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Re: rebase preserve-merges: incorrect merge commits




2018-01-08 19:32 GMT+03:00 Johannes Schindelin <Johannes.Schindelin@xxxxxx>:
> Hi,
>
> On Mon, 8 Jan 2018, Matwey V. Kornilov wrote:
>
>> 2018-01-08 17:42 GMT+03:00 Matwey V. Kornilov <matwey.kornilov@xxxxxxxxx>:
>> > 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
>>
>> Indeed, exactly as you still say in the documentation: "Merge conflict
>> resolutions or manual amendments to merge commits are not preserved."
>> My initial point is that they have to be preserved. Probably in
>> recreate-merges, if preserve-merges is discontinued.
>
> Ah, but that is consistent with how non-merge-preserving rebase works: the
> `pick` commands *also* do not record merge conflict resolution...
>

I am sorry, didn't get it. When I do non-merge-preserving rebase
--interactive there is no way to `pick' merge-commit at all.

> Ciao,
> Johannes



-- 
With best regards,
Matwey V. Kornilov