template <typename Type, Type Func>
struct A
{
};

void func();

A<void(), func> a; // same result with A<void(), &func> a;

This code compiles with Clang (including latest 8.0.0), but not with GCC (including latest 9.1).

GCC says: error: 'void()' is not a valid type for a template non-type parameter

Which compiler is right and why?

Update

I am guessing GCC is wrong, because the following compiles on both Clang and GCC:

template <void()>
struct A
{
};

void func();

A<func> a; // same result with A<&func> a;

So contrary to what GCC reports in the first example, void() seems to be "a valid type for a template non-type parameter"