[Bug c++/72842] non-type template-parameter of type void

["daniel.kruegler at googlemail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72842

--- Comment #5 from Daniel Krügler <daniel.kruegler at googlemail dot com> ---
(In reply to Barry Revzin from comment #4)
> I'll just email. Instantiating foo<void> creates a function template with a
> non-type template parameter of type void. That's not an allowed type of a
> non-type template parameter, so I think it should be ill-formed.

It truely is ill-formed, but the question is whether an implementation is
required to diagnose it. For the non-depending case the diagnostics is a hard
requirement. But for the dependent case we have [temp.res] p8:

"The program is ill-formed, no diagnostic required, if:
[..]
— every valid specialization of a variadic template requires an empty template
parameter pack, or [..]"

My argument is that this is the case we are entering here: Ill-formed, but no
diagnostics required.