From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id EAD8E3858C36; Sat, 12 Aug 2023 19:19:48 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org EAD8E3858C36
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1691867988;
	bh=wlKnoWVtlYa4pZSb5IUqjXCQkgzv5Rvqv57NVmsPt/w=;
	h=From:To:Subject:Date:From;
	b=dOGpVT6/C09wZcdnmWpqc0NaO/PaF3a6JaoSNZWJJ1lCWZVj78DXITxTMtw3gI42G
	 qmx0VoOnAo7Hxksg8Xn0c6P4M/14wut28RM/wO6yMWfFM4YK67Jx36Bpb5tw+HuUAe
	 lsU/OcYE7NpF4nIacTvlEPt4ysj2rC/Z210zFNtk=
From: "deco33000 at yandex dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/111004] New: Visitor and concept error message
Date: Sat, 12 Aug 2023 19:19:48 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 13.2.1
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: deco33000 at yandex dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-111004-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111004

            Bug ID: 111004
           Summary: Visitor and concept error message
           Product: gcc
           Version: 13.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: deco33000 at yandex dot com
  Target Milestone: ---

The error code for the following situation is not clear.

The error is that struct A and B don't have a "bool activated;" member.

The issue is the variant does not reflect what the error is in an helpful w=
ay.
To ease your life, here is the godbolt:
https://godbolt.org/z/Wdr4zn5E1

Do you think it is possible to improve the diagnostic?

---------------------------
Reduced test case:
#include <iostream>
#include <variant>
#include <vector>

using namespace std;

template <class T>
concept My_concept =3D requires(T a) {
    { a.activated } -> std::same_as<bool &>;
};

struct A {

    bool not_activated;
};
struct B {

    bool not_activated;
    int other;
};
auto test(variant<A, B> &v) -> void {

    std::visit([](My_concept auto &&arg) { std::cout << "OK\n"; }, v);
}

int main() {

    variant<A, B> v;

    v =3D A();

    test(v);

    return 0;
}
------------------------
Thanks=