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From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: Elijah Newren <newren@gmail.com>
Cc: "Junio C Hamano" <gitster@pobox.com>,
	"Ævar Arnfjörð" <avarab@gmail.com>,
	corrmage@gmail.com, "Git Mailing List" <git@vger.kernel.org>,
	"Stefan Beller" <sbeller@google.com>
Subject: Re: A rebase regression in Git 2.18.0
Date: Fri, 31 Aug 2018 12:11:56 +0200 (DST)
Message-ID: <nycvar.QRO.7.76.6.1808311158540.71@tvgsbejvaqbjf.bet> (raw)
In-Reply-To: <CABPp-BH8-1YQ49aaM-dXkT9ukKO92MF-FZ2kLwd=KHe4TVbjqQ@mail.gmail.com>

Hi Elijah,

On Thu, 30 Aug 2018, Elijah Newren wrote:

> On Tue, Aug 28, 2018 at 9:58 AM Junio C Hamano <gitster@pobox.com> wrote:
> >
> > Elijah Newren <newren@gmail.com> writes:
> >
> > >   - Add a flag to turn off directory rename detection, and set the
> > > flag for every call from am.c in order to avoid problems like this.
> >
> > I'd say this is the only practical solution, before you deprecate
> > the "pipe format-patch output to am -3" style of "git rebase" (and
> > optionally replace with something else).
> 
> I posted a patch a while back to add an --am flag to "git rebase",
> make "--am" be implied by options which are still am-specific
> (--whitespace, --committer-date-is-author-date, and -C), and change
> --merge to be the default.

Didn't you also post a patch to fold --merge into the --interactive
backend? What's your current state of thinking about this?

As to switching from --am as the default: I still think that --am has
serious speed advantages over --merge (or for that matter, --interactive).
I have no numbers to back that up, though, and I am currently really busy
with working on the CI, so I won't be able to measure these numbers,
either...

Also please note: I converted the `am` backend to pure C (it is waiting at
https://github.com/gitgitgadget/git/pull/24, to be submitted after the
v2.19.0 RC period). Switching to `--merge` as the default would force me
to convert that backend, too ;-)

> I'll post it as an RFC again after the various rebase-rewrite series
> have settled and merged down...along with my other rebase cleanups
> that I was waiting on to avoid conflicts with GSoC stuff.

Thanks for waiting! Please note that I am interested, yet I will be on
vacation for a couple of weeks in September. Don't let that stop you,
though!

> > The whole point of "am -3" is to do _better_ than just "patch" with
> > minimum amount of information available on the pre- and post- image
> > blobs, without knowing the remainder of the tree that the patch did
> > not touch.  It is not surprising that the heuristics that look at
> > the unchanging part of the tree to infer renames that may or may not
> > exist guesses incorrectly, either with false positive or negative.
> > In the context of "rebase", we always have all the trees that are
> > involved.  We should be able to do better than "am -3".

Right. I think that Elijah's right, and --merge is that "do better"
solution.

Ciao,
Dscho

  reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-28 12:27 Nikolay Kasyanov
2018-08-28 13:17 ` Ævar Arnfjörð Bjarmason
2018-08-28 13:33   ` Johannes Schindelin
2018-08-28 13:46     ` Nikolay Kasyanov
2018-08-28 15:35     ` Elijah Newren
2018-08-28 16:58       ` Junio C Hamano
2018-08-29  7:06         ` [PATCH 0/3] Turn off directory rename detection in am -3 Elijah Newren
2018-08-29  7:06           ` [PATCH 1/3] t3401: add another directory rename testcase for rebase and am Elijah Newren
2018-08-29 22:12             ` Junio C Hamano
2018-08-29 23:47               ` Elijah Newren
2018-08-30 16:01                 ` Junio C Hamano
2018-08-30 16:26                   ` Elijah Newren
2018-08-29  7:06           ` [PATCH 2/3] merge-recursive: add ability to turn off directory rename detection Elijah Newren
2018-08-29 12:54             ` Johannes Schindelin
2018-08-29 23:00               ` Elijah Newren
2018-08-29  7:06           ` [PATCH 3/3] am: avoid directory rename detection when calling recursive merge machinery Elijah Newren
2018-08-29 12:51             ` Johannes Schindelin
2018-08-30 16:41         ` A rebase regression in Git 2.18.0 Elijah Newren
2018-08-31 10:11           ` Johannes Schindelin [this message]
2018-08-31 19:37             ` Elijah Newren

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