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Re: rebase preserve-merges: incorrect merge commits




2018-01-08 16:56 GMT+03:00 Johannes Schindelin <Johannes.Schindelin@xxxxxx>:
> Hi Matwey,
>
> On Mon, 8 Jan 2018, Matwey V. Kornilov wrote:
>
>> I think that rebase preserve-merges algorithm needs further
>> improvements. Probably, you already know it.
>
> Yes. preserve-merges is a fundamentally flawed design.
>
> Please have a look here:
>
>         https://github.com/git/git/pull/447
>
> Since we are in a feature freeze in preparation for v2.16.0, I will
> submit these patch series shortly after v2.16.0 is released.
>
>> As far as I understand the root cause of this that when new merge
>> commit is created by rebase it is done simply by git merge
>> $new_parents without taking into account any actual state of the
>> initial merge commit.
>
> Indeed. preserve-merges does not allow commits to be reordered. (Actually,
> it *does* allow it, but then fails to handle it correctly.) We even have
> test cases that mark this as "known breakage".
>
> But really, I do not think it is worth trying to fix the broken design.
> Better to go with the new recreate-merges. (I am biased, of course,
> because I invented recreate-merges. But then, I also invented
> preserve-merges, so ...)

Well. I just checked --recreate-merges=no-rebase-cousins from the PR
and found that it produces the same wrong result in my test example.
The topology is reproduced correctly, but merge-commit content is
broken.
I did git rebase --recreate-merges=no-rebase-cousins --onto abc-0.1 v0.1 abc-0.2

>
> Ciao,
> Johannes
>



-- 
With best regards,
Matwey V. Kornilov