https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59498
--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
And the current development version of clang also rejects this testcase:
wa.C:5:34: error: pack expansion used as argument for non-pack parameter of
alias template
using variadic_alias = alias<T...>;
^~~~
wa.C:1:24: note: template parameter is declared here
template <typename T, typename ...>
^
