[Bug c++/65706] New: [c++14] Pack expansion with variable template incorrectly marked as invalid

[ldionne.2 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65706

            Bug ID: 65706
           Summary: [c++14] Pack expansion with variable template
                    incorrectly marked as invalid
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ldionne.2 at gmail dot com

The following code produces an error on GCC trunk:

------------------------------------------------------------------------------
void allow_expansion(...);

template <int i>
int vtemplate = i;

template <int ...i>
void f() {
    allow_expansion(vtemplate<i>...);
}

template void f<>();
template void f<1>();
template void f<1, 2>();
------------------------------------------------------------------------------

Note that the three above statements trigger the same error. 
The exact output is 

› ~/code/gcc5/bin/g++ ~/code/hana/test/worksheet.cpp -std=c++1y
[...]: In function ‘void f()’:
[...]: error: expansion pattern ‘vtemplate<i>’ contains no argument packs
     allow_expansion(vtemplate<i>...);
                                 ^