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 4AC413858D1E for ; Sun, 6 Aug 2023 19:19:58 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 4AC413858D1E 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=1691349597; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Mzcc75SkgCHkAJu4sE75SC6FyUOhD716iMPy3/vdc6g=; b=MLIOtFZ4pCL6Mya4UkIoWWrpVUxMg4Xu/ChtCALvgsMr9c8LYzFojmefQBHOG7ElQOjac3 IXBU59pvUuDF7zB7E6oXLBrRfOIHWe1Qivouk2+3yMNUX9PNOtv4UNzpu3F1lfJc4LaRrI lnLo8eevciE/ZvYXbD4J2hK4Cr1grM4= Received: from mail-io1-f71.google.com (mail-io1-f71.google.com [209.85.166.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-674-CIS89dQCOaelHz5TeLKbZA-1; Sun, 06 Aug 2023 15:19:56 -0400 X-MC-Unique: CIS89dQCOaelHz5TeLKbZA-1 Received: by mail-io1-f71.google.com with SMTP id ca18e2360f4ac-790b95a4871so364556139f.1 for ; Sun, 06 Aug 2023 12:19:55 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1691349595; x=1691954395; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=Mzcc75SkgCHkAJu4sE75SC6FyUOhD716iMPy3/vdc6g=; b=ZQw8O+Mmc3F53uIz2jYacn7tX1j5Pk+nVuas0ZA5UmEVDgcSYY2o0adP0Dyk51tFb8 7/l2SSAd3j27dXuWX9ffGByeJzySdh0osLevDG42o0C2BMFxdcNoQcIgDna8HGU7OEF+ AgaBMjBZHO/9AiFIGN8Kqjpaa8oBMaMnLljNNdkeAIiO6Rpd5DKLfsz/pk+gYIYlWkgf qpZiUHgDR9OHf37IxwrGw/nTBaHGyrOwRiRW7B+2vnYzlxZRmJERkvVqwJlbq3YwFDhL 0y0pHyTtfg5Z+N+blbDAgIVwUH59FUXzde9ccRJj6Cy8xlpYjKV5spP9wZgMXaKpI3gA Lj/Q== X-Gm-Message-State: AOJu0Yw3JNhbrz/Te3xIQdyAo/4/VnYHwIlIQ80SRdVMk5fy6rApP6+N 4PjTePMENTSXDZIaBr4h/cMXVqZc+uc3j9huBnyUfSdAaTJVEISfZCOwxYJgcA86psqEHSbSI/Y 9WfbM15sSjcOuiLgz17EsH4f85ASIrAA= X-Received: by 2002:a5d:81cc:0:b0:787:1697:1b3b with SMTP id t12-20020a5d81cc000000b0078716971b3bmr7602500iol.8.1691349595263; Sun, 06 Aug 2023 12:19:55 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGBjZbPoXRsFhUDbV7cs/rXZszKtHZfhoHpkoV4/91Kw5D+X2B6yIlBLBdUqjHP/ghOQ0BPrugqVMitz40RxVg= X-Received: by 2002:a5d:81cc:0:b0:787:1697:1b3b with SMTP id t12-20020a5d81cc000000b0078716971b3bmr7602488iol.8.1691349594968; Sun, 06 Aug 2023 12:19:54 -0700 (PDT) MIME-Version: 1.0 References: <3A4C9996-750B-4E3F-8F30-E3DA4366C7B5@berlin.de> In-Reply-To: <3A4C9996-750B-4E3F-8F30-E3DA4366C7B5@berlin.de> From: Jason Merrill Date: Sun, 6 Aug 2023 12:19:44 -0700 Message-ID: Subject: Re: GCC support for extensions from later standards To: Nikolas Klauser Cc: gcc@gcc.gnu.org, Louis Dionne , Mark de Wever , aaron@aaronballman.com, "libstdc++" X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/alternative; boundary="000000000000ccbb9c06024603e7" X-Spam-Status: No, score=-6.2 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,HTML_MESSAGE,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: --000000000000ccbb9c06024603e7 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, Aug 2, 2023 at 12:02=E2=80=AFPM Nikolas Klauser wrote: > Hi everyone! > > I'm working on libc++ and we are currently discussing using language > extensions from later standards ( > https://discourse.llvm.org/t/rfc-use-language-extensions-from-future-stan= dards-in-libc/71898/4). > By that I mean things like using `if constexpr` with `-std=3Dc++11`. GCC = has > quite a lot of these kinds of conforming extensions, but doesn't document > them AFAICT. While discussing using these extensions, the question came up > what GCCs support policy for these is. Aaron was kind enough to answer > these questions for us on the Clang side. Since I couldn't find anything = in > the documentation, I thought I'd ask here. > > So, here are my questions: > > Do you expect that these extensions will ever be removed for some reason? > If yes, what could those reasons be? > Potentially, if they don't actually work properly in earlier standard modes. I recently noticed that while we allow DMI and =3Ddefault in C++03 mode with a pedwarn, combining them doesn't work. Some of the extensions are needed by libstdc++ and are therefore well tested; these are extremely unlikely to ever be removed. libstdc++ folks, is there a list of these? Would you be interested in documenting them? > That would be useful, yes. There is a patch in review to add __has_feature/__has_extension to G++, which would seem like a suitable context for this documentation. Aaron noted that we should ask the Clang folks before using them, so they > can evaluated whether the extension makes sense, since they might not be > aware of them, and some might be broken. So I'd be interested whether you > would also like us to ask whether you want to actually support these > extensions. > Sounds good. Jason --000000000000ccbb9c06024603e7--