Need a proper representation for __arglist argument for IOperation

[genlu]

Take the following example,

        Console.Write("{0} {1} {2} {3} {4}", 1, 2, 3, 4, __arglist(5));

The __arglist is currently returned as:

    IArgument (ArgumentKind.Explicit, Matching Parameter: null) (OperationKind.Argument, IsInvalid) (Syntax: '__arglist(5)')
      IOperation:  (OperationKind.None) (Syntax: '__arglist(5)')
        Children(1): ILiteralExpression (Text: 5) (OperationKind.LiteralExpression, Type: System.Int32, Constant: 5) (Syntax: '5')

I believe this can be solved by simply adding ArgumentKind.ArgList, and create such an IArgument based on underlying BoundArgListOperator.

[genlu]

FYI @heejaechang @jinujoseph

[nguerrera]

#8394

[genlu]

Do we want to discuss this today? @jinujoseph

[jinujoseph]

sure , we should actually discuss #8394 in general

[CyrusNajmabadi]

Design Team Decision
We think we should have:

    public interface IArgList : IOperation
    {
        List<IOperation> Values;
    }

If user uses __arglist(1, 2, 3), then they will have an IArgument with a VAlue that is this IArgList. The IArgList will point at 1, 2, 3. The Kind of the ArgumentKind of the IArgument will be a new value called ... ArgList

[mavasani]

Dupe of #8394