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Re: rebase preserve-merges: incorrect merge commits




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 ...)

Ciao,
Johannes