Marc Singer <elf@xxxxxxxxx> writes:
[I'm shuffling this part to the top]
> Moreover, it isn't clear to me if git-rebase is better than git-merge.
Merge preserves commit ancestry, so if you are hoping it to
clean up your history, that is not the tool to do it. Both
rebase and cherry-pick are to help you create a cleaner,
alternate history. So none is better than the other. They
serve different purposes.
> On Fri, Mar 24, 2006 at 10:08:09PM -0800, Junio C Hamano wrote:
>> > Junio, is there some magic to restart a rebase after you've fixed up the
>> > conflicts?
>>
>> The modern rebase is essentially git-format-patch piped to
>> git-am (with -3 flag to allow falling back to three-way merge),
>> and all the familiar "the patch did not apply -- what now?"
>> techniques can be employed.
>...
> By modern do you mean newer than 1.2.4? I comprehend what you're
> layin' down here, but I don't know if I need to do something
> different.
By modern, I meant v0.99.9-g7f59dbb.
diff-tree 7f59dbb... (from f9039f3...)
Author: Junio C Hamano <junkio@xxxxxxx>
Date: Mon Nov 14 00:41:53 2005 -0800
Rewrite rebase to use git-format-patch piped to git-am.
The current rebase implementation finds commits in our tree but
not in the upstream tree using git-cherry, and tries to apply
them using git-cherry-pick (i.e. always use 3-way) one by one.
Which is fine, but when some of the changes do not apply
cleanly, it punts, and punts badly.
Suppose you have commits A-B-C-D-E since you forked from the
upstream and submitted the changes for inclusion. You fetch
from upstream head U and find that B has been picked up. You
run git-rebase to update your branch, which tries to apply
changes contained in A-C-D-E, in this order, but replaying of C
fails, because the upstream got changes that touch the same area
from elsewhere.
Now what?
It notes that fact, and goes ahead to apply D and E, and at the
very end tells you to deal with C by hand. Even if you somehow
managed to replay C on top of the result, you would now end up
with ...-B-...-U-A-D-E-C.
Breaking the order between B and others was the conscious
decision made by the upstream, so we would not worry about it,
and even if it were worrisome, it is too late for us to fix now.
What D and E do may well depend on having C applied before them,
which is a problem for us.
This rewrites rebase to use git-format-patch piped to git-am,
and when the patch does not apply, have git-am fall back on
3-way merge. The updated diff/patch pair knows how to apply
trivial binary patches as long as the pre- and post-images are
locally available, so this should work on a repository with
binary files as well.
The primary benefit of this change is that it makes rebase
easier to use when some of the changes do not replay cleanly.
In the "unapplicable patch in the middle" case, this "rebase"
works like this:
- A series of patches in e-mail form is created that records
what A-C-D-E do, and is fed to git-am. This is stored in
.dotest/ directory, just like the case you tried to apply
them from your mailbox. Your branch is rewound to the tip of
upstream U, and the original head is kept in .git/ORIG_HEAD,
so you could "git reset --hard ORIG_HEAD" in case the end
result is really messy.
- Patch A applies cleanly. This could either be a clean patch
application on top of rewound head (i.e. same as upstream
head), or git-am might have internally fell back on 3-way
(i.e. it would have done the same thing as git-cherry-pick).
In either case, a rebased commit A is made on top of U.
- Patch C does not apply. git-am stops here, with conflicts to
be resolved in the working tree. Yet-to-be-applied D and E
are still kept in .dotest/ directory at this point. What the
user does is exactly the same as fixing up unapplicable patch
when running git-am:
- Resolve conflict just like any merge conflicts.
- "git am --resolved --3way" to continue applying the patches.
- This applies the fixed-up patch so by definition it had
better apply. "git am" knows the patch after the fixed-up
one is D and then E; it applies them, and you will get the
changes from A-C-D-E commits on top of U, in this order.
I've been using this without noticing any problem, and as people
may know I do a lot of rebases.
Signed-off-by: Junio C Hamano <junkio@xxxxxxx>
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