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: Major modes using `widen' is a good, even essential, programming practice. Date: Sun, 7 Aug 2022 19:20:44 +0000 Message-ID: References: <6ae35c9306ade07b4c45@heytings.org> <835yj4xhh7.fsf@gnu.org> <83y1w0w0gk.fsf@gnu.org> <83pmhcvugm.fsf@gnu.org> 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="18196"; mail-complaints-to="usenet@ciao.gmane.io" Cc: gregory@heytings.org, emacs-devel@gnu.org To: Eli Zaretskii Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Sun Aug 07 21:21:52 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 1oKlqS-0004am-Gd for ged-emacs-devel@m.gmane-mx.org; Sun, 07 Aug 2022 21:21:52 +0200 Original-Received: from localhost ([::1]:41530 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oKlqQ-00072l-Th for ged-emacs-devel@m.gmane-mx.org; Sun, 07 Aug 2022 15:21:50 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:39674) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oKlpS-0006LK-B8 for emacs-devel@gnu.org; Sun, 07 Aug 2022 15:20:50 -0400 Original-Received: from colin.muc.de ([193.149.48.1]:37183 helo=mail.muc.de) by eggs.gnu.org with smtp (Exim 4.90_1) (envelope-from ) id 1oKlpQ-0008Bv-6n for emacs-devel@gnu.org; Sun, 07 Aug 2022 15:20:50 -0400 Original-Received: (qmail 71269 invoked by uid 3782); 7 Aug 2022 19:20:44 -0000 Original-Received: from acm.muc.de (p2e5d5157.dip0.t-ipconnect.de [46.93.81.87]) (using STARTTLS) by colin.muc.de (tmda-ofmipd) with ESMTP; Sun, 07 Aug 2022 21:20:44 +0200 Original-Received: (qmail 5437 invoked by uid 1000); 7 Aug 2022 19:20:44 -0000 Content-Disposition: inline In-Reply-To: <83pmhcvugm.fsf@gnu.org> 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=unavailable 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:293230 Archived-At: Hello, Eli. On Sun, Aug 07, 2022 at 20:23:21 +0300, Eli Zaretskii wrote: > > Date: Sun, 7 Aug 2022 17:01:09 +0000 > > Cc: gregory@heytings.org, emacs-devel@gnu.org > > From: Alan Mackenzie > > > > Consider the second jit-lock chunk > > > > at the beginning of xdisp.c. Fontifying that chunk involves looking > > > > back 1500 characters before BEG to see that it needs > > > > font-lock-comment-face. You might argue that that information will be > > > > in a cache anyway, but that's not dependable. > > > Either in the cache or in the buffer: the previous chunk was > > > fontified, so its end has the font-lock-comment-face. So you know. > > No, you don't. The buffer might be being opened by desktop in a large > > comment in the middle of the file. > You've changed the scenario, yes? Yes. We've got to deal with all scenarios, preferably without special-caseing special cases. > > What jit-lock/font-lock actually do at the moment is to widen, then use > > syntax-ppss, i.e. in effect scan from BOB. > Yes, and that's SLOOOWWWW! On my machine, with an optimised build, it takes just under 20 ms to parse-partial-sexp over xdisp.c (not counting any redisplay at the end). I don't understand any more than Dmitry does, why your unoptimised build is taking 25 times as long. > > > > Also, the (BEG END) region will typically get rounded up to whole > > > > lines, again "violating" that chunk. > > > That's a far cry from going to BOB. And if you ask nicely, we > > > could arrange that jit-lock calls you only on line boundaries > > > (unless lines are longer than some reasonable value). > > The search for line boundaries is done by font-lock.el. > I don't trust it to DTRT when lines are very long. I think I raised the topic a few days ago of font-lock expanding regions to whole lines. Maybe we shouldn't do it for long lines. We'd need something in its place, though. > > > > In principle, font-lock needs to look outside of (BEG END). > > > No, it doesn't. A string cannot begin before a beginning of a > > > function, for example. And if you need to go too far, just give up > > > and blame the user who writes such code. It is much better than > > > letting every use of CC Mode wait because once in a blue moon someone > > > could have a very long string. > > That "needing to go too far" is an instantaneous jump, not a scanning. > Please tell that to someone who doesn't edit C sources as frequently > as I do. Are you saying that long strings and long comments cause a particular slowdown in C Mode, not seen when strings and comments are all short? > > The string start will be in a parse-partial-sexp result somewhere. > > Sometimes people write long strings. They certainly write long comments. > Why do I have top suffer every day just because someone, somewhere, > might do that? I'd rather we "punish" those few people who do it > (rarely). I don't think we should punish people who write comments. I'm thinking of Gerd M., who was likely the writer of the comment at the beginning of xdisp.c. -- Alan Mackenzie (Nuremberg, Germany).