[Bug c++/85124] New: template template parameter is printed incorrectly in the error message

["ensadc at mailnesia dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85124

            Bug ID: 85124
           Summary: template template parameter is printed incorrectly in
                    the error message
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ensadc at mailnesia dot com
  Target Milestone: ---

https://wandbox.org/permlink/0ir0hnoy5jeX9KLT

----
template<class T> using ref = T&;

template<class A>
struct X {
    template<template<class> class F>
    using apply = F<void>;
};

X<int>::apply<ref> a;

----
prog.cc: In substitution of 'template<class T> using ref = T& [with T = void]':
prog.cc:6:26:   required by substitution of 'template<class A>
template<template<template<class> class F> template<class A> template<class>
class F> using apply = F<void> [with F = ref; A = int]'
prog.cc:9:18:   required from here
prog.cc:1:33: error: forming reference to void
 template<class T> using ref = T&;
                                 ^
----

In the second line of the error message ("required by substitution of ..."), it
should be just `template<class> class F`, not `template<template<class> class
F> template<class A> template<class> class F` (i.e. there should be only one
template-head for the template template parameter, not three).

Just to clarify, it's irrelevant what the actual error is.