On Tue, 15 Jun 2021 at 19:28, Jonathan Wakely wrote:
>
> By changing __cust_access::__decay_copy from a function template to a
> function object we avoid ADL. That means it's fine to call it
> unqualified (the compiler won't waste time doing ADL in associated
> namespaces, and won't try to complete associated types).
>
> This also makes some other minor simplications to other concepts for the
> [range.access] CPOs.
>
> Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
>
> libstdc++-v3/ChangeLog:
>
>         * include/bits/iterator_concepts.h (__cust_access::__decay_copy):
>         Replace with function object.
>         (__cust_access::__member_begin, ___cust_access::_adl_begin): Use
>         __decay_copy unqualified.
>         * include/bits/ranges_base.h (__member_end, __adl_end):
>         Likewise. Use __range_iter_t for type of ranges::begin.
>         (__member_rend): Use correct value category for rbegin argument.
>         (__member_data): Use __decay_copy unqualified.
>         (__begin_data): Use __range_iter_t for type of ranges::begin.

That change makes it impossible to import the header in a module.
Fixed by this patch.

Tested powerpc64le-linux. Pushed to trunk.