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

// 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.

import 'dart:collection';

import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/ast/ast_factory.dart';
import 'package:analyzer/dart/ast/standard_resolution_map.dart';
import 'package:analyzer/dart/ast/token.dart';
import 'package:analyzer/dart/ast/visitor.dart';
import 'package:analyzer/dart/element/element.dart';
import 'package:analyzer/dart/element/type.dart';
import 'package:analyzer/error/error.dart';
import 'package:analyzer/error/listener.dart';
import 'package:analyzer/exception/exception.dart';
import 'package:analyzer/file_system/file_system.dart';
import 'package:analyzer/src/context/builder.dart';
import 'package:analyzer/src/dart/ast/ast.dart';
import 'package:analyzer/src/dart/ast/ast_factory.dart';
import 'package:analyzer/src/dart/ast/token.dart';
import 'package:analyzer/src/dart/ast/utilities.dart';
import 'package:analyzer/src/dart/element/element.dart';
import 'package:analyzer/src/dart/element/inheritance_manager2.dart';
import 'package:analyzer/src/dart/element/member.dart' show ConstructorMember;
import 'package:analyzer/src/dart/element/type.dart';
import 'package:analyzer/src/dart/resolver/exit_detector.dart';
import 'package:analyzer/src/dart/resolver/scope.dart';
import 'package:analyzer/src/error/codes.dart';
import 'package:analyzer/src/generated/constant.dart';
import 'package:analyzer/src/generated/element_resolver.dart';
import 'package:analyzer/src/generated/engine.dart';
import 'package:analyzer/src/generated/source.dart';
import 'package:analyzer/src/generated/static_type_analyzer.dart';
import 'package:analyzer/src/generated/testing/element_factory.dart';
import 'package:analyzer/src/generated/type_system.dart';
import 'package:analyzer/src/lint/linter.dart';
import 'package:analyzer/src/workspace/workspace.dart';
import 'package:meta/meta.dart';
import 'package:path/path.dart' as path;

export 'package:analyzer/src/dart/constant/constant_verifier.dart';
export 'package:analyzer/src/dart/resolver/exit_detector.dart';
export 'package:analyzer/src/dart/resolver/inheritance_manager.dart';
export 'package:analyzer/src/dart/resolver/scope.dart';
export 'package:analyzer/src/generated/type_system.dart';

/// A visitor that will re-write an AST to support the optional `new` and
/// `const` feature.
class AstRewriteVisitor extends ScopedVisitor {
  final bool addConstKeyword;
  final TypeSystem typeSystem;

  /// Initialize a newly created visitor.
  AstRewriteVisitor(
      this.typeSystem,
      LibraryElement definingLibrary,
      Source source,
      TypeProvider typeProvider,
      AnalysisErrorListener errorListener,
      {Scope nameScope,
      this.addConstKeyword: false})
      : super(definingLibrary, source, typeProvider, errorListener,
            nameScope: nameScope);

  @override
  void visitMethodInvocation(MethodInvocation node) {
    super.visitMethodInvocation(node);

    SimpleIdentifier methodName = node.methodName;
    if (methodName.isSynthetic) {
      // This isn't a constructor invocation because the method name is
      // synthetic.
      return;
    }

    Expression target = node.target;
    if (target == null) {
      // Possible cases: C() or C<>()
      if (node.realTarget != null) {
        // This isn't a constructor invocation because it's in a cascade.
        return;
      }
      Element element = nameScope.lookup(methodName, definingLibrary);
      if (element is ClassElement) {
        AstFactory astFactory = new AstFactoryImpl();
        TypeName typeName = astFactory.typeName(methodName, node.typeArguments);
        ConstructorName constructorName =
            astFactory.constructorName(typeName, null, null);
        InstanceCreationExpression instanceCreationExpression =
            astFactory.instanceCreationExpression(
                _getKeyword(node), constructorName, node.argumentList);
        InterfaceType type = getType(typeSystem, element, node.typeArguments);
        ConstructorElement constructorElement =
            type.lookUpConstructor(null, definingLibrary);
        methodName.staticElement = element;
        methodName.staticType = type;
        typeName.type = type;
        constructorName.staticElement = constructorElement;
        instanceCreationExpression.staticType = type;
        instanceCreationExpression.staticElement = constructorElement;
        NodeReplacer.replace(node, instanceCreationExpression);
      }
    } else if (target is SimpleIdentifier) {
      // Possible cases: C.n(), p.C() or p.C<>()
      if (node.operator.type == TokenType.QUESTION_PERIOD) {
        // This isn't a constructor invocation because a null aware operator is
        // being used.
      }
      Element element = nameScope.lookup(target, definingLibrary);
      if (element is ClassElement) {
        // Possible case: C.n()
        var constructorElement = element.getNamedConstructor(methodName.name);
        if (constructorElement != null) {
          var typeArguments = node.typeArguments;
          if (typeArguments != null) {
            errorReporter.reportErrorForNode(
                StaticTypeWarningCode
                    .WRONG_NUMBER_OF_TYPE_ARGUMENTS_CONSTRUCTOR,
                typeArguments,
                [element.name, constructorElement.name]);
          }
          AstFactory astFactory = new AstFactoryImpl();
          TypeName typeName = astFactory.typeName(target, null);
          ConstructorName constructorName =
              astFactory.constructorName(typeName, node.operator, methodName);
          InstanceCreationExpression instanceCreationExpression =
              astFactory.instanceCreationExpression(
                  _getKeyword(node), constructorName, node.argumentList,
                  typeArguments: typeArguments);
          InterfaceType type = getType(typeSystem, element, null);
          constructorElement =
              type.lookUpConstructor(methodName.name, definingLibrary);
          methodName.staticElement = element;
          methodName.staticType = type;
          target.staticElement = element;
          target.staticType = type; // TODO(scheglov) remove this
          typeName.type = type;
          constructorName.staticElement = constructorElement;
          instanceCreationExpression.staticType = type;
          instanceCreationExpression.staticElement = constructorElement;
          NodeReplacer.replace(node, instanceCreationExpression);
        }
      } else if (element is PrefixElement) {
        // Possible cases: p.C() or p.C<>()
        AstFactory astFactory = new AstFactoryImpl();
        Identifier identifier = astFactory.prefixedIdentifier(
            astFactory.simpleIdentifier(target.token),
            null,
            astFactory.simpleIdentifier(methodName.token));
        Element prefixedElement = nameScope.lookup(identifier, definingLibrary);
        if (prefixedElement is ClassElement) {
          TypeName typeName = astFactory.typeName(
              astFactory.prefixedIdentifier(target, node.operator, methodName),
              node.typeArguments);
          ConstructorName constructorName =
              astFactory.constructorName(typeName, null, null);
          InstanceCreationExpression instanceCreationExpression =
              astFactory.instanceCreationExpression(
                  _getKeyword(node), constructorName, node.argumentList);
          InterfaceType type =
              getType(typeSystem, prefixedElement, node.typeArguments);
          ConstructorElement constructorElement =
              type.lookUpConstructor(null, definingLibrary);
          methodName.staticElement = element;
          methodName.staticType = type;
          typeName.type = type;
          constructorName.staticElement = constructorElement;
          instanceCreationExpression.staticType = type;
          instanceCreationExpression.staticElement = constructorElement;
          NodeReplacer.replace(node, instanceCreationExpression);
        }
      }
    } else if (target is PrefixedIdentifier) {
      // Possible case: p.C.n()
      Element prefixElement = nameScope.lookup(target.prefix, definingLibrary);
      target.prefix.staticElement = prefixElement;
      if (prefixElement is PrefixElement) {
        Element element = nameScope.lookup(target, definingLibrary);
        if (element is ClassElement) {
          var constructorElement = element.getNamedConstructor(methodName.name);
          if (constructorElement != null) {
            var typeArguments = node.typeArguments;
            if (typeArguments != null) {
              errorReporter.reportErrorForNode(
                  StaticTypeWarningCode
                      .WRONG_NUMBER_OF_TYPE_ARGUMENTS_CONSTRUCTOR,
                  typeArguments,
                  [element.name, constructorElement.name]);
            }
            AstFactory astFactory = new AstFactoryImpl();
            TypeName typeName = astFactory.typeName(target, typeArguments);
            ConstructorName constructorName =
                astFactory.constructorName(typeName, node.operator, methodName);
            InstanceCreationExpression instanceCreationExpression =
                astFactory.instanceCreationExpression(
                    _getKeyword(node), constructorName, node.argumentList);
            InterfaceType type = getType(typeSystem, element, typeArguments);
            constructorElement =
                type.lookUpConstructor(methodName.name, definingLibrary);
            methodName.staticElement = element;
            methodName.staticType = type;
            target.identifier.staticElement = element;
            typeName.type = type;
            constructorName.staticElement = constructorElement;
            instanceCreationExpression.staticType = type;
            instanceCreationExpression.staticElement = constructorElement;
            NodeReplacer.replace(node, instanceCreationExpression);
          }
        }
      }
    }
  }

  /// Return the token that should be used in the [InstanceCreationExpression]
  /// that corresponds to the given invocation [node].
  Token _getKeyword(MethodInvocation node) {
    return addConstKeyword
        ? new KeywordToken(Keyword.CONST, node.offset)
        : null;
  }

  /// Return the type of the given class [element] after substituting any type
  /// arguments from the list of [typeArguments] for the class' type parameters.
  static InterfaceType getType(TypeSystem typeSystem, ClassElement element,
      TypeArgumentList typeArguments) {
    DartType type = element.type;

    List<TypeParameterElement> typeParameters = element.typeParameters;
    if (typeParameters.isEmpty) {
      return type;
    }

    if (typeArguments == null) {
      return typeSystem.instantiateToBounds(type);
    }

    List<DartType> argumentTypes;
    if (typeArguments.arguments.length == typeParameters.length) {
      argumentTypes = typeArguments.arguments
          .map((TypeAnnotation argument) => argument.type)
          .toList();
    } else {
      argumentTypes = List<DartType>.filled(
          typeParameters.length, DynamicTypeImpl.instance);
    }
    List<DartType> parameterTypes = typeParameters
        .map((TypeParameterElement parameter) => parameter.type)
        .toList();
    return type.substitute2(argumentTypes, parameterTypes);
  }
}

/// Instances of the class `BestPracticesVerifier` traverse an AST structure
/// looking for violations of Dart best practices.
class BestPracticesVerifier extends RecursiveAstVisitor<void> {
//  static String _HASHCODE_GETTER_NAME = "hashCode";

  static String _NULL_TYPE_NAME = "Null";

  static String _TO_INT_METHOD_NAME = "toInt";

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

  /// A flag indicating whether a surrounding member (compilation unit or class)
  /// is deprecated.
  bool _inDeprecatedMember;

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

  /// The type [Null].
  final InterfaceType _nullType;

  /// The type Future<Null>, which is needed for determining whether it is safe
  /// to have a bare "return;" in an async method.
  final InterfaceType _futureNullType;

  /// The type system primitives
  final TypeSystem _typeSystem;

  /// The current library
  final LibraryElement _currentLibrary;

  final _InvalidAccessVerifier _invalidAccessVerifier;

  /// The [WorkspacePackage] in which [_currentLibrary] is declared.
  WorkspacePackage _workspacePackage;

  /// The [LinterContext] used for possible const calculations.
  LinterContext _linterContext;

  /// Create a new instance of the [BestPracticesVerifier].
  ///
  /// @param errorReporter the error reporter
  BestPracticesVerifier(
    this._errorReporter,
    TypeProvider typeProvider,
    this._currentLibrary, {
    TypeSystem typeSystem,
    ResourceProvider resourceProvider,
    DeclaredVariables declaredVariables,
    AnalysisOptions analysisOptions,
  })  : _nullType = typeProvider.nullType,
        _futureNullType = typeProvider.futureNullType,
        _typeSystem = typeSystem ?? new Dart2TypeSystem(typeProvider),
        _invalidAccessVerifier =
            new _InvalidAccessVerifier(_errorReporter, _currentLibrary) {
    _inDeprecatedMember = _currentLibrary.hasDeprecated;
    String libraryPath = _currentLibrary.source.fullName;
    ContextBuilder builder = new ContextBuilder(
        resourceProvider, null /* sdkManager */, null /* contentCache */);
    Workspace workspace =
        ContextBuilder.createWorkspace(resourceProvider, libraryPath, builder);
    _workspacePackage = workspace.findPackageFor(libraryPath);
    _linterContext = LinterContextImpl(
        null /* allUnits */,
        null /* currentUnit */,
        declaredVariables,
        typeProvider,
        _typeSystem,
        analysisOptions);
  }

  @override
  void visitAnnotation(Annotation node) {
    ElementAnnotation element =
        resolutionMap.elementAnnotationForAnnotation(node);
    AstNode parent = node.parent;
    if (element?.isFactory == true) {
      if (parent is MethodDeclaration) {
        _checkForInvalidFactory(parent);
      } else {
        _errorReporter
            .reportErrorForNode(HintCode.INVALID_FACTORY_ANNOTATION, node, []);
      }
    } else if (element?.isImmutable == true) {
      if (parent is! ClassOrMixinDeclaration && parent is! ClassTypeAlias) {
        _errorReporter.reportErrorForNode(
            HintCode.INVALID_IMMUTABLE_ANNOTATION, node, []);
      }
    } else if (element?.isLiteral == true) {
      if (parent is! ConstructorDeclaration ||
          (parent as ConstructorDeclaration).constKeyword == null) {
        _errorReporter
            .reportErrorForNode(HintCode.INVALID_LITERAL_ANNOTATION, node, []);
      }
    } else if (element?.isSealed == true) {
      if (!(parent is ClassDeclaration || parent is ClassTypeAlias)) {
        _errorReporter.reportErrorForNode(
            HintCode.INVALID_SEALED_ANNOTATION, node, [node.element.name]);
      }
    } else if (element?.isVisibleForTemplate == true ||
        element?.isVisibleForTesting == true) {
      if (parent is Declaration) {
        reportInvalidAnnotation(Element declaredElement) {
          _errorReporter.reportErrorForNode(
              HintCode.INVALID_VISIBILITY_ANNOTATION,
              node,
              [declaredElement.name, node.name.name]);
        }

        if (parent is TopLevelVariableDeclaration) {
          for (VariableDeclaration variable in parent.variables.variables) {
            if (Identifier.isPrivateName(variable.declaredElement.name)) {
              reportInvalidAnnotation(variable.declaredElement);
            }
          }
        } else if (parent is FieldDeclaration) {
          for (VariableDeclaration variable in parent.fields.variables) {
            if (Identifier.isPrivateName(variable.declaredElement.name)) {
              reportInvalidAnnotation(variable.declaredElement);
            }
          }
        } else if (parent.declaredElement != null &&
            Identifier.isPrivateName(parent.declaredElement.name)) {
          reportInvalidAnnotation(parent.declaredElement);
        }
      } else {
        // Something other than a declaration was annotated. Whatever this is,
        // it probably warrants a Hint, but this has not been specified on
        // visibleForTemplate or visibleForTesting, so leave it alone for now.
      }
    }

    super.visitAnnotation(node);
  }

  @override
  void visitArgumentList(ArgumentList node) {
    for (Expression argument in node.arguments) {
      ParameterElement parameter = argument.staticParameterElement;
      if (parameter?.isOptionalPositional == true) {
        _checkForDeprecatedMemberUse(parameter, argument);
      }
    }
    super.visitArgumentList(node);
  }

  @override
  void visitAsExpression(AsExpression node) {
    _checkForUnnecessaryCast(node);
    super.visitAsExpression(node);
  }

  @override
  void visitAssignmentExpression(AssignmentExpression node) {
    TokenType operatorType = node.operator.type;
    if (operatorType != TokenType.EQ) {
      _checkForDeprecatedMemberUse(node.staticElement, node);
    }
    super.visitAssignmentExpression(node);
  }

  @override
  void visitBinaryExpression(BinaryExpression node) {
    _checkForDivisionOptimizationHint(node);
    _checkForDeprecatedMemberUse(node.staticElement, node);
    super.visitBinaryExpression(node);
  }

  @override
  void visitClassDeclaration(ClassDeclaration node) {
    var element = AbstractClassElementImpl.getImpl(node.declaredElement);
    _enclosingClass = element;
    _invalidAccessVerifier._enclosingClass = element;

    bool wasInDeprecatedMember = _inDeprecatedMember;
    if (element != null && element.hasDeprecated) {
      _inDeprecatedMember = true;
    }

    try {
      // Commented out until we decide that we want this hint in the analyzer
      //    checkForOverrideEqualsButNotHashCode(node);
      _checkForImmutable(node);
      _checkForInvalidSealedSuperclass(node);
      super.visitClassDeclaration(node);
    } finally {
      _enclosingClass = null;
      _invalidAccessVerifier._enclosingClass = null;
      _inDeprecatedMember = wasInDeprecatedMember;
    }
  }

  @override
  void visitClassTypeAlias(ClassTypeAlias node) {
    _checkForImmutable(node);
    _checkForInvalidSealedSuperclass(node);
    super.visitClassTypeAlias(node);
  }

  @override
  void visitConstructorDeclaration(ConstructorDeclaration node) {
    if (resolutionMap.elementDeclaredByConstructorDeclaration(node).isFactory) {
      if (node.body is BlockFunctionBody) {
        // Check the block for a return statement, if not, create the hint.
        if (!ExitDetector.exits(node.body)) {
          _errorReporter.reportErrorForNode(
              HintCode.MISSING_RETURN, node, [node.returnType.name]);
        }
      }
    }
    super.visitConstructorDeclaration(node);
  }

  @override
  void visitExportDirective(ExportDirective node) {
    _checkForDeprecatedMemberUse(node.uriElement, node);
    super.visitExportDirective(node);
  }

  @override
  void visitFieldDeclaration(FieldDeclaration node) {
    bool wasInDeprecatedMember = _inDeprecatedMember;
    if (_hasDeprecatedAnnotation(node.metadata)) {
      _inDeprecatedMember = true;
    }

    try {
      super.visitFieldDeclaration(node);
    } finally {
      _inDeprecatedMember = wasInDeprecatedMember;
    }
  }

  @override
  void visitFormalParameterList(FormalParameterList node) {
    _checkRequiredParameter(node);
    super.visitFormalParameterList(node);
  }

  @override
  void visitFunctionDeclaration(FunctionDeclaration node) {
    bool wasInDeprecatedMember = _inDeprecatedMember;
    ExecutableElement element = node.declaredElement;
    if (element != null && element.hasDeprecated) {
      _inDeprecatedMember = true;
    }
    try {
      _checkForMissingReturn(
          node.returnType, node.functionExpression.body, element, node);
      super.visitFunctionDeclaration(node);
    } finally {
      _inDeprecatedMember = wasInDeprecatedMember;
    }
  }

  @override
  void visitImportDirective(ImportDirective node) {
    _checkForDeprecatedMemberUse(node.uriElement, node);
    ImportElement importElement = node.element;
    if (importElement != null && importElement.isDeferred) {
      _checkForLoadLibraryFunction(node, importElement);
    }
    super.visitImportDirective(node);
  }

  @override
  void visitIndexExpression(IndexExpression node) {
    _checkForDeprecatedMemberUse(node.staticElement, node);
    super.visitIndexExpression(node);
  }

  @override
  void visitInstanceCreationExpression(InstanceCreationExpression node) {
    _checkForDeprecatedMemberUse(node.staticElement, node);
    _checkForLiteralConstructorUse(node);
    super.visitInstanceCreationExpression(node);
  }

  @override
  void visitIsExpression(IsExpression node) {
    _checkAllTypeChecks(node);
    super.visitIsExpression(node);
  }

  @override
  void visitMethodDeclaration(MethodDeclaration node) {
    bool wasInDeprecatedMember = _inDeprecatedMember;
    ExecutableElement element = node.declaredElement;
    if (element != null && element.hasDeprecated) {
      _inDeprecatedMember = true;
    }
    try {
      // This was determined to not be a good hint, see: dartbug.com/16029
      //checkForOverridingPrivateMember(node);
      _checkForMissingReturn(node.returnType, node.body, element, node);
      _checkForUnnecessaryNoSuchMethod(node);
      super.visitMethodDeclaration(node);
    } finally {
      _inDeprecatedMember = wasInDeprecatedMember;
    }
  }

  @override
  void visitMethodInvocation(MethodInvocation node) {
    _checkForNullAwareHints(node, node.operator);
    DartType staticInvokeType = node.staticInvokeType;
    Element callElement = staticInvokeType?.element;
    if (callElement is MethodElement &&
        callElement.name == FunctionElement.CALL_METHOD_NAME) {
      _checkForDeprecatedMemberUse(callElement, node);
    }
    super.visitMethodInvocation(node);
  }

  @override
  void visitMixinDeclaration(MixinDeclaration node) {
    _enclosingClass = node.declaredElement;
    _invalidAccessVerifier._enclosingClass = _enclosingClass;

    bool wasInDeprecatedMember = _inDeprecatedMember;
    if (_hasDeprecatedAnnotation(node.metadata)) {
      _inDeprecatedMember = true;
    }

    try {
      _checkForImmutable(node);
      _checkForInvalidSealedSuperclass(node);
      super.visitMixinDeclaration(node);
    } finally {
      _enclosingClass = null;
      _invalidAccessVerifier._enclosingClass = null;
      _inDeprecatedMember = wasInDeprecatedMember;
    }
  }

  @override
  void visitPostfixExpression(PostfixExpression node) {
    _checkForDeprecatedMemberUse(node.staticElement, node);
    super.visitPostfixExpression(node);
  }

  @override
  void visitPrefixExpression(PrefixExpression node) {
    _checkForDeprecatedMemberUse(node.staticElement, node);
    super.visitPrefixExpression(node);
  }

  @override
  void visitPropertyAccess(PropertyAccess node) {
    _checkForNullAwareHints(node, node.operator);
    super.visitPropertyAccess(node);
  }

  @override
  void visitRedirectingConstructorInvocation(
      RedirectingConstructorInvocation node) {
    _checkForDeprecatedMemberUse(node.staticElement, node);
    super.visitRedirectingConstructorInvocation(node);
  }

  @override
  void visitSimpleIdentifier(SimpleIdentifier node) {
    _checkForDeprecatedMemberUseAtIdentifier(node);
    _invalidAccessVerifier.verify(node);
    super.visitSimpleIdentifier(node);
  }

  @override
  void visitSuperConstructorInvocation(SuperConstructorInvocation node) {
    _checkForDeprecatedMemberUse(node.staticElement, node);
    super.visitSuperConstructorInvocation(node);
  }

  @override
  void visitTopLevelVariableDeclaration(TopLevelVariableDeclaration node) {
    bool wasInDeprecatedMember = _inDeprecatedMember;
    if (_hasDeprecatedAnnotation(node.metadata)) {
      _inDeprecatedMember = true;
    }

    try {
      super.visitTopLevelVariableDeclaration(node);
    } finally {
      _inDeprecatedMember = wasInDeprecatedMember;
    }
  }

  /// Check for the passed is expression for the unnecessary type check hint
  /// codes as well as null checks expressed using an is expression.
  ///
  /// @param node the is expression to check
  /// @return `true` if and only if a hint code is generated on the passed node
  /// See [HintCode.TYPE_CHECK_IS_NOT_NULL], [HintCode.TYPE_CHECK_IS_NULL],
  /// [HintCode.UNNECESSARY_TYPE_CHECK_TRUE], and
  /// [HintCode.UNNECESSARY_TYPE_CHECK_FALSE].
  bool _checkAllTypeChecks(IsExpression node) {
    Expression expression = node.expression;
    TypeAnnotation typeName = node.type;
    DartType lhsType = expression.staticType;
    DartType rhsType = typeName.type;
    if (lhsType == null || rhsType == null) {
      return false;
    }
    String rhsNameStr = typeName is TypeName ? typeName.name.name : null;
    // if x is dynamic
    if (rhsType.isDynamic && rhsNameStr == Keyword.DYNAMIC.lexeme) {
      if (node.notOperator == null) {
        // the is case
        _errorReporter.reportErrorForNode(
            HintCode.UNNECESSARY_TYPE_CHECK_TRUE, node);
      } else {
        // the is not case
        _errorReporter.reportErrorForNode(
            HintCode.UNNECESSARY_TYPE_CHECK_FALSE, node);
      }
      return true;
    }
    Element rhsElement = rhsType.element;
    LibraryElement libraryElement = rhsElement?.library;
    if (libraryElement != null && libraryElement.isDartCore) {
      // if x is Object or null is Null
      if (rhsType.isObject ||
          (expression is NullLiteral && rhsNameStr == _NULL_TYPE_NAME)) {
        if (node.notOperator == null) {
          // the is case
          _errorReporter.reportErrorForNode(
              HintCode.UNNECESSARY_TYPE_CHECK_TRUE, node);
        } else {
          // the is not case
          _errorReporter.reportErrorForNode(
              HintCode.UNNECESSARY_TYPE_CHECK_FALSE, node);
        }
        return true;
      } else if (rhsNameStr == _NULL_TYPE_NAME) {
        if (node.notOperator == null) {
          // the is case
          _errorReporter.reportErrorForNode(HintCode.TYPE_CHECK_IS_NULL, node);
        } else {
          // the is not case
          _errorReporter.reportErrorForNode(
              HintCode.TYPE_CHECK_IS_NOT_NULL, node);
        }
        return true;
      }
    }
    return false;
  }

  /// Given some [Element], look at the associated metadata and report the use
  /// of the member if it is declared as deprecated.
  ///
  /// @param element some element to check for deprecated use of
  /// @param node the node use for the location of the error
  /// See [HintCode.DEPRECATED_MEMBER_USE].
  void _checkForDeprecatedMemberUse(Element element, AstNode node) {
    bool isDeprecated(Element element) {
      if (element is PropertyAccessorElement && element.isSynthetic) {
        // TODO(brianwilkerson) Why isn't this the implementation for PropertyAccessorElement?
        Element variable = element.variable;
        if (variable == null) {
          return false;
        }
        return variable.hasDeprecated;
      }
      return element.hasDeprecated;
    }

    bool isLocalParameter(Element element, AstNode node) {
      if (element is ParameterElement) {
        ExecutableElement definingFunction = element.enclosingElement;
        FunctionBody body = node.thisOrAncestorOfType<FunctionBody>();
        while (body != null) {
          ExecutableElement enclosingFunction;
          AstNode parent = body.parent;
          if (parent is ConstructorDeclaration) {
            enclosingFunction = parent.declaredElement;
          } else if (parent is FunctionExpression) {
            enclosingFunction = parent.declaredElement;
          } else if (parent is MethodDeclaration) {
            enclosingFunction = parent.declaredElement;
          }
          if (enclosingFunction == definingFunction) {
            return true;
          }
          body = parent?.thisOrAncestorOfType<FunctionBody>();
        }
      }
      return false;
    }

    bool isLibraryInWorkspacePackage(LibraryElement library) {
      if (_workspacePackage == null || library == null) {
        // Better to not make a big claim that they _are_ in the same package,
        // if we were unable to determine what package [_currentLibrary] is in.
        return false;
      }
      return _workspacePackage.contains(library.source.fullName);
    }

    if (!_inDeprecatedMember &&
        element != null &&
        isDeprecated(element) &&
        !isLocalParameter(element, node)) {
      String displayName = element.displayName;
      if (element is ConstructorElement) {
        // TODO(jwren) We should modify ConstructorElement.getDisplayName(),
        // or have the logic centralized elsewhere, instead of doing this logic
        // here.
        displayName = element.enclosingElement.displayName;
        if (!element.displayName.isEmpty) {
          displayName = "$displayName.${element.displayName}";
        }
      } else if (element is LibraryElement) {
        displayName = element.definingCompilationUnit.source.uri.toString();
      } else if (displayName == FunctionElement.CALL_METHOD_NAME &&
          node is MethodInvocation &&
          node.staticInvokeType is InterfaceType) {
        DartType staticInvokeType =
            resolutionMap.staticInvokeTypeForInvocationExpression(node);
        displayName = "${staticInvokeType.displayName}.${element.displayName}";
      }
      LibraryElement library =
          element is LibraryElement ? element : element.library;
      HintCode hintCode = isLibraryInWorkspacePackage(library)
          ? HintCode.DEPRECATED_MEMBER_USE_FROM_SAME_PACKAGE
          : HintCode.DEPRECATED_MEMBER_USE;
      _errorReporter.reportErrorForNode(hintCode, node, [displayName]);
    }
  }

  /// For [SimpleIdentifier]s, only call [checkForDeprecatedMemberUse]
  /// if the node is not in a declaration context.
  ///
  /// Also, if the identifier is a constructor name in a constructor invocation,
  /// then calls to the deprecated constructor will be caught by
  /// [visitInstanceCreationExpression] and
  /// [visitSuperConstructorInvocation], and can be ignored by
  /// this visit method.
  ///
  /// @param identifier some simple identifier to check for deprecated use of
  /// @return `true` if and only if a hint code is generated on the passed node
  /// See [HintCode.DEPRECATED_MEMBER_USE].
  void _checkForDeprecatedMemberUseAtIdentifier(SimpleIdentifier identifier) {
    if (identifier.inDeclarationContext()) {
      return;
    }
    AstNode parent = identifier.parent;
    if ((parent is ConstructorName && identical(identifier, parent.name)) ||
        (parent is ConstructorDeclaration &&
            identical(identifier, parent.returnType)) ||
        (parent is SuperConstructorInvocation &&
            identical(identifier, parent.constructorName)) ||
        parent is HideCombinator) {
      return;
    }
    _checkForDeprecatedMemberUse(identifier.staticElement, identifier);
  }

  /// Check for the passed binary expression for the
  /// [HintCode.DIVISION_OPTIMIZATION].
  ///
  /// @param node the binary expression to check
  /// @return `true` if and only if a hint code is generated on the passed node
  /// See [HintCode.DIVISION_OPTIMIZATION].
  bool _checkForDivisionOptimizationHint(BinaryExpression node) {
    // Return if the operator is not '/'
    if (node.operator.type != TokenType.SLASH) {
      return false;
    }
    // Return if the '/' operator is not defined in core, or if we don't know
    // its static type
    MethodElement methodElement = node.staticElement;
    if (methodElement == null) {
      return false;
    }
    LibraryElement libraryElement = methodElement.library;
    if (libraryElement != null && !libraryElement.isDartCore) {
      return false;
    }
    // Report error if the (x/y) has toInt() invoked on it
    AstNode parent = node.parent;
    if (parent is ParenthesizedExpression) {
      ParenthesizedExpression parenthesizedExpression =
          _wrapParenthesizedExpression(parent);
      AstNode grandParent = parenthesizedExpression.parent;
      if (grandParent is MethodInvocation) {
        if (_TO_INT_METHOD_NAME == grandParent.methodName.name &&
            grandParent.argumentList.arguments.isEmpty) {
          _errorReporter.reportErrorForNode(
              HintCode.DIVISION_OPTIMIZATION, grandParent);
          return true;
        }
      }
    }
    return false;
  }

  /// Checks whether [node] violates the rules of [immutable].
  ///
  /// If [node] is marked with [immutable] or inherits from a class or mixin
  /// marked with [immutable], this function searches the fields of [node] and
  /// its superclasses, reporting a hint if any non-final instance fields are
  /// found.
  void _checkForImmutable(NamedCompilationUnitMember node) {
    /// Return `true` if the given class [element] is annotated with the
    /// `@immutable` annotation.
    bool isImmutable(ClassElement element) {
      for (ElementAnnotation annotation in element.metadata) {
        if (annotation.isImmutable) {
          return true;
        }
      }
      return false;
    }

    /// Return `true` if the given class [element] or any superclass of it is
    /// annotated with the `@immutable` annotation.
    bool isOrInheritsImmutable(
        ClassElement element, HashSet<ClassElement> visited) {
      if (visited.add(element)) {
        if (isImmutable(element)) {
          return true;
        }
        for (InterfaceType interface in element.mixins) {
          if (isOrInheritsImmutable(interface.element, visited)) {
            return true;
          }
        }
        for (InterfaceType mixin in element.interfaces) {
          if (isOrInheritsImmutable(mixin.element, visited)) {
            return true;
          }
        }
        if (element.supertype != null) {
          return isOrInheritsImmutable(element.supertype.element, visited);
        }
      }
      return false;
    }

    /// Return `true` if the given class [element] defines a non-final instance
    /// field.
    Iterable<String> nonFinalInstanceFields(ClassElement element) {
      return element.fields
          .where((FieldElement field) =>
              !field.isSynthetic && !field.isFinal && !field.isStatic)
          .map((FieldElement field) => '${element.name}.${field.name}');
    }

    /// Return `true` if the given class [element] defines or inherits a
    /// non-final field.
    Iterable<String> definedOrInheritedNonFinalInstanceFields(
        ClassElement element, HashSet<ClassElement> visited) {
      Iterable<String> nonFinalFields = [];
      if (visited.add(element)) {
        nonFinalFields = nonFinalInstanceFields(element);
        nonFinalFields = nonFinalFields.followedBy(element.mixins.expand(
            (InterfaceType mixin) => nonFinalInstanceFields(mixin.element)));
        if (element.supertype != null) {
          nonFinalFields = nonFinalFields.followedBy(
              definedOrInheritedNonFinalInstanceFields(
                  element.supertype.element, visited));
        }
      }
      return nonFinalFields;
    }

    ClassElement element = node.declaredElement;
    if (isOrInheritsImmutable(element, new HashSet<ClassElement>())) {
      Iterable<String> nonFinalFields =
          definedOrInheritedNonFinalInstanceFields(
              element, new HashSet<ClassElement>());
      if (nonFinalFields.isNotEmpty) {
        _errorReporter.reportErrorForNode(
            HintCode.MUST_BE_IMMUTABLE, node.name, [nonFinalFields.join(', ')]);
      }
    }
  }

  void _checkForInvalidFactory(MethodDeclaration decl) {
    // Check declaration.
    // Note that null return types are expected to be flagged by other analyses.
    DartType returnType = decl.returnType?.type;
    if (returnType is VoidType) {
      _errorReporter.reportErrorForNode(HintCode.INVALID_FACTORY_METHOD_DECL,
          decl.name, [decl.name.toString()]);
      return;
    }

    // Check implementation.

    FunctionBody body = decl.body;
    if (body is EmptyFunctionBody) {
      // Abstract methods are OK.
      return;
    }

    // `new Foo()` or `null`.
    bool factoryExpression(Expression expression) =>
        expression is InstanceCreationExpression || expression is NullLiteral;

    if (body is ExpressionFunctionBody && factoryExpression(body.expression)) {
      return;
    } else if (body is BlockFunctionBody) {
      NodeList<Statement> statements = body.block.statements;
      if (statements.isNotEmpty) {
        Statement last = statements.last;
        if (last is ReturnStatement && factoryExpression(last.expression)) {
          return;
        }
      }
    }

    _errorReporter.reportErrorForNode(HintCode.INVALID_FACTORY_METHOD_IMPL,
        decl.name, [decl.name.toString()]);
  }

  void _checkForInvalidSealedSuperclass(NamedCompilationUnitMember node) {
    bool currentPackageContains(Element element) {
      String elementLibraryPath = element.library.source.fullName;
      return _workspacePackage.contains(elementLibraryPath);
    }

    // [NamedCompilationUnitMember.declaredElement] is not necessarily a
    // ClassElement, but [_checkForInvalidSealedSuperclass] should only be
    // called with a [ClassOrMixinDeclaration], or a [ClassTypeAlias]. The
    // `declaredElement` of these specific classes is a [ClassElement].
    ClassElement element = node.declaredElement;
    // TODO(srawlins): Perhaps replace this with a getter on Element, like
    // `Element.hasOrInheritsSealed`?
    for (InterfaceType supertype in element.allSupertypes) {
      ClassElement superclass = supertype.element;
      if (superclass.hasSealed) {
        if (!currentPackageContains(superclass)) {
          if (element.superclassConstraints.contains(supertype)) {
            // This is a special violation of the sealed class contract,
            // requiring specific messaging.
            _errorReporter.reportErrorForNode(HintCode.MIXIN_ON_SEALED_CLASS,
                node, [superclass.name.toString()]);
          } else {
            // This is a regular violation of the sealed class contract.
            _errorReporter.reportErrorForNode(HintCode.SUBTYPE_OF_SEALED_CLASS,
                node, [superclass.name.toString()]);
          }
        }
      }
    }
  }

  /// Check that the instance creation node is const if the constructor is
  /// marked with [literal].
  _checkForLiteralConstructorUse(InstanceCreationExpression node) {
    ConstructorName constructorName = node.constructorName;
    ConstructorElement constructor = constructorName.staticElement;
    if (constructor == null) {
      return;
    }
    if (!node.isConst &&
        constructor.hasLiteral &&
        _linterContext.canBeConst(node)) {
      // Echoing jwren's TODO from _checkForDeprecatedMemberUse:
      // TODO(jwren) We should modify ConstructorElement.getDisplayName(), or
      // have the logic centralized elsewhere, instead of doing this logic
      // here.
      String fullConstructorName = constructorName.type.name.name;
      if (constructorName.name != null) {
        fullConstructorName = '$fullConstructorName.${constructorName.name}';
      }
      HintCode hint = node.keyword?.keyword == Keyword.NEW
          ? HintCode.NON_CONST_CALL_TO_LITERAL_CONSTRUCTOR_USING_NEW
          : HintCode.NON_CONST_CALL_TO_LITERAL_CONSTRUCTOR;
      _errorReporter.reportErrorForNode(hint, node, [fullConstructorName]);
    }
  }

  /// Check that the imported library does not define a loadLibrary function.
  /// The import has already been determined to be deferred when this is called.
  ///
  /// @param node the import directive to evaluate
  /// @param importElement the [ImportElement] retrieved from the node
  /// @return `true` if and only if an error code is generated on the passed
  ///         node
  /// See [CompileTimeErrorCode.IMPORT_DEFERRED_LIBRARY_WITH_LOAD_FUNCTION].
  bool _checkForLoadLibraryFunction(
      ImportDirective node, ImportElement importElement) {
    LibraryElement importedLibrary = importElement.importedLibrary;
    if (importedLibrary == null) {
      return false;
    }
    if (importedLibrary.hasLoadLibraryFunction) {
      _errorReporter.reportErrorForNode(
          HintCode.IMPORT_DEFERRED_LIBRARY_WITH_LOAD_FUNCTION,
          node,
          [importedLibrary.name]);
      return true;
    }
    return false;
  }

  /// Generate a hint for functions or methods that have a return type, but do
  /// not have a return statement on all branches. At the end of blocks with no
  /// return, Dart implicitly returns `null`, avoiding these implicit returns is
  /// considered a best practice.
  ///
  /// Note: for async functions/methods, this hint only applies when the
  /// function has a return type that Future<Null> is not assignable to.
  ///
  /// @param node the binary expression to check
  /// @param body the function body
  /// @return `true` if and only if a hint code is generated on the passed node
  /// See [HintCode.MISSING_RETURN].
  void _checkForMissingReturn(TypeAnnotation returnNode, FunctionBody body,
      ExecutableElement element, AstNode functionNode) {
    if (body is BlockFunctionBody) {
      // Prefer the type from the element model, in case we've inferred one.
      DartType returnType = element?.returnType ?? returnNode?.type;
      AstNode errorNode = returnNode ?? functionNode;

      // Skip the check if we're missing a return type (e.g. erroneous code).
      // Generators are never required to have a return statement.
      if (returnType == null || body.isGenerator) {
        return;
      }

      var flattenedType =
          body.isAsynchronous ? _typeSystem.flatten(returnType) : returnType;

      // dynamic/Null/void are allowed to omit a return.
      if (flattenedType.isDynamic ||
          flattenedType.isDartCoreNull ||
          flattenedType.isVoid) {
        return;
      }
      // Otherwise issue a warning if the block doesn't have a return.
      if (!ExitDetector.exits(body)) {
        _errorReporter.reportErrorForNode(
            HintCode.MISSING_RETURN, errorNode, [returnType.displayName]);
      }
    }
  }

  /// Produce several null-aware related hints.
  void _checkForNullAwareHints(Expression node, Token operator) {
    if (operator == null || operator.type != TokenType.QUESTION_PERIOD) {
      return;
    }

    // childOfParent is used to know from which branch node comes.
    var childOfParent = node;
    var parent = node.parent;
    while (parent is ParenthesizedExpression) {
      childOfParent = parent;
      parent = parent.parent;
    }

    // CAN_BE_NULL_AFTER_NULL_AWARE
    if (parent is MethodInvocation &&
        parent.operator.type != TokenType.QUESTION_PERIOD &&
        _nullType.lookUpMethod(parent.methodName.name, _currentLibrary) ==
            null) {
      _errorReporter.reportErrorForNode(
          HintCode.CAN_BE_NULL_AFTER_NULL_AWARE, childOfParent);
      return;
    }
    if (parent is PropertyAccess &&
        parent.operator.type != TokenType.QUESTION_PERIOD &&
        _nullType.lookUpGetter(parent.propertyName.name, _currentLibrary) ==
            null) {
      _errorReporter.reportErrorForNode(
          HintCode.CAN_BE_NULL_AFTER_NULL_AWARE, childOfParent);
      return;
    }
    if (parent is CascadeExpression && parent.target == childOfParent) {
      _errorReporter.reportErrorForNode(
          HintCode.CAN_BE_NULL_AFTER_NULL_AWARE, childOfParent);
      return;
    }

    // NULL_AWARE_IN_CONDITION
    if (parent is IfStatement && parent.condition == childOfParent ||
        parent is ForPartsWithDeclarations &&
            parent.condition == childOfParent ||
        parent is DoStatement && parent.condition == childOfParent ||
        parent is WhileStatement && parent.condition == childOfParent ||
        parent is ConditionalExpression && parent.condition == childOfParent ||
        parent is AssertStatement && parent.condition == childOfParent) {
      _errorReporter.reportErrorForNode(
          HintCode.NULL_AWARE_IN_CONDITION, childOfParent);
      return;
    }

    // NULL_AWARE_IN_LOGICAL_OPERATOR
    if (parent is PrefixExpression && parent.operator.type == TokenType.BANG ||
        parent is BinaryExpression &&
            [TokenType.BAR_BAR, TokenType.AMPERSAND_AMPERSAND]
                .contains(parent.operator.type)) {
      _errorReporter.reportErrorForNode(
          HintCode.NULL_AWARE_IN_LOGICAL_OPERATOR, childOfParent);
      return;
    }

    // NULL_AWARE_BEFORE_OPERATOR
    if (parent is BinaryExpression &&
        ![TokenType.EQ_EQ, TokenType.BANG_EQ, TokenType.QUESTION_QUESTION]
            .contains(parent.operator.type) &&
        parent.leftOperand == childOfParent) {
      _errorReporter.reportErrorForNode(
          HintCode.NULL_AWARE_BEFORE_OPERATOR, childOfParent);
      return;
    }
  }

  /// Check for the passed as expression for the [HintCode.UNNECESSARY_CAST]
  /// hint code.
  ///
  /// @param node the as expression to check
  /// @return `true` if and only if a hint code is generated on the passed node
  /// See [HintCode.UNNECESSARY_CAST].
  bool _checkForUnnecessaryCast(AsExpression node) {
    // TODO(jwren) After dartbug.com/13732, revisit this, we should be able to
    // remove the (x is! TypeParameterType) checks.
    AstNode parent = node.parent;
    if (parent is ConditionalExpression &&
        (node == parent.thenExpression || node == parent.elseExpression)) {
      Expression thenExpression = parent.thenExpression;
      DartType thenType;
      if (thenExpression is AsExpression) {
        thenType = thenExpression.expression.staticType;
      } else {
        thenType = thenExpression.staticType;
      }
      Expression elseExpression = parent.elseExpression;
      DartType elseType;
      if (elseExpression is AsExpression) {
        elseType = elseExpression.expression.staticType;
      } else {
        elseType = elseExpression.staticType;
      }
      if (thenType != null &&
          elseType != null &&
          !thenType.isDynamic &&
          !elseType.isDynamic &&
          !thenType.isMoreSpecificThan(elseType) &&
          !elseType.isMoreSpecificThan(thenType)) {
        return false;
      }
    }
    DartType lhsType = node.expression.staticType;
    DartType rhsType = node.type.type;
    if (lhsType != null &&
        rhsType != null &&
        !lhsType.isDynamic &&
        !rhsType.isDynamic &&
        _typeSystem.isMoreSpecificThan(lhsType, rhsType)) {
      _errorReporter.reportErrorForNode(HintCode.UNNECESSARY_CAST, node);
      return true;
    }
    return false;
  }

  /// Generate a hint for `noSuchMethod` methods that do nothing except of
  /// calling another `noSuchMethod` that is not defined by `Object`.
  ///
  /// @return `true` if and only if a hint code is generated on the passed node
  /// See [HintCode.UNNECESSARY_NO_SUCH_METHOD].
  bool _checkForUnnecessaryNoSuchMethod(MethodDeclaration node) {
    if (node.name.name != FunctionElement.NO_SUCH_METHOD_METHOD_NAME) {
      return false;
    }
    bool isNonObjectNoSuchMethodInvocation(Expression invocation) {
      if (invocation is MethodInvocation &&
          invocation.target is SuperExpression &&
          invocation.argumentList.arguments.length == 1) {
        SimpleIdentifier name = invocation.methodName;
        if (name.name == FunctionElement.NO_SUCH_METHOD_METHOD_NAME) {
          Element methodElement = name.staticElement;
          Element classElement = methodElement?.enclosingElement;
          return methodElement is MethodElement &&
              classElement is ClassElement &&
              !classElement.type.isObject;
        }
      }
      return false;
    }

    FunctionBody body = node.body;
    if (body is ExpressionFunctionBody) {
      if (isNonObjectNoSuchMethodInvocation(body.expression)) {
        _errorReporter.reportErrorForNode(
            HintCode.UNNECESSARY_NO_SUCH_METHOD, node);
        return true;
      }
    } else if (body is BlockFunctionBody) {
      List<Statement> statements = body.block.statements;
      if (statements.length == 1) {
        Statement returnStatement = statements.first;
        if (returnStatement is ReturnStatement &&
            isNonObjectNoSuchMethodInvocation(returnStatement.expression)) {
          _errorReporter.reportErrorForNode(
              HintCode.UNNECESSARY_NO_SUCH_METHOD, node);
          return true;
        }
      }
    }
    return false;
  }

  void _checkRequiredParameter(FormalParameterList node) {
    final requiredParameters =
        node.parameters.where((p) => p.declaredElement?.hasRequired == true);
    final nonNamedParamsWithRequired =
        requiredParameters.where((p) => !p.isNamed);
    final namedParamsWithRequiredAndDefault = requiredParameters
        .where((p) => p.isNamed)
        .where((p) => p.declaredElement.defaultValueCode != null);
    final paramsToHint = [
      nonNamedParamsWithRequired,
      namedParamsWithRequiredAndDefault
    ].expand((e) => e);
    for (final param in paramsToHint) {
      _errorReporter.reportErrorForNode(
          HintCode.INVALID_REQUIRED_PARAM, param, [param.identifier.name]);
    }
  }

  /// Check for the passed class declaration for the
  /// [HintCode.OVERRIDE_EQUALS_BUT_NOT_HASH_CODE] hint code.
  ///
  /// @param node the class declaration to check
  /// @return `true` if and only if a hint code is generated on the passed node
  /// See [HintCode.OVERRIDE_EQUALS_BUT_NOT_HASH_CODE].
//  bool _checkForOverrideEqualsButNotHashCode(ClassDeclaration node) {
//    ClassElement classElement = node.element;
//    if (classElement == null) {
//      return false;
//    }
//    MethodElement equalsOperatorMethodElement =
//        classElement.getMethod(sc.TokenType.EQ_EQ.lexeme);
//    if (equalsOperatorMethodElement != null) {
//      PropertyAccessorElement hashCodeElement =
//          classElement.getGetter(_HASHCODE_GETTER_NAME);
//      if (hashCodeElement == null) {
//        _errorReporter.reportErrorForNode(
//            HintCode.OVERRIDE_EQUALS_BUT_NOT_HASH_CODE,
//            node.name,
//            [classElement.displayName]);
//        return true;
//      }
//    }
//    return false;
//  }
//
//  /// Return `true` if the given [type] represents `Future<void>`.
//  bool _isFutureVoid(DartType type) {
//    if (type.isDartAsyncFuture) {
//      List<DartType> typeArgs = (type as InterfaceType).typeArguments;
//      if (typeArgs.length == 1 && typeArgs[0].isVoid) {
//        return true;
//      }
//    }
//    return false;
//  }

  static bool _hasDeprecatedAnnotation(List<Annotation> annotations) {
    for (var i = 0; i < annotations.length; i++) {
      if (annotations[i].elementAnnotation.isDeprecated) {
        return true;
      }
    }
    return false;
  }

  /// Given a parenthesized expression, this returns the parent (or recursively
  /// grand-parent) of the expression that is a parenthesized expression, but
  /// whose parent is not a parenthesized expression.
  ///
  /// For example given the code `(((e)))`: `(e) -> (((e)))`.
  ///
  /// @param parenthesizedExpression some expression whose parent is a
  ///        parenthesized expression
  /// @return the first parent or grand-parent that is a parenthesized
  ///         expression, that does not have a parenthesized expression parent
  static ParenthesizedExpression _wrapParenthesizedExpression(
      ParenthesizedExpression parenthesizedExpression) {
    AstNode parent = parenthesizedExpression.parent;
    if (parent is ParenthesizedExpression) {
      return _wrapParenthesizedExpression(parent);
    }
    return parenthesizedExpression;
  }
}

/// Utilities for [LibraryElementImpl] building.
class BuildLibraryElementUtils {
  /// Look through all of the compilation units defined for the given [library],
  /// looking for getters and setters that are defined in different compilation
  /// units but that have the same names. If any are found, make sure that they
  /// have the same variable element.
  static void patchTopLevelAccessors(LibraryElementImpl library) {
    // Without parts getters/setters already share the same variable element.
    List<CompilationUnitElement> parts = library.parts;
    if (parts.isEmpty) {
      return;
    }
    // Collect getters and setters.
    Map<String, PropertyAccessorElement> getters =
        new HashMap<String, PropertyAccessorElement>();
    List<PropertyAccessorElement> setters = <PropertyAccessorElement>[];
    _collectAccessors(getters, setters, library.definingCompilationUnit);
    int partLength = parts.length;
    for (int i = 0; i < partLength; i++) {
      CompilationUnitElement unit = parts[i];
      _collectAccessors(getters, setters, unit);
    }
    // Move every setter to the corresponding getter's variable (if exists).
    int setterLength = setters.length;
    for (int j = 0; j < setterLength; j++) {
      PropertyAccessorElement setter = setters[j];
      PropertyAccessorElement getter = getters[setter.displayName];
      if (getter != null) {
        TopLevelVariableElementImpl variable = getter.variable;
        TopLevelVariableElementImpl setterVariable = setter.variable;
        CompilationUnitElementImpl setterUnit = setterVariable.enclosingElement;
        setterUnit.replaceTopLevelVariable(setterVariable, variable);
        variable.setter = setter;
        (setter as PropertyAccessorElementImpl).variable = variable;
      }
    }
  }

  /// Add all of the non-synthetic [getters] and [setters] defined in the given
  /// [unit] that have no corresponding accessor to one of the given
  /// collections.
  static void _collectAccessors(Map<String, PropertyAccessorElement> getters,
      List<PropertyAccessorElement> setters, CompilationUnitElement unit) {
    List<PropertyAccessorElement> accessors = unit.accessors;
    int length = accessors.length;
    for (int i = 0; i < length; i++) {
      PropertyAccessorElement accessor = accessors[i];
      if (accessor.isGetter) {
        if (!accessor.isSynthetic && accessor.correspondingSetter == null) {
          getters[accessor.displayName] = accessor;
        }
      } else {
        if (!accessor.isSynthetic && accessor.correspondingGetter == null) {
          setters.add(accessor);
        }
      }
    }
  }
}

/// Instances of the class `Dart2JSVerifier` traverse an AST structure looking
/// for hints for code that will be compiled to JS, such as
/// [HintCode.IS_DOUBLE].
class Dart2JSVerifier extends RecursiveAstVisitor<void> {
  /// The name of the `double` type.
  static String _DOUBLE_TYPE_NAME = "double";

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

  /// Create a new instance of the [Dart2JSVerifier].
  ///
  /// @param errorReporter the error reporter
  Dart2JSVerifier(this._errorReporter);

  @override
  void visitIsExpression(IsExpression node) {
    _checkForIsDoubleHints(node);
    super.visitIsExpression(node);
  }

  /// Check for instances of `x is double`, `x is int`, `x is! double` and
  /// `x is! int`.
  ///
  /// @param node the is expression to check
  /// @return `true` if and only if a hint code is generated on the passed node
  /// See [HintCode.IS_DOUBLE],
  /// [HintCode.IS_INT],
  /// [HintCode.IS_NOT_DOUBLE], and
  /// [HintCode.IS_NOT_INT].
  bool _checkForIsDoubleHints(IsExpression node) {
    DartType type = node.type.type;
    Element element = type?.element;
    if (element != null) {
      String typeNameStr = element.name;
      LibraryElement libraryElement = element.library;
      //      if (typeNameStr.equals(INT_TYPE_NAME) && libraryElement != null
      //          && libraryElement.isDartCore()) {
      //        if (node.getNotOperator() == null) {
      //          errorReporter.reportError(HintCode.IS_INT, node);
      //        } else {
      //          errorReporter.reportError(HintCode.IS_NOT_INT, node);
      //        }
      //        return true;
      //      } else
      if (typeNameStr == _DOUBLE_TYPE_NAME &&
          libraryElement != null &&
          libraryElement.isDartCore) {
        if (node.notOperator == null) {
          _errorReporter.reportErrorForNode(HintCode.IS_DOUBLE, node);
        } else {
          _errorReporter.reportErrorForNode(HintCode.IS_NOT_DOUBLE, node);
        }
        return true;
      }
    }
    return false;
  }
}

/// A visitor that finds dead code and unused labels.
class DeadCodeVerifier extends RecursiveAstVisitor<void> {
  /// The error reporter by which errors will be reported.
  final ErrorReporter _errorReporter;

  ///  The type system for this visitor
  final TypeSystem _typeSystem;

  /// The object used to track the usage of labels within a given label scope.
  _LabelTracker labelTracker;

  /// Is `true` if this unit has been parsed as non-nullable.
  final bool _isNonNullableUnit;

  /// Initialize a newly created dead code verifier that will report dead code
  /// to the given [errorReporter] and will use the given [typeSystem] if one is
  /// provided.
  DeadCodeVerifier(this._errorReporter, this._isNonNullableUnit,
      {TypeSystem typeSystem})
      : this._typeSystem = typeSystem ?? new Dart2TypeSystem(null);

  @override
  void visitAssignmentExpression(AssignmentExpression node) {
    TokenType operatorType = node.operator.type;
    if (operatorType == TokenType.QUESTION_QUESTION_EQ) {
      _checkForDeadNullCoalesce(
          node.leftHandSide.staticType, node.rightHandSide);
    }
    super.visitAssignmentExpression(node);
  }

  @override
  void visitBinaryExpression(BinaryExpression node) {
    Token operator = node.operator;
    bool isAmpAmp = operator.type == TokenType.AMPERSAND_AMPERSAND;
    bool isBarBar = operator.type == TokenType.BAR_BAR;
    bool isQuestionQuestion = operator.type == TokenType.QUESTION_QUESTION;
    if (isAmpAmp || isBarBar) {
      Expression lhsCondition = node.leftOperand;
      if (!_isDebugConstant(lhsCondition)) {
        EvaluationResultImpl lhsResult = _getConstantBooleanValue(lhsCondition);
        if (lhsResult != null) {
          bool value = lhsResult.value.toBoolValue();
          if (value == true && isBarBar) {
            // Report error on "else" block: true || !e!
            _errorReporter.reportErrorForNode(
                HintCode.DEAD_CODE, node.rightOperand);
            // Only visit the LHS:
            lhsCondition?.accept(this);
            return;
          } else if (value == false && isAmpAmp) {
            // Report error on "if" block: false && !e!
            _errorReporter.reportErrorForNode(
                HintCode.DEAD_CODE, node.rightOperand);
            // Only visit the LHS:
            lhsCondition?.accept(this);
            return;
          }
        }
      }
      // How do we want to handle the RHS? It isn't dead code, but "pointless"
      // or "obscure"...
//            Expression rhsCondition = node.getRightOperand();
//            ValidResult rhsResult = getConstantBooleanValue(rhsCondition);
//            if (rhsResult != null) {
//              if (rhsResult == ValidResult.RESULT_TRUE && isBarBar) {
//                // report error on else block: !e! || true
//                errorReporter.reportError(HintCode.DEAD_CODE, node.getRightOperand());
//                // only visit the RHS:
//                rhsCondition?.accept(this);
//                return null;
//              } else if (rhsResult == ValidResult.RESULT_FALSE && isAmpAmp) {
//                // report error on if block: !e! && false
//                errorReporter.reportError(HintCode.DEAD_CODE, node.getRightOperand());
//                // only visit the RHS:
//                rhsCondition?.accept(this);
//                return null;
//              }
//            }
    } else if (isQuestionQuestion && _isNonNullableUnit) {
      _checkForDeadNullCoalesce(node.leftOperand.staticType, node.rightOperand);
    }
    super.visitBinaryExpression(node);
  }

  /// For each block, this method reports and error on all statements between
  /// the end of the block and the first return statement (assuming there it is
  /// not at the end of the block.)
  @override
  void visitBlock(Block node) {
    NodeList<Statement> statements = node.statements;
    _checkForDeadStatementsInNodeList(statements);
  }

  @override
  void visitBreakStatement(BreakStatement node) {
    labelTracker?.recordUsage(node.label?.name);
  }

  @override
  void visitConditionalExpression(ConditionalExpression node) {
    Expression conditionExpression = node.condition;
    conditionExpression?.accept(this);
    if (!_isDebugConstant(conditionExpression)) {
      EvaluationResultImpl result =
          _getConstantBooleanValue(conditionExpression);
      if (result != null) {
        if (result.value.toBoolValue() == true) {
          // Report error on "else" block: true ? 1 : !2!
          _errorReporter.reportErrorForNode(
              HintCode.DEAD_CODE, node.elseExpression);
          node.thenExpression?.accept(this);
          return;
        } else {
          // Report error on "if" block: false ? !1! : 2
          _errorReporter.reportErrorForNode(
              HintCode.DEAD_CODE, node.thenExpression);
          node.elseExpression?.accept(this);
          return;
        }
      }
    }
    super.visitConditionalExpression(node);
  }

  @override
  void visitContinueStatement(ContinueStatement node) {
    labelTracker?.recordUsage(node.label?.name);
  }

  @override
  void visitExportDirective(ExportDirective node) {
    ExportElement exportElement = node.element;
    if (exportElement != null) {
      // The element is null when the URI is invalid.
      LibraryElement library = exportElement.exportedLibrary;
      if (library != null && !library.isSynthetic) {
        for (Combinator combinator in node.combinators) {
          _checkCombinator(library, combinator);
        }
      }
    }
    super.visitExportDirective(node);
  }

  @override
  void visitIfElement(IfElement node) {
    Expression conditionExpression = node.condition;
    conditionExpression?.accept(this);
    if (!_isDebugConstant(conditionExpression)) {
      EvaluationResultImpl result =
          _getConstantBooleanValue(conditionExpression);
      if (result != null) {
        if (result.value.toBoolValue() == true) {
          // Report error on else block: if(true) {} else {!}
          CollectionElement elseElement = node.elseElement;
          if (elseElement != null) {
            _errorReporter.reportErrorForNode(HintCode.DEAD_CODE, elseElement);
            node.thenElement?.accept(this);
            return;
          }
        } else {
          // Report error on if block: if (false) {!} else {}
          _errorReporter.reportErrorForNode(
              HintCode.DEAD_CODE, node.thenElement);
          node.elseElement?.accept(this);
          return;
        }
      }
    }
    super.visitIfElement(node);
  }

  @override
  void visitIfStatement(IfStatement node) {
    Expression conditionExpression = node.condition;
    conditionExpression?.accept(this);
    if (!_isDebugConstant(conditionExpression)) {
      EvaluationResultImpl result =
          _getConstantBooleanValue(conditionExpression);
      if (result != null) {
        if (result.value.toBoolValue() == true) {
          // Report error on else block: if(true) {} else {!}
          Statement elseStatement = node.elseStatement;
          if (elseStatement != null) {
            _errorReporter.reportErrorForNode(
                HintCode.DEAD_CODE, elseStatement);
            node.thenStatement?.accept(this);
            return;
          }
        } else {
          // Report error on if block: if (false) {!} else {}
          _errorReporter.reportErrorForNode(
              HintCode.DEAD_CODE, node.thenStatement);
          node.elseStatement?.accept(this);
          return;
        }
      }
    }
    super.visitIfStatement(node);
  }

  @override
  void visitImportDirective(ImportDirective node) {
    ImportElement importElement = node.element;
    if (importElement != null) {
      // The element is null when the URI is invalid, but not when the URI is
      // valid but refers to a non-existent file.
      LibraryElement library = importElement.importedLibrary;
      if (library != null && !library.isSynthetic) {
        for (Combinator combinator in node.combinators) {
          _checkCombinator(library, combinator);
        }
      }
    }
    super.visitImportDirective(node);
  }

  @override
  void visitLabeledStatement(LabeledStatement node) {
    _pushLabels(node.labels);
    try {
      super.visitLabeledStatement(node);
    } finally {
      _popLabels();
    }
  }

  @override
  void visitSwitchCase(SwitchCase node) {
    _checkForDeadStatementsInNodeList(node.statements, allowMandated: true);
    super.visitSwitchCase(node);
  }

  @override
  void visitSwitchDefault(SwitchDefault node) {
    _checkForDeadStatementsInNodeList(node.statements, allowMandated: true);
    super.visitSwitchDefault(node);
  }

  @override
  void visitSwitchStatement(SwitchStatement node) {
    List<Label> labels = <Label>[];
    for (SwitchMember member in node.members) {
      labels.addAll(member.labels);
    }
    _pushLabels(labels);
    try {
      super.visitSwitchStatement(node);
    } finally {
      _popLabels();
    }
  }

  @override
  void visitTryStatement(TryStatement node) {
    node.body?.accept(this);
    node.finallyBlock?.accept(this);
    NodeList<CatchClause> catchClauses = node.catchClauses;
    int numOfCatchClauses = catchClauses.length;
    List<DartType> visitedTypes = new List<DartType>();
    for (int i = 0; i < numOfCatchClauses; i++) {
      CatchClause catchClause = catchClauses[i];
      if (catchClause.onKeyword != null) {
        // An on-catch clause was found; verify that the exception type is not a
        // subtype of a previous on-catch exception type.
        DartType currentType = catchClause.exceptionType?.type;
        if (currentType != null) {
          if (currentType.isObject) {
            // Found catch clause clause that has Object as an exception type,
            // this is equivalent to having a catch clause that doesn't have an
            // exception type, visit the block, but generate an error on any
            // following catch clauses (and don't visit them).
            catchClause?.accept(this);
            if (i + 1 != numOfCatchClauses) {
              // This catch clause is not the last in the try statement.
              CatchClause nextCatchClause = catchClauses[i + 1];
              CatchClause lastCatchClause = catchClauses[numOfCatchClauses - 1];
              int offset = nextCatchClause.offset;
              int length = lastCatchClause.end - offset;
              _errorReporter.reportErrorForOffset(
                  HintCode.DEAD_CODE_CATCH_FOLLOWING_CATCH, offset, length);
              return;
            }
          }
          int length = visitedTypes.length;
          for (int j = 0; j < length; j++) {
            DartType type = visitedTypes[j];
            if (_typeSystem.isSubtypeOf(currentType, type)) {
              CatchClause lastCatchClause = catchClauses[numOfCatchClauses - 1];
              int offset = catchClause.offset;
              int length = lastCatchClause.end - offset;
              _errorReporter.reportErrorForOffset(
                  HintCode.DEAD_CODE_ON_CATCH_SUBTYPE,
                  offset,
                  length,
                  [currentType.displayName, type.displayName]);
              return;
            }
          }
          visitedTypes.add(currentType);
        }
        catchClause?.accept(this);
      } else {
        // Found catch clause clause that doesn't have an exception type,
        // visit the block, but generate an error on any following catch clauses
        // (and don't visit them).
        catchClause?.accept(this);
        if (i + 1 != numOfCatchClauses) {
          // This catch clause is not the last in the try statement.
          CatchClause nextCatchClause = catchClauses[i + 1];
          CatchClause lastCatchClause = catchClauses[numOfCatchClauses - 1];
          int offset = nextCatchClause.offset;
          int length = lastCatchClause.end - offset;
          _errorReporter.reportErrorForOffset(
              HintCode.DEAD_CODE_CATCH_FOLLOWING_CATCH, offset, length);
          return;
        }
      }
    }
  }

  @override
  void visitWhileStatement(WhileStatement node) {
    Expression conditionExpression = node.condition;
    conditionExpression?.accept(this);
    if (!_isDebugConstant(conditionExpression)) {
      EvaluationResultImpl result =
          _getConstantBooleanValue(conditionExpression);
      if (result != null) {
        if (result.value.toBoolValue() == false) {
          // Report error on while block: while (false) {!}
          _errorReporter.reportErrorForNode(HintCode.DEAD_CODE, node.body);
          return;
        }
      }
    }
    node.body?.accept(this);
  }

  /// Resolve the names in the given [combinator] in the scope of the given
  /// [library].
  void _checkCombinator(LibraryElement library, Combinator combinator) {
    Namespace namespace =
        new NamespaceBuilder().createExportNamespaceForLibrary(library);
    NodeList<SimpleIdentifier> names;
    ErrorCode hintCode;
    if (combinator is HideCombinator) {
      names = combinator.hiddenNames;
      hintCode = HintCode.UNDEFINED_HIDDEN_NAME;
    } else {
      names = (combinator as ShowCombinator).shownNames;
      hintCode = HintCode.UNDEFINED_SHOWN_NAME;
    }
    for (SimpleIdentifier name in names) {
      String nameStr = name.name;
      Element element = namespace.get(nameStr);
      if (element == null) {
        element = namespace.get("$nameStr=");
      }
      if (element == null) {
        _errorReporter
            .reportErrorForNode(hintCode, name, [library.identifier, nameStr]);
      }
    }
  }

  void _checkForDeadNullCoalesce(TypeImpl lhsType, Expression rhs) {
    if (_isNonNullableUnit && _typeSystem.isNonNullable(lhsType)) {
      _errorReporter.reportErrorForNode(HintCode.DEAD_CODE, rhs, []);
    }
  }

  /// Given some list of [statements], loop through the list searching for dead
  /// statements. If [allowMandated] is true, then allow dead statements that
  /// are mandated by the language spec. This allows for a final break,
  /// continue, return, or throw statement at the end of a switch case, that are
  /// mandated by the language spec.
  void _checkForDeadStatementsInNodeList(NodeList<Statement> statements,
      {bool allowMandated: false}) {
    bool statementExits(Statement statement) {
      if (statement is BreakStatement) {
        return statement.label == null;
      } else if (statement is ContinueStatement) {
        return statement.label == null;
      }
      return ExitDetector.exits(statement);
    }

    int size = statements.length;
    for (int i = 0; i < size; i++) {
      Statement currentStatement = statements[i];
      currentStatement?.accept(this);
      if (statementExits(currentStatement) && i != size - 1) {
        Statement nextStatement = statements[i + 1];
        Statement lastStatement = statements[size - 1];
        // If mandated statements are allowed, and only the last statement is
        // dead, and it's a BreakStatement, then assume it is a statement
        // mandated by the language spec, there to avoid a
        // CASE_BLOCK_NOT_TERMINATED error.
        if (allowMandated && i == size - 2 && nextStatement is BreakStatement) {
          return;
        }
        int offset = nextStatement.offset;
        int length = lastStatement.end - offset;
        _errorReporter.reportErrorForOffset(HintCode.DEAD_CODE, offset, length);
        return;
      }
    }
  }

  /// Given some [expression], return [ValidResult.RESULT_TRUE] if it is `true`,
  /// [ValidResult.RESULT_FALSE] if it is `false`, or `null` if the expression
  /// is not a constant boolean value.
  EvaluationResultImpl _getConstantBooleanValue(Expression expression) {
    if (expression is BooleanLiteral) {
      if (expression.value) {
        return new EvaluationResultImpl(
            new DartObjectImpl(null, BoolState.from(true)));
      } else {
        return new EvaluationResultImpl(
            new DartObjectImpl(null, BoolState.from(false)));
      }
    }

    // Don't consider situations where we could evaluate to a constant boolean
    // expression with the ConstantVisitor
    // else {
    // EvaluationResultImpl result = expression.accept(new ConstantVisitor());
    // if (result == ValidResult.RESULT_TRUE) {
    // return ValidResult.RESULT_TRUE;
    // } else if (result == ValidResult.RESULT_FALSE) {
    // return ValidResult.RESULT_FALSE;
    // }
    // return null;
    // }
    return null;
  }

  /// Return `true` if the given [expression] is resolved to a constant
  /// variable.
  bool _isDebugConstant(Expression expression) {
    Element element = null;
    if (expression is Identifier) {
      element = expression.staticElement;
    } else if (expression is PropertyAccess) {
      element = expression.propertyName.staticElement;
    }
    if (element is PropertyAccessorElement) {
      PropertyInducingElement variable = element.variable;
      return variable != null && variable.isConst;
    }
    return false;
  }

  /// Exit the most recently entered label scope after reporting any labels that
  /// were not referenced within that scope.
  void _popLabels() {
    for (Label label in labelTracker.unusedLabels()) {
      _errorReporter
          .reportErrorForNode(HintCode.UNUSED_LABEL, label, [label.label.name]);
    }
    labelTracker = labelTracker.outerTracker;
  }

  /// Enter a new label scope in which the given [labels] are defined.
  void _pushLabels(List<Label> labels) {
    labelTracker = new _LabelTracker(labelTracker, labels);
  }
}

/// A visitor that resolves directives in an AST structure to already built
/// elements.
///
/// The resulting AST must have everything resolved that would have been
/// resolved by a [DirectiveElementBuilder].
class DirectiveResolver extends SimpleAstVisitor {
  final Map<Source, int> sourceModificationTimeMap;
  final Map<Source, SourceKind> importSourceKindMap;
  final Map<Source, SourceKind> exportSourceKindMap;
  final List<AnalysisError> errors = <AnalysisError>[];

  LibraryElement _enclosingLibrary;

  DirectiveResolver(this.sourceModificationTimeMap, this.importSourceKindMap,
      this.exportSourceKindMap);

  @override
  void visitCompilationUnit(CompilationUnit node) {
    _enclosingLibrary =
        resolutionMap.elementDeclaredByCompilationUnit(node).library;
    for (Directive directive in node.directives) {
      directive.accept(this);
    }
  }

  @override
  void visitExportDirective(ExportDirective node) {
    int nodeOffset = node.offset;
    node.element = null;
    for (ExportElement element in _enclosingLibrary.exports) {
      if (element.nameOffset == nodeOffset) {
        node.element = element;
        // Verify the exported source kind.
        LibraryElement exportedLibrary = element.exportedLibrary;
        if (exportedLibrary != null) {
          Source exportedSource = exportedLibrary.source;
          int exportedTime = sourceModificationTimeMap[exportedSource] ?? -1;
          if (exportedTime >= 0 &&
              exportSourceKindMap[exportedSource] != SourceKind.LIBRARY) {
            StringLiteral uriLiteral = node.uri;
            errors.add(new AnalysisError(
                _enclosingLibrary.source,
                uriLiteral.offset,
                uriLiteral.length,
                CompileTimeErrorCode.EXPORT_OF_NON_LIBRARY,
                [uriLiteral.toSource()]));
          }
        }
        break;
      }
    }
  }

  @override
  void visitImportDirective(ImportDirective node) {
    int nodeOffset = node.offset;
    node.element = null;
    for (ImportElement element in _enclosingLibrary.imports) {
      if (element.nameOffset == nodeOffset) {
        node.element = element;
        // Verify the imported source kind.
        LibraryElement importedLibrary = element.importedLibrary;
        if (importedLibrary != null) {
          Source importedSource = importedLibrary.source;
          int importedTime = sourceModificationTimeMap[importedSource] ?? -1;
          if (importedTime >= 0 &&
              importSourceKindMap[importedSource] != SourceKind.LIBRARY) {
            StringLiteral uriLiteral = node.uri;
            ErrorCode errorCode = element.isDeferred
                ? StaticWarningCode.IMPORT_OF_NON_LIBRARY
                : CompileTimeErrorCode.IMPORT_OF_NON_LIBRARY;
            errors.add(new AnalysisError(
                _enclosingLibrary.source,
                uriLiteral.offset,
                uriLiteral.length,
                errorCode,
                [uriLiteral.toSource()]));
          }
        }
        break;
      }
    }
  }

  @override
  void visitLibraryDirective(LibraryDirective node) {
    node.element = _enclosingLibrary;
  }
}

/// Instances of the class `ElementHolder` hold on to elements created while
/// traversing an AST structure so that they can be accessed when creating their
/// enclosing element.
class ElementHolder {
  List<PropertyAccessorElement> _accessors;

  List<ConstructorElement> _constructors;

  List<ClassElement> _enums;

  List<FieldElement> _fields;

  List<FunctionElement> _functions;

  List<LabelElement> _labels;

  List<LocalVariableElement> _localVariables;

  List<MethodElement> _methods;

  List<ClassElement> _mixins;

  List<ParameterElement> _parameters;

  List<TopLevelVariableElement> _topLevelVariables;

  List<ClassElement> _types;

  List<FunctionTypeAliasElement> _typeAliases;

  List<TypeParameterElement> _typeParameters;

  List<PropertyAccessorElement> get accessors {
    if (_accessors == null) {
      return const <PropertyAccessorElement>[];
    }
    List<PropertyAccessorElement> result = _accessors;
    _accessors = null;
    return result;
  }

  List<ConstructorElement> get constructors {
    if (_constructors == null) {
      return const <ConstructorElement>[];
    }
    List<ConstructorElement> result = _constructors;
    _constructors = null;
    return result;
  }

  List<ClassElement> get enums {
    if (_enums == null) {
      return const <ClassElement>[];
    }
    List<ClassElement> result = _enums;
    _enums = null;
    return result;
  }

  List<FieldElement> get fields {
    if (_fields == null) {
      return const <FieldElement>[];
    }
    List<FieldElement> result = _fields;
    _fields = null;
    return result;
  }

  List<FieldElement> get fieldsWithoutFlushing {
    if (_fields == null) {
      return const <FieldElement>[];
    }
    List<FieldElement> result = _fields;
    return result;
  }

  List<FunctionElement> get functions {
    if (_functions == null) {
      return const <FunctionElement>[];
    }
    List<FunctionElement> result = _functions;
    _functions = null;
    return result;
  }

  List<LabelElement> get labels {
    if (_labels == null) {
      return const <LabelElement>[];
    }
    List<LabelElement> result = _labels;
    _labels = null;
    return result;
  }

  List<LocalVariableElement> get localVariables {
    if (_localVariables == null) {
      return const <LocalVariableElement>[];
    }
    List<LocalVariableElement> result = _localVariables;
    _localVariables = null;
    return result;
  }

  List<MethodElement> get methods {
    if (_methods == null) {
      return const <MethodElement>[];
    }
    List<MethodElement> result = _methods;
    _methods = null;
    return result;
  }

  List<ClassElement> get mixins {
    if (_mixins == null) {
      return const <ClassElement>[];
    }
    List<ClassElement> result = _mixins;
    _mixins = null;
    return result;
  }

  List<ParameterElement> get parameters {
    if (_parameters == null) {
      return const <ParameterElement>[];
    }
    List<ParameterElement> result = _parameters;
    _parameters = null;
    return result;
  }

  List<TopLevelVariableElement> get topLevelVariables {
    if (_topLevelVariables == null) {
      return const <TopLevelVariableElement>[];
    }
    List<TopLevelVariableElement> result = _topLevelVariables;
    _topLevelVariables = null;
    return result;
  }

  List<FunctionTypeAliasElement> get typeAliases {
    if (_typeAliases == null) {
      return const <FunctionTypeAliasElement>[];
    }
    List<FunctionTypeAliasElement> result = _typeAliases;
    _typeAliases = null;
    return result;
  }

  List<TypeParameterElement> get typeParameters {
    if (_typeParameters == null) {
      return const <TypeParameterElement>[];
    }
    List<TypeParameterElement> result = _typeParameters;
    _typeParameters = null;
    return result;
  }

  List<ClassElement> get types {
    if (_types == null) {
      return const <ClassElement>[];
    }
    List<ClassElement> result = _types;
    _types = null;
    return result;
  }

  void addAccessor(PropertyAccessorElement element) {
    if (_accessors == null) {
      _accessors = new List<PropertyAccessorElement>();
    }
    _accessors.add(element);
  }

  void addConstructor(ConstructorElement element) {
    if (_constructors == null) {
      _constructors = new List<ConstructorElement>();
    }
    _constructors.add(element);
  }

  void addEnum(ClassElement element) {
    if (_enums == null) {
      _enums = new List<ClassElement>();
    }
    _enums.add(element);
  }

  void addField(FieldElement element) {
    if (_fields == null) {
      _fields = new List<FieldElement>();
    }
    _fields.add(element);
  }

  void addFunction(FunctionElement element) {
    if (_functions == null) {
      _functions = new List<FunctionElement>();
    }
    _functions.add(element);
  }

  void addLabel(LabelElement element) {
    if (_labels == null) {
      _labels = new List<LabelElement>();
    }
    _labels.add(element);
  }

  void addLocalVariable(LocalVariableElement element) {
    if (_localVariables == null) {
      _localVariables = new List<LocalVariableElement>();
    }
    _localVariables.add(element);
  }

  void addMethod(MethodElement element) {
    if (_methods == null) {
      _methods = new List<MethodElement>();
    }
    _methods.add(element);
  }

  void addMixin(ClassElement element) {
    if (_mixins == null) {
      _mixins = new List<ClassElement>();
    }
    _mixins.add(element);
  }

  void addParameter(ParameterElement element) {
    if (_parameters == null) {
      _parameters = new List<ParameterElement>();
    }
    _parameters.add(element);
  }

  void addTopLevelVariable(TopLevelVariableElement element) {
    if (_topLevelVariables == null) {
      _topLevelVariables = new List<TopLevelVariableElement>();
    }
    _topLevelVariables.add(element);
  }

  void addType(ClassElement element) {
    if (_types == null) {
      _types = new List<ClassElement>();
    }
    _types.add(element);
  }

  void addTypeAlias(FunctionTypeAliasElement element) {
    if (_typeAliases == null) {
      _typeAliases = new List<FunctionTypeAliasElement>();
    }
    _typeAliases.add(element);
  }

  void addTypeParameter(TypeParameterElement element) {
    if (_typeParameters == null) {
      _typeParameters = new List<TypeParameterElement>();
    }
    _typeParameters.add(element);
  }

  FieldElement getField(String fieldName, {bool synthetic: false}) {
    if (_fields == null) {
      return null;
    }
    int length = _fields.length;
    for (int i = 0; i < length; i++) {
      FieldElement field = _fields[i];
      if (field.name == fieldName && field.isSynthetic == synthetic) {
        return field;
      }
    }
    return null;
  }

  TopLevelVariableElement getTopLevelVariable(String variableName) {
    if (_topLevelVariables == null) {
      return null;
    }
    int length = _topLevelVariables.length;
    for (int i = 0; i < length; i++) {
      TopLevelVariableElement variable = _topLevelVariables[i];
      if (variable.name == variableName) {
        return variable;
      }
    }
    return null;
  }

  void validate() {
    StringBuffer buffer = new StringBuffer();
    if (_accessors != null) {
      buffer.write(_accessors.length);
      buffer.write(" accessors");
    }
    if (_constructors != null) {
      if (buffer.length > 0) {
        buffer.write("; ");
      }
      buffer.write(_constructors.length);
      buffer.write(" constructors");
    }
    if (_fields != null) {
      if (buffer.length > 0) {
        buffer.write("; ");
      }
      buffer.write(_fields.length);
      buffer.write(" fields");
    }
    if (_functions != null) {
      if (buffer.length > 0) {
        buffer.write("; ");
      }
      buffer.write(_functions.length);
      buffer.write(" functions");
    }
    if (_labels != null) {
      if (buffer.length > 0) {
        buffer.write("; ");
      }
      buffer.write(_labels.length);
      buffer.write(" labels");
    }
    if (_localVariables != null) {
      if (buffer.length > 0) {
        buffer.write("; ");
      }
      buffer.write(_localVariables.length);
      buffer.write(" local variables");
    }
    if (_methods != null) {
      if (buffer.length > 0) {
        buffer.write("; ");
      }
      buffer.write(_methods.length);
      buffer.write(" methods");
    }
    if (_parameters != null) {
      if (buffer.length > 0) {
        buffer.write("; ");
      }
      buffer.write(_parameters.length);
      buffer.write(" parameters");
    }
    if (_topLevelVariables != null) {
      if (buffer.length > 0) {
        buffer.write("; ");
      }
      buffer.write(_topLevelVariables.length);
      buffer.write(" top-level variables");
    }
    if (_types != null) {
      if (buffer.length > 0) {
        buffer.write("; ");
      }
      buffer.write(_types.length);
      buffer.write(" types");
    }
    if (_typeAliases != null) {
      if (buffer.length > 0) {
        buffer.write("; ");
      }
      buffer.write(_typeAliases.length);
      buffer.write(" type aliases");
    }
    if (_typeParameters != null) {
      if (buffer.length > 0) {
        buffer.write("; ");
      }
      buffer.write(_typeParameters.length);
      buffer.write(" type parameters");
    }
    if (buffer.length > 0) {
      AnalysisEngine.instance.logger
          .logError("Failed to capture elements: $buffer");
    }
  }
}

/// Instances of the class `EnumMemberBuilder` build the members in enum
/// declarations.
class EnumMemberBuilder extends RecursiveAstVisitor<void> {
  /// The type provider used to access the types needed to build an element
  /// model for enum declarations.
  final TypeProvider _typeProvider;

  /// Initialize a newly created enum member builder.
  ///
  /// @param typeProvider the type provider used to access the types needed to
  ///        build an element model for enum declarations
  EnumMemberBuilder(this._typeProvider);

  @override
  void visitEnumDeclaration(EnumDeclaration node) {
    //
    // Finish building the enum.
    //
    EnumElementImpl enumElement = node.name.staticElement as EnumElementImpl;
    InterfaceType enumType = enumElement.type;
    //
    // Populate the fields.
    //
    List<FieldElement> fields = new List<FieldElement>();
    List<PropertyAccessorElement> getters = new List<PropertyAccessorElement>();
    InterfaceType intType = _typeProvider.intType;
    String indexFieldName = "index";
    FieldElementImpl indexField = new FieldElementImpl(indexFieldName, -1);
    indexField.isFinal = true;
    indexField.isSynthetic = true;
    indexField.type = intType;
    fields.add(indexField);
    getters.add(_createGetter(indexField));
    ConstFieldElementImpl valuesField = new ConstFieldElementImpl("values", -1);
    valuesField.isStatic = true;
    valuesField.isConst = true;
    valuesField.isSynthetic = true;
    valuesField.type = _typeProvider.listType.instantiate(<DartType>[enumType]);
    fields.add(valuesField);
    getters.add(_createGetter(valuesField));
    //
    // Build the enum constants.
    //
    NodeList<EnumConstantDeclaration> constants = node.constants;
    List<DartObjectImpl> constantValues = new List<DartObjectImpl>();
    int constantCount = constants.length;
    for (int i = 0; i < constantCount; i++) {
      EnumConstantDeclaration constant = constants[i];
      FieldElementImpl constantField = constant.name.staticElement;
      //
      // Create a value for the constant.
      //
      Map<String, DartObjectImpl> fieldMap =
          new HashMap<String, DartObjectImpl>();
      fieldMap[indexFieldName] = new DartObjectImpl(intType, new IntState(i));
      DartObjectImpl value =
          new DartObjectImpl(enumType, new GenericState(fieldMap));
      constantValues.add(value);
      constantField.evaluationResult = new EvaluationResultImpl(value);
      fields.add(constantField);
      getters.add(constantField.getter);
    }
    //
    // Build the value of the 'values' field.
    //
    valuesField.evaluationResult = new EvaluationResultImpl(
        new DartObjectImpl(valuesField.type, new ListState(constantValues)));
    // Update toString() return type.
    {
      MethodElementImpl toStringMethod = enumElement.methods[0];
      toStringMethod.returnType = _typeProvider.stringType;
      toStringMethod.type = new FunctionTypeImpl(toStringMethod);
    }
    //
    // Finish building the enum.
    //
    enumElement.fields = fields;
    enumElement.accessors = getters;
    // Client code isn't allowed to invoke the constructor, so we do not model
    // it.
    super.visitEnumDeclaration(node);
  }

  /// Create a getter that corresponds to the given [field].
  PropertyAccessorElement _createGetter(FieldElementImpl field) {
    return new PropertyAccessorElementImpl_ImplicitGetter(field);
  }
}

/// A visitor that visits ASTs and fills [UsedImportedElements].
class GatherUsedImportedElementsVisitor extends RecursiveAstVisitor {
  final LibraryElement library;
  final UsedImportedElements usedElements = new UsedImportedElements();

  GatherUsedImportedElementsVisitor(this.library);

  @override
  void visitExportDirective(ExportDirective node) {
    _visitDirective(node);
  }

  @override
  void visitImportDirective(ImportDirective node) {
    _visitDirective(node);
  }

  @override
  void visitLibraryDirective(LibraryDirective node) {
    _visitDirective(node);
  }

  @override
  void visitSimpleIdentifier(SimpleIdentifier node) {
    _visitIdentifier(node, node.staticElement);
  }

  /// If the given [identifier] is prefixed with a [PrefixElement], fill the
  /// corresponding `UsedImportedElements.prefixMap` entry and return `true`.
  bool _recordPrefixMap(SimpleIdentifier identifier, Element element) {
    bool recordIfTargetIsPrefixElement(Expression target) {
      if (target is SimpleIdentifier && target.staticElement is PrefixElement) {
        List<Element> prefixedElements = usedElements.prefixMap
            .putIfAbsent(target.staticElement, () => <Element>[]);
        prefixedElements.add(element);
        return true;
      }
      return false;
    }

    AstNode parent = identifier.parent;
    if (parent is MethodInvocation && parent.methodName == identifier) {
      return recordIfTargetIsPrefixElement(parent.target);
    }
    if (parent is PrefixedIdentifier && parent.identifier == identifier) {
      return recordIfTargetIsPrefixElement(parent.prefix);
    }
    return false;
  }

  /// Visit identifiers used by the given [directive].
  void _visitDirective(Directive directive) {
    directive.documentationComment?.accept(this);
    directive.metadata.accept(this);
  }

  void _visitIdentifier(SimpleIdentifier identifier, Element element) {
    if (element == null) {
      return;
    }
    // If the element is multiply defined then call this method recursively for
    // each of the conflicting elements.
    if (element is MultiplyDefinedElement) {
      List<Element> conflictingElements = element.conflictingElements;
      int length = conflictingElements.length;
      for (int i = 0; i < length; i++) {
        Element elt = conflictingElements[i];
        _visitIdentifier(identifier, elt);
      }
      return;
    }

    // Record `importPrefix.identifier` into 'prefixMap'.
    if (_recordPrefixMap(identifier, element)) {
      return;
    }

    if (element is PrefixElement) {
      usedElements.prefixMap.putIfAbsent(element, () => <Element>[]);
      return;
    } else if (element.enclosingElement is! CompilationUnitElement) {
      // Identifiers that aren't a prefix element and whose enclosing element
      // isn't a CompilationUnit are ignored- this covers the case the
      // identifier is a relative-reference, a reference to an identifier not
      // imported by this library.
      return;
    }
    // Ignore if an unknown library.
    LibraryElement containingLibrary = element.library;
    if (containingLibrary == null) {
      return;
    }
    // Ignore if a local element.
    if (library == containingLibrary) {
      return;
    }
    // Remember the element.
    usedElements.elements.add(element);
  }
}

/// An [AstVisitor] that fills [UsedLocalElements].
class GatherUsedLocalElementsVisitor extends RecursiveAstVisitor {
  final UsedLocalElements usedElements = new UsedLocalElements();

  final LibraryElement _enclosingLibrary;
  ClassElement _enclosingClass;
  ExecutableElement _enclosingExec;

  GatherUsedLocalElementsVisitor(this._enclosingLibrary);

  @override
  visitCatchClause(CatchClause node) {
    SimpleIdentifier exceptionParameter = node.exceptionParameter;
    SimpleIdentifier stackTraceParameter = node.stackTraceParameter;
    if (exceptionParameter != null) {
      Element element = exceptionParameter.staticElement;
      usedElements.addCatchException(element);
      if (stackTraceParameter != null || node.onKeyword == null) {
        usedElements.addElement(element);
      }
    }
    if (stackTraceParameter != null) {
      Element element = stackTraceParameter.staticElement;
      usedElements.addCatchStackTrace(element);
    }
    super.visitCatchClause(node);
  }

  @override
  visitClassDeclaration(ClassDeclaration node) {
    ClassElement enclosingClassOld = _enclosingClass;
    try {
      _enclosingClass = node.declaredElement;
      super.visitClassDeclaration(node);
    } finally {
      _enclosingClass = enclosingClassOld;
    }
  }

  @override
  visitFunctionDeclaration(FunctionDeclaration node) {
    ExecutableElement enclosingExecOld = _enclosingExec;
    try {
      _enclosingExec = node.declaredElement;
      super.visitFunctionDeclaration(node);
    } finally {
      _enclosingExec = enclosingExecOld;
    }
  }

  @override
  visitFunctionExpression(FunctionExpression node) {
    if (node.parent is! FunctionDeclaration) {
      usedElements.addElement(node.declaredElement);
    }
    super.visitFunctionExpression(node);
  }

  @override
  visitMethodDeclaration(MethodDeclaration node) {
    ExecutableElement enclosingExecOld = _enclosingExec;
    try {
      _enclosingExec = node.declaredElement;
      super.visitMethodDeclaration(node);
    } finally {
      _enclosingExec = enclosingExecOld;
    }
  }

  @override
  visitSimpleIdentifier(SimpleIdentifier node) {
    if (node.inDeclarationContext()) {
      return;
    }
    Element element = node.staticElement;
    bool isIdentifierRead = _isReadIdentifier(node);
    if (element is PropertyAccessorElement &&
        element.isSynthetic &&
        isIdentifierRead &&
        element.variable is TopLevelVariableElement) {
      usedElements.addElement(element.variable);
    } else if (element is LocalVariableElement) {
      if (isIdentifierRead) {
        usedElements.addElement(element);
      }
    } else {
      _useIdentifierElement(node);
      if (element == null ||
          element.enclosingElement is ClassElement &&
              !identical(element, _enclosingExec)) {
        usedElements.members.add(node.name);
        if (isIdentifierRead) {
          usedElements.readMembers.add(node.name);
        }
      }
    }
  }

  /// Marks an [Element] of [node] as used in the library.
  void _useIdentifierElement(Identifier node) {
    Element element = node.staticElement;
    if (element == null) {
      return;
    }
    // check if a local element
    if (!identical(element.library, _enclosingLibrary)) {
      return;
    }
    // ignore references to an element from itself
    if (identical(element, _enclosingClass)) {
      return;
    }
    if (identical(element, _enclosingExec)) {
      return;
    }
    // ignore places where the element is not actually used
    if (node.parent is TypeName) {
      if (element is ClassElement) {
        AstNode parent2 = node.parent.parent;
        if (parent2 is IsExpression) {
          return;
        }
        if (parent2 is VariableDeclarationList) {
          // If it's a field's type, it still counts as used.
          if (parent2.parent is! FieldDeclaration) {
            return;
          }
        }
      }
    }
    // OK
    usedElements.addElement(element);
  }

  static bool _isReadIdentifier(SimpleIdentifier node) {
    // not reading at all
    if (!node.inGetterContext()) {
      return false;
    }
    // check if useless reading
    AstNode parent = node.parent;
    if (parent.parent is ExpressionStatement) {
      if (parent is PrefixExpression || parent is PostfixExpression) {
        // v++;
        // ++v;
        return false;
      }
      if (parent is AssignmentExpression && parent.leftHandSide == node) {
        // v ??= doSomething();
        //   vs.
        // v += 2;
        TokenType operatorType = parent.operator?.type;
        return operatorType == TokenType.QUESTION_QUESTION_EQ;
      }
    }
    // OK
    return true;
  }
}

/// Instances of the class `ImportsVerifier` visit all of the referenced
/// libraries in the source code verifying that all of the imports are used,
/// otherwise a [HintCode.UNUSED_IMPORT] hint is generated with
/// [generateUnusedImportHints].
///
/// Additionally, [generateDuplicateImportHints] generates
/// [HintCode.DUPLICATE_IMPORT] hints and [HintCode.UNUSED_SHOWN_NAME] hints.
///
/// While this class does not yet have support for an "Organize Imports" action,
/// this logic built up in this class could be used for such an action in the
/// future.
class ImportsVerifier {
  /// All [ImportDirective]s of the current library.
  final List<ImportDirective> _allImports = <ImportDirective>[];

  /// A list of [ImportDirective]s that the current library imports, but does
  /// not use.
  ///
  /// As identifiers are visited by this visitor and an import has been
  /// identified as being used by the library, the [ImportDirective] is removed
  /// from this list. After all the sources in the library have been evaluated,
  /// this list represents the set of unused imports.
  ///
  /// See [ImportsVerifier.generateUnusedImportErrors].
  final List<ImportDirective> _unusedImports = <ImportDirective>[];

  /// After the list of [unusedImports] has been computed, this list is a proper
  /// subset of the unused imports that are listed more than once.
  final List<ImportDirective> _duplicateImports = <ImportDirective>[];

  /// The cache of [Namespace]s for [ImportDirective]s.
  final HashMap<ImportDirective, Namespace> _namespaceMap =
      new HashMap<ImportDirective, Namespace>();

  /// This is a map between prefix elements and the import directives from which
  /// they are derived. In cases where a type is referenced via a prefix
  /// element, the import directive can be marked as used (removed from the
  /// unusedImports) by looking at the resolved `lib` in `lib.X`, instead of
  /// looking at which library the `lib.X` resolves.
  ///
  /// TODO (jwren) Since multiple [ImportDirective]s can share the same
  /// [PrefixElement], it is possible to have an unreported unused import in
  /// situations where two imports use the same prefix and at least one import
  /// directive is used.
  final HashMap<PrefixElement, List<ImportDirective>> _prefixElementMap =
      new HashMap<PrefixElement, List<ImportDirective>>();

  /// A map of identifiers that the current library's imports show, but that the
  /// library does not use.
  ///
  /// Each import directive maps to a list of the identifiers that are imported
  /// via the "show" keyword.
  ///
  /// As each identifier is visited by this visitor, it is identified as being
  /// used by the library, and the identifier is removed from this map (under
  /// the import that imported it). After all the sources in the library have
  /// been evaluated, each list in this map's values present the set of unused
  /// shown elements.
  ///
  /// See [ImportsVerifier.generateUnusedShownNameHints].
  final HashMap<ImportDirective, List<SimpleIdentifier>> _unusedShownNamesMap =
      new HashMap<ImportDirective, List<SimpleIdentifier>>();

  /// A map of names that are hidden more than once.
  final HashMap<NamespaceDirective, List<SimpleIdentifier>>
      _duplicateHiddenNamesMap =
      new HashMap<NamespaceDirective, List<SimpleIdentifier>>();

  /// A map of names that are shown more than once.
  final HashMap<NamespaceDirective, List<SimpleIdentifier>>
      _duplicateShownNamesMap =
      new HashMap<NamespaceDirective, List<SimpleIdentifier>>();

  void addImports(CompilationUnit node) {
    for (Directive directive in node.directives) {
      if (directive is ImportDirective) {
        LibraryElement libraryElement = directive.uriElement;
        if (libraryElement == null) {
          continue;
        }
        _allImports.add(directive);
        _unusedImports.add(directive);
        //
        // Initialize prefixElementMap
        //
        if (directive.asKeyword != null) {
          SimpleIdentifier prefixIdentifier = directive.prefix;
          if (prefixIdentifier != null) {
            Element element = prefixIdentifier.staticElement;
            if (element is PrefixElement) {
              List<ImportDirective> list = _prefixElementMap[element];
              if (list == null) {
                list = new List<ImportDirective>();
                _prefixElementMap[element] = list;
              }
              list.add(directive);
            }
            // TODO (jwren) Can the element ever not be a PrefixElement?
          }
        }
        _addShownNames(directive);
      }
      if (directive is NamespaceDirective) {
        _addDuplicateShownHiddenNames(directive);
      }
    }
    if (_unusedImports.length > 1) {
      // order the list of unusedImports to find duplicates in faster than
      // O(n^2) time
      List<ImportDirective> importDirectiveArray =
          new List<ImportDirective>.from(_unusedImports);
      importDirectiveArray.sort(ImportDirective.COMPARATOR);
      ImportDirective currentDirective = importDirectiveArray[0];
      for (int i = 1; i < importDirectiveArray.length; i++) {
        ImportDirective nextDirective = importDirectiveArray[i];
        if (ImportDirective.COMPARATOR(currentDirective, nextDirective) == 0) {
          // Add either the currentDirective or nextDirective depending on which
          // comes second, this guarantees that the first of the duplicates
          // won't be highlighted.
          if (currentDirective.offset < nextDirective.offset) {
            _duplicateImports.add(nextDirective);
          } else {
            _duplicateImports.add(currentDirective);
          }
        }
        currentDirective = nextDirective;
      }
    }
  }

  /// Any time after the defining compilation unit has been visited by this
  /// visitor, this method can be called to report an
  /// [HintCode.DUPLICATE_IMPORT] hint for each of the import directives in the
  /// [duplicateImports] list.
  ///
  /// @param errorReporter the error reporter to report the set of
  ///        [HintCode.DUPLICATE_IMPORT] hints to
  void generateDuplicateImportHints(ErrorReporter errorReporter) {
    int length = _duplicateImports.length;
    for (int i = 0; i < length; i++) {
      errorReporter.reportErrorForNode(
          HintCode.DUPLICATE_IMPORT, _duplicateImports[i].uri);
    }
  }

  /// Report a [HintCode.DUPLICATE_SHOWN_HIDDEN_NAME] hint for each duplicate
  /// shown or hidden name.
  ///
  /// Only call this method after all of the compilation units have been visited
  /// by this visitor.
  ///
  /// @param errorReporter the error reporter used to report the set of
  ///          [HintCode.UNUSED_SHOWN_NAME] hints
  void generateDuplicateShownHiddenNameHints(ErrorReporter reporter) {
    _duplicateHiddenNamesMap.forEach(
        (NamespaceDirective directive, List<SimpleIdentifier> identifiers) {
      int length = identifiers.length;
      for (int i = 0; i < length; i++) {
        Identifier identifier = identifiers[i];
        reporter.reportErrorForNode(
            HintCode.DUPLICATE_HIDDEN_NAME, identifier, [identifier.name]);
      }
    });
    _duplicateShownNamesMap.forEach(
        (NamespaceDirective directive, List<SimpleIdentifier> identifiers) {
      int length = identifiers.length;
      for (int i = 0; i < length; i++) {
        Identifier identifier = identifiers[i];
        reporter.reportErrorForNode(
            HintCode.DUPLICATE_SHOWN_NAME, identifier, [identifier.name]);
      }
    });
  }

  /// Report an [HintCode.UNUSED_IMPORT] hint for each unused import.
  ///
  /// Only call this method after all of the compilation units have been visited
  /// by this visitor.
  ///
  /// @param errorReporter the error reporter used to report the set of
  ///        [HintCode.UNUSED_IMPORT] hints
  void generateUnusedImportHints(ErrorReporter errorReporter) {
    int length = _unusedImports.length;
    for (int i = 0; i < length; i++) {
      ImportDirective unusedImport = _unusedImports[i];
      // Check that the imported URI exists and isn't dart:core
      ImportElement importElement = unusedImport.element;
      if (importElement != null) {
        LibraryElement libraryElement = importElement.importedLibrary;
        if (libraryElement == null ||
            libraryElement.isDartCore ||
            libraryElement.isSynthetic) {
          continue;
        }
      }
      StringLiteral uri = unusedImport.uri;
      errorReporter
          .reportErrorForNode(HintCode.UNUSED_IMPORT, uri, [uri.stringValue]);
    }
  }

  /// Use the error [reporter] to report an [HintCode.UNUSED_SHOWN_NAME] hint
  /// for each unused shown name.
  ///
  /// This method should only be invoked after all of the compilation units have
  /// been visited by this visitor.
  void generateUnusedShownNameHints(ErrorReporter reporter) {
    _unusedShownNamesMap.forEach(
        (ImportDirective importDirective, List<SimpleIdentifier> identifiers) {