Re: Rebase Question

[Jeff King <peff@peff.net>]

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

> On Tue, May 11, 2021 at 5:07 PM Andrew Ottaviano <andrew_o1995@live.com> 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.

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