Re: [PATCHv2 2/2] pull: support rebased upstream + fetch + pull --rebase

["Santi Béjar" <santi@agolina.net>]

2009/7/17 Santi Béjar <santi@agolina.net>:
> 2009/7/16 Junio C Hamano <gitster@pobox.com>:
>> Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:
>>
>>> How about
>>>
>>>       oldremoteref="$(git rev-list --boundary HEAD --not \
>>>                       $(git rev-list -g $remoteref | sed 's/$/^@/') |
>>>               sed -e '/^[^-]/d' -e q)"
>>>
>>> Explanation: the "git rev-list -g $remoteref" lists the previous commits
>>> the remote ref pointed to, and the ^@ appended to them means all their
>>> parents.  Now, the outer rev-list says to take everything in HEAD but
>>> _not_ in those parents, showing the boundary commits.  The "sed" call
>>> lists the first such boundary commit (which must, by construction, be one
>>> of the commits shown by the first rev-list).
>>
>> Hmm, I am not sure about that "(which must..." part.

Unfortunatly you are right with the "(which must..." part. Even
without the ^@. Normally gives the right answer, but it is not
sure that the first commit boundary is the correct one. For
example:

         o--C
        /
 A--x--y--B--o--z
     \      /
      o----o

A, B, C are upstream@{n}

It involves a merge with a branch forked before the fork commit
for the current branch, and it will not work neither with git
pull --rebase. We could say that it is not supported, but
nevertheless it gives the wrong answer.

The right answer is B, but:
$ git rev-list --boundary z --not C B A
z
o
o
o
-x
-B

in this case we could take the boundaries commits and filter the
commits that are ancestor of some other boundary commit, and
would get B (git show-branch --independent x B -> B).

Here it is a test case to see the above.

rm -rf test
mkdir test
cd test
git init
echo A > file
git add .
git commit -mA
git tag A
echo o > file
git commit -a -mo
git tag fork1
echo z > file
git commit -a -mz
git tag fork2
echo B > file
git commit -a -mB
git tag B
git checkout -b topic fork1
echo oo > filetopic
git add .
git commit -moo
echo ooo > filetopic
git commit -a -mooo
git checkout master
git merge topic
echo c > file
git commit -a -mc
git checkout -b upstream fork2
echo o > fileupstream
git add .
git commit -a -mo5
echo C > fileupstream
git commit -a -mo
git tag C
git rev-list --boundary master --not C B A
echo answer: $(git rev-parse B^{})

HTH,
Santi