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 498863836010; Mon,  9 May 2022 13:00:35 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 498863836010
From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/105510] error: initializer element is not constant
Date: Mon, 09 May 2022 13:00:35 +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: 12.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jakub 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: cc
Message-ID: <bug-105510-4-B9ozjTvRXQ@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-105510-4@http.gcc.gnu.org/bugzilla/>
References: <bug-105510-4@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, 09 May 2022 13:00:35 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105510

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(struct Test2){3, 4}
is a compound literal, see
https://en.cppreference.com/w/c/language/compound_literal
for further details, so it isn't a valid constant expression, it is like
doing
struct Test2
{
    long int x;
    long int y;
};

struct Test
{
    long int x;
    struct Test2 t;
};

struct Test2 tmp2=3D{3, 4};
struct Test tmp1=3D{1, tmp2};
struct Test t=3Dtmp1;
except that the compound literals introduce unnamed, not named objects.
The above is also rejected, by both GCC and Clang.
Note, implementations may accept as constant expressions even expressions t=
he
standard doesn't require to be constant expressions, so probably that is the
reason why Clang chooses to accept it.  Though, at least without using const
struct Test{,2} in the compound literals it is actually an unnamed object t=
hat
can be modified, so it is weird it is accepted.
The above testcase with tmp2/tmp1 is as an extension accepted by GCC when o=
ne
uses const struct Test2 or const struct Test (but rejected by Clang), though
if you use it in the compound literals, we don't accept that.=