// Copyright (c) 2012, 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.

part of dart2js;

class TypeCheckerTask extends CompilerTask {
  TypeCheckerTask(Compiler compiler) : super(compiler);
  String get name => "Type checker";

  void check(TreeElements elements) {
    Element element = elements.currentElement;
    compiler.withCurrentElement(element, () {
      measure(() {
        Node tree = element.parseNode(compiler);
        Visitor visitor =
            new TypeCheckerVisitor(compiler, elements, compiler.types);
        tree.accept(visitor);
      });
    });
  }
}

/**
 * Class used to report different warnings for differrent kinds of members.
 */
class MemberKind {
  static const MemberKind METHOD = const MemberKind("method");
  static const MemberKind OPERATOR = const MemberKind("operator");
  static const MemberKind GETTER = const MemberKind("getter");
  static const MemberKind SETTER = const MemberKind("setter");

  final String name;

  const MemberKind(this.name);

  String toString() => name;
}

/**
 * [ElementAccess] represents the access of [element], either as a property
 * access or invocation.
 */
abstract class ElementAccess {
  Element get element;

  DartType computeType(Compiler compiler);

  /// Returns [: true :] if the element can be access as an invocation.
  bool isCallable(Compiler compiler) {
    if (element.isAbstractField()) {
      AbstractFieldElement abstractFieldElement = element;
      if (abstractFieldElement.getter == null) {
        // Setters cannot be invoked as function invocations.
        return false;
      }
    }
    return compiler.types.isAssignable(
        computeType(compiler), compiler.functionClass.computeType(compiler));
  }
}

/// An access of a instance member.
class MemberAccess extends ElementAccess {
  final InterfaceTypeMember member;

  MemberAccess(InterfaceTypeMember this.member);

  Element get element => member.element;

  DartType computeType(Compiler compiler) => member.computeType(compiler);

  String toString() => 'MemberAccess($member)';
}

/// An access of an unresolved element.
class DynamicAccess implements ElementAccess {
  const DynamicAccess();

  Element get element => null;

  DartType computeType(Compiler compiler) => compiler.types.dynamicType;

  bool isCallable(Compiler compiler) => true;

  String toString() => 'DynamicAccess';
}

/**
 * An access of a resolved top-level or static property or function, or an
 * access of a resolved element through [:this:].
 */
class ResolvedAccess extends ElementAccess {
  final Element element;

  ResolvedAccess(Element this.element) {
    assert(element != null);
  }

  DartType computeType(Compiler compiler) {
    if (element.isGetter()) {
      FunctionType functionType = element.computeType(compiler);
      return functionType.returnType;
    } else if (element.isSetter()) {
      FunctionType functionType = element.computeType(compiler);
      return functionType.parameterTypes.head;
    } else {
      return element.computeType(compiler);
    }
  }

  String toString() => 'ResolvedAccess($element)';
}

/// An access to a promoted variable.
class PromotedAccess extends ElementAccess {
  final VariableElement element;
  final DartType type;

  PromotedAccess(VariableElement this.element, DartType this.type) {
    assert(element != null);
    assert(type != null);
  }

  DartType computeType(Compiler compiler) => type;

  String toString() => 'PromotedAccess($element,$type)';
}

/**
 * An access of a resolved top-level or static property or function, or an
 * access of a resolved element through [:this:].
 */
class TypeAccess extends ElementAccess {
  final DartType type;
  TypeAccess(DartType this.type) {
    assert(type != null);
  }

  Element get element => type.element;

  DartType computeType(Compiler compiler) => type;

  String toString() => 'TypeAccess($type)';
}

/**
 * An access of a type literal.
 */
class TypeLiteralAccess extends ElementAccess {
  final Element element;
  TypeLiteralAccess(Element this.element) {
    assert(element != null);
  }

  DartType computeType(Compiler compiler) =>
      compiler.typeClass.computeType(compiler);

  String toString() => 'TypeLiteralAccess($element)';
}


/// An access to the 'call' method of a function type.
class FunctionCallAccess implements ElementAccess {
  final Element element;
  final DartType type;

  const FunctionCallAccess(this.element, this.type);

  DartType computeType(Compiler compiler) => type;

  bool isCallable(Compiler compiler) => true;

  String toString() => 'FunctionAccess($element, $type)';
}


/// An is-expression that potentially promotes a variable.
class TypePromotion {
  final Send node;
  final VariableElement variable;
  final DartType type;
  final List<TypePromotionMessage> messages = <TypePromotionMessage>[];

  TypePromotion(this.node, this.variable, this.type);

  bool get isValid => messages.isEmpty;

  TypePromotion copy() {
    return new TypePromotion(node, variable, type)..messages.addAll(messages);
  }

  void addHint(Spannable spannable, MessageKind kind, [Map arguments]) {
    messages.add(new TypePromotionMessage(api.Diagnostic.HINT,
        spannable, kind, arguments));
  }

  void addInfo(Spannable spannable, MessageKind kind, [Map arguments]) {
    messages.add(new TypePromotionMessage(api.Diagnostic.INFO,
        spannable, kind, arguments));
  }

  String toString() {
    return 'Promote ${variable} to ${type}${isValid ? '' : ' (invalid)'}';
  }
}

/// A hint or info message attached to a type promotion.
class TypePromotionMessage {
  api.Diagnostic diagnostic;
  Spannable spannable;
  MessageKind messageKind;
  Map messageArguments;

  TypePromotionMessage(this.diagnostic, this.spannable, this.messageKind,
                       [this.messageArguments]);
}

class TypeCheckerVisitor extends Visitor<DartType> {
  final Compiler compiler;
  final TreeElements elements;
  final Types types;

  Node lastSeenNode;
  DartType expectedReturnType;

  final ClassElement currentClass;

  InterfaceType thisType;
  InterfaceType superType;

  Link<DartType> cascadeTypes = const Link<DartType>();

  DartType intType;
  DartType doubleType;
  DartType boolType;
  DartType stringType;
  DartType objectType;
  DartType listType;

  Map<Node, List<TypePromotion>> shownTypePromotionsMap =
      new Map<Node, List<TypePromotion>>();

  Map<VariableElement, Link<TypePromotion>> typePromotionsMap =
      new Map<VariableElement, Link<TypePromotion>>();

  Set<TypePromotion> reportedTypePromotions = new Set<TypePromotion>();

  void showTypePromotion(Node node, TypePromotion typePromotion) {
    List<TypePromotion> shownTypePromotions =
        shownTypePromotionsMap.putIfAbsent(node, () => <TypePromotion>[]);
    shownTypePromotions.add(typePromotion);
  }

  void registerKnownTypePromotion(TypePromotion typePromotion) {
    VariableElement variable = typePromotion.variable;
    Link<TypePromotion> knownTypes =
        typePromotionsMap.putIfAbsent(variable,
                                      () => const Link<TypePromotion>());
    typePromotionsMap[variable] = knownTypes.prepend(typePromotion);
  }

  void unregisterKnownTypePromotion(TypePromotion typePromotion) {
    VariableElement variable = typePromotion.variable;
    Link<TypePromotion> knownTypes = typePromotionsMap[variable].tail;
    if (knownTypes.isEmpty) {
      typePromotionsMap.remove(variable);
    } else {
      typePromotionsMap[variable] = knownTypes;
    }
  }

  List<TypePromotion> getShownTypePromotionsFor(Node node) {
    List<TypePromotion> shownTypePromotions = shownTypePromotionsMap[node];
    return shownTypePromotions != null ? shownTypePromotions : const [];
  }

  TypePromotion getKnownTypePromotion(VariableElement element) {
    Link<TypePromotion> promotions = typePromotionsMap[element];
    if (promotions != null) {
      while (!promotions.isEmpty) {
        TypePromotion typePromotion = promotions.head;
        if (typePromotion.isValid) {
          return typePromotion;
        }
        promotions = promotions.tail;
      }
    }
    return null;
  }

  DartType getKnownType(VariableElement element) {
    TypePromotion typePromotion = getKnownTypePromotion(element);
    if (typePromotion != null) return typePromotion.type;
    return element.computeType(compiler);
  }

  TypeCheckerVisitor(this.compiler, TreeElements elements, this.types)
      : this.elements = elements,
        currentClass = elements.currentElement != null
            ? elements.currentElement.getEnclosingClass() : null {
    intType = compiler.intClass.computeType(compiler);
    doubleType = compiler.doubleClass.computeType(compiler);
    boolType = compiler.boolClass.computeType(compiler);
    stringType = compiler.stringClass.computeType(compiler);
    objectType = compiler.objectClass.computeType(compiler);
    listType = compiler.listClass.computeType(compiler);

    if (currentClass != null) {
      thisType = currentClass.computeType(compiler);
      superType = currentClass.supertype;
    }
  }

  LibraryElement get currentLibrary => elements.currentElement.getLibrary();

  reportTypeWarning(Node node, MessageKind kind, [Map arguments = const {}]) {
    compiler.reportWarning(
        node, new TypeWarning(kind, arguments, compiler.terseDiagnostics));
  }

  reportTypeInfo(Spannable node, MessageKind kind, [Map arguments = const {}]) {
    compiler.reportInfo(node, kind, arguments);
  }

  reportTypePromotionHint(TypePromotion typePromotion) {
    if (!reportedTypePromotions.contains(typePromotion)) {
      reportedTypePromotions.add(typePromotion);
      for (TypePromotionMessage message in typePromotion.messages) {
        switch (message.diagnostic) {
          case api.Diagnostic.HINT:
            compiler.reportHint(message.spannable,
                                message.messageKind,
                                message.messageArguments);
            break;
          case api.Diagnostic.INFO:
            compiler.reportInfo(message.spannable,
                                message.messageKind,
                                message.messageArguments);
            break;
        }
      }
    }
  }

  // TODO(karlklose): remove these functions.
  DartType unhandledExpression() => types.dynamicType;

  DartType analyzeNonVoid(Node node) {
    DartType type = analyze(node);
    if (type == types.voidType) {
      reportTypeWarning(node, MessageKind.VOID_EXPRESSION);
    }
    return type;
  }

  DartType analyzeWithDefault(Node node, DartType defaultValue) {
    return node != null ? analyze(node) : defaultValue;
  }

  DartType analyze(Node node) {
    if (node == null) {
      final String error = 'unexpected node: null';
      if (lastSeenNode != null) {
        compiler.internalError(error, node: lastSeenNode);
      } else {
        compiler.cancel(error);
      }
    } else {
      lastSeenNode = node;
    }
    DartType result = node.accept(this);
    if (result == null) {
      compiler.internalError('type is null', node: node);
    }
    return result;
  }

  void checkTypePromotion(Node node, TypePromotion typePromotion,
                          {bool checkAccesses: false}) {
    VariableElement variable = typePromotion.variable;
    String variableName = variable.name;
    List<Node> potentialMutationsIn =
        elements.getPotentialMutationsIn(node, variable);
    if (!potentialMutationsIn.isEmpty) {
      typePromotion.addHint(typePromotion.node,
          MessageKind.POTENTIAL_MUTATION,
          {'variableName': variableName, 'shownType': typePromotion.type});
      for (Node mutation in potentialMutationsIn) {
        typePromotion.addInfo(mutation,
            MessageKind.POTENTIAL_MUTATION_HERE,
            {'variableName': variableName});
      }
    }
    List<Node> potentialMutationsInClosures =
        elements.getPotentialMutationsInClosure(variable);
    if (!potentialMutationsInClosures.isEmpty) {
      typePromotion.addHint(typePromotion.node,
          MessageKind.POTENTIAL_MUTATION_IN_CLOSURE,
          {'variableName': variableName, 'shownType': typePromotion.type});
      for (Node mutation in potentialMutationsInClosures) {
        typePromotion.addInfo(mutation,
            MessageKind.POTENTIAL_MUTATION_IN_CLOSURE_HERE,
            {'variableName': variableName});
      }
    }
    if (checkAccesses) {
      List<Node> accesses = elements.getAccessesByClosureIn(node, variable);
      List<Node> mutations = elements.getPotentialMutations(variable);
      if (!accesses.isEmpty && !mutations.isEmpty) {
        typePromotion.addHint(typePromotion.node,
            MessageKind.ACCESSED_IN_CLOSURE,
            {'variableName': variableName, 'shownType': typePromotion.type});
        for (Node access in accesses) {
          typePromotion.addInfo(access,
              MessageKind.ACCESSED_IN_CLOSURE_HERE,
              {'variableName': variableName});
        }
        for (Node mutation in mutations) {
          typePromotion.addInfo(mutation,
              MessageKind.POTENTIAL_MUTATION_HERE,
              {'variableName': variableName});
        }
      }
    }
  }

  /// Show type promotions from [left] and [right] in [node] given that the
  /// promoted variables are not potentially mutated in [right].
  void reshowTypePromotions(Node node, Node left, Node right) {
    for (TypePromotion typePromotion in  getShownTypePromotionsFor(left)) {
      typePromotion = typePromotion.copy();
      checkTypePromotion(right, typePromotion);
      showTypePromotion(node, typePromotion);
    }

    for (TypePromotion typePromotion in getShownTypePromotionsFor(right)) {
      typePromotion = typePromotion.copy();
      checkTypePromotion(right, typePromotion);
      showTypePromotion(node, typePromotion);
    }
  }

  /// Analyze [node] in the context of the known types shown in [context].
  DartType analyzeInPromotedContext(Node context, Node node) {
    Link<TypePromotion> knownForNode = const Link<TypePromotion>();
    for (TypePromotion typePromotion in  getShownTypePromotionsFor(context)) {
      typePromotion = typePromotion.copy();
      checkTypePromotion(node, typePromotion, checkAccesses: true);
      knownForNode = knownForNode.prepend(typePromotion);
      registerKnownTypePromotion(typePromotion);
    }

    final DartType type = analyze(node);

    while (!knownForNode.isEmpty) {
      unregisterKnownTypePromotion(knownForNode.head);
      knownForNode = knownForNode.tail;
    }

    return type;
  }

  /**
   * Check if a value of type [from] can be assigned to a variable, parameter or
   * return value of type [to].  If `isConst == true`, an error is emitted in
   * checked mode, otherwise a warning is issued.
   */
  bool checkAssignable(Node node, DartType from, DartType to,
                       {bool isConst: false}) {
    if (!types.isAssignable(from, to)) {
      if (compiler.enableTypeAssertions && isConst) {
        compiler.reportError(node, MessageKind.NOT_ASSIGNABLE.error,
                             {'fromType': from, 'toType': to});
      } else {
        reportTypeWarning(node, MessageKind.NOT_ASSIGNABLE.warning,
                          {'fromType': from, 'toType': to});
      }
      return false;
    }
    return true;
  }

  checkCondition(Expression condition) {
    checkAssignable(condition, analyze(condition), boolType);
  }

  void pushCascadeType(DartType type) {
    cascadeTypes = cascadeTypes.prepend(type);
  }

  DartType popCascadeType() {
    DartType type = cascadeTypes.head;
    cascadeTypes = cascadeTypes.tail;
    return type;
  }

  DartType visitBlock(Block node) {
    return analyze(node.statements);
  }

  DartType visitCascade(Cascade node) {
    analyze(node.expression);
    if (node.expression.asCascadeReceiver() == null) {
      // TODO(karlklose): bug: expressions of the form e..x = y do not have
      // a CascadeReceiver as expression currently.
      return types.dynamicType;
    }
    return popCascadeType();
  }

  DartType visitCascadeReceiver(CascadeReceiver node) {
    DartType type = analyze(node.expression);
    pushCascadeType(type);
    return type;
  }

  DartType visitDoWhile(DoWhile node) {
    StatementType bodyType = analyze(node.body);
    checkCondition(node.condition);
    return bodyType.join(StatementType.NOT_RETURNING);
  }

  DartType visitExpressionStatement(ExpressionStatement node) {
    Expression expression = node.expression;
    analyze(expression);
    return (expression.asThrow() != null)
        ? StatementType.RETURNING
        : StatementType.NOT_RETURNING;
  }

  /** Dart Programming Language Specification: 11.5.1 For Loop */
  DartType visitFor(For node) {
    analyzeWithDefault(node.initializer, StatementType.NOT_RETURNING);
    if (node.condition != null) {
      checkCondition(node.condition);
    }
    analyzeWithDefault(node.update, StatementType.NOT_RETURNING);
    StatementType bodyType = analyze(node.body);
    return bodyType.join(StatementType.NOT_RETURNING);
  }

  DartType visitFunctionDeclaration(FunctionDeclaration node) {
    analyze(node.function);
    return StatementType.NOT_RETURNING;
  }

  DartType visitFunctionExpression(FunctionExpression node) {
    DartType type;
    DartType returnType;
    DartType previousType;
    final FunctionElement element = elements[node];
    assert(invariant(node, element != null,
                     message: 'FunctionExpression with no element'));
    if (Elements.isUnresolved(element)) return types.dynamicType;
    if (identical(element.kind, ElementKind.GENERATIVE_CONSTRUCTOR) ||
        identical(element.kind, ElementKind.GENERATIVE_CONSTRUCTOR_BODY)) {
      type = types.dynamicType;
      returnType = types.voidType;

      element.functionSignature.forEachParameter((Element parameter) {
        if (parameter.isFieldParameter()) {
          FieldParameterElement fieldParameter = parameter;
          checkAssignable(parameter.parseNode(compiler),
              parameter.computeType(compiler),
              fieldParameter.fieldElement.computeType(compiler));
        }
      });
      if (node.initializers != null) {
        analyze(node.initializers);
      }
    } else {
      FunctionType functionType = element.computeType(compiler);
      returnType = functionType.returnType;
      type = functionType;
    }
    DartType previous = expectedReturnType;
    expectedReturnType = returnType;
    StatementType bodyType = analyze(node.body);
    if (returnType != types.voidType && !returnType.treatAsDynamic
        && bodyType != StatementType.RETURNING) {
      MessageKind kind;
      if (bodyType == StatementType.MAYBE_RETURNING) {
        kind = MessageKind.MAYBE_MISSING_RETURN;
      } else {
        kind = MessageKind.MISSING_RETURN;
      }
      reportTypeWarning(node.name, kind);
    }
    expectedReturnType = previous;
    return type;
  }

  DartType visitIdentifier(Identifier node) {
    if (node.isThis()) {
      return thisType;
    } else if (node.isSuper()) {
      return superType;
    } else {
      Element element = elements[node];
      assert(invariant(node, element != null,
          message: 'Missing element for identifier'));
      assert(invariant(node, element.isVariable() ||
                             element.isParameter() ||
                             element.isField(),
          message: 'Unexpected context element ${element}'));
      return element.computeType(compiler);
    }
  }

  DartType visitIf(If node) {
    Expression condition = node.condition.expression;
    Statement thenPart = node.thenPart;

    checkCondition(node.condition);

    StatementType thenType = analyzeInPromotedContext(condition, thenPart);

    StatementType elseType = node.hasElsePart ? analyze(node.elsePart)
                                              : StatementType.NOT_RETURNING;
    return thenType.join(elseType);
  }

  void checkPrivateAccess(Node node, Element element, String name) {
    if (name != null &&
        isPrivateName(name) &&
        element.getLibrary() != currentLibrary) {
      reportTypeWarning(
          node,
          MessageKind.PRIVATE_ACCESS,
          {'name': name,
           'libraryName': element.getLibrary().getLibraryOrScriptName()});
    }

  }

  ElementAccess lookupMember(Node node, DartType receiverType, String name,
                             MemberKind memberKind, Element receiverElement) {
    if (receiverType.treatAsDynamic) {
      return const DynamicAccess();
    }

    // Compute the unaliased type of the first non type variable bound of
    // [type].
    DartType computeUnaliasedBound(DartType type) {
      DartType originalType = type;
      while (identical(type.kind, TypeKind.TYPE_VARIABLE)) {
        TypeVariableType variable = type;
        type = variable.element.bound;
        if (type == originalType) {
          type = compiler.objectClass.rawType;
        }
      }
      return type.unalias(compiler);
    }

    // Compute the interface type of [type]. For type variable it is the
    // interface type of the bound, for function types and typedefs it is the
    // `Function` type.
    InterfaceType computeInterfaceType(DartType type) {
      if (type.kind == TypeKind.FUNCTION) {
         type = compiler.functionClass.rawType;
      }
      assert(invariant(node, type.kind == TypeKind.INTERFACE,
          message: "unexpected type kind ${type.kind}."));
      return type;
    }

    // Compute the access of [name] on [type]. This function takes the special
    // 'call' method into account.
    ElementAccess getAccess(DartType unaliasedBound, InterfaceType interface) {
      InterfaceTypeMember member = interface.lookupMember(name,
          isSetter: identical(memberKind, MemberKind.SETTER));
      if (member != null) {
        return new MemberAccess(member);
      }
      if (name == 'call' && memberKind != MemberKind.SETTER) {
        if (unaliasedBound.kind == TypeKind.FUNCTION) {
          // This is an access the implicit 'call' method of a function type.
          return new FunctionCallAccess(receiverElement, unaliasedBound);
        }
        if (types.isSubtype(interface, compiler.functionClass.rawType)) {
          // This is an access of the special 'call' method implicitly defined
          // on 'Function'. This method can be called with any arguments, which
          // we ensure by giving it the type 'dynamic'.
          return new FunctionCallAccess(null, types.dynamicType);
        }
      }
      return null;
    }

    DartType unaliasedBound = computeUnaliasedBound(receiverType);
    InterfaceType interface = computeInterfaceType(unaliasedBound);
    ElementAccess access = getAccess(unaliasedBound, interface);
    if (access != null) {
      checkPrivateAccess(node, access.element, name);
      return access;
    }
    if (receiverElement != null &&
        (receiverElement.isVariable() || receiverElement.isParameter())) {
      Link<TypePromotion> typePromotions = typePromotionsMap[receiverElement];
      if (typePromotions != null) {
        while (!typePromotions.isEmpty) {
          TypePromotion typePromotion = typePromotions.head;
          if (!typePromotion.isValid) {
            DartType unaliasedBound = computeUnaliasedBound(typePromotion.type);
            InterfaceType interface = computeInterfaceType(unaliasedBound);
            if (getAccess(unaliasedBound, interface) != null) {
              reportTypePromotionHint(typePromotion);
            }
          }
          typePromotions = typePromotions.tail;
        }
      }
    }
    if (!interface.element.isProxy) {
      switch (memberKind) {
        case MemberKind.METHOD:
          reportTypeWarning(node, MessageKind.METHOD_NOT_FOUND,
              {'className': receiverType.name, 'memberName': name});
          break;
        case MemberKind.OPERATOR:
          reportTypeWarning(node, MessageKind.OPERATOR_NOT_FOUND,
              {'className': receiverType.name, 'memberName': name});
          break;
        case MemberKind.GETTER:
          reportTypeWarning(node, MessageKind.MEMBER_NOT_FOUND.warning,
              {'className': receiverType.name, 'memberName': name});
          break;
        case MemberKind.SETTER:
          reportTypeWarning(node, MessageKind.PROPERTY_NOT_FOUND,
              {'className': receiverType.name, 'memberName': name});
          break;
      }
    }
    return const DynamicAccess();
  }

  DartType lookupMemberType(Node node, DartType type, String name,
                            MemberKind memberKind) {
    return lookupMember(node, type, name, memberKind, null).computeType(compiler);
  }

  void analyzeArguments(Send send, Element element, DartType type,
                        [LinkBuilder<DartType> argumentTypes]) {
    Link<Node> arguments = send.arguments;
    DartType unaliasedType = type.unalias(compiler);
    if (identical(unaliasedType.kind, TypeKind.FUNCTION)) {
      bool error = false;
      FunctionType funType = unaliasedType;
      Link<DartType> parameterTypes = funType.parameterTypes;
      Link<DartType> optionalParameterTypes = funType.optionalParameterTypes;
      while (!arguments.isEmpty) {
        Node argument = arguments.head;
        NamedArgument namedArgument = argument.asNamedArgument();
        if (namedArgument != null) {
          argument = namedArgument.expression;
          String argumentName = namedArgument.name.source;
          DartType namedParameterType =
              funType.getNamedParameterType(argumentName);
          if (namedParameterType == null) {
            error = true;
            // TODO(johnniwinther): Provide better information on the called
            // function.
            reportTypeWarning(argument, MessageKind.NAMED_ARGUMENT_NOT_FOUND,
                {'argumentName': argumentName});

            DartType argumentType = analyze(argument);
            if (argumentTypes != null) argumentTypes.addLast(argumentType);
          } else {
            DartType argumentType = analyze(argument);
            if (argumentTypes != null) argumentTypes.addLast(argumentType);
            if (!checkAssignable(argument, argumentType, namedParameterType)) {
              error = true;
            }
          }
        } else {
          if (parameterTypes.isEmpty) {
            if (optionalParameterTypes.isEmpty) {
              error = true;
              // TODO(johnniwinther): Provide better information on the
              // called function.
              reportTypeWarning(argument, MessageKind.ADDITIONAL_ARGUMENT);

              DartType argumentType = analyze(argument);
              if (argumentTypes != null) argumentTypes.addLast(argumentType);
            } else {
              DartType argumentType = analyze(argument);
              if (argumentTypes != null) argumentTypes.addLast(argumentType);
              if (!checkAssignable(argument,
                                   argumentType, optionalParameterTypes.head)) {
                error = true;
              }
              optionalParameterTypes = optionalParameterTypes.tail;
            }
          } else {
            DartType argumentType = analyze(argument);
            if (argumentTypes != null) argumentTypes.addLast(argumentType);
            if (!checkAssignable(argument, argumentType, parameterTypes.head)) {
              error = true;
            }
            parameterTypes = parameterTypes.tail;
          }
        }
        arguments = arguments.tail;
      }
      if (!parameterTypes.isEmpty) {
        error = true;
        // TODO(johnniwinther): Provide better information on the called
        // function.
        reportTypeWarning(send, MessageKind.MISSING_ARGUMENT,
            {'argumentType': parameterTypes.head});
      }
      if (error) {
        // TODO(johnniwinther): Improve access to declaring element and handle
        // synthesized member signatures. Currently function typed instance
        // members provide no access to there own name.
        if (element == null) {
          element = type.element;
        } else if (type.element.isTypedef()) {
          if (element != null) {
            reportTypeInfo(element,
                           MessageKind.THIS_IS_THE_DECLARATION,
                           {'name': element.name});
          }
          element = type.element;
        }
        reportTypeInfo(element, MessageKind.THIS_IS_THE_METHOD);
      }
    } else {
      while(!arguments.isEmpty) {
        DartType argumentType = analyze(arguments.head);
        if (argumentTypes != null) argumentTypes.addLast(argumentType);
        arguments = arguments.tail;
      }
    }
  }

  // Analyze the invocation [node] of [elementAccess].
  //
  // If provided [argumentTypes] is filled with the argument types during
  // analysis.
  DartType analyzeInvocation(Send node, ElementAccess elementAccess,
                             [LinkBuilder<DartType> argumentTypes]) {
    DartType type = elementAccess.computeType(compiler);
    if (elementAccess.isCallable(compiler)) {
      analyzeArguments(node, elementAccess.element, type, argumentTypes);
    } else {
      reportTypeWarning(node, MessageKind.NOT_CALLABLE,
          {'elementName': elementAccess.element.name});
      analyzeArguments(node, elementAccess.element, types.dynamicType,
                       argumentTypes);
    }
    type = type.unalias(compiler);
    if (identical(type.kind, TypeKind.FUNCTION)) {
      FunctionType funType = type;
      return funType.returnType;
    } else {
      return types.dynamicType;
    }
  }

  /**
   * Computes the [ElementAccess] for [name] on the [node] possibly using the
   * [element] provided for [node] by the resolver.
   */
  ElementAccess computeAccess(Send node, String name, Element element,
                              MemberKind memberKind) {
    if (element != null && element.isErroneous()) {
      // An error has already been reported for this node.
      return const DynamicAccess();
    }
    if (node.receiver != null) {
      Element receiverElement = elements[node.receiver];
      if (receiverElement != null) {
        if (receiverElement.isPrefix()) {
          assert(invariant(node, element != null,
              message: 'Prefixed node has no element.'));
          return computeResolvedAccess(node, name, element, memberKind);
        }
      }
      // e.foo() for some expression e.
      DartType receiverType = analyze(node.receiver);
      if (receiverType.treatAsDynamic || receiverType.isVoid) {
        return const DynamicAccess();
      }
      TypeKind receiverKind = receiverType.kind;
      return lookupMember(node, receiverType, name, memberKind,
          elements[node.receiver]);
    } else {
      return computeResolvedAccess(node, name, element, memberKind);
    }
  }

  /**
   * Computes the [ElementAccess] for [name] on the [node] using the [element]
   * provided for [node] by the resolver.
   */
  ElementAccess computeResolvedAccess(Send node, String name,
                                      Element element, MemberKind memberKind) {
    if (element == null) {
      // foo() where foo is unresolved.
      return lookupMember(node, thisType, name, memberKind, null);
    } else if (element.isErroneous()) {
      // foo() where foo is erroneous.
      return const DynamicAccess();
    } else if (element.impliesType()) {
      // The literal `Foo` where Foo is a class, a typedef, or a type variable.
      if (elements.isTypeLiteral(node)) {
        assert(invariant(node, identical(compiler.typeClass,
            elements.getType(node).element),
            message: 'Expected type literal type: '
              '${elements.getType(node)}'));
        return new TypeLiteralAccess(element);
      }
      return createResolvedAccess(node, name, element);
    } else if (element.isMember()) {
      // foo() where foo is an instance member.
      return lookupMember(node, thisType, name, memberKind, null);
    } else if (element.isFunction()) {
      // foo() where foo is a method in the same class.
      return createResolvedAccess(node, name, element);
    } else if (element.isVariable() ||
        element.isParameter() ||
        element.isField()) {
      // foo() where foo is a field in the same class.
      return createResolvedAccess(node, name, element);
    } else if (element.isGetter() || element.isSetter()) {
      return createResolvedAccess(node, name, element);
    } else {
      compiler.internalErrorOnElement(
          element, 'unexpected element kind ${element.kind}');
      return null;
    }
  }

  ElementAccess createResolvedAccess(Send node, String name,
                                     Element element) {
    checkPrivateAccess(node, element, name);
    return createPromotedAccess(element);
  }

  ElementAccess createPromotedAccess(Element element) {
    if (element.isVariable() || element.isParameter()) {
      TypePromotion typePromotion = getKnownTypePromotion(element);
      if (typePromotion != null) {
        return new PromotedAccess(element, typePromotion.type);
      }
    }
    return new ResolvedAccess(element);
  }

  /**
   * Computes the type of the access of [name] on the [node] possibly using the
   * [element] provided for [node] by the resolver.
   */
  DartType computeAccessType(Send node, String name, Element element,
                             MemberKind memberKind) {
    DartType type =
        computeAccess(node, name, element, memberKind).computeType(compiler);
    if (type == null) {
      compiler.internalError('type is null on access of $name on $node',
                             node: node);
    }
    return type;
  }

  /// Compute a version of [shownType] that is more specific that [knownType].
  /// This is used to provided better hints when trying to promote a supertype
  /// to a raw subtype. For instance trying to promote `Iterable<int>` to `List`
  /// we suggest the use of `List<int>`, which would make promotion valid.
  DartType computeMoreSpecificType(DartType shownType,
                                   DartType knownType) {
    if (knownType.kind == TypeKind.INTERFACE &&
        shownType.kind == TypeKind.INTERFACE &&
        types.isSubtype(shownType.asRaw(), knownType)) {
      // For the comments in the block, assume the hierarchy:
      //     class A<T, V> {}
      //     class B<S, U> extends A<S, int> {}
      // and a promotion from a [knownType] of `A<double, int>` to a
      // [shownType] of `B`.
      InterfaceType knownInterfaceType = knownType;
      ClassElement shownClass = shownType.element;

      // Compute `B<double, dynamic>` as the subtype of `A<double, int>` using
      // the relation between `A<S, int>` and `A<double, int>`.
      MoreSpecificSubtypeVisitor visitor =
          new MoreSpecificSubtypeVisitor(compiler);
      InterfaceType shownTypeGeneric = visitor.computeMoreSpecific(
          shownClass, knownInterfaceType);

      if (shownTypeGeneric != null &&
          types.isMoreSpecific(shownTypeGeneric, knownType)) {
        // This should be the case but we double-check.
        // TODO(johnniwinther): Ensure that we don't suggest malbounded types.
        return shownTypeGeneric;
      }
    }
    return null;

  }

  DartType visitSend(Send node) {
    Element element = elements[node];

    if (element != null && element.isConstructor()) {
      DartType receiverType;
      if (node.receiver != null) {
        receiverType = analyze(node.receiver);
      } else if (node.selector.isSuper()) {
        receiverType = superType;
      } else {
        assert(node.selector.isThis());
        receiverType = thisType;
      }
      DartType constructorType = computeConstructorType(element, receiverType);
      analyzeArguments(node, element, constructorType);
      return types.dynamicType;
    }

    if (Elements.isClosureSend(node, element)) {
      if (element != null) {
        // foo() where foo is a local or a parameter.
        return analyzeInvocation(node, createPromotedAccess(element));
      } else {
        // exp() where exp is some complex expression like (o) or foo().
        DartType type = analyze(node.selector);
        return analyzeInvocation(node, new TypeAccess(type));
      }
    }

    Identifier selector = node.selector.asIdentifier();
    String name = selector.source;

    if (node.isOperator && identical(name, 'is')) {
      analyze(node.receiver);
      if (!node.isIsNotCheck) {
        Element variable = elements[node.receiver];
        if (variable == null) {
          // Look for the variable element within parenthesized expressions.
          ParenthesizedExpression parentheses =
              node.receiver.asParenthesizedExpression();
          while (parentheses != null) {
            variable = elements[parentheses.expression];
            if (variable != null) break;
            parentheses = parentheses.expression.asParenthesizedExpression();
          }
        }

        if (variable != null &&
            (variable.isVariable() || variable.isParameter())) {
          DartType knownType = getKnownType(variable);
          if (!knownType.isDynamic) {
            DartType shownType = elements.getType(node.arguments.head);
            TypePromotion typePromotion =
                new TypePromotion(node, variable, shownType);
            if (!types.isMoreSpecific(shownType, knownType)) {
              String variableName = variable.name;
              if (!types.isSubtype(shownType, knownType)) {
                typePromotion.addHint(node,
                    MessageKind.NOT_MORE_SPECIFIC_SUBTYPE,
                    {'variableName': variableName,
                     'shownType': shownType,
                     'knownType': knownType});
              } else {
                DartType shownTypeSuggestion =
                    computeMoreSpecificType(shownType, knownType);
                if (shownTypeSuggestion != null) {
                  typePromotion.addHint(node,
                      MessageKind.NOT_MORE_SPECIFIC_SUGGESTION,
                      {'variableName': variableName,
                       'shownType': shownType,
                       'shownTypeSuggestion': shownTypeSuggestion,
                       'knownType': knownType});
                } else {
                  typePromotion.addHint(node,
                      MessageKind.NOT_MORE_SPECIFIC,
                      {'variableName': variableName,
                       'shownType': shownType,
                       'knownType': knownType});
                }
              }
            }
            showTypePromotion(node, typePromotion);
          }
        }
      }
      return boolType;
    } if (node.isOperator && identical(name, 'as')) {
      analyze(node.receiver);
      return elements.getType(node.arguments.head);
    } else if (node.isOperator) {
      final Node receiver = node.receiver;
      final DartType receiverType = analyze(receiver);
      if (identical(name, '==') || identical(name, '!=')
          // TODO(johnniwinther): Remove these.
          || identical(name, '===') || identical(name, '!==')) {
        // Analyze argument.
        analyze(node.arguments.head);
        return boolType;
      } else if (identical(name, '||')) {
        checkAssignable(receiver, receiverType, boolType);
        final Node argument = node.arguments.head;
        final DartType argumentType = analyze(argument);
        checkAssignable(argument, argumentType, boolType);
        return boolType;
      } else if (identical(name, '&&')) {
        checkAssignable(receiver, receiverType, boolType);
        final Node argument = node.arguments.head;

        final DartType argumentType =
            analyzeInPromotedContext(receiver, argument);

        reshowTypePromotions(node, receiver, argument);

        checkAssignable(argument, argumentType, boolType);
        return boolType;
      } else if (identical(name, '!')) {
        checkAssignable(receiver, receiverType, boolType);
        return boolType;
      } else if (identical(name, '?')) {
        return boolType;
      }
      String operatorName = selector.source;
      if (identical(name, '-') && node.arguments.isEmpty) {
        operatorName = 'unary-';
      }
      assert(invariant(node,
                       identical(name, '+') || identical(name, '=') ||
                       identical(name, '-') || identical(name, '*') ||
                       identical(name, '/') || identical(name, '%') ||
                       identical(name, '~/') || identical(name, '|') ||
                       identical(name, '&') || identical(name, '^') ||
                       identical(name, '~')|| identical(name, '<<') ||
                       identical(name, '>>') ||
                       identical(name, '<') || identical(name, '>') ||
                       identical(name, '<=') || identical(name, '>=') ||
                       identical(name, '[]'),
                       message: 'Unexpected operator $name'));

      // TODO(karlklose): handle `void` in expression context by calling
      // [analyzeNonVoid] instead of [analyze].
      ElementAccess access = receiverType.isVoid ? const DynamicAccess()
          : lookupMember(node, receiverType, operatorName,
                         MemberKind.OPERATOR, null);
      LinkBuilder<DartType> argumentTypesBuilder = new LinkBuilder<DartType>();
      DartType resultType =
          analyzeInvocation(node, access, argumentTypesBuilder);
      if (identical(receiverType.element, compiler.intClass)) {
        if (identical(name, '+') ||
            identical(operatorName, '-') ||
            identical(name, '*') ||
            identical(name, '%')) {
          DartType argumentType = argumentTypesBuilder.toLink().head;
          if (identical(argumentType.element, compiler.intClass)) {
            return intType;
          } else if (identical(argumentType.element, compiler.doubleClass)) {
            return doubleType;
          }
        }
      }
      return resultType;
    } else if (node.isPropertyAccess) {
      ElementAccess access =
          computeAccess(node, selector.source, element, MemberKind.GETTER);
      return access.computeType(compiler);
    } else if (node.isFunctionObjectInvocation) {
      return unhandledExpression();
    } else {
      ElementAccess access =
          computeAccess(node, selector.source, element, MemberKind.METHOD);
      return analyzeInvocation(node, access);
    }
  }

  /// Returns the first type in the list or [:dynamic:] if the list is empty.
  DartType firstType(Link<DartType> link) {
    return link.isEmpty ? types.dynamicType : link.head;
  }

  /**
   * Returns the second type in the list or [:dynamic:] if the list is too
   * short.
   */
  DartType secondType(Link<DartType> link) {
    return link.isEmpty || link.tail.isEmpty
        ? types.dynamicType : link.tail.head;
  }

  /**
   * Checks [: target o= value :] for some operator o, and returns the type
   * of the result. This method also handles increment/decrement expressions
   * like [: target++ :].
   */
  DartType checkAssignmentOperator(SendSet node,
                                   String operatorName,
                                   Node valueNode,
                                   DartType value) {
    assert(invariant(node, !node.isIndex));
    Element setterElement = elements[node];
    Element getterElement = elements[node.selector];
    Identifier selector = node.selector;
    DartType getter = computeAccessType(
        node, selector.source, getterElement, MemberKind.GETTER);
    DartType setter = computeAccessType(
        node, selector.source, setterElement, MemberKind.SETTER);
    // [operator] is the type of operator+ or operator- on [target].
    DartType operator =
        lookupMemberType(node, getter, operatorName, MemberKind.OPERATOR);
    if (operator is FunctionType) {
      FunctionType operatorType = operator;
      // [result] is the type of target o value.
      DartType result = operatorType.returnType;
      DartType operatorArgument = firstType(operatorType.parameterTypes);
      // Check target o value.
      bool validValue = checkAssignable(valueNode, value, operatorArgument);
      if (validValue || !(node.isPrefix || node.isPostfix)) {
        // Check target = result.
        checkAssignable(node.assignmentOperator, result, setter);
      }
      return node.isPostfix ? getter : result;
    }
    return types.dynamicType;
  }

  /**
   * Checks [: base[key] o= value :] for some operator o, and returns the type
   * of the result. This method also handles increment/decrement expressions
   * like [: base[key]++ :].
   */
  DartType checkIndexAssignmentOperator(SendSet node,
                                        String operatorName,
                                        Node valueNode,
                                        DartType value) {
    assert(invariant(node, node.isIndex));
    final DartType base = analyze(node.receiver);
    final Node keyNode = node.arguments.head;
    final DartType key = analyze(keyNode);

    // [indexGet] is the type of operator[] on [base].
    DartType indexGet = lookupMemberType(
        node, base, '[]', MemberKind.OPERATOR);
    if (indexGet is FunctionType) {
      FunctionType indexGetType = indexGet;
      DartType indexGetKey = firstType(indexGetType.parameterTypes);
      // Check base[key].
      bool validKey = checkAssignable(keyNode, key, indexGetKey);

      // [element] is the type of base[key].
      DartType element = indexGetType.returnType;
      // [operator] is the type of operator o on [element].
      DartType operator = lookupMemberType(
          node, element, operatorName, MemberKind.OPERATOR);
      if (operator is FunctionType) {
        FunctionType operatorType = operator;

        // Check base[key] o value.
        DartType operatorArgument = firstType(operatorType.parameterTypes);
        bool validValue = checkAssignable(valueNode, value, operatorArgument);

        // [result] is the type of base[key] o value.
        DartType result = operatorType.returnType;

        // [indexSet] is the type of operator[]= on [base].
        DartType indexSet = lookupMemberType(
            node, base, '[]=', MemberKind.OPERATOR);
        if (indexSet is FunctionType) {
          FunctionType indexSetType = indexSet;
          DartType indexSetKey = firstType(indexSetType.parameterTypes);
          DartType indexSetValue = secondType(indexSetType.parameterTypes);

          if (validKey || indexGetKey != indexSetKey) {
            // Only check base[key] on []= if base[key] was valid for [] or
            // if the key types differ.
            checkAssignable(keyNode, key, indexSetKey);
          }
          // Check base[key] = result
          if (validValue || !(node.isPrefix || node.isPostfix)) {
            checkAssignable(node.assignmentOperator, result, indexSetValue);
          }
        }
        return node.isPostfix ? element : result;
      }
    }
    return types.dynamicType;
  }

  visitSendSet(SendSet node) {
    Element element = elements[node];
    Identifier selector = node.selector;
    final name = node.assignmentOperator.source;
    if (identical(name, '=')) {
      // e1 = value
      if (node.isIndex) {
         // base[key] = value
        final DartType base = analyze(node.receiver);
        final Node keyNode = node.arguments.head;
        final DartType key = analyze(keyNode);
        final Node valueNode = node.arguments.tail.head;
        final DartType value = analyze(valueNode);
        DartType indexSet = lookupMemberType(
            node, base, '[]=', MemberKind.OPERATOR);
        if (indexSet is FunctionType) {
          FunctionType indexSetType = indexSet;
          DartType indexSetKey = firstType(indexSetType.parameterTypes);
          checkAssignable(keyNode, key, indexSetKey);
          DartType indexSetValue = secondType(indexSetType.parameterTypes);
          checkAssignable(node.assignmentOperator, value, indexSetValue);
        }
        return value;
      } else {
        // target = value
        DartType target = computeAccessType(node, selector.source,
                                            element, MemberKind.SETTER);
        final Node valueNode = node.arguments.head;
        final DartType value = analyze(valueNode);
        checkAssignable(node.assignmentOperator, value, target);
        return value;
      }
    } else if (identical(name, '++') || identical(name, '--')) {
      // e++ or e--
      String operatorName = identical(name, '++') ? '+' : '-';
      if (node.isIndex) {
        // base[key]++, base[key]--, ++base[key], or --base[key]
        return checkIndexAssignmentOperator(
            node, operatorName, node.assignmentOperator, intType);
      } else {
        // target++, target--, ++target, or --target
        return checkAssignmentOperator(
            node, operatorName, node.assignmentOperator, intType);
      }
    } else {
      // e1 o= e2 for some operator o.
      String operatorName;
      switch (name) {
        case '+=': operatorName = '+'; break;
        case '-=': operatorName = '-'; break;
        case '*=': operatorName = '*'; break;
        case '/=': operatorName = '/'; break;
        case '%=': operatorName = '%'; break;
        case '~/=': operatorName = '~/'; break;
        case '&=': operatorName = '&'; break;
        case '|=': operatorName = '|'; break;
        case '^=': operatorName = '^'; break;
        case '<<=': operatorName = '<<'; break;
        case '>>=': operatorName = '>>'; break;
        default:
          compiler.internalError(
              'Unexpected assignment operator $name', node: node);
      }
      if (node.isIndex) {
        // base[key] o= value for some operator o.
        final Node valueNode = node.arguments.tail.head;
        final DartType value = analyze(valueNode);
        return checkIndexAssignmentOperator(
            node, operatorName, valueNode, value);
      } else {
        // target o= value for some operator o.
        final Node valueNode = node.arguments.head;
        final DartType value = analyze(valueNode);
        return checkAssignmentOperator(node, operatorName, valueNode, value);
      }
    }
  }

  DartType visitLiteralInt(LiteralInt node) {
    return intType;
  }

  DartType visitLiteralDouble(LiteralDouble node) {
    return doubleType;
  }

  DartType visitLiteralBool(LiteralBool node) {
    return boolType;
  }

  DartType visitLiteralString(LiteralString node) {
    return stringType;
  }

  DartType visitStringJuxtaposition(StringJuxtaposition node) {
    analyze(node.first);
    analyze(node.second);
    return stringType;
  }

  DartType visitLiteralNull(LiteralNull node) {
    return types.dynamicType;
  }

  DartType visitLiteralSymbol(LiteralSymbol node) {
    return compiler.symbolClass.computeType(compiler);
  }

  DartType computeConstructorType(Element constructor, DartType type) {
    if (Elements.isUnresolved(constructor)) return types.dynamicType;
    DartType constructorType = constructor.computeType(compiler);
    if (identical(type.kind, TypeKind.INTERFACE)) {
      if (constructor.isSynthesized) {
        // TODO(johnniwinther): Remove this when synthesized constructors handle
        // type variables correctly.
        InterfaceType interfaceType = type;
        ClassElement receiverElement = interfaceType.element;
        while (receiverElement.isMixinApplication) {
          receiverElement = receiverElement.supertype.element;
        }
        constructorType = constructorType.substByContext(
            interfaceType.asInstanceOf(receiverElement));
      } else {
        constructorType = constructorType.substByContext(type);
      }
    }
    return constructorType;
  }

  DartType visitNewExpression(NewExpression node) {
    Element element = elements[node.send];
    if (Elements.isUnresolved(element)) return types.dynamicType;

    checkPrivateAccess(node, element, element.name);

    DartType newType = elements.getType(node);
    DartType constructorType = computeConstructorType(element, newType);
    analyzeArguments(node.send, element, constructorType);
    return newType;
  }

  DartType visitLiteralList(LiteralList node) {
    InterfaceType listType = elements.getType(node);
    DartType listElementType = firstType(listType.typeArguments);
    for (Link<Node> link = node.elements.nodes;
         !link.isEmpty;
         link = link.tail) {
      Node element = link.head;
      DartType elementType = analyze(element);
      checkAssignable(element, elementType, listElementType,
          isConst: node.isConst());
    }
    return listType;
  }

  DartType visitNodeList(NodeList node) {
    DartType type = StatementType.NOT_RETURNING;
    bool reportedDeadCode = false;
    for (Link<Node> link = node.nodes; !link.isEmpty; link = link.tail) {
      DartType nextType = analyze(link.head);
      if (type == StatementType.RETURNING) {
        if (!reportedDeadCode) {
          reportTypeWarning(link.head, MessageKind.UNREACHABLE_CODE);
          reportedDeadCode = true;
        }
      } else if (type == StatementType.MAYBE_RETURNING){
        if (nextType == StatementType.RETURNING) {
          type = nextType;
        }
      } else {
        type = nextType;
      }
    }
    return type;
  }

  DartType visitRethrow(Rethrow node) {
    return StatementType.RETURNING;
  }

  /** Dart Programming Language Specification: 11.10 Return */
  DartType visitReturn(Return node) {
    if (identical(node.getBeginToken().stringValue, 'native')) {
      return StatementType.RETURNING;
    }
    if (node.isRedirectingFactoryBody) {
      // TODO(lrn): Typecheck the body. It must refer to the constructor
      // of a subtype.
      return StatementType.RETURNING;
    }

    final expression = node.expression;
    final isVoidFunction = (identical(expectedReturnType, types.voidType));

    // Executing a return statement return e; [...] It is a static type warning
    // if the type of e may not be assigned to the declared return type of the
    // immediately enclosing function.
    if (expression != null) {
      final expressionType = analyze(expression);
      Element element = elements.currentElement;
      if (element != null && element.isGenerativeConstructor()) {
        // The resolver already emitted an error for this expression.
      } else if (isVoidFunction
          && !types.isAssignable(expressionType, types.voidType)) {
        reportTypeWarning(expression, MessageKind.RETURN_VALUE_IN_VOID);
      } else {
        checkAssignable(expression, expressionType, expectedReturnType);
      }

    // Let f be the function immediately enclosing a return statement of the
    // form 'return;' It is a static warning if both of the following conditions
    // hold:
    // - f is not a generative constructor.
    // - The return type of f may not be assigned to void.
    } else if (!types.isAssignable(expectedReturnType, types.voidType)) {
      reportTypeWarning(node, MessageKind.RETURN_NOTHING,
                        {'returnType': expectedReturnType});
    }
    return StatementType.RETURNING;
  }

  DartType visitThrow(Throw node) {
    // TODO(johnniwinther): Handle reachability.
    analyze(node.expression);
    return types.dynamicType;
  }

  DartType visitTypeAnnotation(TypeAnnotation node) {
    return elements.getType(node);
  }

  DartType visitVariableDefinitions(VariableDefinitions node) {
    DartType type = analyzeWithDefault(node.type, types.dynamicType);
    if (type == types.voidType) {
      reportTypeWarning(node.type, MessageKind.VOID_VARIABLE);
      type = types.dynamicType;
    }
    for (Link<Node> link = node.definitions.nodes; !link.isEmpty;
         link = link.tail) {
      Node definition = link.head;
      invariant(definition, definition is Identifier || definition is SendSet,
          message: 'expected identifier or initialization');
      if (definition is SendSet) {
        SendSet initialization = definition;
        DartType initializer = analyzeNonVoid(initialization.arguments.head);
        checkAssignable(initialization.assignmentOperator, initializer, type);
      }
    }
    return StatementType.NOT_RETURNING;
  }

  DartType visitWhile(While node) {
    checkCondition(node.condition);
    StatementType bodyType = analyze(node.body);
    Expression cond = node.condition.asParenthesizedExpression().expression;
    if (cond.asLiteralBool() != null && cond.asLiteralBool().value == true) {
      // If the condition is a constant boolean expression denoting true,
      // control-flow always enters the loop body.
      // TODO(karlklose): this should be StatementType.RETURNING unless there
      // is a break in the loop body that has the loop or a label outside the
      // loop as a target.
      return bodyType;
    } else {
      return bodyType.join(StatementType.NOT_RETURNING);
    }
  }

  DartType visitParenthesizedExpression(ParenthesizedExpression node) {
    Expression expression = node.expression;
    DartType type = analyze(expression);
    for (TypePromotion typePromotion in getShownTypePromotionsFor(expression)) {
      showTypePromotion(node, typePromotion);
    }
    return type;
  }

  DartType visitConditional(Conditional node) {
    Expression condition = node.condition;
    Expression thenExpression = node.thenExpression;

    checkCondition(condition);

    DartType thenType = analyzeInPromotedContext(condition, thenExpression);

    DartType elseType = analyzeNonVoid(node.elseExpression);
    return compiler.types.computeLeastUpperBound(thenType, elseType);
  }

  visitStringInterpolation(StringInterpolation node) {
    node.visitChildren(this);
    return stringType;
  }

  visitStringInterpolationPart(StringInterpolationPart node) {
    node.visitChildren(this);
    return stringType;
  }

  visitEmptyStatement(EmptyStatement node) {
    return StatementType.NOT_RETURNING;
  }

  visitBreakStatement(BreakStatement node) {
    return StatementType.NOT_RETURNING;
  }

  visitContinueStatement(ContinueStatement node) {
    return StatementType.NOT_RETURNING;
  }

  visitForIn(ForIn node) {
    analyze(node.expression);
    StatementType bodyType = analyze(node.body);
    return bodyType.join(StatementType.NOT_RETURNING);
  }

  visitLabeledStatement(LabeledStatement node) {
    return analyze(node.statement);
  }

  visitLiteralMap(LiteralMap node) {
    InterfaceType mapType = elements.getType(node);
    DartType mapKeyType = firstType(mapType.typeArguments);
    DartType mapValueType = secondType(mapType.typeArguments);
    bool isConst = node.isConst();
    for (Link<Node> link = node.entries.nodes;
         !link.isEmpty;
         link = link.tail) {
      LiteralMapEntry entry = link.head;
      DartType keyType = analyze(entry.key);
      checkAssignable(entry.key, keyType, mapKeyType, isConst: isConst);
      DartType valueType = analyze(entry.value);
      checkAssignable(entry.value, valueType, mapValueType, isConst: isConst);
    }
    return mapType;
  }

  visitNamedArgument(NamedArgument node) {
    // Named arguments are visited as part of analyzing invocations of
    // unresolved methods. For instance [: foo(a: 42); :] where 'foo' is neither
    // found in the enclosing scope nor through lookup on 'this' or
    // [: x.foo(b: 42); :] where 'foo' cannot be not found through lookup on
    // the static type of 'x'.
    return analyze(node.expression);
  }

  bool invalidSwitchExpressionType(Node diagnosticNode, DartType type) {
    if (type.kind == TypeKind.FUNCTION) return true;
    assert(invariant(diagnosticNode, type.kind == TypeKind.INTERFACE,
        message: "Expected interface type"));
    ClassElement cls = type.element;
    if (cls == compiler.doubleClass) return true;
    if (cls == compiler.intClass || cls == compiler.stringClass) return false;
    if (cls == compiler.typeClass) return true;
    Element equals = cls.lookupMember('==');
    return equals.getEnclosingClass() != compiler.objectClass;
  }

  visitSwitchStatement(SwitchStatement node) {
    // TODO(johnniwinther): Handle reachability based on reachability of
    // switch cases.
    DartType expressionType = analyze(node.expression);
    Map<CaseMatch, DartType> caseTypeMap = new Map<CaseMatch, DartType>();
    for (SwitchCase switchCase in node.cases) {
      for (Node labelOrCase in switchCase.labelsAndCases) {
        CaseMatch caseMatch = labelOrCase.asCaseMatch();
        if (caseMatch == null) continue;

        DartType caseType = analyze(caseMatch.expression);
        caseTypeMap[caseMatch] = caseType;
        checkAssignable(caseMatch, expressionType, caseType);
      }

      analyze(switchCase);
    }
    // Check that all the case expressions have the same type.
    CaseMatch firstCase = null;
    DartType firstCaseType = null;
    bool hasReportedProblem = false;
    caseTypeMap.forEach((CaseMatch caseMatch, DartType caseType) {
      if (firstCaseType == null) {
        firstCase = caseMatch;
        firstCaseType = caseType;
      } else {
        if (caseType != firstCaseType) {
          if (!hasReportedProblem) {
            compiler.reportError(
                node,
                MessageKind.SWITCH_CASE_TYPES_NOT_EQUAL,
                {'type': firstCaseType});
            compiler.reportInfo(
                firstCase.expression,
                MessageKind.SWITCH_CASE_TYPES_NOT_EQUAL_CASE,
                {'type': firstCaseType});
            hasReportedProblem = true;
          }
          compiler.reportInfo(
              caseMatch.expression,
              MessageKind.SWITCH_CASE_TYPES_NOT_EQUAL_CASE,
              {'type': caseType});
        }
      }
    });
    // Check that the type is either [int], [String], or a class that does not
    // implement `operator ==`.
    if (firstCaseType != null &&
        invalidSwitchExpressionType(firstCase, firstCaseType)) {
      compiler.reportError(firstCase.expression,
          MessageKind.SWITCH_CASE_VALUE_OVERRIDES_EQUALS,
          {'type': firstCaseType});
    }
    return StatementType.NOT_RETURNING;
  }

  visitSwitchCase(SwitchCase node) {
    return analyze(node.statements);
  }

  visitTryStatement(TryStatement node) {
    // TODO(johnniwinther): Use reachability information of try-block,
    // catch-blocks and finally-block to compute the whether the try statement
    // is returning.
    analyze(node.tryBlock);
    for (CatchBlock catchBlock in node.catchBlocks) {
      analyze(catchBlock);
    }
    analyzeWithDefault(node.finallyBlock, null);
    return StatementType.NOT_RETURNING;
  }

  visitCatchBlock(CatchBlock node) {
    return analyze(node.block);
  }

  visitTypedef(Typedef node) {
    // Do not typecheck [Typedef] nodes.
  }

  visitNode(Node node) {
    compiler.internalError(
        'Unexpected node ${node.getObjectDescription()} in the type checker.',
        node: node);
  }
}