From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-x534.google.com (mail-ed1-x534.google.com [IPv6:2a00:1450:4864:20::534]) by sourceware.org (Postfix) with ESMTPS id E4731395BC05 for ; Wed, 16 Nov 2022 16:46:13 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org E4731395BC05 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=gmail.com Received: by mail-ed1-x534.google.com with SMTP id i21so27444607edj.10 for ; Wed, 16 Nov 2022 08:46:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=96qCR0dYwW/H3EuuUIXpMcnUqIruy0qbY8DUamTil9E=; b=li5a46WXwm+pPPJIyZqmuTTtIBBuoMN0i9qetV7Vh0rmjYc+Jh9Oa8idSA7qyg9UCR F2mDJpSOoLRsHP8mS/GgXVzAKu/lnNCvwr+gmR5++tefRIHVN5yiQTHyTAOISZyGOqMT 0YrFlsjEU1+aoWamLvBfpXpagY7IXcd5CBRd2f61NaJXmOhGmxGxm/8IVnJAUiKpxz2R 78WcwNHSbkF8TVPjqqW5A3esdgaR+iNvZu7Z3Whxvcwr+cAzJpWkggmGyFJx1/VLgmBm vgOYke5SPK3iqxAB8FD5gj6rHGbPcWn6Lsd7i/k/0pcM2tddlZHJsZbLKEi2I4bfsvf3 RUSA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; 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=96qCR0dYwW/H3EuuUIXpMcnUqIruy0qbY8DUamTil9E=; b=HN/KneG7ZH4Ft/JEzGR95Ld2+ctEp3wVmXKzj+UgkB66CzW/1PXQ5uXdiyoFTO7ZW9 0kuwrXc6XNEmft1uqVxX7bVnyW7h3yRJh8uo0/1KHItwL2VLMor0d17Imcs3ZmXvRIDc O6MNIv/yudL9DZDmEKtdgSSBb8DAtF0enNS9CiFA5GhEqjfYwIv7hGuz+neaTW3GVUvv K/2lRHlSNBvCDd5ldHshRGYYC4rpfep5GwuI/lnFkshGRyi6/+mTeFEF6aZogzuItDMk Zyobu6bphpKu4SuB8VCNUTlr3cTfdIX2hx9am2j9W3JYzIqw+rRkGY+AkpsYgCe7e/Yq Kg5g== X-Gm-Message-State: ANoB5pnck8pyy9lj1kQnZu9kxIVq/7MKLEU/knvvARBrIxZu9zCofS15 apkOGgOIntMStsR9ne5Ie4edRrBem6UJ27oeeBM= X-Google-Smtp-Source: AA0mqf76o0R0CRUzDbJCrgJZkVmTLRhzlnxY+nLOtcNDm23FBkb6LBc3J9hNft0l1zpDgv1o/gQPbLulpq9LH07h2rI= X-Received: by 2002:a50:9557:0:b0:45c:f13b:4b96 with SMTP id v23-20020a509557000000b0045cf13b4b96mr19638390eda.129.1668617172797; Wed, 16 Nov 2022 08:46:12 -0800 (PST) MIME-Version: 1.0 References: <24ed5604-305a-4343-a1b6-a789e4723849@app.fastmail.com> <7ef0ce03-d908-649a-a6ee-89fea374d2b1@cs.ucla.edu> <9cb106e9-16ff-65ec-6a44-6567c77521dc@cs.ucla.edu> <06a5d2cd-44eb-7404-17f3-ff64dd505427@cs.ucla.edu> <27264d94-9496-d7ef-6716-f43db86f38e2@ispras.ru> <00C3EDCD-D2DA-4B0D-8A8A-08B76552D865@gentoo.org> In-Reply-To: From: Jonathan Wakely Date: Wed, 16 Nov 2022 16:46:01 +0000 Message-ID: Subject: Re: How can Autoconf help with the transition to stricter compilation defaults? To: Michael Matz Cc: Sam James , Richard Biener , Aaron Ballman , Alexander Monakov , Paul Eggert , Zack Weinberg , c-std-porting@lists.linux.dev, Autoconf Development , GCC Development , cfe-commits@lists.llvm.org, Gnulib bugs Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-0.5 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,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: On Wed, 16 Nov 2022 at 16:34, Michael Matz wrote: > > Hello, > > On Wed, 16 Nov 2022, Jonathan Wakely wrote: > > > > > Unrelated but I was a bit tempted to ask for throwing in > > > > -Wbuiltin-declaration-mismatch to default -Werror while Clang 16 was at > > > > it, but I suppose we don't want the world to burn too much, > > > > > > :-) It's IMHO a bug in the standard that it misses "if any of its > > > associated headers are included" in the item for reservation of external > > > linkage identifiers; it has that for all other items about reserved > > > identifiers in the Library clause. If that restriction were added you > > > couldn't justify erroring on the example at hand (because it doesn't > > > include e.g. and then printf wouldn't be reserved). A warning > > > is of course always okay and reasonable. As is, you could justify > > > erroring out, but I too think that would be overzealous. > > > > > > I think that's very intentional and not a defect in the standard. > > > > If one TU was allowed to define: > > > > void printf() { } > > > > and have that compiled into the program, then that would cause > > unexpected behaviour for every other TU which includes and > > calls printf. They would get the non-standard rogue printf. > > True. But suppose the restriction would be added. I could argue that > then your problem program (in some other TU) _does_ include the header, > hence the identifier would have been reserved and so the above definition > would have been wrong. I.e. I think adding the restriction wouldn't allow > the problematic situation either. > > I'm aware that the argument would then invoke all the usual problems of > what constitutes a full program, and if that includes the library even > when not including headers and so on. And in any case currently the > standard does say they're reserved so it's idle speculation anyway :) Since we're idly speculating anyway ... I'd always assumed the "if any of its associated headers is included" meant in the current TU, but it doesn't actually say that. Which does suggest that I can't use the identifier "assert" anywhere in a program if any TU in the program includes . Huh.