Rebase Question

Hello all! 
 
I’ve used git for a few years now and I
think it is an amazing tool! Thank you for your hard work in
developing/maintaining it! I really appreciate it! 
 
I have a question. Let’s say that my
colleague and I branch off of master and are working. Let’s say I’m 5 commits
ahead of master and my colleague merges in ahead of me. The logical thing in my
mind is to rebase off of master. The difficulty with this is that if I have
merge conflicts that show up on my first commit, I have to resolve that stupid
thing for every subsequent commit. I could squash, but then I loose branch
history, so I don’t really want to do that. I could rebase in interactive mode,
but if I recall, I still need to resolve all the conflicts on every commit
before it squashes. 
 
The solution that I thought of is instead
of resolving conflicts from the bottom up (starting with earliest history),
resolving from the top down (latest to earliest) and resolving the conflict in
the commit it occurred. If that doesn’t work (or I guess it might be the same
as a merge of master into my branch), then couldn’t git at least store the
conflict resolution? 
 
Maybe I’m silly for asking this question,
I just really like rebase because it is so clean and this is my one frustration
with this method. 


Thanks for humoring me 😊 
Andrew Ottaviano 

On Tue, May 11, 2021 at 5:08 PM Andrew Ottaviano [off-list ref] wrote:

Hello all!

I’ve used git for a few years now and I
think it is an amazing tool! Thank you for your hard work in
developing/maintaining it! I really appreciate it!

I have a question. Let’s say that my
colleague and I branch off of master and are working. Let’s say I’m 5 commits
ahead of master and my colleague merges in ahead of me. The logical thing in my
mind is to rebase off of master. The difficulty with this is that if I have
merge conflicts that show up on my first commit, I have to resolve that stupid
thing for every subsequent commit. I could squash, but then I loose branch
history, so I don’t really want to do that. I could rebase in interactive mode,
but if I recall, I still need to resolve all the conflicts on every commit
before it squashes.

The solution that I thought of is instead
of resolving conflicts from the bottom up (starting with earliest history),
resolving from the top down (latest to earliest) and resolving the conflict in
the commit it occurred. If that doesn’t work (or I guess it might be the same
as a merge of master into my branch), then couldn’t git at least store the
conflict resolution?

You might try looking at git imerge for this
https://github.com/mhagger/git-imerge

It resolves conflicts by doing incremental merges, and then you can
have an option to produce the end result of a merge or a rebase.

Maybe I’m silly for asking this question,
I just really like rebase because it is so clean and this is my one frustration
with this method.

It's definitely a potential frustration that can occur during large
rebases like this.

Thanks,
Jake

Thanks for humoring me
Andrew Ottaviano

On Tue, May 11, 2021 at 5:07 PM Andrew Ottaviano [off-list ref] wrote:

Hello all!

I’ve used git for a few years now and I
think it is an amazing tool! Thank you for your hard work in
developing/maintaining it! I really appreciate it!

I have a question. Let’s say that my
colleague and I branch off of master and are working. Let’s say I’m 5 commits
ahead of master and my colleague merges in ahead of me. The logical thing in my
mind is to rebase off of master. The difficulty with this is that if I have
merge conflicts that show up on my first commit, I have to resolve that stupid
thing for every subsequent commit. I could squash, but then I loose branch
history, so I don’t really want to do that. I could rebase in interactive mode,
but if I recall, I still need to resolve all the conflicts on every commit
before it squashes.

Have you investigated git rerere[1] at all? Documentation indicates it
works for rebase as well as merge, so it might be possible to train
that to resolve the conflicts.

[1] https://git-scm.com/docs/git-rerere

(Pardon the re-send; Gmail being trash.)

On Tue, May 11, 2021 at 05:29:03PM -0700, Bryan Turner wrote:

On Tue, May 11, 2021 at 5:07 PM Andrew Ottaviano [off-list ref] wrote:

quoted

Hello all!

I’ve used git for a few years now and I
think it is an amazing tool! Thank you for your hard work in
developing/maintaining it! I really appreciate it!

I have a question. Let’s say that my
colleague and I branch off of master and are working. Let’s say I’m 5 commits
ahead of master and my colleague merges in ahead of me. The logical thing in my
mind is to rebase off of master. The difficulty with this is that if I have
merge conflicts that show up on my first commit, I have to resolve that stupid
thing for every subsequent commit. I could squash, but then I loose branch
history, so I don’t really want to do that. I could rebase in interactive mode,
but if I recall, I still need to resolve all the conflicts on every commit
before it squashes.

Have you investigated git rerere[1] at all? Documentation indicates it
works for rebase as well as merge, so it might be possible to train
that to resolve the conflicts.

I don't think rerere helps here. In a rebase like this, the problem is
that it _isn't_ the same conflict.

Imagine a case like this:

-- >8 --
git init repo
cd repo

# both branches start with just the line "base"
echo base >file
git add file
git commit -m base

# one side adds a new line
git checkout -b newline
echo another >>file
git commit -am 'add a line'

# and the other modifies the first line
git checkout -b other HEAD^
echo one >file
git commit -am one
echo two >file
git commit -am two

# and now we rebase on top of the newline branch
git rebase newline
-- >8 --

Applying the first commit gets this conflict (in diff3 form)

  <<<<<<< ours
  base
  another
  ||||||| base
  base
  =======
  one
  >>>>>>> theirs

After we fix that up to "one\nanother", the second conflict is:

  <<<<<<< ours
  one
  another
  ||||||| base
  one
  =======
  two
  >>>>>>> theirs

Likewise, even if you had done the original merge between branch tips,
you'd have seen yet another conflict:

  <<<<<<< ours
  two
  ||||||| base
  base
  =======
  base
  another
  >>>>>>> theirs

The actual lines changed are the same, but as the nearby context is
continually shifting, we don't consider these to be the "same" conflict.

-Peff

Andrew Ottaviano wrote:

The difficulty with this is that if I have merge conflicts that show
up on my first commit, I have to resolve that stupid thing for every
subsequent commit.

I don't quite understand that. If you have resolved the chunk, then that
chunk is resolved, and the rest of the commits don't have to worry
about that...

Unless they touch *precisely* the same lines as the first commit, in
which case... Yeah, you have to resolve that stupid thing over and over.

The solution that I thought of is instead of resolving conflicts from
the bottom up (starting with earliest history), resolving from the top
down (latest to earliest) and resolving the conflict in the commit it
occurred.

Well, this is interesting because it's something I've wanted to write
about for a long time, and it's what I call my "pronged approach".


I actually do *both*; I do a rebase and fix the problems from 1) the bottom-up,
but after I have resolved the conflicts from 2) the top-down. In 1)
(bottom-up) I resolve the conflicts in a rebase, and in 2) I resolve the
conflicts in merge, but in *both* the end result sould be the exactly
same [`git diff 1) 2)` is empty].

Yes, it is more work, but at the end of the day I'm 100% sure I did the
rebase right, so I don't have to think about it that much; either
there's a diff or there isn't.

In fact, I rarely do just one rebase, because quite often I miss things,
so I do a second, or third, or fourth rebase, but at the end I make sure
that the diff with the merge (top-down approach) is the same.

To facilitate this work I use two tools: 1) git rerere [1] (others have
mentioned this), and 2) git reintegrate [2] (only useful if there's more
than one branch you are merging).


Yeah, it's a lot of work, but I'd rather do a lot of tedious work that
I'm 100% sure is correct, than do a little bit of work that I can't
easily verify.

Cheers.

[1] https://git-scm.com/docs/git-rerere
[2] https://github.com/felipec/git-reintegrate

-- 
Felipe Contreras