[Bug c++/104594] narrowing of -1 to unsigned char not detected with requires concepts

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104594

--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to Patrick Palka from comment #4)
> N.B. coerce_template_parms sometimes does encode the implicit conversion for
> a dependent NTTP argument, but only for sake of specialization matching (in
> light of 'auto' template parms IIUC), the IMPLICIT_CONV_EXPR built is a
> no-op otherwise.

This IMPLICIT_CONV_EXPRs I'm referring to are built by 
maybe_convert_nontype_argument.