Git Mailing List Archive on lore.kernel.org
 help / color / Atom feed
From: Eugeniu Rosca <roscaeugeniu@gmail.com>
To: Elijah Newren <newren@gmail.com>
Cc: "Eugeniu Rosca" <erosca@de.adit-jv.com>,
	"SZEDER Gábor" <szeder.dev@gmail.com>,
	"Junio C Hamano" <gitster@pobox.com>, "Jeff King" <peff@peff.net>,
	"Ævar Arnfjörð" <avarab@gmail.com>,
	"Git Mailing List" <git@vger.kernel.org>,
	"Eugeniu Rosca" <roscaeugeniu@gmail.com>
Subject: Re: Unreliable 'git rebase --onto'
Date: Fri, 10 Jan 2020 01:06:03 +0100
Message-ID: <20200110000603.GA19040@erosca> (raw)
In-Reply-To: <CABPp-BFiDNb18m8geTCxKLXg0fOd0DS1dWRVWCfnTG0suwGRHg@mail.gmail.com>

Hi Elijah,

On Thu, Jan 09, 2020 at 10:05:52AM -0800, Elijah Newren wrote:
> On Thu, Jan 9, 2020 at 2:53 AM Eugeniu Rosca <erosca@de.adit-jv.com> wrote:
> > Some years ago I was hit by 'git merge' producing slightly different
> > results compared to 'git rebase --onto' and 'git cherry-pick A..B'
> > (maybe I can come up with a reproduction scenario for that too).
> 
> If you can, I'd be interested to see it and take a look.  I'd normally
> assume it was just some case where A..B included "evil" merge commits
> (merge commits that made additional changes not part of the actual
> merging) since rebasing or cherry-picking such a range would exclude
> the merge commits and thus drop those changes -- but you identified a
> real bug with the default rebase backend so I'm interested to see if
> you happen to have more bugs I should know about.

Here is a _simplified_ scenario to get a totally unexpected result from
'git merge' (initially reproduced years ago, but still happening on
2.25.0.rc2):

   ## Preparation
0. git --version
   git version 2.25.0.rc2
1. git clone https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
2. git remote add linux-stable https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
3. git fetch linux-stable

   # Reproduction
4. git checkout f7a8e38f07a1
5. git merge --no-edit e18da11fc0f959
   ## Merge v4.4.3 commit
   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e18da11fc0f959
   which is a linux-stable backport of vanilla v4.5-rc1 commit
   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f7a8e38f07a1
   the latter being checked out at step 4.

6. git show HEAD
   ## Inspect the _automatic_ conflict resolution performed by git in
   drivers/mtd/nand/nand_base.c. Git decided to integrate e18da11fc0f959
   alongside f7a8e38f07a1, while essentially they are the same commit.
   We end up with two times commit f7a8e38f07a1.

What do you think about that?

> Unfortunately, you should note that git-2.25 is going to have the same
> bug you reported; there are still some loose ends with my series to
> make -m the default, and the 2.25 release is expected within a few
> days, so my change of default won't happen until 2.26.  (That series
> would have needed to be completed several weeks ago for it to go into
> 2.25).

Thanks for this piece of information and for the time/effort spent!

-- 
Best Regards,
Eugeniu

  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-08 21:43 Eugeniu Rosca
2020-01-08 22:35 ` SZEDER Gábor
2020-01-09  0:55   ` Elijah Newren
2020-01-09 15:03     ` SZEDER Gábor
2020-01-09 17:53       ` Elijah Newren
2020-01-21 19:18       ` [PATCH v1] rebase -i: stop checking out the tip of the branch to rebase Alban Gruin
2020-01-21 20:07         ` Elijah Newren
2020-01-22 20:24         ` Junio C Hamano
2020-01-22 20:47         ` Junio C Hamano
2020-01-24 14:45           ` Alban Gruin
2020-01-24 14:45         ` [PATCH v2] " Alban Gruin
2020-01-24 14:55           ` Alban Gruin
2020-01-24 18:12             ` Junio C Hamano
2020-01-24 15:05           ` [PATCH v3] " Alban Gruin
2020-01-24 18:30             ` Junio C Hamano
2020-02-05 14:31             ` Johannes Schindelin
2020-01-24 17:11           ` [PATCH v2] " Andrei Rybak
2020-01-09 11:13   ` Unreliable 'git rebase --onto' Eugeniu Rosca
     [not found] ` <CABPp-BHsyMOz+hi7EYoAnAWfzms7FRfwqCoarnu8H+vyDoN6SQ@mail.gmail.com>
2020-01-09 10:53   ` Eugeniu Rosca
2020-01-09 18:05     ` Elijah Newren
2020-01-10  0:06       ` Eugeniu Rosca [this message]
2020-01-10  2:35         ` Elijah Newren

Reply instructions:

You may reply publicly 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

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

  git send-email \
    --in-reply-to=20200110000603.GA19040@erosca \
    --to=roscaeugeniu@gmail.com \
    --cc=avarab@gmail.com \
    --cc=erosca@de.adit-jv.com \
    --cc=git@vger.kernel.org \
    --cc=gitster@pobox.com \
    --cc=newren@gmail.com \
    --cc=peff@peff.net \
    --cc=szeder.dev@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 Mailing List Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/git/0 git/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 git git/ https://lore.kernel.org/git \
		git@vger.kernel.org
	public-inbox-index git

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.git


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