[Bug c++/66184] New: Rejection of partial specialization of a variable template in a non-global namespace

[Casey at Carter dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66184

            Bug ID: 66184
           Summary: Rejection of partial specialization of a variable
                    template in a non-global namespace
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: Casey at Carter dot net
  Target Milestone: ---

Created attachment 35558
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35558&action=edit
testcase.cpp

Both 5.1.0 on Wandbox and 6.0 r223061 reject this program:

namespace foo {
template <class, class> constexpr bool same = false;
template <> constexpr bool same<void,void> = true;
template <class T> constexpr bool same<T,T> = true;

static_assert(same<int*,int*>, "");
static_assert(!same<int,int*>, "");
}

int main() {}

with error message:

bug2.cpp:4:35: error: specialization of ‘template<class, class> constexpr const
bool foo::same< <template-parameter-1-1>, <template-parameter-1-2> >’ in
different namespace [-fpermissive]
 template <class T> constexpr bool same<T,T> = true;
                                   ^
bug2.cpp:2:40: error:   from definition of ‘template<class, class> constexpr
const bool foo::same< <template-parameter-1-1>, <template-parameter-1-2> >’
[-fpermissive]
 template <class, class> constexpr bool same = false;
                                        ^
The full specialization of same<void,void> is accepted regardless of namespace.
Both versions compile the program correctly if "same" is in the global
namespace.