From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.devel Subject: Re: bug#47391: 27.2; static list return from function and nconc Date: Thu, 25 Mar 2021 11:43:20 -0400 Message-ID: References: <87r1k32sir.fsf@hm.sivalik.com> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="31904"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) Cc: Rajeev Narang , 47391@debbugs.gnu.org, Emacs developers To: Philipp Stephani Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Thu Mar 25 16:48:59 2021 Return-path: Envelope-to: ged-emacs-devel@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1lPSEE-00089M-KC for ged-emacs-devel@m.gmane-mx.org; Thu, 25 Mar 2021 16:48:58 +0100 Original-Received: from localhost ([::1]:50092 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lPSED-00076W-KZ for ged-emacs-devel@m.gmane-mx.org; Thu, 25 Mar 2021 11:48:57 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:45128) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lPS8t-0000uQ-Nu for emacs-devel@gnu.org; Thu, 25 Mar 2021 11:43:27 -0400 Original-Received: from mailscanner.iro.umontreal.ca ([132.204.25.50]:3117) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lPS8q-0002Lb-T6 for emacs-devel@gnu.org; Thu, 25 Mar 2021 11:43:26 -0400 Original-Received: from pmg2.iro.umontreal.ca (localhost.localdomain [127.0.0.1]) by pmg2.iro.umontreal.ca (Proxmox) with ESMTP id 88367809E7; Thu, 25 Mar 2021 11:43:23 -0400 (EDT) Original-Received: from mail01.iro.umontreal.ca (unknown [172.31.2.1]) by pmg2.iro.umontreal.ca (Proxmox) with ESMTP id 35FD380675; Thu, 25 Mar 2021 11:43:22 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=iro.umontreal.ca; s=mail; t=1616687002; bh=yjukXNXFZuAbfp8EHWGt8jMMPpNGLNmo074RC9wuREY=; h=From:To:Cc:Subject:References:Date:In-Reply-To:From; b=gLlKN09kzQDSmxTUv5Mz3dgR0YWnDCZ4pdDWMqGjyj3D2FcYtXRlTkMfcjYow4WKB Xc1kh9ZcVxw5CB+k8uqr4gHFAVk29FA0ALsx+nr8mnTT0KOtgKBbQGsoJk+DudJGQA nf0g3qys9fs/2lq0A9qcEVS90QKUODlVdTuvZHSLv0myQ9SKIp4GuOMCQbqRtYaZcE Mm4FJZAHl8PY4TFe3fQsrlge5CtqhQjyFxsGln/qPAdb1M/qIIv/ypvu60pcoZZDqb vDoKcHbSgqVgPHCPZs5WrBMdPQkx5+ELGkUf4vmASc6GD2tD+4fnk9acHTAz8UFOFR NSnFQBX+0lKPA== Original-Received: from alfajor (unknown [216.154.43.249]) by mail01.iro.umontreal.ca (Postfix) with ESMTPSA id E671F12014C; Thu, 25 Mar 2021 11:43:21 -0400 (EDT) In-Reply-To: (Philipp Stephani's message of "Thu, 25 Mar 2021 16:28:26 +0100") Received-SPF: pass client-ip=132.204.25.50; envelope-from=monnier@iro.umontreal.ca; helo=mailscanner.iro.umontreal.ca X-Spam_score_int: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.io gmane.emacs.devel:267025 Archived-At: >> (defun fn () '(1 2)) >> >> (nconc (fn) '(3)) >> -> (1 2 3) > > This is undefined behavior/unsupported. The value that (fn) evaluates > to is immutable, but nconc mutates it. > >> >> (nconc (fn) '(3)) >> -> (1 2 3 3) ? should be (1 2 3) >> >> If this is not a bug, then hfy-invisible, hfy-face-to-style-i may need to be fixed. > > If they use this pattern, then they should indeed be fixed. Note that in the code above, we usually consider that the bug is not in `fn` but in the use of `nconc` on a list which the code doesn't know can safely be mutated (it should hence use `append` instead). Stefan