[Bug c++/120775] [C++26] P2996R13 - Reflection

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120775

--- Comment #28 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #27)
> (In reply to Jakub Jelinek from comment #26)
> > https://forge.sourceware.org/marek/gcc/pulls/96 seems to fix that, shall I
> > merge that or do you want something else?
> 
> Could we do just
> 
> -  refl = cxx_constant_value (refl);
> +  refl = fold_non_dependent_expr (refl, tf_warning_or_error,
> +                 /*manifestly_const_eval=*/true);
> 
> ?

I think we can't.  One, I think we need to handle the processing_template_decl
case more carefully, if it isn't constant, just revert to building SPLICE_EXPR,
while for !processing_template_decl we want to error.  And
fold_non_dependent_expr calls maybe_constant_value instead of
cxx_constant_value, so while it is mce_true as well, it doesn't report errors,
just silently returns non-constant.