From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: "Eric S. Raymond" Newsgroups: gmane.emacs.devel Subject: Re: Removing rollback from VC mode - request for comment Date: Thu, 11 Dec 2014 07:51:45 -0500 Organization: Eric Conspiracy Secret Labs Message-ID: <20141211125145.GB25499@thyrsus.com> References: <20141211092138.6D5F6C008E@snark.thyrsus.com> <874mt2iksu.fsf@fencepost.gnu.org> <87fvcm8jf0.fsf@zigzag.favinet> Reply-To: esr@thyrsus.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="ReaqsoxgOBHFXBhH" X-Trace: ger.gmane.org 1418302359 1268 80.91.229.3 (11 Dec 2014 12:52:39 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 11 Dec 2014 12:52:39 +0000 (UTC) To: emacs-devel@gnu.org Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Thu Dec 11 13:52:30 2014 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Xz3EM-0002UA-71 for ged-emacs-devel@m.gmane.org; Thu, 11 Dec 2014 13:52:30 +0100 Original-Received: from localhost ([::1]:50765 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xz3EL-0005Pf-JO for ged-emacs-devel@m.gmane.org; Thu, 11 Dec 2014 07:52:29 -0500 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:53123) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xz3EE-0005Oi-Na for emacs-devel@gnu.org; Thu, 11 Dec 2014 07:52:26 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xz3EA-0001D1-G1 for emacs-devel@gnu.org; Thu, 11 Dec 2014 07:52:22 -0500 Original-Received: from static-71-162-243-5.phlapa.fios.verizon.net ([71.162.243.5]:37124 helo=snark.thyrsus.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xz3EA-0001Cu-BC for emacs-devel@gnu.org; Thu, 11 Dec 2014 07:52:18 -0500 Original-Received: by snark.thyrsus.com (Postfix, from userid 1000) id 64CD2C008E; Thu, 11 Dec 2014 07:51:45 -0500 (EST) Content-Disposition: inline In-Reply-To: <87fvcm8jf0.fsf@zigzag.favinet> X-Eric-Conspiracy: There is no conspiracy User-Agent: Mutt/1.5.21 (2010-09-15) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 71.162.243.5 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.14 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-bounces+ged-emacs-devel=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.devel:179749 Archived-At: --ReaqsoxgOBHFXBhH Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Thien-Thi Nguyen : > So, i think "rollback" as a concept is actually not far > enough. Being able to select arbitrary commits to drop (like > =E2=80=98d=E2=80=99 and =E2=80=98x=E2=80=99 in Dired) is what i'd like to= see, in its stead. RCCS and SCCS can do this, in theory. But I've never trusted that feature. The obvious problem is that if you delete an earlier delta you may well change the preconditions for a later one, so it will have unexpected effects. =20 I know how RCS's delta representation works; it is *not* smart enough to fully compensate. And no wonder. General patch composition is a hard enough problem that it scuttled Darcs thirty years later! In other VCSes it would be difficult to even attempt this. In view of the known problems, I recommend staying way the hell away from it unless and until David Roundy successfully proves a correct composition algorithm and we integrate it into Emacs somehow. --=20 Eric S. Raymond --ReaqsoxgOBHFXBhH Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iD8DBQFUiZNhrfUW04Qh8RwRAiOEAKCprFtpsWIwMVmzcUNDIi88u3kg6wCgnr4W TL2j73W8lZ1MGV0uKsqxoWo= =F8er -----END PGP SIGNATURE----- --ReaqsoxgOBHFXBhH--