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From: "fchelnokov at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/109159] New: explicit constructor is used in
 copy-initialization
Date: Thu, 16 Mar 2023 19:51:48 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 12.2.1
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109159

            Bug ID: 109159
           Summary: explicit constructor is used in copy-initialization
           Product: gcc
           Version: 12.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fchelnokov at gmail dot com
  Target Milestone: ---

The following code must be accepted (as it does in Clang and MSVC):

struct A {
    A( float ) {}
    template<class U>
    explicit A( U ) {}
};

template<class T>
concept CopyFromIntList =3D requires( T t ) { t =3D { 1 }; };

static_assert( !CopyFromIntList<A> );

because 't =3D {1}' is invalid: chosen constructor is explicit in
copy-initialization.

But in GCC static_assert fails. Online demo:
https://gcc.godbolt.org/z/Pf47E6dno=