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

library analyzer.src.dart.element.element;

import 'dart:collection';
import 'dart:math' show min;

import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/ast/token.dart';
import 'package:analyzer/dart/constant/value.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/src/dart/ast/utilities.dart';
import 'package:analyzer/src/dart/constant/value.dart';
import 'package:analyzer/src/dart/element/handle.dart';
import 'package:analyzer/src/dart/element/type.dart';
import 'package:analyzer/src/error/codes.dart' show CompileTimeErrorCode;
import 'package:analyzer/src/generated/constant.dart' show EvaluationResultImpl;
import 'package:analyzer/src/generated/engine.dart'
    show AnalysisContext, AnalysisEngine;
import 'package:analyzer/src/generated/java_engine.dart';
import 'package:analyzer/src/generated/resolver.dart';
import 'package:analyzer/src/generated/sdk.dart' show DartSdk;
import 'package:analyzer/src/generated/source.dart';
import 'package:analyzer/src/generated/testing/ast_test_factory.dart';
import 'package:analyzer/src/generated/utilities_collection.dart';
import 'package:analyzer/src/generated/utilities_dart.dart';
import 'package:analyzer/src/generated/utilities_general.dart';
import 'package:analyzer/src/summary/idl.dart';
import 'package:analyzer/src/task/dart.dart';

/**
 * Assert that the given [object] is null, which in the places where this
 * function is called means that the element is not resynthesized.
 */
void _assertNotResynthesized(Object object) {
  // TODO(scheglov) I comment this check for now.
  // When we make a decision about switch to the new analysis driver,
  // we will need to rework the analysis code to don't call the setters
  // or restore / inline it.
//  assert(object == null);
}

/**
 * A concrete implementation of a [ClassElement].
 */
abstract class AbstractClassElementImpl extends ElementImpl
    implements ClassElement {
  /**
   * A list containing all of the accessors (getters and setters) contained in
   * this class.
   */
  List<PropertyAccessorElement> _accessors;

  /**
   * A list containing all of the fields contained in this class.
   */
  List<FieldElement> _fields;

  /**
   * Initialize a newly created class element to have the given [name] at the
   * given [offset] in the file that contains the declaration of this element.
   */
  AbstractClassElementImpl(String name, int offset) : super(name, offset);

  /**
   * Initialize a newly created class element to have the given [name].
   */
  AbstractClassElementImpl.forNode(Identifier name) : super.forNode(name);

  /**
   * Initialize using the given serialized information.
   */
  AbstractClassElementImpl.forSerialized(
      CompilationUnitElementImpl enclosingUnit)
      : super.forSerialized(enclosingUnit);

  @override
  List<PropertyAccessorElement> get accessors {
    return _accessors ?? const <PropertyAccessorElement>[];
  }

  /**
   * Set the accessors contained in this class to the given [accessors].
   */
  void set accessors(List<PropertyAccessorElement> accessors) {
    for (PropertyAccessorElement accessor in accessors) {
      (accessor as PropertyAccessorElementImpl).enclosingElement = this;
    }
    this._accessors = accessors;
  }

  @override
  String get displayName => name;

  @override
  List<FieldElement> get fields => _fields ?? const <FieldElement>[];

  /**
   * Set the fields contained in this class to the given [fields].
   */
  void set fields(List<FieldElement> fields) {
    for (FieldElement field in fields) {
      (field as FieldElementImpl).enclosingElement = this;
    }
    this._fields = fields;
  }

  @override
  bool get isEnum;

  @override
  ElementKind get kind => ElementKind.CLASS;

  @override
  /*=T*/ accept/*<T>*/(ElementVisitor<dynamic/*=T*/ > visitor) =>
      visitor.visitClassElement(this);

  @override
  NamedCompilationUnitMember computeNode() {
    if (isEnum) {
      return getNodeMatching((node) => node is EnumDeclaration);
    } else {
      return getNodeMatching(
          (node) => node is ClassDeclaration || node is ClassTypeAlias);
    }
  }

  @override
  ElementImpl getChild(String identifier) {
    //
    // The casts in this method are safe because the set methods would have
    // thrown a CCE if any of the elements in the arrays were not of the
    // expected types.
    //
    for (PropertyAccessorElement accessor in accessors) {
      PropertyAccessorElementImpl accessorImpl = accessor;
      if (accessorImpl.identifier == identifier) {
        return accessorImpl;
      }
    }
    for (FieldElement field in fields) {
      FieldElementImpl fieldImpl = field;
      if (fieldImpl.identifier == identifier) {
        return fieldImpl;
      }
    }
    return null;
  }

  @override
  FieldElement getField(String name) {
    for (FieldElement fieldElement in fields) {
      if (name == fieldElement.name) {
        return fieldElement;
      }
    }
    return null;
  }

  @override
  PropertyAccessorElement getGetter(String getterName) {
    int length = accessors.length;
    for (int i = 0; i < length; i++) {
      PropertyAccessorElement accessor = accessors[i];
      if (accessor.isGetter && accessor.name == getterName) {
        return accessor;
      }
    }
    return null;
  }

  @override
  PropertyAccessorElement getSetter(String setterName) {
    // TODO (jwren) revisit- should we append '=' here or require clients to
    // include it?
    // Do we need the check for isSetter below?
    if (!StringUtilities.endsWithChar(setterName, 0x3D)) {
      setterName += '=';
    }
    for (PropertyAccessorElement accessor in accessors) {
      if (accessor.isSetter && accessor.name == setterName) {
        return accessor;
      }
    }
    return null;
  }

  @override
  MethodElement lookUpConcreteMethod(
          String methodName, LibraryElement library) =>
      _first(_implementationsOfMethod(methodName).where(
          (MethodElement method) =>
              !method.isAbstract && method.isAccessibleIn(library)));

  @override
  PropertyAccessorElement lookUpGetter(
          String getterName, LibraryElement library) =>
      _first(_implementationsOfGetter(getterName).where(
          (PropertyAccessorElement getter) => getter.isAccessibleIn(library)));

  @override
  PropertyAccessorElement lookUpInheritedConcreteGetter(
          String getterName, LibraryElement library) =>
      _first(_implementationsOfGetter(getterName).where(
          (PropertyAccessorElement getter) =>
              !getter.isAbstract &&
              getter.isAccessibleIn(library) &&
              getter.enclosingElement != this));

  @override
  MethodElement lookUpInheritedConcreteMethod(
          String methodName, LibraryElement library) =>
      _first(_implementationsOfMethod(methodName).where(
          (MethodElement method) =>
              !method.isAbstract &&
              method.isAccessibleIn(library) &&
              method.enclosingElement != this));

  @override
  PropertyAccessorElement lookUpInheritedConcreteSetter(
          String setterName, LibraryElement library) =>
      _first(_implementationsOfSetter(setterName).where(
          (PropertyAccessorElement setter) =>
              !setter.isAbstract &&
              setter.isAccessibleIn(library) &&
              setter.enclosingElement != this));

  @override
  MethodElement lookUpInheritedMethod(
          String methodName, LibraryElement library) =>
      _first(_implementationsOfMethod(methodName).where(
          (MethodElement method) =>
              method.isAccessibleIn(library) &&
              method.enclosingElement != this));

  @override
  MethodElement lookUpMethod(String methodName, LibraryElement library) =>
      _first(_implementationsOfMethod(methodName)
          .where((MethodElement method) => method.isAccessibleIn(library)));

  @override
  PropertyAccessorElement lookUpSetter(
          String setterName, LibraryElement library) =>
      _first(_implementationsOfSetter(setterName).where(
          (PropertyAccessorElement setter) => setter.isAccessibleIn(library)));

  @override
  void visitChildren(ElementVisitor visitor) {
    super.visitChildren(visitor);
    safelyVisitChildren(accessors, visitor);
    safelyVisitChildren(fields, visitor);
  }

  /**
   * Return the first element from the given [iterable], or `null` if the
   * iterable is empty.
   */
  Object/*=E*/ _first/*<E>*/(Iterable/*<E>*/ iterable) {
    if (iterable.isEmpty) {
      return null;
    }
    return iterable.first;
  }

  /**
   * Return an iterable containing all of the implementations of a getter with
   * the given [getterName] that are defined in this class any any superclass of
   * this class (but not in interfaces).
   *
   * The getters that are returned are not filtered in any way. In particular,
   * they can include getters that are not visible in some context. Clients must
   * perform any necessary filtering.
   *
   * The getters are returned based on the depth of their defining class; if
   * this class contains a definition of the getter it will occur first, if
   * Object contains a definition of the getter it will occur last.
   */
  Iterable<PropertyAccessorElement> _implementationsOfGetter(
      String getterName) sync* {
    ClassElement classElement = this;
    HashSet<ClassElement> visitedClasses = new HashSet<ClassElement>();
    while (classElement != null && visitedClasses.add(classElement)) {
      PropertyAccessorElement getter = classElement.getGetter(getterName);
      if (getter != null) {
        yield getter;
      }
      for (InterfaceType mixin in classElement.mixins.reversed) {
        getter = mixin.element?.getGetter(getterName);
        if (getter != null) {
          yield getter;
        }
      }
      classElement = classElement.supertype?.element;
    }
  }

  /**
   * Return an iterable containing all of the implementations of a method with
   * the given [methodName] that are defined in this class any any superclass of
   * this class (but not in interfaces).
   *
   * The methods that are returned are not filtered in any way. In particular,
   * they can include methods that are not visible in some context. Clients must
   * perform any necessary filtering.
   *
   * The methods are returned based on the depth of their defining class; if
   * this class contains a definition of the method it will occur first, if
   * Object contains a definition of the method it will occur last.
   */
  Iterable<MethodElement> _implementationsOfMethod(String methodName) sync* {
    ClassElement classElement = this;
    HashSet<ClassElement> visitedClasses = new HashSet<ClassElement>();
    while (classElement != null && visitedClasses.add(classElement)) {
      MethodElement method = classElement.getMethod(methodName);
      if (method != null) {
        yield method;
      }
      for (InterfaceType mixin in classElement.mixins.reversed) {
        method = mixin.element?.getMethod(methodName);
        if (method != null) {
          yield method;
        }
      }
      classElement = classElement.supertype?.element;
    }
  }

  /**
   * Return an iterable containing all of the implementations of a setter with
   * the given [setterName] that are defined in this class any any superclass of
   * this class (but not in interfaces).
   *
   * The setters that are returned are not filtered in any way. In particular,
   * they can include setters that are not visible in some context. Clients must
   * perform any necessary filtering.
   *
   * The setters are returned based on the depth of their defining class; if
   * this class contains a definition of the setter it will occur first, if
   * Object contains a definition of the setter it will occur last.
   */
  Iterable<PropertyAccessorElement> _implementationsOfSetter(
      String setterName) sync* {
    ClassElement classElement = this;
    HashSet<ClassElement> visitedClasses = new HashSet<ClassElement>();
    while (classElement != null && visitedClasses.add(classElement)) {
      PropertyAccessorElement setter = classElement.getSetter(setterName);
      if (setter != null) {
        yield setter;
      }
      for (InterfaceType mixin in classElement.mixins.reversed) {
        setter = mixin.element?.getSetter(setterName);
        if (setter != null) {
          yield setter;
        }
      }
      classElement = classElement.supertype?.element;
    }
  }

  /**
   * Return the [AbstractClassElementImpl] of the given [classElement].  May
   * throw an exception if the [AbstractClassElementImpl] cannot be provided
   * (should not happen though).
   */
  static AbstractClassElementImpl getImpl(ClassElement classElement) {
    if (classElement is ClassElementHandle) {
      return getImpl(classElement.actualElement);
    }
    return classElement as AbstractClassElementImpl;
  }
}

/**
 * For AST nodes that could be in both the getter and setter contexts
 * ([IndexExpression]s and [SimpleIdentifier]s), the additional resolved
 * elements are stored in the AST node, in an [AuxiliaryElements]. Because
 * resolved elements are either statically resolved or resolved using propagated
 * type information, this class is a wrapper for a pair of [ExecutableElement]s,
 * not just a single [ExecutableElement].
 */
class AuxiliaryElements {
  /**
   * The element based on propagated type information, or `null` if the AST
   * structure has not been resolved or if the node could not be resolved.
   */
  final ExecutableElement propagatedElement;

  /**
   * The element based on static type information, or `null` if the AST
   * structure has not been resolved or if the node could not be resolved.
   */
  final ExecutableElement staticElement;

  /**
   * Initialize a newly created pair to have both the [staticElement] and the
   * [propagatedElement].
   */
  AuxiliaryElements(this.staticElement, this.propagatedElement);
}

/**
 * An [AbstractClassElementImpl] which is a class.
 */
class ClassElementImpl extends AbstractClassElementImpl
    with TypeParameterizedElementMixin {
  /**
   * The unlinked representation of the class in the summary.
   */
  final UnlinkedClass _unlinkedClass;

  /**
   * The superclass of the class, or `null` for [Object].
   */
  InterfaceType _supertype;

  /**
   * The type defined by the class.
   */
  InterfaceType _type;

  /**
   * A list containing all of the mixins that are applied to the class being
   * extended in order to derive the superclass of this class.
   */
  List<InterfaceType> _mixins;

  /**
   * A list containing all of the interfaces that are implemented by this class.
   */
  List<InterfaceType> _interfaces;

  /**
   * For classes which are not mixin applications, a list containing all of the
   * constructors contained in this class, or `null` if the list of
   * constructors has not yet been built.
   *
   * For classes which are mixin applications, the list of constructors is
   * computed on the fly by the [constructors] getter, and this field is
   * `null`.
   */
  List<ConstructorElement> _constructors;

  /**
   * A list containing all of the methods contained in this class.
   */
  List<MethodElement> _methods;

  /**
   * A flag indicating whether the types associated with the instance members of
   * this class have been inferred.
   */
  bool _hasBeenInferred = false;

  /**
   * The version of this element. The version is changed when the element is
   * incrementally updated, so that its lists of constructors, accessors and
   * methods might be different.
   */
  int version = 0;

  /**
   * Initialize a newly created class element to have the given [name] at the
   * given [offset] in the file that contains the declaration of this element.
   */
  ClassElementImpl(String name, int offset)
      : _unlinkedClass = null,
        super(name, offset);

  /**
   * Initialize a newly created class element to have the given [name].
   */
  ClassElementImpl.forNode(Identifier name)
      : _unlinkedClass = null,
        super.forNode(name);

  /**
   * Initialize using the given serialized information.
   */
  ClassElementImpl.forSerialized(
      this._unlinkedClass, CompilationUnitElementImpl enclosingUnit)
      : super.forSerialized(enclosingUnit);

  /**
   * Set whether this class is abstract.
   */
  void set abstract(bool isAbstract) {
    _assertNotResynthesized(_unlinkedClass);
    setModifier(Modifier.ABSTRACT, isAbstract);
  }

  @override
  List<PropertyAccessorElement> get accessors {
    if (_unlinkedClass != null && _accessors == null) {
      _resynthesizeFieldsAndPropertyAccessors();
    }
    return _accessors ?? const <PropertyAccessorElement>[];
  }

  @override
  void set accessors(List<PropertyAccessorElement> accessors) {
    _assertNotResynthesized(_unlinkedClass);
    super.accessors = accessors;
  }

  @override
  List<InterfaceType> get allSupertypes {
    List<InterfaceType> list = new List<InterfaceType>();
    _collectAllSupertypes(list);
    return list;
  }

  @override
  int get codeLength {
    if (_unlinkedClass != null) {
      return _unlinkedClass.codeRange?.length;
    }
    return super.codeLength;
  }

  @override
  int get codeOffset {
    if (_unlinkedClass != null) {
      return _unlinkedClass.codeRange?.offset;
    }
    return super.codeOffset;
  }

  @override
  List<ConstructorElement> get constructors {
    if (isMixinApplication) {
      return _computeMixinAppConstructors();
    }
    if (_unlinkedClass != null && _constructors == null) {
      _constructors = _unlinkedClass.executables
          .where((e) => e.kind == UnlinkedExecutableKind.constructor)
          .map((e) => new ConstructorElementImpl.forSerialized(e, this))
          .toList(growable: false);
      // Ensure at least implicit default constructor.
      if (_constructors.isEmpty) {
        ConstructorElementImpl constructor = new ConstructorElementImpl('', -1);
        constructor.isSynthetic = true;
        constructor.enclosingElement = this;
        _constructors = <ConstructorElement>[constructor];
      }
    }
    assert(_constructors != null);
    return _constructors ?? const <ConstructorElement>[];
  }

  /**
   * Set the constructors contained in this class to the given [constructors].
   *
   * Should only be used for class elements that are not mixin applications.
   */
  void set constructors(List<ConstructorElement> constructors) {
    _assertNotResynthesized(_unlinkedClass);
    assert(!isMixinApplication);
    for (ConstructorElement constructor in constructors) {
      (constructor as ConstructorElementImpl).enclosingElement = this;
    }
    this._constructors = constructors;
  }

  @override
  String get documentationComment {
    if (_unlinkedClass != null) {
      return _unlinkedClass?.documentationComment?.text;
    }
    return super.documentationComment;
  }

  /**
   * Return `true` if [CompileTimeErrorCode.MIXIN_HAS_NO_CONSTRUCTORS] should
   * be reported for this class.
   */
  bool get doesMixinLackConstructors {
    if (!isMixinApplication && mixins.isEmpty) {
      // This class is not a mixin application and it doesn't have a "with"
      // clause, so CompileTimeErrorCode.MIXIN_HAS_NO_CONSTRUCTORS is
      // inapplicable.
      return false;
    }
    if (supertype == null) {
      // Should never happen, since Object is the only class that has no
      // supertype, and it should have been caught by the test above.
      assert(false);
      return false;
    }
    // Find the nearest class in the supertype chain that is not a mixin
    // application.
    ClassElement nearestNonMixinClass = supertype.element;
    if (nearestNonMixinClass.isMixinApplication) {
      // Use a list to keep track of the classes we've seen, so that we won't
      // go into an infinite loop in the event of a non-trivial loop in the
      // class hierarchy.
      List<ClassElement> classesSeen = <ClassElement>[this];
      while (nearestNonMixinClass.isMixinApplication) {
        if (classesSeen.contains(nearestNonMixinClass)) {
          // Loop in the class hierarchy (which is reported elsewhere).  Don't
          // confuse the user with further errors.
          return false;
        }
        classesSeen.add(nearestNonMixinClass);
        if (nearestNonMixinClass.supertype == null) {
          // Should never happen, since Object is the only class that has no
          // supertype, and it is not a mixin application.
          assert(false);
          return false;
        }
        nearestNonMixinClass = nearestNonMixinClass.supertype.element;
      }
    }
    return !nearestNonMixinClass.constructors.any(isSuperConstructorAccessible);
  }

  @override
  TypeParameterizedElementMixin get enclosingTypeParameterContext => null;

  @override
  List<FieldElement> get fields {
    if (_unlinkedClass != null && _fields == null) {
      _resynthesizeFieldsAndPropertyAccessors();
    }
    return _fields ?? const <FieldElement>[];
  }

  @override
  void set fields(List<FieldElement> fields) {
    _assertNotResynthesized(_unlinkedClass);
    super.fields = fields;
  }

  bool get hasBeenInferred {
    if (_unlinkedClass != null) {
      return context.analysisOptions.strongMode;
    }
    return _hasBeenInferred;
  }

  void set hasBeenInferred(bool hasBeenInferred) {
    _assertNotResynthesized(_unlinkedClass);
    _hasBeenInferred = hasBeenInferred;
  }

  @override
  bool get hasNonFinalField {
    List<ClassElement> classesToVisit = new List<ClassElement>();
    HashSet<ClassElement> visitedClasses = new HashSet<ClassElement>();
    classesToVisit.add(this);
    while (!classesToVisit.isEmpty) {
      ClassElement currentElement = classesToVisit.removeAt(0);
      if (visitedClasses.add(currentElement)) {
        // check fields
        for (FieldElement field in currentElement.fields) {
          if (!field.isFinal &&
              !field.isConst &&
              !field.isStatic &&
              !field.isSynthetic) {
            return true;
          }
        }
        // check mixins
        for (InterfaceType mixinType in currentElement.mixins) {
          ClassElement mixinElement = mixinType.element;
          classesToVisit.add(mixinElement);
        }
        // check super
        InterfaceType supertype = currentElement.supertype;
        if (supertype != null) {
          ClassElement superElement = supertype.element;
          if (superElement != null) {
            classesToVisit.add(superElement);
          }
        }
      }
    }
    // not found
    return false;
  }

  /**
   * Return `true` if the class has a `noSuchMethod()` method distinct from the
   * one declared in class `Object`, as per the Dart Language Specification
   * (section 10.4).
   */
  bool get hasNoSuchMethod {
    MethodElement method =
        lookUpMethod(FunctionElement.NO_SUCH_METHOD_METHOD_NAME, library);
    ClassElement definingClass = method?.enclosingElement;
    return definingClass != null && !definingClass.type.isObject;
  }

  @override
  bool get hasReferenceToSuper => hasModifier(Modifier.REFERENCES_SUPER);

  /**
   * Set whether this class references 'super'.
   */
  void set hasReferenceToSuper(bool isReferencedSuper) {
    setModifier(Modifier.REFERENCES_SUPER, isReferencedSuper);
  }

  @override
  bool get hasStaticMember {
    for (MethodElement method in methods) {
      if (method.isStatic) {
        return true;
      }
    }
    for (PropertyAccessorElement accessor in accessors) {
      if (accessor.isStatic) {
        return true;
      }
    }
    return false;
  }

  @override
  List<InterfaceType> get interfaces {
    if (_unlinkedClass != null && _interfaces == null) {
      ResynthesizerContext context = enclosingUnit.resynthesizerContext;
      _interfaces = _unlinkedClass.interfaces
          .map((EntityRef t) => context.resolveTypeRef(t, this))
          .where(_isClassInterfaceType)
          .toList(growable: false);
    }
    return _interfaces ?? const <InterfaceType>[];
  }

  void set interfaces(List<InterfaceType> interfaces) {
    _assertNotResynthesized(_unlinkedClass);
    _interfaces = interfaces;
  }

  @override
  bool get isAbstract {
    if (_unlinkedClass != null) {
      return _unlinkedClass.isAbstract;
    }
    return hasModifier(Modifier.ABSTRACT);
  }

  @override
  bool get isEnum => false;

  @override
  bool get isMixinApplication {
    if (_unlinkedClass != null) {
      return _unlinkedClass.isMixinApplication;
    }
    return hasModifier(Modifier.MIXIN_APPLICATION);
  }

  @override
  bool get isOrInheritsProxy =>
      _safeIsOrInheritsProxy(this, new HashSet<ClassElement>());

  @override
  bool get isProxy {
    for (ElementAnnotation annotation in metadata) {
      if (annotation.isProxy) {
        return true;
      }
    }
    return false;
  }

  @override
  bool get isValidMixin {
    if (!context.analysisOptions.enableSuperMixins) {
      if (hasReferenceToSuper) {
        return false;
      }
      if (!supertype.isObject) {
        return false;
      }
    }
    for (ConstructorElement constructor in constructors) {
      if (!constructor.isSynthetic && !constructor.isFactory) {
        return false;
      }
    }
    return true;
  }

  @override
  List<ElementAnnotation> get metadata {
    if (_unlinkedClass != null) {
      return _metadata ??=
          _buildAnnotations(enclosingUnit, _unlinkedClass.annotations);
    }
    return super.metadata;
  }

  @override
  List<MethodElement> get methods {
    if (_unlinkedClass != null) {
      _methods ??= _unlinkedClass.executables
          .where((e) => e.kind == UnlinkedExecutableKind.functionOrMethod)
          .map((e) => new MethodElementImpl.forSerialized(e, this))
          .toList(growable: false);
    }
    return _methods ?? const <MethodElement>[];
  }

  /**
   * Set the methods contained in this class to the given [methods].
   */
  void set methods(List<MethodElement> methods) {
    _assertNotResynthesized(_unlinkedClass);
    for (MethodElement method in methods) {
      (method as MethodElementImpl).enclosingElement = this;
    }
    _methods = methods;
  }

  /**
   * Set whether this class is a mixin application.
   */
  void set mixinApplication(bool isMixinApplication) {
    _assertNotResynthesized(_unlinkedClass);
    setModifier(Modifier.MIXIN_APPLICATION, isMixinApplication);
  }

  @override
  List<InterfaceType> get mixins {
    if (_unlinkedClass != null && _mixins == null) {
      ResynthesizerContext context = enclosingUnit.resynthesizerContext;
      _mixins = _unlinkedClass.mixins
          .map((EntityRef t) => context.resolveTypeRef(t, this))
          .where(_isClassInterfaceType)
          .toList(growable: false);
    }
    return _mixins ?? const <InterfaceType>[];
  }

  void set mixins(List<InterfaceType> mixins) {
    _assertNotResynthesized(_unlinkedClass);
    _mixins = mixins;
  }

  @override
  String get name {
    if (_unlinkedClass != null) {
      return _unlinkedClass.name;
    }
    return super.name;
  }

  @override
  int get nameOffset {
    int offset = super.nameOffset;
    if (offset == 0 && _unlinkedClass != null) {
      return _unlinkedClass.nameOffset;
    }
    return offset;
  }

  @override
  InterfaceType get supertype {
    if (_unlinkedClass != null && _supertype == null) {
      if (_unlinkedClass.supertype != null) {
        DartType type = enclosingUnit.resynthesizerContext
            .resolveTypeRef(_unlinkedClass.supertype, this);
        if (_isClassInterfaceType(type)) {
          _supertype = type;
        } else {
          _supertype = context.typeProvider.objectType;
        }
      } else if (_unlinkedClass.hasNoSupertype) {
        return null;
      } else {
        _supertype = context.typeProvider.objectType;
      }
    }
    return _supertype;
  }

  void set supertype(InterfaceType supertype) {
    _assertNotResynthesized(_unlinkedClass);
    _supertype = supertype;
  }

  @override
  InterfaceType get type {
    if (_type == null) {
      InterfaceTypeImpl type = new InterfaceTypeImpl(this);
      type.typeArguments = typeParameterTypes;
      _type = type;
    }
    return _type;
  }

  /**
   * Set the type parameters defined for this class to the given
   * [typeParameters].
   */
  void set typeParameters(List<TypeParameterElement> typeParameters) {
    _assertNotResynthesized(_unlinkedClass);
    for (TypeParameterElement typeParameter in typeParameters) {
      (typeParameter as TypeParameterElementImpl).enclosingElement = this;
    }
    this._typeParameterElements = typeParameters;
  }

  @override
  List<UnlinkedTypeParam> get unlinkedTypeParams =>
      _unlinkedClass?.typeParameters;

  @override
  ConstructorElement get unnamedConstructor {
    for (ConstructorElement element in constructors) {
      String name = element.displayName;
      if (name == null || name.isEmpty) {
        return element;
      }
    }
    return null;
  }

  @override
  void appendTo(StringBuffer buffer) {
    if (isAbstract) {
      buffer.write('abstract ');
    }
    buffer.write('class ');
    String name = displayName;
    if (name == null) {
      buffer.write("{unnamed class}");
    } else {
      buffer.write(name);
    }
    int variableCount = typeParameters.length;
    if (variableCount > 0) {
      buffer.write("<");
      for (int i = 0; i < variableCount; i++) {
        if (i > 0) {
          buffer.write(", ");
        }
        (typeParameters[i] as TypeParameterElementImpl).appendTo(buffer);
      }
      buffer.write(">");
    }
    if (supertype != null && !supertype.isObject) {
      buffer.write(' extends ');
      buffer.write(supertype.displayName);
    }
    if (mixins.isNotEmpty) {
      buffer.write(' with ');
      buffer.write(mixins.map((t) => t.displayName).join(', '));
    }
    if (interfaces.isNotEmpty) {
      buffer.write(' implements ');
      buffer.write(interfaces.map((t) => t.displayName).join(', '));
    }
  }

  @override
  ElementImpl getChild(String identifier) {
    ElementImpl child = super.getChild(identifier);
    if (child != null) {
      return child;
    }
    //
    // The casts in this method are safe because the set methods would have
    // thrown a CCE if any of the elements in the arrays were not of the
    // expected types.
    //
    for (ConstructorElement constructor in _constructors) {
      ConstructorElementImpl constructorImpl = constructor;
      if (constructorImpl.identifier == identifier) {
        return constructorImpl;
      }
    }
    for (MethodElement method in methods) {
      MethodElementImpl methodImpl = method;
      if (methodImpl.identifier == identifier) {
        return methodImpl;
      }
    }
    for (TypeParameterElement typeParameter in typeParameters) {
      TypeParameterElementImpl typeParameterImpl = typeParameter;
      if (typeParameterImpl.identifier == identifier) {
        return typeParameterImpl;
      }
    }
    return null;
  }

  @override
  MethodElement getMethod(String methodName) {
    int length = methods.length;
    for (int i = 0; i < length; i++) {
      MethodElement method = methods[i];
      if (method.name == methodName) {
        return method;
      }
    }
    return null;
  }

  @override
  ConstructorElement getNamedConstructor(String name) {
    for (ConstructorElement element in constructors) {
      String elementName = element.name;
      if (elementName != null && elementName == name) {
        return element;
      }
    }
    return null;
  }

  @override
  bool isSuperConstructorAccessible(ConstructorElement constructor) {
    // If this class has no mixins, then all superclass constructors are
    // accessible.
    if (mixins.isEmpty) {
      return true;
    }
    // Otherwise only constructors that lack optional parameters are
    // accessible (see dartbug.com/19576).
    for (ParameterElement parameter in constructor.parameters) {
      if (parameter.parameterKind != ParameterKind.REQUIRED) {
        return false;
      }
    }
    return true;
  }

  @override
  void visitChildren(ElementVisitor visitor) {
    super.visitChildren(visitor);
    safelyVisitChildren(constructors, visitor);
    safelyVisitChildren(methods, visitor);
    safelyVisitChildren(typeParameters, visitor);
  }

  void _collectAllSupertypes(List<InterfaceType> supertypes) {
    List<InterfaceType> typesToVisit = new List<InterfaceType>();
    List<ClassElement> visitedClasses = new List<ClassElement>();
    typesToVisit.add(this.type);
    while (!typesToVisit.isEmpty) {
      InterfaceType currentType = typesToVisit.removeAt(0);
      ClassElement currentElement = currentType.element;
      if (!visitedClasses.contains(currentElement)) {
        visitedClasses.add(currentElement);
        if (!identical(currentType, this.type)) {
          supertypes.add(currentType);
        }
        InterfaceType supertype = currentType.superclass;
        if (supertype != null) {
          typesToVisit.add(supertype);
        }
        for (InterfaceType type in currentElement.interfaces) {
          typesToVisit.add(type);
        }
        for (InterfaceType type in currentElement.mixins) {
          ClassElement element = type.element;
          if (!visitedClasses.contains(element)) {
            supertypes.add(type);
          }
        }
      }
    }
  }

  /**
   * Compute a list of constructors for this class, which is a mixin
   * application.  If specified, [visitedClasses] is a list of the other mixin
   * application classes which have been visited on the way to reaching this
   * one (this is used to detect circularities).
   */
  List<ConstructorElement> _computeMixinAppConstructors(
      [List<ClassElementImpl> visitedClasses = null]) {
    // First get the list of constructors of the superclass which need to be
    // forwarded to this class.
    Iterable<ConstructorElement> constructorsToForward;
    if (supertype == null) {
      // Shouldn't ever happen, since the only class with no supertype is
      // Object, and it isn't a mixin application.  But for safety's sake just
      // assume an empty list.
      assert(false);
      constructorsToForward = <ConstructorElement>[];
    } else if (!supertype.element.isMixinApplication) {
      List<ConstructorElement> superclassConstructors =
          supertype.element.constructors;
      // Filter out any constructors with optional parameters (see
      // dartbug.com/15101).
      constructorsToForward =
          superclassConstructors.where(isSuperConstructorAccessible);
    } else {
      if (visitedClasses == null) {
        visitedClasses = <ClassElementImpl>[this];
      } else {
        if (visitedClasses.contains(this)) {
          // Loop in the class hierarchy.  Don't try to forward any
          // constructors.
          return <ConstructorElement>[];
        }
        visitedClasses.add(this);
      }
      try {
        ClassElementImpl superElement = AbstractClassElementImpl
            .getImpl(supertype.element) as ClassElementImpl;
        constructorsToForward =
            superElement._computeMixinAppConstructors(visitedClasses);
      } finally {
        visitedClasses.removeLast();
      }
    }

    // Figure out the type parameter substitution we need to perform in order
    // to produce constructors for this class.  We want to be robust in the
    // face of errors, so drop any extra type arguments and fill in any missing
    // ones with `dynamic`.
    List<DartType> parameterTypes =
        TypeParameterTypeImpl.getTypes(supertype.typeParameters);
    List<DartType> argumentTypes = new List<DartType>.filled(
        parameterTypes.length, DynamicTypeImpl.instance);
    for (int i = 0; i < supertype.typeArguments.length; i++) {
      if (i >= argumentTypes.length) {
        break;
      }
      argumentTypes[i] = supertype.typeArguments[i];
    }

    // Now create an implicit constructor for every constructor found above,
    // substituting type parameters as appropriate.
    return constructorsToForward
        .map((ConstructorElement superclassConstructor) {
      ConstructorElementImpl implicitConstructor =
          new ConstructorElementImpl(superclassConstructor.name, -1);
      implicitConstructor.isSynthetic = true;
      implicitConstructor.redirectedConstructor = superclassConstructor;
      List<ParameterElement> superParameters = superclassConstructor.parameters;
      int count = superParameters.length;
      if (count > 0) {
        List<ParameterElement> implicitParameters =
            new List<ParameterElement>(count);
        for (int i = 0; i < count; i++) {
          ParameterElement superParameter = superParameters[i];
          ParameterElementImpl implicitParameter =
              new ParameterElementImpl(superParameter.name, -1);
          implicitParameter.isConst = superParameter.isConst;
          implicitParameter.isFinal = superParameter.isFinal;
          implicitParameter.parameterKind = superParameter.parameterKind;
          implicitParameter.isSynthetic = true;
          implicitParameter.type =
              superParameter.type.substitute2(argumentTypes, parameterTypes);
          implicitParameters[i] = implicitParameter;
        }
        implicitConstructor.parameters = implicitParameters;
      }
      implicitConstructor.enclosingElement = this;
      return implicitConstructor;
    }).toList(growable: false);
  }

  /**
   * Resynthesize explicit fields and property accessors and fill [_fields] and
   * [_accessors] with explicit and implicit elements.
   */
  void _resynthesizeFieldsAndPropertyAccessors() {
    assert(_fields == null);
    assert(_accessors == null);
    // Build explicit fields and implicit property accessors.
    var explicitFields = <FieldElement>[];
    var implicitAccessors = <PropertyAccessorElement>[];
    for (UnlinkedVariable v in _unlinkedClass.fields) {
      FieldElementImpl field =
          new FieldElementImpl.forSerializedFactory(v, this);
      explicitFields.add(field);
      implicitAccessors.add(
          new PropertyAccessorElementImpl_ImplicitGetter(field)
            ..enclosingElement = this);
      if (!field.isConst && !field.isFinal) {
        implicitAccessors.add(
            new PropertyAccessorElementImpl_ImplicitSetter(field)
              ..enclosingElement = this);
      }
    }
    // Build explicit property accessors and implicit fields.
    var explicitAccessors = <PropertyAccessorElement>[];
    var implicitFields = <String, FieldElementImpl>{};
    for (UnlinkedExecutable e in _unlinkedClass.executables) {
      if (e.kind == UnlinkedExecutableKind.getter ||
          e.kind == UnlinkedExecutableKind.setter) {
        PropertyAccessorElementImpl accessor =
            new PropertyAccessorElementImpl.forSerialized(e, this);
        explicitAccessors.add(accessor);
        // Create or update the implicit field.
        String fieldName = accessor.displayName;
        FieldElementImpl field = implicitFields[fieldName];
        if (field == null) {
          field = new FieldElementImpl(fieldName, -1);
          implicitFields[fieldName] = field;
          field.enclosingElement = this;
          field.isSynthetic = true;
          field.isFinal = e.kind == UnlinkedExecutableKind.getter;
          field.isStatic = e.isStatic;
        } else {
          field.isFinal = false;
        }
        accessor.variable = field;
        if (e.kind == UnlinkedExecutableKind.getter) {
          field.getter = accessor;
        } else {
          field.setter = accessor;
        }
      }
    }
    // Combine explicit and implicit fields and property accessors.
    _fields = <FieldElement>[]
      ..addAll(explicitFields)
      ..addAll(implicitFields.values);
    _accessors = <PropertyAccessorElement>[]
      ..addAll(explicitAccessors)
      ..addAll(implicitAccessors);
  }

  bool _safeIsOrInheritsProxy(
      ClassElement element, HashSet<ClassElement> visited) {
    if (visited.contains(element)) {
      return false;
    }
    visited.add(element);
    if (element.isProxy) {
      return true;
    } else if (element.supertype != null &&
        _safeIsOrInheritsProxy(element.supertype.element, visited)) {
      return true;
    }
    List<InterfaceType> supertypes = element.interfaces;
    for (int i = 0; i < supertypes.length; i++) {
      if (_safeIsOrInheritsProxy(supertypes[i].element, visited)) {
        return true;
      }
    }
    supertypes = element.mixins;
    for (int i = 0; i < supertypes.length; i++) {
      if (_safeIsOrInheritsProxy(supertypes[i].element, visited)) {
        return true;
      }
    }
    return false;
  }

  /**
   * Return `true` if the given [type] is a class [InterfaceType].
   */
  static bool _isClassInterfaceType(DartType type) {
    return type is InterfaceType && !type.element.isEnum;
  }
}

/**
 * A concrete implementation of a [CompilationUnitElement].
 */
class CompilationUnitElementImpl extends UriReferencedElementImpl
    implements CompilationUnitElement {
  /**
   * The context in which this unit is resynthesized, or `null` if the
   * element is not resynthesized a summary.
   */
  final ResynthesizerContext resynthesizerContext;

  /**
   * The unlinked representation of the unit in the summary.
   */
  final UnlinkedUnit _unlinkedUnit;

  /**
   * The unlinked representation of the part in the summary.
   */
  final UnlinkedPart _unlinkedPart;

  /**
   * The source that corresponds to this compilation unit.
   */
  @override
  Source source;

  @override
  LineInfo lineInfo;

  /**
   * The source of the library containing this compilation unit.
   *
   * This is the same as the source of the containing [LibraryElement],
   * except that it does not require the containing [LibraryElement] to be
   * computed.
   */
  Source librarySource;

  /**
   * A table mapping the offset of a directive to the annotations associated
   * with that directive, or `null` if none of the annotations in the
   * compilation unit have annotations.
   */
  Map<int, List<ElementAnnotation>> annotationMap = null;

  /**
   * A list containing all of the top-level accessors (getters and setters)
   * contained in this compilation unit.
   */
  List<PropertyAccessorElement> _accessors;

  /**
   * A list containing all of the enums contained in this compilation unit.
   */
  List<ClassElement> _enums;

  /**
   * A list containing all of the top-level functions contained in this
   * compilation unit.
   */
  List<FunctionElement> _functions;

  /**
   * A list containing all of the function type aliases contained in this
   * compilation unit.
   */
  List<FunctionTypeAliasElement> _typeAliases;

  /**
   * A list containing all of the types contained in this compilation unit.
   */
  List<ClassElement> _types;

  /**
   * A list containing all of the variables contained in this compilation unit.
   */
  List<TopLevelVariableElement> _variables;

  /**
   * A map from offsets to elements of this unit at these offsets.
   */
  final Map<int, Element> _offsetToElementMap = new HashMap<int, Element>();

  /**
   * Resynthesized explicit top-level property accessors.
   */
  UnitExplicitTopLevelAccessors _explicitTopLevelAccessors;

  /**
   * Resynthesized explicit top-level variables.
   */
  UnitExplicitTopLevelVariables _explicitTopLevelVariables;

  /**
   * Description of top-level variable replacements that should be applied
   * to implicit top-level variables because of re-linking top-level property
   * accessors between different unit of the same library.
   */
  Map<TopLevelVariableElement, TopLevelVariableElement>
      _topLevelVariableReplaceMap;

  /**
   * Initialize a newly created compilation unit element to have the given
   * [name].
   */
  CompilationUnitElementImpl(String name)
      : resynthesizerContext = null,
        _unlinkedUnit = null,
        _unlinkedPart = null,
        super(name, -1);

  /**
   * Initialize using the given serialized information.
   */
  CompilationUnitElementImpl.forSerialized(
      LibraryElementImpl enclosingLibrary,
      this.resynthesizerContext,
      this._unlinkedUnit,
      this._unlinkedPart,
      String name)
      : super.forSerialized(null) {
    _enclosingElement = enclosingLibrary;
    _name = name;
    _nameOffset = -1;
  }

  @override
  List<PropertyAccessorElement> get accessors {
    if (_unlinkedUnit != null) {
      if (_accessors == null) {
        _explicitTopLevelAccessors ??=
            resynthesizerContext.buildTopLevelAccessors();
        _explicitTopLevelVariables ??=
            resynthesizerContext.buildTopLevelVariables();
        List<PropertyAccessorElementImpl> accessors =
            <PropertyAccessorElementImpl>[];
        accessors.addAll(_explicitTopLevelAccessors.accessors);
        accessors.addAll(_explicitTopLevelVariables.implicitAccessors);
        _accessors = accessors;
      }
    }
    return _accessors ?? PropertyAccessorElement.EMPTY_LIST;
  }

  /**
   * Set the top-level accessors (getters and setters) contained in this
   * compilation unit to the given [accessors].
   */
  void set accessors(List<PropertyAccessorElement> accessors) {
    for (PropertyAccessorElement accessor in accessors) {
      (accessor as PropertyAccessorElementImpl).enclosingElement = this;
    }
    this._accessors = accessors;
  }

  @override
  int get codeLength {
    if (_unlinkedUnit != null) {
      return _unlinkedUnit.codeRange?.length;
    }
    return super.codeLength;
  }

  @override
  int get codeOffset {
    if (_unlinkedUnit != null) {
      return _unlinkedUnit.codeRange?.offset;
    }
    return super.codeOffset;
  }

  @override
  LibraryElement get enclosingElement =>
      super.enclosingElement as LibraryElement;

  @override
  CompilationUnitElementImpl get enclosingUnit {
    return this;
  }

  @override
  List<ClassElement> get enums {
    if (_unlinkedUnit != null) {
      _enums ??= _unlinkedUnit.enums
          .map((e) => new EnumElementImpl.forSerialized(e, this))
          .toList(growable: false);
    }
    return _enums ?? const <ClassElement>[];
  }

  /**
   * Set the enums contained in this compilation unit to the given [enums].
   */
  void set enums(List<ClassElement> enums) {
    _assertNotResynthesized(_unlinkedUnit);
    for (ClassElement enumDeclaration in enums) {
      (enumDeclaration as EnumElementImpl).enclosingElement = this;
    }
    this._enums = enums;
  }

  @override
  List<FunctionElement> get functions {
    if (_unlinkedUnit != null) {
      _functions ??= _unlinkedUnit.executables
          .where((e) => e.kind == UnlinkedExecutableKind.functionOrMethod)
          .map((e) => new FunctionElementImpl.forSerialized(e, this))
          .toList(growable: false);
    }
    return _functions ?? const <FunctionElement>[];
  }

  /**
   * Set the top-level functions contained in this compilation unit to the given
   * [functions].
   */
  void set functions(List<FunctionElement> functions) {
    for (FunctionElement function in functions) {
      (function as FunctionElementImpl).enclosingElement = this;
    }
    this._functions = functions;
  }

  @override
  List<FunctionTypeAliasElement> get functionTypeAliases {
    if (_unlinkedUnit != null) {
      _typeAliases ??= _unlinkedUnit.typedefs.map((t) {
        if (t.style == TypedefStyle.functionType) {
          return new FunctionTypeAliasElementImpl.forSerialized(t, this);
        } else if (t.style == TypedefStyle.genericFunctionType) {
          return new GenericTypeAliasElementImpl.forSerialized(t, this);
        }
      }).toList(growable: false);
    }
    return _typeAliases ?? const <FunctionTypeAliasElement>[];
  }

  @override
  int get hashCode => source.hashCode;

  @override
  bool get hasLoadLibraryFunction {
    List<FunctionElement> functions = this.functions;
    for (int i = 0; i < functions.length; i++) {
      if (functions[i].name == FunctionElement.LOAD_LIBRARY_NAME) {
        return true;
      }
    }
    return false;
  }

  @override
  String get identifier => source.encoding;

  @override
  ElementKind get kind => ElementKind.COMPILATION_UNIT;

  @override
  List<ElementAnnotation> get metadata {
    if (_unlinkedPart != null) {
      return _metadata ??= _buildAnnotations(
          library.definingCompilationUnit as CompilationUnitElementImpl,
          _unlinkedPart.annotations);
    }
    return super.metadata;
  }

  @override
  List<TopLevelVariableElement> get topLevelVariables {
    if (_unlinkedUnit != null) {
      if (_variables == null) {
        _explicitTopLevelAccessors ??=
            resynthesizerContext.buildTopLevelAccessors();
        _explicitTopLevelVariables ??=
            resynthesizerContext.buildTopLevelVariables();
        List<TopLevelVariableElementImpl> variables =
            <TopLevelVariableElementImpl>[];
        variables.addAll(_explicitTopLevelVariables.variables);
        variables.addAll(_explicitTopLevelAccessors.implicitVariables);
        // Ensure that getters and setters in different units use
        // the same top-level variables.
        (enclosingElement as LibraryElementImpl)
            .resynthesizerContext
            .patchTopLevelAccessors();
        _variables = variables;
        _topLevelVariableReplaceMap?.forEach((from, to) {
          int index = _variables.indexOf(from);
          _variables[index] = to;
        });
        _topLevelVariableReplaceMap = null;
      }
    }
    return _variables ?? TopLevelVariableElement.EMPTY_LIST;
  }

  /**
   * Set the top-level variables contained in this compilation unit to the given
   * [variables].
   */
  void set topLevelVariables(List<TopLevelVariableElement> variables) {
    assert(!isResynthesized);
    for (TopLevelVariableElement field in variables) {
      (field as TopLevelVariableElementImpl).enclosingElement = this;
    }
    this._variables = variables;
  }

  /**
   * Set the function type aliases contained in this compilation unit to the
   * given [typeAliases].
   */
  void set typeAliases(List<FunctionTypeAliasElement> typeAliases) {
    _assertNotResynthesized(_unlinkedUnit);
    for (FunctionTypeAliasElement typeAlias in typeAliases) {
      (typeAlias as ElementImpl).enclosingElement = this;
    }
    this._typeAliases = typeAliases;
  }

  @override
  TypeParameterizedElementMixin get typeParameterContext => null;

  @override
  List<ClassElement> get types {
    if (_unlinkedUnit != null) {
      _types ??= _unlinkedUnit.classes
          .map((c) => new ClassElementImpl.forSerialized(c, this))
          .toList(growable: false);
    }
    return _types ?? const <ClassElement>[];
  }

  /**
   * Set the types contained in this compilation unit to the given [types].
   */
  void set types(List<ClassElement> types) {
    _assertNotResynthesized(_unlinkedUnit);
    for (ClassElement type in types) {
      // Another implementation of ClassElement is _DeferredClassElement,
      // which is used to resynthesize classes lazily. We cannot cast it
      // to ClassElementImpl, and it already can provide correct values of the
      // 'enclosingElement' property.
      if (type is ClassElementImpl) {
        type.enclosingElement = this;
      }
    }
    this._types = types;
  }

  @override
  bool operator ==(Object object) =>
      object is CompilationUnitElementImpl && source == object.source;

  @override
  /*=T*/ accept/*<T>*/(ElementVisitor<dynamic/*=T*/ > visitor) =>
      visitor.visitCompilationUnitElement(this);

  /**
   * This method is invoked after this unit was incrementally resolved.
   */
  void afterIncrementalResolution() {
    _offsetToElementMap.clear();
  }

  @override
  void appendTo(StringBuffer buffer) {
    if (source == null) {
      buffer.write("{compilation unit}");
    } else {
      buffer.write(source.fullName);
    }
  }

  @override
  CompilationUnit computeNode() => unit;

  /**
   * Return the annotations associated with the directive at the given [offset],
   * or an empty list if the directive has no annotations or if there is no
   * directive at the given offset.
   */
  List<ElementAnnotation> getAnnotations(int offset) {
    if (annotationMap == null) {
      return const <ElementAnnotation>[];
    }
    return annotationMap[offset] ?? const <ElementAnnotation>[];
  }

  @override
  ElementImpl getChild(String identifier) {
    //
    // The casts in this method are safe because the set methods would have
    // thrown a CCE if any of the elements in the arrays were not of the
    // expected types.
    //
    for (PropertyAccessorElement accessor in accessors) {
      PropertyAccessorElementImpl accessorImpl = accessor;
      if (accessorImpl.identifier == identifier) {
        return accessorImpl;
      }
    }
    for (TopLevelVariableElement variable in topLevelVariables) {
      TopLevelVariableElementImpl variableImpl = variable;
      if (variableImpl.identifier == identifier) {
        return variableImpl;
      }
    }
    for (FunctionElement function in functions) {
      FunctionElementImpl functionImpl = function;
      if (functionImpl.identifier == identifier) {
        return functionImpl;
      }
    }
    for (FunctionTypeAliasElement typeAlias in functionTypeAliases) {
      FunctionTypeAliasElementImpl typeAliasImpl = typeAlias;
      if (typeAliasImpl.identifier == identifier) {
        return typeAliasImpl;
      }
    }
    for (ClassElement type in types) {
      ClassElementImpl typeImpl = type;
      if (typeImpl.name == identifier) {
        return typeImpl;
      }
    }
    for (ClassElement type in _enums) {
      EnumElementImpl typeImpl = type;
      if (typeImpl.identifier == identifier) {
        return typeImpl;
      }
    }
    return null;
  }

  @override
  Element getElementAt(int offset) {
    if (_offsetToElementMap.isEmpty) {
      accept(new _BuildOffsetToElementMap(_offsetToElementMap));
    }
    return _offsetToElementMap[offset];
  }

  @override
  ClassElement getEnum(String enumName) {
    for (ClassElement enumDeclaration in _enums) {
      if (enumDeclaration.name == enumName) {
        return enumDeclaration;
      }
    }
    return null;
  }

  @override
  ClassElement getType(String className) {
    for (ClassElement type in types) {
      if (type.name == className) {
        return type;
      }
    }
    return null;
  }

  /**
   * Replace the given [from] top-level variable with [to] in this compilation unit.
   */
  void replaceTopLevelVariable(
      TopLevelVariableElement from, TopLevelVariableElement to) {
    if (_unlinkedUnit != null) {
      // Getters and setter in different units should be patched to use the
      // same variables before these variables were asked and returned.
      assert(_variables == null);
      _topLevelVariableReplaceMap ??=
          <TopLevelVariableElement, TopLevelVariableElement>{};
      _topLevelVariableReplaceMap[from] = to;
    } else {
      int index = _variables.indexOf(from);
      _variables[index] = to;
    }
  }

  /**
   * Set the annotations associated with the directive at the given [offset] to
   * the given list of [annotations].
   */
  void setAnnotations(int offset, List<ElementAnnotation> annotations) {
    annotationMap ??= new HashMap<int, List<ElementAnnotation>>();
    annotationMap[offset] = annotations;
  }

  @override
  void visitChildren(ElementVisitor visitor) {
    super.visitChildren(visitor);
    safelyVisitChildren(accessors, visitor);
    safelyVisitChildren(enums, visitor);
    safelyVisitChildren(functions, visitor);
    safelyVisitChildren(functionTypeAliases, visitor);
    safelyVisitChildren(types, visitor);
    safelyVisitChildren(topLevelVariables, visitor);
  }
}

/**
 * A [FieldElement] for a 'const' or 'final' field that has an initializer.
 *
 * TODO(paulberry): we should rename this class to reflect the fact that it's
 * used for both const and final fields.  However, we shouldn't do so until
 * we've created an API for reading the values of constants; until that API is
 * available, clients are likely to read constant values by casting to
 * ConstFieldElementImpl, so it would be a breaking change to rename this
 * class.
 */
class ConstFieldElementImpl extends FieldElementImpl with ConstVariableElement {
  /**
   * Initialize a newly created synthetic field element to have the given
   * [name] and [offset].
   */
  ConstFieldElementImpl(String name, int offset) : super(name, offset);

  /**
   * Initialize a newly created field element to have the given [name].
   */
  ConstFieldElementImpl.forNode(Identifier name) : super.forNode(name);

  /**
   * Initialize using the given serialized information.
   */
  ConstFieldElementImpl.forSerialized(
      UnlinkedVariable unlinkedVariable, ElementImpl enclosingElement)
      : super.forSerialized(unlinkedVariable, enclosingElement);
}

/**
 * A field element representing an enum constant.
 */
class ConstFieldElementImpl_EnumValue extends ConstFieldElementImpl_ofEnum {
  final UnlinkedEnumValue _unlinkedEnumValue;
  final int _index;

  ConstFieldElementImpl_EnumValue(
      EnumElementImpl enumElement, this._unlinkedEnumValue, this._index)
      : super(enumElement);

  @override
  String get documentationComment {
    if (_unlinkedEnumValue != null) {
      return _unlinkedEnumValue?.documentationComment?.text;
    }
    return super.documentationComment;
  }

  @override
  EvaluationResultImpl get evaluationResult {
    if (_evaluationResult == null) {
      Map<String, DartObjectImpl> fieldMap = <String, DartObjectImpl>{
        name: new DartObjectImpl(
            context.typeProvider.intType, new IntState(_index))
      };
      DartObjectImpl value =
          new DartObjectImpl(type, new GenericState(fieldMap));
      _evaluationResult = new EvaluationResultImpl(value);
    }
    return _evaluationResult;
  }

  @override
  String get name {
    if (_unlinkedEnumValue != null) {
      return _unlinkedEnumValue.name;
    }
    return super.name;
  }

  @override
  int get nameOffset {
    int offset = super.nameOffset;
    if (offset == -1 && _unlinkedEnumValue != null) {
      return _unlinkedEnumValue.nameOffset;
    }
    return offset;
  }

  @override
  InterfaceType get type => _enum.type;
}

/**
 * The synthetic `values` field of an enum.
 */
class ConstFieldElementImpl_EnumValues extends ConstFieldElementImpl_ofEnum {
  ConstFieldElementImpl_EnumValues(EnumElementImpl enumElement)
      : super(enumElement) {
    isSynthetic = true;
  }

  @override
  EvaluationResultImpl get evaluationResult {
    if (_evaluationResult == null) {
      List<DartObjectImpl> constantValues = <DartObjectImpl>[];
      for (FieldElement field in _enum.fields) {
        if (field is ConstFieldElementImpl_EnumValue) {
          constantValues.add(field.evaluationResult.value);
        }
      }
      _evaluationResult = new EvaluationResultImpl(
          new DartObjectImpl(type, new ListState(constantValues)));
    }
    return _evaluationResult;
  }

  @override
  String get name => 'values';

  @override
  InterfaceType get type {
    if (_type == null) {
      InterfaceType listType = context.typeProvider.listType;
      return _type = listType.instantiate(<DartType>[_enum.type]);
    }
    return _type;
  }
}

/**
 * An abstract constant field of an enum.
 */
abstract class ConstFieldElementImpl_ofEnum extends ConstFieldElementImpl {
  final EnumElementImpl _enum;

  ConstFieldElementImpl_ofEnum(this._enum) : super(null, -1) {
    enclosingElement = _enum;
  }

  @override
  void set evaluationResult(_) {
    assert(false);
  }

  @override
  bool get isConst => true;

  @override
  void set isConst(bool isConst) {
    assert(false);
  }

  @override
  void set isFinal(bool isFinal) {
    assert(false);
  }

  @override
  bool get isStatic => true;

  @override
  void set isStatic(bool isStatic) {
    assert(false);
  }

  void set type(DartType type) {
    assert(false);
  }
}

/**
 * A [LocalVariableElement] for a local 'const' variable that has an
 * initializer.
 */
class ConstLocalVariableElementImpl extends LocalVariableElementImpl
    with ConstVariableElement {
  /**
   * Initialize a newly created local variable element to have the given [name]
   * and [offset].
   */
  ConstLocalVariableElementImpl(String name, int offset) : super(name, offset);

  /**
   * Initialize a newly created local variable element to have the given [name].
   */
  ConstLocalVariableElementImpl.forNode(Identifier name) : super.forNode(name);

  /**
   * Initialize using the given serialized information.
   */
  ConstLocalVariableElementImpl.forSerialized(UnlinkedVariable unlinkedVariable,
      ExecutableElementImpl enclosingExecutable)
      : super.forSerialized(unlinkedVariable, enclosingExecutable);
}

/**
 * A concrete implementation of a [ConstructorElement].
 */
class ConstructorElementImpl extends ExecutableElementImpl
    implements ConstructorElement {
  /**
   * The constructor to which this constructor is redirecting.
   */
  ConstructorElement _redirectedConstructor;

  /**
   * The initializers for this constructor (used for evaluating constant
   * instance creation expressions).
   */
  List<ConstructorInitializer> _constantInitializers;

  /**
   * The offset of the `.` before this constructor name or `null` if not named.
   */
  int _periodOffset;

  /**
   * Return the offset of the character immediately following the last character
   * of this constructor's name, or `null` if not named.
   */
  int _nameEnd;

  /**
   * True if this constructor has been found by constant evaluation to be free
   * of redirect cycles, and is thus safe to evaluate.
   */
  bool _isCycleFree = false;

  /**
   * Initialize a newly created constructor element to have the given [name] and
   * [offset].
   */
  ConstructorElementImpl(String name, int offset) : super(name, offset);

  /**
   * Initialize a newly created constructor element to have the given [name].
   */
  ConstructorElementImpl.forNode(Identifier name) : super.forNode(name);

  /**
   * Initialize using the given serialized information.
   */
  ConstructorElementImpl.forSerialized(
      UnlinkedExecutable serializedExecutable, ClassElementImpl enclosingClass)
      : super.forSerialized(serializedExecutable, enclosingClass);

  /**
   * Return the constant initializers for this element, which will be empty if
   * there are no initializers, or `null` if there was an error in the source.
   */
  List<ConstructorInitializer> get constantInitializers {
    if (serializedExecutable != null && _constantInitializers == null) {
      _constantInitializers ??= serializedExecutable.constantInitializers
          .map((i) => _buildConstructorInitializer(i))
          .toList(growable: false);
    }
    return _constantInitializers;
  }

  void set constantInitializers(
      List<ConstructorInitializer> constantInitializers) {
    _assertNotResynthesized(serializedExecutable);
    _constantInitializers = constantInitializers;
  }

  @override
  ClassElementImpl get enclosingElement =>
      super.enclosingElement as ClassElementImpl;

  @override
  TypeParameterizedElementMixin get enclosingTypeParameterContext =>
      super.enclosingElement as ClassElementImpl;

  /**
   * Set whether this constructor represents a factory method.
   */
  void set factory(bool isFactory) {
    _assertNotResynthesized(serializedExecutable);
    setModifier(Modifier.FACTORY, isFactory);
  }

  @override
  bool get isConst {
    if (serializedExecutable != null) {
      return serializedExecutable.isConst;
    }
    return hasModifier(Modifier.CONST);
  }

  /**
   * Set whether this constructor represents a 'const' constructor.
   */
  void set isConst(bool isConst) {
    _assertNotResynthesized(serializedExecutable);
    setModifier(Modifier.CONST, isConst);
  }

  bool get isCycleFree {
    if (serializedExecutable != null) {
      return serializedExecutable.isConst &&
          !enclosingUnit.resynthesizerContext
              .isInConstCycle(serializedExecutable.constCycleSlot);
    }
    return _isCycleFree;
  }

  void set isCycleFree(bool isCycleFree) {
    // This property is updated in ConstantEvaluationEngine even for
    // resynthesized constructors, so we don't have the usual assert here.
    _isCycleFree = isCycleFree;
  }

  @override
  bool get isDefaultConstructor {
    // unnamed
    String name = this.name;
    if (name != null && name.length != 0) {
      return false;
    }
    // no required parameters
    for (ParameterElement parameter in parameters) {
      if (parameter.parameterKind == ParameterKind.REQUIRED) {
        return false;
      }
    }
    // OK, can be used as default constructor
    return true;
  }

  @override
  bool get isFactory {
    if (serializedExecutable != null) {
      return serializedExecutable.isFactory;
    }
    return hasModifier(Modifier.FACTORY);
  }

  @override
  bool get isStatic => false;

  @override
  ElementKind get kind => ElementKind.CONSTRUCTOR;

  @override
  int get nameEnd {
    if (serializedExecutable != null) {
      if (serializedExecutable.name.isNotEmpty) {
        return serializedExecutable.nameEnd;
      } else {
        return serializedExecutable.nameOffset + enclosingElement.name.length;
      }
    }
    return _nameEnd;
  }

  void set nameEnd(int nameEnd) {
    _assertNotResynthesized(serializedExecutable);
    _nameEnd = nameEnd;
  }

  @override
  int get periodOffset {
    if (serializedExecutable != null) {
      if (serializedExecutable.name.isNotEmpty) {
        return serializedExecutable.periodOffset;
      }
    }
    return _periodOffset;
  }

  void set periodOffset(int periodOffset) {
    _assertNotResynthesized(serializedExecutable);
    _periodOffset = periodOffset;
  }

  @override
  ConstructorElement get redirectedConstructor {
    if (serializedExecutable != null && _redirectedConstructor == null) {
      if (serializedExecutable.isRedirectedConstructor) {
        if (serializedExecutable.isFactory) {
          _redirectedConstructor = enclosingUnit.resynthesizerContext
              .resolveConstructorRef(
                  enclosingElement, serializedExecutable.redirectedConstructor);
        } else {
          _redirectedConstructor = enclosingElement.getNamedConstructor(
              serializedExecutable.redirectedConstructorName);
        }
      } else {
        return null;
      }
    }
    return _redirectedConstructor;
  }

  void set redirectedConstructor(ConstructorElement redirectedConstructor) {
    _assertNotResynthesized(serializedExecutable);
    _redirectedConstructor = redirectedConstructor;
  }

  @override
  DartType get returnType => enclosingElement.type;

  void set returnType(DartType returnType) {
    assert(false);
  }

  @override
  FunctionType get type {
    return _type ??= new FunctionTypeImpl(this);
  }

  void set type(FunctionType type) {
    assert(false);
  }

  @override
  /*=T*/ accept/*<T>*/(ElementVisitor<dynamic/*=T*/ > visitor) =>
      visitor.visitConstructorElement(this);

  @override
  void appendTo(StringBuffer buffer) {
    if (enclosingElement == null) {
      String message;
      String name = displayName;
      if (name != null && !name.isEmpty) {
        message =
            'Found constructor element named $name with no enclosing element';
      } else {
        message = 'Found unnamed constructor element with no enclosing element';
      }
      AnalysisEngine.instance.logger.logError(message);
      buffer.write('<unknown class>');
    } else {
      buffer.write(enclosingElement.displayName);
    }
    String name = displayName;
    if (name != null && !name.isEmpty) {
      buffer.write(".");
      buffer.write(name);
    }
    super.appendTo(buffer);
  }

  @override
  ConstructorDeclaration computeNode() =>
      getNodeMatching((node) => node is ConstructorDeclaration);

  /**
   * Resynthesize the AST for the given serialized constructor initializer.
   */
  ConstructorInitializer _buildConstructorInitializer(
      UnlinkedConstructorInitializer serialized) {
    UnlinkedConstructorInitializerKind kind = serialized.kind;
    String name = serialized.name;
    List<Expression> arguments = <Expression>[];
    {
      int numArguments = serialized.arguments.length;
      int numNames = serialized.argumentNames.length;
      for (int i = 0; i < numArguments; i++) {
        Expression expression = enclosingUnit.resynthesizerContext
            .buildExpression(this, serialized.arguments[i]);
        int nameIndex = numNames + i - numArguments;
        if (nameIndex >= 0) {
          expression = AstTestFactory.namedExpression2(
              serialized.argumentNames[nameIndex], expression);
        }
        arguments.add(expression);
      }
    }
    switch (kind) {
      case UnlinkedConstructorInitializerKind.field:
        ConstructorFieldInitializer initializer =
            AstTestFactory.constructorFieldInitializer(
                false,
                name,
                enclosingUnit.resynthesizerContext
                    .buildExpression(this, serialized.expression));
        initializer.fieldName.staticElement = enclosingElement.getField(name);
        return initializer;
      case UnlinkedConstructorInitializerKind.assertInvocation:
        return AstTestFactory.assertInitializer(
            arguments[0], arguments.length > 1 ? arguments[1] : null);
      case UnlinkedConstructorInitializerKind.superInvocation:
        SuperConstructorInvocation initializer =
            AstTestFactory.superConstructorInvocation2(
                name.isNotEmpty ? name : null, arguments);
        ClassElement superElement = enclosingElement.supertype.element;
        ConstructorElement element = name.isEmpty
            ? superElement.unnamedConstructor
            : superElement.getNamedConstructor(name);
        initializer.staticElement = element;
        initializer.constructorName?.staticElement = element;
        return initializer;
      case UnlinkedConstructorInitializerKind.thisInvocation:
        RedirectingConstructorInvocation initializer =
            AstTestFactory.redirectingConstructorInvocation2(
                name.isNotEmpty ? name : null, arguments);
        ConstructorElement element = name.isEmpty
            ? enclosingElement.unnamedConstructor
            : enclosingElement.getNamedConstructor(name);
        initializer.staticElement = element;
        initializer.constructorName?.staticElement = element;
        return initializer;
    }
    return null;
  }
}

/**
 * A [TopLevelVariableElement] for a top-level 'const' variable that has an
 * initializer.
 */
class ConstTopLevelVariableElementImpl extends TopLevelVariableElementImpl
    with ConstVariableElement {
  /**
   * Initialize a newly created synthetic top-level variable element to have the
   * given [name] and [offset].
   */
  ConstTopLevelVariableElementImpl(String name, int offset)
      : super(name, offset);

  /**
   * Initialize a newly created top-level variable element to have the given
   * [name].
   */
  ConstTopLevelVariableElementImpl.forNode(Identifier name)
      : super.forNode(name);

  /**
   * Initialize using the given serialized information.
   */
  ConstTopLevelVariableElementImpl.forSerialized(
      UnlinkedVariable unlinkedVariable, ElementImpl enclosingElement)
      : super.forSerialized(unlinkedVariable, enclosingElement);
}

/**
 * Mixin used by elements that represent constant variables and have
 * initializers.
 *
 * Note that in correct Dart code, all constant variables must have
 * initializers.  However, analyzer also needs to handle incorrect Dart code,
 * in which case there might be some constant variables that lack initializers.
 * This interface is only used for constant variables that have initializers.
 *
 * This class is not intended to be part of the public API for analyzer.
 */
abstract class ConstVariableElement
    implements ElementImpl, ConstantEvaluationTarget {
  /**
   * If this element represents a constant variable, and it has an initializer,
   * a copy of the initializer for the constant.  Otherwise `null`.
   *
   * Note that in correct Dart code, all constant variables must have
   * initializers.  However, analyzer also needs to handle incorrect Dart code,
   * in which case there might be some constant variables that lack
   * initializers.
   */
  Expression _constantInitializer;

  EvaluationResultImpl _evaluationResult;

  Expression get constantInitializer {
    if (_constantInitializer == null && _unlinkedConst != null) {
      _constantInitializer = enclosingUnit.resynthesizerContext
          .buildExpression(this, _unlinkedConst);
    }
    return _constantInitializer;
  }

  void set constantInitializer(Expression constantInitializer) {
    _assertNotResynthesized(_unlinkedConst);
    _constantInitializer = constantInitializer;
  }

  EvaluationResultImpl get evaluationResult => _evaluationResult;

  void set evaluationResult(EvaluationResultImpl evaluationResult) {
    _evaluationResult = evaluationResult;
  }

  /**
   * If this element is resynthesized from the summary, return the unlinked
   * initializer, otherwise return `null`.
   */
  UnlinkedExpr get _unlinkedConst;

  /**
   * Return a representation of the value of this variable, forcing the value
   * to be computed if it had not previously been computed, or `null` if either
   * this variable was not declared with the 'const' modifier or if the value of
   * this variable could not be computed because of errors.
   */
  DartObject computeConstantValue() {
    if (evaluationResult == null) {
      context?.computeResult(this, CONSTANT_VALUE);
    }
    return evaluationResult?.value;
  }
}

/**
 * A [FieldFormalParameterElementImpl] for parameters that have an initializer.
 */
class DefaultFieldFormalParameterElementImpl
    extends FieldFormalParameterElementImpl with ConstVariableElement {
  /**
   * Initialize a newly created parameter element to have the given [name] and
   * [nameOffset].
   */
  DefaultFieldFormalParameterElementImpl(String name, int nameOffset)
      : super(name, nameOffset);

  /**
   * Initialize a newly created parameter element to have the given [name].
   */
  DefaultFieldFormalParameterElementImpl.forNode(Identifier name)
      : super.forNode(name);

  /**
   * Initialize using the given serialized information.
   */
  DefaultFieldFormalParameterElementImpl.forSerialized(
      UnlinkedParam unlinkedParam, ElementImpl enclosingElement)
      : super.forSerialized(unlinkedParam, enclosingElement);
}

/**
 * A [ParameterElement] for parameters that have an initializer.
 */
class DefaultParameterElementImpl extends ParameterElementImpl
    with ConstVariableElement {
  /**
   * Initialize a newly created parameter element to have the given [name] and
   * [nameOffset].
   */
  DefaultParameterElementImpl(String name, int nameOffset)
      : super(name, nameOffset);

  /**
   * Initialize a newly created parameter element to have the given [name].
   */
  DefaultParameterElementImpl.forNode(Identifier name) : super.forNode(name);

  /**
   * Initialize using the given serialized information.
   */
  DefaultParameterElementImpl.forSerialized(
      UnlinkedParam unlinkedParam, ElementImpl enclosingElement)
      : super.forSerialized(unlinkedParam, enclosingElement);

  @override
  DefaultFormalParameter computeNode() =>
      getNodeMatching((node) => node is DefaultFormalParameter);
}

/**
 * The synthetic element representing the declaration of the type `dynamic`.
 */
class DynamicElementImpl extends ElementImpl implements TypeDefiningElement {
  /**
   * Return the unique instance of this class.
   */
  static DynamicElementImpl get instance =>
      DynamicTypeImpl.instance.element as DynamicElementImpl;

  @override
  DynamicTypeImpl type;

  /**
   * Initialize a newly created instance of this class. Instances of this class
   * should <b>not</b> be created except as part of creating the type associated
   * with this element. The single instance of this class should be accessed
   * through the method [instance].
   */
  DynamicElementImpl() : super(Keyword.DYNAMIC.syntax, -1) {
    setModifier(Modifier.SYNTHETIC, true);
  }

  @override
  ElementKind get kind => ElementKind.DYNAMIC;

  @override
  /*=T*/ accept/*<T>*/(ElementVisitor<dynamic/*=T*/ > visitor) => null;
}

/**
 * A concrete implementation of an [ElementAnnotation].
 */
class ElementAnnotationImpl implements ElementAnnotation {
  /**
   * The name of the top-level variable used to mark a method parameter as
   * covariant.
   */
  static String _COVARIANT_VARIABLE_NAME = "checked";

  /**
   * The name of the class used to mark an element as being deprecated.
   */
  static String _DEPRECATED_CLASS_NAME = "Deprecated";

  /**
   * The name of the top-level variable used to mark an element as being
   * deprecated.
   */
  static String _DEPRECATED_VARIABLE_NAME = "deprecated";

  /**
   * The name of the top-level variable used to mark a method as being a
   * factory.
   */
  static String _FACTORY_VARIABLE_NAME = "factory";

  /**
   * The name of the top-level variable used to mark a class and its subclasses
   * as being immutable.
   */
  static String _IMMUTABLE_VARIABLE_NAME = "immutable";

  /**
   * The name of the class used to JS annotate an element.
   */
  static String _JS_CLASS_NAME = "JS";

  /**
   * The name of `js` library, used to define JS annotations.
   */
  static String _JS_LIB_NAME = "js";

  /**
   * The name of `meta` library, used to define analysis annotations.
   */
  static String _META_LIB_NAME = "meta";

  /**
   * The name of the top-level variable used to mark a method as requiring
   * overriders to call super.
   */
  static String _MUST_CALL_SUPER_VARIABLE_NAME = "mustCallSuper";

  /**
   * The name of the top-level variable used to mark a method as being expected
   * to override an inherited method.
   */
  static String _OVERRIDE_VARIABLE_NAME = "override";

  /**
   * The name of the top-level variable used to mark a method as being
   * protected.
   */
  static String _PROTECTED_VARIABLE_NAME = "protected";

  /**
   * The name of the top-level variable used to mark a class as implementing a
   * proxy object.
   */
  static String PROXY_VARIABLE_NAME = "proxy";

  /**
   * The name of the class used to mark a parameter as being required.
   */
  static String _REQUIRED_CLASS_NAME = "Required";

  /**
   * The name of the top-level variable used to mark a parameter as being
   * required.
   */
  static String _REQUIRED_VARIABLE_NAME = "required";

  /**
   * The element representing the field, variable, or constructor being used as
   * an annotation.
   */
  Element element;

  /**
   * The compilation unit in which this annotation appears.
   */
  CompilationUnitElementImpl compilationUnit;

  /**
   * The AST of the annotation itself, cloned from the resolved AST for the
   * source code.
   */
  Annotation annotationAst;

  /**
   * The result of evaluating this annotation as a compile-time constant
   * expression, or `null` if the compilation unit containing the variable has
   * not been resolved.
   */
  EvaluationResultImpl evaluationResult;

  /**
   * Initialize a newly created annotation. The given [compilationUnit] is the
   * compilation unit in which the annotation appears.
   */
  ElementAnnotationImpl(this.compilationUnit);

  @override
  DartObject get constantValue => evaluationResult?.value;

  @override
  AnalysisContext get context => compilationUnit.library.context;

  /**
   * Return `true` if this annotation marks the associated parameter as being
   * covariant, meaning it is allowed to have a narrower type in an override.
   */
  bool get isCovariant =>
      element is PropertyAccessorElement &&
      element.name == _COVARIANT_VARIABLE_NAME &&
      element.library?.name == _META_LIB_NAME;

  @override
  bool get isDeprecated {
    if (element?.library?.isDartCore == true) {
      if (element is ConstructorElement) {
        return element.enclosingElement.name == _DEPRECATED_CLASS_NAME;
      } else if (element is PropertyAccessorElement) {
        return element.name == _DEPRECATED_VARIABLE_NAME;
      }
    }
    return false;
  }

  @override
  bool get isFactory =>
      element is PropertyAccessorElement &&
      element.name == _FACTORY_VARIABLE_NAME &&
      element.library?.name == _META_LIB_NAME;

  @override
  bool get isImmutable =>
      element is PropertyAccessorElement &&
      element.name == _IMMUTABLE_VARIABLE_NAME &&
      element.library?.name == _META_LIB_NAME;

  @override
  bool get isJS =>
      element is ConstructorElement &&
      element.enclosingElement.name == _JS_CLASS_NAME &&
      element.library?.name == _JS_LIB_NAME;

  @override
  bool get isMustCallSuper =>
      element is PropertyAccessorElement &&
      element.name == _MUST_CALL_SUPER_VARIABLE_NAME &&
      element.library?.name == _META_LIB_NAME;

  @override
  bool get isOverride =>
      element is PropertyAccessorElement &&
      element.name == _OVERRIDE_VARIABLE_NAME &&
      element.library?.isDartCore == true;

  @override
  bool get isProtected =>
      element is PropertyAccessorElement &&
      element.name == _PROTECTED_VARIABLE_NAME &&
      element.library?.name == _META_LIB_NAME;

  @override
  bool get isProxy =>
      element is PropertyAccessorElement &&
      element.name == PROXY_VARIABLE_NAME &&
      element.library?.isDartCore == true;

  @override
  bool get isRequired =>
      element is ConstructorElement &&
          element.enclosingElement.name == _REQUIRED_CLASS_NAME &&
          element.library?.name == _META_LIB_NAME ||
      element is PropertyAccessorElement &&
          element.name == _REQUIRED_VARIABLE_NAME &&
          element.library?.name == _META_LIB_NAME;

  /**
   * Get the library containing this annotation.
   */
  Source get librarySource => compilationUnit.librarySource;

  @override
  Source get source => compilationUnit.source;

  @override
  DartObject computeConstantValue() {
    if (evaluationResult == null) {
      context?.computeResult(this, CONSTANT_VALUE);
    }
    return constantValue;
  }

  @override
  String toSource() => annotationAst.toSource();

  @override
  String toString() => '@$element';
}

/**
 * A base class for concrete implementations of an [Element].
 */
abstract class ElementImpl implements Element {
  /**
   * An Unicode right arrow.
   */
  static final String RIGHT_ARROW = " \u2192 ";

  static int _NEXT_ID = 0;

  final int id = _NEXT_ID++;

  /**
   * The enclosing element of this element, or `null` if this element is at the
   * root of the element structure.
   */
  ElementImpl _enclosingElement;

  /**
   * The name of this element.
   */
  String _name;

  /**
   * The offset of the name of this element in the file that contains the
   * declaration of this element.
   */
  int _nameOffset = 0;

  /**
   * A bit-encoded form of the modifiers associated with this element.
   */
  int _modifiers = 0;

  /**
   * A list containing all of the metadata associated with this element.
   */
  List<ElementAnnotation> _metadata;

  /**
   * A cached copy of the calculated hashCode for this element.
   */
  int _cachedHashCode;

  /**
   * A cached copy of the calculated location for this element.
   */
  ElementLocation _cachedLocation;

  /**
   * The documentation comment for this element.
   */
  String _docComment;

  /**
   * The offset of the beginning of the element's code in the file that contains
   * the element, or `null` if the element is synthetic.
   */
  int _codeOffset;

  /**
   * The length of the element's code, or `null` if the element is synthetic.
   */
  int _codeLength;

  /**
   * Initialize a newly created element to have the given [name] at the given
   * [_nameOffset].
   */
  ElementImpl(String name, this._nameOffset) {
    this._name = StringUtilities.intern(name);
  }

  /**
   * Initialize a newly created element to have the given [name].
   */
  ElementImpl.forNode(Identifier name)
      : this(name == null ? "" : name.name, name == null ? -1 : name.offset);

  /**
   * Initialize from serialized information.
   */
  ElementImpl.forSerialized(this._enclosingElement);

  /**
   * The length of the element's code, or `null` if the element is synthetic.
   */
  int get codeLength => _codeLength;

  /**
   * The offset of the beginning of the element's code in the file that contains
   * the element, or `null` if the element is synthetic.
   */
  int get codeOffset => _codeOffset;

  @override
  AnalysisContext get context {
    if (_enclosingElement == null) {
      return null;
    }
    return _enclosingElement.context;
  }

  @override
  String get displayName => _name;

  @override
  String get documentationComment => _docComment;

  /**
   * The documentation comment source for this element.
   */
  void set documentationComment(String doc) {
    assert(!isResynthesized);
    _docComment = doc?.replaceAll('\r\n', '\n');
  }

  @override
  Element get enclosingElement => _enclosingElement;

  /**
   * Set the enclosing element of this element to the given [element].
   *
   * Throws [FrozenHashCodeException] if the hashCode can't be changed.
   */
  void set enclosingElement(Element element) {
    _enclosingElement = element as ElementImpl;
  }

  /**
   * Return the enclosing unit element (which might be the same as `this`), or
   * `null` if this element is not contained in any compilation unit.
   */
  CompilationUnitElementImpl get enclosingUnit {
    return _enclosingElement?.enclosingUnit;
  }

  @override
  int get hashCode {
    // TODO: We might want to re-visit this optimization in the future.
    // We cache the hash code value as this is a very frequently called method.
    if (_cachedHashCode == null) {
      _cachedHashCode = location.hashCode;
    }
    return _cachedHashCode;
  }

  /**
   * Return an identifier that uniquely identifies this element among the
   * children of this element's parent.
   */
  String get identifier => name;

  @override
  bool get isDeprecated {
    for (ElementAnnotation annotation in metadata) {
      if (annotation.isDeprecated) {
        return true;
      }
    }
    return false;
  }

  @override
  bool get isFactory {
    for (ElementAnnotation annotation in metadata) {
      if (annotation.isFactory) {
        return true;
      }
    }
    return false;
  }

  @override
  bool get isJS {
    for (ElementAnnotation annotation in metadata) {
      if (annotation.isJS) {
        return true;
      }
    }
    return false;
  }

  @override
  bool get isOverride {
    for (ElementAnnotation annotation in metadata) {
      if (annotation.isOverride) {
        return true;
      }
    }
    return false;
  }

  @override
  bool get isPrivate {
    String name = displayName;
    if (name == null) {
      return true;
    }
    return Identifier.isPrivateName(name);
  }

  @override
  bool get isProtected {
    for (ElementAnnotation annotation in metadata) {
      if (annotation.isProtected) {
        return true;
      }
    }
    return false;
  }

  @override
  bool get isPublic => !isPrivate;

  @override
  bool get isRequired {
    for (ElementAnnotation annotation in metadata) {
      if (annotation.isRequired) {
        return true;
      }
    }
    return false;
  }

  /**
   * Return `true` if this element is resynthesized from a summary.
   */
  bool get isResynthesized => enclosingUnit?.resynthesizerContext != null;

  @override
  bool get isSynthetic => hasModifier(Modifier.SYNTHETIC);

  /**
   * Set whether this element is synthetic.
   */
  void set isSynthetic(bool isSynthetic) {
    setModifier(Modifier.SYNTHETIC, isSynthetic);
  }

  @override
  LibraryElement get library =>
      getAncestor((element) => element is LibraryElement);

  @override
  Source get librarySource => library?.source;

  @override
  ElementLocation get location {
    if (_cachedLocation == null) {
      if (library == null) {
        return new ElementLocationImpl.con1(this);
      }
      _cachedLocation = new ElementLocationImpl.con1(this);
    }
    return _cachedLocation;
  }

  List<ElementAnnotation> get metadata {
    return _metadata ?? const <ElementAnnotation>[];
  }

  void set metadata(List<ElementAnnotation> metadata) {
    assert(!isResynthesized);
    _metadata = metadata;
  }

  @override
  String get name => _name;

  /**
   * Changes the name of this element.
   *
   * Throws [FrozenHashCodeException] if the hashCode can't be changed.
   */
  void set name(String name) {
    this._name = name;
  }

  @override
  int get nameLength => displayName != null ? displayName.length : 0;

  @override
  int get nameOffset => _nameOffset;

  /**
   * Sets the offset of the name of this element in the file that contains the
   * declaration of this element.
   *
   * Throws [FrozenHashCodeException] if the hashCode can't be changed.
   */
  void set nameOffset(int offset) {
    _nameOffset = offset;
  }

  @override
  Source get source {
    if (_enclosingElement == null) {
      return null;
    }
    return _enclosingElement.source;
  }

  /**
   * Return the context to resolve type parameters in, or `null` if neither this
   * element nor any of its ancestors is of a kind that can declare type
   * parameters.
   */
  TypeParameterizedElementMixin get typeParameterContext {
    return _enclosingElement?.typeParameterContext;
  }

  @override
  CompilationUnit get unit => context.resolveCompilationUnit(source, library);

  @override
  bool operator ==(Object object) {
    if (identical(this, object)) {
      return true;
    }
    return object is Element &&
        object.kind == kind &&
        object.location == location;
  }

  /**
   * Append to the given [buffer] a comma-separated list of the names of the
   * types of this element and every enclosing element.
   */
  void appendPathTo(StringBuffer buffer) {
    Element element = this;
    while (element != null) {
      if (element != this) {
        buffer.write(', ');
      }
      buffer.write(element.runtimeType);
      String name = element.name;
      if (name != null) {
        buffer.write(' (');
        buffer.write(name);
        buffer.write(')');
      }
      element = element.enclosingElement;
    }
  }

  /**
   * Append a textual representation of this element to the given [buffer].
   */
  void appendTo(StringBuffer buffer) {
    if (_name == null) {
      buffer.write("<unnamed ");
      buffer.write(runtimeType.toString());
      buffer.write(">");
    } else {
      buffer.write(_name);
    }
  }

  @override
  String computeDocumentationComment() => documentationComment;

  @override
  AstNode computeNode() => getNodeMatching((node) => node is AstNode);

  /**
   * Set this element as the enclosing element for given [element].
   */
  void encloseElement(ElementImpl element) {
    element.enclosingElement = this;
  }

  @override
  Element/*=E*/ getAncestor/*<E extends Element >*/(
      Predicate<Element> predicate) {
    Element ancestor = _enclosingElement;
    while (ancestor != null && !predicate(ancestor)) {
      ancestor = ancestor.enclosingElement;
    }
    return ancestor as Element/*=E*/;
  }

  /**
   * Return the child of this element that is uniquely identified by the given
   * [identifier], or `null` if there is no such child.
   */
  ElementImpl getChild(String identifier) => null;

  @override
  String getExtendedDisplayName(String shortName) {
    if (shortName == null) {
      shortName = displayName;
    }
    Source source = this.source;
    if (source != null) {
      return "$shortName (${source.fullName})";
    }
    return shortName;
  }

  /**
   * Return the resolved [AstNode] of the given type enclosing [getNameOffset].
   */
  AstNode getNodeMatching(Predicate<AstNode> predicate) {
    CompilationUnit unit = this.unit;
    if (unit == null) {
      return null;
    }
    int offset = nameOffset;
    AstNode node = new NodeLocator(offset).searchWithin(unit);
    if (node == null) {
      return null;
    }
    return node.getAncestor(predicate);
  }

  /**
   * Return `true` if this element has the given [modifier] associated with it.
   */
  bool hasModifier(Modifier modifier) =>
      BooleanArray.get(_modifiers, modifier.ordinal);

  @override
  bool isAccessibleIn(LibraryElement library) {
    if (Identifier.isPrivateName(name)) {
      return library == this.library;
    }
    return true;
  }

  /**
   * Use the given [visitor] to visit all of the [children] in the given array.
   */
  void safelyVisitChildren(List<Element> children, ElementVisitor visitor) {
    if (children != null) {
      for (Element child in children) {
        child.accept(visitor);
      }
    }
  }

  /**
   * Set the code range for this element.
   */
  void setCodeRange(int offset, int length) {
    assert(!isResynthesized);
    _codeOffset = offset;
    _codeLength = length;
  }

  /**
   * Set whether the given [modifier] is associated with this element to
   * correspond to the given [value].
   */
  void setModifier(Modifier modifier, bool value) {
    _modifiers = BooleanArray.set(_modifiers, modifier.ordinal, value);
  }

  @override
  String toString() {
    StringBuffer buffer = new StringBuffer();
    appendTo(buffer);
    return buffer.toString();
  }

  @override
  void visitChildren(ElementVisitor visitor) {
    // There are no children to visit
  }

  /**
   * Return annotations for the given [unlinkedConsts] in the [unit].
   */
  List<ElementAnnotation> _buildAnnotations(
      CompilationUnitElementImpl unit, List<UnlinkedExpr> unlinkedConsts) {
    int length = unlinkedConsts.length;
    if (length != 0) {
      List<ElementAnnotation> annotations = new List<ElementAnnotation>(length);
      ResynthesizerContext context = unit.resynthesizerContext;
      for (int i = 0; i < length; i++) {
        annotations[i] = context.buildAnnotation(this, unlinkedConsts[i]);
      }
      return annotations;
    } else {
      return const <ElementAnnotation>[];
    }
  }

  /**
   * If the element associated with the given [type] is a generic function type
   * element, then make it a child of this element. Return the [type] as a
   * convenience.
   */
  DartType _checkElementOfType(DartType type) {
    Element element = type?.element;
    if (element is GenericFunctionTypeElementImpl &&
        element.enclosingElement == null) {
      element.enclosingElement = this;
    }
    return type;
  }

  /**
   * If the given [type] is a generic function type, then the element associated
   * with the type is implicitly a child of this element and should be visted by
   * the given [visitor].
   */
  void _safelyVisitPossibleChild(DartType type, ElementVisitor visitor) {
    Element element = type?.element;
    if (element is GenericFunctionTypeElementImpl) {
      element.accept(visitor);
    }
  }

  static int findElementIndexUsingIdentical(List items, Object item) {
    int length = items.length;
    for (int i = 0; i < length; i++) {
      if (identical(items[i], item)) {
        return i;
      }
    }
    throw new StateError('Unable to find $item in $items');
  }
}

/**
 * A concrete implementation of an [ElementLocation].
 */
class ElementLocationImpl implements ElementLocation {
  /**
   * The character used to separate components in the encoded form.
   */
  static int _SEPARATOR_CHAR = 0x3B;

  /**
   * The path to the element whose location is represented by this object.
   */
  List<String> _components;

  /**
   * The object managing [indexKeyId] and [indexLocationId].
   */
  Object indexOwner;

  /**
   * A cached id of this location in index.
   */
  int indexKeyId;

  /**
   * A cached id of this location in index.
   */
  int indexLocationId;

  /**
   * Initialize a newly created location to represent the given [element].
   */
  ElementLocationImpl.con1(Element element) {
    List<String> components = new List<String>();
    Element ancestor = element;
    while (ancestor != null) {
      components.insert(0, (ancestor as ElementImpl).identifier);
      ancestor = ancestor.enclosingElement;
    }
    this._components = components;
  }

  /**
   * Initialize a newly created location from the given [encoding].
   */
  ElementLocationImpl.con2(String encoding) {
    this._components = _decode(encoding);
  }

  /**
   * Initialize a newly created location from the given [components].