Re: [PATCH v2 2/7] add tests for rebasing with patch-equivalence present

[Martin von Zweigbergk <martinvonz@gmail.com>]

On Thu, May 30, 2013 at 5:54 AM, Johannes Sixt <j6t@kdbg.org> wrote:
> Am 30.05.2013 07:30, schrieb Martin von Zweigbergk:
>> On Wed, May 29, 2013 at 12:09 AM, Johannes Sixt <j.sixt@viscovery.net> wrote:
>>> Am 5/29/2013 8:39, schrieb Martin von Zweigbergk:
>>>> +#       f
>>>> +#      /
>>>> +# a---b---c---g---h
>>>> +#      \
>>>> +#       d---G---i
>>> ...
>>>> +test_run_rebase () {
>>>> +     result=$1
>>>> +     shift
>>>> +     test_expect_$result "rebase $* --onto drops patches in onto" "
>>>> +             reset_rebase &&
>>>> +             git rebase $* --onto h f i &&
>>>> +             test_cmp_rev h HEAD~2 &&
>>>> +             test_linear_range 'd i' h..
>>>
>>> Isn't this expectation wrong? The upstream of the rebased branch is f, and
>>> it does not contain G. Hence, G should be replayed. Since h is the
>>> reversal of g, the state at h is the same as at c, and applying G should
>>> succeed (it is the same change as g). Therefore, I think the correct
>>> expectation is:
>>>
>>>                 test_linear_range 'd G i' h..
>>
>> Good question! It is really not obvious what the right answer is. Some
>> arguments in favor of dropping 'G':
>>
>> 1. Let's say origin/master points to 'b' when you start the 'd G i'
>> branch. You then send the 'G' patch to Junio who applies it as 'g'
>> (cherry-picking direction is reversed compared to figure, but same
>> effect). You then "git pull --rebase" when master on origin points to
>> 'h'. Because of the cleverness in 'git pull --rebase', it issues 'git
>> rebase --onto h b i'.
>
> The reason for this git pull cleverness is to be prepared for rewritten
> history:
>
>    b'--c'--g'--h'
>   /
>  a---b
>       \
>        d---G---i
>
> to avoid that b is rebased.

Right. It doesn't currently drop 'G' and maybe it shouldn't, so let's
leave it as is for now, I would say.

>> 2. In the test a little before the above one, we instead do 'git
>> rebase --onto f h i' and make sure that the 'G' is _not_ lost. In that
>> case it doesn't matter what's in $branch..$upstream. Do we agree that
>> $branch..$upstream should never matter (instead, $upstream is only
>> used to find merge base with $branch)?
>
> No, we do not agree. $branch..$upstream should be the set of patches
> that should be omitted. $branch..$onto should not matter. $onto is only
> used to specify the destination of the rebased commits.

Ok. As I said to Felipe, I'm not sure why I was so convinced that it's
bad to lose the patch in 'git rebase --onto f h i'. It can result in
lost work, but it seems rare enough that no one has reported it,
AFAIK.

I'll change those tests in a re-roll, and perhaps I'll drop a few of
them. Let me know if you (anyone) disagree.


Martin

PS. Thanks for a meticulous review!