Re: [RFC] Rebasing merges: a jorney to the ultimate solution (Road Clear)

From: Igor Djordjevic <igor.d.djordjevic@gmail.com>
Date: Feb 28, 2018, 01:33 UTC
Message-ID: <8829c395-fb84-2db0-9288-f7b28fa0d0d1@gmail.com>
In-Reply-To: <CA+P7+xrzxYSE0OyL8uyF+ErwfWFEgcqnHmaciwWkK-76sQ6ktw@mail.gmail.com>

On 28/02/2018 01:36, Jacob Keller wrote:

Show 18 quoted lines

> 
> > > (3) ---X1---o---o---o---o---o---X2
> > >        |\                       |\
> > >        | A1---A2---A3---U1      | A1'--A2'--A3'--U1'
> > >        |             \          |
> > >        |              M         |
> > >        |             /          |
> > >        \-B1---B2---B3---U2      \-B1'--B2'--B3'--U2'
> > >
> >
> > Meh, I hope I`m rushing it now, but for example, if we had decided to
> > drop commit A2 during an interactive rebase (so losing A2' from
> > diagram above), wouldn`t U2' still introduce those changes back, once
> > U1' and U2' are merged, being incorrect/unwanted behavior...? :/
> 
> In that case, the method won't work well at all, so I think we need a
> different approach.
>

Hmm, still rushing it, but what about adding an additional step, 
something like this: 
 
 (4) ---X1---o---o---o---o---o---X2
        |\                       |\
        | A1---A2---A3---U1      | A1'--A2'--A3'--U1'--R1
        |             \          |
        |              M         |
        |             /          |
        \-B1---B2---B3---U2      \-B1'--B2'--B3'--U2'--R2

... where:

  R1 = git diff U2 U2' | git apply --3way
  R2 = git diff U1 U1' | git apply --3way

(this is just to explain the point, might be there is a better way to produce Rx)

So, we still use Ux' to preserve merge commit M amendments, but also Rx to catch any changes happening between Ux and Ux' caused by interactive rebase commit manipulation (add/amend/drop).

Note that R*1* is produced by applying diff from U*2*' side, and vice versa (as it`s the other side that can erroneously introduce dropped commit changes back, like U2' in case of dropped A2').

From here we continue as before - merging R1 and R2, then rewriting merge commit parents to point to A3' and B3' (dropping Ux` and Rx).

This seems to be working inside my (too trivial?) test case, for interactive adding, dropping, and amending of rebased commits, resulting "rebased" merge containing all the added/modified/dropped changes, plus the original merge amendment, all as expected :P

Regards, Buga