https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65750
--- Comment #3 from Adam Butcher <abutcher at gcc dot gnu.org> ---
Agreed. Upon seeing the 'auto' in the parameter list, we'll synthesize a
template parameter for 'g'. I think Paolo added the diagnostic for virtual to
fix an ICE.
I'm not sure immediately how to handle this one. For function pointer types
"auto (" should have this behavior. Maybe we need a bit of look-ahead to solve
this (either for a function pointer or the trailing return arrow).
Looks like trying to tie down semantics at parse time is biting us again.
