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Subject: [Bug libstdc++/96416] [DR 3545] to_address() is broken by
 static_assert in pointer_traits
Date: Fri, 26 Nov 2021 17:46:00 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96416

--- Comment #22 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:

https://gcc.gnu.org/g:8d3391d64799d490117ad48432a9ad2cf38b0091

commit r11-9317-g8d3391d64799d490117ad48432a9ad2cf38b0091
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Nov 25 23:29:08 2021 +0000

    libstdc++: Make std::pointer_traits SFINAE-friendly [PR96416]

    This is a simplified version of r12-5532 for the release branches.  It
    still removes the problematic static_assert, but rather than making
    std::pointer_traits completely empty when the element_type can't be
    deduced, it just disables element_type and pointer_to. Additionally, the
    pointer_to member is not completely absent when element_type is cv void,
    it just has an unusable signature.

    This is sufficient to avoid errors outside the immediate context when
    trying to use std::to_address.

    libstdc++-v3/ChangeLog:

            PR libstdc++/96416
            * include/bits/ptr_traits.h (pointer_traits): Remove
            static_assert checking for valid element_type.
            (pointer_traits::element_type, pointer_traits::pointer_to):
            Do not define when element type cannot be deduced.
            * testsuite/20_util/pointer_traits/lwg3545.cc: New test.
            * testsuite/20_util/to_address/1_neg.cc: Adjust dg-error line.
            * testsuite/20_util/to_address/lwg3545.cc: New test.

    (cherry picked from commit b8018e5c5ec0e9b6948182f13fba47c67b758d8a)=