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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++/109683] [13/14 Regression] False cyclic dependency error
 reported for constraint
Date: Mon, 01 May 2023 11:58:21 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109683

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=3D105797
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot g=
nu.org
   Last reconfirmed|                            |2023-05-01
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1
           Keywords|                            |rejects-valid
   Target Milestone|---                         |13.2
                 CC|                            |ppalka at gcc dot gnu.org

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Thanks for the bug report.  Started with r13-980-gdf4f95dbd4764f which made
function parameters used in a constraint no longer induce a dependency on a=
ll
contextual template parameters.

So another workaround would be to make the constructor's constraints explic=
itly
depend on the second template parameter of the class:

template <typename T, typename U>
struct VariantConstructors {
  VariantConstructors(T&& t)
    requires(requires { T(t); typename U; });
};

...=