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 EAB4A3840C24; Tue,  9 Jun 2020 18:51:07 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org EAB4A3840C24
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
 s=default; t=1591728667;
 bh=0XkAI2O9JtcUyfcFp5ZS3fHs/XtW7vn9Q0SbNcOHmH8=;
 h=From:To:Subject:Date:From;
 b=aZgnb132gi1ff6YZJd8RNpqkeTFqa0h7Z+owfvIbn0/LYsUCuh9uP2FCPZDVVbMfl
 r8N8DKmOki3hCyPFflvyXY9rrs1VAstsnqNWtxD6FbY/WR6Od4vuLNB+Q8631JAHF+
 33Q7kFa7FLDkVmc6qdHJr4ZBo8Q/ONDUzBhgu5Cs=
From: "lewissbaker.opensource at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/95616] New: [coroutines] coroutines with
 potentially-throwing 'co_await promise.final_suspend()' expressions should be
 ill-formed
Date: Tue, 09 Jun 2020 18:51:07 +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: 10.1.1
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: lewissbaker.opensource 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-95616-4@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: <http://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: <http://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Tue, 09 Jun 2020 18:51:08 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95616

            Bug ID: 95616
           Summary: [coroutines] coroutines with potentially-throwing
                    'co_await promise.final_suspend()' expressions should
                    be ill-formed
           Product: gcc
           Version: 10.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lewissbaker.opensource at gmail dot com
  Target Milestone: ---

The wording of [dcl.fct.def.coroutine]/15 states:
> The expression co_=C2=ADawait promise.final_=C2=ADsuspend() shall not be =
potentially-throwing ([except.spec]).

See http://eel.is/c++draft/dcl.fct.def.coroutine#15
and http://eel.is/c++draft/except.spec#6

I believe this means that the compiler should reject with a diagnostic any
coroutine with a promise_type where `co_await promise.final_suspend()` is n=
ot
noexcept. ie. all of the following must be declared noexcept (if they form =
part
of the await-expression):
- promise_type::final_suspend()
- finalSuspendObj.operator co_await()
- finalSuspendAwaiter.await_ready()
- finalSuspendAwaiter.await_suspend()
- finalSuspendAwaiter.await_resume()
- finalSuspedObj destructor
- finalSuspendAwaiter destructor

GCC (and Clang) currently accepts code that that does not declare
final_suspend() as
noexcept.

e.g. see https://godbolt.org/z/Et_5eo=