[Bug c++/101140] [modules] no matching function for call to ‘operator new(sizetype, void*)’

["nshead at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101140

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
                 CC|                            |nshead at gcc dot gnu.org
   Last reconfirmed|                            |2024-03-26

--- Comment #3 from Nathaniel Shead <nshead at gcc dot gnu.org> ---
I believe this should be valid. The declaration of `::operator new` should be
reachable within the instantiation context of 'construct_at' , and thus
shouldn't need to be exported to be called. (See [module.context] and
[module.reach].)

The issue looks to be that `tsubst_expr` when handling a NEW_EXPR just calls
`build_new`, which ultimately does `build_operator_new_call` that uses normal
`lookup_qualified_name (global_namespace, fnname)` that doesn't consider
non-exported entities. We need some way to signify that lookup should also
consider declarations reachable from other points in the template's
instantiation context.

This could be related to one of the issues causing PR114275, but in that cases
it's failing to find instantiations of friend classes in the instantiation
context.