source: branches/2893_BNLR/HeuristicLab.ExtLibs/HeuristicLab.NRefactory/5.5.0/NRefactory.CSharp-5.5.0/Resolver/ResolveVisitor.cs

// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
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// 
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
// 
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// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
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using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading;
using ICSharpCode.NRefactory.CSharp.Analysis;
using ICSharpCode.NRefactory.CSharp.TypeSystem;
using ICSharpCode.NRefactory.Semantics;
using ICSharpCode.NRefactory.TypeSystem;
using ICSharpCode.NRefactory.TypeSystem.Implementation;

namespace ICSharpCode.NRefactory.CSharp.Resolver
{
  /// <summary>
  /// Traverses the DOM and resolves expressions.
  /// </summary>
  /// <remarks>
  /// The ResolveVisitor does two jobs at the same time: it tracks the resolve context (properties on CSharpResolver)
  /// and it resolves the expressions visited.
  /// To allow using the context tracking without having to resolve every expression in the file (e.g. when you want to resolve
  /// only a single node deep within the DOM), you can use the <see cref="IResolveVisitorNavigator"/> interface.
  /// The navigator allows you to switch the between scanning mode and resolving mode.
  /// In scanning mode, the context is tracked (local variables registered etc.), but nodes are not resolved.
  /// While scanning, the navigator will get asked about every node that the resolve visitor is about to enter.
  /// This allows the navigator whether to keep scanning, whether switch to resolving mode, or whether to completely skip the
  /// subtree rooted at that node.
  /// 
  /// In resolving mode, the context is tracked and nodes will be resolved.
  /// The resolve visitor may decide that it needs to resolve other nodes as well in order to resolve the current node.
  /// In this case, those nodes will be resolved automatically, without asking the navigator interface.
  /// For child nodes that are not essential to resolving, the resolve visitor will switch back to scanning mode (and thus will
  /// ask the navigator for further instructions).
  /// 
  /// Moreover, there is the <c>ResolveAll</c> mode - it works similar to resolving mode, but will not switch back to scanning mode.
  /// The whole subtree will be resolved without notifying the navigator.
  /// </remarks>
  sealed class ResolveVisitor : IAstVisitor<ResolveResult>
  {
    // The ResolveVisitor is also responsible for handling lambda expressions.
    
    static readonly ResolveResult errorResult = ErrorResolveResult.UnknownError;
    
    CSharpResolver resolver;
    /// <summary>Resolve result of the current LINQ query.</summary>
    /// <remarks>We do not have to put this into the stored state (resolver) because
    /// query expressions are always resolved in a single operation.</remarks>
    ResolveResult currentQueryResult;
    readonly CSharpUnresolvedFile unresolvedFile;
    readonly Dictionary<AstNode, ResolveResult> resolveResultCache = new Dictionary<AstNode, ResolveResult>();
    readonly Dictionary<AstNode, CSharpResolver> resolverBeforeDict = new Dictionary<AstNode, CSharpResolver>();
    readonly Dictionary<AstNode, CSharpResolver> resolverAfterDict = new Dictionary<AstNode, CSharpResolver>();
    readonly Dictionary<Expression, ConversionWithTargetType> conversionDict = new Dictionary<Expression, ConversionWithTargetType>();
    
    internal struct ConversionWithTargetType
    {
      public readonly Conversion Conversion;
      public readonly IType TargetType;
      
      public ConversionWithTargetType(Conversion conversion, IType targetType)
      {
        this.Conversion = conversion;
        this.TargetType = targetType;
      }
    }
    
    IResolveVisitorNavigator navigator;
    bool resolverEnabled;
    List<LambdaBase> undecidedLambdas;
    internal CancellationToken cancellationToken;
    
    #region Constructor
    static readonly IResolveVisitorNavigator skipAllNavigator = new ConstantModeResolveVisitorNavigator(ResolveVisitorNavigationMode.Skip, null);
    
    /// <summary>
    /// Creates a new ResolveVisitor instance.
    /// </summary>
    public ResolveVisitor(CSharpResolver resolver, CSharpUnresolvedFile unresolvedFile)
    {
      if (resolver == null)
        throw new ArgumentNullException("resolver");
      this.resolver = resolver;
      this.unresolvedFile = unresolvedFile;
      this.navigator = skipAllNavigator;
    }
    
    internal void SetNavigator(IResolveVisitorNavigator navigator)
    {
      this.navigator = navigator ?? skipAllNavigator;
    }
    
    ResolveResult voidResult {
      get {
        return new ResolveResult(resolver.Compilation.FindType(KnownTypeCode.Void));
      }
    }
    #endregion
    
    #region ResetContext
    /// <summary>
    /// Resets the visitor to the stored position, runs the action, and then reverts the visitor to the previous position.
    /// </summary>
    void ResetContext(CSharpResolver storedContext, Action action)
    {
      var oldResolverEnabled = this.resolverEnabled;
      var oldResolver = this.resolver;
      var oldQueryResult = this.currentQueryResult;
      try {
        this.resolverEnabled = false;
        this.resolver = storedContext;
        this.currentQueryResult = null;
        
        action();
      } finally {
        this.resolverEnabled = oldResolverEnabled;
        this.resolver = oldResolver;
        this.currentQueryResult = oldQueryResult;
      }
    }
    #endregion
    
    #region Scan / Resolve
    /// <summary>
    /// Scans the AST rooted at the given node.
    /// </summary>
    public void Scan(AstNode node)
    {
      if (node == null || node.IsNull)
        return;
      switch (node.NodeType) {
        case NodeType.Token:
        case NodeType.Whitespace:
          return; // skip tokens, identifiers, comments, etc.
      }
      // don't Scan again if the node was already resolved
      if (resolveResultCache.ContainsKey(node)) {
        // Restore state change caused by this node:
        CSharpResolver newResolver;
        if (resolverAfterDict.TryGetValue(node, out newResolver))
          resolver = newResolver;
        return;
      }
      
      var mode = navigator.Scan(node);
      switch (mode) {
        case ResolveVisitorNavigationMode.Skip:
          if (node is VariableDeclarationStatement || node is SwitchSection) {
            // Enforce scanning of variable declarations.
            goto case ResolveVisitorNavigationMode.Scan;
          }
          StoreCurrentState(node);
          break;
        case ResolveVisitorNavigationMode.Scan:
          bool oldResolverEnabled = resolverEnabled;
          var oldResolver = resolver;
          resolverEnabled = false;
          StoreCurrentState(node);
          ResolveResult result = node.AcceptVisitor(this);
          if (result != null) {
            // If the node was resolved, store the result even though it wasn't requested.
            // This is necessary so that Visit-methods that decide to always resolve are
            // guaranteed to get called only once.
            // This is used for lambda registration.
            StoreResult(node, result);
            if (resolver != oldResolver) {
              // The node changed the resolver state:
              resolverAfterDict.Add(node, resolver);
            }
            cancellationToken.ThrowIfCancellationRequested();
          }
          resolverEnabled = oldResolverEnabled;
          break;
        case ResolveVisitorNavigationMode.Resolve:
          Resolve(node);
          break;
        default:
          throw new InvalidOperationException("Invalid value for ResolveVisitorNavigationMode");
      }
    }
    
    /// <summary>
    /// Equivalent to 'Scan', but also resolves the node at the same time.
    /// This method should be only used if the CSharpResolver passed to the ResolveVisitor was manually set
    /// to the correct state.
    /// Otherwise, use <c>resolver.Scan(syntaxTree); var result = resolver.GetResolveResult(node);</c>
    /// instead.
    /// --
    /// This method now is internal, because it is difficult to use correctly.
    /// Users of the public API should use Scan()+GetResolveResult() instead.
    /// </summary>
    internal ResolveResult Resolve(AstNode node)
    {
      if (node == null || node.IsNull)
        return errorResult;
      bool oldResolverEnabled = resolverEnabled;
      resolverEnabled = true;
      ResolveResult result;
      if (!resolveResultCache.TryGetValue(node, out result)) {
        cancellationToken.ThrowIfCancellationRequested();
        StoreCurrentState(node);
        var oldResolver = resolver;
        result = node.AcceptVisitor(this) ?? errorResult;
        StoreResult(node, result);
        if (resolver != oldResolver) {
          // The node changed the resolver state:
          resolverAfterDict.Add(node, resolver);
        }
      }
      resolverEnabled = oldResolverEnabled;
      return result;
    }
    
    IType ResolveType(AstType type)
    {
      return Resolve(type).Type;
    }
    
    void StoreCurrentState(AstNode node)
    {
      // It's possible that we re-visit an expression that we scanned over earlier,
      // so we might have to overwrite an existing state.
      
      #if DEBUG
      CSharpResolver oldResolver;
      if (resolverBeforeDict.TryGetValue(node, out oldResolver)) {
        Debug.Assert(oldResolver.LocalVariables.SequenceEqual(resolver.LocalVariables));
      }
      #endif
      
      resolverBeforeDict[node] = resolver;
    }
    
    void StoreResult(AstNode node, ResolveResult result)
    {
      Debug.Assert(result != null);
      if (node.IsNull)
        return;
      Log.WriteLine("Resolved '{0}' to {1}", node, result);
      Debug.Assert(!CSharpAstResolver.IsUnresolvableNode(node));
      // The state should be stored before the result is.
      Debug.Assert(resolverBeforeDict.ContainsKey(node));
      // Don't store results twice.
      Debug.Assert(!resolveResultCache.ContainsKey(node));
      // Don't use ConversionResolveResult as a result, because it can get
      // confused with an implicit conversion.
      Debug.Assert(!(result is ConversionResolveResult) || result is CastResolveResult);
      resolveResultCache[node] = result;
      if (navigator != null)
        navigator.Resolved(node, result);
    }
    
    void ScanChildren(AstNode node)
    {
      for (AstNode child = node.FirstChild; child != null; child = child.NextSibling) {
        Scan(child);
      }
    }
    #endregion
    
    #region Process Conversions
    sealed class AnonymousFunctionConversion : Conversion
    {
      public readonly IType ReturnType;
      public readonly ExplicitlyTypedLambda ExplicitlyTypedLambda;
      public readonly LambdaTypeHypothesis Hypothesis;
      readonly bool isValid;
      
      public AnonymousFunctionConversion(IType returnType, LambdaTypeHypothesis hypothesis, bool isValid)
      {
        if (returnType == null)
          throw new ArgumentNullException("returnType");
        this.ReturnType = returnType;
        this.Hypothesis = hypothesis;
        this.isValid = isValid;
      }
      
      public AnonymousFunctionConversion(IType returnType, ExplicitlyTypedLambda explicitlyTypedLambda, bool isValid)
      {
        if (returnType == null)
          throw new ArgumentNullException("returnType");
        this.ReturnType = returnType;
        this.ExplicitlyTypedLambda = explicitlyTypedLambda;
        this.isValid = isValid;
      }
      
      public override bool IsValid {
        get { return isValid; }
      }
      
      public override bool IsImplicit {
        get { return true; }
      }
      
      public override bool IsAnonymousFunctionConversion {
        get { return true; }
      }
    }
    
    /// <summary>
    /// Convert 'rr' to the target type using the specified conversion.
    /// </summary>
    void ProcessConversion(Expression expr, ResolveResult rr, Conversion conversion, IType targetType)
    {
      AnonymousFunctionConversion afc = conversion as AnonymousFunctionConversion;
      if (afc != null) {
        Log.WriteLine("Processing conversion of anonymous function to " + targetType + "...");
        
        Log.Indent();
        if (afc.Hypothesis != null)
          afc.Hypothesis.MergeInto(this, afc.ReturnType);
        if (afc.ExplicitlyTypedLambda != null)
          afc.ExplicitlyTypedLambda.ApplyReturnType(this, afc.ReturnType);
        Log.Unindent();
      }
      if (expr != null && !expr.IsNull && conversion != Conversion.IdentityConversion) {
        navigator.ProcessConversion(expr, rr, conversion, targetType);
        conversionDict[expr] = new ConversionWithTargetType(conversion, targetType);
      }
    }
    
    void ImportConversions(ResolveVisitor childVisitor)
    {
      foreach (var pair in childVisitor.conversionDict) {
        conversionDict.Add(pair.Key, pair.Value);
        navigator.ProcessConversion(pair.Key, resolveResultCache[pair.Key], pair.Value.Conversion, pair.Value.TargetType);
      }
    }
    
    /// <summary>
    /// Convert 'rr' to the target type.
    /// </summary>
    void ProcessConversion(Expression expr, ResolveResult rr, IType targetType)
    {
      if (expr == null || expr.IsNull)
        return;
      ProcessConversion(expr, rr, resolver.conversions.ImplicitConversion(rr, targetType), targetType);
    }
    
    /// <summary>
    /// Resolves the specified expression and processes the conversion to targetType.
    /// </summary>
    void ResolveAndProcessConversion(Expression expr, IType targetType)
    {
      if (targetType.Kind == TypeKind.Unknown) {
        // no need to resolve the expression right now
        Scan(expr);
      } else {
        ProcessConversion(expr, Resolve(expr), targetType);
      }
    }
    
    void ProcessConversionResult(Expression expr, ConversionResolveResult rr)
    {
      if (rr != null && !(rr is CastResolveResult))
        ProcessConversion(expr, rr.Input, rr.Conversion, rr.Type);
    }
    
    void ProcessConversionResults(IEnumerable<Expression> expr, IEnumerable<ResolveResult> conversionResolveResults)
    {
      Debug.Assert(expr.Count() == conversionResolveResults.Count());
      using (var e1 = expr.GetEnumerator()) {
        using (var e2 = conversionResolveResults.GetEnumerator()) {
          while (e1.MoveNext() && e2.MoveNext()) {
            ProcessConversionResult(e1.Current, e2.Current as ConversionResolveResult);
          }
        }
      }
    }
    
    void MarkUnknownNamedArguments(IEnumerable<Expression> arguments)
    {
      foreach (var nae in arguments.OfType<NamedArgumentExpression>()) {
        StoreCurrentState(nae);
        StoreResult(nae, new NamedArgumentResolveResult(nae.Name, resolveResultCache[nae.Expression]));
      }
    }
    
    void ProcessInvocationResult(Expression target, IEnumerable<Expression> arguments, ResolveResult invocation)
    {
      if (invocation is CSharpInvocationResolveResult || invocation is DynamicInvocationResolveResult) {
        int i = 0;
        IList<ResolveResult> argumentsRR;
        if (invocation is CSharpInvocationResolveResult) {
          var csi = (CSharpInvocationResolveResult)invocation;
          if (csi.IsExtensionMethodInvocation) {
            Debug.Assert(arguments.Count() + 1 == csi.Arguments.Count);
            ProcessConversionResult(target, csi.Arguments[0] as ConversionResolveResult);
            i = 1;
          } else {
            Debug.Assert(arguments.Count() == csi.Arguments.Count);
          }
          argumentsRR = csi.Arguments;
        }
        else {
          argumentsRR = ((DynamicInvocationResolveResult)invocation).Arguments;
        }

        foreach (Expression arg in arguments) {
          ResolveResult argRR = argumentsRR[i++];
          NamedArgumentExpression nae = arg as NamedArgumentExpression;
          NamedArgumentResolveResult nrr = argRR as NamedArgumentResolveResult;
          Debug.Assert((nae == null) == (nrr == null));
          if (nae != null && nrr != null) {
            StoreCurrentState(nae);
            StoreResult(nae, nrr);
            ProcessConversionResult(nae.Expression, nrr.Argument as ConversionResolveResult);
          } else {
            ProcessConversionResult(arg, argRR as ConversionResolveResult);
          }
        }
      }
      else {
        MarkUnknownNamedArguments(arguments);
      }
    }
    #endregion
    
    #region GetResolveResult
    /// <summary>
    /// Gets the resolve result for the specified node.
    /// If the node was not resolved by the navigator, this method will resolve it.
    /// </summary>
    public ResolveResult GetResolveResult(AstNode node)
    {
      Debug.Assert(!CSharpAstResolver.IsUnresolvableNode(node));
      
      MergeUndecidedLambdas();
      ResolveResult result;
      if (resolveResultCache.TryGetValue(node, out result))
        return result;
      
      AstNode parent;
      CSharpResolver storedResolver = GetPreviouslyScannedContext(node, out parent);
      ResetContext(
        storedResolver,
        delegate {
          navigator = new NodeListResolveVisitorNavigator(node);
          Debug.Assert(!resolverEnabled);
          Scan(parent);
          navigator = skipAllNavigator;
        });
      
      MergeUndecidedLambdas();
      return resolveResultCache[node];
    }
    
    CSharpResolver GetPreviouslyScannedContext(AstNode node, out AstNode parent)
    {
      parent = node;
      CSharpResolver storedResolver;
      while (!resolverBeforeDict.TryGetValue(parent, out storedResolver)) {
        AstNode tmp = parent.Parent;
        if (tmp == null)
          throw new InvalidOperationException("Could not find a resolver state for any parent of the specified node. Are you trying to resolve a node that is not a descendant of the CSharpAstResolver's root node?");
        if (tmp.NodeType == NodeType.Whitespace)
          return resolver; // special case: resolve expression within preprocessor directive
        parent = tmp;
      }
      return storedResolver;
    }
    
    /// <summary>
    /// Gets the resolver state in front of the specified node.
    /// If the node was not visited by a previous scanning process, the
    /// AST will be scanned again to determine the state.
    /// </summary>
    public CSharpResolver GetResolverStateBefore(AstNode node)
    {
      MergeUndecidedLambdas();
      CSharpResolver r;
      if (resolverBeforeDict.TryGetValue(node, out r))
        return r;
      
      AstNode parent;
      CSharpResolver storedResolver = GetPreviouslyScannedContext(node, out parent);
      ResetContext(
        storedResolver,
        delegate {
          navigator = new NodeListResolveVisitorNavigator(new[] { node }, scanOnly: true);
          Debug.Assert(!resolverEnabled);
          // parent might already be resolved if 'node' is an unresolvable node
          Scan(parent);
          navigator = skipAllNavigator;
        });
      
      MergeUndecidedLambdas();
      while (node != null) {
        if (resolverBeforeDict.TryGetValue(node, out r))
          return r;
        node = node.Parent;
      }
      return null;
    }
    
    public CSharpResolver GetResolverStateAfter(AstNode node)
    {
      // Resolve the node to fill the resolverAfterDict
      GetResolveResult(node);
      CSharpResolver result;
      if (resolverAfterDict.TryGetValue(node, out result))
        return result;
      else
        return GetResolverStateBefore(node);
    }
    
    public ConversionWithTargetType GetConversionWithTargetType(Expression expr)
    {
      GetResolverStateBefore(expr);
      ResolveParentForConversion(expr);
      ConversionWithTargetType result;
      if (conversionDict.TryGetValue(expr, out result)) {
        return result;
      } else {
        ResolveResult rr = GetResolveResult(expr);
        return new ConversionWithTargetType(Conversion.IdentityConversion, rr.Type);
      }
    }
    #endregion
    
    #region Track UsingScope
    ResolveResult IAstVisitor<ResolveResult>.VisitSyntaxTree(SyntaxTree unit)
    {
      CSharpResolver previousResolver = resolver;
      try {
        if (unresolvedFile != null) {
          resolver = resolver.WithCurrentUsingScope(unresolvedFile.RootUsingScope.Resolve(resolver.Compilation));
        } else {
          var cv = new TypeSystemConvertVisitor(unit.FileName ?? string.Empty);
          ApplyVisitorToUsings(cv, unit.Children);
          PushUsingScope(cv.UnresolvedFile.RootUsingScope);
        }
        ScanChildren(unit);
        return voidResult;
      } finally {
        resolver = previousResolver;
      }
    }
    
    void ApplyVisitorToUsings(TypeSystemConvertVisitor visitor, IEnumerable<AstNode> children)
    {
      foreach (var child in children) {
        if (child is ExternAliasDeclaration || child is UsingDeclaration || child is UsingAliasDeclaration) {
          child.AcceptVisitor(visitor);
        }
      }
    }
    
    void PushUsingScope(UsingScope usingScope)
    {
      usingScope.Freeze();
      resolver = resolver.WithCurrentUsingScope(new ResolvedUsingScope(resolver.CurrentTypeResolveContext, usingScope));
    }

    ResolveResult IAstVisitor<ResolveResult>.VisitNamespaceDeclaration(NamespaceDeclaration namespaceDeclaration)
    {
      CSharpResolver previousResolver = resolver;
      try {
        var nsName = namespaceDeclaration.NamespaceName;
        AstNode child = namespaceDeclaration.FirstChild;

        for (; child != null && child.Role != Roles.LBrace; child = child.NextSibling) {
          Scan(child);
        }

        if (unresolvedFile != null) {
          resolver = resolver.WithCurrentUsingScope(unresolvedFile.GetUsingScope(namespaceDeclaration.StartLocation).Resolve(resolver.Compilation));

        } else {
//          string fileName = namespaceDeclaration.GetRegion().FileName ?? string.Empty;
          // Fetch parent using scope
          // Create root using scope if necessary
          if (resolver.CurrentUsingScope == null)
            PushUsingScope(new UsingScope());
          
          // Create child using scope
          DomRegion region = namespaceDeclaration.GetRegion();
          var identifiers = namespaceDeclaration.Identifiers.ToList();
          // For all but the last identifier:
          UsingScope usingScope;
          for (int i = 0; i < identifiers.Count - 1; i++) {
            usingScope = new UsingScope(resolver.CurrentUsingScope.UnresolvedUsingScope, identifiers[i]);
            usingScope.Region = region;
            PushUsingScope(usingScope);
          }
          // Last using scope:
          usingScope = new UsingScope(resolver.CurrentUsingScope.UnresolvedUsingScope, identifiers.Last());
          usingScope.Region = region;
          var cv = new TypeSystemConvertVisitor(new CSharpUnresolvedFile(), usingScope);
          ApplyVisitorToUsings(cv, namespaceDeclaration.Children);
          PushUsingScope(usingScope);
        }
        for (; child != null; child = child.NextSibling) {
          Scan(child);
        }

        // merge undecided lambdas before leaving the using scope so that
        // the resolver can make better use of its cache
        MergeUndecidedLambdas();
        if (resolver.CurrentUsingScope != null && resolver.CurrentUsingScope.Namespace != null)
          return new NamespaceResolveResult(resolver.CurrentUsingScope.Namespace);
        else
          return null;
      } finally {
        resolver = previousResolver;
      }
    }
    #endregion
    
    #region Track CurrentTypeDefinition
    ResolveResult VisitTypeOrDelegate(AstNode typeDeclaration, string name, int typeParameterCount)
    {
      CSharpResolver previousResolver = resolver;
      try {
        ITypeDefinition newTypeDefinition = null;
        if (resolver.CurrentTypeDefinition != null) {
          int totalTypeParameterCount = resolver.CurrentTypeDefinition.TypeParameterCount + typeParameterCount;
          foreach (ITypeDefinition nestedType in resolver.CurrentTypeDefinition.NestedTypes) {
            if (nestedType.Name == name && nestedType.TypeParameterCount == totalTypeParameterCount) {
              newTypeDefinition = nestedType;
              break;
            }
          }
        } else if (resolver.CurrentUsingScope != null) {
          newTypeDefinition = resolver.CurrentUsingScope.Namespace.GetTypeDefinition(name, typeParameterCount);
        }
        if (newTypeDefinition != null)
          resolver = resolver.WithCurrentTypeDefinition(newTypeDefinition);
        
        ScanChildren(typeDeclaration);
        
        // merge undecided lambdas before leaving the type definition so that
        // the resolver can make better use of its cache
        MergeUndecidedLambdas();
        
        return newTypeDefinition != null ? new TypeResolveResult(newTypeDefinition) : errorResult;
      } finally {
        resolver = previousResolver;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitTypeDeclaration(TypeDeclaration typeDeclaration)
    {
      return VisitTypeOrDelegate(typeDeclaration, typeDeclaration.Name, typeDeclaration.TypeParameters.Count);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitDelegateDeclaration(DelegateDeclaration delegateDeclaration)
    {
      return VisitTypeOrDelegate(delegateDeclaration, delegateDeclaration.Name, delegateDeclaration.TypeParameters.Count);
    }
    #endregion
    
    #region Track CurrentMember
    ResolveResult IAstVisitor<ResolveResult>.VisitFieldDeclaration(FieldDeclaration fieldDeclaration)
    {
      return VisitFieldOrEventDeclaration(fieldDeclaration, SymbolKind.Field);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitFixedFieldDeclaration(FixedFieldDeclaration fixedFieldDeclaration)
    {
      return VisitFieldOrEventDeclaration(fixedFieldDeclaration, SymbolKind.Field);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitEventDeclaration(EventDeclaration eventDeclaration)
    {
      return VisitFieldOrEventDeclaration(eventDeclaration, SymbolKind.Event);
    }
    
    ResolveResult VisitFieldOrEventDeclaration(EntityDeclaration fieldOrEventDeclaration, SymbolKind symbolKind)
    {
      //int initializerCount = fieldOrEventDeclaration.GetChildrenByRole(Roles.Variable).Count;
      CSharpResolver oldResolver = resolver;
      for (AstNode node = fieldOrEventDeclaration.FirstChild; node != null; node = node.NextSibling) {
        if (node.Role == Roles.Variable || node.Role == FixedFieldDeclaration.VariableRole) {
          IMember member;
          if (unresolvedFile != null) {
            member = GetMemberFromLocation(node);
          } else {
            string name = ((VariableInitializer)node).Name;
            member = AbstractUnresolvedMember.Resolve(resolver.CurrentTypeResolveContext, symbolKind, name);
          }
          resolver = resolver.WithCurrentMember(member);
          
          Scan(node);
          
          resolver = oldResolver;
        } else {
          Scan(node);
        }
      }
      return voidResult;
    }
    
    IMember GetMemberFromLocation(AstNode node)
    {
      ITypeDefinition typeDef = resolver.CurrentTypeDefinition;
      if (typeDef == null)
        return null;
      TextLocation location = TypeSystemConvertVisitor.GetStartLocationAfterAttributes(node);
      return typeDef.GetMembers(
        delegate (IUnresolvedMember m) {
          if (m.UnresolvedFile != unresolvedFile)
            return false;
          DomRegion region = m.Region;
          return !region.IsEmpty && region.Begin <= location && region.End > location;
        },
        GetMemberOptions.IgnoreInheritedMembers | GetMemberOptions.ReturnMemberDefinitions
      ).FirstOrDefault();
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitVariableInitializer(VariableInitializer variableInitializer)
    {
      // Within the variable initializer, the newly declared variable is not yet available:
      var resolverWithVariable = resolver;
      if (variableInitializer.Parent is VariableDeclarationStatement)
        resolver = resolver.PopLastVariable();
      
      ArrayInitializerExpression aie = variableInitializer.Initializer as ArrayInitializerExpression;
      if (resolverEnabled || aie != null) {
        ResolveResult result = errorResult;
        if (variableInitializer.Parent is FieldDeclaration || variableInitializer.Parent is EventDeclaration) {
          if (resolver.CurrentMember != null) {
            result = new MemberResolveResult(null, resolver.CurrentMember, false);
          }
        } else {
          string identifier = variableInitializer.Name;
          foreach (IVariable v in resolverWithVariable.LocalVariables) {
            if (v.Name == identifier) {
              result = new LocalResolveResult(v);
              break;
            }
          }
        }
        ArrayType arrayType = result.Type as ArrayType;
        if (aie != null && arrayType != null) {
          StoreCurrentState(aie);
          List<Expression> initializerElements = new List<Expression>();
          int[] sizes = new int[arrayType.Dimensions];
          UnpackArrayInitializer(initializerElements, sizes, aie, 0, true);
          ResolveResult[] initializerElementResults = new ResolveResult[initializerElements.Count];
          for (int i = 0; i < initializerElementResults.Length; i++) {
            initializerElementResults[i] = Resolve(initializerElements[i]);
          }
          var arrayCreation = resolver.ResolveArrayCreation(arrayType.ElementType, sizes, initializerElementResults);
          StoreResult(aie, arrayCreation);
          ProcessConversionResults(initializerElements, arrayCreation.InitializerElements);
        } else if (variableInitializer.Parent is FixedStatement) {
          var initRR = Resolve(variableInitializer.Initializer);
          PointerType pointerType;
          if (initRR.Type.Kind == TypeKind.Array) {
            pointerType = new PointerType(((ArrayType)initRR.Type).ElementType);
          } else if (ReflectionHelper.GetTypeCode(initRR.Type) == TypeCode.String) {
            pointerType = new PointerType(resolver.Compilation.FindType(KnownTypeCode.Char));
          } else {
            pointerType = null;
            ProcessConversion(variableInitializer.Initializer, initRR, result.Type);
          }
          if (pointerType != null) {
            var conversion = resolver.conversions.ImplicitConversion(pointerType, result.Type);
            if (conversion.IsIdentityConversion)
              conversion = Conversion.ImplicitPointerConversion;
            ProcessConversion(variableInitializer.Initializer, initRR, conversion, result.Type);
          }
        } else {
          ResolveAndProcessConversion(variableInitializer.Initializer, result.Type);
        }
        resolver = resolverWithVariable;
        return result;
      } else {
        Scan(variableInitializer.Initializer);
        resolver = resolverWithVariable;
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitFixedVariableInitializer(FixedVariableInitializer fixedVariableInitializer)
    {
      if (resolverEnabled) {
        ResolveResult result = errorResult;
        if (resolver.CurrentMember != null) {
          result = new MemberResolveResult(null, resolver.CurrentMember, false);
        }
        ResolveAndProcessConversion(fixedVariableInitializer.CountExpression, resolver.Compilation.FindType(KnownTypeCode.Int32));
        return result;
      } else {
        ScanChildren(fixedVariableInitializer);
        return null;
      }
    }
    
    ResolveResult VisitMethodMember(EntityDeclaration memberDeclaration)
    {
      CSharpResolver oldResolver = resolver;
      try {
        IMember member = null;
        if (unresolvedFile != null) {
          member = GetMemberFromLocation(memberDeclaration);
        }
        if (member == null) {
          // Re-discover the method:
          SymbolKind symbolKind = memberDeclaration.SymbolKind;
          var parameterTypes = TypeSystemConvertVisitor.GetParameterTypes(memberDeclaration.GetChildrenByRole(Roles.Parameter), InterningProvider.Dummy);
          if (symbolKind == SymbolKind.Constructor) {
            string name = memberDeclaration.HasModifier(Modifiers.Static) ? ".cctor" : ".ctor";
            member = AbstractUnresolvedMember.Resolve(
              resolver.CurrentTypeResolveContext, symbolKind, name,
              parameterTypeReferences: parameterTypes);
          } else if (symbolKind == SymbolKind.Destructor) {
            member = AbstractUnresolvedMember.Resolve(resolver.CurrentTypeResolveContext, symbolKind, "Finalize");
          } else {
            string[] typeParameterNames = memberDeclaration.GetChildrenByRole(Roles.TypeParameter).Select(tp => tp.Name).ToArray();
            AstType explicitInterfaceAstType = memberDeclaration.GetChildByRole(EntityDeclaration.PrivateImplementationTypeRole);
            ITypeReference explicitInterfaceType = null;
            if (!explicitInterfaceAstType.IsNull) {
              explicitInterfaceType = explicitInterfaceAstType.ToTypeReference();
            }
            member = AbstractUnresolvedMember.Resolve(
              resolver.CurrentTypeResolveContext, symbolKind, memberDeclaration.Name,
              explicitInterfaceType, typeParameterNames, parameterTypes);
          }
        }
        resolver = resolver.WithCurrentMember(member);
        ScanChildren(memberDeclaration);
        
        if (member != null)
          return new MemberResolveResult(null, member, false);
        else
          return errorResult;
      } finally {
        resolver = oldResolver;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitMethodDeclaration(MethodDeclaration methodDeclaration)
    {
      return VisitMethodMember(methodDeclaration);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitOperatorDeclaration(OperatorDeclaration operatorDeclaration)
    {
      return VisitMethodMember(operatorDeclaration);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitConstructorDeclaration(ConstructorDeclaration constructorDeclaration)
    {
      return VisitMethodMember(constructorDeclaration);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitDestructorDeclaration(DestructorDeclaration destructorDeclaration)
    {
      return VisitMethodMember(destructorDeclaration);
    }
    
    // handle properties/indexers
    ResolveResult VisitPropertyMember(EntityDeclaration propertyOrIndexerDeclaration)
    {
      CSharpResolver oldResolver = resolver;
      try {
        IMember member;
        if (unresolvedFile != null) {
          member = GetMemberFromLocation(propertyOrIndexerDeclaration);
        } else {
          // Re-discover the property:
          string name = propertyOrIndexerDeclaration.Name;
          var parameterTypeReferences = TypeSystemConvertVisitor.GetParameterTypes(propertyOrIndexerDeclaration.GetChildrenByRole(Roles.Parameter), InterningProvider.Dummy);
          AstType explicitInterfaceAstType = propertyOrIndexerDeclaration.GetChildByRole(EntityDeclaration.PrivateImplementationTypeRole);
          ITypeReference explicitInterfaceType = null;
          if (!explicitInterfaceAstType.IsNull) {
            explicitInterfaceType = explicitInterfaceAstType.ToTypeReference();
          }
          member = AbstractUnresolvedMember.Resolve(
            resolver.CurrentTypeResolveContext, propertyOrIndexerDeclaration.SymbolKind, name,
            explicitInterfaceType, parameterTypeReferences: parameterTypeReferences);
        }
        // We need to use the property as current member so that indexer parameters can be resolved correctly.
        resolver = resolver.WithCurrentMember(member);
        var resolverWithPropertyAsMember = resolver;
        
        for (AstNode node = propertyOrIndexerDeclaration.FirstChild; node != null; node = node.NextSibling) {
          if (node.Role == PropertyDeclaration.GetterRole && member is IProperty) {
            resolver = resolver.WithCurrentMember(((IProperty)member).Getter);
            Scan(node);
            resolver = resolverWithPropertyAsMember;
          } else if (node.Role == PropertyDeclaration.SetterRole && member is IProperty) {
            resolver = resolver.WithCurrentMember(((IProperty)member).Setter);
            Scan(node);
            resolver = resolverWithPropertyAsMember;
          } else {
            Scan(node);
          }
        }
        if (member != null)
          return new MemberResolveResult(null, member, false);
        else
          return errorResult;
      } finally {
        resolver = oldResolver;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitPropertyDeclaration(PropertyDeclaration propertyDeclaration)
    {
      return VisitPropertyMember(propertyDeclaration);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitIndexerDeclaration(IndexerDeclaration indexerDeclaration)
    {
      return VisitPropertyMember(indexerDeclaration);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitCustomEventDeclaration(CustomEventDeclaration eventDeclaration)
    {
      CSharpResolver oldResolver = resolver;
      try {
        IMember member;
        if (unresolvedFile != null) {
          member = GetMemberFromLocation(eventDeclaration);
        } else {
          string name = eventDeclaration.Name;
          AstType explicitInterfaceAstType = eventDeclaration.PrivateImplementationType;
          if (explicitInterfaceAstType.IsNull) {
            member = AbstractUnresolvedMember.Resolve(resolver.CurrentTypeResolveContext, SymbolKind.Event, name);
          } else {
            member = AbstractUnresolvedMember.Resolve(resolver.CurrentTypeResolveContext, SymbolKind.Event, name,
                                                      explicitInterfaceAstType.ToTypeReference());
          }
        }
        resolver = resolver.WithCurrentMember(member);
        var resolverWithEventAsMember = resolver;
        
        for (AstNode node = eventDeclaration.FirstChild; node != null; node = node.NextSibling) {
          if (node.Role == CustomEventDeclaration.AddAccessorRole && member is IEvent) {
            resolver = resolver.WithCurrentMember(((IEvent)member).AddAccessor);
            Scan(node);
            resolver = resolverWithEventAsMember;
          } else if (node.Role == CustomEventDeclaration.RemoveAccessorRole && member is IEvent) {
            resolver = resolver.WithCurrentMember(((IEvent)member).RemoveAccessor);
            Scan(node);
            resolver = resolverWithEventAsMember;
          } else {
            Scan(node);
          }
        }

        if (member != null)
          return new MemberResolveResult(null, member, false);
        else
          return errorResult;
      } finally {
        resolver = oldResolver;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitParameterDeclaration(ParameterDeclaration parameterDeclaration)
    {
      ScanChildren(parameterDeclaration);
      if (resolverEnabled) {
        string name = parameterDeclaration.Name;
        
        if (parameterDeclaration.Parent is DocumentationReference) {
          // create a dummy parameter
          IType type = ResolveType(parameterDeclaration.Type);
          switch (parameterDeclaration.ParameterModifier) {
            case ParameterModifier.Ref:
            case ParameterModifier.Out:
              type = new ByReferenceType(type);
              break;
          }
          return new LocalResolveResult(new DefaultParameter(
            type, name,
            isRef: parameterDeclaration.ParameterModifier == ParameterModifier.Ref,
            isOut: parameterDeclaration.ParameterModifier == ParameterModifier.Out,
            isParams: parameterDeclaration.ParameterModifier == ParameterModifier.Params));
        }
        
        // Look in lambda parameters:
        foreach (IParameter p in resolver.LocalVariables.OfType<IParameter>()) {
          if (p.Name == name)
            return new LocalResolveResult(p);
        }
        
        IParameterizedMember pm = resolver.CurrentMember as IParameterizedMember;
        if (pm == null && resolver.CurrentTypeDefinition != null) {
          // Also consider delegate parameters:
          pm = resolver.CurrentTypeDefinition.GetDelegateInvokeMethod();
          // pm will be null if the current type isn't a delegate
        }
        if (pm != null) {
          foreach (IParameter p in pm.Parameters) {
            if (p.Name == name) {
              return new LocalResolveResult(p);
            }
          }
        }
        
        return errorResult;
      } else {
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitTypeParameterDeclaration(TypeParameterDeclaration typeParameterDeclaration)
    {
      ScanChildren(typeParameterDeclaration);
      if (resolverEnabled) {
        string name = typeParameterDeclaration.Name;
        IMethod m = resolver.CurrentMember as IMethod;
        if (m != null) {
          foreach (var tp in m.TypeParameters) {
            if (tp.Name == name)
              return new TypeResolveResult(tp);
          }
        }
        if (resolver.CurrentTypeDefinition != null) {
          var typeParameters = resolver.CurrentTypeDefinition.TypeParameters;
          // look backwards so that TPs in the current type take precedence over those copied from outer types
          for (int i = typeParameters.Count - 1; i >= 0; i--) {
            if (typeParameters[i].Name == name)
              return new TypeResolveResult(typeParameters[i]);
          }
        }
        return errorResult;
      } else {
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitEnumMemberDeclaration(EnumMemberDeclaration enumMemberDeclaration)
    {
      CSharpResolver oldResolver = resolver;
      try {
        // Scan enum member attributes before setting resolver.CurrentMember, so that
        // enum values used as attribute arguments have the correct type.
        // (within an enum member, all other enum members are treated as having their underlying type)
        foreach (var attributeSection in enumMemberDeclaration.Attributes)
          Scan(attributeSection);
        
        IMember member = null;
        if (unresolvedFile != null) {
          member = GetMemberFromLocation(enumMemberDeclaration);
        } else if (resolver.CurrentTypeDefinition != null) {
          string name = enumMemberDeclaration.Name;
          member = resolver.CurrentTypeDefinition.GetFields(f => f.Name == name, GetMemberOptions.IgnoreInheritedMembers).FirstOrDefault();
        }
        resolver = resolver.WithCurrentMember(member);
        
        if (resolverEnabled && resolver.CurrentTypeDefinition != null) {
          ResolveAndProcessConversion(enumMemberDeclaration.Initializer, resolver.CurrentTypeDefinition.EnumUnderlyingType);
          if (resolverEnabled && member != null)
            return new MemberResolveResult(null, member, false);
          else
            return errorResult;
        } else {
          Scan(enumMemberDeclaration.Initializer);
          return null;
        }
      } finally {
        resolver = oldResolver;
      }
    }
    #endregion
    
    #region Track CheckForOverflow
    ResolveResult IAstVisitor<ResolveResult>.VisitCheckedExpression(CheckedExpression checkedExpression)
    {
      CSharpResolver oldResolver = resolver;
      try {
        resolver = resolver.WithCheckForOverflow(true);
        if (resolverEnabled) {
          return Resolve(checkedExpression.Expression);
        } else {
          ScanChildren(checkedExpression);
          return null;
        }
      } finally {
        resolver = oldResolver;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitUncheckedExpression(UncheckedExpression uncheckedExpression)
    {
      CSharpResolver oldResolver = resolver;
      try {
        resolver = resolver.WithCheckForOverflow(false);
        if (resolverEnabled) {
          return Resolve(uncheckedExpression.Expression);
        } else {
          ScanChildren(uncheckedExpression);
          return null;
        }
      } finally {
        resolver = oldResolver;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitCheckedStatement(CheckedStatement checkedStatement)
    {
      CSharpResolver oldResolver = resolver;
      try {
        resolver = resolver.WithCheckForOverflow(true);
        ScanChildren(checkedStatement);
        return voidResult;
      } finally {
        resolver = oldResolver;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitUncheckedStatement(UncheckedStatement uncheckedStatement)
    {
      CSharpResolver oldResolver = resolver;
      try {
        resolver = resolver.WithCheckForOverflow(false);
        ScanChildren(uncheckedStatement);
        return voidResult;
      } finally {
        resolver = oldResolver;
      }
    }
    #endregion
    
    #region Visit AnonymousTypeCreateExpression
    static string GetAnonymousTypePropertyName(Expression expr, out Expression resolveExpr)
    {
      if (expr is NamedExpression) {
        var namedArgExpr = (NamedExpression)expr;
        resolveExpr = namedArgExpr.Expression;
        return namedArgExpr.Name;
      }
      // no name given, so it's a projection initializer
      if (expr is MemberReferenceExpression) {
        resolveExpr = expr;
        return ((MemberReferenceExpression)expr).MemberName;
      }
      if (expr is IdentifierExpression) {
        resolveExpr = expr;
        return ((IdentifierExpression)expr).Identifier;
      }
      resolveExpr = null;
      return null;
    }
    
    class AnonymousTypeMember
    {
      public readonly Expression Expression;
      public readonly ResolveResult Initializer;
      
      public AnonymousTypeMember(Expression expression, ResolveResult initializer)
      {
        this.Expression = expression;
        this.Initializer = initializer;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitAnonymousTypeCreateExpression(AnonymousTypeCreateExpression anonymousTypeCreateExpression)
    {
      // 7.6.10.6 Anonymous object creation expressions
      List<IUnresolvedProperty> unresolvedProperties = new List<IUnresolvedProperty>();
      List<AnonymousTypeMember> members = new List<AnonymousTypeMember>();
      foreach (var expr in anonymousTypeCreateExpression.Initializers) {
        Expression resolveExpr;
        var name = GetAnonymousTypePropertyName(expr, out resolveExpr);
        if (resolveExpr != null) {
          var initRR = Resolve(resolveExpr);
          var returnTypeRef = initRR.Type.ToTypeReference();
          var property = new DefaultUnresolvedProperty();
          property.Name = name;
          property.Accessibility = Accessibility.Public;
          property.ReturnType = returnTypeRef;
          property.Getter = new DefaultUnresolvedMethod {
            Name = "get_" + name,
            Accessibility = Accessibility.Public,
            ReturnType = returnTypeRef,
            SymbolKind = SymbolKind.Accessor,
            AccessorOwner = property
          };
          unresolvedProperties.Add(property);
          members.Add(new AnonymousTypeMember(expr, initRR));
        } else {
          Scan(expr);
        }
      }
      var anonymousType = new AnonymousType(resolver.Compilation, unresolvedProperties);
      var properties = anonymousType.GetProperties().ToList();
      Debug.Assert(properties.Count == members.Count);
      List<ResolveResult> assignments = new List<ResolveResult>();
      for (int i = 0; i < members.Count; i++) {
        ResolveResult lhs = new MemberResolveResult(new InitializedObjectResolveResult(anonymousType), properties[i]);
        ResolveResult rhs = members[i].Initializer;
        ResolveResult assignment = resolver.ResolveAssignment(AssignmentOperatorType.Assign, lhs, rhs);
        var ne = members[i].Expression as NamedExpression;
        if (ne != null) {
          StoreCurrentState(ne);
          // ne.Expression was already resolved by the first loop
          StoreResult(ne, lhs);
        }
        assignments.Add(assignment);
      }
      var anonymousCtor = DefaultResolvedMethod.GetDummyConstructor(resolver.Compilation, anonymousType);
      return new InvocationResolveResult(null, anonymousCtor, initializerStatements: assignments);
    }
    #endregion
    
    #region Visit Expressions
    ResolveResult IAstVisitor<ResolveResult>.VisitArrayCreateExpression(ArrayCreateExpression arrayCreateExpression)
    {
      int dimensions = arrayCreateExpression.Arguments.Count;
      IEnumerable<Expression> sizeArgumentExpressions;
      ResolveResult[] sizeArguments;
      IEnumerable<ArraySpecifier> additionalArraySpecifiers;
      if (dimensions == 0) {
        var firstSpecifier = arrayCreateExpression.AdditionalArraySpecifiers.FirstOrDefault();
        if (firstSpecifier != null) {
          dimensions = firstSpecifier.Dimensions;
          additionalArraySpecifiers = arrayCreateExpression.AdditionalArraySpecifiers.Skip(1);
        } else {
          // No array specifiers (neither with nor without size) - can happen if there are syntax errors.
          // Dimensions must be at least one; otherwise 'new ArrayType' will crash.
          dimensions = 1;
          additionalArraySpecifiers = arrayCreateExpression.AdditionalArraySpecifiers;
        }
        sizeArguments = null;
        sizeArgumentExpressions = null;
      } else {
        sizeArgumentExpressions = arrayCreateExpression.Arguments;
        sizeArguments = new ResolveResult[dimensions];
        int pos = 0;
        foreach (var node in sizeArgumentExpressions)
          sizeArguments[pos++] = Resolve(node);
        additionalArraySpecifiers = arrayCreateExpression.AdditionalArraySpecifiers;
      }
      
      int[] sizes;
      List<Expression> initializerElements;
      ResolveResult[] initializerElementResults;
      if (arrayCreateExpression.Initializer.IsNull) {
        sizes = null;
        initializerElements = null;
        initializerElementResults = null;
      } else {
        StoreCurrentState(arrayCreateExpression.Initializer);
        
        initializerElements = new List<Expression>();
        sizes = new int[dimensions];
        UnpackArrayInitializer(initializerElements, sizes, arrayCreateExpression.Initializer, 0, true);
        initializerElementResults = new ResolveResult[initializerElements.Count];
        for (int i = 0; i < initializerElementResults.Length; i++) {
          initializerElementResults[i] = Resolve(initializerElements[i]);
        }
        StoreResult(arrayCreateExpression.Initializer, voidResult);
      }
      
      IType elementType;
      if (arrayCreateExpression.Type.IsNull) {
        elementType = null;
      } else {
        elementType = ResolveType(arrayCreateExpression.Type);
        foreach (var spec in additionalArraySpecifiers.Reverse()) {
          elementType = new ArrayType(resolver.Compilation, elementType, spec.Dimensions);
        }
      }
      ArrayCreateResolveResult acrr;
      if (sizeArguments != null) {
        acrr = resolver.ResolveArrayCreation(elementType, sizeArguments, initializerElementResults);
      } else if (sizes != null) {
        acrr = resolver.ResolveArrayCreation(elementType, sizes, initializerElementResults);
      } else {
        // neither size arguments nor an initializer exist -> error
        return new ErrorResolveResult(new ArrayType(resolver.Compilation, elementType ?? SpecialType.UnknownType, dimensions));
      }
      if (sizeArgumentExpressions != null)
        ProcessConversionResults(sizeArgumentExpressions, acrr.SizeArguments);
      if (acrr.InitializerElements != null)
        ProcessConversionResults(initializerElements, acrr.InitializerElements);
      return acrr;
    }
    
    void UnpackArrayInitializer(List<Expression> elementList, int[] sizes, ArrayInitializerExpression initializer, int dimension, bool resolveNestedInitializersToVoid)
    {
      Debug.Assert(dimension < sizes.Length);
      int elementCount = 0;
      if (dimension + 1 < sizes.Length) {
        foreach (var node in initializer.Elements) {
          ArrayInitializerExpression aie = node as ArrayInitializerExpression;
          if (aie != null) {
            if (resolveNestedInitializersToVoid) {
              StoreCurrentState(aie);
              StoreResult(aie, voidResult);
            }
            UnpackArrayInitializer(elementList, sizes, aie, dimension + 1, resolveNestedInitializersToVoid);
          } else {
            elementList.Add(node);
          }
          elementCount++;
        }
      } else {
        foreach (var expr in initializer.Elements) {
          elementList.Add(expr);
          elementCount++;
        }
      }
      if (sizes[dimension] == 0) // 0 = uninitialized
        sizes[dimension] = elementCount;
      else if (sizes[dimension] != elementCount)
        sizes[dimension] = -1; // -1 = error
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitArrayInitializerExpression(ArrayInitializerExpression arrayInitializerExpression)
    {
      // Array initializers are handled by their parent expression.
      ScanChildren(arrayInitializerExpression);
      return errorResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitAsExpression(AsExpression asExpression)
    {
      if (resolverEnabled) {
        ResolveResult input = Resolve(asExpression.Expression);
        var targetType = ResolveType(asExpression.Type);
        return new CastResolveResult(targetType, input, Conversion.TryCast, resolver.CheckForOverflow);
      } else {
        ScanChildren(asExpression);
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitAssignmentExpression(AssignmentExpression assignmentExpression)
    {
      if (resolverEnabled) {
        Expression left = assignmentExpression.Left;
        Expression right = assignmentExpression.Right;
        ResolveResult leftResult = Resolve(left);
        ResolveResult rightResult = Resolve(right);
        ResolveResult rr = resolver.ResolveAssignment(assignmentExpression.Operator, leftResult, rightResult);
        ProcessConversionsInBinaryOperatorResult(left, right, rr);
        return rr;
      } else {
        ScanChildren(assignmentExpression);
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitBaseReferenceExpression(BaseReferenceExpression baseReferenceExpression)
    {
      if (resolverEnabled) {
        return resolver.ResolveBaseReference();
      } else {
        ScanChildren(baseReferenceExpression);
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitBinaryOperatorExpression(BinaryOperatorExpression binaryOperatorExpression)
    {
      if (resolverEnabled) {
        Expression left = binaryOperatorExpression.Left;
        Expression right = binaryOperatorExpression.Right;
        ResolveResult leftResult = Resolve(left);
        ResolveResult rightResult = Resolve(right);
        ResolveResult rr = resolver.ResolveBinaryOperator(binaryOperatorExpression.Operator, leftResult, rightResult);
        ProcessConversionsInBinaryOperatorResult(left, right, rr);
        return rr;
      } else {
        ScanChildren(binaryOperatorExpression);
        return null;
      }
    }
    
    ResolveResult ProcessConversionsInBinaryOperatorResult(Expression left, Expression right, ResolveResult rr)
    {
      OperatorResolveResult orr = rr as OperatorResolveResult;
      if (orr != null && orr.Operands.Count == 2) {
        ProcessConversionResult(left, orr.Operands[0] as ConversionResolveResult);
        ProcessConversionResult(right, orr.Operands[1] as ConversionResolveResult);
      } else {
        InvocationResolveResult irr = rr as InvocationResolveResult;
        if (irr != null && irr.Arguments.Count == 2) {
          ProcessConversionResult(left, irr.Arguments[0] as ConversionResolveResult);
          ProcessConversionResult(right, irr.Arguments[1] as ConversionResolveResult);
        }
      }
      return rr;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitCastExpression(CastExpression castExpression)
    {
      if (resolverEnabled) {
        var targetType = ResolveType(castExpression.Type);
        var expr = castExpression.Expression;
        var rr = resolver.ResolveCast(targetType, Resolve(expr));
        var crr = rr as ConversionResolveResult;
        if (crr != null) {
          Debug.Assert(!(crr is CastResolveResult));
          ProcessConversion(expr, crr.Input, crr.Conversion, targetType);
          rr = new CastResolveResult(crr);
        }
        return rr;
      } else {
        ScanChildren(castExpression);
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitConditionalExpression(ConditionalExpression conditionalExpression)
    {
      if (resolverEnabled) {
        Expression condition = conditionalExpression.Condition;
        Expression trueExpr = conditionalExpression.TrueExpression;
        Expression falseExpr = conditionalExpression.FalseExpression;
        
        ResolveResult rr = resolver.ResolveConditional(Resolve(condition), Resolve(trueExpr), Resolve(falseExpr));
        OperatorResolveResult corr = rr as OperatorResolveResult;
        if (corr != null && corr.Operands.Count == 3) {
          ProcessConversionResult(condition, corr.Operands[0] as ConversionResolveResult);
          ProcessConversionResult(trueExpr, corr.Operands[1] as ConversionResolveResult);
          ProcessConversionResult(falseExpr, corr.Operands[2] as ConversionResolveResult);
        }
        return rr;
      } else {
        ScanChildren(conditionalExpression);
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitDefaultValueExpression(DefaultValueExpression defaultValueExpression)
    {
      if (resolverEnabled) {
        return resolver.ResolveDefaultValue(ResolveType(defaultValueExpression.Type));
      } else {
        ScanChildren(defaultValueExpression);
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitDirectionExpression(DirectionExpression directionExpression)
    {
      if (resolverEnabled) {
        ResolveResult rr = Resolve(directionExpression.Expression);
        return new ByReferenceResolveResult(rr, directionExpression.FieldDirection == FieldDirection.Out);
      } else {
        ScanChildren(directionExpression);
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitIndexerExpression(IndexerExpression indexerExpression)
    {
      if (resolverEnabled || NeedsResolvingDueToNamedArguments(indexerExpression)) {
        Expression target = indexerExpression.Target;
        ResolveResult targetResult = Resolve(target);
        string[] argumentNames;
        ResolveResult[] arguments = GetArguments(indexerExpression.Arguments, out argumentNames);
        ResolveResult rr = resolver.ResolveIndexer(targetResult, arguments, argumentNames);
        ArrayAccessResolveResult aarr = rr as ArrayAccessResolveResult;
        if (aarr != null) {
          MarkUnknownNamedArguments(indexerExpression.Arguments);
          ProcessConversionResults(indexerExpression.Arguments, aarr.Indexes);
        } else {
          ProcessInvocationResult(target, indexerExpression.Arguments, rr);
        }
        return rr;
      } else {
        ScanChildren(indexerExpression);
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitIsExpression(IsExpression isExpression)
    {
      if (resolverEnabled) {
        ResolveResult input = Resolve(isExpression.Expression);
        IType targetType = ResolveType(isExpression.Type);
        IType booleanType = resolver.Compilation.FindType(KnownTypeCode.Boolean);
        return new TypeIsResolveResult(input, targetType, booleanType);
      } else {
        ScanChildren(isExpression);
        return null;
      }
    }
    
    // NamedArgumentExpression is "identifier: Expression"
    ResolveResult IAstVisitor<ResolveResult>.VisitNamedArgumentExpression(NamedArgumentExpression namedArgumentExpression)
    {
      // The parent expression takes care of handling NamedArgumentExpressions
      // by calling GetArguments().
      // This method gets called only when scanning, or when the named argument is used
      // in an invalid context.
      if (resolverEnabled) {
        return new NamedArgumentResolveResult(namedArgumentExpression.Name, Resolve(namedArgumentExpression.Expression));
      } else {
        Scan(namedArgumentExpression.Expression);
        return null;
      }
    }
    
    // NamedExpression is "identifier = Expression" in object initializers and attributes
    ResolveResult IAstVisitor<ResolveResult>.VisitNamedExpression(NamedExpression namedExpression)
    {
      // The parent expression takes care of handling NamedExpression
      // by calling HandleObjectInitializer() or HandleNamedExpression().
      // This method gets called only when scanning, or when the named expression is used
      // in an invalid context.
      ScanChildren(namedExpression);
      return null;
    }
    
    void HandleNamedExpression(NamedExpression namedExpression, List<ResolveResult> initializerStatements)
    {
      StoreCurrentState(namedExpression);
      Expression rhs = namedExpression.Expression;
      ResolveResult lhsRR = resolver.ResolveIdentifierInObjectInitializer(namedExpression.Name);
      if (rhs is ArrayInitializerExpression) {
        HandleObjectInitializer(lhsRR, (ArrayInitializerExpression)rhs, initializerStatements);
      } else {
        var rhsRR = Resolve(rhs);
        var rr = resolver.ResolveAssignment(AssignmentOperatorType.Assign, lhsRR, rhsRR) as OperatorResolveResult;
        if (rr != null) {
          ProcessConversionResult(rhs, rr.Operands[1] as ConversionResolveResult);
          initializerStatements.Add(rr);
        }
      }
      StoreResult(namedExpression, lhsRR);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitNullReferenceExpression(NullReferenceExpression nullReferenceExpression)
    {
      return resolver.ResolvePrimitive(null);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitObjectCreateExpression(ObjectCreateExpression objectCreateExpression)
    {
      var typeResolveResult = Resolve(objectCreateExpression.Type);
      if (typeResolveResult.IsError) {
        ScanChildren (objectCreateExpression);
        return typeResolveResult;
      }
      IType type = typeResolveResult.Type;
      
      List<ResolveResult> initializerStatements = null;
      var initializer = objectCreateExpression.Initializer;
      if (!initializer.IsNull) {
        initializerStatements = new List<ResolveResult>();
        HandleObjectInitializer(new InitializedObjectResolveResult(type), initializer, initializerStatements);
      }
      
      string[] argumentNames;
      ResolveResult[] arguments = GetArguments(objectCreateExpression.Arguments, out argumentNames);
      
      ResolveResult rr = resolver.ResolveObjectCreation(type, arguments, argumentNames, false, initializerStatements);
      if (arguments.Length == 1 && rr.Type.Kind == TypeKind.Delegate) {
        MarkUnknownNamedArguments(objectCreateExpression.Arguments);
        // Apply conversion to argument if it directly wraps the argument
        // (but not when creating a delegate from a delegate, as then there would be a MGRR for .Invoke in between)
        // This is necessary for lambda type inference.
        var crr = rr as ConversionResolveResult;
        if (crr != null) {
          if (objectCreateExpression.Arguments.Count == 1)
            ProcessConversionResult(objectCreateExpression.Arguments.Single(), crr);
          
          // wrap the result so that the delegate creation is not handled as a reference
          // to the target method - otherwise FindReferencedEntities would produce two results for
          // the same delegate creation.
          return new CastResolveResult(crr);
        } else {
          return rr;
        }
      } else {
        // process conversions in all other cases
        ProcessInvocationResult(null, objectCreateExpression.Arguments, rr);
        return rr;
      }
    }
    
    void HandleObjectInitializer(ResolveResult initializedObject, ArrayInitializerExpression initializer, List<ResolveResult> initializerStatements)
    {
      StoreCurrentState(initializer);
      resolver = resolver.PushObjectInitializer(initializedObject);
      foreach (Expression element in initializer.Elements) {
        ArrayInitializerExpression aie = element as ArrayInitializerExpression;
        if (aie != null) {
          StoreCurrentState(aie);
          // constructor argument list in collection initializer
          ResolveResult[] addArguments = new ResolveResult[aie.Elements.Count];
          int i = 0;
          foreach (var addArgument in aie.Elements) {
            addArguments[i++] = Resolve(addArgument);
          }
          MemberLookup memberLookup = resolver.CreateMemberLookup();
          var addRR = memberLookup.Lookup(initializedObject, "Add", EmptyList<IType>.Instance, true);
          var mgrr = addRR as MethodGroupResolveResult;
          if (mgrr != null) {
            OverloadResolution or = mgrr.PerformOverloadResolution(resolver.Compilation, addArguments, null, false, false, false, resolver.CheckForOverflow, resolver.conversions);
            var invocationRR = or.CreateResolveResult(initializedObject);
            StoreResult(aie, invocationRR);
            ProcessInvocationResult(null, aie.Elements, invocationRR);
            initializerStatements.Add(invocationRR);
          } else {
            StoreResult(aie, addRR);
          }
        } else if (element is NamedExpression) {
          HandleNamedExpression((NamedExpression)element, initializerStatements);
        } else {
          // unknown kind of expression
          Scan(element);
        }
      }
      resolver = resolver.PopObjectInitializer();
      StoreResult(initializer, voidResult);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitParenthesizedExpression(ParenthesizedExpression parenthesizedExpression)
    {
      if (resolverEnabled) {
        return Resolve(parenthesizedExpression.Expression);
      } else {
        Scan(parenthesizedExpression.Expression);
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitPointerReferenceExpression(PointerReferenceExpression pointerReferenceExpression)
    {
      if (resolverEnabled) {
        ResolveResult target = Resolve(pointerReferenceExpression.Target);
        ResolveResult deferencedTarget = resolver.ResolveUnaryOperator(UnaryOperatorType.Dereference, target);
        List<IType> typeArguments = new List<IType>();
        foreach (AstType typeArgument in pointerReferenceExpression.TypeArguments) {
          typeArguments.Add(ResolveType(typeArgument));
        }
        return resolver.ResolveMemberAccess(deferencedTarget, pointerReferenceExpression.MemberName,
                                            typeArguments,
                                            GetNameLookupMode(pointerReferenceExpression));
      } else {
        ScanChildren(pointerReferenceExpression);
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitPrimitiveExpression(PrimitiveExpression primitiveExpression)
    {
      return resolver.ResolvePrimitive(primitiveExpression.Value);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitSizeOfExpression(SizeOfExpression sizeOfExpression)
    {
      return resolver.ResolveSizeOf(ResolveType(sizeOfExpression.Type));
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitStackAllocExpression(StackAllocExpression stackAllocExpression)
    {
      ResolveAndProcessConversion(stackAllocExpression.CountExpression, resolver.Compilation.FindType(KnownTypeCode.Int32));
      return new ResolveResult(new PointerType(ResolveType(stackAllocExpression.Type)));
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitThisReferenceExpression(ThisReferenceExpression thisReferenceExpression)
    {
      return resolver.ResolveThisReference();
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitTypeOfExpression(TypeOfExpression typeOfExpression)
    {
      if (resolverEnabled) {
        return resolver.ResolveTypeOf(ResolveType(typeOfExpression.Type));
      } else {
        Scan(typeOfExpression.Type);
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitTypeReferenceExpression(TypeReferenceExpression typeReferenceExpression)
    {
      if (resolverEnabled) {
        return Resolve(typeReferenceExpression.Type).ShallowClone();
      } else {
        Scan(typeReferenceExpression.Type);
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitUnaryOperatorExpression(UnaryOperatorExpression unaryOperatorExpression)
    {
      if (resolverEnabled) {
        Expression expr = unaryOperatorExpression.Expression;
        ResolveResult input = Resolve(expr);
        ITypeDefinition inputTypeDef = input.Type.GetDefinition();
        if (input.IsCompileTimeConstant && expr is PrimitiveExpression && inputTypeDef != null) {
          // Special cases for int.MinValue and long.MinValue
          if (inputTypeDef.KnownTypeCode == KnownTypeCode.UInt32 && 2147483648.Equals(input.ConstantValue)) {
            return new ConstantResolveResult(resolver.Compilation.FindType(KnownTypeCode.Int32), -2147483648);
          } else if (inputTypeDef.KnownTypeCode == KnownTypeCode.UInt64 && 9223372036854775808.Equals(input.ConstantValue)) {
            return new ConstantResolveResult(resolver.Compilation.FindType(KnownTypeCode.Int64), -9223372036854775808);
          }
        }
        ResolveResult rr = resolver.ResolveUnaryOperator(unaryOperatorExpression.Operator, input);
        OperatorResolveResult uorr = rr as OperatorResolveResult;
        if (uorr != null && uorr.Operands.Count == 1) {
          ProcessConversionResult(expr, uorr.Operands[0] as ConversionResolveResult);
        } else {
          InvocationResolveResult irr = rr as InvocationResolveResult;
          if (irr != null && irr.Arguments.Count == 1) {
            ProcessConversionResult(expr, irr.Arguments[0] as ConversionResolveResult);
          }
        }
        return rr;
      } else {
        ScanChildren(unaryOperatorExpression);
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitUndocumentedExpression(UndocumentedExpression undocumentedExpression)
    {
      ScanChildren(undocumentedExpression);
      IType resultType;
      switch (undocumentedExpression.UndocumentedExpressionType) {
        case UndocumentedExpressionType.ArgListAccess:
        case UndocumentedExpressionType.ArgList:
          resultType = resolver.Compilation.FindType(typeof(RuntimeArgumentHandle));
          break;
        case UndocumentedExpressionType.RefValue:
          var tre = undocumentedExpression.Arguments.ElementAtOrDefault(1) as TypeReferenceExpression;
          if (tre != null)
            resultType = ResolveType(tre.Type);
          else
            resultType = SpecialType.UnknownType;
          break;
        case UndocumentedExpressionType.RefType:
          resultType = resolver.Compilation.FindType(KnownTypeCode.Type);
          break;
        case UndocumentedExpressionType.MakeRef:
          resultType = resolver.Compilation.FindType(typeof(TypedReference));
          break;
        default:
          throw new InvalidOperationException("Invalid value for UndocumentedExpressionType");
      }
      return new ResolveResult(resultType);
    }
    #endregion
    
    #region Visit Identifier/MemberReference/Invocation-Expression
    // IdentifierExpression, MemberReferenceExpression and InvocationExpression
    // are grouped together because they have to work together for
    // "7.6.4.1 Identical simple names and type names" support
    List<IType> ResolveTypeArguments(IEnumerable<AstType> typeArguments)
    {
      List<IType> result = new List<IType>();
      foreach (AstType typeArgument in typeArguments) {
        result.Add(ResolveType(typeArgument));
      }
      return result;
    }
    
    /// <summary>
    /// Gets and resolves the arguments; unpacking any NamedArgumentExpressions.
    /// </summary>
    /// <remarks>
    /// Callers of GetArguments must also call either ProcessConversionsInInvocation or MarkUnknownNamedArguments
    /// to ensure the named arguments get resolved.
    /// Also, as named arguments get resolved by the parent node, the parent node must not scan
    /// into the argument list without being resolved - see NeedsResolvingDueToNamedArguments().
    /// </remarks>
    ResolveResult[] GetArguments(IEnumerable<Expression> argumentExpressions, out string[] argumentNames)
    {
      argumentNames = null;
      ResolveResult[] arguments = new ResolveResult[argumentExpressions.Count()];
      int i = 0;
      foreach (AstNode argument in argumentExpressions) {
        NamedArgumentExpression nae = argument as NamedArgumentExpression;
        AstNode argumentValue;
        if (nae != null) {
          if (argumentNames == null)
            argumentNames = new string[arguments.Length];
          argumentNames[i] = nae.Name;
          argumentValue = nae.Expression;
        } else {
          argumentValue = argument;
        }
        arguments[i++] = Resolve(argumentValue);
      }
      return arguments;
    }
    
    bool NeedsResolvingDueToNamedArguments(Expression nodeWithArguments)
    {
      for (AstNode child = nodeWithArguments.FirstChild; child != null; child = child.NextSibling) {
        if (child is NamedArgumentExpression)
          return true;
      }
      return false;
    }

    static NameLookupMode GetNameLookupMode(Expression expr)
    {
      InvocationExpression ie = expr.Parent as InvocationExpression;
      if (ie != null && ie.Target == expr)
        return NameLookupMode.InvocationTarget;
      else
        return NameLookupMode.Expression;
    }

    /// <summary>
    /// Gets whether 'rr' is considered a static access on the target identifier.
    /// </summary>
    /// <param name="rr">Resolve Result of the MemberReferenceExpression</param>
    /// <param name="invocationRR">Resolve Result of the InvocationExpression</param>
    bool IsStaticResult(ResolveResult rr, ResolveResult invocationRR)
    {
      if (rr is TypeResolveResult)
        return true;
      MemberResolveResult mrr = (rr is MethodGroupResolveResult ? invocationRR : rr) as MemberResolveResult;
      return mrr != null && mrr.Member.IsStatic;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitIdentifierExpression(IdentifierExpression identifierExpression)
    {
      // Note: this method is not called when it occurs in a situation where an ambiguity between
      // simple names and type names might occur.
      if (resolverEnabled) {
        var typeArguments = ResolveTypeArguments(identifierExpression.TypeArguments);
        var lookupMode = GetNameLookupMode(identifierExpression);
        return resolver.LookupSimpleNameOrTypeName(
          identifierExpression.Identifier, typeArguments, lookupMode);
      } else {
        ScanChildren(identifierExpression);
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitMemberReferenceExpression(MemberReferenceExpression memberReferenceExpression)
    {
      // target = Resolve(identifierExpression = memberReferenceExpression.Target)
      // trr = ResolveType(identifierExpression)
      // rr = Resolve(memberReferenceExpression)
      
      IdentifierExpression identifierExpression = memberReferenceExpression.Target as IdentifierExpression;
      if (identifierExpression != null && identifierExpression.TypeArguments.Count == 0) {
        // Special handling for §7.6.4.1 Identicial simple names and type names
        StoreCurrentState(identifierExpression);
        ResolveResult target = resolver.ResolveSimpleName(identifierExpression.Identifier, EmptyList<IType>.Instance);
        TypeResolveResult trr;
        if (resolver.IsVariableReferenceWithSameType(target, identifierExpression.Identifier, out trr)) {
          // It's ambiguous
          ResolveResult rr = ResolveMemberReferenceOnGivenTarget(target, memberReferenceExpression);
          ResolveResult simpleNameRR = IsStaticResult(rr, null) ? trr : target;
          Log.WriteLine("Ambiguous simple name '{0}' was resolved to {1}", identifierExpression, simpleNameRR);
          StoreResult(identifierExpression, simpleNameRR);
          return rr;
        } else {
          // It's not ambiguous
          Log.WriteLine("Simple name '{0}' was resolved to {1}", identifierExpression, target);
          StoreResult(identifierExpression, target);
          return ResolveMemberReferenceOnGivenTarget(target, memberReferenceExpression);
        }
      } else {
        // Regular code path
        if (resolverEnabled) {
          ResolveResult target = Resolve(memberReferenceExpression.Target);
          return ResolveMemberReferenceOnGivenTarget(target, memberReferenceExpression);
        } else {
          ScanChildren(memberReferenceExpression);
          return null;
        }
      }
    }
    
    ResolveResult ResolveMemberReferenceOnGivenTarget(ResolveResult target, MemberReferenceExpression memberReferenceExpression)
    {
      var typeArguments = ResolveTypeArguments(memberReferenceExpression.TypeArguments);
      return resolver.ResolveMemberAccess(
        target, memberReferenceExpression.MemberName, typeArguments,
        GetNameLookupMode(memberReferenceExpression));
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitInvocationExpression(InvocationExpression invocationExpression)
    {
      // rr = Resolve(invocationExpression)
      // target = Resolve(memberReferenceExpression = invocationExpression.Target)
      // idRR = Resolve(identifierExpression = memberReferenceExpression.Target)
      // trr = ResolveType(identifierExpression)
      
      MemberReferenceExpression mre = invocationExpression.Target as MemberReferenceExpression;
      IdentifierExpression identifierExpression = mre != null ? mre.Target as IdentifierExpression : null;
      if (identifierExpression != null && identifierExpression.TypeArguments.Count == 0) {
        // Special handling for §7.6.4.1 Identicial simple names and type names
        
        StoreCurrentState(identifierExpression);
        StoreCurrentState(mre);
        
        ResolveResult idRR = resolver.ResolveSimpleName(identifierExpression.Identifier, EmptyList<IType>.Instance);
        ResolveResult target = ResolveMemberReferenceOnGivenTarget(idRR, mre);
        Log.WriteLine("Member reference '{0}' on potentially-ambiguous simple-name was resolved to {1}", mre, target);
        StoreResult(mre, target);
        TypeResolveResult trr;
        if (resolver.IsVariableReferenceWithSameType(idRR, identifierExpression.Identifier, out trr)) {
          // It's ambiguous
          ResolveResult rr = ResolveInvocationOnGivenTarget(target, invocationExpression);
          ResolveResult simpleNameRR = IsStaticResult(target, rr) ? trr : idRR;
          Log.WriteLine("Ambiguous simple name '{0}' was resolved to {1}",
                        identifierExpression, simpleNameRR);
          StoreResult(identifierExpression, simpleNameRR);
          return rr;
        } else {
          // It's not ambiguous
          Log.WriteLine("Simple name '{0}' was resolved to {1}", identifierExpression, idRR);
          StoreResult(identifierExpression, idRR);
          return ResolveInvocationOnGivenTarget(target, invocationExpression);
        }
      } else {
        // Regular code path
        if (resolverEnabled || NeedsResolvingDueToNamedArguments(invocationExpression)) {
          ResolveResult target = Resolve(invocationExpression.Target);
          return ResolveInvocationOnGivenTarget(target, invocationExpression);
        } else {
          ScanChildren(invocationExpression);
          return null;
        }
      }
    }
    
    ResolveResult ResolveInvocationOnGivenTarget(ResolveResult target, InvocationExpression invocationExpression)
    {
      string[] argumentNames;
      ResolveResult[] arguments = GetArguments(invocationExpression.Arguments, out argumentNames);
      ResolveResult rr = resolver.ResolveInvocation(target, arguments, argumentNames);
      ProcessInvocationResult(invocationExpression.Target, invocationExpression.Arguments, rr);
      return rr;
    }
    #endregion
    
    #region Lamdbas / Anonymous Functions
    ResolveResult IAstVisitor<ResolveResult>.VisitAnonymousMethodExpression(AnonymousMethodExpression anonymousMethodExpression)
    {
      return HandleExplicitlyTypedLambda(
        anonymousMethodExpression.Parameters, anonymousMethodExpression.Body,
        isAnonymousMethod: true,
        hasParameterList: anonymousMethodExpression.HasParameterList,
        isAsync: anonymousMethodExpression.IsAsync);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitLambdaExpression(LambdaExpression lambdaExpression)
    {
      bool isExplicitlyTyped = false;
      bool isImplicitlyTyped = false;
      foreach (var p in lambdaExpression.Parameters) {
        isImplicitlyTyped |= p.Type.IsNull;
        isExplicitlyTyped |= !p.Type.IsNull;
      }
      if (isExplicitlyTyped || !isImplicitlyTyped) {
        return HandleExplicitlyTypedLambda(
          lambdaExpression.Parameters, lambdaExpression.Body,
          isAnonymousMethod: false, hasParameterList: true, isAsync: lambdaExpression.IsAsync);
      } else {
        return new ImplicitlyTypedLambda(lambdaExpression, this);
      }
    }
    
    #region Explicitly typed
    ExplicitlyTypedLambda HandleExplicitlyTypedLambda(
      AstNodeCollection<ParameterDeclaration> parameterDeclarations,
      AstNode body, bool isAnonymousMethod, bool hasParameterList, bool isAsync)
    {
      CSharpResolver oldResolver = resolver;
      List<IParameter> parameters = (hasParameterList || parameterDeclarations.Any()) ? new List<IParameter>() : null;
      //bool oldIsWithinLambdaExpression = resolver.IsWithinLambdaExpression;
      resolver = resolver.WithIsWithinLambdaExpression(true);
      foreach (var pd in parameterDeclarations) {
        IType type = ResolveType(pd.Type);
        if (pd.ParameterModifier == ParameterModifier.Ref || pd.ParameterModifier == ParameterModifier.Out)
          type = new ByReferenceType(type);
        
        IParameter p = new DefaultParameter(type, pd.Name,
                                            region: MakeRegion(pd),
                                            isRef: pd.ParameterModifier == ParameterModifier.Ref,
                                            isOut: pd.ParameterModifier == ParameterModifier.Out);
        // The parameter declaration must be scanned in the current context (without the new parameter)
        // in order to be consistent with the context in which we resolved pd.Type.
        StoreCurrentState(pd);
        StoreResult(pd, new LocalResolveResult(p));
        ScanChildren(pd);
        
        resolver = resolver.AddVariable(p);
        parameters.Add(p);
      }
      
      var lambda = new ExplicitlyTypedLambda(parameters, isAnonymousMethod, isAsync, resolver, this, body);
      
      // Don't scan the lambda body here - we'll do that later when analyzing the ExplicitlyTypedLambda.
      
      resolver = oldResolver;
      return lambda;
    }
    
    DomRegion MakeRegion(AstNode node)
    {
      if (unresolvedFile != null)
        return new DomRegion(unresolvedFile.FileName, node.StartLocation, node.EndLocation);
      else
        return node.GetRegion();
    }
    
    sealed class ExplicitlyTypedLambda : LambdaBase
    {
      readonly IList<IParameter> parameters;
      readonly bool isAnonymousMethod;
      readonly bool isAsync;
      
      CSharpResolver storedContext;
      ResolveVisitor visitor;
      AstNode body;
      ResolveResult bodyRR;
      
      IType inferredReturnType;
      IList<Expression> returnExpressions;
      IList<ResolveResult> returnValues;
      bool isValidAsVoidMethod;
      bool isEndpointUnreachable;
      
      // The actual return type is set when the lambda is applied by the conversion.
      // For async lambdas, this includes the task type
      IType actualReturnType;
      
      internal override bool IsUndecided {
        get { return actualReturnType == null; }
      }
      
      internal override AstNode LambdaExpression {
        get { return body.Parent; }
      }
      
      internal override AstNode BodyExpression {
        get { return body; }
      }
      
      public override ResolveResult Body {
        get {
          if (bodyRR != null)
            return bodyRR;

          if (body is Expression) {
            Analyze();
            if (returnValues.Count == 1) {
              bodyRR = returnValues[0];
              if (actualReturnType != null) {
                IType unpackedActualReturnType = isAsync ? visitor.UnpackTask(actualReturnType) : actualReturnType;
                if (unpackedActualReturnType.Kind != TypeKind.Void) {
                  var conv = storedContext.conversions.ImplicitConversion(bodyRR, unpackedActualReturnType);
                  if (!conv.IsIdentityConversion)
                    bodyRR = new ConversionResolveResult(unpackedActualReturnType, bodyRR, conv, storedContext.CheckForOverflow);
                }
              }
              return bodyRR;
            }
          }
          return bodyRR = visitor.voidResult;
        }
      }
      
      public ExplicitlyTypedLambda(IList<IParameter> parameters, bool isAnonymousMethod, bool isAsync, CSharpResolver storedContext, ResolveVisitor visitor, AstNode body)
      {
        this.parameters = parameters;
        this.isAnonymousMethod = isAnonymousMethod;
        this.isAsync = isAsync;
        this.storedContext = storedContext;
        this.visitor = visitor;
        this.body = body;
        
        if (visitor.undecidedLambdas == null)
          visitor.undecidedLambdas = new List<LambdaBase>();
        visitor.undecidedLambdas.Add(this);
        Log.WriteLine("Added undecided explicitly-typed lambda: " + this.LambdaExpression);
      }
      
      public override IList<IParameter> Parameters {
        get {
          return parameters ?? EmptyList<IParameter>.Instance;
        }
      }
      
      bool Analyze()
      {
        // If it's not already analyzed
        if (inferredReturnType == null) {
          Log.WriteLine("Analyzing " + this.LambdaExpression + "...");
          Log.Indent();
          
          visitor.ResetContext(
            storedContext,
            delegate {
              var oldNavigator = visitor.navigator;
              visitor.navigator = new ConstantModeResolveVisitorNavigator(ResolveVisitorNavigationMode.Resolve, oldNavigator);
              visitor.AnalyzeLambda(body, isAsync, out isValidAsVoidMethod, out isEndpointUnreachable, out inferredReturnType, out returnExpressions, out returnValues);
              visitor.navigator = oldNavigator;
            });
          Log.Unindent();
          Log.WriteLine("Finished analyzing " + this.LambdaExpression);
          
          if (inferredReturnType == null)
            throw new InvalidOperationException("AnalyzeLambda() didn't set inferredReturnType");
        }
        return true;
      }
      
      public override Conversion IsValid(IType[] parameterTypes, IType returnType, CSharpConversions conversions)
      {
        Log.WriteLine("Testing validity of {0} for return-type {1}...", this, returnType);
        Log.Indent();
        bool valid = Analyze() && IsValidLambda(isValidAsVoidMethod, isEndpointUnreachable, isAsync, returnValues, returnType, conversions);
        Log.Unindent();
        Log.WriteLine("{0} is {1} for return-type {2}", this, valid ? "valid" : "invalid", returnType);
        return new AnonymousFunctionConversion(returnType, this, valid);
      }
      
      public override IType GetInferredReturnType(IType[] parameterTypes)
      {
        Analyze();
        return inferredReturnType;
      }
      
      public override IType ReturnType {
        get {
          return actualReturnType ?? SpecialType.UnknownType;
        }
      }
      
      public override bool IsImplicitlyTyped {
        get { return false; }
      }
      
      public override bool IsAsync {
        get { return isAsync; }
      }
      
      public override bool IsAnonymousMethod {
        get { return isAnonymousMethod; }
      }
      
      public override bool HasParameterList {
        get { return parameters != null; }
      }
      
      public override string ToString()
      {
        return "[ExplicitlyTypedLambda " + this.LambdaExpression + "]";
      }
      
      public void ApplyReturnType(ResolveVisitor parentVisitor, IType returnType)
      {
        if (returnType == null)
          throw new ArgumentNullException("returnType");
        if (parentVisitor != visitor) {
          // Explicitly typed lambdas do not use a nested visitor
          throw new InvalidOperationException();
        }
        if (actualReturnType != null) {
          if (actualReturnType.Equals(returnType))
            return; // return type already set
          throw new InvalidOperationException("inconsistent return types for explicitly-typed lambda");
        }
        actualReturnType = returnType;
        visitor.undecidedLambdas.Remove(this);
        Analyze();
        IType unpackedReturnType = isAsync ? visitor.UnpackTask(returnType) : returnType;
        Log.WriteLine("Applying return type {0} to explicitly-typed lambda {1}", unpackedReturnType, this.LambdaExpression);
        if (unpackedReturnType.Kind != TypeKind.Void || body is BlockStatement) {
          for (int i = 0; i < returnExpressions.Count; i++) {
            visitor.ProcessConversion(returnExpressions[i], returnValues[i], unpackedReturnType);
          }
        }
      }
      
      internal override void EnforceMerge(ResolveVisitor parentVisitor)
      {
        ApplyReturnType(parentVisitor, SpecialType.UnknownType);
      }
    }
    #endregion
    
    #region Implicitly typed
    // Implicitly-typed lambdas are really complex, as the lambda depends on the target type (the delegate to which
    // the lambda is converted), but figuring out the target type might involve overload resolution (for method
    // calls in which the lambda is used as argument), which requires knowledge about the lamdba.
    // 
    // The implementation in NRefactory works like this:
    // 1. The lambda resolves to a ImplicitlyTypedLambda (derived from LambdaResolveResult).
    //     The lambda body is not resolved yet (one of the few places where ResolveVisitor
    //     deviates from the usual depth-first AST traversal).
    // 2. The parent statement is resolved as usual. This might require analyzing the lambda in detail (for example
    //    as part of overload resolution). Such analysis happens using LambdaResolveResult.IsValid, where the caller
    //    (i.e. the overload resolution algorithm) supplies the parameter types to the lambda body. For every IsValid()
    //    call, a nested LambdaTypeHypothesis is constructed for analyzing the lambda using the supplied type assignment.
    //    Multiple IsValid() calls may use several LambdaTypeHypothesis instances, one for each set of parameter types.
    // 3. When the resolver reports the conversions that occurred as part of the parent statement (as with any
    //    conversions), the results from the LambdaTypeHypothesis corresponding to the actually chosen
    //    conversion are merged into the main resolver.
    // 4. LambdaResolveResult.Body is set to the main resolve result from the chosen nested resolver. I think this
    //    is the only place where NRefactory is mutating a ResolveResult (normally all resolve results are immutable).
    //    As this step is guaranteed to occur before the resolver returns the LamdbaResolveResult to user code, the
    //    mutation shouldn't cause any problems.
    sealed class ImplicitlyTypedLambda : LambdaBase
    {
      readonly LambdaExpression lambda;
      readonly QuerySelectClause selectClause;
      
      readonly CSharpResolver storedContext;
      readonly CSharpUnresolvedFile unresolvedFile;
      readonly List<LambdaTypeHypothesis> hypotheses = new List<LambdaTypeHypothesis>();
      internal IList<IParameter> parameters = new List<IParameter>();
      
      internal IType actualReturnType;
      internal LambdaTypeHypothesis winningHypothesis;
      internal ResolveResult bodyResult;
      internal readonly ResolveVisitor parentVisitor;
      
      internal override bool IsUndecided {
        get { return winningHypothesis == null;  }
      }
      
      internal override AstNode LambdaExpression {
        get {
          if (selectClause != null)
            return selectClause.Expression;
          else
            return lambda;
        }
      }
      
      internal override AstNode BodyExpression {
        get {
          if (selectClause != null)
            return selectClause.Expression;
          else
            return lambda.Body;
        }
      }
      
      public override ResolveResult Body {
        get { return bodyResult; }
      }
      
      private ImplicitlyTypedLambda(ResolveVisitor parentVisitor)
      {
        this.parentVisitor = parentVisitor;
        this.storedContext = parentVisitor.resolver;
        this.unresolvedFile = parentVisitor.unresolvedFile;
        this.bodyResult = parentVisitor.voidResult;
      }
      
      public ImplicitlyTypedLambda(LambdaExpression lambda, ResolveVisitor parentVisitor)
        : this(parentVisitor)
      {
        this.lambda = lambda;
        foreach (var pd in lambda.Parameters) {
          parameters.Add(new DefaultParameter(SpecialType.UnknownType, pd.Name, region: parentVisitor.MakeRegion(pd)));
        }
        RegisterUndecidedLambda();
      }
      
      public ImplicitlyTypedLambda(QuerySelectClause selectClause, IEnumerable<IParameter> parameters, ResolveVisitor parentVisitor)
        : this(parentVisitor)
      {
        this.selectClause = selectClause;
        foreach (IParameter p in parameters)
          this.parameters.Add(p);
        
        RegisterUndecidedLambda();
      }
      
      void RegisterUndecidedLambda()
      {
        if (parentVisitor.undecidedLambdas == null)
          parentVisitor.undecidedLambdas = new List<LambdaBase>();
        parentVisitor.undecidedLambdas.Add(this);
        Log.WriteLine("Added undecided implicitly-typed lambda: " + this.LambdaExpression);
      }
      
      public override IList<IParameter> Parameters {
        get { return parameters; }
      }
      
      public override Conversion IsValid(IType[] parameterTypes, IType returnType, CSharpConversions conversions)
      {
        Log.WriteLine("Testing validity of {0} for parameters ({1}) and return-type {2}...",
                      this, string.Join<IType>(", ", parameterTypes), returnType);
        Log.Indent();
        var hypothesis = GetHypothesis(parameterTypes);
        Conversion c = hypothesis.IsValid(returnType, conversions);
        Log.Unindent();
        Log.WriteLine("{0} is {1} for return-type {2}", hypothesis, c.IsValid ? "valid" : "invalid", returnType);
        return c;
      }
      
      public override IType GetInferredReturnType(IType[] parameterTypes)
      {
        return GetHypothesis(parameterTypes).inferredReturnType;
      }
      
      LambdaTypeHypothesis GetHypothesis(IType[] parameterTypes)
      {
        if (parameterTypes.Length != parameters.Count)
          throw new ArgumentException("Incorrect parameter type count");
        foreach (var h in hypotheses) {
          bool ok = true;
          for (int i = 0; i < parameterTypes.Length; i++) {
            if (!parameterTypes[i].Equals(h.parameterTypes[i])) {
              ok = false;
              break;
            }
          }
          if (ok)
            return h;
        }
        ResolveVisitor visitor = new ResolveVisitor(storedContext, unresolvedFile);
        var newHypothesis = new LambdaTypeHypothesis(this, parameterTypes, visitor, lambda != null ? lambda.Parameters : null, storedContext);
        hypotheses.Add(newHypothesis);
        return newHypothesis;
      }
      
      /// <summary>
      /// Get any hypothesis for this lambda.
      /// This method is used as fallback if the lambda isn't merged the normal way (AnonymousFunctionConversion)
      /// </summary>
      internal LambdaTypeHypothesis GetAnyHypothesis()
      {
        if (winningHypothesis != null)
          return winningHypothesis;
        if (hypotheses.Count == 0) {
          // make a new hypothesis with unknown parameter types
          IType[] parameterTypes = new IType[parameters.Count];
          for (int i = 0; i < parameterTypes.Length; i++) {
            parameterTypes[i] = SpecialType.UnknownType;
          }
          return GetHypothesis(parameterTypes);
        } else {
          // We have the choice, so pick the hypothesis with the least missing parameter types
          LambdaTypeHypothesis bestHypothesis = hypotheses[0];
          int bestHypothesisUnknownParameters = bestHypothesis.CountUnknownParameters();
          for (int i = 1; i < hypotheses.Count; i++) {
            int c = hypotheses[i].CountUnknownParameters();
            if (c < bestHypothesisUnknownParameters ||
                (c == bestHypothesisUnknownParameters && hypotheses[i].success && !bestHypothesis.success))
            {
              bestHypothesis = hypotheses[i];
              bestHypothesisUnknownParameters = c;
            }
          }
          return bestHypothesis;
        }
      }
      
      internal override void EnforceMerge(ResolveVisitor parentVisitor)
      {
        GetAnyHypothesis().MergeInto(parentVisitor, SpecialType.UnknownType);
      }
      
      public override IType ReturnType {
        get { return actualReturnType ?? SpecialType.UnknownType; }
      }
      
      public override bool IsImplicitlyTyped {
        get { return true; }
      }
      
      public override bool IsAnonymousMethod {
        get { return false; }
      }
      
      public override bool HasParameterList {
        get { return true; }
      }
      
      public override bool IsAsync {
        get { return lambda != null && lambda.IsAsync; }
      }
      
      public override string ToString()
      {
        return "[ImplicitlyTypedLambda " + this.LambdaExpression + "]";
      }
    }
    
    /// <summary>
    /// Every possible set of parameter types gets its own 'hypothetical world'.
    /// It uses a nested ResolveVisitor that has its own resolve cache, so that resolve results cannot leave the hypothetical world.
    /// 
    /// Only after overload resolution is applied and the actual parameter types are known, the winning hypothesis will be merged
    /// with the parent ResolveVisitor.
    /// This is done when the AnonymousFunctionConversion is applied on the parent visitor.
    /// </summary>
    sealed class LambdaTypeHypothesis : IResolveVisitorNavigator
    {
      readonly ImplicitlyTypedLambda lambda;
      readonly IParameter[] lambdaParameters;
      internal readonly IType[] parameterTypes;
      readonly ResolveVisitor visitor;
      readonly CSharpResolver storedContext;
      
      internal readonly IType inferredReturnType;
      IList<Expression> returnExpressions;
      IList<ResolveResult> returnValues;
      bool isValidAsVoidMethod;
      bool isEndpointUnreachable;
      internal bool success;
      
      public LambdaTypeHypothesis(ImplicitlyTypedLambda lambda, IType[] parameterTypes, ResolveVisitor visitor,
                                  ICollection<ParameterDeclaration> parameterDeclarations, CSharpResolver storedContext)
      {
        Debug.Assert(parameterTypes.Length == lambda.Parameters.Count);
        
        this.lambda = lambda;
        this.parameterTypes = parameterTypes;
        this.visitor = visitor;
        this.storedContext = storedContext;
        visitor.SetNavigator(this);
        
        Log.WriteLine("Analyzing " + ToString() + "...");
        Log.Indent();
        CSharpResolver oldResolver = visitor.resolver;
        visitor.resolver = visitor.resolver.WithIsWithinLambdaExpression(true);
        lambdaParameters = new IParameter[parameterTypes.Length];
        if (parameterDeclarations != null) {
          int i = 0;
          foreach (var pd in parameterDeclarations) {
            lambdaParameters[i] = new DefaultParameter(parameterTypes[i], pd.Name, region: visitor.MakeRegion(pd));
            visitor.resolver = visitor.resolver.AddVariable(lambdaParameters[i]);
            i++;
            visitor.Scan(pd);
          }
        } else {
          for (int i = 0; i < parameterTypes.Length; i++) {
            var p = lambda.Parameters[i];
            lambdaParameters[i] = new DefaultParameter(parameterTypes[i], p.Name, region: p.Region);
            visitor.resolver = visitor.resolver.AddVariable(lambdaParameters[i]);
          }
        }
        
        success = true;
        visitor.AnalyzeLambda(lambda.BodyExpression, lambda.IsAsync, out isValidAsVoidMethod, out isEndpointUnreachable, out inferredReturnType, out returnExpressions, out returnValues);
        visitor.resolver = oldResolver;
        Log.Unindent();
        Log.WriteLine("Finished analyzing " + ToString());
      }
      
      ResolveVisitorNavigationMode IResolveVisitorNavigator.Scan(AstNode node)
      {
        return ResolveVisitorNavigationMode.Resolve;
      }
      
      void IResolveVisitorNavigator.Resolved(AstNode node, ResolveResult result)
      {
        if (result.IsError)
          success = false;
      }
      
      void IResolveVisitorNavigator.ProcessConversion(Expression expression, ResolveResult result, Conversion conversion, IType targetType)
      {
        success &= conversion.IsValid;
      }
      
      internal int CountUnknownParameters()
      {
        int c = 0;
        foreach (IType t in parameterTypes) {
          if (t.Kind == TypeKind.Unknown)
            c++;
        }
        return c;
      }
      
      public Conversion IsValid(IType returnType, CSharpConversions conversions)
      {
        bool valid = success && IsValidLambda(isValidAsVoidMethod, isEndpointUnreachable, lambda.IsAsync, returnValues, returnType, conversions);
        return new AnonymousFunctionConversion(returnType, this, valid);
      }
      
      public void MergeInto(ResolveVisitor parentVisitor, IType returnType)
      {
        if (returnType == null)
          throw new ArgumentNullException("returnType");
        if (parentVisitor != lambda.parentVisitor)
          throw new InvalidOperationException("parent visitor mismatch");
        
        if (lambda.winningHypothesis == this)
          return;
        else if (lambda.winningHypothesis != null)
          throw new InvalidOperationException("Trying to merge conflicting hypotheses");
        
        lambda.actualReturnType = returnType;
        if (lambda.IsAsync)
          returnType = parentVisitor.UnpackTask(returnType);
        
        lambda.winningHypothesis = this;
        lambda.parameters = lambdaParameters; // replace untyped parameters with typed parameters
        if (lambda.BodyExpression is Expression && returnValues.Count == 1) {
          lambda.bodyResult = returnValues[0];
          if (returnType.Kind != TypeKind.Void) {
            var conv = storedContext.conversions.ImplicitConversion(lambda.bodyResult, returnType);
            if (!conv.IsIdentityConversion)
              lambda.bodyResult = new ConversionResolveResult(returnType, lambda.bodyResult, conv, storedContext.CheckForOverflow);
          }
        }
        
        Log.WriteLine("Applying return type {0} to implicitly-typed lambda {1}", returnType, lambda.LambdaExpression);
        if (returnType.Kind != TypeKind.Void || lambda.BodyExpression is Statement) {
          for (int i = 0; i < returnExpressions.Count; i++) {
            visitor.ProcessConversion(returnExpressions[i], returnValues[i], returnType);
          }
        }
        
        visitor.MergeUndecidedLambdas();
        Log.WriteLine("Merging " + ToString());
        foreach (var pair in visitor.resolverBeforeDict) {
          Debug.Assert(!parentVisitor.resolverBeforeDict.ContainsKey(pair.Key));
          parentVisitor.resolverBeforeDict[pair.Key] = pair.Value;
        }
        foreach (var pair in visitor.resolverAfterDict) {
          Debug.Assert(!parentVisitor.resolverAfterDict.ContainsKey(pair.Key));
          parentVisitor.resolverAfterDict[pair.Key] = pair.Value;
        }
        foreach (var pair in visitor.resolveResultCache) {
          parentVisitor.StoreResult(pair.Key, pair.Value);
        }
        parentVisitor.ImportConversions(visitor);
        parentVisitor.undecidedLambdas.Remove(lambda);
      }
      
      public override string ToString()
      {
        StringBuilder b = new StringBuilder();
        b.Append("[LambdaTypeHypothesis (");
        for (int i = 0; i < parameterTypes.Length; i++) {
          if (i > 0) b.Append(", ");
          b.Append(parameterTypes[i]);
          b.Append(' ');
          b.Append(lambda.Parameters[i].Name);
        }
        b.Append(") => ");
        b.Append(lambda.BodyExpression.ToString());
        b.Append(']');
        return b.ToString();
      }
    }
    #endregion
    
    #region MergeUndecidedLambdas
    abstract class LambdaBase : LambdaResolveResult
    {
      internal abstract bool IsUndecided { get; }
      internal abstract AstNode LambdaExpression { get; }
      internal abstract AstNode BodyExpression { get; }
      
      internal abstract void EnforceMerge(ResolveVisitor parentVisitor);
      
      public override ResolveResult ShallowClone()
      {
        if (IsUndecided)
          throw new NotSupportedException();
        return base.ShallowClone();
      }
    }
    
    void MergeUndecidedLambdas()
    {
      if (undecidedLambdas == null || undecidedLambdas.Count == 0)
        return;
      Log.WriteLine("MergeUndecidedLambdas()...");
      Log.Indent();
      while (undecidedLambdas.Count > 0) {
        LambdaBase lambda = undecidedLambdas[0];
        // may happen caused by parse error l =>
        if (lambda.LambdaExpression == null) {
          undecidedLambdas.Remove (lambda);
          continue;
        }
        ResolveParentForConversion(lambda.LambdaExpression);
        if (lambda.IsUndecided) {
          // Lambda wasn't merged by resolving its parent -> enforce merging
          Log.WriteLine("Lambda wasn't merged by conversion - enforce merging");
          lambda.EnforceMerge(this);
        }
      }
      Log.Unindent();
      Log.WriteLine("MergeUndecidedLambdas() finished.");
    }
    
    void ResolveParentForConversion(AstNode expression)
    {
      AstNode parent = expression.Parent;
      // Continue going upwards until we find a node that can be resolved and provides
      // an expected type.
      while (ParenthesizedExpression.ActsAsParenthesizedExpression(parent) || CSharpAstResolver.IsUnresolvableNode(parent)) {
        parent = parent.Parent;
      }
      CSharpResolver storedResolver;
      if (parent != null && resolverBeforeDict.TryGetValue(parent, out storedResolver)) {
        Log.WriteLine("Trying to resolve '" + parent + "' in order to find the conversion applied to '" + expression + "'...");
        Log.Indent();
        ResetContext(storedResolver, delegate { Resolve(parent); });
        Log.Unindent();
      } else {
        Log.WriteLine("Could not find a suitable parent for '" + expression + "'");
      }
    }
    #endregion
    
    #region AnalyzeLambda
    IType GetTaskType(IType resultType)
    {
      if (resultType.Kind == TypeKind.Unknown)
        return SpecialType.UnknownType;
      if (resultType.Kind == TypeKind.Void)
        return resolver.Compilation.FindType(KnownTypeCode.Task);
      
      ITypeDefinition def = resolver.Compilation.FindType(KnownTypeCode.TaskOfT).GetDefinition();
      if (def != null)
        return new ParameterizedType(def, new[] { resultType });
      else
        return SpecialType.UnknownType;
    }
    
    void AnalyzeLambda(AstNode body, bool isAsync, out bool isValidAsVoidMethod, out bool isEndpointUnreachable, out IType inferredReturnType, out IList<Expression> returnExpressions, out IList<ResolveResult> returnValues)
    {
      isEndpointUnreachable = false;
      Expression expr = body as Expression;
      if (expr != null) {
        isValidAsVoidMethod = ExpressionPermittedAsStatement(expr);
        returnExpressions = new [] { expr };
        returnValues = new[] { Resolve(expr) };
        inferredReturnType = returnValues[0].Type;
      } else {
        Scan(body);
        
        AnalyzeLambdaVisitor alv = new AnalyzeLambdaVisitor();
        body.AcceptVisitor(alv);
        isValidAsVoidMethod = (alv.ReturnExpressions.Count == 0);
        if (alv.HasVoidReturnStatements) {
          returnExpressions = EmptyList<Expression>.Instance;
          returnValues = EmptyList<ResolveResult>.Instance;
          inferredReturnType = resolver.Compilation.FindType(KnownTypeCode.Void);
        } else {
          returnExpressions = alv.ReturnExpressions;
          returnValues = new ResolveResult[returnExpressions.Count];
          for (int i = 0; i < returnValues.Count; i++) {
            returnValues[i] = resolveResultCache[returnExpressions[i]];
          }

          // async lambdas without return statements are resolved as Task return types.
          if (returnExpressions.Count == 0 && isAsync) {
            inferredReturnType = resolver.Compilation.FindType(KnownTypeCode.Task);
            Log.WriteLine("Lambda return type was inferred to: " + inferredReturnType);
            return;
          }

          TypeInference ti = new TypeInference(resolver.Compilation, resolver.conversions);
          bool tiSuccess;
          inferredReturnType = ti.GetBestCommonType(returnValues, out tiSuccess);
          // Failure to infer a return type does not make the lambda invalid,
          // so we can ignore the 'tiSuccess' value
          if (isValidAsVoidMethod && returnExpressions.Count == 0 && body is Statement) {
            var reachabilityAnalysis = ReachabilityAnalysis.Create(
              (Statement)body, (node, _) => resolveResultCache[node],
              resolver.CurrentTypeResolveContext, cancellationToken);
            isEndpointUnreachable = !reachabilityAnalysis.IsEndpointReachable((Statement)body);
          }
        }
      }
      if (isAsync)
        inferredReturnType = GetTaskType(inferredReturnType);
      Log.WriteLine("Lambda return type was inferred to: " + inferredReturnType);
    }
    
    static bool ExpressionPermittedAsStatement(Expression expr)
    {
      UnaryOperatorExpression uoe = expr as UnaryOperatorExpression;
      if (uoe != null) {
        switch (uoe.Operator) {
          case UnaryOperatorType.Increment:
          case UnaryOperatorType.Decrement:
          case UnaryOperatorType.PostIncrement:
          case UnaryOperatorType.PostDecrement:
          case UnaryOperatorType.Await:
            return true;
          default:
            return false;
        }
      }
      return expr is InvocationExpression
        || expr is ObjectCreateExpression
        || expr is AssignmentExpression;
    }
    
    static bool IsValidLambda(bool isValidAsVoidMethod, bool isEndpointUnreachable, bool isAsync, IList<ResolveResult> returnValues, IType returnType, CSharpConversions conversions)
    {
      if (returnType.Kind == TypeKind.Void) {
        // Lambdas that are valid statement lambdas or expression lambdas with a statement-expression
        // can be converted to delegates with void return type.
        // This holds for both async and regular lambdas.
        return isValidAsVoidMethod;
      } else if (isAsync && TaskType.IsTask(returnType) && returnType.TypeParameterCount == 0) {
        // Additionally, async lambdas with the above property can be converted to non-generic Task.
        return isValidAsVoidMethod;
      } else {
        if (returnValues.Count == 0)
          return isEndpointUnreachable;
        if (isAsync) {
          // async lambdas must return Task<T>
          if (!(TaskType.IsTask(returnType) && returnType.TypeParameterCount == 1))
            return false;
          // unpack Task<T> for testing the implicit conversions
          returnType = ((ParameterizedType)returnType).GetTypeArgument(0);
        }
        foreach (ResolveResult returnRR in returnValues) {
          if (!conversions.ImplicitConversion(returnRR, returnType).IsValid)
            return false;
        }
        return true;
      }
    }
    
    IType UnpackTask(IType type)
    {
      return TaskType.UnpackTask(resolver.Compilation, type);
    }
    
    sealed class AnalyzeLambdaVisitor : DepthFirstAstVisitor
    {
      public bool HasVoidReturnStatements;
      public List<Expression> ReturnExpressions = new List<Expression>();
      
      public override void VisitReturnStatement(ReturnStatement returnStatement)
      {
        Expression expr = returnStatement.Expression;
        if (expr.IsNull) {
          HasVoidReturnStatements = true;
        } else {
          ReturnExpressions.Add(expr);
        }
      }
      
      public override void VisitAnonymousMethodExpression(AnonymousMethodExpression anonymousMethodExpression)
      {
        // don't go into nested lambdas
      }
      
      public override void VisitLambdaExpression(LambdaExpression lambdaExpression)
      {
        // don't go into nested lambdas
      }
    }
    #endregion
    #endregion
    
    #region ForEach Statement
    ResolveResult IAstVisitor<ResolveResult>.VisitForeachStatement(ForeachStatement foreachStatement)
    {
      var compilation = resolver.Compilation;
      ResolveResult expression = Resolve(foreachStatement.InExpression);
      bool isImplicitlyTypedVariable = foreachStatement.VariableType.IsVar();
      var memberLookup = resolver.CreateMemberLookup();
      
      IType collectionType, enumeratorType, elementType;
      ResolveResult getEnumeratorInvocation;
      ResolveResult currentRR = null;
      // C# 4.0 spec: §8.8.4 The foreach statement
      if (expression.Type.Kind == TypeKind.Array || expression.Type.Kind == TypeKind.Dynamic) {
        collectionType = compilation.FindType(KnownTypeCode.IEnumerable);
        enumeratorType = compilation.FindType(KnownTypeCode.IEnumerator);
        if (expression.Type.Kind == TypeKind.Array) {
          elementType = ((ArrayType)expression.Type).ElementType;
        } else {
          elementType = isImplicitlyTypedVariable ? SpecialType.Dynamic : compilation.FindType(KnownTypeCode.Object);
        }
        getEnumeratorInvocation = resolver.ResolveCast(collectionType, expression);
        getEnumeratorInvocation = resolver.ResolveMemberAccess(getEnumeratorInvocation, "GetEnumerator", EmptyList<IType>.Instance, NameLookupMode.InvocationTarget);
        getEnumeratorInvocation = resolver.ResolveInvocation(getEnumeratorInvocation, new ResolveResult[0]);
      } else {
        var getEnumeratorMethodGroup = memberLookup.Lookup(expression, "GetEnumerator", EmptyList<IType>.Instance, true) as MethodGroupResolveResult;
        if (getEnumeratorMethodGroup != null) {
          var or = getEnumeratorMethodGroup.PerformOverloadResolution(
            compilation, new ResolveResult[0],
            allowExtensionMethods: false, allowExpandingParams: false, allowOptionalParameters: false);
          if (or.FoundApplicableCandidate && !or.IsAmbiguous && !or.BestCandidate.IsStatic && or.BestCandidate.IsPublic) {
            collectionType = expression.Type;
            getEnumeratorInvocation = or.CreateResolveResult(expression);
            enumeratorType = getEnumeratorInvocation.Type;
            currentRR = memberLookup.Lookup(new ResolveResult(enumeratorType), "Current", EmptyList<IType>.Instance, false);
            elementType = currentRR.Type;
          } else {
            CheckForEnumerableInterface(expression, out collectionType, out enumeratorType, out elementType, out getEnumeratorInvocation);
          }
        } else {
          CheckForEnumerableInterface(expression, out collectionType, out enumeratorType, out elementType, out getEnumeratorInvocation);
        }
      }
      IMethod moveNextMethod = null;
      var moveNextMethodGroup = memberLookup.Lookup(new ResolveResult(enumeratorType), "MoveNext", EmptyList<IType>.Instance, false) as MethodGroupResolveResult;
      if (moveNextMethodGroup != null) {
        var or = moveNextMethodGroup.PerformOverloadResolution(
          compilation, new ResolveResult[0],
          allowExtensionMethods: false, allowExpandingParams: false, allowOptionalParameters: false);
        moveNextMethod = or.GetBestCandidateWithSubstitutedTypeArguments() as IMethod;
      }
      
      if (currentRR == null)
        currentRR = memberLookup.Lookup(new ResolveResult(enumeratorType), "Current", EmptyList<IType>.Instance, false);
      IProperty currentProperty = null;
      if (currentRR is MemberResolveResult)
        currentProperty = ((MemberResolveResult)currentRR).Member as IProperty;
      // end of foreach resolve logic
      // back to resolve visitor:
      
      resolver = resolver.PushBlock();
      IVariable v;
      if (isImplicitlyTypedVariable) {
        StoreCurrentState(foreachStatement.VariableType);
        StoreResult(foreachStatement.VariableType, new TypeResolveResult(elementType));
        v = MakeVariable(elementType, foreachStatement.VariableNameToken);
      } else {
        IType variableType = ResolveType(foreachStatement.VariableType);
        v = MakeVariable(variableType, foreachStatement.VariableNameToken);
      }
      StoreCurrentState(foreachStatement.VariableNameToken);
      resolver = resolver.AddVariable(v);
      
      StoreResult(foreachStatement.VariableNameToken, new LocalResolveResult(v));
      
      Scan(foreachStatement.EmbeddedStatement);
      resolver = resolver.PopBlock();
      return new ForEachResolveResult(getEnumeratorInvocation, collectionType, enumeratorType, elementType,
                                      v, currentProperty, moveNextMethod, voidResult.Type);
    }
    
    void CheckForEnumerableInterface(ResolveResult expression, out IType collectionType, out IType enumeratorType, out IType elementType, out ResolveResult getEnumeratorInvocation)
    {
      var compilation = resolver.Compilation;
      bool? isGeneric;
      elementType = GetElementTypeFromIEnumerable(expression.Type, compilation, false, out isGeneric);
      if (isGeneric == true) {
        ITypeDefinition enumerableOfT = compilation.FindType(KnownTypeCode.IEnumerableOfT).GetDefinition();
        if (enumerableOfT != null)
          collectionType = new ParameterizedType(enumerableOfT, new [] { elementType });
        else
          collectionType = SpecialType.UnknownType;
        
        ITypeDefinition enumeratorOfT = compilation.FindType(KnownTypeCode.IEnumeratorOfT).GetDefinition();
        if (enumeratorOfT != null)
          enumeratorType = new ParameterizedType(enumeratorOfT, new [] { elementType });
        else
          enumeratorType = SpecialType.UnknownType;
      } else if (isGeneric == false) {
        collectionType = compilation.FindType(KnownTypeCode.IEnumerable);
        enumeratorType = compilation.FindType(KnownTypeCode.IEnumerator);
      } else {
        collectionType = SpecialType.UnknownType;
        enumeratorType = SpecialType.UnknownType;
      }
      getEnumeratorInvocation = resolver.ResolveCast(collectionType, expression);
      getEnumeratorInvocation = resolver.ResolveMemberAccess(getEnumeratorInvocation, "GetEnumerator", EmptyList<IType>.Instance, NameLookupMode.InvocationTarget);
      getEnumeratorInvocation = resolver.ResolveInvocation(getEnumeratorInvocation, new ResolveResult[0]);
    }
    #endregion
    
    #region Local Variable Scopes (Block Statements)
    ResolveResult IAstVisitor<ResolveResult>.VisitBlockStatement(BlockStatement blockStatement)
    {
      resolver = resolver.PushBlock();
      ScanChildren(blockStatement);
      resolver = resolver.PopBlock();
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitUsingStatement(UsingStatement usingStatement)
    {
      resolver = resolver.PushBlock();
      if (resolverEnabled) {
        for (AstNode child = usingStatement.FirstChild; child != null; child = child.NextSibling) {
          if (child.Role == UsingStatement.ResourceAcquisitionRole && child is Expression) {
            ResolveAndProcessConversion((Expression)child, resolver.Compilation.FindType(KnownTypeCode.IDisposable));
          } else {
            Scan(child);
          }
        }
      } else {
        ScanChildren(usingStatement);
      }
      resolver = resolver.PopBlock();
      return resolverEnabled ? voidResult : null;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitFixedStatement(FixedStatement fixedStatement)
    {
      resolver = resolver.PushBlock();
      IType type = ResolveType(fixedStatement.Type);
      foreach (VariableInitializer vi in fixedStatement.Variables) {
        resolver = resolver.AddVariable(MakeVariable(type, vi.NameToken));
        Scan(vi);
      }
      Scan(fixedStatement.EmbeddedStatement);
      resolver = resolver.PopBlock();
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitSwitchStatement(SwitchStatement switchStatement)
    {
      resolver = resolver.PushBlock();
      ScanChildren(switchStatement);
      resolver = resolver.PopBlock();
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitCatchClause(CatchClause catchClause)
    {
      resolver = resolver.PushBlock();
      if (string.IsNullOrEmpty(catchClause.VariableName)) {
        Scan(catchClause.Type);
      } else {
        //DomRegion region = MakeRegion(catchClause.VariableNameToken);
        StoreCurrentState(catchClause.VariableNameToken);
        IVariable v = MakeVariable(ResolveType(catchClause.Type), catchClause.VariableNameToken);
        resolver = resolver.AddVariable(v);
        StoreResult(catchClause.VariableNameToken, new LocalResolveResult(v));
      }
      Scan(catchClause.Body);
      resolver = resolver.PopBlock();
      return voidResult;
    }
    #endregion
    
    #region VariableDeclarationStatement
    ResolveResult IAstVisitor<ResolveResult>.VisitVariableDeclarationStatement(VariableDeclarationStatement variableDeclarationStatement)
    {
      bool isConst = (variableDeclarationStatement.Modifiers & Modifiers.Const) != 0;
      if (!isConst && variableDeclarationStatement.Type.IsVar() && variableDeclarationStatement.Variables.Count == 1) {
        VariableInitializer vi = variableDeclarationStatement.Variables.Single();
        StoreCurrentState(variableDeclarationStatement.Type);
        IType type = Resolve(vi.Initializer).Type;
        StoreResult(variableDeclarationStatement.Type, new TypeResolveResult(type));
        IVariable v = MakeVariable(type, vi.NameToken);
        resolver = resolver.AddVariable(v);
        Scan(vi);
      } else {
        IType type = ResolveType(variableDeclarationStatement.Type);

        foreach (VariableInitializer vi in variableDeclarationStatement.Variables) {
          IVariable v;
          if (isConst) {
            ResolveResult rr = Resolve(vi.Initializer);
            rr = resolver.ResolveCast(type, rr);
            v = MakeConstant(type, vi.NameToken, rr.ConstantValue);
          } else {
            v = MakeVariable(type, vi.NameToken);
          }
          resolver = resolver.AddVariable(v);
          Scan(vi);
        }
      }
      return voidResult;
    }
    #endregion
    
    #region Condition Statements
    ResolveResult IAstVisitor<ResolveResult>.VisitForStatement(ForStatement forStatement)
    {
      resolver = resolver.PushBlock();
      var result = HandleConditionStatement(forStatement);
      resolver = resolver.PopBlock();
      return result;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitIfElseStatement(IfElseStatement ifElseStatement)
    {
      return HandleConditionStatement(ifElseStatement);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitWhileStatement(WhileStatement whileStatement)
    {
      return HandleConditionStatement(whileStatement);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitDoWhileStatement(DoWhileStatement doWhileStatement)
    {
      return HandleConditionStatement(doWhileStatement);
    }
    
    ResolveResult HandleConditionStatement(Statement conditionStatement)
    {
      if (resolverEnabled) {
        for (AstNode child = conditionStatement.FirstChild; child != null; child = child.NextSibling) {
          if (child.Role == Roles.Condition) {
            Expression condition = (Expression)child;
            ResolveResult conditionRR = Resolve(condition);
            ResolveResult convertedRR = resolver.ResolveCondition(conditionRR);
            if (convertedRR != conditionRR)
              ProcessConversionResult(condition, convertedRR as ConversionResolveResult);
          } else {
            Scan(child);
          }
        }
        return voidResult;
      } else {
        ScanChildren(conditionStatement);
        return null;
      }
    }
    #endregion
    
    #region Return Statements
    ResolveResult IAstVisitor<ResolveResult>.VisitReturnStatement(ReturnStatement returnStatement)
    {
      if (resolverEnabled && !resolver.IsWithinLambdaExpression && resolver.CurrentMember != null) {
        IType type = resolver.CurrentMember.ReturnType;
        if (TaskType.IsTask(type)) {
          var methodDecl = returnStatement.Ancestors.OfType<EntityDeclaration>().FirstOrDefault();
          if (methodDecl != null && (methodDecl.Modifiers & Modifiers.Async) == Modifiers.Async)
            type = UnpackTask(type);
        }
        ResolveAndProcessConversion(returnStatement.Expression, type);
      } else {
        Scan(returnStatement.Expression);
      }
      return resolverEnabled ? voidResult : null;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitYieldReturnStatement(YieldReturnStatement yieldStatement)
    {
      if (resolverEnabled && resolver.CurrentMember != null) {
        IType returnType = resolver.CurrentMember.ReturnType;
        bool? isGeneric;
        IType elementType = GetElementTypeFromIEnumerable(returnType, resolver.Compilation, true, out isGeneric);
        ResolveAndProcessConversion(yieldStatement.Expression, elementType);
      } else {
        Scan(yieldStatement.Expression);
      }
      return resolverEnabled ? voidResult : null;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitYieldBreakStatement(YieldBreakStatement yieldBreakStatement)
    {
      return voidResult;
    }
    #endregion
    
    #region Other statements
    ResolveResult IAstVisitor<ResolveResult>.VisitExpressionStatement(ExpressionStatement expressionStatement)
    {
      ScanChildren(expressionStatement);
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitLockStatement(LockStatement lockStatement)
    {
      ScanChildren(lockStatement);
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitEmptyStatement(EmptyStatement emptyStatement)
    {
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitBreakStatement(BreakStatement breakStatement)
    {
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitContinueStatement(ContinueStatement continueStatement)
    {
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitThrowStatement(ThrowStatement throwStatement)
    {
      if (resolverEnabled) {
        ResolveAndProcessConversion(throwStatement.Expression, resolver.Compilation.FindType(KnownTypeCode.Exception));
        return voidResult;
      } else {
        Scan(throwStatement.Expression);
        return null;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitTryCatchStatement(TryCatchStatement tryCatchStatement)
    {
      ScanChildren(tryCatchStatement);
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitGotoCaseStatement(GotoCaseStatement gotoCaseStatement)
    {
      ScanChildren(gotoCaseStatement);
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitGotoDefaultStatement(GotoDefaultStatement gotoDefaultStatement)
    {
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitGotoStatement(GotoStatement gotoStatement)
    {
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitLabelStatement(LabelStatement labelStatement)
    {
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitUnsafeStatement(UnsafeStatement unsafeStatement)
    {
      resolver = resolver.PushBlock();
      ScanChildren(unsafeStatement);
      resolver = resolver.PopBlock();
      return voidResult;
    }
    #endregion
    
    #region Local Variable Type Inference
    IVariable MakeVariable(IType type, Identifier variableName)
    {
      return new SimpleVariable(MakeRegion(variableName), type, variableName.Name);
    }
    
    IVariable MakeConstant(IType type, Identifier variableName, object constantValue)
    {
      return new SimpleConstant(MakeRegion(variableName), type, variableName.Name, constantValue);
    }
    
    class SimpleVariable : IVariable
    {
      readonly DomRegion region;
      readonly IType type;
      readonly string name;
      
      public SimpleVariable(DomRegion region, IType type, string name)
      {
        Debug.Assert(type != null);
        Debug.Assert(name != null);
        this.region = region;
        this.type = type;
        this.name = name;
      }
      
      public SymbolKind SymbolKind {
        get { return SymbolKind.Variable; }
      }
      
      public string Name {
        get { return name; }
      }
      
      public DomRegion Region {
        get { return region; }
      }
      
      public IType Type {
        get { return type; }
      }
      
      public virtual bool IsConst {
        get { return false; }
      }
      
      public virtual object ConstantValue {
        get { return null; }
      }
      
      public override string ToString()
      {
        return type.ToString() + " " + name + ";";
      }

      public ISymbolReference ToReference()
      {
        return new VariableReference(type.ToTypeReference(), name, region, IsConst, ConstantValue);
      }
    }
    
    sealed class SimpleConstant : SimpleVariable
    {
      readonly object constantValue;
      
      public SimpleConstant(DomRegion region, IType type, string name, object constantValue)
        : base(region, type, name)
      {
        this.constantValue = constantValue;
      }
      
      public override bool IsConst {
        get { return true; }
      }
      
      public override object ConstantValue {
        get { return constantValue; }
      }
      
      public override string ToString()
      {
        return Type.ToString() + " " + Name + " = " + new PrimitiveExpression(constantValue).ToString() + ";";
      }
    }
    
    static IType GetElementTypeFromIEnumerable(IType collectionType, ICompilation compilation, bool allowIEnumerator, out bool? isGeneric)
    {
      bool foundNonGenericIEnumerable = false;
      foreach (IType baseType in collectionType.GetAllBaseTypes()) {
        ITypeDefinition baseTypeDef = baseType.GetDefinition();
        if (baseTypeDef != null) {
          KnownTypeCode typeCode = baseTypeDef.KnownTypeCode;
          if (typeCode == KnownTypeCode.IEnumerableOfT || (allowIEnumerator && typeCode == KnownTypeCode.IEnumeratorOfT)) {
            ParameterizedType pt = baseType as ParameterizedType;
            if (pt != null) {
              isGeneric = true;
              return pt.GetTypeArgument(0);
            }
          }
          if (typeCode == KnownTypeCode.IEnumerable || (allowIEnumerator && typeCode == KnownTypeCode.IEnumerator))
            foundNonGenericIEnumerable = true;
        }
      }
      // System.Collections.IEnumerable found in type hierarchy -> Object is element type.
      if (foundNonGenericIEnumerable) {
        isGeneric = false;
        return compilation.FindType(KnownTypeCode.Object);
      }
      isGeneric = null;
      return SpecialType.UnknownType;
    }
    #endregion
    
    #region Attributes
    ResolveResult IAstVisitor<ResolveResult>.VisitAttribute(Attribute attribute)
    {
      var type = ResolveType(attribute.Type);
      
      // Separate arguments into ctor arguments and non-ctor arguments:
      var constructorArguments = attribute.Arguments.Where(a => !(a is NamedExpression));
      var nonConstructorArguments = attribute.Arguments.OfType<NamedExpression>();
      
      // Scan the non-constructor arguments
      resolver = resolver.PushObjectInitializer(new InitializedObjectResolveResult(type));
      List<ResolveResult> initializerStatements = new List<ResolveResult>();
      foreach (var arg in nonConstructorArguments)
        HandleNamedExpression(arg, initializerStatements);
      resolver = resolver.PopObjectInitializer();
      
      // Resolve the ctor arguments and find the matching ctor overload
      string[] argumentNames;
      ResolveResult[] arguments = GetArguments(constructorArguments, out argumentNames);
      ResolveResult rr = resolver.ResolveObjectCreation(type, arguments, argumentNames, false, initializerStatements);
      ProcessInvocationResult(null, constructorArguments, rr);
      return rr;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitAttributeSection(AttributeSection attributeSection)
    {
      ScanChildren(attributeSection);
      return voidResult;
    }
    #endregion
    
    #region Using Declaration
    ResolveResult IAstVisitor<ResolveResult>.VisitUsingDeclaration(UsingDeclaration usingDeclaration)
    {
      ScanChildren(usingDeclaration);
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitUsingAliasDeclaration(UsingAliasDeclaration usingDeclaration)
    {
      ScanChildren(usingDeclaration);
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitExternAliasDeclaration(ExternAliasDeclaration externAliasDeclaration)
    {
      return voidResult;
    }
    #endregion
    
    #region Type References
    ResolveResult IAstVisitor<ResolveResult>.VisitPrimitiveType(PrimitiveType primitiveType)
    {
      if (!resolverEnabled)
        return null;
      KnownTypeCode typeCode = primitiveType.KnownTypeCode;
      if (typeCode == KnownTypeCode.None && primitiveType.Parent is Constraint && primitiveType.Role == Roles.BaseType) {
        switch (primitiveType.Keyword) {
          case "class":
          case "struct":
          case "new":
            return voidResult;
        }
      }
      IType type = resolver.Compilation.FindType(typeCode);
      return new TypeResolveResult(type);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitSimpleType(SimpleType simpleType)
    {
      if (!resolverEnabled) {
        ScanChildren(simpleType);
        return null;
      }
      
      // Figure out the correct lookup mode:
      NameLookupMode lookupMode = simpleType.GetNameLookupMode();
      
      var typeArguments = ResolveTypeArguments(simpleType.TypeArguments);
      Identifier identifier = simpleType.IdentifierToken;
      if (string.IsNullOrEmpty(identifier.Name))
        return new TypeResolveResult(SpecialType.UnboundTypeArgument);
      ResolveResult rr = resolver.LookupSimpleNameOrTypeName(identifier.Name, typeArguments, lookupMode);
      if (simpleType.Parent is Attribute && !identifier.IsVerbatim) {
        var withSuffix = resolver.LookupSimpleNameOrTypeName(identifier.Name + "Attribute", typeArguments, lookupMode);
        if (AttributeTypeReference.PreferAttributeTypeWithSuffix(rr.Type, withSuffix.Type, resolver.Compilation))
          return withSuffix;
      }
      return rr;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitMemberType(MemberType memberType)
    {
      ResolveResult target;
      NameLookupMode lookupMode = memberType.GetNameLookupMode();
      if (memberType.IsDoubleColon && memberType.Target is SimpleType) {
        SimpleType t = (SimpleType)memberType.Target;
        StoreCurrentState(t);
        target = resolver.ResolveAlias(t.Identifier);
        StoreResult(t, target);
      } else {
        if (!resolverEnabled) {
          ScanChildren(memberType);
          return null;
        }
        target = Resolve(memberType.Target);
      }
      var typeArguments = ResolveTypeArguments(memberType.TypeArguments);
      Identifier identifier = memberType.MemberNameToken;
      ResolveResult rr = resolver.ResolveMemberAccess(target, identifier.Name, typeArguments, lookupMode);
      if (memberType.Parent is Attribute && !identifier.IsVerbatim) {
        var withSuffix = resolver.ResolveMemberAccess(target, identifier.Name + "Attribute", typeArguments, lookupMode);
        if (AttributeTypeReference.PreferAttributeTypeWithSuffix(rr.Type, withSuffix.Type, resolver.Compilation))
          return withSuffix;
      }
      return rr;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitComposedType(ComposedType composedType)
    {
      if (!resolverEnabled) {
        ScanChildren(composedType);
        return null;
      }
      IType t = ResolveType(composedType.BaseType);
      if (composedType.HasNullableSpecifier) {
        t = NullableType.Create(resolver.Compilation, t);
      }
      for (int i = 0; i < composedType.PointerRank; i++) {
        t = new PointerType(t);
      }
      foreach (var a in composedType.ArraySpecifiers.Reverse()) {
        t = new ArrayType(resolver.Compilation, t, a.Dimensions);
      }
      return new TypeResolveResult(t);
    }
    #endregion
    
    #region Query Expressions
    ResolveResult IAstVisitor<ResolveResult>.VisitQueryExpression(QueryExpression queryExpression)
    {
      resolver = resolver.PushBlock();
      var oldQueryResult = currentQueryResult;
      var oldCancellationToken = cancellationToken;
      try {
        // Because currentQueryResult isn't part of the stored state,
        // query expressions must be resolved in a single operation.
        // This means we can't allow cancellation within the query expression.
        cancellationToken = CancellationToken.None;
        currentQueryResult = null;
        foreach (var clause in queryExpression.Clauses) {
          currentQueryResult = Resolve(clause);
        }
        return WrapResult(currentQueryResult);
      } finally {
        currentQueryResult = oldQueryResult;
        cancellationToken = oldCancellationToken;
        resolver = resolver.PopBlock();
      }
    }
    
    IType GetTypeForQueryVariable(IType type)
    {
      bool? isGeneric;
      // This assumes queries are only used on IEnumerable.
      var result = GetElementTypeFromIEnumerable(type, resolver.Compilation, false, out isGeneric);

      // If that fails try to resolve the Select method and resolve the projection.
      if (result.Kind == TypeKind.Unknown) {
        var selectAccess = resolver.ResolveMemberAccess(new ResolveResult (type), "Select", EmptyList<IType>.Instance);
        ResolveResult[] arguments = {
          new QueryExpressionLambda(1, voidResult) 
        };
         
        var rr = resolver.ResolveInvocation(selectAccess, arguments) as CSharpInvocationResolveResult; 
        if (rr != null && rr.Arguments.Count == 2) {
          var invokeMethod = rr.Arguments[1].Type.GetDelegateInvokeMethod();
          if (invokeMethod != null && invokeMethod.Parameters.Count > 0)
            return invokeMethod.Parameters[0].Type;
        }
      }
      return result;
    }
    
    ResolveResult MakeTransparentIdentifierResolveResult()
    {
      return new ResolveResult(new AnonymousType(resolver.Compilation, EmptyList<IUnresolvedProperty>.Instance));
    }
    
    sealed class QueryExpressionLambdaConversion : Conversion
    {
      internal readonly IType[] ParameterTypes;
      
      public QueryExpressionLambdaConversion(IType[] parameterTypes)
      {
        this.ParameterTypes = parameterTypes;
      }
      
      public override bool IsImplicit {
        get { return true; }
      }
      
      public override bool IsAnonymousFunctionConversion {
        get { return true; }
      }
    }
    
    sealed class QueryExpressionLambda : LambdaResolveResult
    {
      readonly IParameter[] parameters;
      readonly ResolveResult bodyExpression;
      
      internal IType[] inferredParameterTypes;
      
      public QueryExpressionLambda(int parameterCount, ResolveResult bodyExpression)
      {
        this.parameters = new IParameter[parameterCount];
        for (int i = 0; i < parameterCount; i++) {
          parameters[i] = new DefaultParameter(SpecialType.UnknownType, "x" + i);
        }
        this.bodyExpression = bodyExpression;
      }
      
      public override IList<IParameter> Parameters {
        get { return parameters; }
      }
      
      public override Conversion IsValid(IType[] parameterTypes, IType returnType, CSharpConversions conversions)
      {
        if (parameterTypes.Length == parameters.Length) {
          this.inferredParameterTypes = parameterTypes;
          return new QueryExpressionLambdaConversion(parameterTypes);
        } else {
          return Conversion.None;
        }
      }
      
      public override bool IsAsync {
        get { return false; }
      }
      
      public override bool IsImplicitlyTyped {
        get { return true; }
      }
      
      public override bool IsAnonymousMethod {
        get { return false; }
      }
      
      public override bool HasParameterList {
        get { return true; }
      }
      
      public override ResolveResult Body {
        get { return bodyExpression; }
      }
      
      public override IType GetInferredReturnType(IType[] parameterTypes)
      {
        return bodyExpression.Type;
      }
      
      public override IType ReturnType {
        get {
          return bodyExpression.Type;
        }
      }
      
      public override string ToString()
      {
        return string.Format("[QueryExpressionLambda ({0}) => {1}]", string.Join(",", parameters.Select(p => p.Name)), bodyExpression);
      }
    }
    
    QueryClause GetPreviousQueryClause(QueryClause clause)
    {
      for (AstNode node = clause.PrevSibling; node != null; node = node.PrevSibling) {
        if (node.Role == QueryExpression.ClauseRole)
          return (QueryClause)node;
      }
      return null;
    }
    
    QueryClause GetNextQueryClause(QueryClause clause)
    {
      for (AstNode node = clause.NextSibling; node != null; node = node.NextSibling) {
        if (node.Role == QueryExpression.ClauseRole)
          return (QueryClause)node;
      }
      return null;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitQueryFromClause(QueryFromClause queryFromClause)
    {
      ResolveResult result = errorResult;
      ResolveResult expr = Resolve(queryFromClause.Expression);
      IVariable v;
      if (queryFromClause.Type.IsNull) {
        v = MakeVariable(GetTypeForQueryVariable(expr.Type), queryFromClause.IdentifierToken);
        result = expr;
      } else {
        v = MakeVariable(ResolveType(queryFromClause.Type), queryFromClause.IdentifierToken);
        
        // resolve the .Cast<>() call
        ResolveResult methodGroup = resolver.ResolveMemberAccess(expr, "Cast", new[] { v.Type }, NameLookupMode.InvocationTarget);
        result = resolver.ResolveInvocation(methodGroup, new ResolveResult[0]);
      }
      
      StoreCurrentState(queryFromClause.IdentifierToken);
      resolver = resolver.AddVariable(v);
      StoreResult(queryFromClause.IdentifierToken, new LocalResolveResult(v));
      
      if (currentQueryResult != null) {
        // this is a second 'from': resolve the .SelectMany() call
        QuerySelectClause selectClause = GetNextQueryClause(queryFromClause) as QuerySelectClause;
        ResolveResult selectResult;
        if (selectClause != null) {
          // from ... from ... select - the SelectMany call also performs the Select operation
          selectResult = Resolve(selectClause.Expression);
        } else {
          // from .. from ... ... - introduce a transparent identifier
          selectResult = MakeTransparentIdentifierResolveResult();
        }
        ResolveResult methodGroup = resolver.ResolveMemberAccess(currentQueryResult, "SelectMany", EmptyList<IType>.Instance, NameLookupMode.InvocationTarget);
        ResolveResult[] arguments = {
          new QueryExpressionLambda(1, result),
          new QueryExpressionLambda(2, selectResult)
        };
        result = resolver.ResolveInvocation(methodGroup, arguments);
      }
      if (result == expr)
        return WrapResult(result);
      else
        return result;
    }
    
    /// <summary>
    /// Wraps the result in an identity conversion.
    /// This is necessary so that '$from x in variable$ select x*2' does not resolve
    /// to the LocalResolveResult for the variable, which would confuse find references.
    /// </summary>
    ResolveResult WrapResult(ResolveResult result)
    {
      return new CastResolveResult(result.Type, result, Conversion.IdentityConversion, resolver.CheckForOverflow);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitQueryContinuationClause(QueryContinuationClause queryContinuationClause)
    {
      ResolveResult rr = Resolve(queryContinuationClause.PrecedingQuery);
      IType variableType = GetTypeForQueryVariable(rr.Type);
      StoreCurrentState(queryContinuationClause.IdentifierToken);
      IVariable v = MakeVariable(variableType, queryContinuationClause.IdentifierToken);
      resolver = resolver.AddVariable(v);
      StoreResult(queryContinuationClause.IdentifierToken, new LocalResolveResult(v));
      return WrapResult(rr);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitQueryLetClause(QueryLetClause queryLetClause)
    {
      ResolveResult expr = Resolve(queryLetClause.Expression);
      StoreCurrentState(queryLetClause.IdentifierToken);
      IVariable v = MakeVariable(expr.Type, queryLetClause.IdentifierToken);
      resolver = resolver.AddVariable(v);
      StoreResult(queryLetClause.IdentifierToken, new LocalResolveResult(v));
      if (currentQueryResult != null) {
        // resolve the .Select() call
        ResolveResult methodGroup = resolver.ResolveMemberAccess(currentQueryResult, "Select", EmptyList<IType>.Instance, NameLookupMode.InvocationTarget);
        ResolveResult[] arguments = { new QueryExpressionLambda(1, MakeTransparentIdentifierResolveResult()) };
        return resolver.ResolveInvocation(methodGroup, arguments);
      } else {
        return errorResult;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitQueryJoinClause(QueryJoinClause queryJoinClause)
    {
      // join v in expr on onExpr equals equalsExpr [into g]
      ResolveResult inResult = null;
      ResolveResult expr = Resolve(queryJoinClause.InExpression);
      IType variableType;
      if (queryJoinClause.Type.IsNull) {
        variableType = GetTypeForQueryVariable(expr.Type);
        inResult = expr;
      } else {
        variableType = ResolveType(queryJoinClause.Type);
        
        // resolve the .Cast<>() call
        ResolveResult methodGroup = resolver.ResolveMemberAccess(expr, "Cast", new[] { variableType }, NameLookupMode.InvocationTarget);
        inResult = resolver.ResolveInvocation(methodGroup, new ResolveResult[0]);
      }
      
      // resolve the 'On' expression in a context that contains only the previously existing range variables:
      // (before adding any variable)
      ResolveResult onResult = Resolve(queryJoinClause.OnExpression);
      
      // scan the 'Equals' expression in a context that contains only the variable 'v'
      CSharpResolver resolverOutsideQuery = resolver;
      resolverOutsideQuery = resolverOutsideQuery.PopBlock(); // pop all variables from the current query expression
      IVariable v = MakeVariable(variableType, queryJoinClause.JoinIdentifierToken);
      resolverOutsideQuery = resolverOutsideQuery.AddVariable(v);
      ResolveResult equalsResult = errorResult;
      ResetContext(resolverOutsideQuery, delegate {
                    equalsResult = Resolve(queryJoinClause.EqualsExpression);
                   });
      StoreCurrentState(queryJoinClause.JoinIdentifierToken);
      StoreResult(queryJoinClause.JoinIdentifierToken, new LocalResolveResult(v));
      
      if (queryJoinClause.IsGroupJoin) {
        return ResolveGroupJoin(queryJoinClause, inResult, onResult, equalsResult);
      } else {
        resolver = resolver.AddVariable(v);
        if (currentQueryResult != null) {
          QuerySelectClause selectClause = GetNextQueryClause(queryJoinClause) as QuerySelectClause;
          ResolveResult selectResult;
          if (selectClause != null) {
            // from ... join ... select - the Join call also performs the Select operation
            selectResult = Resolve(selectClause.Expression);
          } else {
            // from .. join ... ... - introduce a transparent identifier
            selectResult = MakeTransparentIdentifierResolveResult();
          }
          
          var methodGroup = resolver.ResolveMemberAccess(currentQueryResult, "Join", EmptyList<IType>.Instance);
          ResolveResult[] arguments = {
            inResult,
            new QueryExpressionLambda(1, onResult),
            new QueryExpressionLambda(1, equalsResult),
            new QueryExpressionLambda(2, selectResult)
          };
          return resolver.ResolveInvocation(methodGroup, arguments);
        } else {
          return errorResult;
        }
      }
    }
    
    ResolveResult ResolveGroupJoin(QueryJoinClause queryJoinClause,
                                   ResolveResult inResult, ResolveResult onResult, ResolveResult equalsResult)
    {
      Debug.Assert(queryJoinClause.IsGroupJoin);
      
      DomRegion intoIdentifierRegion = MakeRegion(queryJoinClause.IntoIdentifierToken);
      
      // We need to declare the group variable, but it's a bit tricky to determine its type:
      // We'll have to resolve the GroupJoin invocation and take a look at the inferred types
      // for the lambda given as last parameter.
      var methodGroup = resolver.ResolveMemberAccess(currentQueryResult, "GroupJoin", EmptyList<IType>.Instance);
      QuerySelectClause selectClause = GetNextQueryClause(queryJoinClause) as QuerySelectClause;
      LambdaResolveResult groupJoinLambda;
      if (selectClause != null) {
        // from ... join ... into g select - the GroupJoin call also performs the Select operation
        IParameter[] selectLambdaParameters = {
          new DefaultParameter(SpecialType.UnknownType, "<>transparentIdentifier"),
          new DefaultParameter(SpecialType.UnknownType, queryJoinClause.IntoIdentifier, region: intoIdentifierRegion)
        };
        groupJoinLambda = new ImplicitlyTypedLambda(selectClause, selectLambdaParameters, this);
      } else {
        // from .. join ... ... - introduce a transparent identifier
        groupJoinLambda = new QueryExpressionLambda(2, MakeTransparentIdentifierResolveResult());
      }
      
      ResolveResult[] arguments = {
        inResult,
        new QueryExpressionLambda(1, onResult),
        new QueryExpressionLambda(1, equalsResult),
        groupJoinLambda
      };
      ResolveResult rr = resolver.ResolveInvocation(methodGroup, arguments);
      InvocationResolveResult invocationRR = rr as InvocationResolveResult;
      
      IVariable groupVariable;
      if (groupJoinLambda is ImplicitlyTypedLambda) {
        var implicitlyTypedLambda = (ImplicitlyTypedLambda)groupJoinLambda;
        
        if (invocationRR != null && invocationRR.Arguments.Count > 0) {
          ConversionResolveResult crr = invocationRR.Arguments[invocationRR.Arguments.Count - 1] as ConversionResolveResult;
          if (crr != null)
            ProcessConversion(null, crr.Input, crr.Conversion, crr.Type);
        }
        
        implicitlyTypedLambda.EnforceMerge(this);
        if (implicitlyTypedLambda.Parameters.Count == 2) {
          StoreCurrentState(queryJoinClause.IntoIdentifierToken);
          groupVariable = implicitlyTypedLambda.Parameters[1];
        } else {
          groupVariable = null;
        }
      } else {
        Debug.Assert(groupJoinLambda is QueryExpressionLambda);
        
        // Add the variable if the query expression continues after the group join
        // (there's no need to do this if there's only a select clause remaining, as
        // we already handled that in the ImplicitlyTypedLambda).
        
        // Get the inferred type of the group variable:
        IType[] inferredParameterTypes = null;
        if (invocationRR != null && invocationRR.Arguments.Count > 0) {
          ConversionResolveResult crr = invocationRR.Arguments[invocationRR.Arguments.Count - 1] as ConversionResolveResult;
          if (crr != null && crr.Conversion is QueryExpressionLambdaConversion) {
            inferredParameterTypes = ((QueryExpressionLambdaConversion)crr.Conversion).ParameterTypes;
          }
        }
        if (inferredParameterTypes == null)
          inferredParameterTypes = ((QueryExpressionLambda)groupJoinLambda).inferredParameterTypes;
        
        IType groupParameterType;
        if (inferredParameterTypes != null && inferredParameterTypes.Length == 2)
          groupParameterType = inferredParameterTypes[1];
        else
          groupParameterType = SpecialType.UnknownType;
        
        StoreCurrentState(queryJoinClause.IntoIdentifierToken);
        groupVariable = MakeVariable(groupParameterType, queryJoinClause.IntoIdentifierToken);
        resolver = resolver.AddVariable(groupVariable);
      }
      
      if (groupVariable != null) {
        StoreResult(queryJoinClause.IntoIdentifierToken, new LocalResolveResult(groupVariable));
      }
      
      return rr;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitQueryWhereClause(QueryWhereClause queryWhereClause)
    {
      ResolveResult condition = Resolve(queryWhereClause.Condition);
      IType boolType = resolver.Compilation.FindType(KnownTypeCode.Boolean);
      Conversion conversionToBool = resolver.conversions.ImplicitConversion(condition, boolType);
      ProcessConversion(queryWhereClause.Condition, condition, conversionToBool, boolType);
      if (currentQueryResult != null) {
        if (conversionToBool != Conversion.IdentityConversion && conversionToBool != Conversion.None) {
          condition = new ConversionResolveResult(boolType, condition, conversionToBool, resolver.CheckForOverflow);
        }
        
        var methodGroup = resolver.ResolveMemberAccess(currentQueryResult, "Where", EmptyList<IType>.Instance);
        ResolveResult[] arguments = { new QueryExpressionLambda(1, condition) };
        return resolver.ResolveInvocation(methodGroup, arguments);
      } else {
        return errorResult;
      }
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitQuerySelectClause(QuerySelectClause querySelectClause)
    {
      if (currentQueryResult == null) {
        ScanChildren(querySelectClause);
        return errorResult;
      }
      QueryClause previousQueryClause = GetPreviousQueryClause(querySelectClause);
      // If the 'select' follows on a 'SelectMany', 'Join' or 'GroupJoin' clause, then the 'select' portion
      // was already done as part of the previous clause.
      if (((previousQueryClause is QueryFromClause && GetPreviousQueryClause(previousQueryClause) != null))
          || previousQueryClause is QueryJoinClause)
      {
        // GroupJoin already scans the following select clause in a different context,
        // so we must not scan it again.
        if (!(previousQueryClause is QueryJoinClause && ((QueryJoinClause)previousQueryClause).IsGroupJoin))
          Scan(querySelectClause.Expression);
        return WrapResult(currentQueryResult);
      }
      
      QueryExpression query = querySelectClause.Parent as QueryExpression;
      string rangeVariable = GetSingleRangeVariable(query);
      if (rangeVariable != null) {
        IdentifierExpression ident = ParenthesizedExpression.UnpackParenthesizedExpression(querySelectClause.Expression) as IdentifierExpression;
        if (ident != null && ident.Identifier == rangeVariable && !ident.TypeArguments.Any()) {
          // selecting the single identifier that is the range variable
          if (query.Clauses.Count > 2) {
            // only if the query is not degenerate:
            // the Select call will be optimized away, so directly return the previous result
            Scan(querySelectClause.Expression);
            return WrapResult(currentQueryResult);
          }
        }
      }
      
      ResolveResult expr = Resolve(querySelectClause.Expression);
      var methodGroup = resolver.ResolveMemberAccess(currentQueryResult, "Select", EmptyList<IType>.Instance);
      ResolveResult[] arguments = { new QueryExpressionLambda(1, expr) };
      return resolver.ResolveInvocation(methodGroup, arguments);
    }
    
    /// <summary>
    /// Gets the name of the range variable in the specified query.
    /// If the query has multiple range variables, this method returns null.
    /// </summary>
    string GetSingleRangeVariable(QueryExpression query)
    {
      if (query == null)
        return null;
      foreach (QueryClause clause in query.Clauses.Skip(1)) {
        if (clause is QueryFromClause || clause is QueryJoinClause || clause is QueryLetClause) {
          // query has more than 1 range variable
          return null;
        }
      }
      QueryFromClause fromClause = query.Clauses.FirstOrDefault() as QueryFromClause;
      if (fromClause != null)
        return fromClause.Identifier;
      QueryContinuationClause continuationClause = query.Clauses.FirstOrDefault() as QueryContinuationClause;
      if (continuationClause != null)
        return continuationClause.Identifier;
      return null;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitQueryGroupClause(QueryGroupClause queryGroupClause)
    {
      if (currentQueryResult == null) {
        ScanChildren(queryGroupClause);
        return errorResult;
      }
      
      // ... group projection by key
      ResolveResult projection = Resolve(queryGroupClause.Projection);
      ResolveResult key = Resolve(queryGroupClause.Key);
      
      var methodGroup = resolver.ResolveMemberAccess(currentQueryResult, "GroupBy", EmptyList<IType>.Instance);
      ResolveResult[] arguments = {
        new QueryExpressionLambda(1, key),
        new QueryExpressionLambda(1, projection)
      };
      return resolver.ResolveInvocation(methodGroup, arguments);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitQueryOrderClause(QueryOrderClause queryOrderClause)
    {
      foreach (QueryOrdering ordering in queryOrderClause.Orderings) {
        currentQueryResult = Resolve(ordering);
      }
      return WrapResult(currentQueryResult);
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitQueryOrdering(QueryOrdering queryOrdering)
    {
      if (currentQueryResult == null) {
        ScanChildren(queryOrdering);
        return errorResult;
      }
      // ... orderby sortKey [descending]
      ResolveResult sortKey = Resolve(queryOrdering.Expression);
      
      QueryOrderClause parentClause = queryOrdering.Parent as QueryOrderClause;
      bool isFirst = (parentClause == null || parentClause.Orderings.FirstOrDefault() == queryOrdering);
      string methodName = isFirst ? "OrderBy" : "ThenBy";
      if (queryOrdering.Direction == QueryOrderingDirection.Descending)
        methodName += "Descending";
      
      var methodGroup = resolver.ResolveMemberAccess(currentQueryResult, methodName, EmptyList<IType>.Instance);
      ResolveResult[] arguments = {
        new QueryExpressionLambda(1, sortKey),
      };
      return resolver.ResolveInvocation(methodGroup, arguments);
    }
    #endregion
    
    #region Constructor Initializer
    ResolveResult IAstVisitor<ResolveResult>.VisitConstructorInitializer(ConstructorInitializer constructorInitializer)
    {
      ResolveResult target;
      if (constructorInitializer.ConstructorInitializerType == ConstructorInitializerType.Base) {
        target = resolver.ResolveBaseReference();
      } else {
        target = resolver.ResolveThisReference();
      }
      string[] argumentNames;
      ResolveResult[] arguments = GetArguments(constructorInitializer.Arguments, out argumentNames);
      ResolveResult rr = resolver.ResolveObjectCreation(target.Type, arguments, argumentNames, allowProtectedAccess: true);
      ProcessInvocationResult(null, constructorInitializer.Arguments, rr);
      return rr;
    }
    #endregion
    
    #region Other Nodes
    // Token nodes
    ResolveResult IAstVisitor<ResolveResult>.VisitIdentifier(Identifier identifier)
    {
      return null;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitComment (Comment comment)
    {
      return null;
    }

    ResolveResult IAstVisitor<ResolveResult>.VisitNewLine (NewLineNode comment)
    {
      return null;
    }

    ResolveResult IAstVisitor<ResolveResult>.VisitWhitespace(WhitespaceNode whitespaceNode)
    {
      return null;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitText(TextNode textNode)
    {
      return null;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitPreProcessorDirective (PreProcessorDirective preProcessorDirective)
    {
      return null;
    }

    ResolveResult IAstVisitor<ResolveResult>.VisitCSharpTokenNode(CSharpTokenNode cSharpTokenNode)
    {
      return null;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitArraySpecifier(ArraySpecifier arraySpecifier)
    {
      return null;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitNullNode(AstNode nullNode)
    {
      return null;
    }

    ResolveResult IAstVisitor<ResolveResult>.VisitErrorNode(AstNode errorNode)
    {
      return null;
    }

    ResolveResult IAstVisitor<ResolveResult>.VisitPatternPlaceholder(AstNode placeholder, ICSharpCode.NRefactory.PatternMatching.Pattern pattern)
    {
      return null;
    }
    
    // Nodes where we just need to visit the children:
    ResolveResult IAstVisitor<ResolveResult>.VisitAccessor(Accessor accessor)
    {
      ScanChildren(accessor);
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitSwitchSection(SwitchSection switchSection)
    {
      ScanChildren(switchSection);
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitCaseLabel(CaseLabel caseLabel)
    {
      ScanChildren(caseLabel);
      return voidResult;
    }
    
    ResolveResult IAstVisitor<ResolveResult>.VisitConstraint(Constraint constraint)
    {
      ScanChildren(constraint);
      return voidResult;
    }
    #endregion
    
    #region Documentation Reference
    ResolveResult IAstVisitor<ResolveResult>.VisitDocumentationReference(DocumentationReference documentationReference)
    {
      // Resolve child nodes:
      ITypeDefinition declaringTypeDef;
      if (documentationReference.DeclaringType.IsNull)
        declaringTypeDef = resolver.CurrentTypeDefinition;
      else
        declaringTypeDef = ResolveType(documentationReference.DeclaringType).GetDefinition();
      IType[] typeArguments = documentationReference.TypeArguments.Select(ResolveType).ToArray();
      IType conversionOperatorReturnType = ResolveType(documentationReference.ConversionOperatorReturnType);
      IParameter[] parameters = documentationReference.Parameters.Select(ResolveXmlDocParameter).ToArray();
      
      if (documentationReference.SymbolKind == SymbolKind.TypeDefinition) {
        if (declaringTypeDef != null)
          return new TypeResolveResult(declaringTypeDef);
        else
          return errorResult;
      }
      
      if (documentationReference.SymbolKind == SymbolKind.None) {
        // might be a type, member or ctor
        string memberName = documentationReference.MemberName;
        ResolveResult rr;
        if (documentationReference.DeclaringType.IsNull) {
          rr = resolver.LookupSimpleNameOrTypeName(memberName, typeArguments, NameLookupMode.Expression);
        } else {
          var target = Resolve(documentationReference.DeclaringType);
          rr = resolver.ResolveMemberAccess(target, memberName, typeArguments);
        }
        // reduce to definition:
        if (rr.IsError) {
          return rr;
        } else if (rr is TypeResolveResult) {
          var typeDef = rr.Type.GetDefinition();
          if (typeDef == null)
            return errorResult;
          if (documentationReference.HasParameterList) {
            var ctors = typeDef.GetConstructors(options: GetMemberOptions.IgnoreInheritedMembers | GetMemberOptions.ReturnMemberDefinitions);
            return FindByParameters(ctors, parameters);
          } else {
            return new TypeResolveResult(typeDef);
          }
        } else if (rr is MemberResolveResult) {
          var mrr = (MemberResolveResult)rr;
          return new MemberResolveResult(null, mrr.Member.MemberDefinition);
        } else if (rr is MethodGroupResolveResult) {
          var mgrr = (MethodGroupResolveResult)rr;
          var methods = mgrr.MethodsGroupedByDeclaringType.Reverse()
            .SelectMany(ml => ml.Select(m => (IParameterizedMember)m.MemberDefinition));
          return FindByParameters(methods, parameters);
        }
        return rr;
      }
      
      // Indexer or operator
      if (declaringTypeDef == null)
        return errorResult;
      if (documentationReference.SymbolKind == SymbolKind.Indexer) {
        var indexers = declaringTypeDef.Properties.Where(p => p.IsIndexer && !p.IsExplicitInterfaceImplementation);
        return FindByParameters(indexers, parameters);
      } else if (documentationReference.SymbolKind == SymbolKind.Operator) {
        var opType = documentationReference.OperatorType;
        string memberName = OperatorDeclaration.GetName(opType);
        var methods = declaringTypeDef.Methods.Where(m => m.IsOperator && m.Name == memberName);
        if (opType == OperatorType.Implicit || opType == OperatorType.Explicit) {
          // conversion operator
          foreach (var method in methods) {
            if (ParameterListComparer.Instance.Equals(method.Parameters, parameters)) {
              if (method.ReturnType.Equals(conversionOperatorReturnType))
                return new MemberResolveResult(null, method);
            }
          }
          return new MemberResolveResult(null, methods.FirstOrDefault());
        } else {
          // not a conversion operator
          return FindByParameters(methods, parameters);
        }
      } else {
        throw new NotSupportedException(); // unknown entity type
      }
    }
    
    IParameter ResolveXmlDocParameter(ParameterDeclaration p)
    {
      var lrr = Resolve(p) as LocalResolveResult;
      if (lrr != null && lrr.IsParameter)
        return (IParameter)lrr.Variable;
      else
        return new DefaultParameter(SpecialType.UnknownType, string.Empty);
    }
    
    ResolveResult FindByParameters(IEnumerable<IParameterizedMember> methods, IList<IParameter> parameters)
    {
      foreach (var method in methods) {
        if (ParameterListComparer.Instance.Equals(method.Parameters, parameters))
          return new MemberResolveResult(null, method);
      }
      return new MemberResolveResult(null, methods.FirstOrDefault());
    }
    #endregion
  }
}