Is "template argument deduction for class templates" supposed to deduce empty parameter packs for variadic class templates?

Question

The "Template argument deduction for class templates" proposal (P0091R2) contains the following example:

template<class ... Ts> struct X { X(Ts...) };
X x1{1}; // OK X<int>
X x11; // OK X<>

(Apart from the fact that the constructor definition is missing a body), the example seems to suggest that a variadic class template constructed with zero argument will be deduced with an empty parameter pack.

Unfortunately, the latest version of g++ does not agree:

int main()
{
    X x1{1};
    X x11;
}

 In function 'int main()':
 error: invalid use of template-name 'X' without an argument list
 X x11;
 ^
 note: class template argument deduction requires an initializer

example on wandbox

---

I could not find explicit wording in the proposal that clarifies this interaction. Is g++ wrong here?

Answer 1

This is now well-formed after P0620R0 removed the cited restriction right before C++17's publication.

_{Previous answer kept for reference:}

---

N4618 [dcl.type.class.deduct]/1:

If a placeholder for a deduced class type appears as a decl-specifier in the decl-specifier-seq of a simple-declaration, the init-declarator of that declaration shall be of the form

declarator-id attribute-specifier-seq_optinitializer

The initializer is not optional.