Why does the Standard prohibit friend declarations of partial specializations?

Question

The C++ standard prohibits friend declarations of partial specializations. (§14.5.3/8):

Friend declarations shall not declare partial specializations. [Example:

template<class T> class A { };
class X {
    template <class T> friend class A<T*>;   //error
};

--end example]

Other questions, e.g. this one, have received answers that invoke this prohibition, but I would like to know the rationale. I don't see it and can't find it with my favourite search engine. I can find however that it goes right back to the C++98 standard, so presumably the rationale is quite basic and clear. Can someone explain it to me?

Answer 1

I don't have a reference but I suspect that this is because it would result in the partial specialization being declared in the scope of the friend-declaring class rather than the scope of the template in question, and rather than creating a bunch of rules to force the friend declaration to result in the specialization being in the correct scope, they simply prohibit it.