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 25E013885C24; Sat, 25 May 2024 00:53:31 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 25E013885C24
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1716598412;
	bh=SlbW0+WccF2utiVpbY/2TwOJQr9/b9GSWSk33W/qO5E=;
	h=From:To:Subject:Date:From;
	b=p9KALTrN102N83LhQkhtPSNzHMsD2vBEM5ZgSuiidEtNNH2gOE8qFpG0sFZOy4P2r
	 KvXs2rnQDtjbY1zIsenM1tb3SH+6Yom+cYmzg4+E3PfPBXbVMsPJhm6EclIG8YeHwx
	 r2XRVi+ZRRrhdD2dw/GNG3FJrW5XGp6Y98VP4B7I=
From: "pobrn at protonmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/115222] New: clang does not think libstdc++'s std::optional
 is nothrow destructible
Date: Sat, 25 May 2024 00:53:31 +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: 15.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: pobrn at protonmail 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-115222-4@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=3D115222

            Bug ID: 115222
           Summary: clang does not think libstdc++'s std::optional is
                    nothrow destructible
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pobrn at protonmail dot com
  Target Milestone: ---

clang and gcc disagree whether libstdc++'s std::optional<T> is nothrow
destructible when T is not. My reading of https://eel.is/c++draft/optional.=
dtor
suggests that the destructor should be `noexcept(true)` (by omission).

Consider the following piece of C++ code:

```
#include <optional>
#include <type_traits>

struct A { ~A() noexcept(false); };

static_assert(std::is_nothrow_destructible_v<std::optional<A>>);
```

the assertion passes on gcc, while it fails on clang:
https://gcc.godbolt.org/z/1ndxK1avM

Now I have tried to reduce the input, and arrived at something like this (
https://gcc.godbolt.org/z/orx5j1Eaf ):

```
template <typename _Tp> _Tp declval() noexcept;

template <typename _Tp>
inline constexpr bool is_nothrow_destructible_v =3D noexcept(declval<_Tp>()=
);

template <typename _Tp>
struct _Optional_payload_base {
  union _Storage {
    _Tp _M_value;
  } _M_payload;
};

template <typename _Tp>
struct _Optional_payload : _Optional_payload_base<_Tp> {
    ~_Optional_payload();
};

struct A {
  ~A() noexcept(false);
};

static_assert(is_nothrow_destructible_v<_Optional_payload<A>>);
```

The assertion passes on gcc, but fails on clang (and edg).=