrivateOptionalParameter(node);
     _checkForTypeAnnotationDeferredClass(node.type);
     return super.visitSimpleFormalParameter(node);
   }

   @override
   Object visitSimpleIdentifier(SimpleIdentifier node) {
     _checkForImplicitThisReferenceInInitializer(node);
     if (!_isUnqualifiedReferenceToNonLocalStaticMemberAllowed(node)) {
       _checkForUnqualifiedReferenceToNonLocalStaticMember(node);
     }
     return super.visitSimpleIdentifier(node);
   }

   @override
   Object visitSuperConstructorInvocation(SuperConstructorInvocation node) {
     _isInConstructorInitializer = true;
     try {
       return super.visitSuperConstructorInvocation(node);
     } finally {
       _isInConstructorInitializer = false;
     }
   }

   @override
   Object visitSwitchStatement(SwitchStatement node) {
     _checkForSwitchExpressionNotAssignable(node);
     _checkForCaseBlocksNotTerminated(node);
     _checkForMissingEnumConstantInSwitch(node);
     return super.visitSwitchStatement(node);
   }

   @override
   Object visitThisExpression(ThisExpression node) {
     _checkForInvalidReferenceToThis(node);
     return super.visitThisExpression(node);
   }

   @override
   Object visitThrowExpression(ThrowExpression node) {
     _checkForConstEvalThrowsException(node);
     return super.visitThrowExpression(node);
   }

   @override
   Object visitTopLevelVariableDeclaration(TopLevelVariableDeclaration node) {
     _checkForFinalNotInitialized(node.variables);
     return super.visitTopLevelVariableDeclaration(node);
   }

   @override
   Object visitTypeArgumentList(TypeArgumentList node) {
     NodeList<TypeName> list = node.arguments;
     for (TypeName typeName in list) {
       _checkForTypeAnnotationDeferredClass(typeName);
     }
     return super.visitTypeArgumentList(node);
   }

   @override
   Object visitTypeName(TypeName node) {
     _checkForTypeArgumentNotMatchingBounds(node);
     _checkForTypeParameterReferencedByStatic(node);
     return super.visitTypeName(node);
   }

   @override
   Object visitTypeParameter(TypeParameter node) {
     _checkForBuiltInIdentifierAsName(node.name,
         CompileTimeErrorCode.BUILT_IN_IDENTIFIER_AS_TYPE_PARAMETER_NAME);
     _checkForTypeParameterSupertypeOfItsBound(node);
     _checkForTypeAnnotationDeferredClass(node.bound);
     return super.visitTypeParameter(node);
   }

   @override
   Object visitVariableDeclaration(VariableDeclaration node) {
     SimpleIdentifier nameNode = node.name;
     Expression initializerNode = node.initializer;
     // do checks
     _checkForInvalidAssignment(nameNode, initializerNode);
     // visit name
     nameNode.accept(this);
     // visit initializer
     String name = nameNode.name;
     _namesForReferenceToDeclaredVariableInInitializer.add(name);
     bool wasInInstanceVariableInitializer = _isInInstanceVariableInitializer;
     _isInInstanceVariableInitializer = _isInInstanceVariableDeclaration;
     try {
       if (initializerNode != null) {
         initializerNode.accept(this);
       }
     } finally {
       _isInInstanceVariableInitializer = wasInInstanceVariableInitializer;
       _namesForReferenceToDeclaredVariableInInitializer.remove(name);
     }
     // done
     return null;
   }

   @override
   Object visitVariableDeclarationList(VariableDeclarationList node) {
     _checkForTypeAnnotationDeferredClass(node.type);
     return super.visitVariableDeclarationList(node);
   }

   @override
   Object visitVariableDeclarationStatement(VariableDeclarationStatement node) {
     _checkForFinalNotInitialized(node.variables);
     return super.visitVariableDeclarationStatement(node);
   }

   @override
   Object visitWhileStatement(WhileStatement node) {
     _checkForNonBoolCondition(node.condition);
     return super.visitWhileStatement(node);
   }

   @override
   Object visitYieldStatement(YieldStatement node) {
     if (_inGenerator) {
       _checkForYieldOfInvalidType(node.expression, node.star != null);
     } else {
       CompileTimeErrorCode errorCode;
       if (node.star != null) {
         errorCode = CompileTimeErrorCode.YIELD_EACH_IN_NON_GENERATOR;
       } else {
         errorCode = CompileTimeErrorCode.YIELD_IN_NON_GENERATOR;
       }
       _errorReporter.reportErrorForNode(errorCode, node);
     }
     return super.visitYieldStatement(node);
   }

   /**
    * Verify that the given list of [typeArguments] contains exactly two
    * elements.
    *
    * See [StaticTypeWarningCode.EXPECTED_TWO_MAP_TYPE_ARGUMENTS].
    */
   bool _checkExpectedTwoMapTypeArguments(TypeArgumentList typeArguments) {
     // check number of type arguments
     int num = typeArguments.arguments.length;
     if (num == 2) {
       return false;
     }
     // report problem
     _errorReporter.reportErrorForNode(
         StaticTypeWarningCode.EXPECTED_TWO_MAP_TYPE_ARGUMENTS,
         typeArguments,
         [num]);
     return true;
   }

   /**
    * Verify that the given [constructor] declaration does not violate any of the
    * error codes relating to the initialization of fields in the enclosing
    * class.
    *
    * See [_initialFieldElementsMap],
    * [StaticWarningCode.FINAL_INITIALIZED_IN_DECLARATION_AND_CONSTRUCTOR], and
    * [CompileTimeErrorCode.FINAL_INITIALIZED_MULTIPLE_TIMES].
    */
   bool _checkForAllFinalInitializedErrorCodes(
       ConstructorDeclaration constructor) {
     if (constructor.factoryKeyword != null ||
         constructor.redirectedConstructor != null ||
         constructor.externalKeyword != null) {
       return false;
     }
     // Ignore if native class.
     if (_isInNativeClass) {
       return false;
     }
     bool foundError = false;
     HashMap<FieldElement, INIT_STATE> fieldElementsMap =
         new HashMap<FieldElement, INIT_STATE>.from(_initialFieldElementsMap);
     // Visit all of the field formal parameters
     NodeList<FormalParameter> formalParameters =
         constructor.parameters.parameters;
     for (FormalParameter formalParameter in formalParameters) {
       FormalParameter parameter = formalParameter;
       if (parameter is DefaultFormalParameter) {
         parameter = (parameter as DefaultFormalParameter).parameter;
       }
       if (parameter is FieldFormalParameter) {
         FieldElement fieldElement =
             (parameter.element as FieldFormalParameterElementImpl).field;
         INIT_STATE state = fieldElementsMap[fieldElement];
         if (state == INIT_STATE.NOT_INIT) {
           fieldElementsMap[fieldElement] = INIT_STATE.INIT_IN_FIELD_FORMAL;
         } else if (state == INIT_STATE.INIT_IN_DECLARATION) {
           if (fieldElement.isFinal || fieldElement.isConst) {
             _errorReporter.reportErrorForNode(
                 StaticWarningCode.FINAL_INITIALIZED_IN_DECLARATION_AND_CONSTRUCTOR,
                 formalParameter.identifier,
                 [fieldElement.displayName]);
             foundError = true;
           }
         } else if (state == INIT_STATE.INIT_IN_FIELD_FORMAL) {
           if (fieldElement.isFinal || fieldElement.isConst) {
             _errorReporter.reportErrorForNode(
                 CompileTimeErrorCode.FINAL_INITIALIZED_MULTIPLE_TIMES,
                 formalParameter.identifier,
                 [fieldElement.displayName]);
             foundError = true;
           }
         }
       }
     }
     // Visit all of the initializers
     NodeList<ConstructorInitializer> initializers = constructor.initializers;
     for (ConstructorInitializer constructorInitializer in initializers) {
       if (constructorInitializer is RedirectingConstructorInvocation) {
         return false;
       }
       if (constructorInitializer is ConstructorFieldInitializer) {
         ConstructorFieldInitializer constructorFieldInitializer =
             constructorInitializer;
         SimpleIdentifier fieldName = constructorFieldInitializer.fieldName;
         Element element = fieldName.staticElement;
         if (element is FieldElement) {
           FieldElement fieldElement = element;
           INIT_STATE state = fieldElementsMap[fieldElement];
           if (state == INIT_STATE.NOT_INIT) {
             fieldElementsMap[fieldElement] = INIT_STATE.INIT_IN_INITIALIZERS;
           } else if (state == INIT_STATE.INIT_IN_DECLARATION) {
             if (fieldElement.isFinal || fieldElement.isConst) {
               _errorReporter.reportErrorForNode(
                   StaticWarningCode.FIELD_INITIALIZED_IN_INITIALIZER_AND_DECLARATION,
                   fieldName);
               foundError = true;
             }
           } else if (state == INIT_STATE.INIT_IN_FIELD_FORMAL) {
             _errorReporter.reportErrorForNode(
                 CompileTimeErrorCode.FIELD_INITIALIZED_IN_PARAMETER_AND_INITIALIZER,
                 fieldName);
             foundError = true;
           } else if (state == INIT_STATE.INIT_IN_INITIALIZERS) {
             _errorReporter.reportErrorForNode(
                 CompileTimeErrorCode.FIELD_INITIALIZED_BY_MULTIPLE_INITIALIZERS,
                 fieldName,
                 [fieldElement.displayName]);
             foundError = true;
           }
         }
       }
     }
     // Prepare a list of not initialized fields.
     List<FieldElement> notInitFinalFields = <FieldElement>[];
     fieldElementsMap.forEach((FieldElement fieldElement, INIT_STATE state) {
       if (state == INIT_STATE.NOT_INIT) {
         if (fieldElement.isFinal) {
           notInitFinalFields.add(fieldElement);
         }
       }
     });
     // Visit all of the states in the map to ensure that none were never
     // initialized.
     fieldElementsMap.forEach((FieldElement fieldElement, INIT_STATE state) {
       if (state == INIT_STATE.NOT_INIT) {
         if (fieldElement.isConst) {
           _errorReporter.reportErrorForNode(
               CompileTimeErrorCode.CONST_NOT_INITIALIZED,
               constructor.returnType,
               [fieldElement.name]);
           foundError = true;
         }
       }
     });
     if (notInitFinalFields.isNotEmpty) {
       foundError = true;
       AnalysisErrorWithProperties analysisError;
       if (notInitFinalFields.length == 1) {
         analysisError = _errorReporter.newErrorWithProperties(
             StaticWarningCode.FINAL_NOT_INITIALIZED_CONSTRUCTOR_1,
             constructor.returnType,
             [notInitFinalFields[0].name]);
       } else if (notInitFinalFields.length == 2) {
         analysisError = _errorReporter.newErrorWithProperties(
             StaticWarningCode.FINAL_NOT_INITIALIZED_CONSTRUCTOR_2,
             constructor.returnType,
             [notInitFinalFields[0].name, notInitFinalFields[1].name]);
       } else {
         analysisError = _errorReporter.newErrorWithProperties(
             StaticWarningCode.FINAL_NOT_INITIALIZED_CONSTRUCTOR_3_PLUS,
             constructor.returnType, [
           notInitFinalFields[0].name,
           notInitFinalFields[1].name,
           notInitFinalFields.length - 2
         ]);
       }
       analysisError.setProperty(
           ErrorProperty.NOT_INITIALIZED_FIELDS, notInitFinalFields);
       _errorReporter.reportError(analysisError);
     }
     return foundError;
   }

   /**
    * Check the given [executableElement] against override-error codes. The
    * [overriddenExecutable] is the element that the executable element is
    * overriding. The [parameters] is the parameters of the executable element.
    * The [errorNameTarget] is the node to report problems on.
    *
    * See [StaticWarningCode.INSTANCE_METHOD_NAME_COLLIDES_WITH_SUPERCLASS_STATIC],
    * [CompileTimeErrorCode.INVALID_OVERRIDE_REQUIRED],
    * [CompileTimeErrorCode.INVALID_OVERRIDE_POSITIONAL],
    * [CompileTimeErrorCode.INVALID_OVERRIDE_NAMED],
    * [StaticWarningCode.INVALID_GETTER_OVERRIDE_RETURN_TYPE],
    * [StaticWarningCode.INVALID_METHOD_OVERRIDE_RETURN_TYPE],
    * [StaticWarningCode.INVALID_METHOD_OVERRIDE_NORMAL_PARAM_TYPE],
    * [StaticWarningCode.INVALID_SETTER_OVERRIDE_NORMAL_PARAM_TYPE],
    * [StaticWarningCode.INVALID_METHOD_OVERRIDE_OPTIONAL_PARAM_TYPE],
    * [StaticWarningCode.INVALID_METHOD_OVERRIDE_NAMED_PARAM_TYPE], and
    * [StaticWarningCode.INVALID_OVERRIDE_DIFFERENT_DEFAULT_VALUES].
    */
   bool _checkForAllInvalidOverrideErrorCodes(
       ExecutableElement executableElement,
       ExecutableElement overriddenExecutable,
       List<ParameterElement> parameters,
       List<AstNode> parameterLocations,
       SimpleIdentifier errorNameTarget) {
     bool isGetter = false;
     bool isSetter = false;
     if (executableElement is PropertyAccessorElement) {
       PropertyAccessorElement accessorElement = executableElement;
       isGetter = accessorElement.isGetter;
       isSetter = accessorElement.isSetter;
     }
     String executableElementName = executableElement.name;
     FunctionType overridingFT = executableElement.type;
     FunctionType overriddenFT = overriddenExecutable.type;
     InterfaceType enclosingType = _enclosingClass.type;
     overriddenFT = _inheritanceManager
         .substituteTypeArgumentsInMemberFromInheritance(
             overriddenFT, executableElementName, enclosingType);
     if (overridingFT == null || overriddenFT == null) {
       return false;
     }
     DartType overridingFTReturnType = overridingFT.returnType;
     DartType overriddenFTReturnType = overriddenFT.returnType;
     List<DartType> overridingNormalPT = overridingFT.normalParameterTypes;
     List<DartType> overriddenNormalPT = overriddenFT.normalParameterTypes;
     List<DartType> overridingPositionalPT = overridingFT.optionalParameterTypes;
     List<DartType> overriddenPositionalPT = overriddenFT.optionalParameterTypes;
     Map<String, DartType> overridingNamedPT = overridingFT.namedParameterTypes;
     Map<String, DartType> overriddenNamedPT = overriddenFT.namedParameterTypes;
     // CTEC.INVALID_OVERRIDE_REQUIRED, CTEC.INVALID_OVERRIDE_POSITIONAL and
     // CTEC.INVALID_OVERRIDE_NAMED
     if (overridingNormalPT.length > overriddenNormalPT.length) {
       _errorReporter.reportErrorForNode(
           StaticWarningCode.INVALID_OVERRIDE_REQUIRED, errorNameTarget, [
         overriddenNormalPT.length,
         overriddenExecutable.enclosingElement.displayName
       ]);
       return true;
     }
     if (overridingNormalPT.length + overridingPositionalPT.length <
         overriddenPositionalPT.length + overriddenNormalPT.length) {
       _errorReporter.reportErrorForNode(
           StaticWarningCode.INVALID_OVERRIDE_POSITIONAL, errorNameTarget, [
         overriddenPositionalPT.length + overriddenNormalPT.length,
         overriddenExecutable.enclosingElement.displayName
       ]);
       return true;
     }
     // For each named parameter in the overridden method, verify that there is
     // the same name in the overriding method.
     for (String overriddenParamName in overriddenNamedPT.keys) {
       if (!overridingNamedPT.containsKey(overriddenParamName)) {
         // The overridden method expected the overriding method to have
         // overridingParamName, but it does not.
         _errorReporter.reportErrorForNode(
             StaticWarningCode.INVALID_OVERRIDE_NAMED, errorNameTarget, [
           overriddenParamName,
           overriddenExecutable.enclosingElement.displayName
         ]);
         return true;
       }
     }
     // SWC.INVALID_METHOD_OVERRIDE_RETURN_TYPE
     if (overriddenFTReturnType != VoidTypeImpl.instance &&
         !_typeSystem.isAssignableTo(
             overridingFTReturnType, overriddenFTReturnType)) {
       _errorReporter.reportTypeErrorForNode(
           !isGetter
               ? StaticWarningCode.INVALID_METHOD_OVERRIDE_RETURN_TYPE
               : StaticWarningCode.INVALID_GETTER_OVERRIDE_RETURN_TYPE,
           errorNameTarget,
           [
         overridingFTReturnType,
         overriddenFTReturnType,
         overriddenExecutable.enclosingElement.displayName
       ]);
       return true;
     }
     // SWC.INVALID_METHOD_OVERRIDE_NORMAL_PARAM_TYPE
     if (parameterLocations == null) {
       return false;
     }
     int parameterIndex = 0;
     for (int i = 0; i < overridingNormalPT.length; i++) {
       if (!_typeSystem.isAssignableTo(
           overridingNormalPT[i], overriddenNormalPT[i])) {
         _errorReporter.reportTypeErrorForNode(
             !isSetter
                 ? StaticWarningCode.INVALID_METHOD_OVERRIDE_NORMAL_PARAM_TYPE
                 : StaticWarningCode.INVALID_SETTER_OVERRIDE_NORMAL_PARAM_TYPE,
             parameterLocations[parameterIndex],
             [
           overridingNormalPT[i],
           overriddenNormalPT[i],
           overriddenExecutable.enclosingElement.displayName
         ]);
         return true;
       }
       parameterIndex++;
     }
     // SWC.INVALID_METHOD_OVERRIDE_OPTIONAL_PARAM_TYPE
     for (int i = 0; i < overriddenPositionalPT.length; i++) {
       if (!_typeSystem.isAssignableTo(
           overridingPositionalPT[i], overriddenPositionalPT[i])) {
         _errorReporter.reportTypeErrorForNode(
             StaticWarningCode.INVALID_METHOD_OVERRIDE_OPTIONAL_PARAM_TYPE,
             parameterLocations[parameterIndex], [
           overridingPositionalPT[i],
           overriddenPositionalPT[i],
           overriddenExecutable.enclosingElement.displayName
         ]);
         return true;
       }
       parameterIndex++;
     }
     // SWC.INVALID_METHOD_OVERRIDE_NAMED_PARAM_TYPE &
     // SWC.INVALID_OVERRIDE_DIFFERENT_DEFAULT_VALUES
     for (String overriddenName in overriddenNamedPT.keys) {
       DartType overridingType = overridingNamedPT[overriddenName];
       if (overridingType == null) {
         // Error, this is never reached- INVALID_OVERRIDE_NAMED would have been
         // created above if this could be reached.
         continue;
       }
       DartType overriddenType = overriddenNamedPT[overriddenName];
       if (!_typeSystem.isAssignableTo(overriddenType, overridingType)) {
         // lookup the parameter for the error to select
         ParameterElement parameterToSelect = null;
         AstNode parameterLocationToSelect = null;
         for (int i = 0; i < parameters.length; i++) {
           ParameterElement parameter = parameters[i];
           if (parameter.parameterKind == ParameterKind.NAMED &&
               overriddenName == parameter.name) {
             parameterToSelect = parameter;
             parameterLocationToSelect = parameterLocations[i];
             break;
           }
         }
         if (parameterToSelect != null) {
           _errorReporter.reportTypeErrorForNode(
               StaticWarningCode.INVALID_METHOD_OVERRIDE_NAMED_PARAM_TYPE,
               parameterLocationToSelect, [
             overridingType,
             overriddenType,
             overriddenExecutable.enclosingElement.displayName
           ]);
           return true;
         }
       }
     }
     // SWC.INVALID_OVERRIDE_DIFFERENT_DEFAULT_VALUES
     //
     // Create three lists: a list of the optional parameter ASTs
     // (FormalParameters), a list of the optional parameters elements from our
     // method, and finally a list of the optional parameter elements from the
     // method we are overriding.
     //
     bool foundError = false;
     List<AstNode> formalParameters = new List<AstNode>();
     List<ParameterElementImpl> parameterElts = new List<ParameterElementImpl>();
     List<ParameterElementImpl> overriddenParameterElts =
         new List<ParameterElementImpl>();
     List<ParameterElement> overriddenPEs = overriddenExecutable.parameters;
     for (int i = 0; i < parameters.length; i++) {
       ParameterElement parameter = parameters[i];
       if (parameter.parameterKind.isOptional) {
         formalParameters.add(parameterLocations[i]);
         parameterElts.add(parameter as ParameterElementImpl);
       }
     }
     for (ParameterElement parameterElt in overriddenPEs) {
       if (parameterElt.parameterKind.isOptional) {
         if (parameterElt is ParameterElementImpl) {
           overriddenParameterElts.add(parameterElt);
         }
       }
     }
     //
     // Next compare the list of optional parameter elements to the list of
     // overridden optional parameter elements.
     //
     if (parameterElts.length > 0) {
       if (parameterElts[0].parameterKind == ParameterKind.NAMED) {
         // Named parameters, consider the names when matching the parameterElts
         // to the overriddenParameterElts
         for (int i = 0; i < parameterElts.length; i++) {
           ParameterElementImpl parameterElt = parameterElts[i];
           EvaluationResultImpl result = parameterElt.evaluationResult;
           // TODO (jwren) Ignore Object types, see Dart bug 11287
           if (_isUserDefinedObject(result)) {
             continue;
           }
           String parameterName = parameterElt.name;
           for (int j = 0; j < overriddenParameterElts.length; j++) {
             ParameterElementImpl overriddenParameterElt =
                 overriddenParameterElts[j];
             if (overriddenParameterElt.initializer == null) {
               // There is no warning if the overridden parameter has an
               // implicit default.
               continue;
             }
             String overriddenParameterName = overriddenParameterElt.name;
             if (parameterName != null &&
                 parameterName == overriddenParameterName) {
               EvaluationResultImpl overriddenResult =
                   overriddenParameterElt.evaluationResult;
               if (_isUserDefinedObject(overriddenResult)) {
                 break;
               }
               if (!result.equalValues(_typeProvider, overriddenResult)) {
                 _errorReporter.reportErrorForNode(
                     StaticWarningCode.INVALID_OVERRIDE_DIFFERENT_DEFAULT_VALUES_NAMED,
                     formalParameters[i], [
                   overriddenExecutable.enclosingElement.displayName,
                   overriddenExecutable.displayName,
                   parameterName
                 ]);
                 foundError = true;
               }
             }
           }
         }
       } else {
         // Positional parameters, consider the positions when matching the
         // parameterElts to the overriddenParameterElts
         for (int i = 0;
             i < parameterElts.length && i < overriddenParameterElts.length;
             i++) {
           ParameterElementImpl parameterElt = parameterElts[i];
           EvaluationResultImpl result = parameterElt.evaluationResult;
           // TODO (jwren) Ignore Object types, see Dart bug 11287
           if (_isUserDefinedObject(result)) {
             continue;
           }
           ParameterElementImpl overriddenParameterElt =
               overriddenParameterElts[i];
           if (overriddenParameterElt.initializer == null) {
             // There is no warning if the overridden parameter has an implicit
             // default.
             continue;
           }
           EvaluationResultImpl overriddenResult =
               overriddenParameterElt.evaluationResult;
           if (_isUserDefinedObject(overriddenResult)) {
             continue;
           }
           if (!result.equalValues(_typeProvider, overriddenResult)) {
             _errorReporter.reportErrorForNode(
                 StaticWarningCode.INVALID_OVERRIDE_DIFFERENT_DEFAULT_VALUES_POSITIONAL,
                 formalParameters[i], [
               overriddenExecutable.enclosingElement.displayName,
               overriddenExecutable.displayName
             ]);
             foundError = true;
           }
         }
       }
     }
     return foundError;
   }

   /**
    * Check the given [executableElement] against override-error codes. This
    * method computes the given executableElement is overriding and calls
    * [_checkForAllInvalidOverrideErrorCodes] when the [InheritanceManager]
    * returns a [MultiplyInheritedExecutableElement], this method loops through
    * the list in the [MultiplyInheritedExecutableElement]. The [parameters] are
    * the parameters of the executable element. The [errorNameTarget] is the node
    * to report problems on.
    */
   bool _checkForAllInvalidOverrideErrorCodesForExecutable(
       ExecutableElement executableElement,
       List<ParameterElement> parameters,
       List<AstNode> parameterLocations,
       SimpleIdentifier errorNameTarget) {
     //
     // Compute the overridden executable from the InheritanceManager
     //
     List<ExecutableElement> overriddenExecutables = _inheritanceManager
         .lookupOverrides(_enclosingClass, executableElement.name);
     if (_checkForInstanceMethodNameCollidesWithSuperclassStatic(
         executableElement, errorNameTarget)) {
       return true;
     }
     for (ExecutableElement overriddenElement in overriddenExecutables) {
       if (_checkForAllInvalidOverrideErrorCodes(executableElement,
           overriddenElement, parameters, parameterLocations, errorNameTarget)) {
         return true;
       }
     }
     return false;
   }

   /**
    * Check the given field [declaration] against override-error codes.
    *
    * See [_checkForAllInvalidOverrideErrorCodes].
    */
   bool _checkForAllInvalidOverrideErrorCodesForField(
       FieldDeclaration declaration) {
     if (_enclosingClass == null || declaration.isStatic) {
       return false;
     }
     bool hasProblems = false;
     VariableDeclarationList fields = declaration.fields;
     for (VariableDeclaration field in fields.variables) {
       FieldElement element = field.element as FieldElement;
       if (element == null) {
         continue;
       }
       PropertyAccessorElement getter = element.getter;
       PropertyAccessorElement setter = element.setter;
       SimpleIdentifier fieldName = field.name;
       if (getter != null) {
         if (_checkForAllInvalidOverrideErrorCodesForExecutable(getter,
             ParameterElement.EMPTY_LIST, AstNode.EMPTY_LIST, fieldName)) {
           hasProblems = true;
         }
       }
       if (setter != null) {
         if (_checkForAllInvalidOverrideErrorCodesForExecutable(
             setter, setter.parameters, <AstNode>[fieldName], fieldName)) {
           hasProblems = true;
         }
       }
     }
     return hasProblems;
   }

   /**
    * Check the given [method] declaration against override-error codes.
    *
    * See [_checkForAllInvalidOverrideErrorCodes].
    */
   bool _checkForAllInvalidOverrideErrorCodesForMethod(
       MethodDeclaration method) {
     if (_enclosingClass == null ||
         method.isStatic ||
         method.body is NativeFunctionBody) {
       return false;
     }
     ExecutableElement executableElement = method.element;
     if (executableElement == null) {
       return false;
     }
     SimpleIdentifier methodName = method.name;
     if (methodName.isSynthetic) {
       return false;
     }
     FormalParameterList formalParameterList = method.parameters;
     NodeList<FormalParameter> parameterList =
         formalParameterList != null ? formalParameterList.parameters : null;
     List<AstNode> parameters =
         parameterList != null ? new List.from(parameterList) : null;
     return _checkForAllInvalidOverrideErrorCodesForExecutable(executableElement,
         executableElement.parameters, parameters, methodName);
   }

   /**
    * Verify that all classes of the given [withClause] are valid.
    *
    * See [CompileTimeErrorCode.MIXIN_DECLARES_CONSTRUCTOR],
    * [CompileTimeErrorCode.MIXIN_INHERITS_FROM_NOT_OBJECT], and
    * [CompileTimeErrorCode.MIXIN_REFERENCES_SUPER].
    */
   bool _checkForAllMixinErrorCodes(WithClause withClause) {
     if (withClause == null) {
       return false;
     }
     bool problemReported = false;
     for (TypeName mixinName in withClause.mixinTypes) {
       DartType mixinType = mixinName.type;
       if (mixinType is! InterfaceType) {
         continue;
       }
       if (_checkForExtendsOrImplementsDisallowedClass(
           mixinName, CompileTimeErrorCode.MIXIN_OF_DISALLOWED_CLASS)) {
         problemReported = true;
       } else {
         ClassElement mixinElement = (mixinType as InterfaceType).element;
         if (_checkForExtendsOrImplementsDeferredClass(
             mixinName, CompileTimeErrorCode.MIXIN_DEFERRED_CLASS)) {
           problemReported = true;
         }
         if (_checkForMixinDeclaresConstructor(mixinName, mixinElement)) {
           problemReported = true;
         }
         if (!enableSuperMixins &&
             _checkForMixinInheritsNotFromObject(mixinName, mixinElement)) {
           problemReported = true;
         }
         if (_checkForMixinReferencesSuper(mixinName, mixinElement)) {
           problemReported = true;
         }
       }
     }
     return problemReported;
   }

   /**
    * Check for errors related to the redirected constructors.
    *
    * See [StaticWarningCode.REDIRECT_TO_INVALID_RETURN_TYPE],
    * [StaticWarningCode.REDIRECT_TO_INVALID_FUNCTION_TYPE], and
    * [StaticWarningCode.REDIRECT_TO_MISSING_CONSTRUCTOR].
    */
   bool _checkForAllRedirectConstructorErrorCodes(
       ConstructorDeclaration declaration) {
     //
     // Prepare redirected constructor node
     //
     ConstructorName redirectedConstructor = declaration.redirectedConstructor;
     if (redirectedConstructor == null) {
       return false;
     }
     //
     // Prepare redirected constructor type
     //
     ConstructorElement redirectedElement = redirectedConstructor.staticElement;
     if (redirectedElement == null) {
       //
       // If the element is null, we check for the
       // REDIRECT_TO_MISSING_CONSTRUCTOR case
       //
       TypeName constructorTypeName = redirectedConstructor.type;
       DartType redirectedType = constructorTypeName.type;
       if (redirectedType != null &&
           redirectedType.element != null &&
           !redirectedType.isDynamic) {
         //
         // Prepare the constructor name
         //
         String constructorStrName = constructorTypeName.name.name;
         if (redirectedConstructor.name != null) {
           constructorStrName += ".${redirectedConstructor.name.name}";
         }
         ErrorCode errorCode = (declaration.constKeyword != null
             ? CompileTimeErrorCode.REDIRECT_TO_MISSING_CONSTRUCTOR
             : StaticWarningCode.REDIRECT_TO_MISSING_CONSTRUCTOR);
         _errorReporter.reportErrorForNode(errorCode, redirectedConstructor,
             [constructorStrName, redirectedType.displayName]);
         return true;
       }
       return false;
     }
     FunctionType redirectedType = redirectedElement.type;
     DartType redirectedReturnType = redirectedType.returnType;
     //
     // Report specific problem when return type is incompatible
     //
     FunctionType constructorType = declaration.element.type;
     DartType constructorReturnType = constructorType.returnType;
     if (!_typeSystem.isAssignableTo(
         redirectedReturnType, constructorReturnType)) {
       _errorReporter.reportErrorForNode(
           StaticWarningCode.REDIRECT_TO_INVALID_RETURN_TYPE,
           redirectedConstructor,
           [redirectedReturnType, constructorReturnType]);
       return true;
     }
     //
     // Check parameters
     //
     if (!_typeSystem.isSubtypeOf(redirectedType, constructorType)) {
       _errorReporter.reportErrorForNode(
           StaticWarningCode.REDIRECT_TO_INVALID_FUNCTION_TYPE,
           redirectedConstructor,
           [redirectedType, constructorType]);
       return true;
     }
     return false;
   }

   /**
    * Check that the return [statement] of the form <i>return e;</i> is not in a
    * generative constructor.
    *
    * Check that return statements without expressions are not in a generative
    * constructor and the return type is not assignable to `null`; that is, we
    * don't have `return;` if the enclosing method has a return type.
    *
    * Check that the return type matches the type of the declared return type in
    * the enclosing method or function.
    *
    * See [CompileTimeErrorCode.RETURN_IN_GENERATIVE_CONSTRUCTOR],
    * [StaticWarningCode.RETURN_WITHOUT_VALUE], and
    * [StaticTypeWarningCode.RETURN_OF_INVALID_TYPE].
    */
   bool _checkForAllReturnStatementErrorCodes(ReturnStatement statement) {
     FunctionType functionType =
         _enclosingFunction == null ? null : _enclosingFunction.type;
     DartType expectedReturnType = functionType == null
         ? DynamicTypeImpl.instance
         : functionType.returnType;
     Expression returnExpression = statement.expression;
     // RETURN_IN_GENERATIVE_CONSTRUCTOR
     bool isGenerativeConstructor = _enclosingFunction is ConstructorElement &&
         !(_enclosingFunction as ConstructorElement).isFactory;
     if (isGenerativeConstructor) {
       if (returnExpression == null) {
         return false;
       }
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.RETURN_IN_GENERATIVE_CONSTRUCTOR,
           returnExpression);
       return true;
     }
     // RETURN_WITHOUT_VALUE
     if (returnExpression == null) {
       if (_inGenerator ||
           _typeSystem.isAssignableTo(
               _computeReturnTypeForMethod(null), expectedReturnType)) {
         return false;
       }
       _hasReturnWithoutValue = true;
       _errorReporter.reportErrorForNode(
           StaticWarningCode.RETURN_WITHOUT_VALUE, statement);
       return true;
     } else if (_inGenerator) {
       // RETURN_IN_GENERATOR
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.RETURN_IN_GENERATOR, statement);
     }
     // RETURN_OF_INVALID_TYPE
     return _checkForReturnOfInvalidType(returnExpression, expectedReturnType);
   }

   /**
    * Verify that the export namespace of the given export [directive] does not
    * export any name already exported by another export directive. The
    * [exportElement] is the [ExportElement] retrieved from the node. If the
    * element in the node was `null`, then this method is not called. The
    * [exportedLibrary] is the library element containing the exported element.
    *
    * See [CompileTimeErrorCode.AMBIGUOUS_EXPORT].
    */
   bool _checkForAmbiguousExport(ExportDirective directive,
       ExportElement exportElement, LibraryElement exportedLibrary) {
     if (exportedLibrary == null) {
       return false;
     }
     // check exported names
     Namespace namespace =
         new NamespaceBuilder().createExportNamespaceForDirective(exportElement);
     Map<String, Element> definedNames = namespace.definedNames;
     for (String name in definedNames.keys) {
       Element element = definedNames[name];
       Element prevElement = _exportedElements[name];
       if (element != null && prevElement != null && prevElement != element) {
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.AMBIGUOUS_EXPORT, directive, [
           name,
           prevElement.library.definingCompilationUnit.displayName,
           element.library.definingCompilationUnit.displayName
         ]);
         return true;
       } else {
         _exportedElements[name] = element;
       }
     }
     return false;
   }

   /**
    * Verify that the given [expression] can be assigned to its corresponding
    * parameters. The [expectedStaticType] is the expected static type of the
    * parameter. The [actualStaticType] is the actual static type of the
    * argument.
    *
    * This method corresponds to
    * [BestPracticesVerifier.checkForArgumentTypeNotAssignable].
    *
    * See [StaticWarningCode.ARGUMENT_TYPE_NOT_ASSIGNABLE],
    * [CompileTimeErrorCode.LIST_ELEMENT_TYPE_NOT_ASSIGNABLE],
    * [StaticWarningCode.LIST_ELEMENT_TYPE_NOT_ASSIGNABLE],
    * [CompileTimeErrorCode.MAP_KEY_TYPE_NOT_ASSIGNABLE],
    * [CompileTimeErrorCode.MAP_VALUE_TYPE_NOT_ASSIGNABLE],
    * [StaticWarningCode.MAP_KEY_TYPE_NOT_ASSIGNABLE], and
    * [StaticWarningCode.MAP_VALUE_TYPE_NOT_ASSIGNABLE].
    */
   bool _checkForArgumentTypeNotAssignable(
       Expression expression,
       DartType expectedStaticType,
       DartType actualStaticType,
       ErrorCode errorCode) {
     //
     // Warning case: test static type information
     //
     if (actualStaticType != null && expectedStaticType != null) {
       if (!_typeSystem.isAssignableTo(actualStaticType, expectedStaticType)) {
         _errorReporter.reportTypeErrorForNode(
             errorCode, expression, [actualStaticType, expectedStaticType]);
         return true;
       }
     }
     return false;
   }

   /**
    * Verify that the given [argument] can be assigned to its corresponding
    * parameter.
    *
    * This method corresponds to
    * [BestPracticesVerifier.checkForArgumentTypeNotAssignableForArgument].
    *
    * See [StaticWarningCode.ARGUMENT_TYPE_NOT_ASSIGNABLE].
    */
   bool _checkForArgumentTypeNotAssignableForArgument(Expression argument) {
     if (argument == null) {
       return false;
     }
     ParameterElement staticParameterElement = argument.staticParameterElement;
     DartType staticParameterType =
         staticParameterElement == null ? null : staticParameterElement.type;
     return _checkForArgumentTypeNotAssignableWithExpectedTypes(argument,
         staticParameterType, StaticWarningCode.ARGUMENT_TYPE_NOT_ASSIGNABLE);
   }

   /**
    * Verify that the given [expression] can be assigned to its corresponding
    * parameters. The [expectedStaticType] is the expected static type.
    *
    * This method corresponds to
    * [BestPracticesVerifier.checkForArgumentTypeNotAssignableWithExpectedTypes].
    *
    * See [StaticWarningCode.ARGUMENT_TYPE_NOT_ASSIGNABLE],
    * [CompileTimeErrorCode.LIST_ELEMENT_TYPE_NOT_ASSIGNABLE],
    * [StaticWarningCode.LIST_ELEMENT_TYPE_NOT_ASSIGNABLE],
    * [CompileTimeErrorCode.MAP_KEY_TYPE_NOT_ASSIGNABLE],
    * [CompileTimeErrorCode.MAP_VALUE_TYPE_NOT_ASSIGNABLE],
    * [StaticWarningCode.MAP_KEY_TYPE_NOT_ASSIGNABLE], and
    * [StaticWarningCode.MAP_VALUE_TYPE_NOT_ASSIGNABLE].
    */
   bool _checkForArgumentTypeNotAssignableWithExpectedTypes(
           Expression expression,
           DartType expectedStaticType,
           ErrorCode errorCode) =>
       _checkForArgumentTypeNotAssignable(
           expression, expectedStaticType, getStaticType(expression), errorCode);

   /**
    * Verify that the arguments in the given [argumentList] can be assigned to
    * their corresponding parameters.
    *
    * This method corresponds to
    * [BestPracticesVerifier.checkForArgumentTypesNotAssignableInList].
    *
    * See [StaticWarningCode.ARGUMENT_TYPE_NOT_ASSIGNABLE].
    */
   bool _checkForArgumentTypesNotAssignableInList(ArgumentList argumentList) {
     if (argumentList == null) {
       return false;
     }
     bool problemReported = false;
     for (Expression argument in argumentList.arguments) {
       if (_checkForArgumentTypeNotAssignableForArgument(argument)) {
         problemReported = true;
       }
     }
     return problemReported;
   }

   /**
    * Check that the static type of the given expression is assignable to the
    * given type. If it isn't, report an error with the given error code. The
    * [type] is the type that the expression must be assignable to. The
    * [errorCode] is the error code to be reported. The [arguments] are the
    * arguments to pass in when creating the error.
    */
   bool _checkForAssignability(Expression expression, InterfaceType type,
       ErrorCode errorCode, List<Object> arguments) {
     if (expression == null) {
       return false;
     }
     DartType expressionType = expression.staticType;
     if (expressionType == null) {
       return false;
     }
     if (_typeSystem.isAssignableTo(expressionType, type)) {
       return false;
     }
     _errorReporter.reportErrorForNode(errorCode, expression, arguments);
     return true;
   }

   /**
    * Verify that the given [expression] is not final.
    *
    * See [StaticWarningCode.ASSIGNMENT_TO_CONST],
    * [StaticWarningCode.ASSIGNMENT_TO_FINAL], and
    * [StaticWarningCode.ASSIGNMENT_TO_METHOD].
    */
   bool _checkForAssignmentToFinal(Expression expression) {
     // prepare element
     Element element = null;
     AstNode highlightedNode = expression;
     if (expression is Identifier) {
       element = expression.staticElement;
       if (expression is PrefixedIdentifier) {
         highlightedNode = expression.identifier;
       }
     } else if (expression is PropertyAccess) {
       PropertyAccess propertyAccess = expression;
       element = propertyAccess.propertyName.staticElement;
       highlightedNode = propertyAccess.propertyName;
     }
     // check if element is assignable
     if (element is PropertyAccessorElement) {
       PropertyAccessorElement accessor = element as PropertyAccessorElement;
       element = accessor.variable;
     }
     if (element is VariableElement) {
       if (element.isConst) {
         _errorReporter.reportErrorForNode(
             StaticWarningCode.ASSIGNMENT_TO_CONST, expression);
         return true;
       }
       if (element.isFinal) {
         if (element is FieldElementImpl &&
             element.setter == null &&
             element.isSynthetic) {
           _errorReporter.reportErrorForNode(
               StaticWarningCode.ASSIGNMENT_TO_FINAL_NO_SETTER,
               highlightedNode,
               [element.name, element.enclosingElement.displayName]);
           return true;
         }
         _errorReporter.reportErrorForNode(StaticWarningCode.ASSIGNMENT_TO_FINAL,
             highlightedNode, [element.name]);
         return true;
       }
       return false;
     }
     if (element is FunctionElement) {
       _errorReporter.reportErrorForNode(
           StaticWarningCode.ASSIGNMENT_TO_FUNCTION, expression);
       return true;
     }
     if (element is MethodElement) {
       _errorReporter.reportErrorForNode(
           StaticWarningCode.ASSIGNMENT_TO_METHOD, expression);
       return true;
     }
     if (element is ClassElement ||
         element is FunctionTypeAliasElement ||
         element is TypeParameterElement) {
       _errorReporter.reportErrorForNode(
           StaticWarningCode.ASSIGNMENT_TO_TYPE, expression);
       return true;
     }
     return false;
   }

   /**
    * Verify that the given [identifier] is not a keyword, and generates the
    * given [errorCode] on the identifier if it is a keyword.
    *
    * See [CompileTimeErrorCode.BUILT_IN_IDENTIFIER_AS_TYPE_NAME],
    * [CompileTimeErrorCode.BUILT_IN_IDENTIFIER_AS_TYPE_PARAMETER_NAME], and
    * [CompileTimeErrorCode.BUILT_IN_IDENTIFIER_AS_TYPEDEF_NAME].
    */
   bool _checkForBuiltInIdentifierAsName(
       SimpleIdentifier identifier, ErrorCode errorCode) {
     sc.Token token = identifier.token;
     if (token.type == sc.TokenType.KEYWORD) {
       _errorReporter.reportErrorForNode(
           errorCode, identifier, [identifier.name]);
       return true;
     }
     return false;
   }

   /**
    * Verify that the given [switchCase] is terminated with 'break', 'continue',
    * 'return' or 'throw'.
    *
    * see [StaticWarningCode.CASE_BLOCK_NOT_TERMINATED].
    */
   bool _checkForCaseBlockNotTerminated(SwitchCase switchCase) {
     NodeList<Statement> statements = switchCase.statements;
     if (statements.isEmpty) {
       // fall-through without statements at all
       AstNode parent = switchCase.parent;
       if (parent is SwitchStatement) {
         SwitchStatement switchStatement = parent;
         NodeList<SwitchMember> members = switchStatement.members;
         int index = members.indexOf(switchCase);
         if (index != -1 && index < members.length - 1) {
           return false;
         }
       }
       // no other switch member after this one
     } else {
       Statement statement = statements[statements.length - 1];
       // terminated with statement
       if (statement is BreakStatement ||
           statement is ContinueStatement ||
           statement is ReturnStatement) {
         return false;
       }
       // terminated with 'throw' expression
       if (statement is ExpressionStatement) {
         Expression expression = statement.expression;
         if (expression is ThrowExpression) {
           return false;
         }
       }
     }
     // report error
     _errorReporter.reportErrorForToken(
         StaticWarningCode.CASE_BLOCK_NOT_TERMINATED, switchCase.keyword);
     return true;
   }

   /**
    * Verify that the switch cases in the given switch [statement] are terminated
    * with 'break', 'continue', 'return' or 'throw'.
    *
    * See [StaticWarningCode.CASE_BLOCK_NOT_TERMINATED].
    */
   bool _checkForCaseBlocksNotTerminated(SwitchStatement statement) {
     bool foundError = false;
     NodeList<SwitchMember> members = statement.members;
     int lastMember = members.length - 1;
     for (int i = 0; i < lastMember; i++) {
       SwitchMember member = members[i];
       if (member is SwitchCase && _checkForCaseBlockNotTerminated(member)) {
         foundError = true;
       }
     }
     return foundError;
   }

   /**
    * Verify that the given [method] declaration is abstract only if the
    * enclosing class is also abstract.
    *
    * See [StaticWarningCode.CONCRETE_CLASS_WITH_ABSTRACT_MEMBER].
    */
   bool _checkForConcreteClassWithAbstractMember(MethodDeclaration method) {
     if (method.isAbstract &&
         _enclosingClass != null &&
         !_enclosingClass.isAbstract) {
       SimpleIdentifier nameNode = method.name;
       String memberName = nameNode.name;
       ExecutableElement overriddenMember;
       if (method.isGetter) {
         overriddenMember = _enclosingClass.lookUpInheritedConcreteGetter(
             memberName, _currentLibrary);
       } else if (method.isSetter) {
         overriddenMember = _enclosingClass.lookUpInheritedConcreteSetter(
             memberName, _currentLibrary);
       } else {
         overriddenMember = _enclosingClass.lookUpInheritedConcreteMethod(
             memberName, _currentLibrary);
       }
       if (overriddenMember == null) {
         _errorReporter.reportErrorForNode(
             StaticWarningCode.CONCRETE_CLASS_WITH_ABSTRACT_MEMBER,
             nameNode,
             [memberName, _enclosingClass.displayName]);
         return true;
       }
     }
     return false;
   }

   /**
    * Verify all possible conflicts of the given [constructor]'s name with other
    * constructors and members of the same class. The [constructorElement] is the
    * constructor's element.
    *
    * See [CompileTimeErrorCode.DUPLICATE_CONSTRUCTOR_DEFAULT],
    * [CompileTimeErrorCode.DUPLICATE_CONSTRUCTOR_NAME],
    * [CompileTimeErrorCode.CONFLICTING_CONSTRUCTOR_NAME_AND_FIELD], and
    * [CompileTimeErrorCode.CONFLICTING_CONSTRUCTOR_NAME_AND_METHOD].
    */
   bool _checkForConflictingConstructorNameAndMember(
       ConstructorDeclaration constructor,
       ConstructorElement constructorElement) {
     SimpleIdentifier constructorName = constructor.name;
     String name = constructorElement.name;
     ClassElement classElement = constructorElement.enclosingElement;
     // constructors
     List<ConstructorElement> constructors = classElement.constructors;
     for (ConstructorElement otherConstructor in constructors) {
       if (identical(otherConstructor, constructorElement)) {
         continue;
       }
       if (name == otherConstructor.name) {
         if (name == null || name.length == 0) {
           _errorReporter.reportErrorForNode(
               CompileTimeErrorCode.DUPLICATE_CONSTRUCTOR_DEFAULT, constructor);
         } else {
           _errorReporter.reportErrorForNode(
               CompileTimeErrorCode.DUPLICATE_CONSTRUCTOR_NAME,
               constructor,
               [name]);
         }
         return true;
       }
     }
     // conflict with class member
     if (constructorName != null &&
         constructorElement != null &&
         !constructorName.isSynthetic) {
       // fields
       FieldElement field = classElement.getField(name);
       if (field != null) {
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.CONFLICTING_CONSTRUCTOR_NAME_AND_FIELD,
             constructor,
             [name]);
         return true;
       }
       // methods
       MethodElement method = classElement.getMethod(name);
       if (method != null) {
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.CONFLICTING_CONSTRUCTOR_NAME_AND_METHOD,
             constructor,
             [name]);
         return true;
       }
     }
     return false;
   }

   /**
    * Verify that the [_enclosingClass] does not have a method and getter pair
    * with the same name on, via inheritance.
    *
    * See [CompileTimeErrorCode.CONFLICTING_GETTER_AND_METHOD], and
    * [CompileTimeErrorCode.CONFLICTING_METHOD_AND_GETTER].
    */
   bool _checkForConflictingGetterAndMethod() {
     if (_enclosingClass == null) {
       return false;
     }
     bool hasProblem = false;
     // method declared in the enclosing class vs. inherited getter
     for (MethodElement method in _enclosingClass.methods) {
       String name = method.name;
       // find inherited property accessor (and can be only getter)
       ExecutableElement inherited =
           _inheritanceManager.lookupInheritance(_enclosingClass, name);
       if (inherited is! PropertyAccessorElement) {
         continue;
       }
       // report problem
       hasProblem = true;
       _errorReporter.reportErrorForElement(
           CompileTimeErrorCode.CONFLICTING_GETTER_AND_METHOD, method, [
         _enclosingClass.displayName,
         inherited.enclosingElement.displayName,
         name
       ]);
     }
     // getter declared in the enclosing class vs. inherited method
     for (PropertyAccessorElement accessor in _enclosingClass.accessors) {
       if (!accessor.isGetter) {
         continue;
       }
       String name = accessor.name;
       // find inherited method
       ExecutableElement inherited =
           _inheritanceManager.lookupInheritance(_enclosingClass, name);
       if (inherited is! MethodElement) {
         continue;
       }
       // report problem
       hasProblem = true;
       _errorReporter.reportErrorForElement(
           CompileTimeErrorCode.CONFLICTING_METHOD_AND_GETTER, accessor, [
         _enclosingClass.displayName,
         inherited.enclosingElement.displayName,
         name
       ]);
     }
     // done
     return hasProblem;
   }

   /**
    * Verify that the superclass of the [_enclosingClass] does not declare
    * accessible static members with the same name as the instance
    * getters/setters declared in [_enclosingClass].
    *
    * See [StaticWarningCode.CONFLICTING_INSTANCE_GETTER_AND_SUPERCLASS_MEMBER], and
    * [StaticWarningCode.CONFLICTING_INSTANCE_SETTER_AND_SUPERCLASS_MEMBER].
    */
   bool _checkForConflictingInstanceGetterAndSuperclassMember() {
     if (_enclosingClass == null) {
       return false;
     }
     InterfaceType enclosingType = _enclosingClass.type;
     // check every accessor
     bool hasProblem = false;
     for (PropertyAccessorElement accessor in _enclosingClass.accessors) {
       // we analyze instance accessors here
       if (accessor.isStatic) {
         continue;
       }
       // prepare accessor properties
       String name = accessor.displayName;
       bool getter = accessor.isGetter;
       // if non-final variable, ignore setter - we alreay reported problem for
       // getter
       if (accessor.isSetter && accessor.isSynthetic) {
         continue;
       }
       // try to find super element
       ExecutableElement superElement;
       superElement =
           enclosingType.lookUpGetterInSuperclass(name, _currentLibrary);
       if (superElement == null) {
         superElement =
             enclosingType.lookUpSetterInSuperclass(name, _currentLibrary);
       }
       if (superElement == null) {
         superElement =
             enclosingType.lookUpMethodInSuperclass(name, _currentLibrary);
       }
       if (superElement == null) {
         continue;
       }
       // OK, not static
       if (!superElement.isStatic) {
         continue;
       }
       // prepare "super" type to report its name
       ClassElement superElementClass =
           superElement.enclosingElement as ClassElement;
       InterfaceType superElementType = superElementClass.type;
       // report problem
       hasProblem = true;
       if (getter) {
         _errorReporter.reportErrorForElement(
             StaticWarningCode.CONFLICTING_INSTANCE_GETTER_AND_SUPERCLASS_MEMBER,
             accessor,
             [superElementType.displayName]);
       } else {
         _errorReporter.reportErrorForElement(
             StaticWarningCode.CONFLICTING_INSTANCE_SETTER_AND_SUPERCLASS_MEMBER,
             accessor,
             [superElementType.displayName]);
       }
     }
     // done
     return hasProblem;
   }

   /**
    * Verify that the enclosing class does not have a setter with the same name
    * as the given instance method declaration.
    *
    * TODO(jwren) add other "conflicting" error codes into algorithm/ data
    * structure.
    *
    * See [StaticWarningCode.CONFLICTING_INSTANCE_METHOD_SETTER].
    */
   bool _checkForConflictingInstanceMethodSetter(ClassDeclaration declaration) {
     // Reference all of the class members in this class.
     NodeList<ClassMember> classMembers = declaration.members;
     if (classMembers.isEmpty) {
       return false;
     }
     // Create a HashMap to track conflicting members, and then loop through
     // members in the class to construct the HashMap, at the same time,
     // look for violations.  Don't add members if they are part of a conflict,
     // this prevents multiple warnings for one issue.
     bool foundError = false;
     HashMap<String, ClassMember> memberHashMap =
         new HashMap<String, ClassMember>();
     for (ClassMember classMember in classMembers) {
       if (classMember is MethodDeclaration) {
         MethodDeclaration method = classMember;
         if (method.isStatic) {
           continue;
         }
         // prepare name
         SimpleIdentifier name = method.name;
         if (name == null) {
           continue;
         }
         bool addThisMemberToTheMap = true;
         bool isGetter = method.isGetter;
         bool isSetter = method.isSetter;
         bool isOperator = method.isOperator;
         bool isMethod = !isGetter && !isSetter && !isOperator;
         // Do lookups in the enclosing class (and the inherited member) if the
         // member is a method or a setter for
         // StaticWarningCode.CONFLICTING_INSTANCE_METHOD_SETTER warning.
         if (isMethod) {
           String setterName = "${name.name}=";
           Element enclosingElementOfSetter = null;
           ClassMember conflictingSetter = memberHashMap[setterName];
           if (conflictingSetter != null) {
             enclosingElementOfSetter =
                 conflictingSetter.element.enclosingElement;
           } else {
             ExecutableElement elementFromInheritance = _inheritanceManager
                 .lookupInheritance(_enclosingClass, setterName);
             if (elementFromInheritance != null) {
               enclosingElementOfSetter =
                   elementFromInheritance.enclosingElement;
             }
           }
           if (enclosingElementOfSetter != null) {
             // report problem
             _errorReporter.reportErrorForNode(
                 StaticWarningCode.CONFLICTING_INSTANCE_METHOD_SETTER, name, [
               _enclosingClass.displayName,
               name.name,
               enclosingElementOfSetter.displayName
             ]);
             foundError = true;
             addThisMemberToTheMap = false;
           }
         } else if (isSetter) {
           String methodName = name.name;
           ClassMember conflictingMethod = memberHashMap[methodName];
           if (conflictingMethod != null &&
               conflictingMethod is MethodDeclaration &&
               !conflictingMethod.isGetter) {
             // report problem
             _errorReporter.reportErrorForNode(
                 StaticWarningCode.CONFLICTING_INSTANCE_METHOD_SETTER2,
                 name,
                 [_enclosingClass.displayName, name.name]);
             foundError = true;
             addThisMemberToTheMap = false;
           }
         }
         // Finally, add this member into the HashMap.
         if (addThisMemberToTheMap) {
           if (method.isSetter) {
             memberHashMap["${name.name}="] = method;
           } else {
             memberHashMap[name.name] = method;
           }
         }
       }
     }
     return foundError;
   }

   /**
    * Verify that the enclosing class does not have an instance member with the
    * same name as the given static [method] declaration.
    *
    * See [StaticWarningCode.CONFLICTING_STATIC_GETTER_AND_INSTANCE_SETTER].
    */
   bool _checkForConflictingStaticGetterAndInstanceSetter(
       MethodDeclaration method) {
     if (!method.isStatic) {
       return false;
     }
     // prepare name
     SimpleIdentifier nameNode = method.name;
     if (nameNode == null) {
       return false;
     }
     String name = nameNode.name;
     // prepare enclosing type
     if (_enclosingClass == null) {
       return false;
     }
     InterfaceType enclosingType = _enclosingClass.type;
     // try to find setter
     ExecutableElement setter =
         enclosingType.lookUpSetter(name, _currentLibrary);
     if (setter == null) {
       return false;
     }
     // OK, also static
     if (setter.isStatic) {
       return false;
     }
     // prepare "setter" type to report its name
     ClassElement setterClass = setter.enclosingElement as ClassElement;
     InterfaceType setterType = setterClass.type;
     // report problem
     _errorReporter.reportErrorForNode(
         StaticWarningCode.CONFLICTING_STATIC_GETTER_AND_INSTANCE_SETTER,
         nameNode,
         [setterType.displayName]);
     return true;
   }

   /**
    * Verify that the enclosing class does not have an instance member with the
    * same name as the given static [method] declaration.
    *
    * See [StaticWarningCode.CONFLICTING_STATIC_SETTER_AND_INSTANCE_MEMBER].
    */
   bool _checkForConflictingStaticSetterAndInstanceMember(
       MethodDeclaration method) {
     if (!method.isStatic) {
       return false;
     }
     // prepare name
     SimpleIdentifier nameNode = method.name;
     if (nameNode == null) {
       return false;
     }
     String name = nameNode.name;
     // prepare enclosing type
     if (_enclosingClass == null) {
       return false;
     }
     InterfaceType enclosingType = _enclosingClass.type;
     // try to find member
     ExecutableElement member;
     member = enclosingType.lookUpMethod(name, _currentLibrary);
     if (member == null) {
       member = enclosingType.lookUpGetter(name, _currentLibrary);
     }
     if (member == null) {
       member = enclosingType.lookUpSetter(name, _currentLibrary);
     }
     if (member == null) {
       return false;
     }
     // OK, also static
     if (member.isStatic) {
       return false;
     }
     // prepare "member" type to report its name
     ClassElement memberClass = member.enclosingElement as ClassElement;
     InterfaceType memberType = memberClass.type;
     // report problem
     _errorReporter.reportErrorForNode(
         StaticWarningCode.CONFLICTING_STATIC_SETTER_AND_INSTANCE_MEMBER,
         nameNode,
         [memberType.displayName]);
     return true;
   }

   /**
    * Verify all conflicts between type variable and enclosing class.
    * TODO(scheglov)
    *
    * See [CompileTimeErrorCode.CONFLICTING_TYPE_VARIABLE_AND_CLASS], and
    * [CompileTimeErrorCode.CONFLICTING_TYPE_VARIABLE_AND_MEMBER].
    */
   bool _checkForConflictingTypeVariableErrorCodes(
       ClassDeclaration declaration) {
     bool problemReported = false;
     for (TypeParameterElement typeParameter in _enclosingClass.typeParameters) {
       String name = typeParameter.name;
       // name is same as the name of the enclosing class
       if (_enclosingClass.name == name) {
         _errorReporter.reportErrorForElement(
             CompileTimeErrorCode.CONFLICTING_TYPE_VARIABLE_AND_CLASS,
             typeParameter,
             [name]);
         problemReported = true;
       }
       // check members
       if (_enclosingClass.getMethod(name) != null ||
           _enclosingClass.getGetter(name) != null ||
           _enclosingClass.getSetter(name) != null) {
         _errorReporter.reportErrorForElement(
             CompileTimeErrorCode.CONFLICTING_TYPE_VARIABLE_AND_MEMBER,
             typeParameter,
             [name]);
         problemReported = true;
       }
     }
     return problemReported;
   }

   /**
    * Verify that if the given [constructor] declaration is 'const' then there
    * are no invocations of non-'const' super constructors.
    *
    * See [CompileTimeErrorCode.CONST_CONSTRUCTOR_WITH_NON_CONST_SUPER].
    */
   bool _checkForConstConstructorWithNonConstSuper(
       ConstructorDeclaration constructor) {
     if (!_isEnclosingConstructorConst) {
       return false;
     }
     // OK, const factory, checked elsewhere
     if (constructor.factoryKeyword != null) {
       return false;
     }
     // check for mixins
     if (_enclosingClass.mixins.length != 0) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.CONST_CONSTRUCTOR_WITH_MIXIN,
           constructor.returnType);
       return true;
     }
     // try to find and check super constructor invocation
     for (ConstructorInitializer initializer in constructor.initializers) {
       if (initializer is SuperConstructorInvocation) {
         SuperConstructorInvocation superInvocation = initializer;
         ConstructorElement element = superInvocation.staticElement;
         if (element == null || element.isConst) {
           return false;
         }
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.CONST_CONSTRUCTOR_WITH_NON_CONST_SUPER,
             superInvocation,
             [element.enclosingElement.displayName]);
         return true;
       }
     }
     // no explicit super constructor invocation, check default constructor
     InterfaceType supertype = _enclosingClass.supertype;
     if (supertype == null) {
       return false;
     }
     if (supertype.isObject) {
       return false;
     }
     ConstructorElement unnamedConstructor =
         supertype.element.unnamedConstructor;
     if (unnamedConstructor == null) {
       return false;
     }
     if (unnamedConstructor.isConst) {
       return false;
     }
     // default constructor is not 'const', report problem
     _errorReporter.reportErrorForNode(
         CompileTimeErrorCode.CONST_CONSTRUCTOR_WITH_NON_CONST_SUPER,
         constructor.returnType,
         [supertype.displayName]);
     return true;
   }

   /**
    * Verify that if the given [constructor] declaration is 'const' then there
    * are no non-final instance variable. The [constructorElement] is the
    * constructor element.
    *
    * See [CompileTimeErrorCode.CONST_CONSTRUCTOR_WITH_NON_FINAL_FIELD].
    */
   bool _checkForConstConstructorWithNonFinalField(
       ConstructorDeclaration constructor,
       ConstructorElement constructorElement) {
     if (!_isEnclosingConstructorConst) {
       return false;
     }
     // check if there is non-final field
     ClassElement classElement = constructorElement.enclosingElement;
     if (!classElement.hasNonFinalField) {
       return false;
     }
     // report problem
     _errorReporter.reportErrorForNode(
         CompileTimeErrorCode.CONST_CONSTRUCTOR_WITH_NON_FINAL_FIELD,
         constructor);
     return true;
   }

   /**
    * Verify that the given 'const' instance creation [expression] is not
    * creating a deferred type. The [constructorName] is the constructor name,
    * always non-`null`. The [typeName] is the name of the type defining the
    * constructor, always non-`null`.
    *
    * See [CompileTimeErrorCode.CONST_DEFERRED_CLASS].
    */
   bool _checkForConstDeferredClass(InstanceCreationExpression expression,
       ConstructorName constructorName, TypeName typeName) {
     if (typeName.isDeferred) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.CONST_DEFERRED_CLASS,
           constructorName,
           [typeName.name.name]);
       return true;
     }
     return false;
   }

   /**
    * Verify that the given throw [expression] is not enclosed in a 'const'
    * constructor declaration.
    *
    * See [CompileTimeErrorCode.CONST_CONSTRUCTOR_THROWS_EXCEPTION].
    */
   bool _checkForConstEvalThrowsException(ThrowExpression expression) {
     if (_isEnclosingConstructorConst) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.CONST_CONSTRUCTOR_THROWS_EXCEPTION, expression);
       return true;
     }
     return false;
   }

   /**
    * Verify that the given normal formal [parameter] is not 'const'.
    *
    * See [CompileTimeErrorCode.CONST_FORMAL_PARAMETER].
    */
   bool _checkForConstFormalParameter(NormalFormalParameter parameter) {
     if (parameter.isConst) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.CONST_FORMAL_PARAMETER, parameter);
       return true;
     }
     return false;
   }

   /**
    * Verify that the given instance creation [expression] is not being invoked
    * on an abstract class. The [typeName] is the [TypeName] of the
    * [ConstructorName] from the [InstanceCreationExpression], this is the AST
    * node that the error is attached to. The [type] is the type being
    * constructed with this [InstanceCreationExpression].
    *
    * See [StaticWarningCode.CONST_WITH_ABSTRACT_CLASS], and
    * [StaticWarningCode.NEW_WITH_ABSTRACT_CLASS].
    */
   bool _checkForConstOrNewWithAbstractClass(
       InstanceCreationExpression expression,
       TypeName typeName,
       InterfaceType type) {
     if (type.element.isAbstract) {
       ConstructorElement element = expression.staticElement;
       if (element != null && !element.isFactory) {
         if ((expression.keyword as sc.KeywordToken).keyword ==
             sc.Keyword.CONST) {
           _errorReporter.reportErrorForNode(
               StaticWarningCode.CONST_WITH_ABSTRACT_CLASS, typeName);
         } else {
           _errorReporter.reportErrorForNode(
               StaticWarningCode.NEW_WITH_ABSTRACT_CLASS, typeName);
         }
         return true;
       }
     }
     return false;
   }

   /**
    * Verify that the given instance creation [expression] is not being invoked
    * on an enum. The [typeName] is the [TypeName] of the [ConstructorName] from
    * the [InstanceCreationExpression], this is the AST node that the error is
    * attached to. The [type] is the type being constructed with this
    * [InstanceCreationExpression].
    *
    * See [CompileTimeErrorCode.INSTANTIATE_ENUM].
    */
   bool _checkForConstOrNewWithEnum(InstanceCreationExpression expression,
       TypeName typeName, InterfaceType type) {
     if (type.element.isEnum) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.INSTANTIATE_ENUM, typeName);
       return true;
     }
     return false;
   }

   /**
    * Verify that the given 'const' instance creation [expression] is not being
    * invoked on a constructor that is not 'const'.
    *
    * This method assumes that the instance creation was tested to be 'const'
    * before being called.
    *
    * See [CompileTimeErrorCode.CONST_WITH_NON_CONST].
    */
   bool _checkForConstWithNonConst(InstanceCreationExpression expression) {
     ConstructorElement constructorElement = expression.staticElement;
     if (constructorElement != null && !constructorElement.isConst) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.CONST_WITH_NON_CONST, expression);
       return true;
     }
     return false;
   }

   /**
    * Verify that the given [typeName] does not reference any type parameters.
    *
    * See [CompileTimeErrorCode.CONST_WITH_TYPE_PARAMETERS].
    */
   bool _checkForConstWithTypeParameters(TypeName typeName) {
     // something wrong with AST
     if (typeName == null) {
       return false;
     }
     Identifier name = typeName.name;
     if (name == null) {
       return false;
     }
     // should not be a type parameter
     if (name.staticElement is TypeParameterElement) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.CONST_WITH_TYPE_PARAMETERS, name);
     }
     // check type arguments
     TypeArgumentList typeArguments = typeName.typeArguments;
     if (typeArguments != null) {
       bool hasError = false;
       for (TypeName argument in typeArguments.arguments) {
         if (_checkForConstWithTypeParameters(argument)) {
           hasError = true;
         }
       }
       return hasError;
     }
     // OK
     return false;
   }

   /**
    * Verify that if the given 'const' instance creation [expression] is being
    * invoked on the resolved constructor. The [constructorName] is the
    * constructor name, always non-`null`. The [typeName] is the name of the type
    * defining the constructor, always non-`null`.
    *
    * This method assumes that the instance creation was tested to be 'const'
    * before being called.
    *
    * See [CompileTimeErrorCode.CONST_WITH_UNDEFINED_CONSTRUCTOR], and
    * [CompileTimeErrorCode.CONST_WITH_UNDEFINED_CONSTRUCTOR_DEFAULT].
    */
   bool _checkForConstWithUndefinedConstructor(
       InstanceCreationExpression expression,
       ConstructorName constructorName,
       TypeName typeName) {
     // OK if resolved
     if (expression.staticElement != null) {
       return false;
     }
     DartType type = typeName.type;
     if (type is InterfaceType) {
       ClassElement element = type.element;
       if (element != null && element.isEnum) {
         // We have already reported the error.
         return false;
       }
     }
     Identifier className = typeName.name;
     // report as named or default constructor absence
     SimpleIdentifier name = constructorName.name;
     if (name != null) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.CONST_WITH_UNDEFINED_CONSTRUCTOR,
           name,
           [className, name]);
     } else {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.CONST_WITH_UNDEFINED_CONSTRUCTOR_DEFAULT,
           constructorName,
           [className]);
     }
     return true;
   }

   /**
    * Verify that there are no default parameters in the given function type
    * [alias].
    *
    * See [CompileTimeErrorCode.DEFAULT_VALUE_IN_FUNCTION_TYPE_ALIAS].
    */
   bool _checkForDefaultValueInFunctionTypeAlias(FunctionTypeAlias alias) {
     bool result = false;
     FormalParameterList formalParameterList = alias.parameters;
     NodeList<FormalParameter> parameters = formalParameterList.parameters;
     for (FormalParameter formalParameter in parameters) {
       if (formalParameter is DefaultFormalParameter) {
         DefaultFormalParameter defaultFormalParameter = formalParameter;
         if (defaultFormalParameter.defaultValue != null) {
           _errorReporter.reportErrorForNode(
               CompileTimeErrorCode.DEFAULT_VALUE_IN_FUNCTION_TYPE_ALIAS, alias);
           result = true;
         }
       }
     }
     return result;
   }

   /**
    * Verify that the given default formal [parameter] is not part of a function
    * typed parameter.
    *
    * See [CompileTimeErrorCode.DEFAULT_VALUE_IN_FUNCTION_TYPED_PARAMETER].
    */
   bool _checkForDefaultValueInFunctionTypedParameter(
       DefaultFormalParameter parameter) {
     // OK, not in a function typed parameter.
     if (!_isInFunctionTypedFormalParameter) {
       return false;
     }
     // OK, no default value.
     if (parameter.defaultValue == null) {
       return false;
     }
     // Report problem.
     _errorReporter.reportErrorForNode(
         CompileTimeErrorCode.DEFAULT_VALUE_IN_FUNCTION_TYPED_PARAMETER,
         parameter);
     return true;
   }

   /**
    * Verify that any deferred imports in the given compilation [unit] have a
    * unique prefix.
    *
    * See [CompileTimeErrorCode.SHARED_DEFERRED_PREFIX].
    */
   bool _checkForDeferredPrefixCollisions(CompilationUnit unit) {
     bool foundError = false;
     NodeList<Directive> directives = unit.directives;
     int count = directives.length;
     if (count > 0) {
       HashMap<PrefixElement, List<ImportDirective>> prefixToDirectivesMap =
           new HashMap<PrefixElement, List<ImportDirective>>();
       for (int i = 0; i < count; i++) {
         Directive directive = directives[i];
         if (directive is ImportDirective) {
           ImportDirective importDirective = directive;
           SimpleIdentifier prefix = importDirective.prefix;
           if (prefix != null) {
             Element element = prefix.staticElement;
             if (element is PrefixElement) {
               PrefixElement prefixElement = element;
               List<ImportDirective> elements =
                   prefixToDirectivesMap[prefixElement];
               if (elements == null) {
                 elements = new List<ImportDirective>();
                 prefixToDirectivesMap[prefixElement] = elements;
               }
               elements.add(importDirective);
             }
           }
         }
       }
       for (List<ImportDirective> imports in prefixToDirectivesMap.values) {
         if (_hasDeferredPrefixCollision(imports)) {
           foundError = true;
         }
       }
     }
     return foundError;
   }

   /**
    * Verify that the enclosing class does not have an instance member with the
    * given name of the static member.
    *
    * See [CompileTimeErrorCode.DUPLICATE_DEFINITION_INHERITANCE].
    */
   bool _checkForDuplicateDefinitionInheritance() {
     if (_enclosingClass == null) {
       return false;
     }
     bool hasProblem = false;
     for (ExecutableElement member in _enclosingClass.methods) {
       if (member.isStatic && _checkForDuplicateDefinitionOfMember(member)) {
         hasProblem = true;
       }
     }
     for (ExecutableElement member in _enclosingClass.accessors) {
       if (member.isStatic && _checkForDuplicateDefinitionOfMember(member)) {
         hasProblem = true;
       }
     }
     return hasProblem;
   }

   /**
    * Verify that the enclosing class does not have an instance member with the
    * given name of the [staticMember].
    *
    * See [CompileTimeErrorCode.DUPLICATE_DEFINITION_INHERITANCE].
    */
   bool _checkForDuplicateDefinitionOfMember(ExecutableElement staticMember) {
     // prepare name
     String name = staticMember.name;
     if (name == null) {
       return false;
     }
     // try to find member
     ExecutableElement inheritedMember =
         _inheritanceManager.lookupInheritance(_enclosingClass, name);
     if (inheritedMember == null) {
       return false;
     }
     // OK, also static
     if (inheritedMember.isStatic) {
       return false;
     }
     // determine the display name, use the extended display name if the
     // enclosing class of the inherited member is in a different source
     String displayName;
     Element enclosingElement = inheritedMember.enclosingElement;
     if (enclosingElement.source == _enclosingClass.source) {
       displayName = enclosingElement.displayName;
     } else {
       displayName = enclosingElement.getExtendedDisplayName(null);
     }
     // report problem
     _errorReporter.reportErrorForElement(
         CompileTimeErrorCode.DUPLICATE_DEFINITION_INHERITANCE,
         staticMember,
         [name, displayName]);
     return true;
   }

   /**
    * Verify that if the given list [literal] has type arguments then there is
    * exactly one. The [typeArguments] are the type arguments.
    *
    * See [StaticTypeWarningCode.EXPECTED_ONE_LIST_TYPE_ARGUMENTS].
    */
   bool _checkForExpectedOneListTypeArgument(
       ListLiteral literal, TypeArgumentList typeArguments) {
     // check number of type arguments
     int num = typeArguments.arguments.length;
     if (num == 1) {
       return false;
     }
     // report problem
     _errorReporter.reportErrorForNode(
         StaticTypeWarningCode.EXPECTED_ONE_LIST_TYPE_ARGUMENTS,
         typeArguments,
         [num]);
     return true;
   }

   /**
    * Verify that the given export [directive] has a unique name among other
    * exported libraries. The [exportElement] is the [ExportElement] retrieved
    * from the node, if the element in the node was `null`, then this method is
    * not called. The [exportedLibrary] is the library element containing the
    * exported element.
    *
    * See [CompileTimeErrorCode.EXPORT_DUPLICATED_LIBRARY_NAME].
    */
   bool _checkForExportDuplicateLibraryName(ExportDirective directive,
       ExportElement exportElement, LibraryElement exportedLibrary) {
     if (exportedLibrary == null) {
       return false;
     }
     String name = exportedLibrary.name;
     // check if there is other exported library with the same name
     LibraryElement prevLibrary = _nameToExportElement[name];
     if (prevLibrary != null) {
       if (prevLibrary != exportedLibrary) {
         if (!name.isEmpty) {
           _errorReporter.reportErrorForNode(
               StaticWarningCode.EXPORT_DUPLICATED_LIBRARY_NAMED, directive, [
             prevLibrary.definingCompilationUnit.displayName,
             exportedLibrary.definingCompilationUnit.displayName,
             name
           ]);
         }
         return true;
       }
     } else {
       _nameToExportElement[name] = exportedLibrary;
     }
     // OK
     return false;
   }

   /**
    * Check that if the visiting library is not system, then any given library
    * should not be SDK internal library. The [exportElement] is the
    * [ExportElement] retrieved from the node, if the element in the node was
    * `null`, then this method is not called.
    *
    * See [CompileTimeErrorCode.EXPORT_INTERNAL_LIBRARY].
    */
   bool _checkForExportInternalLibrary(
       ExportDirective directive, ExportElement exportElement) {
     if (_isInSystemLibrary) {
       return false;
     }
     // should be private
     DartSdk sdk = _currentLibrary.context.sourceFactory.dartSdk;
     String uri = exportElement.uri;
     SdkLibrary sdkLibrary = sdk.getSdkLibrary(uri);
     if (sdkLibrary == null) {
       return false;
     }
     if (!sdkLibrary.isInternal) {
       return false;
     }
     // report problem
     _errorReporter.reportErrorForNode(
         CompileTimeErrorCode.EXPORT_INTERNAL_LIBRARY,
         directive,
         [directive.uri]);
     return true;
   }

   /**
    * Verify that the given extends [clause] does not extend a deferred class.
    *
    * See [CompileTimeErrorCode.EXTENDS_DEFERRED_CLASS].
    */
   bool _checkForExtendsDeferredClass(ExtendsClause clause) {
     if (clause == null) {
       return false;
     }
     return _checkForExtendsOrImplementsDeferredClass(
         clause.superclass, CompileTimeErrorCode.EXTENDS_DEFERRED_CLASS);
   }

   /**
    * Verify that the given type [alias] does not extend a deferred class.
    *
    * See [CompileTimeErrorCode.EXTENDS_DISALLOWED_CLASS].
    */
   bool _checkForExtendsDeferredClassInTypeAlias(ClassTypeAlias alias) {
     if (alias == null) {
       return false;
     }
     return _checkForExtendsOrImplementsDeferredClass(
         alias.superclass, CompileTimeErrorCode.EXTENDS_DEFERRED_CLASS);
   }

   /**
    * Verify that the given extends [clause] does not extend classes such as
    * 'num' or 'String'.
    *
    * See [CompileTimeErrorCode.EXTENDS_DISALLOWED_CLASS].
    */
   bool _checkForExtendsDisallowedClass(ExtendsClause clause) {
     if (clause == null) {
       return false;
     }
     return _checkForExtendsOrImplementsDisallowedClass(
         clause.superclass, CompileTimeErrorCode.EXTENDS_DISALLOWED_CLASS);
   }

   /**
    * Verify that the given type [alias] does not extend classes such as 'num' or
    * 'String'.
    *
    * See [CompileTimeErrorCode.EXTENDS_DISALLOWED_CLASS].
    */
   bool _checkForExtendsDisallowedClassInTypeAlias(ClassTypeAlias alias) {
     if (alias == null) {
       return false;
     }
     return _checkForExtendsOrImplementsDisallowedClass(
         alias.superclass, CompileTimeErrorCode.EXTENDS_DISALLOWED_CLASS);
   }

   /**
    * Verify that the given [typeName] does not extend, implement or mixin
    * classes that are deferred.
    *
    * See [_checkForExtendsDeferredClass],
    * [_checkForExtendsDeferredClassInTypeAlias],
    * [_checkForImplementsDeferredClass],
    * [_checkForAllMixinErrorCodes],
    * [CompileTimeErrorCode.EXTENDS_DEFERRED_CLASS],
    * [CompileTimeErrorCode.IMPLEMENTS_DEFERRED_CLASS], and
    * [CompileTimeErrorCode.MIXIN_DEFERRED_CLASS].
    */
   bool _checkForExtendsOrImplementsDeferredClass(
       TypeName typeName, ErrorCode errorCode) {
     if (typeName.isSynthetic) {
       return false;
     }
     if (typeName.isDeferred) {
       _errorReporter.reportErrorForNode(
           errorCode, typeName, [typeName.name.name]);
       return true;
     }
     return false;
   }

   /**
    * Verify that the given [typeName] does not extend, implement or mixin
    * classes such as 'num' or 'String'.
    *
    * See [_checkForExtendsDisallowedClass],
    * [_checkForExtendsDisallowedClassInTypeAlias],
    * [_checkForImplementsDisallowedClass],
    * [_checkForAllMixinErrorCodes],
    * [CompileTimeErrorCode.EXTENDS_DISALLOWED_CLASS],
    * [CompileTimeErrorCode.IMPLEMENTS_DISALLOWED_CLASS], and
    * [CompileTimeErrorCode.MIXIN_OF_DISALLOWED_CLASS].
    */
   bool _checkForExtendsOrImplementsDisallowedClass(
       TypeName typeName, ErrorCode errorCode) {
     if (typeName.isSynthetic) {
       return false;
     }
     // The SDK implementation may implement disallowed types. For example,
     // JSNumber in dart2js and _Smi in Dart VM both implement int.
     if (_currentLibrary.source.isInSystemLibrary) {
       return false;
     }
     DartType superType = typeName.type;
     for (InterfaceType disallowedType
         in _DISALLOWED_TYPES_TO_EXTEND_OR_IMPLEMENT) {
       if (superType != null && superType == disallowedType) {
         // if the violating type happens to be 'num', we need to rule out the
         // case where the enclosing class is 'int' or 'double'
         if (superType == _typeProvider.numType) {
           AstNode grandParent = typeName.parent.parent;
           // Note: this is a corner case that won't happen often, so adding a
           // field currentClass (see currentFunction) to ErrorVerifier isn't
           // worth if for this case, but if the field currentClass is added,
           // then this message should become a todo to not lookup the
           // grandparent node.
           if (grandParent is ClassDeclaration) {
             ClassElement classElement = grandParent.element;
             DartType classType = classElement.type;
             if (classType != null &&
                 (classType == _intType ||
                     classType == _typeProvider.doubleType)) {
               return false;
             }
           }
         }
         // otherwise, report the error
         _errorReporter.reportErrorForNode(
             errorCode, typeName, [disallowedType.displayName]);
         return true;
       }
     }
     return false;
   }

   /**
    * Verify that the given constructor field [initializer] has compatible field
    * and initializer expression types. The [staticElement] is the static element
    * from the name in the [ConstructorFieldInitializer].
    *
    * See [CompileTimeErrorCode.CONST_FIELD_INITIALIZER_NOT_ASSIGNABLE], and
    * [StaticWarningCode.FIELD_INITIALIZER_NOT_ASSIGNABLE].
    */
   bool _checkForFieldInitializerNotAssignable(
       ConstructorFieldInitializer initializer, Element staticElement) {
     // prepare field element
     if (staticElement is! FieldElement) {
       return false;
     }
     FieldElement fieldElement = staticElement as FieldElement;
     // prepare field type
     DartType fieldType = fieldElement.type;
     // prepare expression type
     Expression expression = initializer.expression;
     if (expression == null) {
       return false;
     }
     // test the static type of the expression
     DartType staticType = getStaticType(expression);
     if (staticType == null) {
       return false;
     }
     if (_typeSystem.isAssignableTo(staticType, fieldType)) {
       return false;
     }
     // report problem
     if (_isEnclosingConstructorConst) {
       // TODO(paulberry): this error should be based on the actual type of the
       // constant, not the static type.  See dartbug.com/21119.
       _errorReporter.reportTypeErrorForNode(
           CheckedModeCompileTimeErrorCode.CONST_FIELD_INITIALIZER_NOT_ASSIGNABLE,
           expression,
           [staticType, fieldType]);
     }
     _errorReporter.reportTypeErrorForNode(
         StaticWarningCode.FIELD_INITIALIZER_NOT_ASSIGNABLE,
         expression,
         [staticType, fieldType]);
     return true;
     // TODO(brianwilkerson) Define a hint corresponding to these errors and
     // report it if appropriate.
 //        // test the propagated type of the expression
 //        Type propagatedType = expression.getPropagatedType();
 //        if (propagatedType != null && propagatedType.isAssignableTo(fieldType)) {
 //          return false;
 //        }
 //        // report problem
 //        if (isEnclosingConstructorConst) {
 //          errorReporter.reportTypeErrorForNode(
 //              CompileTimeErrorCode.CONST_FIELD_INITIALIZER_NOT_ASSIGNABLE,
 //              expression,
 //              propagatedType == null ? staticType : propagatedType,
 //              fieldType);
 //        } else {
 //          errorReporter.reportTypeErrorForNode(
 //              StaticWarningCode.FIELD_INITIALIZER_NOT_ASSIGNABLE,
 //              expression,
 //              propagatedType == null ? staticType : propagatedType,
 //              fieldType);
 //        }
 //        return true;
   }

   /**
    * Verify that the given field formal [parameter] is in a constructor
    * declaration.
    *
    * See [CompileTimeErrorCode.FIELD_INITIALIZER_OUTSIDE_CONSTRUCTOR].
    */
   bool _checkForFieldInitializingFormalRedirectingConstructor(
       FieldFormalParameter parameter) {
     ConstructorDeclaration constructor =
         parameter.getAncestor((node) => node is ConstructorDeclaration);
     if (constructor == null) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.FIELD_INITIALIZER_OUTSIDE_CONSTRUCTOR,
           parameter);
       return true;
     }
     // constructor cannot be a factory
     if (constructor.factoryKeyword != null) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.FIELD_INITIALIZER_FACTORY_CONSTRUCTOR,
           parameter);
       return true;
     }
     // constructor cannot have a redirection
     for (ConstructorInitializer initializer in constructor.initializers) {
       if (initializer is RedirectingConstructorInvocation) {
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.FIELD_INITIALIZER_REDIRECTING_CONSTRUCTOR,
             parameter);
         return true;
       }
     }
     // OK
     return false;
   }

   /**
    * Verify that the given variable declaration [list] has only initialized
    * variables if the list is final or const.
    *
    * See [CompileTimeErrorCode.CONST_NOT_INITIALIZED], and
    * [StaticWarningCode.FINAL_NOT_INITIALIZED].
    */
   bool _checkForFinalNotInitialized(VariableDeclarationList list) {
     if (_isInNativeClass) {
       return false;
     }
     bool foundError = false;
     if (!list.isSynthetic) {
       NodeList<VariableDeclaration> variables = list.variables;
       for (VariableDeclaration variable in variables) {
         if (variable.initializer == null) {
           if (list.isConst) {
             _errorReporter.reportErrorForNode(
                 CompileTimeErrorCode.CONST_NOT_INITIALIZED,
                 variable.name,
                 [variable.name.name]);
           } else if (list.isFinal) {
             _errorReporter.reportErrorForNode(
                 StaticWarningCode.FINAL_NOT_INITIALIZED,
                 variable.name,
                 [variable.name.name]);
           }
           foundError = true;
         }
       }
     }
     return foundError;
   }

   /**
    * Verify that final fields in the given clas [declaration] that are declared,
    * without any constructors in the enclosing class, are initialized. Cases in
    * which there is at least one constructor are handled at the end of
    * [_checkForAllFinalInitializedErrorCodes].
    *
    * See [CompileTimeErrorCode.CONST_NOT_INITIALIZED], and
    * [StaticWarningCode.FINAL_NOT_INITIALIZED].
    */
   bool _checkForFinalNotInitializedInClass(ClassDeclaration declaration) {
     NodeList<ClassMember> classMembers = declaration.members;
     for (ClassMember classMember in classMembers) {
       if (classMember is ConstructorDeclaration) {
         return false;
       }
     }
     bool foundError = false;
     for (ClassMember classMember in classMembers) {
       if (classMember is FieldDeclaration &&
           _checkForFinalNotInitialized(classMember.fields)) {
         foundError = true;
       }
     }
     return foundError;
   }

   /**
    * If the current function is async, async*, or sync*, verify that its
    * declared return type is assignable to Future, Stream, or Iterable,
    * respectively.  If not, report the error using [returnType].
    */
   void _checkForIllegalReturnType(TypeName returnType) {
     if (returnType == null) {
       // No declared return type, so the return type must be dynamic, which is
       // assignable to everything.
       return;
     }
     if (_enclosingFunction.isAsynchronous) {
       if (_enclosingFunction.isGenerator) {
         if (!_typeSystem.isAssignableTo(
             _enclosingFunction.returnType, _typeProvider.streamDynamicType)) {
           _errorReporter.reportErrorForNode(
               StaticTypeWarningCode.ILLEGAL_ASYNC_GENERATOR_RETURN_TYPE,
               returnType);
         }
       } else {
         if (!_typeSystem.isAssignableTo(
             _enclosingFunction.returnType, _typeProvider.futureDynamicType)) {
           _errorReporter.reportErrorForNode(
               StaticTypeWarningCode.ILLEGAL_ASYNC_RETURN_TYPE, returnType);
         }
       }
     } else if (_enclosingFunction.isGenerator) {
       if (!_typeSystem.isAssignableTo(
           _enclosingFunction.returnType, _typeProvider.iterableDynamicType)) {
         _errorReporter.reportErrorForNode(
             StaticTypeWarningCode.ILLEGAL_SYNC_GENERATOR_RETURN_TYPE,
             returnType);
       }
     }
   }

   /**
    * Verify that the given implements [clause] does not implement classes that
    * are deferred.
    *
    * See [CompileTimeErrorCode.IMPLEMENTS_DEFERRED_CLASS].
    */
   bool _checkForImplementsDeferredClass(ImplementsClause clause) {
     if (clause == null) {
       return false;
     }
     bool foundError = false;
     for (TypeName type in clause.interfaces) {
       if (_checkForExtendsOrImplementsDeferredClass(
           type, CompileTimeErrorCode.IMPLEMENTS_DEFERRED_CLASS)) {
         foundError = true;
       }
     }
     return foundError;
   }

   /**
    * Verify that the given implements [clause] does not implement classes such
    * as 'num' or 'String'.
    *
    * See [CompileTimeErrorCode.IMPLEMENTS_DISALLOWED_CLASS].
    */
   bool _checkForImplementsDisallowedClass(ImplementsClause clause) {
     if (clause == null) {
       return false;
     }
     bool foundError = false;
     for (TypeName type in clause.interfaces) {
       if (_checkForExtendsOrImplementsDisallowedClass(
           type, CompileTimeErrorCode.IMPLEMENTS_DISALLOWED_CLASS)) {
         foundError = true;
       }
     }
     return foundError;
   }

   /**
    * Verify that if the given [identifier] is part of a constructor initializer,
    * then it does not implicitly reference 'this' expression.
    *
    * See [CompileTimeErrorCode.IMPLICIT_THIS_REFERENCE_IN_INITIALIZER], and
    * [CompileTimeErrorCode.INSTANCE_MEMBER_ACCESS_FROM_STATIC].
    * TODO(scheglov) rename thid method
    */
   bool _checkForImplicitThisReferenceInInitializer(
       SimpleIdentifier identifier) {
     if (!_isInConstructorInitializer &&
         !_isInStaticMethod &&
         !_isInFactory &&
         !_isInInstanceVariableInitializer &&
         !_isInStaticVariableDeclaration) {
       return false;
     }
     // prepare element
     Element element = identifier.staticElement;
     if (!(element is MethodElement || element is PropertyAccessorElement)) {
       return false;
     }
     // static element
     ExecutableElement executableElement = element as ExecutableElement;
     if (executableElement.isStatic) {
       return false;
     }
     // not a class member
     Element enclosingElement = element.enclosingElement;
     if (enclosingElement is! ClassElement) {
       return false;
     }
     // comment
     AstNode parent = identifier.parent;
     if (parent is CommentReference) {
       return false;
     }
     // qualified method invocation
     if (parent is MethodInvocation) {
       MethodInvocation invocation = parent;
       if (identical(invocation.methodName, identifier) &&
           invocation.realTarget != null) {
         return false;
       }
     }
     // qualified property access
     if (parent is PropertyAccess) {
       PropertyAccess access = parent;
       if (identical(access.propertyName, identifier) &&
           access.realTarget != null) {
         return false;
       }
     }
     if (parent is PrefixedIdentifier) {
       PrefixedIdentifier prefixed = parent;
       if (identical(prefixed.identifier, identifier)) {
         return false;
       }
     }
     // report problem
     if (_isInStaticMethod) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.INSTANCE_MEMBER_ACCESS_FROM_STATIC, identifier);
     } else if (_isInFactory) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.INSTANCE_MEMBER_ACCESS_FROM_FACTORY, identifier);
     } else {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.IMPLICIT_THIS_REFERENCE_IN_INITIALIZER,
           identifier);
     }
     return true;
   }

   /**
    * Verify that the given import [directive] has a unique name among other
    * imported libraries. The [importElement] is the [ImportElement] retrieved
    * from the node, if the element in the node was `null`, then this method is
    * not called.
    *
    * See [CompileTimeErrorCode.IMPORT_DUPLICATED_LIBRARY_NAME].
    */
   bool _checkForImportDuplicateLibraryName(
       ImportDirective directive, ImportElement importElement) {
     // prepare imported library
     LibraryElement nodeLibrary = importElement.importedLibrary;
     if (nodeLibrary == null) {
       return false;
     }
     String name = nodeLibrary.name;
     // check if there is another imported library with the same name
     LibraryElement prevLibrary = _nameToImportElement[name];
     if (prevLibrary != null) {
       if (prevLibrary != nodeLibrary) {
         if (!name.isEmpty) {
           _errorReporter.reportErrorForNode(
               StaticWarningCode.IMPORT_DUPLICATED_LIBRARY_NAMED, directive, [
             prevLibrary.definingCompilationUnit.displayName,
             nodeLibrary.definingCompilationUnit.displayName,
             name
           ]);
         }
         return true;
       }
     } else {
       _nameToImportElement[name] = nodeLibrary;
     }
     // OK
     return false;
   }

   /**
    * Check that if the visiting library is not system, then any given library
    * should not be SDK internal library. The [importElement] is the
    * [ImportElement] retrieved from the node, if the element in the node was
    * `null`, then this method is not called
    *
    * See [CompileTimeErrorCode.IMPORT_INTERNAL_LIBRARY].
    */
   bool _checkForImportInternalLibrary(
       ImportDirective directive, ImportElement importElement) {
     if (_isInSystemLibrary) {
       return false;
     }
     // should be private
     DartSdk sdk = _currentLibrary.context.sourceFactory.dartSdk;
     String uri = importElement.uri;
     SdkLibrary sdkLibrary = sdk.getSdkLibrary(uri);
     if (sdkLibrary == null) {
       return false;
     }
     if (!sdkLibrary.isInternal) {
       return false;
     }
     // report problem
     _errorReporter.reportErrorForNode(
         CompileTimeErrorCode.IMPORT_INTERNAL_LIBRARY,
         directive,
         [directive.uri]);
     return true;
   }

   /**
    * For each class declaration, this method is called which verifies that all
    * inherited members are inherited consistently.
    *
    * See [StaticTypeWarningCode.INCONSISTENT_METHOD_INHERITANCE].
    */
   bool _checkForInconsistentMethodInheritance() {
     // Ensure that the inheritance manager has a chance to generate all errors
     // we may care about, note that we ensure that the interfaces data since
     // there are no errors.
     _inheritanceManager.getMapOfMembersInheritedFromInterfaces(_enclosingClass);
     HashSet<AnalysisError> errors =
         _inheritanceManager.getErrors(_enclosingClass);
     if (errors == null || errors.isEmpty) {
       return false;
     }
     for (AnalysisError error in errors) {
       _errorReporter.reportError(error);
     }
     return true;
   }

   /**
    * Check that the given [typeReference] is not a type reference and that then
    * the [name] is reference to an instance member.
    *
    * See [StaticTypeWarningCode.INSTANCE_ACCESS_TO_STATIC_MEMBER].
    */
   bool _checkForInstanceAccessToStaticMember(
       ClassElement typeReference, SimpleIdentifier name) {
     // OK, in comment
     if (_isInComment) {
       return false;
     }
     // OK, target is a type
     if (typeReference != null) {
       return false;
     }
     // prepare member Element
     Element element = name.staticElement;
     if (element is! ExecutableElement) {
       return false;
     }
     ExecutableElement executableElement = element as ExecutableElement;
     // OK, top-level element
     if (executableElement.enclosingElement is! ClassElement) {
       return false;
     }
     // OK, instance member
     if (!executableElement.isStatic) {
       return false;
     }
     // report problem
     _errorReporter.reportErrorForNode(
         StaticTypeWarningCode.INSTANCE_ACCESS_TO_STATIC_MEMBER,
         name,
         [name.name]);
     return true;
   }

   /**
    * Check whether the given [executableElement] collides with the name of a
    * static method in one of its superclasses, and reports the appropriate
    * warning if it does. The [errorNameTarget] is the node to report problems
    * on.
    *
    * See [StaticTypeWarningCode.INSTANCE_METHOD_NAME_COLLIDES_WITH_SUPERCLASS_STATIC].
    */
   bool _checkForInstanceMethodNameCollidesWithSuperclassStatic(
       ExecutableElement executableElement, SimpleIdentifier errorNameTarget) {
     String executableElementName = executableElement.name;
     if (executableElement is! PropertyAccessorElement &&
         !executableElement.isOperator) {
       HashSet<ClassElement> visitedClasses = new HashSet<ClassElement>();
       InterfaceType superclassType = _enclosingClass.supertype;
       ClassElement superclassElement =
           superclassType == null ? null : superclassType.element;
       bool executableElementPrivate =
           Identifier.isPrivateName(executableElementName);
       while (superclassElement != null &&
           !visitedClasses.contains(superclassElement)) {
         visitedClasses.add(superclassElement);
         LibraryElement superclassLibrary = superclassElement.library;
         // Check fields.
         FieldElement fieldElt =
             superclassElement.getField(executableElementName);
         if (fieldElt != null) {
           // Ignore if private in a different library - cannot collide.
           if (executableElementPrivate &&
               _currentLibrary != superclassLibrary) {
             continue;
           }
           // instance vs. static
           if (fieldElt.isStatic) {
             _errorReporter.reportErrorForNode(
                 StaticWarningCode.INSTANCE_METHOD_NAME_COLLIDES_WITH_SUPERCLASS_STATIC,
                 errorNameTarget,
                 [executableElementName, fieldElt.enclosingElement.displayName]);
             return true;
           }
         }
         // Check methods.
         List<MethodElement> methodElements = superclassElement.methods;
         for (MethodElement methodElement in methodElements) {
           // We need the same name.
           if (methodElement.name != executableElementName) {
             continue;
           }
           // Ignore if private in a different library - cannot collide.
           if (executableElementPrivate &&
               _currentLibrary != superclassLibrary) {
             continue;
           }
           // instance vs. static
           if (methodElement.isStatic) {
             _errorReporter.reportErrorForNode(
                 StaticWarningCode.INSTANCE_METHOD_NAME_COLLIDES_WITH_SUPERCLASS_STATIC,
                 errorNameTarget, [
               executableElementName,
               methodElement.enclosingElement.displayName
             ]);
             return true;
           }
         }
         superclassType = superclassElement.supertype;
         superclassElement =
             superclassType == null ? null : superclassType.element;
       }
     }
     return false;
   }

   /**
    * Verify that an 'int' can be assigned to the parameter corresponding to the
    * given [argument]. This is used for prefix and postfix expressions where
    * the argument value is implicit.
    *
    * See [StaticWarningCode.ARGUMENT_TYPE_NOT_ASSIGNABLE].
    */
   bool _checkForIntNotAssignable(Expression argument) {
     if (argument == null) {
       return false;
     }
     ParameterElement staticParameterElement = argument.staticParameterElement;
     DartType staticParameterType =
         staticParameterElement == null ? null : staticParameterElement.type;
     return _checkForArgumentTypeNotAssignable(argument, staticParameterType,
         _intType, StaticWarningCode.ARGUMENT_TYPE_NOT_ASSIGNABLE);
   }

   /**
    * Verify that the given [annotation] isn't defined in a deferred library.
    *
    * See [CompileTimeErrorCode.INVALID_ANNOTATION_FROM_DEFERRED_LIBRARY].
    */
   bool _checkForInvalidAnnotationFromDeferredLibrary(Annotation annotation) {
     Identifier nameIdentifier = annotation.name;
     if (nameIdentifier is PrefixedIdentifier) {
       if (nameIdentifier.isDeferred) {
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.INVALID_ANNOTATION_FROM_DEFERRED_LIBRARY,
             annotation.name);
         return true;
       }
     }
     return false;
   }

   /**
    * Verify that the given left hand side ([lhs]) and right hand side ([rhs])
    * represent a valid assignment.
    *
    * See [StaticTypeWarningCode.INVALID_ASSIGNMENT].
    */
   bool _checkForInvalidAssignment(Expression lhs, Expression rhs) {
     if (lhs == null || rhs == null) {
       return false;
     }
     VariableElement leftVariableElement = getVariableElement(lhs);
     DartType leftType = (leftVariableElement == null)
         ? getStaticType(lhs)
         : leftVariableElement.type;
     DartType staticRightType = getStaticType(rhs);
     if (!_typeSystem.isAssignableTo(staticRightType, leftType)) {
       _errorReporter.reportTypeErrorForNode(
           StaticTypeWarningCode.INVALID_ASSIGNMENT,
           rhs,
           [staticRightType, leftType]);
       return true;
     }
     return false;
   }

   /**
    * Given an [assignment] using a compound assignment operator, this verifies
    * that the given assignment is valid. The [lhs] is the left hand side
    * expression. The [rhs] is the right hand side expression.
    *
    * See [StaticTypeWarningCode.INVALID_ASSIGNMENT].
    */
   bool _checkForInvalidCompoundAssignment(
       AssignmentExpression assignment, Expression lhs, Expression rhs) {
     if (lhs == null) {
       return false;
     }
     VariableElement leftVariableElement = getVariableElement(lhs);
     DartType leftType = (leftVariableElement == null)
         ? getStaticType(lhs)
         : leftVariableElement.type;
     MethodElement invokedMethod = assignment.staticElement;
     if (invokedMethod == null) {
       return false;
     }
     DartType rightType = invokedMethod.type.returnType;
     if (leftType == null || rightType == null) {
       return false;
     }
     if (!_typeSystem.isAssignableTo(rightType, leftType)) {
       _errorReporter.reportTypeErrorForNode(
           StaticTypeWarningCode.INVALID_ASSIGNMENT, rhs, [rightType, leftType]);
       return true;
     }
     return false;
   }

   /**
    * Check the given [initializer] to ensure that the field being initialized is
    * a valid field. The [fieldName] is the field name from the
    * [ConstructorFieldInitializer]. The [staticElement] is the static element
    * from the name in the [ConstructorFieldInitializer].
    */
   void _checkForInvalidField(ConstructorFieldInitializer initializer,
       SimpleIdentifier fieldName, Element staticElement) {
     if (staticElement is FieldElement) {
       FieldElement fieldElement = staticElement;
       if (fieldElement.isSynthetic) {
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.INITIALIZER_FOR_NON_EXISTENT_FIELD,
             initializer,
             [fieldName]);
       } else if (fieldElement.isStatic) {
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.INITIALIZER_FOR_STATIC_FIELD,
             initializer,
             [fieldName]);
       }
     } else {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.INITIALIZER_FOR_NON_EXISTENT_FIELD,
           initializer,
           [fieldName]);
       return;
     }
   }

   /**
    * Check to see whether the given function [body] has a modifier associated
    * with it, and report it as an error if it does.
    */
   bool _checkForInvalidModifierOnBody(
       FunctionBody body, CompileTimeErrorCode errorCode) {
     sc.Token keyword = body.keyword;
     if (keyword != null) {
       _errorReporter.reportErrorForToken(errorCode, keyword, [keyword.lexeme]);
       return true;
     }
     return false;
   }

   /**
    * Verify that the usage of the given 'this' is valid.
    *
    * See [CompileTimeErrorCode.INVALID_REFERENCE_TO_THIS].
    */
   bool _checkForInvalidReferenceToThis(ThisExpression expression) {
     if (!_isThisInValidContext(expression)) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.INVALID_REFERENCE_TO_THIS, expression);
       return true;
     }
     return false;
   }

   /**
    * Checks to ensure that the given list of type [arguments] does not have a
    * type parameter as a type argument. The [errorCode] is either
    * [CompileTimeErrorCode.INVALID_TYPE_ARGUMENT_IN_CONST_LIST] or
    * [CompileTimeErrorCode.INVALID_TYPE_ARGUMENT_IN_CONST_MAP].
    */
   bool _checkForInvalidTypeArgumentInConstTypedLiteral(
       NodeList<TypeName> arguments, ErrorCode errorCode) {
     bool foundError = false;
     for (TypeName typeName in arguments) {
       if (typeName.type is TypeParameterType) {
         _errorReporter.reportErrorForNode(errorCode, typeName, [typeName.name]);
         foundError = true;
       }
     }
     return foundError;
   }

   /**
    * Verify that the elements given list [literal] are subtypes of the specified
    * element type. The [typeArguments] are the type arguments.
    *
    * See [CompileTimeErrorCode.LIST_ELEMENT_TYPE_NOT_ASSIGNABLE], and
    * [StaticWarningCode.LIST_ELEMENT_TYPE_NOT_ASSIGNABLE].
    */
   bool _checkForListElementTypeNotAssignable(
       ListLiteral literal, TypeArgumentList typeArguments) {
     NodeList<TypeName> typeNames = typeArguments.arguments;
     if (typeNames.length < 1) {
       return false;
     }
     DartType listElementType = typeNames[0].type;
     // Check every list element.
     bool hasProblems = false;
     for (Expression element in literal.elements) {
       if (literal.constKeyword != null) {
         // TODO(paulberry): this error should be based on the actual type of the
         // list element, not the static type.  See dartbug.com/21119.
         if (_checkForArgumentTypeNotAssignableWithExpectedTypes(
             element,
             listElementType,
             CheckedModeCompileTimeErrorCode.LIST_ELEMENT_TYPE_NOT_ASSIGNABLE)) {
           hasProblems = true;
         }
       }
       if (_checkForArgumentTypeNotAssignableWithExpectedTypes(
           element,
           listElementType,
           StaticWarningCode.LIST_ELEMENT_TYPE_NOT_ASSIGNABLE)) {
         hasProblems = true;
       }
     }
     return hasProblems;
   }

   /**
    * Verify that the key/value of entries of the given map [literal] are
    * subtypes of the key/value types specified in the type arguments. The
    * [typeArguments] are the type arguments.
    *
    * See [CompileTimeErrorCode.MAP_KEY_TYPE_NOT_ASSIGNABLE],
    * [CompileTimeErrorCode.MAP_VALUE_TYPE_NOT_ASSIGNABLE],
    * [StaticWarningCode.MAP_KEY_TYPE_NOT_ASSIGNABLE], and
    * [StaticWarningCode.MAP_VALUE_TYPE_NOT_ASSIGNABLE].
    */
   bool _checkForMapTypeNotAssignable(
       MapLiteral literal, TypeArgumentList typeArguments) {
     // Prepare maps key/value types.
     NodeList<TypeName> typeNames = typeArguments.arguments;
     if (typeNames.length < 2) {
       return false;
     }
     DartType keyType = typeNames[0].type;
     DartType valueType = typeNames[1].type;
     // Check every map entry.
     bool hasProblems = false;
     NodeList<MapLiteralEntry> entries = literal.entries;
     for (MapLiteralEntry entry in entries) {
       Expression key = entry.key;
       Expression value = entry.value;
       if (literal.constKeyword != null) {
         // TODO(paulberry): this error should be based on the actual type of the
         // list element, not the static type.  See dartbug.com/21119.
         if (_checkForArgumentTypeNotAssignableWithExpectedTypes(key, keyType,
             CheckedModeCompileTimeErrorCode.MAP_KEY_TYPE_NOT_ASSIGNABLE)) {
           hasProblems = true;
         }
         if (_checkForArgumentTypeNotAssignableWithExpectedTypes(
             value,
             valueType,
             CheckedModeCompileTimeErrorCode.MAP_VALUE_TYPE_NOT_ASSIGNABLE)) {
           hasProblems = true;
         }
       }
       if (_checkForArgumentTypeNotAssignableWithExpectedTypes(
           key, keyType, StaticWarningCode.MAP_KEY_TYPE_NOT_ASSIGNABLE)) {
         hasProblems = true;
       }
       if (_checkForArgumentTypeNotAssignableWithExpectedTypes(
           value, valueType, StaticWarningCode.MAP_VALUE_TYPE_NOT_ASSIGNABLE)) {
         hasProblems = true;
       }
     }
     return hasProblems;
   }

   /**
    * Verify that the [_enclosingClass] does not define members with the same name
    * as the enclosing class.
    *
    * See [CompileTimeErrorCode.MEMBER_WITH_CLASS_NAME].
    */
   bool _checkForMemberWithClassName() {
     if (_enclosingClass == null) {
       return false;
     }
     String className = _enclosingClass.name;
     if (className == null) {
       return false;
     }
     bool problemReported = false;
     // check accessors
     for (PropertyAccessorElement accessor in _enclosingClass.accessors) {
       if (className == accessor.name) {
         _errorReporter.reportErrorForElement(
             CompileTimeErrorCode.MEMBER_WITH_CLASS_NAME, accessor);
         problemReported = true;
       }
     }
     // don't check methods, they would be constructors
     // done
     return problemReported;
   }

   /**
    * Check to make sure that all similarly typed accessors are of the same type
    * (including inherited accessors).
    *
    * See [StaticWarningCode.MISMATCHED_GETTER_AND_SETTER_TYPES], and
    * [StaticWarningCode.MISMATCHED_GETTER_AND_SETTER_TYPES_FROM_SUPERTYPE].
    */
   bool _checkForMismatchedAccessorTypes(
       Declaration accessorDeclaration, String accessorTextName) {
     ExecutableElement accessorElement =
         accessorDeclaration.element as ExecutableElement;
     if (accessorElement is! PropertyAccessorElement) {
       return false;
     }
     PropertyAccessorElement propertyAccessorElement =
         accessorElement as PropertyAccessorElement;
     PropertyAccessorElement counterpartAccessor = null;
     ClassElement enclosingClassForCounterpart = null;
     if (propertyAccessorElement.isGetter) {
       counterpartAccessor = propertyAccessorElement.correspondingSetter;
     } else {
       counterpartAccessor = propertyAccessorElement.correspondingGetter;
       // If the setter and getter are in the same enclosing element, return,
       // this prevents having MISMATCHED_GETTER_AND_SETTER_TYPES reported twice.
       if (counterpartAccessor != null &&
           identical(counterpartAccessor.enclosingElement,
               propertyAccessorElement.enclosingElement)) {
         return false;
       }
     }
     if (counterpartAccessor == null) {
       // If the accessor is declared in a class, check the superclasses.
       if (_enclosingClass != null) {
         // Figure out the correct identifier to lookup in the inheritance graph,
         // if 'x', then 'x=', or if 'x=', then 'x'.
         String lookupIdentifier = propertyAccessorElement.name;
         if (StringUtilities.endsWithChar(lookupIdentifier, 0x3D)) {
           lookupIdentifier =
               lookupIdentifier.substring(0, lookupIdentifier.length - 1);
         } else {
           lookupIdentifier += "=";
         }
         // lookup with the identifier.
         ExecutableElement elementFromInheritance = _inheritanceManager
             .lookupInheritance(_enclosingClass, lookupIdentifier);
         // Verify that we found something, and that it is an accessor
         if (elementFromInheritance != null &&
             elementFromInheritance is PropertyAccessorElement) {
           enclosingClassForCounterpart =
               elementFromInheritance.enclosingElement as ClassElement;
           counterpartAccessor = elementFromInheritance;
         }
       }
       if (counterpartAccessor == null) {
         return false;
       }
     }
     // Default of null == no accessor or no type (dynamic)
     DartType getterType = null;
     DartType setterType = null;
     // Get an existing counterpart accessor if any.
     if (propertyAccessorElement.isGetter) {
       getterType = _getGetterType(propertyAccessorElement);
       setterType = _getSetterType(counterpartAccessor);
     } else if (propertyAccessorElement.isSetter) {
       setterType = _getSetterType(propertyAccessorElement);
       getterType = _getGetterType(counterpartAccessor);
     }
     // If either types are not assignable to each other, report an error
     // (if the getter is null, it is dynamic which is assignable to everything).
     if (setterType != null &&
         getterType != null &&
         !_typeSystem.isAssignableTo(getterType, setterType)) {
       if (enclosingClassForCounterpart == null) {
         _errorReporter.reportTypeErrorForNode(
             StaticWarningCode.MISMATCHED_GETTER_AND_SETTER_TYPES,
             accessorDeclaration,
             [accessorTextName, setterType, getterType]);
         return true;
       } else {
         _errorReporter.reportTypeErrorForNode(
             StaticWarningCode.MISMATCHED_GETTER_AND_SETTER_TYPES_FROM_SUPERTYPE,
             accessorDeclaration, [
           accessorTextName,
           setterType,
           getterType,
           enclosingClassForCounterpart.displayName
         ]);
       }
     }
     return false;
   }

   /**
    * Check to make sure that the given switch [statement] whose static type is
    * an enum type either have a default case or include all of the enum
    * constants.
    */
   bool _checkForMissingEnumConstantInSwitch(SwitchStatement statement) {
     // TODO(brianwilkerson) This needs to be checked after constant values have
     // been computed.
     Expression expression = statement.expression;
     DartType expressionType = getStaticType(expression);
     if (expressionType == null) {
       return false;
     }
     Element expressionElement = expressionType.element;
     if (expressionElement is! ClassElement) {
       return false;
     }
     ClassElement classElement = expressionElement as ClassElement;
     if (!classElement.isEnum) {
       return false;
     }
     List<String> constantNames = new List<String>();
     List<FieldElement> fields = classElement.fields;
     int fieldCount = fields.length;
     for (int i = 0; i < fieldCount; i++) {
       FieldElement field = fields[i];
       if (field.isStatic && !field.isSynthetic) {
         constantNames.add(field.name);
       }
     }
     NodeList<SwitchMember> members = statement.members;
     int memberCount = members.length;
     for (int i = 0; i < memberCount; i++) {
       SwitchMember member = members[i];
       if (member is SwitchDefault) {
         return false;
       }
       String constantName = _getConstantName((member as SwitchCase).expression);
       if (constantName != null) {
         constantNames.remove(constantName);
       }
     }
     int nameCount = constantNames.length;
     if (nameCount == 0) {
       return false;
     }
     for (int i = 0; i < nameCount; i++) {
       int offset = statement.offset;
       int end = statement.rightParenthesis.end;
       _errorReporter.reportErrorForOffset(
           CompileTimeErrorCode.MISSING_ENUM_CONSTANT_IN_SWITCH,
           offset,
           end - offset,
           [constantNames[i]]);
     }
     return true;
   }

   /**
    * Verify that the given function [body] does not contain return statements
    * that both have and do not have return values.
    *
    * See [StaticWarningCode.MIXED_RETURN_TYPES].
    */
   bool _checkForMixedReturns(BlockFunctionBody body) {
     if (_hasReturnWithoutValue) {
       return false;
     }
     int withCount = _returnsWith.length;
     int withoutCount = _returnsWithout.length;
     if (withCount > 0 && withoutCount > 0) {
       for (int i = 0; i < withCount; i++) {
         _errorReporter.reportErrorForToken(StaticWarningCode.MIXED_RETURN_TYPES,
             _returnsWith[i].returnKeyword);
       }
       for (int i = 0; i < withoutCount; i++) {
         _errorReporter.reportErrorForToken(StaticWarningCode.MIXED_RETURN_TYPES,
             _returnsWithout[i].returnKeyword);
       }
       return true;
     }
     return false;
   }

   /**
    * Verify that the given mixin does not have an explicitly declared
    * constructor. The [mixinName] is the node to report problem on. The
    * [mixinElement] is the mixing to evaluate.
    *
    * See [CompileTimeErrorCode.MIXIN_DECLARES_CONSTRUCTOR].
    */
   bool _checkForMixinDeclaresConstructor(
       TypeName mixinName, ClassElement mixinElement) {
     for (ConstructorElement constructor in mixinElement.constructors) {
       if (!constructor.isSynthetic && !constructor.isFactory) {
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.MIXIN_DECLARES_CONSTRUCTOR,
             mixinName,
             [mixinElement.name]);
         return true;
       }
     }
     return false;
   }

   /**
    * Report the error [CompileTimeErrorCode.MIXIN_HAS_NO_CONSTRUCTORS] if
    * appropriate.
    */
   void _checkForMixinHasNoConstructors(AstNode node) {
     if ((_enclosingClass as ClassElementImpl).doesMixinLackConstructors) {
       ErrorCode errorCode = CompileTimeErrorCode.MIXIN_HAS_NO_CONSTRUCTORS;
       _errorReporter.reportErrorForNode(
           errorCode, node, [_enclosingClass.supertype]);
     }
   }

   /**
    * Verify that the given mixin has the 'Object' superclass. The [mixinName] is
    * the node to report problem on. The [mixinElement] is the mixing to
    * evaluate.
    *
    * See [CompileTimeErrorCode.MIXIN_INHERITS_FROM_NOT_OBJECT].
    */
   bool _checkForMixinInheritsNotFromObject(
       TypeName mixinName, ClassElement mixinElement) {
     InterfaceType mixinSupertype = mixinElement.supertype;
     if (mixinSupertype != null) {
       if (!mixinSupertype.isObject ||
           !mixinElement.isMixinApplication && mixinElement.mixins.length != 0) {
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.MIXIN_INHERITS_FROM_NOT_OBJECT,
             mixinName,
             [mixinElement.name]);
         return true;
       }
     }
     return false;
   }

   /**
    * Verify that the given mixin does not reference 'super'. The [mixinName] is
    * the node to report problem on. The [mixinElement] is the mixing to
    * evaluate.
    *
    * See [CompileTimeErrorCode.MIXIN_REFERENCES_SUPER].
    */
   bool _checkForMixinReferencesSuper(
       TypeName mixinName, ClassElement mixinElement) {
     if (!enableSuperMixins && mixinElement.hasReferenceToSuper) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.MIXIN_REFERENCES_SUPER,
           mixinName,
           [mixinElement.name]);
     }
     return false;
   }

   /**
    * Verify that the given [constructor] has at most one 'super' initializer.
    *
    * See [CompileTimeErrorCode.MULTIPLE_SUPER_INITIALIZERS].
    */
   bool _checkForMultipleSuperInitializers(ConstructorDeclaration constructor) {
     int numSuperInitializers = 0;
     for (ConstructorInitializer initializer in constructor.initializers) {
       if (initializer is SuperConstructorInvocation) {
         numSuperInitializers++;
         if (numSuperInitializers > 1) {
           _errorReporter.reportErrorForNode(
               CompileTimeErrorCode.MULTIPLE_SUPER_INITIALIZERS, initializer);
         }
       }
     }
     return numSuperInitializers > 0;
   }

   /**
    * Checks to ensure that the given native function [body] is in SDK code.
    *
    * See [ParserErrorCode.NATIVE_FUNCTION_BODY_IN_NON_SDK_CODE].
    */
   bool _checkForNativeFunctionBodyInNonSDKCode(NativeFunctionBody body) {
     if (!_isInSystemLibrary && !_hasExtUri) {
       _errorReporter.reportErrorForNode(
           ParserErrorCode.NATIVE_FUNCTION_BODY_IN_NON_SDK_CODE, body);
       return true;
     }
     return false;
   }

   /**
    * Verify that the given instance creation [expression] invokes an existing
    * constructor. The [constructorName] is the constructor name. The [typeName]
    * is the name of the type defining the constructor.
    *
    * This method assumes that the instance creation was tested to be 'new'
    * before being called.
    *
    * See [StaticWarningCode.NEW_WITH_UNDEFINED_CONSTRUCTOR].
    */
   bool _checkForNewWithUndefinedConstructor(
       InstanceCreationExpression expression,
       ConstructorName constructorName,
       TypeName typeName) {
     // OK if resolved
     if (expression.staticElement != null) {
       return false;
     }
     DartType type = typeName.type;
     if (type is InterfaceType) {
       ClassElement element = type.element;
       if (element != null && element.isEnum) {
         // We have already reported the error.
         return false;
       }
     }
     // prepare class name
     Identifier className = typeName.name;
     // report as named or default constructor absence
     SimpleIdentifier name = constructorName.name;
     if (name != null) {
       _errorReporter.reportErrorForNode(
           StaticWarningCode.NEW_WITH_UNDEFINED_CONSTRUCTOR,
           name,
           [className, name]);
     } else {
       _errorReporter.reportErrorForNode(
           StaticWarningCode.NEW_WITH_UNDEFINED_CONSTRUCTOR_DEFAULT,
           constructorName,
           [className]);
     }
     return true;
   }

   /**
    * Check that if the given class [declaration] implicitly calls default
    * constructor of its superclass, there should be such default constructor -
    * implicit or explicit.
    *
    * See [CompileTimeErrorCode.NO_DEFAULT_SUPER_CONSTRUCTOR_IMPLICIT].
    */
   bool _checkForNoDefaultSuperConstructorImplicit(
       ClassDeclaration declaration) {
     // do nothing if mixin errors have already been reported for this class.
     ClassElementImpl enclosingClass = _enclosingClass;
     if (enclosingClass.doesMixinLackConstructors) {
       return false;
     }
     // do nothing if there is explicit constructor
     List<ConstructorElement> constructors = _enclosingClass.constructors;
     if (!constructors[0].isSynthetic) {
       return false;
     }
     // prepare super
     InterfaceType superType = _enclosingClass.supertype;
     if (superType == null) {
       return false;
     }
     ClassElement superElement = superType.element;
     // try to find default generative super constructor
     ConstructorElement superUnnamedConstructor =
         superElement.unnamedConstructor;
     if (superUnnamedConstructor != null) {
       if (superUnnamedConstructor.isFactory) {
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.NON_GENERATIVE_CONSTRUCTOR,
             declaration.name,
             [superUnnamedConstructor]);
         return true;
       }
       if (superUnnamedConstructor.isDefaultConstructor &&
           _enclosingClass
               .isSuperConstructorAccessible(superUnnamedConstructor)) {
         return true;
       }
     }
     // report problem
     _errorReporter.reportErrorForNode(
         CompileTimeErrorCode.NO_DEFAULT_SUPER_CONSTRUCTOR_IMPLICIT,
         declaration.name,
         [superType.displayName]);
     return true;
   }

   /**
    * Check that the given class declaration overrides all members required by
    * its superclasses and interfaces. The [classNameNode] is the
    * [SimpleIdentifier] to be used if there is a violation, this is either the
    * named from the [ClassDeclaration] or from the [ClassTypeAlias].
    *
    * See [StaticWarningCode.NON_ABSTRACT_CLASS_INHERITS_ABSTRACT_MEMBER_ONE],
    * [StaticWarningCode.NON_ABSTRACT_CLASS_INHERITS_ABSTRACT_MEMBER_TWO],
    * [StaticWarningCode.NON_ABSTRACT_CLASS_INHERITS_ABSTRACT_MEMBER_THREE],
    * [StaticWarningCode.NON_ABSTRACT_CLASS_INHERITS_ABSTRACT_MEMBER_FOUR], and
    * [StaticWarningCode.NON_ABSTRACT_CLASS_INHERITS_ABSTRACT_MEMBER_FIVE_PLUS].
    */
   bool _checkForNonAbstractClassInheritsAbstractMember(
       SimpleIdentifier classNameNode) {
     if (_enclosingClass.isAbstract) {
       return false;
     }
     //
     // Store in local sets the set of all method and accessor names
     //
     MethodElement method =
         _enclosingClass.getMethod(FunctionElement.NO_SUCH_METHOD_METHOD_NAME);
     if (method != null) {
       // If the enclosing class declares the method noSuchMethod(), then return.
       // From Spec:  It is a static warning if a concrete class does not have an
       // implementation for a method in any of its superinterfaces unless it
       // declares its own noSuchMethod method (7.10).
       return false;
     }
     HashSet<ExecutableElement> missingOverrides =
         new HashSet<ExecutableElement>();
     //
     // Loop through the set of all executable elements declared in the implicit
     // interface.
     //
     MemberMap membersInheritedFromInterfaces = _inheritanceManager
         .getMapOfMembersInheritedFromInterfaces(_enclosingClass);
     MemberMap membersInheritedFromSuperclasses = _inheritanceManager
         .getMapOfMembersInheritedFromClasses(_enclosingClass);
     for (int i = 0; i < membersInheritedFromInterfaces.size; i++) {
       String memberName = membersInheritedFromInterfaces.getKey(i);
       ExecutableElement executableElt =
           membersInheritedFromInterfaces.getValue(i);
       if (memberName == null) {
         break;
       }
       // If the element is not synthetic and can be determined to be defined in
       // Object, skip it.
       if (executableElt.enclosingElement != null &&
           (executableElt.enclosingElement as ClassElement).type.isObject) {
         continue;
       }
       // Check to see if some element is in local enclosing class that matches
       // the name of the required member.
       if (_isMemberInClassOrMixin(executableElt, _enclosingClass)) {
         // We do not have to verify that this implementation of the found method
         // matches the required function type: the set of
         // StaticWarningCode.INVALID_METHOD_OVERRIDE_* warnings break out the
         // different specific situations.
         continue;
       }
       // First check to see if this element was declared in the superclass
       // chain, in which case there is already a concrete implementation.
       ExecutableElement elt = membersInheritedFromSuperclasses.get(memberName);
       // Check to see if an element was found in the superclass chain with the
       // correct name.
       if (elt != null) {
         // Reference the types, if any are null then continue.
         InterfaceType enclosingType = _enclosingClass.type;
         FunctionType concreteType = elt.type;
         FunctionType requiredMemberType = executableElt.type;
         if (enclosingType == null ||
             concreteType == null ||
             requiredMemberType == null) {
           continue;
         }
         // Some element was found in the superclass chain that matches the name
         // of the required member.
         // If it is not abstract and it is the correct one (types match- the
         // version of this method that we have has the correct number of
         // parameters, etc), then this class has a valid implementation of this
         // method, so skip it.
         if ((elt is MethodElement && !elt.isAbstract) ||
             (elt is PropertyAccessorElement && !elt.isAbstract)) {
           // Since we are comparing two function types, we need to do the
           // appropriate type substitutions first ().
           FunctionType foundConcreteFT = _inheritanceManager
               .substituteTypeArgumentsInMemberFromInheritance(
                   concreteType, memberName, enclosingType);
           FunctionType requiredMemberFT = _inheritanceManager
               .substituteTypeArgumentsInMemberFromInheritance(
                   requiredMemberType, memberName, enclosingType);
           if (_typeSystem.isSubtypeOf(foundConcreteFT, requiredMemberFT)) {
             continue;
           }
         }
       }
       // The not qualifying concrete executable element was found, add it to the
       // list.
       missingOverrides.add(executableElt);
     }
     // Now that we have the set of missing overrides, generate a warning on this
     // class.
     int missingOverridesSize = missingOverrides.length;
     if (missingOverridesSize == 0) {
       return false;
     }
     List<ExecutableElement> missingOverridesArray =
         new List.from(missingOverrides);
     List<String> stringMembersArrayListSet = new List<String>();
     for (int i = 0; i < missingOverridesArray.length; i++) {
       String newStrMember;
       Element enclosingElement = missingOverridesArray[i].enclosingElement;
       String prefix = StringUtilities.EMPTY;
       if (missingOverridesArray[i] is PropertyAccessorElement) {
         PropertyAccessorElement propertyAccessorElement =
             missingOverridesArray[i] as PropertyAccessorElement;
         if (propertyAccessorElement.isGetter) {
           prefix = _GETTER_SPACE;
           // "getter "
         } else {
           prefix = _SETTER_SPACE;
           // "setter "
         }
       }
       if (enclosingElement != null) {
         newStrMember =
             "$prefix'${enclosingElement.displayName}.${missingOverridesArray[i].displayName}'";
       } else {
         newStrMember = "$prefix'${missingOverridesArray[i].displayName}'";
       }
       stringMembersArrayListSet.add(newStrMember);
     }
     List<String> stringMembersArray = new List.from(stringMembersArrayListSet);
     AnalysisErrorWithProperties analysisError;
     if (stringMembersArray.length == 1) {
       analysisError = _errorReporter.newErrorWithProperties(
           StaticWarningCode.NON_ABSTRACT_CLASS_INHERITS_ABSTRACT_MEMBER_ONE,
           classNameNode,
           [stringMembersArray[0]]);
     } else if (stringMembersArray.length == 2) {
       analysisError = _errorReporter.newErrorWithProperties(
           StaticWarningCode.NON_ABSTRACT_CLASS_INHERITS_ABSTRACT_MEMBER_TWO,
           classNameNode,
           [stringMembersArray[0], stringMembersArray[1]]);
     } else if (stringMembersArray.length == 3) {
       analysisError = _errorReporter.newErrorWithProperties(
           StaticWarningCode.NON_ABSTRACT_CLASS_INHERITS_ABSTRACT_MEMBER_THREE,
           classNameNode, [
         stringMembersArray[0],
         stringMembersArray[1],
         stringMembersArray[2]
       ]);
     } else if (stringMembersArray.length == 4) {
       analysisError = _errorReporter.newErrorWithProperties(
           StaticWarningCode.NON_ABSTRACT_CLASS_INHERITS_ABSTRACT_MEMBER_FOUR,
           classNameNode, [
         stringMembersArray[0],
         stringMembersArray[1],
         stringMembersArray[2],
         stringMembersArray[3]
       ]);
     } else {
       analysisError = _errorReporter.newErrorWithProperties(
           StaticWarningCode.NON_ABSTRACT_CLASS_INHERITS_ABSTRACT_MEMBER_FIVE_PLUS,
           classNameNode, [
         stringMembersArray[0],
         stringMembersArray[1],
         stringMembersArray[2],
         stringMembersArray[3],
         stringMembersArray.length - 4
       ]);
     }
     analysisError.setProperty(
         ErrorProperty.UNIMPLEMENTED_METHODS, missingOverridesArray);
     _errorReporter.reportError(analysisError);
     return true;
   }

   /**
    * Check to ensure that the [condition] is of type bool, are. Otherwise an
    * error is reported on the expression.
    *
    * See [StaticTypeWarningCode.NON_BOOL_CONDITION].
    */
   bool _checkForNonBoolCondition(Expression condition) {
     DartType conditionType = getStaticType(condition);
     if (conditionType != null &&
         !_typeSystem.isAssignableTo(conditionType, _boolType)) {
       _errorReporter.reportErrorForNode(
           StaticTypeWarningCode.NON_BOOL_CONDITION, condition);
       return true;
     }
     return false;
   }

   /**
    * Verify that the given assert [statement] has either a 'bool' or
    * '() -> bool' input.
    *
    * See [StaticTypeWarningCode.NON_BOOL_EXPRESSION].
    */
   bool _checkForNonBoolExpression(AssertStatement statement) {
     Expression expression = statement.condition;
     DartType type = getStaticType(expression);
     if (type is InterfaceType) {
       if (!_typeSystem.isAssignableTo(type, _boolType)) {
         _errorReporter.reportErrorForNode(
             StaticTypeWarningCode.NON_BOOL_EXPRESSION, expression);
         return true;
       }
     } else if (type is FunctionType) {
       FunctionType functionType = type;
       if (functionType.typeArguments.length == 0 &&
           !_typeSystem.isAssignableTo(functionType.returnType, _boolType)) {
         _errorReporter.reportErrorForNode(
             StaticTypeWarningCode.NON_BOOL_EXPRESSION, expression);
         return true;
       }
     }
     return false;
   }

   /**
    * Checks to ensure that the given [expression] is assignable to bool.
    *
    * See [StaticTypeWarningCode.NON_BOOL_NEGATION_EXPRESSION].
    */
   bool _checkForNonBoolNegationExpression(Expression expression) {
     DartType conditionType = getStaticType(expression);
     if (conditionType != null &&
         !_typeSystem.isAssignableTo(conditionType, _boolType)) {
       _errorReporter.reportErrorForNode(
           StaticTypeWarningCode.NON_BOOL_NEGATION_EXPRESSION, expression);
       return true;
     }
     return false;
   }

   /**
    * Verify the given map [literal] either:
    * * has `const modifier`
    * * has explicit type arguments
    * * is not start of the statement
    *
    * See [CompileTimeErrorCode.NON_CONST_MAP_AS_EXPRESSION_STATEMENT].
    */
   bool _checkForNonConstMapAsExpressionStatement(MapLiteral literal) {
     // "const"
     if (literal.constKeyword != null) {
       return false;
     }
     // has type arguments
     if (literal.typeArguments != null) {
       return false;
     }
     // prepare statement
     Statement statement =
         literal.getAncestor((node) => node is ExpressionStatement);
     if (statement == null) {
       return false;
     }
     // OK, statement does not start with map
     if (!identical(statement.beginToken, literal.beginToken)) {
       return false;
     }
     // report problem
     _errorReporter.reportErrorForNode(
         CompileTimeErrorCode.NON_CONST_MAP_AS_EXPRESSION_STATEMENT, literal);
     return true;
   }

   /**
    * Verify that the given method [declaration] of operator `[]=`, has `void`
    * return type.
    *
    * See [StaticWarningCode.NON_VOID_RETURN_FOR_OPERATOR].
    */
   bool _checkForNonVoidReturnTypeForOperator(MethodDeclaration declaration) {
     // check that []= operator
     SimpleIdentifier name = declaration.name;
     if (name.name != "[]=") {
       return false;
     }
     // check return type
     TypeName typeName = declaration.returnType;
     if (typeName != null) {
       DartType type = typeName.type;
       if (type != null && !type.isVoid) {
         _errorReporter.reportErrorForNode(
             StaticWarningCode.NON_VOID_RETURN_FOR_OPERATOR, typeName);
       }
     }
     // no warning
     return false;
   }

   /**
    * Verify the [typeName], used as the return type of a setter, is valid
    * (either `null` or the type 'void').
    *
    * See [StaticWarningCode.NON_VOID_RETURN_FOR_SETTER].
    */
   bool _checkForNonVoidReturnTypeForSetter(TypeName typeName) {
     if (typeName != null) {
       DartType type = typeName.type;
       if (type != null && !type.isVoid) {
         _errorReporter.reportErrorForNode(
             StaticWarningCode.NON_VOID_RETURN_FOR_SETTER, typeName);
       }
     }
     return false;
   }

   /**
    * Verify the given operator-method [declaration], does not have an optional
    * parameter. This method assumes that the method declaration was tested to be
    * an operator declaration before being called.
    *
    * See [CompileTimeErrorCode.OPTIONAL_PARAMETER_IN_OPERATOR].
    */
   bool _checkForOptionalParameterInOperator(MethodDeclaration declaration) {
     FormalParameterList parameterList = declaration.parameters;
     if (parameterList == null) {
       return false;
     }
     bool foundError = false;
     NodeList<FormalParameter> formalParameters = parameterList.parameters;
     for (FormalParameter formalParameter in formalParameters) {
       if (formalParameter.kind.isOptional) {
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.OPTIONAL_PARAMETER_IN_OPERATOR,
             formalParameter);
         foundError = true;
       }
     }
     return foundError;
   }

   /**
    * Check that the given named optional [parameter] does not begin with '_'.
    *
    * See [CompileTimeErrorCode.PRIVATE_OPTIONAL_PARAMETER].
    */
   bool _checkForPrivateOptionalParameter(FormalParameter parameter) {
     // should be named parameter
     if (parameter.kind != ParameterKind.NAMED) {
       return false;
     }
     // name should start with '_'
     SimpleIdentifier name = parameter.identifier;
     if (name.isSynthetic || !StringUtilities.startsWithChar(name.name, 0x5F)) {
       return false;
     }
     // report problem
     _errorReporter.reportErrorForNode(
         CompileTimeErrorCode.PRIVATE_OPTIONAL_PARAMETER, parameter);
     return true;
   }

   /**
    * Check whether the given constructor [declaration] is the redirecting
    * generative constructor and references itself directly or indirectly. The
    * [constructorElement] is the constructor element.
    *
    * See [CompileTimeErrorCode.RECURSIVE_CONSTRUCTOR_REDIRECT].
    */
   bool _checkForRecursiveConstructorRedirect(ConstructorDeclaration declaration,
       ConstructorElement constructorElement) {
     // we check generative constructor here
     if (declaration.factoryKeyword != null) {
       return false;
     }
     // try to find redirecting constructor invocation and analyzer it for
     // recursion
     for (ConstructorInitializer initializer in declaration.initializers) {
       if (initializer is RedirectingConstructorInvocation) {
         // OK if no cycle
         if (!_hasRedirectingFactoryConstructorCycle(constructorElement)) {
           return false;
         }
         // report error
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.RECURSIVE_CONSTRUCTOR_REDIRECT, initializer);
         return true;
       }
     }
     // OK, no redirecting constructor invocation
     return false;
   }

   /**
    * Check whether the given constructor [declaration] has redirected
    * constructor and references itself directly or indirectly. The
    * constructor [element] is the element introduced by the declaration.
    *
    * See [CompileTimeErrorCode.RECURSIVE_FACTORY_REDIRECT].
    */
   bool _checkForRecursiveFactoryRedirect(
       ConstructorDeclaration declaration, ConstructorElement element) {
     // prepare redirected constructor
     ConstructorName redirectedConstructorNode =
         declaration.redirectedConstructor;
     if (redirectedConstructorNode == null) {
       return false;
     }
     // OK if no cycle
     if (!_hasRedirectingFactoryConstructorCycle(element)) {
       return false;
     }
     // report error
     _errorReporter.reportErrorForNode(
         CompileTimeErrorCode.RECURSIVE_FACTORY_REDIRECT,
         redirectedConstructorNode);
     return true;
   }

   /**
    * Check that the class [element] is not a superinterface to itself.
    *
    * See [CompileTimeErrorCode.RECURSIVE_INTERFACE_INHERITANCE],
    * [CompileTimeErrorCode.RECURSIVE_INTERFACE_INHERITANCE_BASE_CASE_EXTENDS], and
    * [CompileTimeErrorCode.RECURSIVE_INTERFACE_INHERITANCE_BASE_CASE_IMPLEMENTS].
    */
   bool _checkForRecursiveInterfaceInheritance(ClassElement element) {
     if (element == null) {
       return false;
     }
     return _safeCheckForRecursiveInterfaceInheritance(
         element, new List<ClassElement>());
   }

   /**
    * Check that the given constructor [declaration] has a valid combination of
    * redirected constructor invocation(s), super constructor invocations and
    * field initializers.
    *
    * See [CompileTimeErrorCode.DEFAULT_VALUE_IN_REDIRECTING_FACTORY_CONSTRUCTOR],
    * [CompileTimeErrorCode.FIELD_INITIALIZER_REDIRECTING_CONSTRUCTOR],
    * [CompileTimeErrorCode.MULTIPLE_REDIRECTING_CONSTRUCTOR_INVOCATIONS],
    * [CompileTimeErrorCode.SUPER_IN_REDIRECTING_CONSTRUCTOR], and
    * [CompileTimeErrorCode.REDIRECT_GENERATIVE_TO_NON_GENERATIVE_CONSTRUCTOR].
    */
   bool _checkForRedirectingConstructorErrorCodes(
       ConstructorDeclaration declaration) {
     bool errorReported = false;
     //
     // Check for default values in the parameters
     //
     ConstructorName redirectedConstructor = declaration.redirectedConstructor;
     if (redirectedConstructor != null) {
       for (FormalParameter parameter in declaration.parameters.parameters) {
         if (parameter is DefaultFormalParameter &&
             parameter.defaultValue != null) {
           _errorReporter.reportErrorForNode(
               CompileTimeErrorCode.DEFAULT_VALUE_IN_REDIRECTING_FACTORY_CONSTRUCTOR,
               parameter.identifier);
           errorReported = true;
         }
       }
     }
     // check if there are redirected invocations
     int numRedirections = 0;
     for (ConstructorInitializer initializer in declaration.initializers) {
       if (initializer is RedirectingConstructorInvocation) {
         if (numRedirections > 0) {
           _errorReporter.reportErrorForNode(
               CompileTimeErrorCode.MULTIPLE_REDIRECTING_CONSTRUCTOR_INVOCATIONS,
               initializer);
           errorReported = true;
         }
         if (declaration.factoryKeyword == null) {
           RedirectingConstructorInvocation invocation = initializer;
           ConstructorElement redirectingElement = invocation.staticElement;
           if (redirectingElement == null) {
             String enclosingTypeName = _enclosingClass.displayName;
             String constructorStrName = enclosingTypeName;
             if (invocation.constructorName != null) {
               constructorStrName += ".${invocation.constructorName.name}";
             }
             _errorReporter.reportErrorForNode(
                 CompileTimeErrorCode.REDIRECT_GENERATIVE_TO_MISSING_CONSTRUCTOR,
                 invocation,
                 [constructorStrName, enclosingTypeName]);
           } else {
             if (redirectingElement.isFactory) {
               _errorReporter.reportErrorForNode(
                   CompileTimeErrorCode.REDIRECT_GENERATIVE_TO_NON_GENERATIVE_CONSTRUCTOR,
                   initializer);
             }
           }
         }
         numRedirections++;
       }
     }
     // check for other initializers
     if (numRedirections > 0) {
       for (ConstructorInitializer initializer in declaration.initializers) {
         if (initializer is SuperConstructorInvocation) {
           _errorReporter.reportErrorForNode(
               CompileTimeErrorCode.SUPER_IN_REDIRECTING_CONSTRUCTOR,
               initializer);
           errorReported = true;
         }
         if (initializer is ConstructorFieldInitializer) {
           _errorReporter.reportErrorForNode(
               CompileTimeErrorCode.FIELD_INITIALIZER_REDIRECTING_CONSTRUCTOR,
               initializer);
           errorReported = true;
         }
       }
     }
     // done
     return errorReported;
   }

   /**
    * Check whether the given constructor [declaration] has redirected
    * constructor and references itself directly or indirectly. The
    * constructor [element] is the element introduced by the declaration.
    *
    * See [CompileTimeErrorCode.REDIRECT_TO_NON_CONST_CONSTRUCTOR].
    */
   bool _checkForRedirectToNonConstConstructor(
       ConstructorDeclaration declaration, ConstructorElement element) {
     // prepare redirected constructor
     ConstructorName redirectedConstructorNode =
         declaration.redirectedConstructor;
     if (redirectedConstructorNode == null) {
       return false;
     }
     // prepare element
     if (element == null) {
       return false;
     }
     // OK, it is not 'const'
     if (!element.isConst) {
       return false;
     }
     // prepare redirected constructor
     ConstructorElement redirectedConstructor = element.redirectedConstructor;
     if (redirectedConstructor == null) {
       return false;
     }
     // OK, it is also 'const'
     if (redirectedConstructor.isConst) {
       return false;
     }
     // report error
     _errorReporter.reportErrorForNode(
         CompileTimeErrorCode.REDIRECT_TO_NON_CONST_CONSTRUCTOR,
         redirectedConstructorNode);
     return true;
   }

   /**
    * Check that the given rethrow [expression] is inside of a catch clause.
    *
    * See [CompileTimeErrorCode.RETHROW_OUTSIDE_CATCH].
    */
   bool _checkForRethrowOutsideCatch(RethrowExpression expression) {
     if (!_isInCatchClause) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.RETHROW_OUTSIDE_CATCH, expression);
       return true;
     }
     return false;
   }

   /**
    * Check that if the the given constructor [declaration] is generative, then
    * it does not have an expression function body.
    *
    * See [CompileTimeErrorCode.RETURN_IN_GENERATIVE_CONSTRUCTOR].
    */
   bool _checkForReturnInGenerativeConstructor(
       ConstructorDeclaration declaration) {
     // ignore factory
     if (declaration.factoryKeyword != null) {
       return false;
     }
     // block body (with possible return statement) is checked elsewhere
     FunctionBody body = declaration.body;
     if (body is! ExpressionFunctionBody) {
       return false;
     }
     // report error
     _errorReporter.reportErrorForNode(
         CompileTimeErrorCode.RETURN_IN_GENERATIVE_CONSTRUCTOR, body);
     return true;
   }

   /**
    * Check that a type mis-match between the type of the [returnExpression] and
    * the [expectedReturnType] by the enclosing method or function.
    *
    * This method is called both by [_checkForAllReturnStatementErrorCodes]
    * and [visitExpressionFunctionBody].
    *
    * See [StaticTypeWarningCode.RETURN_OF_INVALID_TYPE].
    */
   bool _checkForReturnOfInvalidType(
       Expression returnExpression, DartType expectedReturnType) {
     if (_enclosingFunction == null) {
       return false;
     }
     if (_inGenerator) {
       // "return expression;" is disallowed in generators, but this is checked
       // elsewhere.  Bare "return" is always allowed in generators regardless
       // of the return type.  So no need to do any further checking.
       return false;
     }
     DartType staticReturnType = _computeReturnTypeForMethod(returnExpression);
     if (expectedReturnType.isVoid) {
       if (staticReturnType.isVoid ||
           staticReturnType.isDynamic ||
           staticReturnType.isBottom) {
         return false;
       }
       _errorReporter.reportTypeErrorForNode(
           StaticTypeWarningCode.RETURN_OF_INVALID_TYPE, returnExpression, [
         staticReturnType,
         expectedReturnType,
         _enclosingFunction.displayName
       ]);
       return true;
     }
     if (_typeSystem.isAssignableTo(staticReturnType, expectedReturnType)) {
       return false;
     }
     _errorReporter.reportTypeErrorForNode(
         StaticTypeWarningCode.RETURN_OF_INVALID_TYPE,
         returnExpression,
         [staticReturnType, expectedReturnType, _enclosingFunction.displayName]);
     return true;
     // TODO(brianwilkerson) Define a hint corresponding to the warning and
     // report it if appropriate.
 //        Type propagatedReturnType = returnExpression.getPropagatedType();
 //        boolean isPropagatedAssignable = propagatedReturnType.isAssignableTo(expectedReturnType);
 //        if (isStaticAssignable || isPropagatedAssignable) {
 //          return false;
 //        }
 //        errorReporter.reportTypeErrorForNode(
 //            StaticTypeWarningCode.RETURN_OF_INVALID_TYPE,
 //            returnExpression,
 //            staticReturnType,
 //            expectedReturnType,
 //            enclosingFunction.getDisplayName());
 //        return true;
   }

   /**
    * Check the given [typeReference] and that the [name] is not the reference to
    * an instance member.
    *
    * See [StaticWarningCode.STATIC_ACCESS_TO_INSTANCE_MEMBER].
    */
   bool _checkForStaticAccessToInstanceMember(
       ClassElement typeReference, SimpleIdentifier name) {
     // OK, target is not a type
     if (typeReference == null) {
       return false;
     }
     // prepare member Element
     Element element = name.staticElement;
     if (element is! ExecutableElement) {
       return false;
     }
     ExecutableElement memberElement = element as ExecutableElement;
     // OK, static
     if (memberElement.isStatic) {
       return false;
     }
     // report problem
     _errorReporter.reportErrorForNode(
         StaticWarningCode.STATIC_ACCESS_TO_INSTANCE_MEMBER, name, [name.name]);
     return true;
   }

   /**
    * Check that the type of the expression in the given 'switch' [statement] is
    * assignable to the type of the 'case' members.
    *
    * See [StaticWarningCode.SWITCH_EXPRESSION_NOT_ASSIGNABLE].
    */
   bool _checkForSwitchExpressionNotAssignable(SwitchStatement statement) {
     // prepare 'switch' expression type
     Expression expression = statement.expression;
     DartType expressionType = getStaticType(expression);
     if (expressionType == null) {
       return false;
     }
     // compare with type of the first 'case'
     NodeList<SwitchMember> members = statement.members;
     for (SwitchMember switchMember in members) {
       if (switchMember is! SwitchCase) {
         continue;
       }
       SwitchCase switchCase = switchMember as SwitchCase;
       // prepare 'case' type
       Expression caseExpression = switchCase.expression;
       DartType caseType = getStaticType(caseExpression);
       // check types
       if (_typeSystem.isAssignableTo(expressionType, caseType)) {
         return false;
       }
       // report problem
       _errorReporter.reportErrorForNode(
           StaticWarningCode.SWITCH_EXPRESSION_NOT_ASSIGNABLE,
           expression,
           [expressionType, caseType]);
       return true;
     }
     return false;
   }

   /**
    * Verify that the given function type [alias] does not reference itself
    * directly.
    *
    * See [CompileTimeErrorCode.TYPE_ALIAS_CANNOT_REFERENCE_ITSELF].
    */
   bool _checkForTypeAliasCannotReferenceItself_function(
       FunctionTypeAlias alias) {
     FunctionTypeAliasElement element = alias.element;
     if (!_hasTypedefSelfReference(element)) {
       return false;
     }
     _errorReporter.reportErrorForNode(
         CompileTimeErrorCode.TYPE_ALIAS_CANNOT_REFERENCE_ITSELF, alias);
     return true;
   }

   /**
    * Verify that the given type [name] is not a deferred type.
    *
    * See [StaticWarningCode.TYPE_ANNOTATION_DEFERRED_CLASS].
    */
   bool _checkForTypeAnnotationDeferredClass(TypeName name) {
     if (name != null && name.isDeferred) {
       _errorReporter.reportErrorForNode(
           StaticWarningCode.TYPE_ANNOTATION_DEFERRED_CLASS, name, [name.name]);
     }
     return false;
   }

   /**
    * Verify that the type arguments in the given [typeName] are all within
    * their bounds.
    *
    * See [StaticTypeWarningCode.TYPE_ARGUMENT_NOT_MATCHING_BOUNDS].
    */
   bool _checkForTypeArgumentNotMatchingBounds(TypeName typeName) {
     if (typeName.typeArguments == null) {
       return false;
     }
     // prepare Type
     DartType type = typeName.type;
     if (type == null) {
       return false;
     }
     // prepare ClassElement
     Element element = type.element;
     if (element is! ClassElement) {
       return false;
     }
     ClassElement classElement = element as ClassElement;
     // prepare type parameters
     List<DartType> typeParameters = classElement.type.typeArguments;
     List<TypeParameterElement> boundingElts = classElement.typeParameters;
     // iterate over each bounded type parameter and corresponding argument
     NodeList<TypeName> typeNameArgList = typeName.typeArguments.arguments;
     List<DartType> typeArguments = (type as InterfaceType).typeArguments;
     int loopThroughIndex =
         math.min(typeNameArgList.length, boundingElts.length);
     bool foundError = false;
     for (int i = 0; i < loopThroughIndex; i++) {
       TypeName argTypeName = typeNameArgList[i];
       DartType argType = argTypeName.type;
       DartType boundType = boundingElts[i].bound;
       if (argType != null && boundType != null) {
         if (typeArguments.length != 0 &&
             typeArguments.length == typeParameters.length) {
           boundType = boundType.substitute2(typeArguments, typeParameters);
         }
         if (!_typeSystem.isSubtypeOf(argType, boundType)) {
           ErrorCode errorCode;
           if (_isInConstInstanceCreation) {
             errorCode = CompileTimeErrorCode.TYPE_ARGUMENT_NOT_MATCHING_BOUNDS;
           } else {
             errorCode = StaticTypeWarningCode.TYPE_ARGUMENT_NOT_MATCHING_BOUNDS;
           }
           _errorReporter.reportTypeErrorForNode(
               errorCode, argTypeName, [argType, boundType]);
           foundError = true;
         }
       }
     }
     return foundError;
   }

   /**
    * Check whether the given type [name] is a type parameter being used to
    * define a static member.
    *
    * See [StaticWarningCode.TYPE_PARAMETER_REFERENCED_BY_STATIC].
    */
   bool _checkForTypeParameterReferencedByStatic(TypeName name) {
     if (_isInStaticMethod || _isInStaticVariableDeclaration) {
       DartType type = name.type;
       if (type is TypeParameterType) {
         _errorReporter.reportErrorForNode(
             StaticWarningCode.TYPE_PARAMETER_REFERENCED_BY_STATIC, name);
         return true;
       }
     }
     return false;
   }

   /**
    * Check whether the given type [parameter] is a supertype of its bound.
    *
    * See [StaticTypeWarningCode.TYPE_PARAMETER_SUPERTYPE_OF_ITS_BOUND].
    */
   bool _checkForTypeParameterSupertypeOfItsBound(TypeParameter parameter) {
     TypeParameterElement element = parameter.element;
     // prepare bound
     DartType bound = element.bound;
     if (bound == null) {
       return false;
     }
     // OK, type parameter is not supertype of its bound
     if (!bound.isMoreSpecificThan(element.type)) {
       return false;
     }
     // report problem
     _errorReporter.reportErrorForNode(
         StaticTypeWarningCode.TYPE_PARAMETER_SUPERTYPE_OF_ITS_BOUND,
         parameter,
         [element.displayName]);
     return true;
   }

   /**
    * Check that if the given generative [constructor] has neither an explicit
    * super constructor invocation nor a redirecting constructor invocation, that
    * the superclass has a default generative constructor.
    *
    * See [CompileTimeErrorCode.UNDEFINED_CONSTRUCTOR_IN_INITIALIZER_DEFAULT],
    * [CompileTimeErrorCode.NON_GENERATIVE_CONSTRUCTOR], and
    * [StaticWarningCode.NO_DEFAULT_SUPER_CONSTRUCTOR_EXPLICIT].
    */
   bool _checkForUndefinedConstructorInInitializerImplicit(
       ConstructorDeclaration constructor) {
     if (_enclosingClass == null) {
       return false;
     }
     // do nothing if mixin errors have already been reported for this class.
     ClassElementImpl enclosingClass = _enclosingClass;
     if (enclosingClass.doesMixinLackConstructors) {
       return false;
     }
     //
     // Ignore if the constructor is not generative.
     //
     if (constructor.factoryKeyword != null) {
       return false;
     }
     //
     // Ignore if the constructor has either an implicit super constructor
     // invocation or a redirecting constructor invocation.
     //
     for (ConstructorInitializer constructorInitializer
         in constructor.initializers) {
       if (constructorInitializer is SuperConstructorInvocation ||
           constructorInitializer is RedirectingConstructorInvocation) {
         return false;
       }
     }
     //
     // Check to see whether the superclass has a non-factory unnamed
     // constructor.
     //
     InterfaceType superType = _enclosingClass.supertype;
     if (superType == null) {
       return false;
     }
     ClassElement superElement = superType.element;
     ConstructorElement superUnnamedConstructor =
         superElement.unnamedConstructor;
     if (superUnnamedConstructor != null) {
       if (superUnnamedConstructor.isFactory) {
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.NON_GENERATIVE_CONSTRUCTOR,
             constructor.returnType,
             [superUnnamedConstructor]);
         return true;
       }
       if (!superUnnamedConstructor.isDefaultConstructor ||
           !_enclosingClass
               .isSuperConstructorAccessible(superUnnamedConstructor)) {
         int offset;
         int length;
         {
           Identifier returnType = constructor.returnType;
           SimpleIdentifier name = constructor.name;
           offset = returnType.offset;
           length = (name != null ? name.end : returnType.end) - offset;
         }
         _errorReporter.reportErrorForOffset(
             CompileTimeErrorCode.NO_DEFAULT_SUPER_CONSTRUCTOR_EXPLICIT,
             offset,
             length,
             [superType.displayName]);
       }
       return false;
     }
     _errorReporter.reportErrorForNode(
         CompileTimeErrorCode.UNDEFINED_CONSTRUCTOR_IN_INITIALIZER_DEFAULT,
         constructor.returnType,
         [superElement.name]);
     return true;
   }

   /**
    * Check that if the given [name] is a reference to a static member it is
    * defined in the enclosing class rather than in a superclass.
    *
    * See [StaticTypeWarningCode.UNQUALIFIED_REFERENCE_TO_NON_LOCAL_STATIC_MEMBER].
    */
   bool _checkForUnqualifiedReferenceToNonLocalStaticMember(
       SimpleIdentifier name) {
     Element element = name.staticElement;
     if (element == null || element is TypeParameterElement) {
       return false;
     }
     Element enclosingElement = element.enclosingElement;
     if (enclosingElement is! ClassElement) {
       return false;
     }
     if ((element is MethodElement && !element.isStatic) ||
         (element is PropertyAccessorElement && !element.isStatic)) {
       return false;
     }
     if (identical(enclosingElement, _enclosingClass)) {
       return false;
     }
     _errorReporter.reportErrorForNode(
         StaticTypeWarningCode.UNQUALIFIED_REFERENCE_TO_NON_LOCAL_STATIC_MEMBER,
         name,
         [name.name]);
     return true;
   }

   void _checkForValidField(FieldFormalParameter parameter) {
     ParameterElement element = parameter.element;
     if (element is FieldFormalParameterElement) {
       FieldElement fieldElement = element.field;
       if (fieldElement == null || fieldElement.isSynthetic) {
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.INITIALIZING_FORMAL_FOR_NON_EXISTENT_FIELD,
             parameter,
             [parameter.identifier.name]);
       } else {
         ParameterElement parameterElement = parameter.element;
         if (parameterElement is FieldFormalParameterElementImpl) {
           FieldFormalParameterElementImpl fieldFormal = parameterElement;
           DartType declaredType = fieldFormal.type;
           DartType fieldType = fieldElement.type;
           if (fieldElement.isSynthetic) {
             _errorReporter.reportErrorForNode(
                 CompileTimeErrorCode.INITIALIZING_FORMAL_FOR_NON_EXISTENT_FIELD,
                 parameter,
                 [parameter.identifier.name]);
           } else if (fieldElement.isStatic) {
             _errorReporter.reportErrorForNode(
                 CompileTimeErrorCode.INITIALIZING_FORMAL_FOR_STATIC_FIELD,
                 parameter,
                 [parameter.identifier.name]);
           } else if (declaredType != null &&
               fieldType != null &&
               !_typeSystem.isAssignableTo(declaredType, fieldType)) {
             _errorReporter.reportTypeErrorForNode(
                 StaticWarningCode.FIELD_INITIALIZING_FORMAL_NOT_ASSIGNABLE,
                 parameter,
                 [declaredType, fieldType]);
           }
         } else {
           if (fieldElement.isSynthetic) {
             _errorReporter.reportErrorForNode(
                 CompileTimeErrorCode.INITIALIZING_FORMAL_FOR_NON_EXISTENT_FIELD,
                 parameter,
                 [parameter.identifier.name]);
           } else if (fieldElement.isStatic) {
             _errorReporter.reportErrorForNode(
                 CompileTimeErrorCode.INITIALIZING_FORMAL_FOR_STATIC_FIELD,
                 parameter,
                 [parameter.identifier.name]);
           }
         }
       }
     }
 //        else {
 //        // TODO(jwren) Report error, constructor initializer variable is a top level element
 //        // (Either here or in ErrorVerifier.checkForAllFinalInitializedErrorCodes)
 //        }
   }

   /**
    * Verify that the given [getter] does not have a return type of 'void'.
    *
    * See [StaticWarningCode.VOID_RETURN_FOR_GETTER].
    */
   bool _checkForVoidReturnType(MethodDeclaration getter) {
     TypeName returnType = getter.returnType;
     if (returnType == null || returnType.name.name != "void") {
       return false;
     }
     _errorReporter.reportErrorForNode(
         StaticWarningCode.VOID_RETURN_FOR_GETTER, returnType);
     return true;
   }

   /**
    * Verify the given operator-method [declaration], has correct number of
    * parameters.
    *
    * This method assumes that the method declaration was tested to be an
    * operator declaration before being called.
    *
    * See [CompileTimeErrorCode.WRONG_NUMBER_OF_PARAMETERS_FOR_OPERATOR].
    */
   bool _checkForWrongNumberOfParametersForOperator(
       MethodDeclaration declaration) {
     // prepare number of parameters
     FormalParameterList parameterList = declaration.parameters;
     if (parameterList == null) {
       return false;
     }
     int numParameters = parameterList.parameters.length;
     // prepare operator name
     SimpleIdentifier nameNode = declaration.name;
     if (nameNode == null) {
       return false;
     }
     String name = nameNode.name;
     // check for exact number of parameters
     int expected = -1;
     if ("[]=" == name) {
       expected = 2;
     } else if ("<" == name ||
         ">" == name ||
         "<=" == name ||
         ">=" == name ||
         "==" == name ||
         "+" == name ||
         "/" == name ||
         "~/" == name ||
         "*" == name ||
         "%" == name ||
         "|" == name ||
         "^" == name ||
         "&" == name ||
         "<<" == name ||
         ">>" == name ||
         "[]" == name) {
       expected = 1;
     } else if ("~" == name) {
       expected = 0;
     }
     if (expected != -1 && numParameters != expected) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.WRONG_NUMBER_OF_PARAMETERS_FOR_OPERATOR,
           nameNode,
           [name, expected, numParameters]);
       return true;
     }
     // check for operator "-"
     if ("-" == name && numParameters > 1) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.WRONG_NUMBER_OF_PARAMETERS_FOR_OPERATOR_MINUS,
           nameNode,
           [numParameters]);
       return true;
     }
     // OK
     return false;
   }

   /**
    * Verify that the given setter [parameterList] has only one required
    * parameter. The [setterName] is the name of the setter to report problems
    * on.
    *
    * This method assumes that the method declaration was tested to be a setter
    * before being called.
    *
    * See [CompileTimeErrorCode.WRONG_NUMBER_OF_PARAMETERS_FOR_SETTER].
    */
   bool _checkForWrongNumberOfParametersForSetter(
       SimpleIdentifier setterName, FormalParameterList parameterList) {
     if (setterName == null) {
       return false;
     }
     if (parameterList == null) {
       return false;
     }
     NodeList<FormalParameter> parameters = parameterList.parameters;
     if (parameters.length != 1 ||
         parameters[0].kind != ParameterKind.REQUIRED) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.WRONG_NUMBER_OF_PARAMETERS_FOR_SETTER,
           setterName);
       return true;
     }
     return false;
   }

   /**
    * Check for a type mis-match between the yielded type and the declared
    * return type of a generator function.
    *
    * This method should only be called in generator functions.
    */
   bool _checkForYieldOfInvalidType(
       Expression yieldExpression, bool isYieldEach) {
     assert(_inGenerator);
     if (_enclosingFunction == null) {
       return false;
     }
     DartType declaredReturnType = _enclosingFunction.returnType;
     DartType staticYieldedType = getStaticType(yieldExpression);
     DartType impliedReturnType;
     if (isYieldEach) {
       impliedReturnType = staticYieldedType;
     } else if (_enclosingFunction.isAsynchronous) {
       impliedReturnType =
           _typeProvider.streamType.substitute4(<DartType>[staticYieldedType]);
     } else {
       impliedReturnType =
           _typeProvider.iterableType.substitute4(<DartType>[staticYieldedType]);
     }
     if (!_typeSystem.isAssignableTo(impliedReturnType, declaredReturnType)) {
       _errorReporter.reportTypeErrorForNode(
           StaticTypeWarningCode.YIELD_OF_INVALID_TYPE,
           yieldExpression,
           [impliedReturnType, declaredReturnType]);
       return true;
     }
     if (isYieldEach) {
       // Since the declared return type might have been "dynamic", we need to
       // also check that the implied return type is assignable to generic
       // Stream/Iterable.
       DartType requiredReturnType;
       if (_enclosingFunction.isAsynchronous) {
         requiredReturnType = _typeProvider.streamDynamicType;
       } else {
         requiredReturnType = _typeProvider.iterableDynamicType;
       }
       if (!_typeSystem.isAssignableTo(impliedReturnType, requiredReturnType)) {
         _errorReporter.reportTypeErrorForNode(
             StaticTypeWarningCode.YIELD_OF_INVALID_TYPE,
             yieldExpression,
             [impliedReturnType, requiredReturnType]);
         return true;
       }
     }
     return false;
   }

   /**
    * Verify that if the given class [declaration] implements the class Function
    * that it has a concrete implementation of the call method.
    *
    * See [StaticWarningCode.FUNCTION_WITHOUT_CALL].
    */
   bool _checkImplementsFunctionWithoutCall(ClassDeclaration declaration) {
     if (declaration.isAbstract) {
       return false;
     }
     ClassElement classElement = declaration.element;
     if (classElement == null) {
       return false;
     }
     if (!_typeSystem.isSubtypeOf(
         classElement.type, _typeProvider.functionType)) {
       return false;
     }
     // If there is a noSuchMethod method, then don't report the warning,
     // see dartbug.com/16078
     if (classElement.getMethod(FunctionElement.NO_SUCH_METHOD_METHOD_NAME) !=
         null) {
       return false;
     }
     ExecutableElement callMethod = _inheritanceManager.lookupMember(
         classElement, FunctionElement.CALL_METHOD_NAME);
     if (callMethod == null ||
         callMethod is! MethodElement ||
         (callMethod as MethodElement).isAbstract) {
       _errorReporter.reportErrorForNode(
           StaticWarningCode.FUNCTION_WITHOUT_CALL, declaration.name);
       return true;
     }
     return false;
   }

   /**
    * Verify that the given class [declaration] does not have the same class in
    * the 'extends' and 'implements' clauses.
    *
    * See [CompileTimeErrorCode.IMPLEMENTS_SUPER_CLASS].
    */
   bool _checkImplementsSuperClass(ClassDeclaration declaration) {
     // prepare super type
     InterfaceType superType = _enclosingClass.supertype;
     if (superType == null) {
       return false;
     }
     // prepare interfaces
     ImplementsClause implementsClause = declaration.implementsClause;
     if (implementsClause == null) {
       return false;
     }
     // check interfaces
     bool hasProblem = false;
     for (TypeName interfaceNode in implementsClause.interfaces) {
       if (interfaceNode.type == superType) {
         hasProblem = true;
         _errorReporter.reportErrorForNode(
             CompileTimeErrorCode.IMPLEMENTS_SUPER_CLASS,
             interfaceNode,
             [superType.displayName]);
       }
     }
     // done
     return hasProblem;
   }

   DartType _computeReturnTypeForMethod(Expression returnExpression) {
     // This method should never be called for generators, since generators are
     // never allowed to contain return statements with expressions.
     assert(!_inGenerator);
     if (returnExpression == null) {
       if (_enclosingFunction.isAsynchronous) {
         return _typeProvider.futureNullType;
       } else {
         return VoidTypeImpl.instance;
       }
     }
     DartType staticReturnType = getStaticType(returnExpression);
     if (staticReturnType != null && _enclosingFunction.isAsynchronous) {
       return _typeProvider.futureType.substitute4(<DartType>[
         StaticTypeAnalyzer.flattenFutures(_typeProvider, staticReturnType)
       ]);
     }
     return staticReturnType;
   }

   /**
    * Return the error code that should be used when the given class [element]
    * references itself directly.
    */
   ErrorCode _getBaseCaseErrorCode(ClassElement element) {
     InterfaceType supertype = element.supertype;
     if (supertype != null && _enclosingClass == supertype.element) {
       return CompileTimeErrorCode.RECURSIVE_INTERFACE_INHERITANCE_BASE_CASE_EXTENDS;
     }
     List<InterfaceType> mixins = element.mixins;
     for (int i = 0; i < mixins.length; i++) {
       if (_enclosingClass == mixins[i].element) {
         return CompileTimeErrorCode.RECURSIVE_INTERFACE_INHERITANCE_BASE_CASE_WITH;
       }
     }
     return CompileTimeErrorCode.RECURSIVE_INTERFACE_INHERITANCE_BASE_CASE_IMPLEMENTS;
   }

   /**
    * Given an [expression] in a switch case whose value is expected to be an
    * enum constant, return the name of the constant.
    */
   String _getConstantName(Expression expression) {
     // TODO(brianwilkerson) Convert this to return the element representing the
     // constant.
     if (expression is SimpleIdentifier) {
       return expression.name;
     } else if (expression is PrefixedIdentifier) {
       return expression.identifier.name;
     } else if (expression is PropertyAccess) {
       return expression.propertyName.name;
     }
     return null;
   }

   /**
    * Return the return type of the given [getter].
    */
   DartType _getGetterType(PropertyAccessorElement getter) {
     FunctionType functionType = getter.type;
     if (functionType != null) {
       return functionType.returnType;
     } else {
       return null;
     }
   }

   /**
    * Return the type of the first and only parameter of the given [setter].
    */
   DartType _getSetterType(PropertyAccessorElement setter) {
     // Get the parameters for MethodDeclaration or FunctionDeclaration
     List<ParameterElement> setterParameters = setter.parameters;
     // If there are no setter parameters, return no type.
     if (setterParameters.length == 0) {
       return null;
     }
     return setterParameters[0].type;
   }

   /**
    * Given a list of [directives] that have the same prefix, generate an error
    * if there is more than one import and any of those imports is deferred.
    *
    * See [CompileTimeErrorCode.SHARED_DEFERRED_PREFIX].
    */
   bool _hasDeferredPrefixCollision(List<ImportDirective> directives) {
     bool foundError = false;
     int count = directives.length;
     if (count > 1) {
       for (int i = 0; i < count; i++) {
         sc.Token deferredToken = directives[i].deferredKeyword;
         if (deferredToken != null) {
           _errorReporter.reportErrorForToken(
               CompileTimeErrorCode.SHARED_DEFERRED_PREFIX, deferredToken);
           foundError = true;
         }
       }
     }
     return foundError;
   }

   /**
    * Return `true` if the given [constructor] redirects to itself, directly or
    * indirectly.
    */
   bool _hasRedirectingFactoryConstructorCycle(ConstructorElement constructor) {
     Set<ConstructorElement> constructors = new HashSet<ConstructorElement>();
     ConstructorElement current = constructor;
     while (current != null) {
       if (constructors.contains(current)) {
         return identical(current, constructor);
       }
       constructors.add(current);
       current = current.redirectedConstructor;
       if (current is ConstructorMember) {
         current = (current as ConstructorMember).baseElement;
       }
     }
     return false;
   }

   /**
    * Return `true` if the given [element] has direct or indirect reference to
    * itself from anywhere except a class element or type parameter bounds.
    */
   bool _hasTypedefSelfReference(Element element) {
     Set<Element> checked = new HashSet<Element>();
     List<Element> toCheck = new List<Element>();
     GeneralizingElementVisitor_ErrorVerifier_hasTypedefSelfReference elementVisitor =
         new GeneralizingElementVisitor_ErrorVerifier_hasTypedefSelfReference(
             toCheck);
     toCheck.add(element);
     bool firstIteration = true;
     while (true) {
       Element current;
       // get next element
       while (true) {
         // may be no more elements to check
         if (toCheck.isEmpty) {
           return false;
         }
         // try to get next element
         current = toCheck.removeAt(toCheck.length - 1);
         if (element == current) {
           if (firstIteration) {
             firstIteration = false;
             break;
           } else {
             return true;
           }
         }
         if (current != null && !checked.contains(current)) {
           break;
         }
       }
       // check current element
       current.accept(elementVisitor);
       checked.add(current);
     }
   }

   bool _isFunctionType(DartType type) {
     if (type.isDynamic || type.isBottom) {
       return true;
     } else if (type is FunctionType || type.isDartCoreFunction) {
       return true;
     } else if (type is InterfaceType) {
       MethodElement callMethod =
           type.lookUpMethod(FunctionElement.CALL_METHOD_NAME, _currentLibrary);
       return callMethod != null;
     }
     return false;
   }

   /**
    * Return `true` iff the given [classElement] has a concrete method, getter or
    * setter that matches the name of the given [executableElement] in either the
    * class itself, or one of its' mixins.
    *
    * By "match", only the name of the member is tested to match, it does not
    * have to equal or be a subtype of the given executable element, this is due
    * to the specific use where this method is used in
    * [_checkForNonAbstractClassInheritsAbstractMember].
    */
   bool _isMemberInClassOrMixin(
       ExecutableElement executableElement, ClassElement classElement) {
     ExecutableElement foundElt = null;
     String executableName = executableElement.name;
     if (executableElement is MethodElement) {
       foundElt = classElement.getMethod(executableName);
       if (foundElt != null && !(foundElt as MethodElement).isAbstract) {
         return true;
       }
       List<InterfaceType> mixins = classElement.mixins;
       for (int i = 0; i < mixins.length && foundElt == null; i++) {
         foundElt = mixins[i].getMethod(executableName);
       }
       if (foundElt != null && !(foundElt as MethodElement).isAbstract) {
         return true;
       }
     } else if (executableElement is PropertyAccessorElement) {
       PropertyAccessorElement propertyAccessorElement = executableElement;
       if (propertyAccessorElement.isGetter) {
         foundElt = classElement.getGetter(executableName);
       }
       if (foundElt == null && propertyAccessorElement.isSetter) {
         foundElt = classElement.getSetter(executableName);
       }
       if (foundElt != null &&
           !(foundElt as PropertyAccessorElement).isAbstract) {
         return true;
       }
       List<InterfaceType> mixins = classElement.mixins;
       for (int i = 0; i < mixins.length && foundElt == null; i++) {
         foundElt = mixins[i].getGetter(executableName);
         if (foundElt == null) {
           foundElt = mixins[i].getSetter(executableName);
         }
       }
       if (foundElt != null &&
           !(foundElt as PropertyAccessorElement).isAbstract) {
         return true;
       }
     }
     return false;
   }

   /**
    * Return `true` if the given 'this' [expression] is in a valid context.
    */
   bool _isThisInValidContext(ThisExpression expression) {
     for (AstNode node = expression.parent; node != null; node = node.parent) {
       if (node is CompilationUnit) {
         return false;
       }
       if (node is ConstructorDeclaration) {
         return node.factoryKeyword == null;
       }
       if (node is ConstructorInitializer) {
         return false;
       }
       if (node is MethodDeclaration) {
         return !node.isStatic;
       }
     }
     return false;
   }

   /**
    * Return `true` if the given [identifier] is in a location where it is
    * allowed to resolve to a static member of a supertype.
    */
   bool _isUnqualifiedReferenceToNonLocalStaticMemberAllowed(
       SimpleIdentifier identifier) {
     if (identifier.inDeclarationContext()) {
       return true;
     }
     AstNode parent = identifier.parent;
     if (parent is ConstructorName ||
         parent is MethodInvocation ||
         parent is PropertyAccess ||
         parent is SuperConstructorInvocation) {
       return true;
     }
     if (parent is PrefixedIdentifier &&
         identical(parent.identifier, identifier)) {
       return true;
     }
     if (parent is Annotation && identical(parent.constructorName, identifier)) {
       return true;
     }
     if (parent is CommentReference) {
       CommentReference commentReference = parent;
       if (commentReference.newKeyword != null) {
         return true;
       }
     }
     return false;
   }

   bool _isUserDefinedObject(EvaluationResultImpl result) => result == null ||
       (result.value != null && result.value.isUserDefinedObject);

   /**
    * Check that the given class [element] is not a superinterface to itself. The
    * [path] is a list containing the potentially cyclic implements path.
    *
    * See [CompileTimeErrorCode.RECURSIVE_INTERFACE_INHERITANCE],
    * [CompileTimeErrorCode.RECURSIVE_INTERFACE_INHERITANCE_BASE_CASE_EXTENDS],
    * [CompileTimeErrorCode.RECURSIVE_INTERFACE_INHERITANCE_BASE_CASE_IMPLEMENTS],
    * and [CompileTimeErrorCode.RECURSIVE_INTERFACE_INHERITANCE_BASE_CASE_WITH].
    */
   bool _safeCheckForRecursiveInterfaceInheritance(
       ClassElement element, List<ClassElement> path) {
     // Detect error condition.
     int size = path.length;
     // If this is not the base case (size > 0), and the enclosing class is the
     // given class element then an error an error.
     if (size > 0 && _enclosingClass == element) {
       String enclosingClassName = _enclosingClass.displayName;
       if (size > 1) {
         // Construct a string showing the cyclic implements path:
         // "A, B, C, D, A"
         String separator = ", ";
         StringBuffer buffer = new StringBuffer();
         for (int i = 0; i < size; i++) {
           buffer.write(path[i].displayName);
           buffer.write(separator);
         }
         buffer.write(element.displayName);
         _errorReporter.reportErrorForElement(
             CompileTimeErrorCode.RECURSIVE_INTERFACE_INHERITANCE,
             _enclosingClass,
             [enclosingClassName, buffer.toString()]);
         return true;
       } else {
         // RECURSIVE_INTERFACE_INHERITANCE_BASE_CASE_EXTENDS or
         // RECURSIVE_INTERFACE_INHERITANCE_BASE_CASE_IMPLEMENTS or
         // RECURSIVE_INTERFACE_INHERITANCE_BASE_CASE_WITH
         _errorReporter.reportErrorForElement(_getBaseCaseErrorCode(element),
             _enclosingClass, [enclosingClassName]);
         return true;
       }
     }
     if (path.indexOf(element) > 0) {
       return false;
     }
     path.add(element);
     // n-case
     InterfaceType supertype = element.supertype;
     if (supertype != null &&
         _safeCheckForRecursiveInterfaceInheritance(supertype.element, path)) {
       return true;
     }
     List<InterfaceType> interfaceTypes = element.interfaces;
     for (InterfaceType interfaceType in interfaceTypes) {
       if (_safeCheckForRecursiveInterfaceInheritance(
           interfaceType.element, path)) {
         return true;
       }
     }
     List<InterfaceType> mixinTypes = element.mixins;
     for (InterfaceType mixinType in mixinTypes) {
       if (_safeCheckForRecursiveInterfaceInheritance(mixinType.element, path)) {
         return true;
       }
     }
     path.removeAt(path.length - 1);
     return false;
   }

   /**
    * Return the static type of the given [expression] that is to be used for
    * type analysis.
    */
   static DartType getStaticType(Expression expression) {
     DartType type = expression.staticType;
     if (type == null) {
       // TODO(brianwilkerson) This should never happen.
       return DynamicTypeImpl.instance;
     }
     return type;
   }

   /**
    * Return the variable element represented by the given [expression], or
    * `null` if there is no such element.
    */
   static VariableElement getVariableElement(Expression expression) {
     if (expression is Identifier) {
       Element element = expression.staticElement;
       if (element is VariableElement) {
         return element;
       }
     }
     return null;
   }
 }

 class GeneralizingElementVisitor_ErrorVerifier_hasTypedefSelfReference
     extends GeneralizingElementVisitor<Object> {
   List<Element> toCheck;

   GeneralizingElementVisitor_ErrorVerifier_hasTypedefSelfReference(this.toCheck)
       : super();

   @override
   Object visitClassElement(ClassElement element) {
     // Typedefs are allowed to reference themselves via classes.
     return null;
   }

   @override
   Object visitFunctionTypeAliasElement(FunctionTypeAliasElement element) {
     _addTypeToCheck(element.returnType);
     return super.visitFunctionTypeAliasElement(element);
   }

   @override
   Object visitParameterElement(ParameterElement element) {
     _addTypeToCheck(element.type);
     return super.visitParameterElement(element);
   }

   @override
   Object visitTypeParameterElement(TypeParameterElement element) {
     _addTypeToCheck(element.bound);
     return super.visitTypeParameterElement(element);
   }

   void _addTypeToCheck(DartType type) {
     if (type == null) {
       return;
     }
     // schedule for checking
     toCheck.add(type.element);
     // type arguments
     if (type is InterfaceType) {
       InterfaceType interfaceType = type;
       for (DartType typeArgument in interfaceType.typeArguments) {
         _addTypeToCheck(typeArgument);
       }
     }
   }
 }