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From: "ppalka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/108393] circular concept false-positive
Date: Fri, 13 Jan 2023 16:28:05 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108393

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=3D99599
                 CC|                            |ppalka at gcc dot gnu.org

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
IIUC this is a consequence of CWG2369, which made us check check constraints
before checking non-dependent conversions, and which AFAIK only GCC impleme=
nts.

It can be worked around by encoding the conversion to unreachable_sentinel_=
t as
an additional constraint guarding the real constraint:

  template<std::convertible_to<unreachable_sentinel_t> T, C _Iter>
  friend constexpr bool operator=3D=3D(T, const _Iter&) noexcept;

See also PR99599=