[Bug c++/127081] Within std::format, constexpr expansion of std::basic_format_string errors with: strong_ordering is not a member of 'std'

[nshead at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127081

Nathaniel Shead <nshead at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |nshead at gcc dot gnu.org

--- Comment #3 from Nathaniel Shead <nshead at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #1)
> I think this is a similar problem to PR124888, as I've mentioned in
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124888#c5
> there are various cases of the FE performing lookups after parsing.
> Unfortunately the simple fix for that PR can't handle cases like this easily.
> So I think we need some mapping, if IL contains this, then we stream also
> std::that if it exists (say __builtin_source_location call ->
> std::source_location::__impl, SPACESHIP_EXPR ->
> std::{strong,weak,partial}_ordering, etc.).

See PR122609 for some more discussion on this.  (Also related is PR101140 which
possibly should be reopened?)

A proper fix for handling arbitrary names in the GMF shouldn't require such an
extra mapping, I don't think.