internal TypeInference(ICompilation compilation, CSharpConversions conversions)
		{
			Debug.Assert(compilation != null);
			Debug.Assert(conversions != null);
			this.compilation = compilation;
			this.conversions = conversions;
		}

 public override void VisitForeachStatement(ForeachStatement foreachStatement)
 {
     base.VisitForeachStatement(foreachStatement);
     var rr = ctx.Resolve(foreachStatement) as ForEachResolveResult;
     if (rr == null)
         return;
     if (rr.ElementType.Kind == TypeKind.Unknown)
         return;
     if (ReflectionHelper.GetTypeCode(rr.ElementType) == TypeCode.Object)
         return;
     if (conversions == null) {
         conversions = CSharpConversions.Get(ctx.Compilation);
     }
     Conversion c = conversions.ImplicitConversion(rr.ElementType, rr.ElementVariable.Type);
     if (c.IsValid)
         return;
     var csResolver = ctx.GetResolverStateBefore(foreachStatement);
     var builder = new TypeSystemAstBuilder(csResolver);
     AstType elementType = builder.ConvertType(rr.ElementType);
     AstType variableType = foreachStatement.VariableType;
     string issueText = ctx.TranslateString("Collection element type '{0}' is not implicitly convertible to '{1}'");
     string fixText = ctx.TranslateString("Use type '{0}'");
     AddIssue(variableType, string.Format(issueText, elementType.GetText(), variableType.GetText()),
              new CodeAction(string.Format(fixText, elementType.GetText()),
                             script => script.Replace(variableType, elementType)));
 }

		public CSharpResolver(ICompilation compilation)
		{
			if (compilation == null)
				throw new ArgumentNullException("compilation");
			this.compilation = compilation;
			this.conversions = CSharpConversions.Get(compilation);
			this.context = new CSharpTypeResolveContext(compilation.MainAssembly);
		}

        public CSharpResolver(ICompilation compilation)
        {
            if (compilation == null)
                throw new ArgumentNullException("compilation");
            this.compilation = compilation;
            this.conversions = CSharpConversions.Get(compilation);
            this.context = new CSharpTypeResolveContext(compilation.MainAssembly);

            var pc = compilation.MainAssembly.UnresolvedAssembly as CSharpProjectContent;
            if (pc != null) {
                this.checkForOverflow = pc.CompilerSettings.CheckForOverflow;
            }
        }

		public SupportsIndexingCriterion(IType returnType, IEnumerable<IType> argumentTypes, CSharpConversions conversions, bool isWriteAccess = false)
		{
			if (returnType == null)
				throw new ArgumentNullException("returnType");
			if (argumentTypes == null)
				throw new ArgumentNullException("argumentTypes");
			if (conversions == null)
				throw new ArgumentNullException("conversions");

			this.returnType = returnType;
			this.argumentTypes = argumentTypes.ToList();
			this.conversions = conversions;
			this.isWriteAccess = isWriteAccess;
		}

        public OverloadResolution(ICompilation compilation, ResolveResult[] arguments, string[] argumentNames = null, IType[] typeArguments = null, CSharpConversions conversions = null)
        {
            if (compilation == null)
                throw new ArgumentNullException("compilation");
            if (arguments == null)
                throw new ArgumentNullException("arguments");
            if (argumentNames == null)
                argumentNames = new string[arguments.Length];
            else if (argumentNames.Length != arguments.Length)
                throw new ArgumentException("argumentsNames.Length must be equal to arguments.Length");
            this.compilation = compilation;
            this.arguments = arguments;
            this.argumentNames = argumentNames;

            // keep explicitlyGivenTypeArguments==null when no type arguments were specified
            if (typeArguments != null && typeArguments.Length > 0)
                this.explicitlyGivenTypeArguments = typeArguments;

            this.conversions = conversions ?? CSharpConversions.Get(compilation);
            this.AllowExpandingParams = true;
            this.AllowOptionalParameters = true;
        }

			public override Conversion IsValid(IType[] parameterTypes, IType returnType, CSharpConversions conversions)
			{
				return conversions.ImplicitConversion(inferredReturnType, returnType);
			}

		/// <summary>
		/// Gets whether the lambda body is valid for the given parameter types and return type.
		/// </summary>
		/// <returns>
		/// Produces a conversion with <see cref="Conversion.IsAnonymousFunctionConversion"/>=<c>true</c> if the lambda is valid;
		/// otherwise returns <see cref="Conversion.None"/>.
		/// </returns>
		public abstract Conversion IsValid(IType[] parameterTypes, IType returnType, CSharpConversions conversions);

 public override void SetUp()
 {
     base.SetUp();
     conversions = new CSharpConversions(compilation);
 }

		static bool IsEligibleExtensionMethod(ICompilation compilation, CSharpConversions conversions, IType targetType, IMethod method, bool useTypeInference, out IType[] outInferredTypes)
		{
			outInferredTypes = null;
			if (targetType == null)
				return true;
			if (method.Parameters.Count == 0)
				return false;
			IType thisParameterType = method.Parameters[0].Type;
			if (useTypeInference && method.TypeParameters.Count > 0) {
				// We need to infer type arguments from targetType:
				TypeInference ti = new TypeInference(compilation, conversions);
				ResolveResult[] arguments = { new ResolveResult(targetType) };
				IType[] parameterTypes = { method.Parameters[0].Type };
				bool success;
				var inferredTypes = ti.InferTypeArguments(method.TypeParameters, arguments, parameterTypes, out success);
				var substitution = new TypeParameterSubstitution(null, inferredTypes);
				// Validate that the types that could be inferred (aren't unknown) satisfy the constraints:
				bool hasInferredTypes = false;
				for (int i = 0; i < inferredTypes.Length; i++) {
					if (inferredTypes[i].Kind != TypeKind.Unknown && inferredTypes[i].Kind != TypeKind.UnboundTypeArgument) {
						hasInferredTypes = true;
						if (!OverloadResolution.ValidateConstraints(method.TypeParameters[i], inferredTypes[i], substitution, conversions))
							return false;
					} else {
						inferredTypes[i] = method.TypeParameters[i]; // do not substitute types that could not be inferred
					}
				}
				if (hasInferredTypes)
					outInferredTypes = inferredTypes;
				thisParameterType = thisParameterType.AcceptVisitor(substitution);
			}
			Conversion c = conversions.ImplicitConversion(targetType, thisParameterType);
			return c.IsValid && (c.IsIdentityConversion || c.IsReferenceConversion || c.IsBoxingConversion);
		}

		internal static bool ValidateConstraints(ITypeParameter typeParameter, IType typeArgument, TypeVisitor substitution, CSharpConversions conversions)
		{
			switch (typeArgument.Kind) { // void, null, and pointers cannot be used as type arguments
				case TypeKind.Void:
				case TypeKind.Null:
				case TypeKind.Pointer:
					return false;
			}
			if (typeParameter.HasReferenceTypeConstraint) {
				if (typeArgument.IsReferenceType != true)
					return false;
			}
			if (typeParameter.HasValueTypeConstraint) {
				if (!NullableType.IsNonNullableValueType(typeArgument))
					return false;
			}
			if (typeParameter.HasDefaultConstructorConstraint) {
				ITypeDefinition def = typeArgument.GetDefinition();
				if (def != null && def.IsAbstract)
					return false;
				var ctors = typeArgument.GetConstructors(
					m => m.Parameters.Count == 0 && m.Accessibility == Accessibility.Public,
					GetMemberOptions.IgnoreInheritedMembers | GetMemberOptions.ReturnMemberDefinitions
				);
				if (!ctors.Any())
					return false;
			}
			foreach (IType constraintType in typeParameter.DirectBaseTypes) {
				IType c = constraintType;
				if (substitution != null)
					c = c.AcceptVisitor(substitution);
				if (!conversions.IsConstraintConvertible(typeArgument, c))
					return false;
			}
			return true;
		}

			public override Conversion IsValid(IType[] parameterTypes, IType returnType, CSharpConversions conversions)
			{
				Assert.AreEqual(expectedParameterTypes, parameterTypes);
				return conversions.ImplicitConversion(inferredReturnType, returnType);
			}

			public GatherVisitor (BaseRefactoringContext ctx)
				: base (ctx)
			{
				conversions = CSharpConversions.Get(ctx.Compilation);
			}

		public void SetUp()
		{
			compilation = new SimpleCompilation(CecilLoaderTests.Mscorlib);
			conversions = new CSharpConversions(compilation);
		}

			public ConstraintValidatingSubstitution(IList<IType> classTypeArguments, IList<IType> methodTypeArguments, OverloadResolution overloadResolution)
				: base(classTypeArguments, methodTypeArguments)
			{
				this.conversions = overloadResolution.conversions;
			}