From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id C2B493858C52 for ; Fri, 15 Sep 2023 09:32:24 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org C2B493858C52 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1694770344; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=vMHiTEpcbPk3X2sa87NemhMgskrufXXmTz25uWXEQ0Q=; b=WO4rayeDuUn4ARia2tPoAMW4E95gMZf13JBQsiRlJrK0eagerzx29CvEvJ6bklknUIMKWl kcmthqGUR9o31ND0Gd1I16v8sYW8C76CVdh7RN3Ut582Pks2HenHv1SDBFl8AHoo9k6n4n 90Vr9a+XfUJiSO15/QfrIgmhp05m/KY= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-182-w86KruWzN4CIzozCo_fDKg-1; Fri, 15 Sep 2023 05:32:21 -0400 X-MC-Unique: w86KruWzN4CIzozCo_fDKg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 10A59858281; Fri, 15 Sep 2023 09:32:21 +0000 (UTC) Received: from localhost (unknown [10.42.28.190]) by smtp.corp.redhat.com (Postfix) with ESMTP id C8F9610069B4; Fri, 15 Sep 2023 09:32:20 +0000 (UTC) From: Jonathan Wakely To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Subject: [committed] libstdc++: Fix constraints for std::variant default constructor Date: Fri, 15 Sep 2023 10:27:38 +0100 Message-ID: <20230915093220.2192265-1-jwakely@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-11.8 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Tested x86_64-linux. Pushed to trunk. Thanks to Nina Ranns for noticing this bug. Removing the base class isn't an ABI change. It's an empty base class with a type that's unique to the std::variant that derives from it, so doesn't change whether two std::variant subobjects can be overlapping. -- >8 -- The standard says the default ctor should be constrained, not deleted. Our use of a defaulted default ctor and _Enable_default_constructor base class results in it being deleted. libstdc++-v3/ChangeLog: * include/std/variant (variant): Remove derivation from _Enable_default_constructor base class. (variant::variant()): Constrain. * testsuite/20_util/variant/default_ctor.cc: New test. --- libstdc++-v3/include/std/variant | 24 +++++++++---------- .../testsuite/20_util/variant/default_ctor.cc | 11 +++++++++ 2 files changed, 23 insertions(+), 12 deletions(-) create mode 100644 libstdc++-v3/testsuite/20_util/variant/default_ctor.cc diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant index 36eec8d829b..c0e41740dcf 100644 --- a/libstdc++-v3/include/std/variant +++ b/libstdc++-v3/include/std/variant @@ -1332,9 +1332,6 @@ namespace __variant template class variant : private __detail::__variant::_Variant_base<_Types...>, - private _Enable_default_constructor< - __detail::__variant::_Traits<_Types...>::_S_default_ctor, - variant<_Types...>>, private _Enable_copy_move< __detail::__variant::_Traits<_Types...>::_S_copy_ctor, __detail::__variant::_Traits<_Types...>::_S_copy_assign, @@ -1355,10 +1352,6 @@ namespace __variant "variant must have no void alternative"); using _Base = __detail::__variant::_Variant_base<_Types...>; - using _Default_ctor_enabler = - _Enable_default_constructor< - __detail::__variant::_Traits<_Types...>::_S_default_ctor, - variant<_Types...>>; template static constexpr bool __not_self @@ -1396,7 +1389,16 @@ namespace __variant = !__is_in_place_tag<__remove_cvref_t<_Tp>>::value; public: - variant() = default; +#if __cpp_concepts + variant() requires is_default_constructible_v<__to_type<0>> = default; +#else + template, + typename = enable_if_t>> + constexpr + variant() noexcept(is_nothrow_default_constructible_v<__to_type<0>>) + { } +#endif + variant(const variant& __rhs) = default; variant(variant&&) = default; variant& operator=(const variant&) = default; @@ -1441,8 +1443,7 @@ namespace __variant typename = enable_if_t>> constexpr explicit variant(in_place_index_t<_Np>, _Args&&... __args) - : _Base(in_place_index<_Np>, std::forward<_Args>(__args)...), - _Default_ctor_enabler(_Enable_default_constructor_tag{}) + : _Base(in_place_index<_Np>, std::forward<_Args>(__args)...) { } template, initializer_list<_Up> __il, _Args&&... __args) - : _Base(in_place_index<_Np>, __il, std::forward<_Args>(__args)...), - _Default_ctor_enabler(_Enable_default_constructor_tag{}) + : _Base(in_place_index<_Np>, __il, std::forward<_Args>(__args)...) { } template diff --git a/libstdc++-v3/testsuite/20_util/variant/default_ctor.cc b/libstdc++-v3/testsuite/20_util/variant/default_ctor.cc new file mode 100644 index 00000000000..d0d9235a59c --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/variant/default_ctor.cc @@ -0,0 +1,11 @@ +// { dg-do compile { target c++17 } } + +#include + +struct A{ A(int); }; +struct B{ B(){}; }; + +void f(std::variant); +int f(B); + +int unambiguous = f({}); // { dg-bogus "ambiguous" } -- 2.41.0