From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Alan Mackenzie Newsgroups: gmane.emacs.devel Subject: Re: Why is it so difficult to get a Lisp backtrace? Date: Sat, 25 Jun 2022 15:26:02 +0000 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="1488"; mail-complaints-to="usenet@ciao.gmane.io" To: emacs-devel@gnu.org Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Sat Jun 25 17:27:02 2022 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 1o57gb-0000Ck-Jb for ged-emacs-devel@m.gmane-mx.org; Sat, 25 Jun 2022 17:27:01 +0200 Original-Received: from localhost ([::1]:57724 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1o57ga-0004Kz-2k for ged-emacs-devel@m.gmane-mx.org; Sat, 25 Jun 2022 11:27:00 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:55944) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1o57fk-0003bI-Qp for emacs-devel@gnu.org; Sat, 25 Jun 2022 11:26:08 -0400 Original-Received: from colin.muc.de ([193.149.48.1]:57492 helo=mail.muc.de) by eggs.gnu.org with smtp (Exim 4.90_1) (envelope-from ) id 1o57fh-0005lA-K1 for emacs-devel@gnu.org; Sat, 25 Jun 2022 11:26:08 -0400 Original-Received: (qmail 7290 invoked by uid 3782); 25 Jun 2022 15:26:03 -0000 Original-Received: from acm.muc.de (p4fe15baa.dip0.t-ipconnect.de [79.225.91.170]) (using STARTTLS) by colin.muc.de (tmda-ofmipd) with ESMTP; Sat, 25 Jun 2022 17:26:02 +0200 Original-Received: (qmail 6304 invoked by uid 1000); 25 Jun 2022 15:26:02 -0000 Content-Disposition: inline In-Reply-To: X-Submission-Agent: TMDA/1.3.x (Ph3nix) X-Primary-Address: acm@muc.de Received-SPF: pass client-ip=193.149.48.1; envelope-from=acm@muc.de; helo=mail.muc.de X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.29 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:291610 Archived-At: Hello, again. On Sat, Jun 25, 2022 at 13:42:04 +0000, Alan Mackenzie wrote: > (setq debug-on-error t) ought to be useful to get backtraces. It is, > sometimes, but far from always. > There seem to be three use cases for debug-on-error: > (i) The vast bulk of users, who are barely, if at all, aware of its > existence. They will enable it on request from a maintainer to help > debug a bug. > (ii) Hard-core maintainers, who run with it enabled constantly. Here > debug-ignored-errors helps suppress certain unhelpful errors which > would otherwise occur too often and irritate. > (iii) Those maintainers who run with it disabled, but when an error > occurs, want to be able to repeat that error and get a backtrace. > This third group of users is poorly catered for by the current collection > of mechanisms. See also bug #56201, with thanks to Andreas and Lars who > helped me get to the bottom of it. To be reasonably sure of getting a > backtrace, it seems one needs to do all of the following: > (i) (setq debug-on-error t). > (ii) (setq debug-on-signal t). > (iii) Bind debug-ignored-errors to nil. > (iv) Pray. > (v) Execute the erring command again. > I put it to people that we need a new command or variable not called > something like `backtrace-next-and-I-really-mean-it' which would allow > step (v) to generate the desired backtrace without having to go through > steps (i) to (iv) individually. The lack of such a command/variable is > making (at least) my Emacs development less pleasant than it might > otherwise be. I mean something like the following, which to a first approximation, works. To use it, do M-x debug-next-command and the execute the command expected to give errors: ;; -*- lexical-binding: t -*- (defvar debug-next-command-save-debug-on-error nil) (defvar debug-next-command-save-debug-on-signal nil) (defvar debug-next-command-save-debug-on-quit nil) (defvar debug-next-command-save-debug-ignored-errors nil) (defvar debug-next-command-stay-on-post-command nil) (defun debug-next-command-end () "Undo the effects of debug-next-command." (if debug-next-command-stay-on-post-command (setq debug-next-command-stay-on-post-command nil) (setq debug-on-error debug-next-command-save-debug-on-error debug-on-signal debug-next-command-save-debug-on-signal debug-on-quit debug-next-command-save-debug-on-quit debug-ignored-errors debug-next-command-save-debug-ignored-errors) (remove-hook 'post-command-hook #'debug-next-command-end))) (defun debug-next-command () "Produce a bactrace in the next command should an error occur." (interactive) (setq debug-next-command-save-debug-on-error debug-on-error debug-next-command-save-debug-on-signal debug-on-signal debug-next-command-save-debug-on-quit debug-on-quit debug-next-command-save-debug-ignored-errors debug-ignored-errors) (setq debug-on-error t debug-on-signal t debug-on-quit t debug-ignored-errors nil) (setq debug-next-command-stay-on-post-command t) (add-hook 'post-command-hook #'debug-next-command-end)) -- Alan Mackenzie (Nuremberg, Germany).