Expand parameter pack which still has unfulfilled args

[tong...@gmail.com]

In the following example:

template<class... T>

struct S
{
    template<class... U>
    static void f(T(*...p)(U));
};

template<class... T, class... U>
void f(T(*...p)(U));

Intuitively, I expect S<int, void>::f would be expanded to something like:

template<class... U>
void S<int, void>::f(int(*p$0)(U$0), void(*p$1)(U$1));

and f<int, void> would be:

template<class... T, class... U>
void f<int, void>(int(*p$0)(U$0), void(*p$1)(U$1), T(*...p)(U));

If pack expansion works this way, we should be able to do:

// Some overloaded functions
void f1(int);
int f1(char);

// Non-overloaded function
void f2(int);

// Case A - These should work.
S<int>::f(f1);
S<void>::f(f1);
S<int, void>::f(f1, f1);

// Case B - These should work too.
f<int>(f1);
f<void>(f1);
f<int, void>(f1, f1, f2); // f2 extends the explicitly specified template args

Unfortunately, it doesn't work that way. Clang rejects both case A & B, GCC accepts only case B.

I'm not familiar with the standard wording. Is it possible to refine pack expansion as illustrated above?