From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.devel Subject: Re: Unbalanced change hooks (part 2) [Documentation fix still remaining] Date: Tue, 30 Aug 2016 21:00:16 +0300 Message-ID: <83bn0am91r.fsf@gnu.org> References: <20160811112951.GA2154@acm.fritz.box> <7e1478b6-cf00-fcbf-8c24-43bdaa57e2b6@dancol.org> <415d1cca-f32c-624e-a4be-9aadcf8a0f17@dancol.org> <83inujbpek.fsf@gnu.org> <20160830171222.GA6672@acm.fritz.box> <5857ab7e-e85c-c6ae-ba1a-b1337ae57f2c@dancol.org> <83fupmm9ul.fsf@gnu.org> <67e1e007-c944-b91e-6c4b-b06b51beddc1@dancol.org> Reply-To: Eli Zaretskii NNTP-Posting-Host: blaine.gmane.org X-Trace: blaine.gmane.org 1472580086 5658 195.159.176.226 (30 Aug 2016 18:01:26 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 30 Aug 2016 18:01:26 +0000 (UTC) Cc: acm@muc.de, monnier@iro.umontreal.ca, emacs-devel@gnu.org To: Daniel Colascione Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Tue Aug 30 20:01:18 2016 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1benLU-0000Ix-Rg for ged-emacs-devel@m.gmane.org; Tue, 30 Aug 2016 20:01:12 +0200 Original-Received: from localhost ([::1]:50571 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1benLS-0007fI-Ir for ged-emacs-devel@m.gmane.org; Tue, 30 Aug 2016 14:01:10 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:59853) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1benKz-0007Si-DS for emacs-devel@gnu.org; Tue, 30 Aug 2016 14:00:42 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1benKv-0001W8-3V for emacs-devel@gnu.org; Tue, 30 Aug 2016 14:00:40 -0400 Original-Received: from fencepost.gnu.org ([2001:4830:134:3::e]:58544) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1benKu-0001Vq-JF; Tue, 30 Aug 2016 14:00:37 -0400 Original-Received: from 84.94.185.246.cable.012.net.il ([84.94.185.246]:1995 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_128_CBC_SHA1:128) (Exim 4.82) (envelope-from ) id 1benKq-00066I-ID; Tue, 30 Aug 2016 14:00:35 -0400 In-reply-to: <67e1e007-c944-b91e-6c4b-b06b51beddc1@dancol.org> (message from Daniel Colascione on Tue, 30 Aug 2016 10:46:44 -0700) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 2001:4830:134:3::e X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.21 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.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.org gmane.emacs.devel:206985 Archived-At: > Cc: acm@muc.de, monnier@iro.umontreal.ca, emacs-devel@gnu.org > From: Daniel Colascione > Date: Tue, 30 Aug 2016 10:46:44 -0700 > > >> - Do @emph{not} expect the before-change hooks and the after-change > >> -hooks be called in balanced pairs around each buffer change. Also > >> -don't expect the before-change hooks to be called for every chunk of > >> -text Emacs is about to delete. These hooks are provided on the > >> -assumption that Lisp programs will use either before- or the > >> -after-change hooks, but not both, and the boundaries of the region > >> -where the changes happen might include more than just the actual > >> -changed text, or even lump together several changes done piecemeal. > >> + Do @emph{not} expect the before-change hooks and the after-change > >> +hooks be called in balanced pairs around each buffer change. > >> +The before-change-functions region is a conservative bound on the zero > >> +or more fine-grained changes to follow. Emacs informs user code about > >> +the actual changes to the buffer through calls to > >> +after-change-functions; these fine-grained changes will always fall > >> +inside the broad change region Emacs describes by calling > >> +before-change-functions. > > > > You removed the part about text deletion, which is not specific to > > revert-buffer, so that information is now lost. I don't want to lose > > it. > > The text deletion part is a real and serious bug. As Stefan points out, > it makes it impossible to use b-c-f to invalidate caches. You misunderstand what Stefan says. He says not calling the before-change hook _at_all_ is a bug. Not calling it for every chunk of deleted text is not necessarily a bug, if there's a previous less fine-grained call to the hook. And that's what the text above conveys: that note every chunk to be deleted will have its own call to a hook. > > Other than that, I don't see how your text is more accurate, it's just > > a different wording dancing around the same issues trying to side-step > > them by replacing one vague description by another. > > My proposed description highlights how the b-c-f region contains the > a-c-f regions. I understand that you believe that the existing > documentation communicates this fact, but I strongly disagree. The > relationship between the b-c-f region and the a-c-f regions needs to be > spelled out explicitly. They cannot be spelled out explicitly without going into a lot more internal details that are inappropriate for the Lisp-level manual. > > If all you want is to remove this part: > > > > These hooks are provided on the assumption that Lisp programs will > > use either before- or the after-change hooks, but not both > > > > then I don't necessarily mind, although I do believe it is true, and > > the readers should be aware of that. > > I strongly disagree. b-c-f is a perfectly good way to invalidate caches. So the readers need to know they cannot rely on that.