https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80096
--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> --- G++ 6: w.C:1:10: error: ‘auto’ parameter not permitted in this context template<auto> struct A ^~~~ w.C:6:4: note: invalid template non-type parameter A<0> a; ^