pkg/analyzer/lib/src/dart/ast/ast.dart

// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'dart:collection';

import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/ast/syntactic_entity.dart';
import 'package:analyzer/dart/ast/token.dart';
import 'package:analyzer/dart/element/element.dart';
import 'package:analyzer/dart/element/type.dart';
import 'package:analyzer/error/error.dart';
import 'package:analyzer/error/listener.dart';
import 'package:analyzer/exception/exception.dart';
import 'package:analyzer/src/dart/ast/token.dart';
import 'package:analyzer/src/dart/ast/utilities.dart';
import 'package:analyzer/src/dart/element/element.dart';
import 'package:analyzer/src/dart/element/type.dart';
import 'package:analyzer/src/error/codes.dart';
import 'package:analyzer/src/generated/engine.dart' show AnalysisEngine;
import 'package:analyzer/src/generated/engine.dart';
import 'package:analyzer/src/generated/java_engine.dart';
import 'package:analyzer/src/generated/parser.dart';
import 'package:analyzer/src/generated/resolver.dart';
import 'package:analyzer/src/generated/source.dart' show LineInfo, Source;
import 'package:analyzer/src/generated/utilities_dart.dart';
import 'package:analyzer/src/fasta/token_utils.dart' as util show findPrevious;

/**
 * Two or more string literals that are implicitly concatenated because of being
 * adjacent (separated only by whitespace).
 *
 * While the grammar only allows adjacent strings when all of the strings are of
 * the same kind (single line or multi-line), this class doesn't enforce that
 * restriction.
 *
 *    adjacentStrings ::=
 *        [StringLiteral] [StringLiteral]+
 */
class AdjacentStringsImpl extends StringLiteralImpl implements AdjacentStrings {
  /**
   * The strings that are implicitly concatenated.
   */
  NodeList<StringLiteral> _strings;

  /**
   * Initialize a newly created list of adjacent strings. To be syntactically
   * valid, the list of [strings] must contain at least two elements.
   */
  AdjacentStringsImpl(List<StringLiteral> strings) {
    _strings = new NodeListImpl<StringLiteral>(this, strings);
  }

  @override
  Token get beginToken => _strings.beginToken;

  @override
  Iterable<SyntacticEntity> get childEntities =>
      new ChildEntities()..addAll(_strings);

  @override
  Token get endToken => _strings.endToken;

  @override
  NodeList<StringLiteral> get strings => _strings;

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitAdjacentStrings(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _strings.accept(visitor);
  }

  @override
  void _appendStringValue(StringBuffer buffer) {
    int length = strings.length;
    for (int i = 0; i < length; i++) {
      StringLiteralImpl stringLiteral = strings[i];
      stringLiteral._appendStringValue(buffer);
    }
  }
}

/**
 * An AST node that can be annotated with both a documentation comment and a
 * list of annotations.
 */
abstract class AnnotatedNodeImpl extends AstNodeImpl implements AnnotatedNode {
  /**
   * The documentation comment associated with this node, or `null` if this node
   * does not have a documentation comment associated with it.
   */
  CommentImpl _comment;

  /**
   * The annotations associated with this node.
   */
  NodeList<Annotation> _metadata;

  /**
   * Initialize a newly created annotated node. Either or both of the [comment]
   * and [metadata] can be `null` if the node does not have the corresponding
   * attribute.
   */
  AnnotatedNodeImpl(CommentImpl comment, List<Annotation> metadata) {
    _comment = _becomeParentOf(comment);
    _metadata = new NodeListImpl<Annotation>(this, metadata);
  }

  @override
  Token get beginToken {
    if (_comment == null) {
      if (_metadata.isEmpty) {
        return firstTokenAfterCommentAndMetadata;
      }
      return _metadata.beginToken;
    } else if (_metadata.isEmpty) {
      return _comment.beginToken;
    }
    Token commentToken = _comment.beginToken;
    Token metadataToken = _metadata.beginToken;
    if (commentToken.offset < metadataToken.offset) {
      return commentToken;
    }
    return metadataToken;
  }

  @override
  Comment get documentationComment => _comment;

  @override
  void set documentationComment(Comment comment) {
    _comment = _becomeParentOf(comment as CommentImpl);
  }

  @override
  NodeList<Annotation> get metadata => _metadata;

  @override
  List<AstNode> get sortedCommentAndAnnotations {
    return <AstNode>[]
      ..add(_comment)
      ..addAll(_metadata)
      ..sort(AstNode.LEXICAL_ORDER);
  }

  /**
   * Return a holder of child entities that subclasses can add to.
   */
  ChildEntities get _childEntities {
    ChildEntities result = new ChildEntities();
    if (_commentIsBeforeAnnotations()) {
      result
        ..add(_comment)
        ..addAll(_metadata);
    } else {
      result.addAll(sortedCommentAndAnnotations);
    }
    return result;
  }

  @override
  void visitChildren(AstVisitor visitor) {
    if (_commentIsBeforeAnnotations()) {
      _comment?.accept(visitor);
      _metadata.accept(visitor);
    } else {
      List<AstNode> children = sortedCommentAndAnnotations;
      int length = children.length;
      for (int i = 0; i < length; i++) {
        children[i].accept(visitor);
      }
    }
  }

  /**
   * Return `true` if there are no annotations before the comment. Note that a
   * result of `true` does not imply that there is a comment, nor that there are
   * annotations associated with this node.
   */
  bool _commentIsBeforeAnnotations() {
    if (_comment == null || _metadata.isEmpty) {
      return true;
    }
    Annotation firstAnnotation = _metadata[0];
    return _comment.offset < firstAnnotation.offset;
  }
}

/**
 * An annotation that can be associated with an AST node.
 *
 *    metadata ::=
 *        annotation*
 *
 *    annotation ::=
 *        '@' [Identifier] ('.' [SimpleIdentifier])? [ArgumentList]?
 */
class AnnotationImpl extends AstNodeImpl implements Annotation {
  /**
   * The at sign that introduced the annotation.
   */
  @override
  Token atSign;

  /**
   * The name of the class defining the constructor that is being invoked or the
   * name of the field that is being referenced.
   */
  IdentifierImpl _name;

  /**
   * The period before the constructor name, or `null` if this annotation is not
   * the invocation of a named constructor.
   */
  @override
  Token period;

  /**
   * The name of the constructor being invoked, or `null` if this annotation is
   * not the invocation of a named constructor.
   */
  SimpleIdentifierImpl _constructorName;

  /**
   * The arguments to the constructor being invoked, or `null` if this
   * annotation is not the invocation of a constructor.
   */
  ArgumentListImpl _arguments;

  /**
   * The element associated with this annotation, or `null` if the AST structure
   * has not been resolved or if this annotation could not be resolved.
   */
  Element _element;

  /**
   * The element annotation representing this annotation in the element model.
   */
  @override
  ElementAnnotation elementAnnotation;

  /**
   * Initialize a newly created annotation. Both the [period] and the
   * [constructorName] can be `null` if the annotation is not referencing a
   * named constructor. The [arguments] can be `null` if the annotation is not
   * referencing a constructor.
   */
  AnnotationImpl(this.atSign, IdentifierImpl name, this.period,
      SimpleIdentifierImpl constructorName, ArgumentListImpl arguments) {
    _name = _becomeParentOf(name);
    _constructorName = _becomeParentOf(constructorName);
    _arguments = _becomeParentOf(arguments);
  }

  @override
  ArgumentList get arguments => _arguments;

  @override
  void set arguments(ArgumentList arguments) {
    _arguments = _becomeParentOf(arguments as ArgumentListImpl);
  }

  @override
  Token get beginToken => atSign;

  @override
  Iterable<SyntacticEntity> get childEntities => new ChildEntities()
    ..add(atSign)
    ..add(_name)
    ..add(period)
    ..add(_constructorName)
    ..add(_arguments);

  @override
  SimpleIdentifier get constructorName => _constructorName;

  @override
  void set constructorName(SimpleIdentifier name) {
    _constructorName = _becomeParentOf(name as SimpleIdentifierImpl);
  }

  @override
  Element get element {
    if (_element != null) {
      return _element;
    } else if (_constructorName == null && _name != null) {
      return _name.staticElement;
    }
    return null;
  }

  @override
  void set element(Element element) {
    _element = element;
  }

  @override
  Token get endToken {
    if (_arguments != null) {
      return _arguments.endToken;
    } else if (_constructorName != null) {
      return _constructorName.endToken;
    }
    return _name.endToken;
  }

  @override
  Identifier get name => _name;

  @override
  void set name(Identifier name) {
    _name = _becomeParentOf(name as IdentifierImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitAnnotation(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _name?.accept(visitor);
    _constructorName?.accept(visitor);
    _arguments?.accept(visitor);
  }
}

/**
 * A list of arguments in the invocation of an executable element (that is, a
 * function, method, or constructor).
 *
 *    argumentList ::=
 *        '(' arguments? ')'
 *
 *    arguments ::=
 *        [NamedExpression] (',' [NamedExpression])*
 *      | [Expression] (',' [Expression])* (',' [NamedExpression])*
 */
class ArgumentListImpl extends AstNodeImpl implements ArgumentList {
  /**
   * The left parenthesis.
   */
  @override
  Token leftParenthesis;

  /**
   * The expressions producing the values of the arguments.
   */
  NodeList<Expression> _arguments;

  /**
   * The right parenthesis.
   */
  @override
  Token rightParenthesis;

  /**
   * A list containing the elements representing the parameters corresponding to
   * each of the arguments in this list, or `null` if the AST has not been
   * resolved or if the function or method being invoked could not be determined
   * based on static type information. The list must be the same length as the
   * number of arguments, but can contain `null` entries if a given argument
   * does not correspond to a formal parameter.
   */
  List<ParameterElement> _correspondingStaticParameters;

  /**
   * A list containing the elements representing the parameters corresponding to
   * each of the arguments in this list, or `null` if the AST has not been
   * resolved or if the function or method being invoked could not be determined
   * based on propagated type information. The list must be the same length as
   * the number of arguments, but can contain `null` entries if a given argument
   * does not correspond to a formal parameter.
   */
  List<ParameterElement> _correspondingPropagatedParameters;

  /**
   * Initialize a newly created list of arguments. The list of [arguments] can
   * be `null` if there are no arguments.
   */
  ArgumentListImpl(
      this.leftParenthesis, List<Expression> arguments, this.rightParenthesis) {
    _arguments = new NodeListImpl<Expression>(this, arguments);
  }

  @override
  NodeList<Expression> get arguments => _arguments;

  @override
  Token get beginToken => leftParenthesis;

  @override
  // TODO(paulberry): Add commas.
  Iterable<SyntacticEntity> get childEntities => new ChildEntities()
    ..add(leftParenthesis)
    ..addAll(_arguments)
    ..add(rightParenthesis);

  List<ParameterElement> get correspondingPropagatedParameters =>
      _correspondingPropagatedParameters;

  @override
  void set correspondingPropagatedParameters(
      List<ParameterElement> parameters) {
    if (parameters != null && parameters.length != _arguments.length) {
      throw new ArgumentError(
          "Expected ${_arguments.length} parameters, not ${parameters.length}");
    }
    _correspondingPropagatedParameters = parameters;
  }

  List<ParameterElement> get correspondingStaticParameters =>
      _correspondingStaticParameters;

  @override
  void set correspondingStaticParameters(List<ParameterElement> parameters) {
    if (parameters != null && parameters.length != _arguments.length) {
      throw new ArgumentError(
          "Expected ${_arguments.length} parameters, not ${parameters.length}");
    }
    _correspondingStaticParameters = parameters;
  }

  @override
  Token get endToken => rightParenthesis;

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitArgumentList(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _arguments.accept(visitor);
  }

  /**
   * If
   * * the given [expression] is a child of this list,
   * * the AST structure has been resolved,
   * * the function being invoked is known based on propagated type information,
   *   and
   * * the expression corresponds to one of the parameters of the function being
   *   invoked,
   * then return the parameter element representing the parameter to which the
   * value of the given expression will be bound. Otherwise, return `null`.
   */
  ParameterElement _getPropagatedParameterElementFor(Expression expression) {
    if (_correspondingPropagatedParameters == null ||
        _correspondingPropagatedParameters.length != _arguments.length) {
      // Either the AST structure has not been resolved, the invocation of which
      // this list is a part could not be resolved, or the argument list was
      // modified after the parameters were set.
      return null;
    }
    int index = _arguments.indexOf(expression);
    if (index < 0) {
      // The expression isn't a child of this node.
      return null;
    }
    return _correspondingPropagatedParameters[index];
  }

  /**
   * If
   * * the given [expression] is a child of this list,
   * * the AST structure has been resolved,
   * * the function being invoked is known based on static type information, and
   * * the expression corresponds to one of the parameters of the function being
   *   invoked,
   * then return the parameter element representing the parameter to which the
   * value of the given expression will be bound. Otherwise, return `null`.
   */
  ParameterElement _getStaticParameterElementFor(Expression expression) {
    if (_correspondingStaticParameters == null ||
        _correspondingStaticParameters.length != _arguments.length) {
      // Either the AST structure has not been resolved, the invocation of which
      // this list is a part could not be resolved, or the argument list was
      // modified after the parameters were set.
      return null;
    }
    int index = _arguments.indexOf(expression);
    if (index < 0) {
      // The expression isn't a child of this node.
      return null;
    }
    return _correspondingStaticParameters[index];
  }
}

/**
 * An as expression.
 *
 *    asExpression ::=
 *        [Expression] 'as' [TypeName]
 */
class AsExpressionImpl extends ExpressionImpl implements AsExpression {
  /**
   * The expression used to compute the value being cast.
   */
  ExpressionImpl _expression;

  /**
   * The 'as' operator.
   */
  @override
  Token asOperator;

  /**
   * The type being cast to.
   */
  TypeAnnotationImpl _type;

  /**
   * Initialize a newly created as expression.
   */
  AsExpressionImpl(
      ExpressionImpl expression, this.asOperator, TypeAnnotationImpl type) {
    _expression = _becomeParentOf(expression);
    _type = _becomeParentOf(type);
  }

  @override
  Token get beginToken => _expression.beginToken;

  @override
  Iterable<SyntacticEntity> get childEntities =>
      new ChildEntities()..add(_expression)..add(asOperator)..add(_type);

  @override
  Token get endToken => _type.endToken;

  @override
  Expression get expression => _expression;

  @override
  void set expression(Expression expression) {
    _expression = _becomeParentOf(expression as ExpressionImpl);
  }

  @override
  int get precedence => 7;

  @override
  TypeAnnotation get type => _type;

  @override
  void set type(TypeAnnotation type) {
    _type = _becomeParentOf(type as TypeAnnotationImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitAsExpression(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _expression?.accept(visitor);
    _type?.accept(visitor);
  }
}

/**
 * An assert in the initializer list of a constructor.
 *
 *    assertInitializer ::=
 *        'assert' '(' [Expression] (',' [Expression])? ')'
 */
class AssertInitializerImpl extends ConstructorInitializerImpl
    implements AssertInitializer {
  @override
  Token assertKeyword;

  @override
  Token leftParenthesis;

  /**
   * The condition that is being asserted to be `true`.
   */
  ExpressionImpl _condition;

  @override
  Token comma;

  /**
   * The message to report if the assertion fails, or `null` if no message was
   * supplied.
   */
  ExpressionImpl _message;

  @override
  Token rightParenthesis;

  /**
   * Initialize a newly created assert initializer.
   */
  AssertInitializerImpl(
      this.assertKeyword,
      this.leftParenthesis,
      ExpressionImpl condition,
      this.comma,
      ExpressionImpl message,
      this.rightParenthesis) {
    _condition = _becomeParentOf(condition);
    _message = _becomeParentOf(message);
  }

  @override
  Token get beginToken => assertKeyword;

  @override
  Iterable<SyntacticEntity> get childEntities => new ChildEntities()
    ..add(assertKeyword)
    ..add(leftParenthesis)
    ..add(_condition)
    ..add(comma)
    ..add(_message)
    ..add(rightParenthesis);

  @override
  Expression get condition => _condition;

  @override
  void set condition(Expression condition) {
    _condition = _becomeParentOf(condition as ExpressionImpl);
  }

  @override
  Token get endToken => rightParenthesis;

  @override
  Expression get message => _message;

  @override
  void set message(Expression expression) {
    _message = _becomeParentOf(expression as ExpressionImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitAssertInitializer(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _condition?.accept(visitor);
    message?.accept(visitor);
  }
}

/**
 * An assert statement.
 *
 *    assertStatement ::=
 *        'assert' '(' [Expression] ')' ';'
 */
class AssertStatementImpl extends StatementImpl implements AssertStatement {
  @override
  Token assertKeyword;

  @override
  Token leftParenthesis;

  /**
   * The condition that is being asserted to be `true`.
   */
  ExpressionImpl _condition;

  @override
  Token comma;

  /**
   * The message to report if the assertion fails, or `null` if no message was
   * supplied.
   */
  ExpressionImpl _message;

  @override
  Token rightParenthesis;

  @override
  Token semicolon;

  /**
   * Initialize a newly created assert statement.
   */
  AssertStatementImpl(
      this.assertKeyword,
      this.leftParenthesis,
      ExpressionImpl condition,
      this.comma,
      ExpressionImpl message,
      this.rightParenthesis,
      this.semicolon) {
    _condition = _becomeParentOf(condition);
    _message = _becomeParentOf(message);
  }

  @override
  Token get beginToken => assertKeyword;

  @override
  Iterable<SyntacticEntity> get childEntities => new ChildEntities()
    ..add(assertKeyword)
    ..add(leftParenthesis)
    ..add(_condition)
    ..add(comma)
    ..add(_message)
    ..add(rightParenthesis)
    ..add(semicolon);

  @override
  Expression get condition => _condition;

  @override
  void set condition(Expression condition) {
    _condition = _becomeParentOf(condition as ExpressionImpl);
  }

  @override
  Token get endToken => semicolon;

  @override
  Expression get message => _message;

  @override
  void set message(Expression expression) {
    _message = _becomeParentOf(expression as ExpressionImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitAssertStatement(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _condition?.accept(visitor);
    message?.accept(visitor);
  }
}

/**
 * An assignment expression.
 *
 *    assignmentExpression ::=
 *        [Expression] operator [Expression]
 */
class AssignmentExpressionImpl extends ExpressionImpl
    implements AssignmentExpression {
  /**
   * The expression used to compute the left hand side.
   */
  ExpressionImpl _leftHandSide;

  /**
   * The assignment operator being applied.
   */
  @override
  Token operator;

  /**
   * The expression used to compute the right hand side.
   */
  ExpressionImpl _rightHandSide;

  /**
   * The element associated with the operator based on the static type of the
   * left-hand-side, or `null` if the AST structure has not been resolved, if
   * the operator is not a compound operator, or if the operator could not be
   * resolved.
   */
  @override
  MethodElement staticElement;

  /**
   * The element associated with the operator based on the propagated type of
   * the left-hand-side, or `null` if the AST structure has not been resolved,
   * if the operator is not a compound operator, or if the operator could not be
   * resolved.
   */
  @override
  MethodElement propagatedElement;

  /**
   * Initialize a newly created assignment expression.
   */
  AssignmentExpressionImpl(ExpressionImpl leftHandSide, this.operator,
      ExpressionImpl rightHandSide) {
    if (leftHandSide == null || rightHandSide == null) {
      String message;
      if (leftHandSide == null) {
        if (rightHandSide == null) {
          message = "Both the left-hand and right-hand sides are null";
        } else {
          message = "The left-hand size is null";
        }
      } else {
        message = "The right-hand size is null";
      }
      AnalysisEngine.instance.logger.logError(
          message, new CaughtException(new AnalysisException(message), null));
    }
    _leftHandSide = _becomeParentOf(leftHandSide);
    _rightHandSide = _becomeParentOf(rightHandSide);
  }

  @override
  Token get beginToken => _leftHandSide.beginToken;

  @override
  MethodElement get bestElement {
    MethodElement element = propagatedElement;
    if (element == null) {
      element = staticElement;
    }
    return element;
  }

  @override
  Iterable<SyntacticEntity> get childEntities => new ChildEntities()
    ..add(_leftHandSide)
    ..add(operator)
    ..add(_rightHandSide);

  @override
  Token get endToken => _rightHandSide.endToken;

  @override
  Expression get leftHandSide => _leftHandSide;

  @override
  void set leftHandSide(Expression expression) {
    _leftHandSide = _becomeParentOf(expression as ExpressionImpl);
  }

  @override
  int get precedence => 1;

  @override
  Expression get rightHandSide => _rightHandSide;

  @override
  void set rightHandSide(Expression expression) {
    _rightHandSide = _becomeParentOf(expression as ExpressionImpl);
  }

  /**
   * If the AST structure has been resolved, and the function being invoked is
   * known based on propagated type information, then return the parameter
   * element representing the parameter to which the value of the right operand
   * will be bound. Otherwise, return `null`.
   */
  ParameterElement get _propagatedParameterElementForRightHandSide {
    ExecutableElement executableElement = null;
    if (propagatedElement != null) {
      executableElement = propagatedElement;
    } else {
      Expression left = _leftHandSide;
      if (left is Identifier) {
        Element leftElement = left.propagatedElement;
        if (leftElement is ExecutableElement) {
          executableElement = leftElement;
        }
      } else if (left is PropertyAccess) {
        Element leftElement = left.propertyName.propagatedElement;
        if (leftElement is ExecutableElement) {
          executableElement = leftElement;
        }
      }
    }
    if (executableElement == null) {
      return null;
    }
    List<ParameterElement> parameters = executableElement.parameters;
    if (parameters.length < 1) {
      return null;
    }
    return parameters[0];
  }

  /**
   * If the AST structure has been resolved, and the function being invoked is
   * known based on static type information, then return the parameter element
   * representing the parameter to which the value of the right operand will be
   * bound. Otherwise, return `null`.
   */
  ParameterElement get _staticParameterElementForRightHandSide {
    ExecutableElement executableElement = null;
    if (staticElement != null) {
      executableElement = staticElement;
    } else {
      Expression left = _leftHandSide;
      if (left is Identifier) {
        Element leftElement = left.staticElement;
        if (leftElement is ExecutableElement) {
          executableElement = leftElement;
        }
      } else if (left is PropertyAccess) {
        Element leftElement = left.propertyName.staticElement;
        if (leftElement is ExecutableElement) {
          executableElement = leftElement;
        }
      }
    }
    if (executableElement == null) {
      return null;
    }
    List<ParameterElement> parameters = executableElement.parameters;
    if (parameters.length < 1) {
      return null;
    }
    return parameters[0];
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitAssignmentExpression(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _leftHandSide?.accept(visitor);
    _rightHandSide?.accept(visitor);
  }
}

/**
 * A node in the AST structure for a Dart program.
 */
abstract class AstNodeImpl implements AstNode {
  /**
   * The parent of the node, or `null` if the node is the root of an AST
   * structure.
   */
  AstNode _parent;

  /**
   * A table mapping the names of properties to their values, or `null` if this
   * node does not have any properties associated with it.
   */
  Map<String, Object> _propertyMap;

  @override
  int get end => offset + length;

  @override
  bool get isSynthetic => false;

  @override
  int get length {
    Token beginToken = this.beginToken;
    Token endToken = this.endToken;
    if (beginToken == null || endToken == null) {
      return -1;
    }
    return endToken.offset + endToken.length - beginToken.offset;
  }

  @override
  int get offset {
    Token beginToken = this.beginToken;
    if (beginToken == null) {
      return -1;
    }
    return beginToken.offset;
  }

  @override
  AstNode get parent => _parent;

  @override
  AstNode get root {
    AstNode root = this;
    AstNode parent = this.parent;
    while (parent != null) {
      root = parent;
      parent = root.parent;
    }
    return root;
  }

  @override
  E getAncestor<E extends AstNode>(Predicate<AstNode> predicate) {
    // TODO(brianwilkerson) It is a bug that this method can return `this`.
    AstNode node = this;
    while (node != null && !predicate(node)) {
      node = node.parent;
    }
    return node as E;
  }

  @override
  E getProperty<E>(String name) {
    if (_propertyMap == null) {
      return null;
    }
    return _propertyMap[name] as E;
  }

  Token findPrevious(Token target) =>
      util.findPrevious(beginToken, target) ?? parent?.findPrevious(target);

  @override
  void setProperty(String name, Object value) {
    if (value == null) {
      if (_propertyMap != null) {
        _propertyMap.remove(name);
        if (_propertyMap.isEmpty) {
          _propertyMap = null;
        }
      }
    } else {
      if (_propertyMap == null) {
        _propertyMap = new HashMap<String, Object>();
      }
      _propertyMap[name] = value;
    }
  }

  @override
  String toSource() {
    StringBuffer buffer = new StringBuffer();
    accept(new ToSourceVisitor2(buffer));
    return buffer.toString();
  }

  @override
  String toString() => toSource();

  /**
   * Make this node the parent of the given [child] node. Return the child node.
   */
  T _becomeParentOf<T extends AstNodeImpl>(T child) {
    if (child != null) {
      child._parent = this;
    }
    return child;
  }
}

/**
 * An await expression.
 *
 *    awaitExpression ::=
 *        'await' [Expression]
 */
class AwaitExpressionImpl extends ExpressionImpl implements AwaitExpression {
  /**
   * The 'await' keyword.
   */
  @override
  Token awaitKeyword;

  /**
   * The expression whose value is being waited on.
   */
  ExpressionImpl _expression;

  /**
   * Initialize a newly created await expression.
   */
  AwaitExpressionImpl(this.awaitKeyword, ExpressionImpl expression) {
    _expression = _becomeParentOf(expression);
  }

  @override
  Token get beginToken {
    if (awaitKeyword != null) {
      return awaitKeyword;
    }
    return _expression.beginToken;
  }

  @override
  Iterable<SyntacticEntity> get childEntities =>
      new ChildEntities()..add(awaitKeyword)..add(_expression);

  @override
  Token get endToken => _expression.endToken;

  @override
  Expression get expression => _expression;

  @override
  void set expression(Expression expression) {
    _expression = _becomeParentOf(expression as ExpressionImpl);
  }

  @override
  int get precedence => 0;

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitAwaitExpression(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _expression?.accept(visitor);
  }
}

/**
 * A binary (infix) expression.
 *
 *    binaryExpression ::=
 *        [Expression] [Token] [Expression]
 */
class BinaryExpressionImpl extends ExpressionImpl implements BinaryExpression {
  /**
   * The expression used to compute the left operand.
   */
  ExpressionImpl _leftOperand;

  /**
   * The binary operator being applied.
   */
  @override
  Token operator;

  /**
   * The expression used to compute the right operand.
   */
  ExpressionImpl _rightOperand;

  /**
   * The element associated with the operator based on the static type of the
   * left operand, or `null` if the AST structure has not been resolved, if the
   * operator is not user definable, or if the operator could not be resolved.
   */
  @override
  MethodElement staticElement;

  /**
   * The element associated with the operator based on the propagated type of
   * the left operand, or `null` if the AST structure has not been resolved, if
   * the operator is not user definable, or if the operator could not be
   * resolved.
   */
  @override
  MethodElement propagatedElement;

  /**
   * Initialize a newly created binary expression.
   */
  BinaryExpressionImpl(
      ExpressionImpl leftOperand, this.operator, ExpressionImpl rightOperand) {
    _leftOperand = _becomeParentOf(leftOperand);
    _rightOperand = _becomeParentOf(rightOperand);
  }

  @override
  Token get beginToken => _leftOperand.beginToken;

  @override
  MethodElement get bestElement {
    MethodElement element = propagatedElement;
    if (element == null) {
      element = staticElement;
    }
    return element;
  }

  @override
  Iterable<SyntacticEntity> get childEntities =>
      new ChildEntities()..add(_leftOperand)..add(operator)..add(_rightOperand);

  @override
  Token get endToken => _rightOperand.endToken;

  @override
  Expression get leftOperand => _leftOperand;

  @override
  void set leftOperand(Expression expression) {
    _leftOperand = _becomeParentOf(expression as ExpressionImpl);
  }

  @override
  int get precedence => operator.type.precedence;

  @override
  Expression get rightOperand => _rightOperand;

  @override
  void set rightOperand(Expression expression) {
    _rightOperand = _becomeParentOf(expression as ExpressionImpl);
  }

  /**
   * If the AST structure has been resolved, and the function being invoked is
   * known based on propagated type information, then return the parameter
   * element representing the parameter to which the value of the right operand
   * will be bound. Otherwise, return `null`.
   */
  ParameterElement get _propagatedParameterElementForRightOperand {
    if (propagatedElement == null) {
      return null;
    }
    List<ParameterElement> parameters = propagatedElement.parameters;
    if (parameters.length < 1) {
      return null;
    }
    return parameters[0];
  }

  /**
   * If the AST structure has been resolved, and the function being invoked is
   * known based on static type information, then return the parameter element
   * representing the parameter to which the value of the right operand will be
   * bound. Otherwise, return `null`.
   */
  ParameterElement get _staticParameterElementForRightOperand {
    if (staticElement == null) {
      return null;
    }
    List<ParameterElement> parameters = staticElement.parameters;
    if (parameters.length < 1) {
      return null;
    }
    return parameters[0];
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitBinaryExpression(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _leftOperand?.accept(visitor);
    _rightOperand?.accept(visitor);
  }
}

/**
 * A function body that consists of a block of statements.
 *
 *    blockFunctionBody ::=
 *        ('async' | 'async' '*' | 'sync' '*')? [Block]
 */
class BlockFunctionBodyImpl extends FunctionBodyImpl
    implements BlockFunctionBody {
  /**
   * The token representing the 'async' or 'sync' keyword, or `null` if there is
   * no such keyword.
   */
  @override
  Token keyword;

  /**
   * The star optionally following the 'async' or 'sync' keyword, or `null` if
   * there is wither no such keyword or no star.
   */
  @override
  Token star;

  /**
   * The block representing the body of the function.
   */
  BlockImpl _block;

  /**
   * Initialize a newly created function body consisting of a block of
   * statements. The [keyword] can be `null` if there is no keyword specified
   * for the block. The [star] can be `null` if there is no star following the
   * keyword (and must be `null` if there is no keyword).
   */
  BlockFunctionBodyImpl(this.keyword, this.star, BlockImpl block) {
    _block = _becomeParentOf(block);
  }

  @override
  Token get beginToken {
    if (keyword != null) {
      return keyword;
    }
    return _block.beginToken;
  }

  @override
  Block get block => _block;

  @override
  void set block(Block block) {
    _block = _becomeParentOf(block as BlockImpl);
  }

  @override
  Iterable<SyntacticEntity> get childEntities =>
      new ChildEntities()..add(keyword)..add(star)..add(_block);

  @override
  Token get endToken => _block.endToken;

  @override
  bool get isAsynchronous => keyword != null && keyword.lexeme == Parser.ASYNC;

  @override
  bool get isGenerator => star != null;

  @override
  bool get isSynchronous => keyword == null || keyword.lexeme != Parser.ASYNC;

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitBlockFunctionBody(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _block?.accept(visitor);
  }
}

/**
 * A sequence of statements.
 *
 *    block ::=
 *        '{' statement* '}'
 */
class BlockImpl extends StatementImpl implements Block {
  /**
   * The left curly bracket.
   */
  @override
  Token leftBracket;

  /**
   * The statements contained in the block.
   */
  NodeList<Statement> _statements;

  /**
   * The right curly bracket.
   */
  @override
  Token rightBracket;

  /**
   * Initialize a newly created block of code.
   */
  BlockImpl(this.leftBracket, List<Statement> statements, this.rightBracket) {
    _statements = new NodeListImpl<Statement>(this, statements);
  }

  @override
  Token get beginToken => leftBracket;

  @override
  Iterable<SyntacticEntity> get childEntities => new ChildEntities()
    ..add(leftBracket)
    ..addAll(_statements)
    ..add(rightBracket);

  @override
  Token get endToken => rightBracket;

  @override
  NodeList<Statement> get statements => _statements;

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitBlock(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _statements.accept(visitor);
  }
}

/**
 * A boolean literal expression.
 *
 *    booleanLiteral ::=
 *        'false' | 'true'
 */
class BooleanLiteralImpl extends LiteralImpl implements BooleanLiteral {
  /**
   * The token representing the literal.
   */
  @override
  Token literal;

  /**
   * The value of the literal.
   */
  @override
  bool value = false;

  /**
   * Initialize a newly created boolean literal.
   */
  BooleanLiteralImpl(this.literal, this.value);

  @override
  Token get beginToken => literal;

  @override
  Iterable<SyntacticEntity> get childEntities =>
      new ChildEntities()..add(literal);

  @override
  Token get endToken => literal;

  @override
  bool get isSynthetic => literal.isSynthetic;

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitBooleanLiteral(this);

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

/**
 * A break statement.
 *
 *    breakStatement ::=
 *        'break' [SimpleIdentifier]? ';'
 */
class BreakStatementImpl extends StatementImpl implements BreakStatement {
  /**
   * The token representing the 'break' keyword.
   */
  @override
  Token breakKeyword;

  /**
   * The label associated with the statement, or `null` if there is no label.
   */
  SimpleIdentifierImpl _label;

  /**
   * The semicolon terminating the statement.
   */
  @override
  Token semicolon;

  /**
   * The AstNode which this break statement is breaking from.  This will be
   * either a [Statement] (in the case of breaking out of a loop), a
   * [SwitchMember] (in the case of a labeled break statement whose label
   * matches a label on a switch case in an enclosing switch statement), or
   * `null` if the AST has not yet been resolved or if the target could not be
   * resolved. Note that if the source code has errors, the target might be
   * invalid (e.g. trying to break to a switch case).
   */
  @override
  AstNode target;

  /**
   * Initialize a newly created break statement. The [label] can be `null` if
   * there is no label associated with the statement.
   */
  BreakStatementImpl(
      this.breakKeyword, SimpleIdentifierImpl label, this.semicolon) {
    _label = _becomeParentOf(label);
  }

  @override
  Token get beginToken => breakKeyword;

  @override
  Iterable<SyntacticEntity> get childEntities =>
      new ChildEntities()..add(breakKeyword)..add(_label)..add(semicolon);

  @override
  Token get endToken => semicolon;

  @override
  SimpleIdentifier get label => _label;

  @override
  void set label(SimpleIdentifier identifier) {
    _label = _becomeParentOf(identifier as SimpleIdentifierImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitBreakStatement(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _label?.accept(visitor);
  }
}

/**
 * A sequence of cascaded expressions: expressions that share a common target.
 * There are three kinds of expressions that can be used in a cascade
 * expression: [IndexExpression], [MethodInvocation] and [PropertyAccess].
 *
 *    cascadeExpression ::=
 *        [Expression] cascadeSection*
 *
 *    cascadeSection ::=
 *        '..'  (cascadeSelector arguments*) (assignableSelector arguments*)*
 *        (assignmentOperator expressionWithoutCascade)?
 *
 *    cascadeSelector ::=
 *        '[ ' expression '] '
 *      | identifier
 */
class CascadeExpressionImpl extends ExpressionImpl
    implements CascadeExpression {
  /**
   * The target of the cascade sections.
   */
  ExpressionImpl _target;

  /**
   * The cascade sections sharing the common target.
   */
  NodeList<Expression> _cascadeSections;

  /**
   * Initialize a newly created cascade expression. The list of
   * [cascadeSections] must contain at least one element.
   */
  CascadeExpressionImpl(
      ExpressionImpl target, List<Expression> cascadeSections) {
    _target = _becomeParentOf(target);
    _cascadeSections = new NodeListImpl<Expression>(this, cascadeSections);
  }

  @override
  Token get beginToken => _target.beginToken;

  @override
  NodeList<Expression> get cascadeSections => _cascadeSections;

  @override
  Iterable<SyntacticEntity> get childEntities => new ChildEntities()
    ..add(_target)
    ..addAll(_cascadeSections);

  @override
  Token get endToken => _cascadeSections.endToken;

  @override
  int get precedence => 2;

  @override
  Expression get target => _target;

  @override
  void set target(Expression target) {
    _target = _becomeParentOf(target as ExpressionImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitCascadeExpression(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _target?.accept(visitor);
    _cascadeSections.accept(visitor);
  }
}

/**
 * A catch clause within a try statement.
 *
 *    onPart ::=
 *        catchPart [Block]
 *      | 'on' type catchPart? [Block]
 *
 *    catchPart ::=
 *        'catch' '(' [SimpleIdentifier] (',' [SimpleIdentifier])? ')'
 */
class CatchClauseImpl extends AstNodeImpl implements CatchClause {
  /**
   * The token representing the 'on' keyword, or `null` if there is no 'on'
   * keyword.
   */
  @override
  Token onKeyword;

  /**
   * The type of exceptions caught by this catch clause, or `null` if this catch
   * clause catches every type of exception.
   */
  TypeAnnotationImpl _exceptionType;

  /**
   * The token representing the 'catch' keyword, or `null` if there is no
   * 'catch' keyword.
   */
  @override
  Token catchKeyword;

  /**
   * The left parenthesis, or `null` if there is no 'catch' keyword.
   */
  @override
  Token leftParenthesis;

  /**
   * The parameter whose value will be the exception that was thrown, or `null`
   * if there is no 'catch' keyword.
   */
  SimpleIdentifierImpl _exceptionParameter;

  /**
   * The comma separating the exception parameter from the stack trace
   * parameter, or `null` if there is no stack trace parameter.
   */
  @override
  Token comma;

  /**
   * The parameter whose value will be the stack trace associated with the
   * exception, or `null` if there is no stack trace parameter.
   */
  SimpleIdentifierImpl _stackTraceParameter;

  /**
   * The right parenthesis, or `null` if there is no 'catch' keyword.
   */
  @override
  Token rightParenthesis;

  /**
   * The body of the catch block.
   */
  BlockImpl _body;

  /**
   * Initialize a newly created catch clause. The [onKeyword] and
   * [exceptionType] can be `null` if the clause will catch all exceptions. The
   * [comma] and [stackTraceParameter] can be `null` if the stack trace
   * parameter is not defined.
   */
  CatchClauseImpl(
      this.onKeyword,
      TypeAnnotationImpl exceptionType,
      this.catchKeyword,
      this.leftParenthesis,
      SimpleIdentifierImpl exceptionParameter,
      this.comma,
      SimpleIdentifierImpl stackTraceParameter,
      this.rightParenthesis,
      BlockImpl body) {
    _exceptionType = _becomeParentOf(exceptionType);
    _exceptionParameter = _becomeParentOf(exceptionParameter);
    _stackTraceParameter = _becomeParentOf(stackTraceParameter);
    _body = _becomeParentOf(body);
  }

  @override
  Token get beginToken {
    if (onKeyword != null) {
      return onKeyword;
    }
    return catchKeyword;
  }

  @override
  Block get body => _body;

  @override
  void set body(Block block) {
    _body = _becomeParentOf(block as BlockImpl);
  }

  @override
  Iterable<SyntacticEntity> get childEntities => new ChildEntities()
    ..add(onKeyword)
    ..add(_exceptionType)
    ..add(catchKeyword)
    ..add(leftParenthesis)
    ..add(_exceptionParameter)
    ..add(comma)
    ..add(_stackTraceParameter)
    ..add(rightParenthesis)
    ..add(_body);

  @override
  Token get endToken => _body.endToken;

  @override
  SimpleIdentifier get exceptionParameter => _exceptionParameter;

  @override
  void set exceptionParameter(SimpleIdentifier parameter) {
    _exceptionParameter = _becomeParentOf(parameter as SimpleIdentifierImpl);
  }

  @override
  TypeAnnotation get exceptionType => _exceptionType;

  @override
  void set exceptionType(TypeAnnotation exceptionType) {
    _exceptionType = _becomeParentOf(exceptionType as TypeAnnotationImpl);
  }

  @override
  SimpleIdentifier get stackTraceParameter => _stackTraceParameter;

  @override
  void set stackTraceParameter(SimpleIdentifier parameter) {
    _stackTraceParameter = _becomeParentOf(parameter as SimpleIdentifierImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitCatchClause(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _exceptionType?.accept(visitor);
    _exceptionParameter?.accept(visitor);
    _stackTraceParameter?.accept(visitor);
    _body?.accept(visitor);
  }
}

/**
 * Helper class to allow iteration of child entities of an AST node.
 */
class ChildEntities extends Object
    with IterableMixin<SyntacticEntity>
    implements Iterable<SyntacticEntity> {
  /**
   * The list of child entities to be iterated over.
   */
  List<SyntacticEntity> _entities = [];

  @override
  Iterator<SyntacticEntity> get iterator => _entities.iterator;

  /**
   * Add an AST node or token as the next child entity, if it is not null.
   */
  void add(SyntacticEntity entity) {
    if (entity != null) {
      _entities.add(entity);
    }
  }

  /**
   * Add the given items as the next child entities, if [items] is not null.
   */
  void addAll(Iterable<SyntacticEntity> items) {
    if (items != null) {
      _entities.addAll(items);
    }
  }
}

/**
 * The declaration of a class.
 *
 *    classDeclaration ::=
 *        'abstract'? 'class' [SimpleIdentifier] [TypeParameterList]?
 *        ([ExtendsClause] [WithClause]?)?
 *        [ImplementsClause]?
 *        '{' [ClassMember]* '}'
 */
class ClassDeclarationImpl extends NamedCompilationUnitMemberImpl
    implements ClassDeclaration {
  /**
   * The 'abstract' keyword, or `null` if the keyword was absent.
   */
  @override
  Token abstractKeyword;

  /**
   * The token representing the 'class' keyword.
   */
  @override
  Token classKeyword;

  /**
   * The type parameters for the class, or `null` if the class does not have any
   * type parameters.
   */
  TypeParameterListImpl _typeParameters;

  /**
   * The extends clause for the class, or `null` if the class does not extend
   * any other class.
   */
  ExtendsClauseImpl _extendsClause;

  /**
   * The with clause for the class, or `null` if the class does not have a with
   * clause.
   */
  WithClauseImpl _withClause;

  /**
   * The implements clause for the class, or `null` if the class does not
   * implement any interfaces.
   */
  ImplementsClauseImpl _implementsClause;

  /**
   * The native clause for the class, or `null` if the class does not have a
   * native clause.
   */
  NativeClauseImpl _nativeClause;

  /**
   * The left curly bracket.
   */
  @override
  Token leftBracket;

  /**
   * The members defined by the class.
   */
  NodeList<ClassMember> _members;

  /**
   * The right curly bracket.
   */
  @override
  Token rightBracket;

  /**
   * Initialize a newly created class declaration. Either or both of the
   * [comment] and [metadata] can be `null` if the class does not have the
   * corresponding attribute. The [abstractKeyword] can be `null` if the class
   * is not abstract. The [typeParameters] can be `null` if the class does not
   * have any type parameters. Any or all of the [extendsClause], [withClause],
   * and [implementsClause] can be `null` if the class does not have the
   * corresponding clause. The list of [members] can be `null` if the class does
   * not have any members.
   */
  ClassDeclarationImpl(
      CommentImpl comment,
      List<Annotation> metadata,
      this.abstractKeyword,
      this.classKeyword,
      SimpleIdentifierImpl name,
      TypeParameterListImpl typeParameters,
      ExtendsClauseImpl extendsClause,
      WithClauseImpl withClause,
      ImplementsClauseImpl implementsClause,
      this.leftBracket,
      List<ClassMember> members,
      this.rightBracket)
      : super(comment, metadata, name) {
    _typeParameters = _becomeParentOf(typeParameters);
    _extendsClause = _becomeParentOf(extendsClause);
    _withClause = _becomeParentOf(withClause);
    _implementsClause = _becomeParentOf(implementsClause);
    _members = new NodeListImpl<ClassMember>(this, members);
  }

  @override
  Iterable<SyntacticEntity> get childEntities => super._childEntities
    ..add(abstractKeyword)
    ..add(classKeyword)
    ..add(_name)
    ..add(_typeParameters)
    ..add(_extendsClause)
    ..add(_withClause)
    ..add(_implementsClause)
    ..add(_nativeClause)
    ..add(leftBracket)
    ..addAll(members)
    ..add(rightBracket);

  @override
  ClassElement get element => _name?.staticElement as ClassElement;

  @override
  Token get endToken => rightBracket;

  @override
  ExtendsClause get extendsClause => _extendsClause;

  @override
  void set extendsClause(ExtendsClause extendsClause) {
    _extendsClause = _becomeParentOf(extendsClause as ExtendsClauseImpl);
  }

  @override
  Token get firstTokenAfterCommentAndMetadata {
    if (abstractKeyword != null) {
      return abstractKeyword;
    }
    return classKeyword;
  }

  @override
  ImplementsClause get implementsClause => _implementsClause;

  @override
  void set implementsClause(ImplementsClause implementsClause) {
    _implementsClause =
        _becomeParentOf(implementsClause as ImplementsClauseImpl);
  }

  @override
  bool get isAbstract => abstractKeyword != null;

  @override
  NodeList<ClassMember> get members => _members;

  @override
  NativeClause get nativeClause => _nativeClause;

  @override
  void set nativeClause(NativeClause nativeClause) {
    _nativeClause = _becomeParentOf(nativeClause as NativeClauseImpl);
  }

  @override
  TypeParameterList get typeParameters => _typeParameters;

  @override
  void set typeParameters(TypeParameterList typeParameters) {
    _typeParameters = _becomeParentOf(typeParameters as TypeParameterListImpl);
  }

  @override
  WithClause get withClause => _withClause;

  @override
  void set withClause(WithClause withClause) {
    _withClause = _becomeParentOf(withClause as WithClauseImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitClassDeclaration(this);

  @override
  ConstructorDeclaration getConstructor(String name) {
    int length = _members.length;
    for (int i = 0; i < length; i++) {
      ClassMember classMember = _members[i];
      if (classMember is ConstructorDeclaration) {
        ConstructorDeclaration constructor = classMember;
        SimpleIdentifier constructorName = constructor.name;
        if (name == null && constructorName == null) {
          return constructor;
        }
        if (constructorName != null && constructorName.name == name) {
          return constructor;
        }
      }
    }
    return null;
  }

  @override
  VariableDeclaration getField(String name) {
    int memberLength = _members.length;
    for (int i = 0; i < memberLength; i++) {
      ClassMember classMember = _members[i];
      if (classMember is FieldDeclaration) {
        FieldDeclaration fieldDeclaration = classMember;
        NodeList<VariableDeclaration> fields =
            fieldDeclaration.fields.variables;
        int fieldLength = fields.length;
        for (int i = 0; i < fieldLength; i++) {
          VariableDeclaration field = fields[i];
          SimpleIdentifier fieldName = field.name;
          if (fieldName != null && name == fieldName.name) {
            return field;
          }
        }
      }
    }
    return null;
  }

  @override
  MethodDeclaration getMethod(String name) {
    int length = _members.length;
    for (int i = 0; i < length; i++) {
      ClassMember classMember = _members[i];
      if (classMember is MethodDeclaration) {
        MethodDeclaration method = classMember;
        SimpleIdentifier methodName = method.name;
        if (methodName != null && name == methodName.name) {
          return method;
        }
      }
    }
    return null;
  }

  @override
  void visitChildren(AstVisitor visitor) {
    super.visitChildren(visitor);
    _name?.accept(visitor);
    _typeParameters?.accept(visitor);
    _extendsClause?.accept(visitor);
    _withClause?.accept(visitor);
    _implementsClause?.accept(visitor);
    _nativeClause?.accept(visitor);
    members.accept(visitor);
  }
}

/**
 * A node that declares a name within the scope of a class.
 */
abstract class ClassMemberImpl extends DeclarationImpl implements ClassMember {
  /**
   * Initialize a newly created member of a class. Either or both of the
   * [comment] and [metadata] can be `null` if the member does not have the
   * corresponding attribute.
   */
  ClassMemberImpl(CommentImpl comment, List<Annotation> metadata)
      : super(comment, metadata);
}

/**
 * A class type alias.
 *
 *    classTypeAlias ::=
 *        [SimpleIdentifier] [TypeParameterList]? '=' 'abstract'? mixinApplication
 *
 *    mixinApplication ::=
 *        [TypeName] [WithClause] [ImplementsClause]? ';'
 */
class ClassTypeAliasImpl extends TypeAliasImpl implements ClassTypeAlias {
  /**
   * The type parameters for the class, or `null` if the class does not have any
   * type parameters.
   */
  TypeParameterListImpl _typeParameters;

  /**
   * The token for the '=' separating the name from the definition.
   */
  @override
  Token equals;

  /**
   * The token for the 'abstract' keyword, or `null` if this is not defining an
   * abstract class.
   */
  @override
  Token abstractKeyword;

  /**
   * The name of the superclass of the class being declared.
   */
  TypeNameImpl _superclass;

  /**
   * The with clause for this class.
   */
  WithClauseImpl _withClause;

  /**
   * The implements clause for this class, or `null` if there is no implements
   * clause.
   */
  ImplementsClauseImpl _implementsClause;

  /**
   * Initialize a newly created class type alias. Either or both of the
   * [comment] and [metadata] can be `null` if the class type alias does not
   * have the corresponding attribute. The [typeParameters] can be `null` if the
   * class does not have any type parameters. The [abstractKeyword] can be
   * `null` if the class is not abstract. The [implementsClause] can be `null`
   * if the class does not implement any interfaces.
   */
  ClassTypeAliasImpl(
      CommentImpl comment,
      List<Annotation> metadata,
      Token keyword,
      SimpleIdentifierImpl name,
      TypeParameterListImpl typeParameters,
      this.equals,
      this.abstractKeyword,
      TypeNameImpl superclass,
      WithClauseImpl withClause,
      ImplementsClauseImpl implementsClause,
      Token semicolon)
      : super(comment, metadata, keyword, name, semicolon) {
    _typeParameters = _becomeParentOf(typeParameters);
    _superclass = _becomeParentOf(superclass);
    _withClause = _becomeParentOf(withClause);
    _implementsClause = _becomeParentOf(implementsClause);
  }

  @override
  Iterable<SyntacticEntity> get childEntities => super._childEntities
    ..add(typedefKeyword)
    ..add(_name)
    ..add(_typeParameters)
    ..add(equals)
    ..add(abstractKeyword)
    ..add(_superclass)
    ..add(_withClause)
    ..add(_implementsClause)
    ..add(semicolon);

  @override
  ClassElement get element => _name?.staticElement as ClassElement;

  @override
  Token get firstTokenAfterCommentAndMetadata {
    if (abstractKeyword != null) {
      return abstractKeyword;
    }
    return typedefKeyword;
  }

  @override
  ImplementsClause get implementsClause => _implementsClause;

  @override
  void set implementsClause(ImplementsClause implementsClause) {
    _implementsClause =
        _becomeParentOf(implementsClause as ImplementsClauseImpl);
  }

  @override
  bool get isAbstract => abstractKeyword != null;

  @override
  TypeName get superclass => _superclass;

  @override
  void set superclass(TypeName superclass) {
    _superclass = _becomeParentOf(superclass as TypeNameImpl);
  }

  @override
  TypeParameterList get typeParameters => _typeParameters;

  @override
  void set typeParameters(TypeParameterList typeParameters) {
    _typeParameters = _becomeParentOf(typeParameters as TypeParameterListImpl);
  }

  @override
  WithClause get withClause => _withClause;

  @override
  void set withClause(WithClause withClause) {
    _withClause = _becomeParentOf(withClause as WithClauseImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitClassTypeAlias(this);

  @override
  void visitChildren(AstVisitor visitor) {
    super.visitChildren(visitor);
    _name?.accept(visitor);
    _typeParameters?.accept(visitor);
    _superclass?.accept(visitor);
    _withClause?.accept(visitor);
    _implementsClause?.accept(visitor);
  }
}

/**
 * A combinator associated with an import or export directive.
 *
 *    combinator ::=
 *        [HideCombinator]
 *      | [ShowCombinator]
 */
abstract class CombinatorImpl extends AstNodeImpl implements Combinator {
  /**
   * The 'hide' or 'show' keyword specifying what kind of processing is to be
   * done on the names.
   */
  @override
  Token keyword;

  /**
   * Initialize a newly created combinator.
   */
  CombinatorImpl(this.keyword);

  @override
  Token get beginToken => keyword;
}

/**
 * A comment within the source code.
 *
 *    comment ::=
 *        endOfLineComment
 *      | blockComment
 *      | documentationComment
 *
 *    endOfLineComment ::=
 *        '//' (CHARACTER - EOL)* EOL
 *
 *    blockComment ::=
 *        '/ *' CHARACTER* '&#42;/'
 *
 *    documentationComment ::=
 *        '/ **' (CHARACTER | [CommentReference])* '&#42;/'
 *      | ('///' (CHARACTER - EOL)* EOL)+
 */
class CommentImpl extends AstNodeImpl implements Comment {
  /**
   * The tokens representing the comment.
   */
  @override
  final List<Token> tokens;

  /**
   * The type of the comment.
   */
  final CommentType _type;

  /**
   * The references embedded within the documentation comment. This list will be
   * empty unless this is a documentation comment that has references embedded
   * within it.
   */
  NodeList<CommentReference> _references;

  /**
   * Initialize a newly created comment. The list of [tokens] must contain at
   * least one token. The [_type] is the type of the comment. The list of
   * [references] can be empty if the comment does not contain any embedded
   * references.
   */
  CommentImpl(this.tokens, this._type, List<CommentReference> references) {
    _references = new NodeListImpl<CommentReference>(this, references);
  }

  @override
  Token get beginToken => tokens[0];

  @override
  Iterable<SyntacticEntity> get childEntities =>
      new ChildEntities()..addAll(tokens);

  @override
  Token get endToken => tokens[tokens.length - 1];

  @override
  bool get isBlock => _type == CommentType.BLOCK;

  @override
  bool get isDocumentation => _type == CommentType.DOCUMENTATION;

  @override
  bool get isEndOfLine => _type == CommentType.END_OF_LINE;

  @override
  NodeList<CommentReference> get references => _references;

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitComment(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _references.accept(visitor);
  }

  /**
   * Create a block comment consisting of the given [tokens].
   */
  static Comment createBlockComment(List<Token> tokens) =>
      new CommentImpl(tokens, CommentType.BLOCK, null);

  /**
   * Create a documentation comment consisting of the given [tokens].
   */
  static Comment createDocumentationComment(List<Token> tokens) =>
      new CommentImpl(
          tokens, CommentType.DOCUMENTATION, new List<CommentReference>());

  /**
   * Create a documentation comment consisting of the given [tokens] and having
   * the given [references] embedded within it.
   */
  static Comment createDocumentationCommentWithReferences(
          List<Token> tokens, List<CommentReference> references) =>
      new CommentImpl(tokens, CommentType.DOCUMENTATION, references);

  /**
   * Create an end-of-line comment consisting of the given [tokens].
   */
  static Comment createEndOfLineComment(List<Token> tokens) =>
      new CommentImpl(tokens, CommentType.END_OF_LINE, null);
}

/**
 * A reference to a Dart element that is found within a documentation comment.
 *
 *    commentReference ::=
 *        '[' 'new'? [Identifier] ']'
 */
class CommentReferenceImpl extends AstNodeImpl implements CommentReference {
  /**
   * The token representing the 'new' keyword, or `null` if there was no 'new'
   * keyword.
   */
  @override
  Token newKeyword;

  /**
   * The identifier being referenced.
   */
  IdentifierImpl _identifier;

  /**
   * Initialize a newly created reference to a Dart element. The [newKeyword]
   * can be `null` if the reference is not to a constructor.
   */
  CommentReferenceImpl(this.newKeyword, IdentifierImpl identifier) {
    _identifier = _becomeParentOf(identifier);
  }

  @override
  Token get beginToken => _identifier.beginToken;

  @override
  Iterable<SyntacticEntity> get childEntities =>
      new ChildEntities()..add(newKeyword)..add(_identifier);

  @override
  Token get endToken => _identifier.endToken;

  @override
  Identifier get identifier => _identifier;

  @override
  void set identifier(Identifier identifier) {
    _identifier = _becomeParentOf(identifier as IdentifierImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitCommentReference(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _identifier?.accept(visitor);
  }
}

/**
 * The possible types of comments that are recognized by the parser.
 */
class CommentType {
  /**
   * A block comment.
   */
  static const CommentType BLOCK = const CommentType('BLOCK');

  /**
   * A documentation comment.
   */
  static const CommentType DOCUMENTATION = const CommentType('DOCUMENTATION');

  /**
   * An end-of-line comment.
   */
  static const CommentType END_OF_LINE = const CommentType('END_OF_LINE');

  /**
   * The name of the comment type.
   */
  final String name;

  /**
   * Initialize a newly created comment type to have the given [name].
   */
  const CommentType(this.name);

  @override
  String toString() => name;
}

/**
 * A compilation unit.
 *
 * While the grammar restricts the order of the directives and declarations
 * within a compilation unit, this class does not enforce those restrictions.
 * In particular, the children of a compilation unit will be visited in lexical
 * order even if lexical order does not conform to the restrictions of the
 * grammar.
 *
 *    compilationUnit ::=
 *        directives declarations
 *
 *    directives ::=
 *        [ScriptTag]? [LibraryDirective]? namespaceDirective* [PartDirective]*
 *      | [PartOfDirective]
 *
 *    namespaceDirective ::=
 *        [ImportDirective]
 *      | [ExportDirective]
 *
 *    declarations ::=
 *        [CompilationUnitMember]*
 */
class CompilationUnitImpl extends AstNodeImpl implements CompilationUnit {
  /**
   * The first token in the token stream that was parsed to form this
   * compilation unit.
   */
  @override
  Token beginToken;

  /**
   * The script tag at the beginning of the compilation unit, or `null` if there
   * is no script tag in this compilation unit.
   */
  ScriptTagImpl _scriptTag;

  /**
   * The directives contained in this compilation unit.
   */
  NodeList<Directive> _directives;

  /**
   * The declarations contained in this compilation unit.
   */
  NodeList<CompilationUnitMember> _declarations;

  /**
   * The last token in the token stream that was parsed to form this compilation
   * unit. This token should always have a type of [TokenType.EOF].
   */
  @override
  Token endToken;

  /**
   * The element associated with this compilation unit, or `null` if the AST
   * structure has not been resolved.
   */
  @override
  CompilationUnitElement element;

  /**
   * The line information for this compilation unit.
   */
  @override
  LineInfo lineInfo;

  Map<int, AstNode> localDeclarations;

  /**
   * Initialize a newly created compilation unit to have the given directives
   * and declarations. The [scriptTag] can be `null` if there is no script tag
   * in the compilation unit. The list of [directives] can be `null` if there
   * are no directives in the compilation unit. The list of [declarations] can
   * be `null` if there are no declarations in the compilation unit.
   */
  CompilationUnitImpl(
      this.beginToken,
      ScriptTagImpl scriptTag,
      List<Directive> directives,
      List<CompilationUnitMember> declarations,
      this.endToken) {
    _scriptTag = _becomeParentOf(scriptTag);
    _directives = new NodeListImpl<Directive>(this, directives);
    _declarations = new NodeListImpl<CompilationUnitMember>(this, declarations);
  }

  @override
  Iterable<SyntacticEntity> get childEntities {
    ChildEntities result = new ChildEntities()..add(_scriptTag);
    if (_directivesAreBeforeDeclarations) {
      result..addAll(_directives)..addAll(_declarations);
    } else {
      result.addAll(sortedDirectivesAndDeclarations);
    }
    return result;
  }

  @override
  NodeList<CompilationUnitMember> get declarations => _declarations;

  @override
  NodeList<Directive> get directives => _directives;

  @override
  int get length {
    Token endToken = this.endToken;
    if (endToken == null) {
      return 0;
    }
    return endToken.offset + endToken.length;
  }

  @override
  int get offset => 0;

  @override
  ScriptTag get scriptTag => _scriptTag;

  @override
  void set scriptTag(ScriptTag scriptTag) {
    _scriptTag = _becomeParentOf(scriptTag as ScriptTagImpl);
  }

  @override
  List<AstNode> get sortedDirectivesAndDeclarations {
    return <AstNode>[]
      ..addAll(_directives)
      ..addAll(_declarations)
      ..sort(AstNode.LEXICAL_ORDER);
  }

  /**
   * Return `true` if all of the directives are lexically before any
   * declarations.
   */
  bool get _directivesAreBeforeDeclarations {
    if (_directives.isEmpty || _declarations.isEmpty) {
      return true;
    }
    Directive lastDirective = _directives[_directives.length - 1];
    CompilationUnitMember firstDeclaration = _declarations[0];
    return lastDirective.offset < firstDeclaration.offset;
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitCompilationUnit(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _scriptTag?.accept(visitor);
    if (_directivesAreBeforeDeclarations) {
      _directives.accept(visitor);
      _declarations.accept(visitor);
    } else {
      List<AstNode> sortedMembers = sortedDirectivesAndDeclarations;
      int length = sortedMembers.length;
      for (int i = 0; i < length; i++) {
        AstNode child = sortedMembers[i];
        child.accept(visitor);
      }
    }
  }
}

/**
 * A node that declares one or more names within the scope of a compilation
 * unit.
 *
 *    compilationUnitMember ::=
 *        [ClassDeclaration]
 *      | [TypeAlias]
 *      | [FunctionDeclaration]
 *      | [MethodDeclaration]
 *      | [VariableDeclaration]
 *      | [VariableDeclaration]
 */
abstract class CompilationUnitMemberImpl extends DeclarationImpl
    implements CompilationUnitMember {
  /**
   * Initialize a newly created generic compilation unit member. Either or both
   * of the [comment] and [metadata] can be `null` if the member does not have
   * the corresponding attribute.
   */
  CompilationUnitMemberImpl(CommentImpl comment, List<Annotation> metadata)
      : super(comment, metadata);
}

/**
 * A conditional expression.
 *
 *    conditionalExpression ::=
 *        [Expression] '?' [Expression] ':' [Expression]
 */
class ConditionalExpressionImpl extends ExpressionImpl
    implements ConditionalExpression {
  /**
   * The condition used to determine which of the expressions is executed next.
   */
  ExpressionImpl _condition;

  /**
   * The token used to separate the condition from the then expression.
   */
  @override
  Token question;

  /**
   * The expression that is executed if the condition evaluates to `true`.
   */
  ExpressionImpl _thenExpression;

  /**
   * The token used to separate the then expression from the else expression.
   */
  @override
  Token colon;

  /**
   * The expression that is executed if the condition evaluates to `false`.
   */
  ExpressionImpl _elseExpression;

  /**
   * Initialize a newly created conditional expression.
   */
  ConditionalExpressionImpl(
      ExpressionImpl condition,
      this.question,
      ExpressionImpl thenExpression,
      this.colon,
      ExpressionImpl elseExpression) {
    _condition = _becomeParentOf(condition);
    _thenExpression = _becomeParentOf(thenExpression);
    _elseExpression = _becomeParentOf(elseExpression);
  }

  @override
  Token get beginToken => _condition.beginToken;

  @override
  Iterable<SyntacticEntity> get childEntities => new ChildEntities()
    ..add(_condition)
    ..add(question)
    ..add(_thenExpression)
    ..add(colon)
    ..add(_elseExpression);

  @override
  Expression get condition => _condition;

  @override
  void set condition(Expression expression) {
    _condition = _becomeParentOf(expression as ExpressionImpl);
  }

  @override
  Expression get elseExpression => _elseExpression;

  @override
  void set elseExpression(Expression expression) {
    _elseExpression = _becomeParentOf(expression as ExpressionImpl);
  }

  @override
  Token get endToken => _elseExpression.endToken;

  @override
  int get precedence => 3;

  @override
  Expression get thenExpression => _thenExpression;

  @override
  void set thenExpression(Expression expression) {
    _thenExpression = _becomeParentOf(expression as ExpressionImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) =>
      visitor.visitConditionalExpression(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _condition?.accept(visitor);
    _thenExpression?.accept(visitor);
    _elseExpression?.accept(visitor);
  }
}

/**
 * A configuration in either an import or export directive.
 *
 *     configuration ::=
 *         'if' '(' test ')' uri
 *
 *     test ::=
 *         dottedName ('==' stringLiteral)?
 *
 *     dottedName ::=
 *         identifier ('.' identifier)*
 */
class ConfigurationImpl extends AstNodeImpl implements Configuration {
  @override
  Token ifKeyword;

  @override
  Token leftParenthesis;

  DottedNameImpl _name;

  @override
  Token equalToken;

  StringLiteralImpl _value;

  @override
  Token rightParenthesis;

  StringLiteralImpl _uri;

  @override
  Source uriSource;

  ConfigurationImpl(
      this.ifKeyword,
      this.leftParenthesis,
      DottedNameImpl name,
      this.equalToken,
      StringLiteralImpl value,
      this.rightParenthesis,
      StringLiteralImpl libraryUri) {
    _name = _becomeParentOf(name);
    _value = _becomeParentOf(value);
    _uri = _becomeParentOf(libraryUri);
  }

  @override
  Token get beginToken => ifKeyword;

  @override
  Iterable<SyntacticEntity> get childEntities => new ChildEntities()
    ..add(ifKeyword)
    ..add(leftParenthesis)
    ..add(_name)
    ..add(equalToken)
    ..add(_value)
    ..add(rightParenthesis)
    ..add(_uri);

  @override
  Token get endToken => _uri.endToken;

  @deprecated
  @override
  StringLiteral get libraryUri => _uri;

  @deprecated
  @override
  void set libraryUri(StringLiteral libraryUri) {
    _uri = _becomeParentOf(libraryUri as StringLiteralImpl);
  }

  @override
  DottedName get name => _name;

  @override
  void set name(DottedName name) {
    _name = _becomeParentOf(name as DottedNameImpl);
  }

  @override
  StringLiteral get uri => _uri;

  @override
  void set uri(StringLiteral uri) {
    _uri = _becomeParentOf(uri as StringLiteralImpl);
  }

  @override
  StringLiteral get value => _value;

  @override
  void set value(StringLiteral value) {
    _value = _becomeParentOf(value as StringLiteralImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitConfiguration(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _name?.accept(visitor);
    _value?.accept(visitor);
    _uri?.accept(visitor);
  }
}

/**
 * An error listener that only records whether any constant related errors have
 * been reported.
 */
class ConstantAnalysisErrorListener extends AnalysisErrorListener {
  /**
   * A flag indicating whether any constant related errors have been reported to
   * this listener.
   */
  bool hasConstError = false;

  @override
  void onError(AnalysisError error) {
    ErrorCode errorCode = error.errorCode;
    if (errorCode is CompileTimeErrorCode) {
      switch (errorCode) {
        case CompileTimeErrorCode.CONST_EVAL_TYPE_BOOL:
        case CompileTimeErrorCode.CONST_EVAL_TYPE_BOOL_NUM_STRING:
        case CompileTimeErrorCode.CONST_EVAL_TYPE_INT:
        case CompileTimeErrorCode.CONST_EVAL_TYPE_NUM:
        case CompileTimeErrorCode.CONST_EVAL_THROWS_EXCEPTION:
        case CompileTimeErrorCode.CONST_EVAL_THROWS_IDBZE:
        case CompileTimeErrorCode.CONST_WITH_NON_CONSTANT_ARGUMENT:
        case CompileTimeErrorCode.NON_CONSTANT_VALUE_IN_INITIALIZER:
        case CompileTimeErrorCode
            .CONST_CONSTRUCTOR_WITH_FIELD_INITIALIZED_BY_NON_CONST:
        case CompileTimeErrorCode.INVALID_CONSTANT:
        case CompileTimeErrorCode.MISSING_CONST_IN_LIST_LITERAL:
          hasConstError = true;
      }
    }
  }
}

/**
 * A constructor declaration.
 *
 *    constructorDeclaration ::=
 *        constructorSignature [FunctionBody]?
 *      | constructorName formalParameterList ':' 'this' ('.' [SimpleIdentifier])? arguments
 *
 *    constructorSignature ::=
 *        'external'? constructorName formalParameterList initializerList?
 *      | 'external'? 'factory' factoryName formalParameterList initializerList?
 *      | 'external'? 'const'  constructorName formalParameterList initializerList?
 *
 *    constructorName ::=
 *        [SimpleIdentifier] ('.' [SimpleIdentifier])?
 *
 *    factoryName ::=
 *        [Identifier] ('.' [SimpleIdentifier])?
 *
 *    initializerList ::=
 *        ':' [ConstructorInitializer] (',' [ConstructorInitializer])*
 */
class ConstructorDeclarationImpl extends ClassMemberImpl
    implements ConstructorDeclaration {
  /**
   * The token for the 'external' keyword, or `null` if the constructor is not
   * external.
   */
  @override
  Token externalKeyword;

  /**
   * The token for the 'const' keyword, or `null` if the constructor is not a
   * const constructor.
   */
  @override
  Token constKeyword;

  /**
   * The token for the 'factory' keyword, or `null` if the constructor is not a
   * factory constructor.
   */
  @override
  Token factoryKeyword;

  /**
   * The type of object being created. This can be different than the type in
   * which the constructor is being declared if the constructor is the
   * implementation of a factory constructor.
   */
  IdentifierImpl _returnType;

  /**
   * The token for the period before the constructor name, or `null` if the
   * constructor being declared is unnamed.
   */
  @override
  Token period;

  /**
   * The name of the constructor, or `null` if the constructor being declared is
   * unnamed.
   */
  SimpleIdentifierImpl _name;

  /**
   * The parameters associated with the constructor.
   */
  FormalParameterListImpl _parameters;

  /**
   * The token for the separator (colon or equals) before the initializer list
   * or redirection, or `null` if there are no initializers.
   */
  @override
  Token separator;

  /**
   * The initializers associated with the constructor.
   */
  NodeList<ConstructorInitializer> _initializers;

  /**
   * The name of the constructor to which this constructor will be redirected,
   * or `null` if this is not a redirecting factory constructor.
   */
  ConstructorNameImpl _redirectedConstructor;

  /**
   * The body of the constructor, or `null` if the constructor does not have a
   * body.
   */
  FunctionBodyImpl _body;

  /**
   * The element associated with this constructor, or `null` if the AST
   * structure has not been resolved or if this constructor could not be
   * resolved.
   */
  @override
  ConstructorElement element;

  /**
   * Initialize a newly created constructor declaration. The [externalKeyword]
   * can be `null` if the constructor is not external. Either or both of the
   * [comment] and [metadata] can be `null` if the constructor does not have the
   * corresponding attribute. The [constKeyword] can be `null` if the
   * constructor cannot be used to create a constant. The [factoryKeyword] can
   * be `null` if the constructor is not a factory. The [period] and [name] can
   * both be `null` if the constructor is not a named constructor. The
   * [separator] can be `null` if the constructor does not have any initializers
   * and does not redirect to a different constructor. The list of
   * [initializers] can be `null` if the constructor does not have any
   * initializers. The [redirectedConstructor] can be `null` if the constructor
   * does not redirect to a different constructor. The [body] can be `null` if
   * the constructor does not have a body.
   */
  ConstructorDeclarationImpl(
      CommentImpl comment,
      List<Annotation> metadata,
      this.externalKeyword,
      this.constKeyword,
      this.factoryKeyword,
      IdentifierImpl returnType,
      this.period,
      SimpleIdentifierImpl name,
      FormalParameterListImpl parameters,
      this.separator,
      List<ConstructorInitializer> initializers,
      ConstructorNameImpl redirectedConstructor,
      FunctionBodyImpl body)
      : super(comment, metadata) {
    _returnType = _becomeParentOf(returnType);
    _name = _becomeParentOf(name);
    _parameters = _becomeParentOf(parameters);
    _initializers =
        new NodeListImpl<ConstructorInitializer>(this, initializers);
    _redirectedConstructor = _becomeParentOf(redirectedConstructor);
    _body = _becomeParentOf(body);
  }

  @override
  FunctionBody get body => _body;

  @override
  void set body(FunctionBody functionBody) {
    _body = _becomeParentOf(functionBody as FunctionBodyImpl);
  }

  @override
  Iterable<SyntacticEntity> get childEntities => super._childEntities
    ..add(externalKeyword)
    ..add(constKeyword)
    ..add(factoryKeyword)
    ..add(_returnType)
    ..add(period)
    ..add(_name)
    ..add(_parameters)
    ..add(separator)
    ..addAll(initializers)
    ..add(_redirectedConstructor)
    ..add(_body);

  @override
  Token get endToken {
    if (_body != null) {
      return _body.endToken;
    } else if (!_initializers.isEmpty) {
      return _initializers.endToken;
    }
    return _parameters.endToken;
  }

  @override
  Token get firstTokenAfterCommentAndMetadata {
    Token leftMost =
        Token.lexicallyFirst([externalKeyword, constKeyword, factoryKeyword]);
    if (leftMost != null) {
      return leftMost;
    }
    return _returnType.beginToken;
  }

  @override
  NodeList<ConstructorInitializer> get initializers => _initializers;

  @override
  SimpleIdentifier get name => _name;

  @override
  void set name(SimpleIdentifier identifier) {
    _name = _becomeParentOf(identifier as SimpleIdentifierImpl);
  }

  @override
  FormalParameterList get parameters => _parameters;

  @override
  void set parameters(FormalParameterList parameters) {
    _parameters = _becomeParentOf(parameters as FormalParameterListImpl);
  }

  @override
  ConstructorName get redirectedConstructor => _redirectedConstructor;

  @override
  void set redirectedConstructor(ConstructorName redirectedConstructor) {
    _redirectedConstructor =
        _becomeParentOf(redirectedConstructor as ConstructorNameImpl);
  }

  @override
  Identifier get returnType => _returnType;

  @override
  void set returnType(Identifier typeName) {
    _returnType = _becomeParentOf(typeName as IdentifierImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) =>
      visitor.visitConstructorDeclaration(this);

  @override
  void visitChildren(AstVisitor visitor) {
    super.visitChildren(visitor);
    _returnType?.accept(visitor);
    _name?.accept(visitor);
    _parameters?.accept(visitor);
    _initializers.accept(visitor);
    _redirectedConstructor?.accept(visitor);
    _body?.accept(visitor);
  }
}

/**
 * The initialization of a field within a constructor's initialization list.
 *
 *    fieldInitializer ::=
 *        ('this' '.')? [SimpleIdentifier] '=' [Expression]
 */
class ConstructorFieldInitializerImpl extends ConstructorInitializerImpl
    implements ConstructorFieldInitializer {
  /**
   * The token for the 'this' keyword, or `null` if there is no 'this' keyword.
   */
  @override
  Token thisKeyword;

  /**
   * The token for the period after the 'this' keyword, or `null` if there is no
   * 'this' keyword.
   */
  @override
  Token period;

  /**
   * The name of the field being initialized.
   */
  SimpleIdentifierImpl _fieldName;

  /**
   * The token for the equal sign between the field name and the expression.
   */
  @override
  Token equals;

  /**
   * The expression computing the value to which the field will be initialized.
   */
  ExpressionImpl _expression;

  /**
   * Initialize a newly created field initializer to initialize the field with
   * the given name to the value of the given expression. The [thisKeyword] and
   * [period] can be `null` if the 'this' keyword was not specified.
   */
  ConstructorFieldInitializerImpl(this.thisKeyword, this.period,
      SimpleIdentifierImpl fieldName, this.equals, ExpressionImpl expression) {
    _fieldName = _becomeParentOf(fieldName);
    _expression = _becomeParentOf(expression);
  }

  @override
  Token get beginToken {
    if (thisKeyword != null) {
      return thisKeyword;
    }
    return _fieldName.beginToken;
  }

  @override
  Iterable<SyntacticEntity> get childEntities => new ChildEntities()
    ..add(thisKeyword)
    ..add(period)
    ..add(_fieldName)
    ..add(equals)
    ..add(_expression);

  @override
  Token get endToken => _expression.endToken;

  @override
  Expression get expression => _expression;

  @override
  void set expression(Expression expression) {
    _expression = _becomeParentOf(expression as ExpressionImpl);
  }

  @override
  SimpleIdentifier get fieldName => _fieldName;

  @override
  void set fieldName(SimpleIdentifier identifier) {
    _fieldName = _becomeParentOf(identifier as SimpleIdentifierImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) =>
      visitor.visitConstructorFieldInitializer(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _fieldName?.accept(visitor);
    _expression?.accept(visitor);
  }
}

/**
 * A node that can occur in the initializer list of a constructor declaration.
 *
 *    constructorInitializer ::=
 *        [SuperConstructorInvocation]
 *      | [ConstructorFieldInitializer]
 *      | [RedirectingConstructorInvocation]
 */
abstract class ConstructorInitializerImpl extends AstNodeImpl
    implements ConstructorInitializer {}

/**
 * The name of the constructor.
 *
 *    constructorName ::=
 *        type ('.' identifier)?
 */
class ConstructorNameImpl extends AstNodeImpl implements ConstructorName {
  /**
   * The name of the type defining the constructor.
   */
  TypeNameImpl _type;

  /**
   * The token for the period before the constructor name, or `null` if the
   * specified constructor is the unnamed constructor.
   */
  @override
  Token period;

  /**
   * The name of the constructor, or `null` if the specified constructor is the
   * unnamed constructor.
   */
  SimpleIdentifierImpl _name;

  /**
   * The element associated with this constructor name based on static type
   * information, or `null` if the AST structure has not been resolved or if
   * this constructor name could not be resolved.
   */
  @override
  ConstructorElement staticElement;

  /**
   * Initialize a newly created constructor name. The [period] and [name] can be
   * `null` if the constructor being named is the unnamed constructor.
   */
  ConstructorNameImpl(
      TypeNameImpl type, this.period, SimpleIdentifierImpl name) {
    _type = _becomeParentOf(type);
    _name = _becomeParentOf(name);
  }

  @override
  Token get beginToken => _type.beginToken;

  @override
  Iterable<SyntacticEntity> get childEntities =>
      new ChildEntities()..add(_type)..add(period)..add(_name);

  @override
  Token get endToken {
    if (_name != null) {
      return _name.endToken;
    }
    return _type.endToken;
  }

  @override
  SimpleIdentifier get name => _name;

  @override
  void set name(SimpleIdentifier name) {
    _name = _becomeParentOf(name as SimpleIdentifierImpl);
  }

  @override
  TypeName get type => _type;

  @override
  void set type(TypeName type) {
    _type = _becomeParentOf(type as TypeNameImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitConstructorName(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _type?.accept(visitor);
    _name?.accept(visitor);
  }
}

/**
 * A continue statement.
 *
 *    continueStatement ::=
 *        'continue' [SimpleIdentifier]? ';'
 */
class ContinueStatementImpl extends StatementImpl implements ContinueStatement {
  /**
   * The token representing the 'continue' keyword.
   */
  @override
  Token continueKeyword;

  /**
   * The label associated with the statement, or `null` if there is no label.
   */
  SimpleIdentifierImpl _label;

  /**
   * The semicolon terminating the statement.
   */
  @override
  Token semicolon;

  /**
   * The AstNode which this continue statement is continuing to.  This will be
   * either a Statement (in the case of continuing a loop) or a SwitchMember
   * (in the case of continuing from one switch case to another).  Null if the
   * AST has not yet been resolved or if the target could not be resolved.
   * Note that if the source code has errors, the target may be invalid (e.g.
   * the target may be in an enclosing function).
   */
  AstNode target;

  /**
   * Initialize a newly created continue statement. The [label] can be `null` if
   * there is no label associated with the statement.
   */
  ContinueStatementImpl(
      this.continueKeyword, SimpleIdentifierImpl label, this.semicolon) {
    _label = _becomeParentOf(label);
  }

  @override
  Token get beginToken => continueKeyword;

  @override
  Iterable<SyntacticEntity> get childEntities =>
      new ChildEntities()..add(continueKeyword)..add(_label)..add(semicolon);

  @override
  Token get endToken => semicolon;

  @override
  SimpleIdentifier get label => _label;

  @override
  void set label(SimpleIdentifier identifier) {
    _label = _becomeParentOf(identifier as SimpleIdentifierImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitContinueStatement(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _label?.accept(visitor);
  }
}

/**
 * A node that represents the declaration of one or more names. Each declared
 * name is visible within a name scope.
 */
abstract class DeclarationImpl extends AnnotatedNodeImpl
    implements Declaration {
  /**
   * Initialize a newly created declaration. Either or both of the [comment] and
   * [metadata] can be `null` if the declaration does not have the corresponding
   * attribute.
   */
  DeclarationImpl(CommentImpl comment, List<Annotation> metadata)
      : super(comment, metadata);
}

/**
 * The declaration of a single identifier.
 *
 *    declaredIdentifier ::=
 *        [Annotation] finalConstVarOrType [SimpleIdentifier]
 */
class DeclaredIdentifierImpl extends DeclarationImpl
    implements DeclaredIdentifier {
  /**
   * The token representing either the 'final', 'const' or 'var' keyword, or
   * `null` if no keyword was used.
   */
  @override
  Token keyword;

  /**
   * The name of the declared type of the parameter, or `null` if the parameter
   * does not have a declared type.
   */
  TypeAnnotationImpl _type;

  /**
   * The name of the variable being declared.
   */
  SimpleIdentifierImpl _identifier;

  /**
   * Initialize a newly created formal parameter. Either or both of the
   * [comment] and [metadata] can be `null` if the declaration does not have the
   * corresponding attribute. The [keyword] can be `null` if a type name is
   * given. The [type] must be `null` if the keyword is 'var'.
   */
  DeclaredIdentifierImpl(CommentImpl comment, List<Annotation> metadata,
      this.keyword, TypeAnnotationImpl type, SimpleIdentifierImpl identifier)
      : super(comment, metadata) {
    _type = _becomeParentOf(type);
    _identifier = _becomeParentOf(identifier);
  }

  @override
  Iterable<SyntacticEntity> get childEntities =>
      super._childEntities..add(keyword)..add(_type)..add(_identifier);

  @override
  LocalVariableElement get element {
    if (_identifier == null) {
      return null;
    }
    return _identifier.staticElement as LocalVariableElement;
  }

  @override
  Token get endToken => _identifier.endToken;

  @override
  Token get firstTokenAfterCommentAndMetadata {
    if (keyword != null) {
      return keyword;
    } else if (_type != null) {
      return _type.beginToken;
    }
    return _identifier.beginToken;
  }

  @override
  SimpleIdentifier get identifier => _identifier;

  @override
  void set identifier(SimpleIdentifier identifier) {
    _identifier = _becomeParentOf(identifier as SimpleIdentifierImpl);
  }

  @override
  bool get isConst => keyword?.keyword == Keyword.CONST;

  @override
  bool get isFinal => keyword?.keyword == Keyword.FINAL;

  @override
  TypeAnnotation get type => _type;

  @override
  void set type(TypeAnnotation type) {
    _type = _becomeParentOf(type as TypeAnnotationImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) => visitor.visitDeclaredIdentifier(this);

  @override
  void visitChildren(AstVisitor visitor) {
    super.visitChildren(visitor);
    _type?.accept(visitor);
    _identifier?.accept(visitor);
  }
}

/**
 * A simple identifier that declares a name.
 */
// TODO(rnystrom): Consider making this distinct from [SimpleIdentifier] and
// get rid of all of the:
//
//     if (node.inDeclarationContext()) { ... }
//
// code and instead visit this separately. A declaration is semantically pretty
// different from a use, so using the same node type doesn't seem to buy us
// much.
class DeclaredSimpleIdentifier extends SimpleIdentifierImpl {
  DeclaredSimpleIdentifier(Token token) : super(token);

  @override
  bool inDeclarationContext() => true;
}

/**
 * A formal parameter with a default value. There are two kinds of parameters
 * that are both represented by this class: named formal parameters and
 * positional formal parameters.
 *
 *    defaultFormalParameter ::=
 *        [NormalFormalParameter] ('=' [Expression])?
 *
 *    defaultNamedParameter ::=
 *        [NormalFormalParameter] (':' [Expression])?
 */
class DefaultFormalParameterImpl extends FormalParameterImpl
    implements DefaultFormalParameter {
  /**
   * The formal parameter with which the default value is associated.
   */
  NormalFormalParameterImpl _parameter;

  /**
   * The kind of this parameter.
   */
  @override
  ParameterKind kind;

  /**
   * The token separating the parameter from the default value, or `null` if
   * there is no default value.
   */
  @override
  Token separator;

  /**
   * The expression computing the default value for the parameter, or `null` if
   * there is no default value.
   */
  ExpressionImpl _defaultValue;

  /**
   * Initialize a newly created default formal parameter. The [separator] and
   * [defaultValue] can be `null` if there is no default value.
   */
  DefaultFormalParameterImpl(NormalFormalParameterImpl parameter, this.kind,
      this.separator, ExpressionImpl defaultValue) {
    _parameter = _becomeParentOf(parameter);
    _defaultValue = _becomeParentOf(defaultValue);
  }

  @override
  Token get beginToken => _parameter.beginToken;

  @override
  Iterable<SyntacticEntity> get childEntities =>
      new ChildEntities()..add(_parameter)..add(separator)..add(_defaultValue);

  @override
  Token get covariantKeyword => null;

  @override
  Expression get defaultValue => _defaultValue;

  @override
  void set defaultValue(Expression expression) {
    _defaultValue = _becomeParentOf(expression as ExpressionImpl);
  }

  @override
  Token get endToken {
    if (_defaultValue != null) {
      return _defaultValue.endToken;
    }
    return _parameter.endToken;
  }

  @override
  SimpleIdentifier get identifier => _parameter.identifier;

  @override
  bool get isConst => _parameter != null && _parameter.isConst;

  @override
  bool get isFinal => _parameter != null && _parameter.isFinal;

  @override
  NodeList<Annotation> get metadata => _parameter.metadata;

  @override
  NormalFormalParameter get parameter => _parameter;

  @override
  void set parameter(NormalFormalParameter formalParameter) {
    _parameter = _becomeParentOf(formalParameter as NormalFormalParameterImpl);
  }

  @override
  E accept<E>(AstVisitor<E> visitor) =>
      visitor.visitDefaultFormalParameter(this);

  @override
  void visitChildren(AstVisitor visitor) {
    _parameter?.accept(visitor);
    _defaultValue?.accept(visitor);
  }
}

/**
 * A node that represents a directive.
 *
 *    directive ::=
 *        [ExportDirective]
 *      | [ImportDirective]
 *      | [LibraryDirective]
 *      | [PartDirective]
 *      | [PartOfDirective]
 */
abstract class DirectiveImpl extends AnnotatedNodeImpl implements Directive {
  /**
   * The element associated with this directive, or `null` if the AST structure
   * has not been resolved or if this directive could not be resolved.
   */
  Element _element;

  /**
   * Initialize a newly create directive. Either or both of the [comment] and
   * [metadata] can be `null` if the directive does not have the corresponding
   * attribute.
   */
  DirectiveImpl(CommentImpl comment, List<Annotation> metadata)
      : super(comment, metadata);

  @override
  Element get element => _element;

  /**
   * Set the element associated with this directive to be the given [element].
   */
  void set element(Element element) {
    _element = element;
  }
}

/**
 * A do statement.
 *
 *    doStatement ::=
 *        'do' [Statement] 'while' '(' [Expression] ')' ';'
 */
class DoStatementImpl extends StatementImpl implements DoStatement {
  /**
   * The token representing the 'do' keyword.
   */
  @override
  Token doKeyword;