[Bug c++/86747] [8/9 Regression] rejects-valid with redundant friend declaration

[nathan at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86747

Nathan Sidwell <nathan at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2018-07-30
     Ever confirmed|0                           |1

--- Comment #2 from Nathan Sidwell <nathan at gcc dot gnu.org> ---
Let's reduce the anonymousness:

template <typename T> class A {
  template <void (A::*p)()> class C; // #1
  template <void (A::*q)()> friend class C; // #2
};

A<double> a;

tf.cc: In instantiation of ‘class A<double>’:
tf.cc:6:11:   required from here
tf.cc:2:26: error: template parameter ‘void (A<T>::* p)()’
   template <void (A::*p)()> class C;
                          ^
tf.cc:3:42: error: redeclared here as ‘void (A<double>::* q)()’
   template <void (A::*q)()> friend class C;

It looks like we're not tsubsting the declaration of #1 in A<double>, but are
doing so for the friend decl #2.