internal SourceCustomEventAccessorSymbol(
            SourceEventSymbol @event,
            AccessorDeclarationSyntax syntax,
            EventSymbol explicitlyImplementedEventOpt,
            string aliasQualifierOpt,
            DiagnosticBag diagnostics)
            : base(@event,
                   syntax.GetReference(),
                   ImmutableArray.Create(syntax.Keyword.GetLocation()))
        {
            Debug.Assert(syntax != null);
            Debug.Assert(syntax.Kind() == SyntaxKind.AddAccessorDeclaration || syntax.Kind() == SyntaxKind.RemoveAccessorDeclaration);

            bool isAdder = syntax.Kind() == SyntaxKind.AddAccessorDeclaration;

            string name;
            ImmutableArray <MethodSymbol> explicitInterfaceImplementations;

            if ((object)explicitlyImplementedEventOpt == null)
            {
                name = SourceEventSymbol.GetAccessorName(@event.Name, isAdder);
                explicitInterfaceImplementations = ImmutableArray <MethodSymbol> .Empty;
            }
            else
            {
                MethodSymbol implementedAccessor = isAdder ? explicitlyImplementedEventOpt.AddMethod : explicitlyImplementedEventOpt.RemoveMethod;
                string       accessorName        = (object)implementedAccessor != null ? implementedAccessor.Name : SourceEventSymbol.GetAccessorName(explicitlyImplementedEventOpt.Name, isAdder);

                name = ExplicitInterfaceHelpers.GetMemberName(accessorName, explicitlyImplementedEventOpt.ContainingType, aliasQualifierOpt);
                explicitInterfaceImplementations = (object)implementedAccessor == null ? ImmutableArray <MethodSymbol> .Empty : ImmutableArray.Create <MethodSymbol>(implementedAccessor);
            }

            _explicitInterfaceImplementations = explicitInterfaceImplementations;
            _name = name;
            this.MakeFlags(
                isAdder ? MethodKind.EventAdd : MethodKind.EventRemove,
                @event.Modifiers,
                returnsVoid: false, // until we learn otherwise (in LazyMethodChecks).
                isExtensionMethod: false,
                isMetadataVirtualIgnoringModifiers: explicitInterfaceImplementations.Any());

            if (@event.ContainingType.IsInterface)
            {
                diagnostics.Add(ErrorCode.ERR_EventPropertyInInterface, this.Location);
            }
            else
            {
                if (syntax.Body != null || syntax.ExpressionBody != null)
                {
                    if (IsExtern && !IsAbstract)
                    {
                        diagnostics.Add(ErrorCode.ERR_ExternHasBody, this.Location, this);
                    }
                    else if (IsAbstract && !IsExtern)
                    {
                        diagnostics.Add(ErrorCode.ERR_AbstractHasBody, this.Location, this);
                    }
                    // Do not report error for IsAbstract && IsExtern. Dev10 reports CS0180 only
                    // in that case ("member cannot be both extern and abstract").
                }
            }

            _name = GetOverriddenAccessorName(@event, isAdder) ?? _name;

            if (syntax.Modifiers.Count > 0)
            {
                diagnostics.Add(ErrorCode.ERR_NoModifiersOnAccessor, syntax.Modifiers[0].GetLocation());
            }

            CheckForBlockAndExpressionBody(
                syntax.Body, syntax.ExpressionBody, syntax, diagnostics);
        }