outside definition of member class of an explicitly specialized member class

Question

this example is from N4527 14.7.3[temp.expl.spec]/5, a little bit of change.

template<class T>
struct A {
    struct B{};
};

template<> struct A<char>::B{
    void f();
    struct C;
    struct D{}; // ok
};

void A<char>::B::f(){}// ok in gcc5.1.0 and clang3.6.0

struct A<char>::B::C{};// error in gcc5.1.0, ok in clang3.6.0

int main()
{
    return 0;
}

Answer 1

I think it is a bug, I have reported. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67402