[Bug c++/59254] New: confusing diagnostic for undefined template shadowed by declaration in inline namespace

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59254

            Bug ID: 59254
           Summary: confusing diagnostic for undefined template shadowed
                    by declaration in inline namespace
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org

namespace outer {
  inline namespace inner {
#ifndef OK
    template<typename T> struct A;
#endif
  }

  template<typename T> struct A;

  template class A<int>;
}

This gives a confusing diagnostic:

$ g++ -std=gnu++11 n.cc -c
n.cc:10:18: error: ‘A’ is not a class template
   template class A<int>;
                  ^
n.cc:10:18: error: template argument required for ‘class A’


That's particularly confusing because A is a class template, and so is inner::A
(although if it's just a class type the error is the same) and because a
template argument is given.


Without the previous definition in the inline namespace we get the expected
explanation:

$ g++ -std=gnu++11 n.cc -c -DOK
n.cc:10:18: error: explicit instantiation of ‘class outer::A<int>’ before
definition of template
   template class A<int>;
                  ^