Re: Sharing merge conflict resolution between multiple developers

[Chris Packham <judge.packham@gmail.com>]

On Tue, Aug 12, 2014 at 6:44 AM, Junio C Hamano <gitster@pobox.com> wrote:
> Chris Packham <judge.packham@gmail.com> writes:
>
>> Is there any way where we could share the conflict resolution around
>> but still end up with a single merge commit.
>
> One idea that immediately comes to me is to use something like
> "rerere" (not its implementation and storage, but the underlying
> idea) enhanced with the trick I use to fix-up merges in my daily
> integration cycle (look for "merge-fix" in howto/maintain-git.txt
> in Documentation/).
>
>> developer A:
>>   git merge $upstream
>>   <conflicts>
>
> And then commit this immediately, together with conflict markers
> (i.e. "commit -a"), and discard it with "reset --hard HEAD^" *after*
> storing it somewhere safe.  And then redo the same merge, resolve
> the conflicts and commit the usual way.
>
> The difference between the final conflict resolution and the
> original conflicted state can be used as a reference for others to
> redo the same conflict resolution later elsewhere.  That can most
> easily be done by creating a commit that records the final state
> whose parent is the one you recorded the initial conflicted state.
>
> So, the "recording" phase may go something like this:
>
>     git checkout $this
>     git merge $that
>     git commit -a -m 'merge-fix/$this-$that preimage'
>     git branch merge-fix/$this-$that
>     git reset --hard HEAD^
>     git merge $that
>     edit
>     git commit -a -m 'merge $that to $this'
>     git checkout merge-fix/$this-$that
>     git read-tree -m -u HEAD $this
>     git commit -a -m 'merge-fix/$this-$that postimage'
>
> The rough idea is "git show merge-fix/$this-$that" will show the
> "patch" you can apply on top of the conflicted state other people
> would get by running "git merge $that" while on "$this" branch.

So how would someone else pickup that postimage and use it?

  git checkout $this
  git merge $that
  git fetch $remote ':/merge-fix/$this-$that postimage'
  git show ':/merge-fix/$this-$that postimage' | git apply (or patch -p1)
  edit

>
> "rerere" essentially does the above recording (and replaying)
> per-path and it comes with a clever indexing scheme to identify
> which previous conflict resolution would apply to the conflicts you
> see in your working tree.

I feel a toy patch coming on.