/// <summary>
        /// Lookup an immediately nested type referenced from metadata, names should be
        /// compared case-sensitively.
        /// </summary>
        /// <param name="emittedTypeName">
        /// Simple type name, possibly with generic name mangling.
        /// </param>
        /// <returns>
        /// Symbol for the type, or MissingMetadataSymbol if the type isn't found.
        /// </returns>
        internal virtual NamedTypeSymbol LookupMetadataType(ref MetadataTypeName emittedTypeName)
        {
            Debug.Assert(!emittedTypeName.IsNull);

            NamespaceOrTypeSymbol scope = this;

            if (scope.Kind == SymbolKind.ErrorType)
            {
                return(new MissingMetadataTypeSymbol.Nested((NamedTypeSymbol)scope, ref emittedTypeName));
            }

            NamedTypeSymbol namedType = null;

            ImmutableArray <NamedTypeSymbol> namespaceOrTypeMembers;
            bool isTopLevel = scope.IsNamespace;

            Debug.Assert(!isTopLevel || scope.ToDisplayString(SymbolDisplayFormat.QualifiedNameOnlyFormat) == emittedTypeName.NamespaceName);

            if (emittedTypeName.IsMangled)
            {
                Debug.Assert(!emittedTypeName.UnmangledTypeName.Equals(emittedTypeName.TypeName) && emittedTypeName.InferredArity > 0);

                if (emittedTypeName.ForcedArity == -1 || emittedTypeName.ForcedArity == emittedTypeName.InferredArity)
                {
                    // Let's handle mangling case first.
                    namespaceOrTypeMembers = scope.GetTypeMembers(emittedTypeName.UnmangledTypeName);

                    foreach (var named in namespaceOrTypeMembers)
                    {
                        if (emittedTypeName.InferredArity == named.Arity && named.MangleName)
                        {
                            if ((object)namedType != null)
                            {
                                namedType = null;
                                break;
                            }

                            namedType = named;
                        }
                    }
                }
            }
            else
            {
                Debug.Assert(ReferenceEquals(emittedTypeName.UnmangledTypeName, emittedTypeName.TypeName) && emittedTypeName.InferredArity == 0);
            }

            // Now try lookup without removing generic arity mangling.
            int forcedArity = emittedTypeName.ForcedArity;

            if (emittedTypeName.UseCLSCompliantNameArityEncoding)
            {
                // Only types with arity 0 are acceptable, we already examined types with mangled names.
                if (emittedTypeName.InferredArity > 0)
                {
                    goto Done;
                }
                else if (forcedArity == -1)
                {
                    forcedArity = 0;
                }
                else if (forcedArity != 0)
                {
                    goto Done;
                }
                else
                {
                    Debug.Assert(forcedArity == emittedTypeName.InferredArity);
                }
            }

            namespaceOrTypeMembers = scope.GetTypeMembers(emittedTypeName.TypeName);

            foreach (var named in namespaceOrTypeMembers)
            {
                if (!named.MangleName && (forcedArity == -1 || forcedArity == named.Arity))
                {
                    if ((object)namedType != null)
                    {
                        namedType = null;
                        break;
                    }

                    namedType = named;
                }
            }

Done:
            if ((object)namedType == null)
            {
                if (isTopLevel)
                {
                    return(new MissingMetadataTypeSymbol.TopLevel(scope.ContainingModule, ref emittedTypeName));
                }
                else
                {
                    return(new MissingMetadataTypeSymbol.Nested((NamedTypeSymbol)scope, ref emittedTypeName));
                }
            }

            return(namedType);
        }