From mboxrd@z Thu Jan 1 00:00:00 1970 From: Junio C Hamano Subject: Re: [PATCH] Detached HEAD (experimental) Date: Tue, 09 Jan 2007 14:37:35 -0800 Message-ID: <7vy7obj07k.fsf@assigned-by-dhcp.cox.net> References: <7vac11yirf.fsf@assigned-by-dhcp.cox.net> <87ps9xgkjo.wl%cworth@cworth.org> <7virfprquo.fsf@assigned-by-dhcp.cox.net> <87odphgfzz.wl%cworth@cworth.org> <7vbql9ydd7.fsf@assigned-by-dhcp.cox.net> <20070108131735.GA2647@coredump.intra.peff.net> <7vzm8tt5kf.fsf@assigned-by-dhcp.cox.net> <20070109142130.GA10633@coredump.intra.peff.net> <7virffkick.fsf@assigned-by-dhcp.cox.net> <20070109213117.GB25012@fieldses.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jeff King , git@vger.kernel.org X-From: git-owner@vger.kernel.org Tue Jan 09 23:37:48 2007 Return-path: Envelope-to: gcvg-git@gmane.org Received: from vger.kernel.org ([209.132.176.167]) by lo.gmane.org with esmtp (Exim 4.50) id 1H4PbB-0005NA-4U for gcvg-git@gmane.org; Tue, 09 Jan 2007 23:37:41 +0100 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932432AbXAIWhi (ORCPT ); Tue, 9 Jan 2007 17:37:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932463AbXAIWhi (ORCPT ); Tue, 9 Jan 2007 17:37:38 -0500 Received: from fed1rmmtao01.cox.net ([68.230.241.38]:63516 "EHLO fed1rmmtao01.cox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932432AbXAIWhh (ORCPT ); Tue, 9 Jan 2007 17:37:37 -0500 Received: from fed1rmimpo01.cox.net ([70.169.32.71]) by fed1rmmtao01.cox.net (InterMail vM.6.01.06.03 201-2131-130-104-20060516) with ESMTP id <20070109223736.OCIL9173.fed1rmmtao01.cox.net@fed1rmimpo01.cox.net>; Tue, 9 Jan 2007 17:37:36 -0500 Received: from assigned-by-dhcp.cox.net ([68.5.247.80]) by fed1rmimpo01.cox.net with bizsmtp id 9Acl1W00Q1kojtg0000000; Tue, 09 Jan 2007 17:36:46 -0500 To: "J. Bruce Fields" In-Reply-To: <20070109213117.GB25012@fieldses.org> (J. Bruce Fields's message of "Tue, 9 Jan 2007 16:31:17 -0500") User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) Sender: git-owner@vger.kernel.org Precedence: bulk X-Mailing-List: git@vger.kernel.org Archived-At: "J. Bruce Fields" writes: > On Tue, Jan 09, 2007 at 01:20:27PM -0800, Junio C Hamano wrote: >> Jeff King writes: >> >> > For example, with what's in next now, I can do this: >> > >> > git checkout v1.4.0 >> > hack hack hack >> > git commit -m -a 'some changes which will never be seen again' >> > git checkout v1.2.0 >> > >> > I thought the _point_ of the safety valve was not to lose those changes. >> >> Fair enough. >> >> We could always do the check upon "git checkout" from a detached >> HEAD state, whether it takes you back on some existing branch or >> leaves your HEAD still detached. > > Stupid question: why can't checkout do something like this? > > if we're currently not on a branch, fail if .git/PREV > doesn't point to the same commit as .git/HEAD. > > if we're checking out a non-branch, store its SHA1 into > .git/PREV. I do not want to think about the consequences of adding more cruft under .git/ directory. For example, should PREV be noticed by fsck and prune? What should various forms of 'git-reset' do with it? How does it interact with 'git-bisect'? Being able to test merge or even make commits without being on a branch is vastly useful. It might or might not lead to anywhere even after you make a handful commits -- and I would imagine that it would be very handy to be able to be lazy and not having to decide if it is worth a new branch. But that may be just my imagination; I generally prefer any feature that allows me to defer decision over something that makes me decide early. If Carl wants to do a patch to teach 'git-commit' (and all other things that can create commits) not to do things from working in a detached HEAD, I would probably not opposed to it too much, but I am fairly certain that I won't be coding it myself. It's tempting to forget about this whole "safety" business. Because we allow "reset --hard" and other forms of operations that can lose history if they were done while on a branch, only giving the safety to "git checkout" feels somewhat silly. And the primary motive for detached HEAD as I understand it is for sightseeing, and not allowing "reset --hard" to jump around is just plain silly. That is, after: git checkout v1.4.0 you are not on any branch, and we would still allow git reset --hard v1.2.0 which is exactly the same as: git checkout v1.2.0 You can still say: git checkout master and we do not even check. Which makes the "merge-base --check-ancestry" stuff I did last night pretty much unnecessary, but that's Ok. It will find other uses.