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 A4F9138582A0; Tue,  1 Nov 2022 11:16:50 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org A4F9138582A0
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1667301410;
	bh=fdDOmiQqaJ/AtqJ+n8f6ke2kINKnPVdRsxa2PKTd0Kc=;
	h=From:To:Subject:Date:From;
	b=dLD5qX3vrY2f62dQMr5u0kBC5tAjHt1QdlzigtkgVvviRO/k4pspBsEPY5ZVeYpJe
	 T5zeutOAa6wsJ6HbfDUA84nlEkHrFWEm1tqVPADeczkKBWO4kOsNJUm1IiKsNjqJow
	 MTFOfof6jrLciPmG2w6mGui9nohBZiEUnNycfcsE=
From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/107492] New: Unhelpful -Wignored-qualifiers warning in
 template specialization
Date: Tue, 01 Nov 2022 11:16:49 +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: 12.2.1
X-Bugzilla-Keywords: diagnostic
X-Bugzilla-Severity: normal
X-Bugzilla-Who: redi at gcc dot gnu.org
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
 keywords bug_severity priority component assigned_to reporter
 target_milestone
Message-ID: <bug-107492-4@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=3D107492

            Bug ID: 107492
           Summary: Unhelpful -Wignored-qualifiers warning in template
                    specialization
           Product: gcc
           Version: 12.2.1
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

GCC warns about this with -Wextra:

template<typename T> struct S { };
template<> struct S<void(*)()> { };
template<> struct S<const void(*)()> { };

template<typename T, typename U> constexpr bool is_same_v =3D false;
template<typename T> constexpr bool is_same_v<T, T> =3D true;

static_assert( ! is_same_v< void(*)(), const void(*)() > );


spec.cc:3:21: warning: type qualifiers ignored on function return type
[-Wignored-qualifiers]
    3 | template<> struct S<const void(*)()> { };
      |                     ^~~~~
spec.cc:8:40: warning: type qualifiers ignored on function return type
[-Wignored-qualifiers]
    8 | static_assert( ! is_same_v< void(*)(), const void(*)() > );
      |                                        ^~~~~


The warning is wrong, the qualifiers are not ignored here. The two types are
distinct, as shown by the fact that the explicit specializations are not
redefinitions of each other, and the static assert passes.=