git@vger.kernel.org mailing list mirror (one of many)
 help / Atom feed
From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: phillip.wood@dunelm.org.uk
Cc: Igor Djordjevic <igor.d.djordjevic@gmail.com>,
	Sergey Organov <sorganov@gmail.com>,
	Git mailing list <git@vger.kernel.org>,
	Jacob Keller <jacob.keller@gmail.com>,
	Johannes Sixt <j6t@kdbg.org>, Junio C Hamano <gitster@pobox.com>
Subject: Re: [RFC] Rebasing merges: a jorney to the ultimate solution (Road Clear)
Date: Tue, 6 Mar 2018 19:12:10 +0100 (STD)
Message-ID: <nycvar.QRO.7.76.6.1803061829460.20700@ZVAVAG-6OXH6DA.rhebcr.pbec.zvpebfbsg.pbz> (raw)
In-Reply-To: <1c912980-8ce8-6281-fa99-040a5e3e1103@talktalk.net>

Hi Phillip,

On Tue, 6 Mar 2018, Phillip Wood wrote:

> On 03/03/18 00:29, Igor Djordjevic wrote:
> > 
> > On 02/03/2018 12:31, Phillip Wood wrote:
> >>
> >>> Thinking about it overnight, I now suspect that original proposal
> >>> had a mistake in the final merge step. I think that what you did is
> >>> a way to fix it, and I want to try to figure what exactly was wrong
> >>> in the original proposal and to find simpler way of doing it right.
> >>>
> >>> The likely solution is to use original UM as a merge-base for final
> >>> 3-way merge of U1' and U2', but I'm not sure yet. Sounds pretty
> >>> natural though, as that's exactly UM from which both U1' and U2'
> >>> have diverged due to rebasing and other history editing.
> >>
> >> Hi Sergey, I've been following this discussion from the sidelines,
> >> though I haven't had time to study all the posts in this thread in
> >> detail. I wonder if it would be helpful to think of rebasing a merge
> >> as merging the changes in the parents due to the rebase back into the
> >> original merge. So for a merge M with parents A B C that are rebased
> >> to A' B' C' the rebased merge M' would be constructed by (ignoring
> >> shell quoting issues)
> >>
> >> git checkout --detach M
> >> git merge-recursive A -- M A'
> >> tree=$(git write-tree)
> >> git merge-recursive B -- $tree B'
> >> tree=$(git write-tree)
> >> git merge-recursive C -- $tree C'
> >> tree=$(git write-tree)
> >> M'=$(git log --pretty=%B -1 M | git commit-tree -pA' -pB' -pC')
> >>
> >> This should pull in all the changes from the parents while preserving
> >> any evil conflict resolution in the original merge. It superficially
> >> reminds me of incremental merging [1] but it's so long since I looked at
> >> that I'm not sure if there are any significant similarities.
> >>
> >> [1] https://github.com/mhagger/git-imerge
> > 
> > Interesting, from quick test[3], this seems to produce the same 
> > result as that other test I previously provided[2], where temporary 
> > commits U1' and U2' are finally merged with original M as a base :)
> > 
> > Just that this looks like even more straight-forward approach...?
> > 
> > The only thing I wonder of here is how would we check if the 
> > "rebased" merge M' was "clean", or should we stop for user amendment? 
> > With that other approach Sergey described, we have U1'==U2' to test with.
> 
> I think (though I haven't rigorously proved to myself) that in the
> absence of conflicts this scheme has well defined semantics (the merges
> can be commuted), so the result should be predicable from the users
> point of view so maybe it could just offer an option to stop.

I am not so sure that the result is independent of the order of the
merges. In other words, I am not necessarily certain that it is impossible
to concoct A,A',B,B' commits where merging B'/B before A'/A has a
different result than merging A'/A before B'/B.

Remember, when constructing counter-examples to hypotheses, those
counter-examples do not really *have* to make sense on their own. For
example, A' could introduce *completely different* changes from A, and the
same is true for B' and B.

I could imagine, for example, that using a ton of consecutive empty lines,
and using patches that insert something into these empty lines (and are
thusly inherently ambiguous when said set of empty lines has changed),
could even introduce a merge conflict in one order, but no conflict in the
other.

Even so, I think that merging in the order of the parents makes the most
sense, and that using that strategy makes sense, too, because you really
have to try hard to make it fail.

Ciao,
Dscho

  parent reply index

Thread overview: 173+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-16 13:08 Sergey Organov
2018-02-18  4:16 ` Jacob Keller
2018-02-19  5:28   ` Sergey Organov
2018-02-19 23:44 ` Igor Djordjevic
2018-02-20 12:42   ` Sergey Organov
2018-02-27  0:07   ` Johannes Schindelin
2018-02-27  5:01     ` Sergey Organov
2018-02-27  5:30     ` Jacob Keller
2018-02-27 16:21       ` Johannes Schindelin
2018-02-27 18:55         ` Igor Djordjevic
2018-02-27 19:59           ` Igor Djordjevic
2018-02-27 23:27             ` Johannes Schindelin
2018-02-28  2:12               ` Igor Djordjevic
2018-02-28  4:35                 ` Igor Djordjevic
2018-02-28  6:14                   ` Sergey Organov
2018-02-28 20:53                     ` Igor Djordjevic
2018-02-28  5:44               ` Sergey Organov
2018-02-28 19:42                 ` Igor Djordjevic
2018-02-27 23:40             ` Igor Djordjevic
2018-02-28  0:10               ` Junio C Hamano
2018-02-28  2:35                 ` Igor Djordjevic
2018-02-28  5:27                 ` Sergey Organov
2018-02-28  0:36               ` Jacob Keller
2018-02-28  1:33                 ` Igor Djordjevic
2018-02-28  1:43                   ` Igor Djordjevic
2018-02-28  5:21                   ` Sergey Organov
2018-02-28 19:09                     ` Igor Djordjevic
2018-03-01  5:27                       ` Sergey Organov
2018-02-28  5:19               ` Sergey Organov
2018-02-28 20:25                 ` Igor Djordjevic
2018-02-28 22:17                   ` Igor Djordjevic
2018-03-01  5:19                     ` Sergey Organov
2018-03-01  5:39                   ` Sergey Organov
2018-03-02  1:16                     ` Igor Djordjevic
2018-03-02  5:40                       ` Sergey Organov
2018-03-02 17:45                         ` Igor Djordjevic
2018-03-02 11:17                       ` [RFC] Rebasing merges: a jorney to the ultimate solution(RoadClear) Phillip Wood
2018-03-02 12:36                         ` Phillip Wood
2018-03-02 16:02                           ` Jacob Keller
2018-03-02 23:33                             ` Igor Djordjevic
2018-03-06 10:36                               ` Phillip Wood
2018-03-06 18:12                                 ` Johannes Schindelin
2018-03-06 19:43                                   ` Igor Djordjevic
2018-03-07  7:26                                     ` Johannes Schindelin
2018-03-08 11:20                                       ` Phillip Wood
2018-03-08 12:16                                         ` Phillip Wood
2018-03-08 16:05                                           ` Igor Djordjevic
2018-03-11 12:00                                             ` Johannes Schindelin
2018-03-11 16:33                                               ` Igor Djordjevic
2018-03-12 10:37                                                 ` Johannes Schindelin
2018-03-12 12:56                                                   ` Sergey Organov
2018-03-13  0:01                                                     ` Igor Djordjevic
2018-03-26 12:03                                                       ` Johannes Schindelin
2018-03-27  5:08                                                         ` Sergey Organov
2018-03-27 13:35                                                           ` Johannes Schindelin
2018-04-02  6:07                                                             ` Sergey Organov
2018-03-12 23:54                                                   ` Igor Djordjevic
2018-03-13  6:25                                                     ` Sergey Organov
2018-03-08 15:56                                         ` Igor Djordjevic
2018-03-11 12:08                                           ` Johannes Schindelin
2018-03-11 17:34                                             ` Igor Djordjevic
2018-03-12 10:46                                               ` Johannes Schindelin
2018-03-13  0:16                                                 ` Igor Djordjevic
2018-03-26 13:07                                                   ` Johannes Schindelin
2018-03-27  5:51                                                     ` Sergey Organov
2018-03-27 13:49                                                       ` Johannes Schindelin
2018-03-28  5:57                                                         ` Sergey Organov
2018-03-30 13:41                                                           ` Johannes Schindelin
2018-03-30 16:36                                                             ` Sergey Organov
2018-03-28  5:57                                                         ` Sergey Organov
     [not found]                                                           ` <CA+P7+xoDQ2mzhxeZPFhaY+TaSoKkQm=5AtoduHH06-VggOJ2jg@mail.gmail.com>
2018-03-28 11:29                                                             ` Sergey Organov
     [not found]                                                               ` <CA+P7+xo19mHrWz9Fy-ifgCcVJM2xwzcLj7F2NvFe2LwGbaJiDQ@mail.gmail.com>
2018-03-29  5:53                                                                 ` Sergey Organov
2018-03-30 10:38                                                                   ` Johannes Schindelin
2018-03-30 12:36                                                                     ` Sergey Organov
2018-03-30 13:33                                                                       ` Johannes Schindelin
2018-03-30 15:13                                                                         ` Sergey Organov
2018-03-28 12:10                                                             ` Sergey Organov
2018-03-08 16:07                                         ` Jacob Keller
2018-03-11 12:11                                           ` Johannes Schindelin
2018-03-11 17:46                                             ` Igor Djordjevic
2018-03-08 15:16                                       ` Igor Djordjevic
2018-03-08 16:21                                         ` Igor Djordjevic
2018-03-11 12:22                                           ` Johannes Schindelin
2018-03-14 14:24                                         ` Sergey Organov
2018-03-14 23:11                                           ` Igor Djordjevic
2018-03-15  6:00                                             ` Sergey Organov
2018-03-15 21:51                                               ` Igor Djordjevic
2018-03-17  2:08                                             ` Igor Djordjevic
2018-03-19  5:44                                               ` Sergey Organov
2018-03-19 21:35                                                 ` Igor Djordjevic
2018-03-20 14:43                                                   ` Sergey Organov
2018-03-26 13:47                                           ` Johannes Schindelin
2018-03-06 23:24                                   ` Junio C Hamano
2018-03-07  7:09                                     ` Johannes Schindelin
2018-03-07 18:20                                       ` Junio C Hamano
2018-03-08  7:03                                         ` Johannes Schindelin
2018-03-08  8:11                                           ` Junio C Hamano
2018-03-09 17:09                                             ` Johannes Schindelin
2018-03-02 16:00                         ` Jacob Keller
2018-03-02 18:14                           ` Igor Djordjevic
2018-03-03 17:29                             ` Igor Djordjevic
2018-03-05  5:35                               ` Sergey Organov
2018-03-02 11:31                     ` [RFC] Rebasing merges: a jorney to the ultimate solution (Road Clear) Phillip Wood
2018-03-03  0:29                       ` Igor Djordjevic
2018-03-05  5:00                         ` Sergey Organov
2018-03-06 10:52                           ` Phillip Wood
2018-03-06 16:56                             ` Junio C Hamano
2018-03-08  7:05                               ` Johannes Schindelin
2018-03-08  8:18                                 ` Junio C Hamano
2018-03-11 11:56                                   ` Johannes Schindelin
2018-03-13 18:24                                     ` Junio C Hamano
2018-03-26 13:17                                       ` Johannes Schindelin
2018-03-05 17:29                         ` Johannes Schindelin
2018-03-06 23:21                           ` Igor Djordjevic
2018-03-07  7:04                             ` Johannes Schindelin
2018-03-06 10:45                         ` Phillip Wood
2018-03-06 11:45                           ` Sergey Organov
2018-03-08 16:30                             ` Igor Djordjevic
2018-03-06 18:12                           ` Johannes Schindelin [this message]
2018-03-07  5:08                             ` Sergey Organov
2018-03-07  6:58                               ` Johannes Schindelin
2018-03-07 14:34                                 ` Sergey Organov
2018-03-08  6:45                                   ` Johannes Schindelin
2018-03-12 12:31                                     ` Sergey Organov
2018-03-26 11:37                                       ` Johannes Schindelin
2018-03-27  5:11                                         ` Sergey Organov
2018-03-27 12:55                                           ` Johannes Schindelin
2018-03-28  4:32                                             ` Sergey Organov
2018-03-08 11:08                             ` Phillip Wood
2018-03-05 17:52                       ` Johannes Schindelin
2018-03-13 16:10                       ` Sergey Organov
2018-03-14  1:12                         ` Igor Djordjevic
2018-03-14  7:21                           ` Sergey Organov
2018-03-15  0:09                             ` Igor Djordjevic
2018-03-15  7:52                               ` Sergey Organov
2018-03-15 23:08                                 ` Igor Djordjevic
2018-03-16  7:31                                   ` Sergey Organov
2018-03-17  3:04                                     ` Igor Djordjevic
2018-03-19  6:01                                       ` Sergey Organov
2018-03-26 14:11                                   ` Johannes Schindelin
2018-02-28  0:29         ` Jacob Keller
2018-02-27 11:57     ` Sergey Organov
2018-02-27 18:14       ` Junio C Hamano
2018-02-28  0:30         ` Jacob Keller
2018-02-28  5:54           ` Sergey Organov
2018-02-28  4:53         ` Sergey Organov
2018-03-06 13:26 ` [RFC v2] " Sergey Organov
2018-03-07  6:46   ` Johannes Schindelin
2018-03-07 13:27     ` Sergey Organov
2018-03-07 14:08       ` Johannes Schindelin
2018-03-07 15:16         ` Sergey Organov
2018-03-08  7:01           ` Johannes Schindelin
2018-03-12 12:42             ` Sergey Organov
2018-03-26 11:50               ` Johannes Schindelin
2018-03-08 19:58         ` Igor Djordjevic
2018-03-08 20:27           ` Igor Djordjevic
2018-03-08 22:05             ` Igor Djordjevic
2018-03-08 23:31               ` Igor Djordjevic
2018-03-11 15:47                 ` Johannes Schindelin
2018-03-11 20:53                   ` Igor Djordjevic
2018-03-12 10:20                     ` Johannes Schindelin
2018-03-12 13:49                       ` Sergey Organov
2018-03-26 12:44                         ` Johannes Schindelin
2018-03-27  5:32                           ` Sergey Organov
2018-03-13  0:29                       ` Igor Djordjevic
2018-03-26 13:58                         ` Johannes Schindelin
2018-03-12 13:07                     ` Sergey Organov
2018-03-11 15:40           ` Johannes Schindelin
2018-03-11 22:04             ` Igor Djordjevic
2018-03-12 12:05               ` Sergey Organov
2018-03-26 11:33                 ` Johannes Schindelin
2018-03-27  5:34                   ` Sergey Organov
2018-03-12 22:41               ` Igor Djordjevic

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: http://vger.kernel.org/majordomo-info.html

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=nycvar.QRO.7.76.6.1803061829460.20700@ZVAVAG-6OXH6DA.rhebcr.pbec.zvpebfbsg.pbz \
    --to=johannes.schindelin@gmx.de \
    --cc=git@vger.kernel.org \
    --cc=gitster@pobox.com \
    --cc=igor.d.djordjevic@gmail.com \
    --cc=j6t@kdbg.org \
    --cc=jacob.keller@gmail.com \
    --cc=phillip.wood@dunelm.org.uk \
    --cc=sorganov@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

git@vger.kernel.org mailing list mirror (one of many)

Archives are clonable:
	git clone --mirror https://public-inbox.org/git
	git clone --mirror http://ou63pmih66umazou.onion/git
	git clone --mirror http://czquwvybam4bgbro.onion/git
	git clone --mirror http://hjrcffqmbrq6wope.onion/git

Newsgroups are available over NNTP:
	nntp://news.public-inbox.org/inbox.comp.version-control.git
	nntp://ou63pmih66umazou.onion/inbox.comp.version-control.git
	nntp://czquwvybam4bgbro.onion/inbox.comp.version-control.git
	nntp://hjrcffqmbrq6wope.onion/inbox.comp.version-control.git
	nntp://news.gmane.org/gmane.comp.version-control.git

 note: .onion URLs require Tor: https://www.torproject.org/
       or Tor2web: https://www.tor2web.org/

AGPL code for this site: git clone https://public-inbox.org/ public-inbox