pkg/analyzer/lib/src/generated/error_verifier.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 "dart:math" as math;

import 'package:analyzer/dart/ast/ast.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/dart/element/visitor.dart';
import 'package:analyzer/error/error.dart';
import 'package:analyzer/error/listener.dart';
import 'package:analyzer/src/dart/ast/ast.dart';
import 'package:analyzer/src/dart/element/element.dart';
import 'package:analyzer/src/dart/element/member.dart';
import 'package:analyzer/src/dart/element/type.dart';
import 'package:analyzer/src/dart/resolver/inheritance_manager.dart';
import 'package:analyzer/src/error/codes.dart';
import 'package:analyzer/src/error/pending_error.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/java_engine.dart';
import 'package:analyzer/src/generated/parser.dart' show ParserErrorCode;
import 'package:analyzer/src/generated/resolver.dart';
import 'package:analyzer/src/generated/sdk.dart' show DartSdk, SdkLibrary;
import 'package:analyzer/src/generated/source.dart';
import 'package:analyzer/src/task/dart.dart';

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

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

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

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

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

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

  /**
   * The options for verification.
   */
  AnalysisOptionsImpl _options;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  /**
   * The enum containing the AST nodes being visited, or `null` if we are not
   * in the scope of an enum.
   */
  ClassElement _enclosingEnum;

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

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

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

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

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

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

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

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

  /**
   * The elements that will be defined later in the current scope, but right
   * now are not declared.
   */
  HiddenElements _hiddenElements = null;

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

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

  final _UninstantiatedBoundChecker _uninstantiatedBoundChecker;

  /// Setting this flag to `true` disables the check for conflicting generics.
  /// This is used when running with the old task model to work around
  /// dartbug.com/32421.
  ///
  /// TODO(paulberry): remove this flag once dartbug.com/32421 is properly
  /// fixed.
  final bool disableConflictingGenericsCheck;

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

  ClassElement get enclosingClass => _enclosingClass;

  /**
   * For consumers of error verification as a library, (currently just the
   * angular plugin), expose a setter that can make the errors reported more
   * accurate when dangling code snippets are being resolved from a class
   * context. Note that this setter is very defensive for potential misuse; it
   * should not be modified in the middle of visiting a tree and requires an
   * analyzer-provided Impl instance to work.
   */
  set enclosingClass(ClassElement classElement) {
    assert(classElement is ClassElementImpl);
    assert(_enclosingClass == null);
    assert(_enclosingEnum == null);
    assert(_enclosingFunction == null);
    _enclosingClass = classElement;
  }

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

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

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

  @override
  Object visitAssertInitializer(AssertInitializer node) {
    _checkForNonBoolExpression(node);
    return super.visitAssertInitializer(node);
  }

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

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

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

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

  @override
  Object visitBlock(Block node) {
    _hiddenElements = new HiddenElements(_hiddenElements, node);
    try {
      _checkDuplicateDeclarationInStatements(node.statements);
      return super.visitBlock(node);
    } finally {
      _hiddenElements = _hiddenElements.outerElements;
    }
  }

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

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

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

  @override
  Object visitClassDeclaration(ClassDeclaration node) {
    ClassElementImpl outerClass = _enclosingClass;
    try {
      _isInNativeClass = node.nativeClause != null;
      _enclosingClass = AbstractClassElementImpl.getImpl(node.element);
      _checkDuplicateClassMembers(node);
      _checkForBuiltInIdentifierAsName(
          node.name, CompileTimeErrorCode.BUILT_IN_IDENTIFIER_AS_TYPE_NAME);
      _checkForMemberWithClassName();
      _checkForNoDefaultSuperConstructorImplicit(node);
      _checkForConflictingTypeVariableErrorCodes(node);
      TypeName superclass = node.extendsClause?.superclass;
      ImplementsClause implementsClause = node.implementsClause;
      WithClause withClause = node.withClause;

      // Only do error checks on the clause nodes if there is a non-null clause
      if (implementsClause != null ||
          superclass != null ||
          withClause != null) {
        _checkClassInheritance(node, superclass, withClause, implementsClause);
      }
      visitClassDeclarationIncrementally(node);
      _checkForFinalNotInitializedInClass(node);
      _checkForDuplicateDefinitionInheritance();
      _checkForConflictingInstanceMethodSetter(node);
      _checkForBadFunctionUse(node);
      return super.visitClassDeclaration(node);
    } finally {
      _isInNativeClass = false;
      _initialFieldElementsMap = null;
      _enclosingClass = outerClass;
    }
  }

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

  @override
  Object visitClassTypeAlias(ClassTypeAlias node) {
    _checkForBuiltInIdentifierAsName(
        node.name, CompileTimeErrorCode.BUILT_IN_IDENTIFIER_AS_TYPEDEF_NAME);
    ClassElementImpl outerClassElement = _enclosingClass;
    try {
      _enclosingClass = AbstractClassElementImpl.getImpl(node.element);
      _checkClassInheritance(
          node, node.superclass, node.withClause, node.implementsClause);
    } finally {
      _enclosingClass = outerClassElement;
    }
    return super.visitClassTypeAlias(node);
  }

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

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

  @override
  Object visitConditionalExpression(ConditionalExpression node) {
    _checkForNonBoolCondition(node.condition);
    // TODO(mfairhurst) Enable this and get code compliant.
    //_checkForUseOfVoidResult(node.thenExpression);
    //_checkForUseOfVoidResult(node.elseExpression);
    return super.visitConditionalExpression(node);
  }

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

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

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

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

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

  @override
  Object visitEnumDeclaration(EnumDeclaration node) {
    ClassElement outerEnum = _enclosingEnum;
    try {
      _enclosingEnum = node.element;
      _checkDuplicateEnumMembers(node);
      return super.visitEnumDeclaration(node);
    } finally {
      _enclosingEnum = outerEnum;
    }
  }

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

  @override
  Object visitExpressionFunctionBody(ExpressionFunctionBody node) {
    bool wasInAsync = _inAsync;
    bool wasInGenerator = _inGenerator;
    try {
      _inAsync = node.isAsynchronous;
      _inGenerator = node.isGenerator;
      FunctionType functionType = _enclosingFunction?.type;
      DartType expectedReturnType = functionType == null
          ? DynamicTypeImpl.instance
          : functionType.returnType;
      ExecutableElement function = _enclosingFunction;
      bool isSetterWithImplicitReturn = function.hasImplicitReturnType &&
          function is PropertyAccessorElement &&
          function.isSetter;
      if (!isSetterWithImplicitReturn) {
        _checkForReturnOfInvalidType(node.expression, expectedReturnType,
            isArrowFunction: true);
      }
      return super.visitExpressionFunctionBody(node);
    } finally {
      _inAsync = wasInAsync;
      _inGenerator = wasInGenerator;
    }
  }

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

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

  @override
  Object visitForEachStatement(ForEachStatement node) {
    _checkForInIterable(node);
    return super.visitForEachStatement(node);
  }

  @override
  Object visitFormalParameterList(FormalParameterList node) {
    _checkDuplicateDefinitionInParameterList(node);
    _checkUseOfCovariantInParameters(node);
    return super.visitFormalParameterList(node);
  }

  @override
  Object visitForStatement(ForStatement node) {
    if (node.condition != null) {
      _checkForNonBoolCondition(node.condition);
    }
    if (node.variables != null) {
      _checkDuplicateVariables(node.variables);
    }
    return super.visitForStatement(node);
  }

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

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

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

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

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

      // TODO(jmesserly): ideally we'd use _checkForImplicitDynamicReturn, and
      // we can get the function element via `node?.element?.type?.element` but
      // it doesn't have hasImplicitReturnType set correctly.
      if (!_options.implicitDynamic && node.returnType == null) {
        DartType parameterType =
            resolutionMap.elementDeclaredByFormalParameter(node).type;
        if (parameterType is FunctionType &&
            parameterType.returnType.isDynamic) {
          _errorReporter.reportErrorForNode(
              StrongModeCode.IMPLICIT_DYNAMIC_RETURN,
              node.identifier,
              [node.identifier]);
        }
      }

      // TODO(paulberry): remove this once dartbug.com/28515 is fixed.
      if (node.typeParameters != null) {
        _errorReporter.reportErrorForNode(
            CompileTimeErrorCode.GENERIC_FUNCTION_TYPED_PARAM_UNSUPPORTED,
            node);
      }

      return super.visitFunctionTypedFormalParameter(node);
    } finally {
      _isInFunctionTypedFormalParameter = old;
    }
  }

  @override
  Object visitGenericTypeAlias(GenericTypeAlias node) {
    if (_hasTypedefSelfReference(node.element)) {
      _errorReporter.reportErrorForNode(
          CompileTimeErrorCode.TYPE_ALIAS_CANNOT_REFERENCE_ITSELF, node);
    }
    return super.visitGenericTypeAlias(node);
  }

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

  @override
  Object visitImplementsClause(ImplementsClause node) {
    node.interfaces.forEach(_checkForImplicitDynamicType);
    return super.visitImplementsClause(node);
  }

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

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

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

  @override
  Object visitIntegerLiteral(IntegerLiteral node) {
    _checkForOutOfRange(node);
    return super.visitIntegerLiteral(node);
  }

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

  @override
  Object visitListLiteral(ListLiteral node) {
    TypeArgumentList typeArguments = node.typeArguments;
    if (typeArguments != null) {
      if (!_options.strongMode && node.isConst) {
        NodeList<TypeAnnotation> arguments = typeArguments.arguments;
        if (arguments.isNotEmpty) {
          _checkForInvalidTypeArgumentInConstTypedLiteral(arguments,
              CompileTimeErrorCode.INVALID_TYPE_ARGUMENT_IN_CONST_LIST);
        }
      }
      _checkForExpectedOneListTypeArgument(node, typeArguments);
    }
    _checkForImplicitDynamicTypedLiteral(node);
    _checkForListElementTypeNotAssignable(node);

    return super.visitListLiteral(node);
  }

  @override
  Object visitMapLiteral(MapLiteral node) {
    TypeArgumentList typeArguments = node.typeArguments;
    if (typeArguments != null) {
      NodeList<TypeAnnotation> arguments = typeArguments.arguments;
      if (!_options.strongMode && arguments.isNotEmpty) {
        if (node.isConst) {
          _checkForInvalidTypeArgumentInConstTypedLiteral(arguments,
              CompileTimeErrorCode.INVALID_TYPE_ARGUMENT_IN_CONST_MAP);
        }
      }
      _checkExpectedTwoMapTypeArguments(typeArguments);
    }
    _checkForImplicitDynamicTypedLiteral(node);
    _checkForMapTypeNotAssignable(node);
    _checkForNonConstMapAsExpressionStatement(node);
    return super.visitMapLiteral(node);
  }

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

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

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

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

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

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

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

  @override
  Object visitPropertyAccess(PropertyAccess node) {
    ClassElement typeReference =
        ElementResolver.getTypeReference(node.realTarget);
    SimpleIdentifier propertyName = node.propertyName;
    _checkForStaticAccessToInstanceMember(typeReference, propertyName);
    _checkForInstanceAccessToStaticMember(typeReference, propertyName);
    return super.visitPropertyAccess(node);
  }

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

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

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

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

    // Checks for an implicit dynamic parameter type.
    //
    // We can skip other parameter kinds besides simple formal, because:
    // - DefaultFormalParameter contains a simple one, so it gets here,
    // - FieldFormalParameter error should be reported on the field,
    // - FunctionTypedFormalParameter is a function type, not dynamic.
    _checkForImplicitDynamicIdentifier(node, node.identifier);

    return super.visitSimpleFormalParameter(node);
  }

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

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

  @override
  Object visitSwitchCase(SwitchCase node) {
    _checkDuplicateDeclarationInStatements(node.statements);
    return super.visitSwitchCase(node);
  }

  @override
  Object visitSwitchDefault(SwitchDefault node) {
    _checkDuplicateDeclarationInStatements(node.statements);
    return super.visitSwitchDefault(node);
  }

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

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

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

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

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

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

  @override
  Object visitTypeParameter(TypeParameter node) {
    _checkForBuiltInIdentifierAsName(node.name,
        CompileTimeErrorCode.BUILT_IN_IDENTIFIER_AS_TYPE_PARAMETER_NAME);
    _checkForTypeParameterSupertypeOfItsBound(node);
    _checkForTypeAnnotationDeferredClass(node.bound);
    _checkForImplicitDynamicType(node.bound);
    _checkForGenericFunctionType(node.bound);
    if (_options.strongMode) node.bound?.accept(_uninstantiatedBoundChecker);
    return super.visitTypeParameter(node);
  }

  @override
  Object visitTypeParameterList(TypeParameterList node) {
    _checkDuplicateDefinitionInTypeParameterList(node);
    return super.visitTypeParameterList(node);
  }

  @override
  Object visitVariableDeclaration(VariableDeclaration node) {
    SimpleIdentifier nameNode = node.name;
    Expression initializerNode = node.initializer;
    // do checks
    _checkForInvalidAssignment(nameNode, initializerNode,
        isDeclarationCast: true);
    _checkForImplicitDynamicIdentifier(node, nameNode);
    // visit name
    nameNode.accept(this);
    // visit initializer
    String name = nameNode.name;
    _namesForReferenceToDeclaredVariableInInitializer.add(name);
    bool wasInInstanceVariableInitializer = _isInInstanceVariableInitializer;
    _isInInstanceVariableInitializer = _isInInstanceVariableDeclaration;
    try {
      if (initializerNode != null) {
        initializerNode.accept(this);
      }
    } finally {
      _isInInstanceVariableInitializer = wasInInstanceVariableInitializer;
      _namesForReferenceToDeclaredVariableInInitializer.remove(name);
    }
    // declare the variable
    AstNode grandparent = node.parent.parent;
    if (grandparent is! TopLevelVariableDeclaration &&
        grandparent is! FieldDeclaration) {
      VariableElement element = node.element;
      if (element != null) {
        _hiddenElements.declare(element);
      }
    }
    // done
    return null;
  }

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

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

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

  @override
  Object visitWithClause(WithClause node) {
    node.mixinTypes.forEach(_checkForImplicitDynamicType);
    return super.visitWithClause(node);
  }

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

  /**
   * Checks the class for problems with the superclass, mixins, or implemented
   * interfaces.
   */
  void _checkClassInheritance(
      NamedCompilationUnitMember node,
      TypeName superclass,
      WithClause withClause,
      ImplementsClause implementsClause) {
    // Only check for all of the inheritance logic around clauses if there
    // isn't an error code such as "Cannot extend double" already on the
    // class.
    if (!_checkForExtendsDisallowedClass(superclass) &&
        !_checkForImplementsDisallowedClass(implementsClause) &&
        !_checkForAllMixinErrorCodes(withClause)) {
      _checkForImplicitDynamicType(superclass);
      _checkForExtendsDeferredClass(superclass);
      _checkForImplementsDeferredClass(implementsClause);
      _checkForNonAbstractClassInheritsAbstractMember(node.name);
      _checkForInconsistentMethodInheritance();
      _checkForRecursiveInterfaceInheritance(_enclosingClass);
      _checkForConflictingGetterAndMethod();
      _checkForConflictingInstanceGetterAndSuperclassMember();
      _checkImplementsSuperClass(implementsClause);
      _checkImplementsFunctionWithoutCall(node.name);
      _checkForMixinHasNoConstructors(node);
      _checkMixinInference(node, withClause);

      if (_options.strongMode) {
        _checkForMixinWithConflictingPrivateMember(withClause, superclass);
        if (!disableConflictingGenericsCheck) {
          _checkForConflictingGenerics(node);
        }
      }
    }
  }

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

  /**
   * Check that there are no members with the same name.
   */
  void _checkDuplicateClassMembers(ClassDeclaration node) {
    Map<String, Element> definedNames = new HashMap<String, Element>();
    Set<String> visitedFields = new HashSet<String>();
    for (ClassMember member in node.members) {
      // We ignore constructors because they are checked in the method
      // _checkForConflictingConstructorNameAndMember.
      if (member is FieldDeclaration) {
        for (VariableDeclaration field in member.fields.variables) {
          SimpleIdentifier identifier = field.name;
          _checkDuplicateIdentifier(definedNames, identifier);
          String name = identifier.name;
          if (!field.isFinal &&
              !field.isConst &&
              !visitedFields.contains(name)) {
            _checkDuplicateIdentifier(definedNames, identifier,
                implicitSetter: true);
          }
          visitedFields.add(name);
        }
      } else if (member is MethodDeclaration) {
        _checkDuplicateIdentifier(definedNames, member.name);
      }
    }
  }

  /**
   * Check that all of the parameters have unique names.
   */
  void _checkDuplicateDeclarationInStatements(List<Statement> statements) {
    Map<String, Element> definedNames = new HashMap<String, Element>();
    for (Statement statement in statements) {
      if (statement is VariableDeclarationStatement) {
        for (VariableDeclaration variable in statement.variables.variables) {
          _checkDuplicateIdentifier(definedNames, variable.name);
        }
      } else if (statement is FunctionDeclarationStatement) {
        _checkDuplicateIdentifier(
            definedNames, statement.functionDeclaration.name);
      }
    }
  }

  /**
   * Check that the exception and stack trace parameters have different names.
   */
  void _checkDuplicateDefinitionInCatchClause(CatchClause node) {
    SimpleIdentifier exceptionParameter = node.exceptionParameter;
    SimpleIdentifier stackTraceParameter = node.stackTraceParameter;
    if (exceptionParameter != null && stackTraceParameter != null) {
      String exceptionName = exceptionParameter.name;
      if (exceptionName == stackTraceParameter.name) {
        _errorReporter.reportErrorForNode(
            CompileTimeErrorCode.DUPLICATE_DEFINITION,
            stackTraceParameter,
            [exceptionName]);
      }
    }
  }

  /**
   * Check that all of the parameters have unique names.
   */
  void _checkDuplicateDefinitionInParameterList(FormalParameterList node) {
    Map<String, Element> definedNames = new HashMap<String, Element>();
    for (FormalParameter parameter in node.parameters) {
      SimpleIdentifier identifier = parameter.identifier;
      if (identifier != null) {
        // The identifier can be null if this is a parameter list for a generic
        // function type.
        _checkDuplicateIdentifier(definedNames, identifier);
      }
    }
  }

  /**
   * Check that all of the parameters have unique names.
   */
  void _checkDuplicateDefinitionInTypeParameterList(TypeParameterList node) {
    Map<String, Element> definedNames = new HashMap<String, Element>();
    for (TypeParameter parameter in node.typeParameters) {
      _checkDuplicateIdentifier(definedNames, parameter.name);
    }
  }

  /**
   * Check that there are no members with the same name.
   */
  void _checkDuplicateEnumMembers(EnumDeclaration node) {
    Map<String, Element> definedNames = new HashMap<String, Element>();
    ClassElement element = node.element;
    String indexName = 'index';
    String valuesName = 'values';
    definedNames[indexName] = element.getField(indexName);
    definedNames[valuesName] = element.getField(valuesName);
    for (EnumConstantDeclaration constant in node.constants) {
      _checkDuplicateIdentifier(definedNames, constant.name);
    }
  }

  /**
   * Check whether the given [identifier] is already in the set of
   * [definedNames], and produce an error if it is. If [implicitSetter] is
   * `true`, then the identifier represents the definition of a setter.
   */
  void _checkDuplicateIdentifier(
      Map<String, Element> definedNames, SimpleIdentifier identifier,
      {bool implicitSetter: false}) {
    ErrorCode getError(Element previous, Element current) {
      if (previous is MethodElement && current is PropertyAccessorElement) {
        if (current.isGetter) {
          return CompileTimeErrorCode.GETTER_AND_METHOD_WITH_SAME_NAME;
        }
      } else if (previous is PropertyAccessorElement &&
          current is MethodElement) {
        if (previous.isGetter) {
          return CompileTimeErrorCode.METHOD_AND_GETTER_WITH_SAME_NAME;
        }
      } else if (previous is PrefixElement) {
        return CompileTimeErrorCode.PREFIX_COLLIDES_WITH_TOP_LEVEL_MEMBER;
      }
      return CompileTimeErrorCode.DUPLICATE_DEFINITION;
    }

    Element current = identifier.staticElement;
    String name = identifier.name;
    if (current is PropertyAccessorElement && current.isSetter) {
      name += '=';
    } else if (current is MethodElement && current.isOperator && name == '-') {
      if (current.parameters.length == 0) {
        name = 'unary-';
      }
    } else if (implicitSetter) {
      name += '=';
    }
    Element previous = definedNames[name];
    if (previous != null) {
      _errorReporter
          .reportErrorForNode(getError(previous, current), identifier, [name]);
    } else {
      definedNames[name] = identifier.staticElement;
    }
  }

  /**
   * Check that there are no members with the same name.
   */
  void _checkDuplicateUnitMembers(CompilationUnit node) {
    Map<String, Element> definedNames = new HashMap<String, Element>();
    void addWithoutChecking(CompilationUnitElement element) {
      for (PropertyAccessorElement accessor in element.accessors) {
        String name = accessor.name;
        if (accessor.isSetter) {
          name += '=';
        }
        definedNames[name] = accessor;
      }
      for (ClassElement type in element.enums) {
        definedNames[type.name] = type;
      }
      for (FunctionElement function in element.functions) {
        definedNames[function.name] = function;
      }
      for (FunctionTypeAliasElement alias in element.functionTypeAliases) {
        definedNames[alias.name] = alias;
      }
      for (TopLevelVariableElement variable in element.topLevelVariables) {
        definedNames[variable.name] = variable;
        if (!variable.isFinal && !variable.isConst) {
          definedNames[variable.name + '='] = variable;
        }
      }
      for (ClassElement type in element.types) {
        definedNames[type.name] = type;
      }
    }

    for (ImportElement importElement in _currentLibrary.imports) {
      PrefixElement prefix = importElement.prefix;
      if (prefix != null) {
        definedNames[prefix.name] = prefix;
      }
    }
    CompilationUnitElement element = node.element;
    if (element != _currentLibrary.definingCompilationUnit) {
      addWithoutChecking(_currentLibrary.definingCompilationUnit);
      for (CompilationUnitElement part in _currentLibrary.parts) {
        if (element == part) {
          break;
        }
        addWithoutChecking(part);
      }
    }
    for (CompilationUnitMember member in node.declarations) {
      if (member is NamedCompilationUnitMember) {
        _checkDuplicateIdentifier(definedNames, member.name);
      } else if (member is TopLevelVariableDeclaration) {
        for (VariableDeclaration variable in member.variables.variables) {
          _checkDuplicateIdentifier(definedNames, variable.name);
          if (!variable.isFinal && !variable.isConst) {
            _checkDuplicateIdentifier(definedNames, variable.name,
                implicitSetter: true);
          }
        }
      }
    }
  }

  /**
   * Check that the given list of variable declarations does not define multiple
   * variables of the same name.
   */
  void _checkDuplicateVariables(VariableDeclarationList node) {
    Map<String, Element> definedNames = new HashMap<String, Element>();
    for (VariableDeclaration variable in node.variables) {
      _checkDuplicateIdentifier(definedNames, variable.name);
    }
  }

  /**
   * Verify that the given list of [typeArguments] contains exactly two
   * elements.
   *
   * See [StaticTypeWarningCode.EXPECTED_TWO_MAP_TYPE_ARGUMENTS].
   */
  void _checkExpectedTwoMapTypeArguments(TypeArgumentList typeArguments) {
    int num = typeArguments.arguments.length;
    if (num != 2) {
      _errorReporter.reportErrorForNode(
          StaticTypeWarningCode.EXPECTED_TWO_MAP_TYPE_ARGUMENTS,
          typeArguments,
          [num]);
    }
  }

  /**
   * Check that return statements without expressions are not in a generative
   * constructor and the return type is not assignable to `null`; that is, we
   * don't have `return;` if the enclosing method has a non-void containing
   * return type.
   *
   * See [CompileTimeErrorCode.RETURN_IN_GENERATIVE_CONSTRUCTOR],
   * [StaticWarningCode.RETURN_WITHOUT_VALUE], and
   * [StaticTypeWarningCode.RETURN_OF_INVALID_TYPE].
   */
  void _checkForAllEmptyReturnStatementErrorCodes(
      ReturnStatement statement, DartType expectedReturnType) {
    if (_inGenerator) {
      return;
    }
    if (_options.strongMode) {
      var returnType = _inAsync
          ? expectedReturnType.flattenFutures(_typeSystem)
          : expectedReturnType;
      if (returnType.isDynamic ||
          returnType.isDartCoreNull ||
          returnType.isVoid) {
        return;
      }
    } else {
      // TODO(leafp): Delete this non-strong path
      if (_inAsync) {
        if (expectedReturnType.isDynamic || expectedReturnType.isVoid) {
          return;
        }
        if (expectedReturnType is InterfaceType &&
            expectedReturnType.isDartAsyncFuture) {
          DartType futureArgument = expectedReturnType.typeArguments[0];
          if (futureArgument.isDynamic ||
              futureArgument.isDartCoreNull ||
              futureArgument.isVoid ||
              futureArgument.isObject) {
            return;
          }
        }
      } else if (expectedReturnType.isDynamic || expectedReturnType.isVoid) {
        return;
      }
    }
    // If we reach here, this is an invalid return
    _hasReturnWithoutValue = true;
    _errorReporter.reportErrorForNode(
        StaticWarningCode.RETURN_WITHOUT_VALUE, statement);
    return;
  }

  /**
   * Verify that the given [constructor] declaration does not violate any of the
   * error codes relating to the initialization of fields in the enclosing
   * class.
   *
   * See [_initialFieldElementsMap],
   * [StaticWarningCode.FINAL_INITIALIZED_IN_DECLARATION_AND_CONSTRUCTOR], and
   * [CompileTimeErrorCode.FINAL_INITIALIZED_MULTIPLE_TIMES].
   */
  void _checkForAllFinalInitializedErrorCodes(
      ConstructorDeclaration constructor) {
    if (constructor.factoryKeyword != null ||
        constructor.redirectedConstructor != null ||
        constructor.externalKeyword != null) {
      return;
    }
    // Ignore if native class.
    if (_isInNativeClass) {
      return;
    }

    Map<FieldElement, INIT_STATE> fieldElementsMap =
        new HashMap<FieldElement, INIT_STATE>.from(_initialFieldElementsMap);
    // Visit all of the field formal parameters
    NodeList<FormalParameter> formalParameters =
        constructor.parameters.parameters;
    for (FormalParameter formalParameter in formalParameters) {
      FormalParameter baseParameter(FormalParameter parameter) {
        if (parameter is DefaultFormalParameter) {
          return parameter.parameter;
        }
        return parameter;
      }

      FormalParameter parameter = baseParameter(formalParameter);
      if (parameter is FieldFormalParameter) {
        FieldElement fieldElement =
            (parameter.element as FieldFormalParameterElementImpl).field;
        INIT_STATE state = fieldElementsMap[fieldElement];
        if (state == INIT_STATE.NOT_INIT) {
          fieldElementsMap[fieldElement] = INIT_STATE.INIT_IN_FIELD_FORMAL;
        } else if (state == INIT_STATE.INIT_IN_DECLARATION) {
          if (fieldElement.isFinal || fieldElement.isConst) {
            _errorReporter.reportErrorForNode(
                StaticWarningCode
                    .FINAL_INITIALIZED_IN_DECLARATION_AND_CONSTRUCTOR,
                formalParameter.identifier,
                [fieldElement.displayName]);
          }
        } else if (state == INIT_STATE.INIT_IN_FIELD_FORMAL) {
          if (fieldElement.isFinal || fieldElement.isConst) {
            _errorReporter.reportErrorForNode(
                CompileTimeErrorCode.FINAL_INITIALIZED_MULTIPLE_TIMES,
                formalParameter.identifier,
                [fieldElement.displayName]);
          }
        }
      }
    }
    // Visit all of the initializers
    NodeList<ConstructorInitializer> initializers = constructor.initializers;
    for (ConstructorInitializer constructorInitializer in initializers) {
      if (constructorInitializer is RedirectingConstructorInvocation) {
        return;
      }
      if (constructorInitializer is ConstructorFieldInitializer) {
        SimpleIdentifier fieldName = constructorInitializer.fieldName;
        Element element = fieldName.staticElement;
        if (element is FieldElement) {
          INIT_STATE state = fieldElementsMap[element];
          if (state == INIT_STATE.NOT_INIT) {
            fieldElementsMap[element] = INIT_STATE.INIT_IN_INITIALIZERS;
          } else if (state == INIT_STATE.INIT_IN_DECLARATION) {
            if (element.isFinal || element.isConst) {
              _errorReporter.reportErrorForNode(
                  StaticWarningCode
                      .FIELD_INITIALIZED_IN_INITIALIZER_AND_DECLARATION,
                  fieldName);
            }
          } else if (state == INIT_STATE.INIT_IN_FIELD_FORMAL) {
            _errorReporter.reportErrorForNode(
                CompileTimeErrorCode
                    .FIELD_INITIALIZED_IN_PARAMETER_AND_INITIALIZER,
                fieldName);
          } else if (state == INIT_STATE.INIT_IN_INITIALIZERS) {
            _errorReporter.reportErrorForNode(
                CompileTimeErrorCode.FIELD_INITIALIZED_BY_MULTIPLE_INITIALIZERS,
                fieldName,
                [element.displayName]);
          }
        }
      }
    }
    // Prepare a list of not initialized fields.
    List<FieldElement> notInitFinalFields = <FieldElement>[];
    fieldElementsMap.forEach((FieldElement fieldElement, INIT_STATE state) {
      if (state == INIT_STATE.NOT_INIT) {
        if (fieldElement.isFinal) {
          notInitFinalFields.add(fieldElement);
        }
      }
    });
    // Visit all of the states in the map to ensure that none were never
    // initialized.
    fieldElementsMap.forEach((FieldElement fieldElement, INIT_STATE state) {
      if (state == INIT_STATE.NOT_INIT) {
        if (fieldElement.isConst) {
          _errorReporter.reportErrorForNode(
              CompileTimeErrorCode.CONST_NOT_INITIALIZED,
              constructor.returnType,
              [fieldElement.name]);
        }
      }
    });

    if (notInitFinalFields.isNotEmpty) {
      List<String> names = notInitFinalFields.map((item) => item.name).toList();
      names.sort();
      if (names.length == 1) {
        _errorReporter.reportErrorForNode(
            StaticWarningCode.FINAL_NOT_INITIALIZED_CONSTRUCTOR_1,
            constructor.returnType,
            names);
      } else if (names.length == 2) {
        _errorReporter.reportErrorForNode(
            StaticWarningCode.FINAL_NOT_INITIALIZED_CONSTRUCTOR_2,
            constructor.returnType,
            names);
      } else {
        _errorReporter.reportErrorForNode(
            StaticWarningCode.FINAL_NOT_INITIALIZED_CONSTRUCTOR_3_PLUS,
            constructor.returnType,
            [names[0], names[1], names.length - 2]);
      }
    }
  }

  /**
   * Check the given [derivedElement] against override-error codes. The
   * [baseElement] is the element that the executable element is
   * overriding. The [parameters] is the parameters of the executable element.
   * The [errorNameTarget] is the node to report problems on.
   *
   * See [CompileTimeErrorCode.INVALID_OVERRIDE_REQUIRED],
   * [CompileTimeErrorCode.INVALID_OVERRIDE_POSITIONAL],
   * [CompileTimeErrorCode.INVALID_OVERRIDE_NAMED],
   * [StaticWarningCode.INVALID_GETTER_OVERRIDE_RETURN_TYPE],
   * [StaticWarningCode.INVALID_METHOD_OVERRIDE_RETURN_TYPE],
   * [StaticWarningCode.INVALID_METHOD_OVERRIDE_NORMAL_PARAM_TYPE],
   * [StaticWarningCode.INVALID_SETTER_OVERRIDE_NORMAL_PARAM_TYPE],
   * [StaticWarningCode.INVALID_METHOD_OVERRIDE_OPTIONAL_PARAM_TYPE],
   * [StaticWarningCode.INVALID_METHOD_OVERRIDE_NAMED_PARAM_TYPE], and
   * [StaticWarningCode.INVALID_OVERRIDE_DIFFERENT_DEFAULT_VALUES].
   */
  bool _checkForAllInvalidOverrideErrorCodes(
      ExecutableElement derivedElement,
      ExecutableElement baseElement,
      List<ParameterElement> parameters,
      List<AstNode> parameterLocations,
      SimpleIdentifier errorNameTarget) {
    if (_options.strongMode) {
      return false; // strong mode already checked for this
    }

    bool isGetter = false;
    bool isSetter = false;
    if (derivedElement is PropertyAccessorElement) {
      isGetter = derivedElement.isGetter;
      isSetter = derivedElement.isSetter;
    }
    String executableElementName = derivedElement.name;
    FunctionType derivedFT = derivedElement.type;
    FunctionType baseFT = baseElement.type;
    InterfaceType enclosingType = _enclosingClass.type;
    baseFT = _inheritanceManager.substituteTypeArgumentsInMemberFromInheritance(
        baseFT, executableElementName, enclosingType);
    if (derivedFT == null || baseFT == null) {
      return false;
    }

    // Handle generic function type parameters.
    // TODO(jmesserly): this duplicates some code in isSubtypeOf and most of
    // _isGenericFunctionSubtypeOf. Ideally, we'd let TypeSystem produce
    // an error message once it's ready to "return false".
    if (!derivedFT.typeFormals.isEmpty) {
      if (baseFT.typeFormals.isEmpty) {
        derivedFT = _typeSystem.instantiateToBounds(derivedFT);
      } else {
        List<TypeParameterElement> params1 = derivedFT.typeFormals;
        List<TypeParameterElement> params2 = baseFT.typeFormals;
        int count = params1.length;
        if (params2.length != count) {
          _errorReporter.reportErrorForNode(
              HintCode.INVALID_METHOD_OVERRIDE_TYPE_PARAMETERS,
              errorNameTarget, [
            count,
            params2.length,
            baseElement.enclosingElement.displayName
          ]);
          return true;
        }
        // We build up a substitution matching up the type parameters
        // from the two types, {variablesFresh/variables1} and
        // {variablesFresh/variables2}
        List<DartType> variables1 = new List<DartType>();
        List<DartType> variables2 = new List<DartType>();
        List<DartType> variablesFresh = new List<DartType>();
        for (int i = 0; i < count; i++) {
          TypeParameterElement p1 = params1[i];
          TypeParameterElement p2 = params2[i];
          TypeParameterElementImpl pFresh =
              new TypeParameterElementImpl(p1.name, -1);

          DartType variable1 = p1.type;
          DartType variable2 = p2.type;
          DartType variableFresh = new TypeParameterTypeImpl(pFresh);

          variables1.add(variable1);
          variables2.add(variable2);
          variablesFresh.add(variableFresh);
          DartType bound1 = p1.bound ?? DynamicTypeImpl.instance;
          DartType bound2 = p2.bound ?? DynamicTypeImpl.instance;
          bound1 = bound1.substitute2(variablesFresh, variables1);
          bound2 = bound2.substitute2(variablesFresh, variables2);
          pFresh.bound = bound2;
          if (!_typeSystem.isSubtypeOf(bound2, bound1)) {
            _errorReporter.reportErrorForNode(
                HintCode.INVALID_METHOD_OVERRIDE_TYPE_PARAMETER_BOUND,
                errorNameTarget, [
              p1.displayName,
              p1.bound,
              p2.displayName,
              p2.bound,
              baseElement.enclosingElement.displayName
            ]);
            return true;
          }
        }
        // Proceed with the rest of the checks, using instantiated types.
        derivedFT = derivedFT.instantiate(variablesFresh);
        baseFT = baseFT.instantiate(variablesFresh);
      }
    }

    DartType derivedFTReturnType = derivedFT.returnType;
    DartType baseFTReturnType = baseFT.returnType;
    List<DartType> derivedNormalPT = derivedFT.normalParameterTypes;
    List<DartType> baseNormalPT = baseFT.normalParameterTypes;
    List<DartType> derivedPositionalPT = derivedFT.optionalParameterTypes;
    List<DartType> basePositionalPT = baseFT.optionalParameterTypes;
    Map<String, DartType> derivedNamedPT = derivedFT.namedParameterTypes;
    Map<String, DartType> baseNamedPT = baseFT.namedParameterTypes;
    // CTEC.INVALID_OVERRIDE_REQUIRED, CTEC.INVALID_OVERRIDE_POSITIONAL and
    // CTEC.INVALID_OVERRIDE_NAMED
    if (derivedNormalPT.length > baseNormalPT.length) {
      _errorReporter.reportErrorForNode(
          StaticWarningCode.INVALID_OVERRIDE_REQUIRED, errorNameTarget, [
        baseNormalPT.length,
        baseElement,
        baseElement.enclosingElement.displayName
      ]);
      return true;
    }
    if (derivedNormalPT.length + derivedPositionalPT.length <
        basePositionalPT.length + baseNormalPT.length) {
      _errorReporter.reportErrorForNode(
          StaticWarningCode.INVALID_OVERRIDE_POSITIONAL, errorNameTarget, [
        basePositionalPT.length + baseNormalPT.length,
        baseElement,
        baseElement.enclosingElement.displayName
      ]);
      return true;
    }
    // For each named parameter in the overridden method, verify that there is
    // the same name in the overriding method.
    for (String overriddenParamName in baseNamedPT.keys) {
      if (!derivedNamedPT.containsKey(overriddenParamName)) {
        // The overridden method expected the overriding method to have
        // overridingParamName, but it does not.
        _errorReporter.reportErrorForNode(
            StaticWarningCode.INVALID_OVERRIDE_NAMED, errorNameTarget, [
          overriddenParamName,
          baseElement,
          baseElement.enclosingElement.displayName
        ]);
        return true;
      }
    }
    // SWC.INVALID_METHOD_OVERRIDE_RETURN_TYPE
    if (baseFTReturnType != VoidTypeImpl.instance &&
        !_typeSystem.isAssignableTo(derivedFTReturnType, baseFTReturnType)) {
      _errorReporter.reportTypeErrorForNode(
          !isGetter
              ? StaticWarningCode.INVALID_METHOD_OVERRIDE_RETURN_TYPE
              : StaticWarningCode.INVALID_GETTER_OVERRIDE_RETURN_TYPE,
          errorNameTarget,
          [
            derivedFTReturnType,
            baseFTReturnType,
            baseElement.enclosingElement.displayName
          ]);
      return true;
    }
    // SWC.INVALID_METHOD_OVERRIDE_NORMAL_PARAM_TYPE
    if (parameterLocations == null) {
      return false;
    }
    int parameterIndex = 0;
    for (int i = 0; i < derivedNormalPT.length; i++) {
      if (!_typeSystem.isAssignableTo(baseNormalPT[i], derivedNormalPT[i])) {
        _errorReporter.reportTypeErrorForNode(
            !isSetter
                ? StaticWarningCode.INVALID_METHOD_OVERRIDE_NORMAL_PARAM_TYPE
                : StaticWarningCode.INVALID_SETTER_OVERRIDE_NORMAL_PARAM_TYPE,
            parameterLocations[parameterIndex],
            [
              derivedNormalPT[i],
              baseNormalPT[i],
              baseElement.enclosingElement.displayName
            ]);
        return true;
      }
      parameterIndex++;
    }
    // SWC.INVALID_METHOD_OVERRIDE_OPTIONAL_PARAM_TYPE
    for (int i = 0; i < basePositionalPT.length; i++) {
      if (!_typeSystem.isAssignableTo(
          basePositionalPT[i], derivedPositionalPT[i])) {
        _errorReporter.reportTypeErrorForNode(
            StaticWarningCode.INVALID_METHOD_OVERRIDE_OPTIONAL_PARAM_TYPE,
            parameterLocations[parameterIndex], [
          derivedPositionalPT[i],
          basePositionalPT[i],
          baseElement.enclosingElement.displayName
        ]);
        return true;
      }
      parameterIndex++;
    }
    // SWC.INVALID_METHOD_OVERRIDE_NAMED_PARAM_TYPE &
    // SWC.INVALID_OVERRIDE_DIFFERENT_DEFAULT_VALUES
    for (String overriddenName in baseNamedPT.keys) {
      DartType derivedType = derivedNamedPT[overriddenName];
      if (derivedType == null) {
        // Error, this is never reached- INVALID_OVERRIDE_NAMED would have been
        // created above if this could be reached.
        continue;
      }
      DartType baseType = baseNamedPT[overriddenName];
      if (!_typeSystem.isAssignableTo(baseType, derivedType)) {
        // lookup the parameter for the error to select
        ParameterElement parameterToSelect = null;
        AstNode parameterLocationToSelect = null;
        for (int i = 0; i < parameters.length; i++) {
          ParameterElement parameter = parameters[i];
          if (parameter.isNamed && overriddenName == parameter.name) {
            parameterToSelect = parameter;
            parameterLocationToSelect = parameterLocations[i];
            break;
          }
        }
        if (parameterToSelect != null) {
          _errorReporter.reportTypeErrorForNode(
              StaticWarningCode.INVALID_METHOD_OVERRIDE_NAMED_PARAM_TYPE,
              parameterLocationToSelect, [
            derivedType,
            baseType,
            baseElement.enclosingElement.displayName
          ]);
          return true;
        }
      }
    }
    // SWC.INVALID_OVERRIDE_DIFFERENT_DEFAULT_VALUES
    //
    // Create three lists: a list of the optional parameter ASTs
    // (FormalParameters), a list of the optional parameters elements from our
    // method, and finally a list of the optional parameter elements from the
    // method we are overriding.
    //
    bool foundError = false;
    List<AstNode> formalParameters = new List<AstNode>();
    List<ParameterElementImpl> parameterElts = new List<ParameterElementImpl>();
    List<ParameterElementImpl> overriddenParameterElts =
        new List<ParameterElementImpl>();
    List<ParameterElement> overriddenPEs = baseElement.parameters;
    for (int i = 0; i < parameters.length; i++) {
      ParameterElement parameter = parameters[i];
      if (parameter.isOptional) {
        formalParameters.add(parameterLocations[i]);
        parameterElts.add(parameter as ParameterElementImpl);
      }
    }
    for (ParameterElement parameterElt in overriddenPEs) {
      if (parameterElt.isOptional) {
        if (parameterElt is ParameterElementImpl) {
          overriddenParameterElts.add(parameterElt);
        }
      }
    }
    //
    // Next compare the list of optional parameter elements to the list of
    // overridden optional parameter elements.
    //
    if (parameterElts.length > 0) {
      if (parameterElts[0].isNamed) {
        // Named parameters, consider the names when matching the parameterElts
        // to the overriddenParameterElts
        for (int i = 0; i < parameterElts.length; i++) {
          ParameterElementImpl parameterElt = parameterElts[i];
          EvaluationResultImpl result = parameterElt.evaluationResult;
          // TODO (jwren) Ignore Object types, see Dart bug 11287
          if (_isUserDefinedObject(result)) {
            continue;
          }
          String parameterName = parameterElt.name;
          for (int j = 0; j < overriddenParameterElts.length; j++) {
            ParameterElementImpl overriddenParameterElt =
                overriddenParameterElts[j];
            if (overriddenParameterElt.initializer == null) {
              // There is no warning if the overridden parameter has an
              // implicit default.
              continue;
            }
            String overriddenParameterName = overriddenParameterElt.name;
            if (parameterName != null &&
                parameterName == overriddenParameterName) {
              EvaluationResultImpl overriddenResult =
                  overriddenParameterElt.evaluationResult;
              if (_isUserDefinedObject(overriddenResult)) {
                break;
              }
              if (!result.equalValues(_typeProvider, overriddenResult)) {
                _errorReporter.reportErrorForNode(
                    StaticWarningCode
                        .INVALID_OVERRIDE_DIFFERENT_DEFAULT_VALUES_NAMED,
                    formalParameters[i],
                    [
                      baseElement.enclosingElement.displayName,
                      baseElement.displayName,
                      parameterName
                    ]);
                foundError = true;
              }
            }
          }
        }
      } else {
        // Positional parameters, consider the positions when matching the
        // parameterElts to the overriddenParameterElts
        for (int i = 0;
            i < parameterElts.length && i < overriddenParameterElts.length;
            i++) {
          ParameterElementImpl parameterElt = parameterElts[i];
          EvaluationResultImpl result = parameterElt.evaluationResult;
          // TODO (jwren) Ignore Object types, see Dart bug 11287
          if (_isUserDefinedObject(result)) {
            continue;
          }
          ParameterElementImpl overriddenParameterElt =
              overriddenParameterElts[i];
          if (overriddenParameterElt.initializer == null) {
            // There is no warning if the overridden parameter has an implicit
            // default.
            continue;
          }
          EvaluationResultImpl overriddenResult =
              overriddenParameterElt.evaluationResult;
          if (_isUserDefinedObject(overriddenResult)) {
            continue;
          }
          if (!result.equalValues(_typeProvider, overriddenResult)) {
            _errorReporter.reportErrorForNode(
                StaticWarningCode
                    .INVALID_OVERRIDE_DIFFERENT_DEFAULT_VALUES_POSITIONAL,
                formalParameters[i],
                [
                  baseElement.enclosingElement.displayName,
                  baseElement.displayName
                ]);
            foundError = true;
          }
        }
      }
    }
    return foundError;
  }

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

  /**
   * Check the given field [declaration] against override-error codes.
   *
   * See [_checkForAllInvalidOverrideErrorCodes].
   */
  void _checkForAllInvalidOverrideErrorCodesForField(
      FieldDeclaration declaration) {
    if (_options.strongMode) {
      return; // strong mode already checked for this
    }

    if (_enclosingClass == null || declaration.isStatic) {
      return;
    }

    VariableDeclarationList fields = declaration.fields;
    for (VariableDeclaration field in fields.variables) {
      FieldElement element = field.element as FieldElement;
      if (element == null) {
        continue;
      }
      PropertyAccessorElement getter = element.getter;
      PropertyAccessorElement setter = element.setter;
      SimpleIdentifier fieldName = field.name;
      if (getter != null) {
        _checkForAllInvalidOverrideErrorCodesForExecutable(
            getter, ParameterElement.EMPTY_LIST, AstNode.EMPTY_LIST, fieldName);
      }
      if (setter != null) {
        _checkForAllInvalidOverrideErrorCodesForExecutable(
            setter, setter.parameters, <AstNode>[fieldName], fieldName);
      }
    }
  }

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

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

  /**
   * Check for errors related to the redirected constructors.
   *
   * See [StaticWarningCode.REDIRECT_TO_INVALID_RETURN_TYPE],
   * [StaticWarningCode.REDIRECT_TO_INVALID_FUNCTION_TYPE], and
   * [StaticWarningCode.REDIRECT_TO_MISSING_CONSTRUCTOR].
   */
  void _checkForAllRedirectConstructorErrorCodes(
      ConstructorDeclaration declaration) {
    // Prepare redirected constructor node
    ConstructorName redirectedConstructor = declaration.redirectedConstructor;
    if (redirectedConstructor == null) {
      return;
    }

    // Prepare redirected constructor type
    ConstructorElement redirectedElement = redirectedConstructor.staticElement;
    if (redirectedElement == null) {
      // If the element is null, we check for the
      // REDIRECT_TO_MISSING_CONSTRUCTOR case
      TypeName constructorTypeName = redirectedConstructor.type;
      DartType redirectedType = constructorTypeName.type;
      if (redirectedType != null &&
          redirectedType.element != null &&
          !redirectedType.isDynamic) {
        // Prepare the constructor name
        String constructorStrName = constructorTypeName.name.name;
        if (redirectedConstructor.name != null) {
          constructorStrName += ".${redirectedConstructor.name.name}";
        }
        ErrorCode errorCode = (declaration.constKeyword != null
            ? CompileTimeErrorCode.REDIRECT_TO_MISSING_CONSTRUCTOR
            : StaticWarningCode.REDIRECT_TO_MISSING_CONSTRUCTOR);
        _errorReporter.reportErrorForNode(errorCode, redirectedConstructor,
            [constructorStrName, redirectedType.displayName]);
      }
      return;
    }
    FunctionType redirectedType = redirectedElement.type;
    DartType redirectedReturnType = redirectedType.returnType;

    // Report specific problem when return type is incompatible
    FunctionType constructorType =
        resolutionMap.elementDeclaredByConstructorDeclaration(declaration).type;
    DartType constructorReturnType = constructorType.returnType;
    if (!_typeSystem.isAssignableTo(
        redirectedReturnType, constructorReturnType)) {
      _errorReporter.reportErrorForNode(
          StaticWarningCode.REDIRECT_TO_INVALID_RETURN_TYPE,
          redirectedConstructor,
          [redirectedReturnType, constructorReturnType]);
      return;
    } else if (!_typeSystem.isSubtypeOf(redirectedType, constructorType)) {
      // Check parameters.
      _errorReporter.reportErrorForNode(
          StaticWarningCode.REDIRECT_TO_INVALID_FUNCTION_TYPE,
          redirectedConstructor,
          [redirectedType, constructorType]);
    }
  }

  /**
   * Check that the return [statement] of the form <i>return e;</i> is not in a
   * generative constructor.
   *
   * Check that return statements without expressions are not in a generative
   * constructor and the return type is not assignable to `null`; that is, we
   * don't have `return;` if the enclosing method has a non-void containing
   * return type.
   *
   * Check that the return type matches the type of the declared return type in
   * the enclosing method or function.
   *
   * See [CompileTimeErrorCode.RETURN_IN_GENERATIVE_CONSTRUCTOR],
   * [StaticWarningCode.RETURN_WITHOUT_VALUE], and
   * [StaticTypeWarningCode.RETURN_OF_INVALID_TYPE].
   */
  void _checkForAllReturnStatementErrorCodes(ReturnStatement statement) {
    FunctionType functionType = _enclosingFunction?.type;
    DartType expectedReturnType = functionType == null
        ? DynamicTypeImpl.instance
        : functionType.returnType;
    Expression returnExpression = statement.expression;

    // RETURN_IN_GENERATIVE_CONSTRUCTOR
    bool isGenerativeConstructor(ExecutableElement element) =>
        element is ConstructorElement && !element.isFactory;
    if (isGenerativeConstructor(_enclosingFunction)) {
      if (returnExpression == null) {
        return;
      }
      _errorReporter.reportErrorForNode(
          CompileTimeErrorCode.RETURN_IN_GENERATIVE_CONSTRUCTOR,
          returnExpression);
      return;
    }
    // RETURN_WITHOUT_VALUE
    if (returnExpression == null) {
      _checkForAllEmptyReturnStatementErrorCodes(statement, expectedReturnType);
      return;
    } else if (_inGenerator) {
      // RETURN_IN_GENERATOR
      _errorReporter.reportErrorForNode(
          CompileTimeErrorCode.RETURN_IN_GENERATOR,
          statement,
          [_inAsync ? "async*" : "sync*"]);
      return;
    }

    _checkForReturnOfInvalidType(returnExpression, expectedReturnType);
  }

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

  /**
   * Check the given node to see whether it was ambiguous because the name was
   * imported from two or more imports.
   */
  void _checkForAmbiguousImport(SimpleIdentifier node) {
    Element element = node.staticElement;
    if (element is MultiplyDefinedElementImpl) {
      String name = element.displayName;
      List<Element> conflictingMembers = element.conflictingElements;
      int count = conflictingMembers.length;
      List<String> libraryNames = new List<String>(count);
      for (int i = 0; i < count; i++) {
        libraryNames[i] = _getLibraryName(conflictingMembers[i]);
      }
      libraryNames.sort();
      _errorReporter.reportErrorForNode(StaticWarningCode.AMBIGUOUS_IMPORT,
          node, [name, StringUtilities.printListOfQuotedNames(libraryNames)]);
    } else if (element != null) {
      List<Element> sdkElements =
          node.getProperty(LibraryImportScope.conflictingSdkElements);
      if (sdkElements != null) {
        _errorReporter.reportErrorForNode(
            StaticWarningCode.CONFLICTING_DART_IMPORT, node, [
          element.displayName,
          _getLibraryName(sdkElements[0]),
          _getLibraryName(element)
        ]);
      }
    }
  }

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

      _checkForAssignableExpressionAtType(
          expression, actualStaticType, expectedStaticType, errorCode);
    }
  }

  /**
   * Verify that the given [argument] can be assigned to its corresponding
   * parameter.
   *
   * This method corresponds to
   * [BestPracticesVerifier.checkForArgumentTypeNotAssignableForArgument].
   *
   * See [StaticWarningCode.ARGUMENT_TYPE_NOT_ASSIGNABLE].
   */
  void _checkForArgumentTypeNotAssignableForArgument(Expression argument) {
    if (argument == null) {
      return;
    }

    ParameterElement staticParameterElement = argument.staticParameterElement;
    DartType staticParameterType = staticParameterElement?.type;
    _checkForArgumentTypeNotAssignableWithExpectedTypes(argument,
        staticParameterType, StaticWarningCode.ARGUMENT_TYPE_NOT_ASSIGNABLE);
  }

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

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

    for (Expression argument in argumentList.arguments) {
      _checkForArgumentTypeNotAssignableForArgument(argument);
    }
  }

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

  bool _checkForAssignableExpression(
      Expression expression, DartType expectedStaticType, ErrorCode errorCode,
      {bool isDeclarationCast = false}) {
    DartType actualStaticType = getStaticType(expression);
    return actualStaticType != null &&
        _checkForAssignableExpressionAtType(
            expression, actualStaticType, expectedStaticType, errorCode,
            isDeclarationCast: isDeclarationCast);
  }

  bool _checkForAssignableExpressionAtType(
      Expression expression,
      DartType actualStaticType,
      DartType expectedStaticType,
      ErrorCode errorCode,
      {bool isDeclarationCast = false}) {
    if (!_expressionIsAssignableAtType(
        expression, actualStaticType, expectedStaticType,
        isDeclarationCast: isDeclarationCast)) {
      _errorReporter.reportTypeErrorForNode(
          errorCode, expression, [actualStaticType, expectedStaticType]);
      return false;
    }
    return true;
  }

  /**
   * Verify that the given [expression] is not final.
   *
   * See [StaticWarningCode.ASSIGNMENT_TO_CONST],
   * [StaticWarningCode.ASSIGNMENT_TO_FINAL], and
   * [StaticWarningCode.ASSIGNMENT_TO_METHOD].
   */
  void _checkForAssignmentToFinal(Expression expression) {
    // prepare element
    Element element = null;
    AstNode highlightedNode = expression;
    if (expression is Identifier) {
      element = expression.staticElement;
      if (expression is PrefixedIdentifier) {
        highlightedNode = expression.identifier;
      }
    } else if (expression is PropertyAccess) {
      element = expression.propertyName.staticElement;
      highlightedNode = expression.propertyName;
    }
    // check if element is assignable
    Element toVariable(Element element) {
      return element is PropertyAccessorElement ? element.variable : element;
    }

    element = toVariable(element);
    if (element is VariableElement) {
      if (element.isConst) {
        _errorReporter.reportErrorForNode(
            StaticWarningCode.ASSIGNMENT_TO_CONST, expression);
      } else if (element.isFinal) {
        if (element is FieldElementImpl) {
          if (element.setter == null && element.isSynthetic) {
            _errorReporter.reportErrorForNode(
                StaticWarningCode.ASSIGNMENT_TO_FINAL_NO_SETTER,
                highlightedNode,
                [element.name, element.enclosingElement.displayName]);
          } else {
            _errorReporter.reportErrorForNode(
                StaticWarningCode.ASSIGNMENT_TO_FINAL,
                highlightedNode,
                [element.name]);
          }
          return;
        }
        _errorReporter.reportErrorForNode(
            StaticWarningCode.ASSIGNMENT_TO_FINAL_LOCAL,
            highlightedNode,
            [element.name]);
      }
    } else if (element is FunctionElement) {
      _errorReporter.reportErrorForNode(
          StaticWarningCode.ASSIGNMENT_TO_FUNCTION, expression);
    } else if (element is MethodElement) {
      _errorReporter.reportErrorForNode(
          StaticWarningCode.ASSIGNMENT_TO_METHOD, expression);
    } else if (element is ClassElement ||
        element is FunctionTypeAliasElement ||
        element is TypeParameterElement) {
      _errorReporter.reportErrorForNode(
          StaticWarningCode.ASSIGNMENT_TO_TYPE, expression);
    }
  }

  /**
   * Verifies that the class is not named `Function` and that it doesn't
   * extends/implements/mixes in `Function`.
   */
  void _checkForBadFunctionUse(ClassDeclaration node) {
    ExtendsClause extendsClause = node.extendsClause;
    WithClause withClause = node.withClause;

    if (node.name.name == "Function") {
      _errorReporter.reportErrorForNode(
          HintCode.DEPRECATED_FUNCTION_CLASS_DECLARATION, node.name);
    }

    if (extendsClause != null) {
      InterfaceType superclassType = _enclosingClass.supertype;
      ClassElement superclassElement = superclassType?.element;
      if (superclassElement != null && superclassElement.name == "Function") {
        _errorReporter.reportErrorForNode(
            HintCode.DEPRECATED_EXTENDS_FUNCTION, extendsClause.superclass);
      }
    }

    if (withClause != null) {
      for (TypeName type in withClause.mixinTypes) {
        Element mixinElement = type.name.staticElement;
        if (mixinElement != null && mixinElement.name == "Function") {
          _errorReporter.reportErrorForNode(
              HintCode.DEPRECATED_MIXIN_FUNCTION, type);
        }
      }
    }
  }

  /**
   * Verify that the given [identifier] is not a keyword, and generates the
   * given [errorCode] on the identifier if it is a keyword.
   *
   * See [CompileTimeErrorCode.BUILT_IN_IDENTIFIER_AS_TYPE_NAME],
   * [CompileTimeErrorCode.BUILT_IN_IDENTIFIER_AS_TYPE_PARAMETER_NAME], and
   * [CompileTimeErrorCode.BUILT_IN_IDENTIFIER_AS_TYPEDEF_NAME].
   */
  void _checkForBuiltInIdentifierAsName(
      SimpleIdentifier identifier, ErrorCode errorCode) {
    Token token = identifier.token;
    if (token.type.isKeyword && token.keyword?.isPseudo != true) {
      _errorReporter
          .reportErrorForNode(errorCode, identifier, [identifier.name]);
    }
  }

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

    _errorReporter.reportErrorForToken(
        StaticWarningCode.CASE_BLOCK_NOT_TERMINATED, switchCase.keyword);
  }

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

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

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

  void _checkForConflictingGenerics(NamedCompilationUnitMember node) {
    var visitedClasses = <ClassElement>[];
    var interfaces = <ClassElement, InterfaceType>{};
    void visit(InterfaceType type) {
      if (type == null) return;
      var element = type.element;
      if (visitedClasses.contains(element)) return;
      visitedClasses.add(element);
      if (element.typeParameters.isNotEmpty) {
        var oldType = interfaces[element];
        if (oldType == null) {
          interfaces[element] = type;
        } else if (oldType != type) {
          _errorReporter.reportErrorForNode(
              CompileTimeErrorCode.CONFLICTING_GENERIC_INTERFACES,
              node,
              [_enclosingClass.name, oldType, type]);
        }
      }
      visit(type.superclass);
      type.mixins.forEach(visit);
      type.interfaces.forEach(visit);
      visitedClasses.removeLast();
    }

    visit(_enclosingClass.type);
  }

  /**
   * Verify that the [_enclosingClass] does not have a method and getter pair
   * with the same name on, via inheritance.
   *
   * See [CompileTimeErrorCode.CONFLICTING_GETTER_AND_METHOD], and
   * [CompileTimeErrorCode.CONFLICTING_METHOD_AND_GETTER].
   */
  void _checkForConflictingGetterAndMethod() {
    if (_enclosingClass == null) {
      return;
    }

    // method declared in the enclosing class vs. inherited getter
    for (MethodElement method in _enclosingClass.methods) {
      String name = method.name;
      // find inherited property accessor (and can be only getter)
      ExecutableElement inherited =
          _inheritanceManager.lookupInheritance(_enclosingClass, name);
      if (inherited is! PropertyAccessorElement) {
        continue;
      }

      _errorReporter.reportErrorForElement(
          CompileTimeErrorCode.CONFLICTING_GETTER_AND_METHOD, method, [
        _enclosingClass.displayName,
        inherited.enclosingElement.displayName,
        name
      ]);
    }
    // getter declared in the enclosing class vs. inherited method
    for (PropertyAccessorElement accessor in _enclosingClass.accessors) {
      if (!accessor.isGetter) {
        continue;
      }
      String name = accessor.name;
      // find inherited method
      ExecutableElement inherited =
          _inheritanceManager.lookupInheritance(_enclosingClass, name);
      if (inherited is! MethodElement) {
        continue;
      }

      _errorReporter.reportErrorForElement(
          CompileTimeErrorCode.CONFLICTING_METHOD_AND_GETTER, accessor, [
        _enclosingClass.displayName,
        inherited.enclosingElement.displayName,
        name
      ]);
    }
  }

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

      if (getter) {
        _errorReporter.reportErrorForElement(
            StaticWarningCode.CONFLICTING_INSTANCE_GETTER_AND_SUPERCLASS_MEMBER,
            accessor,
            [superElementType.displayName]);
      } else {
        _errorReporter.reportErrorForElement(
            StaticWarningCode.CONFLICTING_INSTANCE_SETTER_AND_SUPERCLASS_MEMBER,
            accessor,
            [superElementType.displayName]);
      }
    }
  }

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