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 6F5C038708F5; Fri, 30 Jun 2023 13:44:36 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 6F5C038708F5
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1688132676;
	bh=BPSYI1Z+Z1P/8c8j0bzTszecrif+WvnVicOaHiOygzk=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=s7b5NmpFU8AjQ50Tm0bntzD394KU6i7ARU+fkja+ZVOL6wEMRjXCIRNZ0PEkbeOBQ
	 SJ7M7FqwWQ4ki+LCRRc43Ay10wglyzKJjnSOvM/HlGTOYLJZxCCuHRMJVHMuMjaMZe
	 hg+We0tu0rjY6tbWYKBDxeejS5nL2Sjgm51ZtsP0=
From: "ppalka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/110497] Wrong error on non-static data member referenced in
 concept definition
Date: Fri, 30 Jun 2023 13:44:35 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 13.1.0
X-Bugzilla-Keywords: rejects-valid
X-Bugzilla-Severity: normal
X-Bugzilla-Who: ppalka at gcc dot gnu.org
X-Bugzilla-Status: NEW
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: blocked cc
Message-ID: <bug-110497-4-E2hWcDFGdt@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-110497-4@http.gcc.gnu.org/bugzilla/>
References: <bug-110497-4@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=3D110497

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |67491
                 CC|                            |ppalka at gcc dot gnu.org

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
It seems we're issuing a hard error during satisfaction here because
substitution failure didn't occur, and the substituted constraint is
non-constant which renders the program ill-formed as per
[temp.constr.atomic]/3:

> If substitution results in an invalid type or expression, the constraint =
is not satisfied. Otherwise, the lvalue-to-rvalue conversion is performed i=
f necessary, and E shall be a constant expression of type bool.

One might argue substitution failure should occur for T::b with T=3DB, but =
this
seems to be permitted by [expr.prim.id.general]/3 since constraint-expressi=
ons
are unevaluated contexts.

Note that if we use B::b directly in the concept definition then Clang also
rejects the program due to non-constant satisfaction rule:

struct B { const bool b =3D true; };
template <typename T>
concept C =3D B::b;
static_assert( !C<B> );

error: substitution into constraint expression resulted in a non-constant
expression

So GCC might be correct to reject the original program.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D67491
[Bug 67491] [meta-bug] concepts issues=