From: Junio C Hamano <gitster@pobox•com>
To: Sergey Organov <sorganov@gmail•com>
Cc: Johannes Sixt <j6t@kdbg•org>,
Sebastian Schuberth <sschuberth@gmail•com>,
Git Mailing List <git@vger•kernel.org>
Subject: Re: [PATCH] docs: Clarify what git-rebase's "--preserve-merges" does
Date: Tue, 31 Mar 2015 10:04:16 -0700 [thread overview]
Message-ID: <xmqq8uedrtdb.fsf@gitster.dls.corp.google.com> (raw)
In-Reply-To: <xmqqh9t1rv0r.fsf@gitster.dls.corp.google.com> (Junio C. Hamano's message of "Tue, 31 Mar 2015 09:28:36 -0700")
Junio C Hamano <gitster@pobox•com> writes:
> I wonder if it will be the right way to get a correct result to
> apply the difference to go from B to Z on top of an old commit when
> you are side-porting.
>
> Imagine you want to backport the same X-Y history by redoing the
> merge Z on top of another child of O (i.e. A's sibling). That is,
> you start from this:
>
>
> X---Y
> / \
> O---A---B---Z---
> \
> M---N
>
> and would want to create this:
>
>
> O X'--Y'
> \ / \
> M---N---A'--B'--Z'--
>
> As long as everything down to the merge-base of the parents of the
> original merge (in this example, merge-base across Y and B that are
> Z's parents, which is A) is being transplanted, "apply the
> difference going from B to Z, on top of B', to obtain Z'" should
> work, I would think.
And just after I send the message because I needed to catch a bus, I
notice that there is a problem.
Actually, "replay diff going from B to Z instead of merging" must be
done very carefully. Imagine when Y in the original history were a
cherry-pick of M. What you would be creating would look more like
this instead:
O X'--.
\ / \
M---N---A'--B'--Z'--
because Y' becomes a no-op, as the transplanted history already has
M applied. But the original "diff going from B to Z" has the effect
of M already in there. You would end up adding the same hunk twice
without noticing. You somehow need to come up with a way to deal
with this.
If you did a real merge between X' and B' to recreate Z', you would
not have such a problem.
One way to be careful when recreating Z' out of Z might be:
- Retry a merge between the original B and Y, with conflict
markers intact;
- Compare the result with what is recorded in Z. The
differences are textual conflict resolution and evil merge
changes;
- Now try a merge between B' and Y', with conflict markers
intact;
- Apply the difference you obtained in the second step to the
result of the third step.
which is essentially the same as what rerere does.
next prev parent reply other threads:[~2015-03-31 17:04 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-26 13:04 [PATCH] docs: Clarify what git-rebase's "--preserve-merges" does Sebastian Schuberth
2015-03-26 18:18 ` Junio C Hamano
2015-03-26 20:28 ` Sebastian Schuberth
2015-03-26 20:55 ` Junio C Hamano
2015-03-26 21:17 ` Sergey Organov
2015-03-26 21:41 ` Johannes Sixt
2015-03-31 9:13 ` Sergey Organov
2015-03-31 16:28 ` Junio C Hamano
2015-03-31 17:03 ` Sergey Organov
2015-03-31 17:04 ` Junio C Hamano [this message]
2015-04-01 11:27 ` Sergey Organov
2015-04-01 17:03 ` Junio C Hamano
2015-04-02 9:53 ` Sergey Organov
2015-03-30 9:29 ` Sebastian Schuberth
2015-03-30 17:23 ` Junio C Hamano
2015-03-30 19:42 ` Sebastian Schuberth
2015-03-30 19:58 ` Junio C Hamano
2015-03-30 20:23 ` Junio C Hamano
2015-03-30 21:09 ` Sebastian Schuberth
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