From: Jonathan Nieder <jrnieder@gmail.com>
To: Martin von Zweigbergk <martin.von.zweigbergk@gmail.com>
Cc: Marius Storm-Olsen <mstormo@gmail.com>,
git@vger.kernel.org,
Johannes Schindelin <Johannes.Schindelin@gmx.de>
Subject: Re: git rebase -p doesn't understand -X
Date: Wed, 20 Apr 2011 18:40:04 -0500 [thread overview]
Message-ID: <20110420233949.GA10305@elie> (raw)
In-Reply-To: <BANLkTi=sW_J4LGS=XRuLrwYZTgx4GP65PA@mail.gmail.com>
Hi Martin,
Martin von Zweigbergk wrote:
> Interactive rebase uses cherry-pick internally. Jonathan added support
> for -X to that command not too long ago (in commit 67ac1e1, late last
> year), so it should be pretty straight-forward to add support for what
> you want. Maybe I'll do that in a few weeks when I get back from
> vacation.
That would be excellent.
> A related topic is _when_ to use the strategy (and strategy options).
I agree with your analysis. In particular:
> Example:
>
> X
> \
> A---M---B
> /
> ---o---O---P---Q
>
> When the current HEAD is "B", "git rebase -i -p --onto Q O" will yield
>
> X
> \
> ---o---O---P---Q---A'---M'---B'
I have a vague feeling that honoring --strategy and --strategy-option
would be confusing here. The merge used in cherry-picking A does not
have much to do with the merge used to reincorporate changes from X.
Well, that is my intuition, but most of the examples I can think of
lead to the opposite conclusion! If I use -Xrenormalize, because P
changed the line-ending style, then I will want the same option when
merging X on top. Similarly, if I use -Xsubtree=src, because Q moved
all existing files in the source tree under src/, then with luck the
same trick will work when replaying the merge of X.
Luckily there is an exception to prove the intuition ok. If X was the
first parent of M and I am using -Xours to sloppily favor upstream's
decisions when rebasing my history on top of it, using -Xours to favor
choices from X (which is my own) would be just plain wrong. (Phew.)
> C---D
> / \
> A---B---M
> /
> ---o---O---P---Q
>
> which would yield
>
> C'---D'
> / \
> ---o---O---P---Q---A'---B'---M'
Likewise in this case.
> A more advanced solution would be recreate the merge using rerere.
[...]
Here's a vague and probably wrong idea about another way to re-create
merges.
When cherry-picking a patch (A, say), we run a three-way merge, with
A^ as merge base, A as "their" change, and the new parent for A (= Q)
as "our" change.
Maybe the same trick could work for re-creating merges. In your first
example, run a three-way merge with M^ (= A) as merge base, M as
"their" change, and the new parent for M (= A') as "our" change. That
only works in such a straightforward way if only one of M's parents
was rewritten, though. More generally it could be possible to run a
sequence of three-way merges:
base=M^1, theirs=M, ours=(M^1)' => call the result "m_1"
base=M^2, theirs=m_1, ours=(M^2)' => call the result "m_2"
...
At this point it gets ugly enough that just redoing the merge might be
simpler.
The main problem with rerere is that it can make mistakes. In the
long run, I wonder if rebase could learn to take into account
something more explicit like Junio's merge-fix mechanism (see
origin/todo:Reintegrate).
Thanks; that was interesting.
Jonathan
prev parent reply other threads:[~2011-04-20 23:40 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-15 17:21 git rebase -p doesn't understand -X Marius Storm-Olsen
2011-04-19 9:06 ` Martin von Zweigbergk
2011-04-20 23:40 ` Jonathan Nieder [this message]
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