https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118347
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> --- The key here is: https://timsong-cpp.github.io/cppwp/n4868/temp.names#4.sentence-4 Which says: In these contexts, a < token is always assumed to introduce a template-argument-list. The context reffered to here is "typename-specifier ([temp.res]), elaborated-type-specifier ([dcl.type.elab]), using-declaration ([namespace.udecl]), or class-or-decltype ([class.derived])" . In case of comment #0, the context is a class-or-decltype context. So yes this is invalid.
