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 75EAA3857823; Mon, 12 Oct 2020 04:38:17 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 75EAA3857823
From: "anders.granlund.0 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/97376] New: Function type to function pointer type
 adjustment for non-type template paramter does not work when using
 decltype(auto)
Date: Mon, 12 Oct 2020 04:38:17 +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: unknown
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: anders.granlund.0 at gmail 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-97376-4@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
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Mon, 12 Oct 2020 04:38:17 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97376

            Bug ID: 97376
           Summary: Function type to function pointer type adjustment for
                    non-type template paramter does not work when using
                    decltype(auto)
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: anders.granlund.0 at gmail dot com
  Target Milestone: ---

Consider the following program:

  #include <iostream>
  #include <type_traits>

  template<decltype(auto) X>
  void f1()
  {
  }

  template<void X()>
  void f2()
  {
  }

  void ff()
  {
  }

  int main()
  {
    f1<ff>();
    f2<ff>();
  }

When compiling it with  -std=3Dc++17 -pedantic-errors  it gives a compilati=
on
error complaining that the non-type parameter  X  of the template  f1  has =
type
 void ()  and that this is not a valid type for a non-type template paramte=
r.

The expected behaviour is that the type of  X  in  f1  should instead be
ajusted to  void (*)() . This is what happens in template  f2 .

Note that clang gives the expected behaviour (no compilation errors). Compi=
ler
explorer link comparing clang and gcc:

  https://godbolt.org/z/PGbrYE=