Re: [PATCH 2/3] git-p4: Search for parent commit on branch creation

> vitor.hda@gmail.com wrote on Tue, 17 Jan 2012 00:10 +0000:
>> On Mon, Jan 16, 2012 at 11:41 PM, Vitor Antunes <vitor.hda@gmail.com> wrote:
>> > On Mon, Jan 16, 2012 at 6:57 PM, Pete Wyckoff <pw@padd.com> wrote:
>> >> 1.  Move the tempBranch commit outside of the "for blob" loop.
>> >>    It can have no parent, and the diff-tree will still tell you
>> >>    if you found the same contents.  Instead of a ref for
>> >>    each blob inspected for each change, you'll just have one ref
>> >>    per change.  Only one checkpoint() after the tempBranch
>> >>    commit should be needed.
>> >
>> > You're right. Completely oversaw that. Will improve the code
>> > accordingly.
>>
>> Apparently I did not oversee it. Assume you have added a new file to
>> HEAD of parent branch, but you branched from a previous commit. When the
>> new branch is committed over HEAD the new file will, incorrectly, be
>> part of it and diff-tree will not work as expected.
>
> I don't get it.  This algorithm works on the fact that a "branch"
> in p4 creates a new change that looks exactly like a previous
> change.
>
> The git-p4 sync step, when it detects a branch, starts by saving
> the change in a commit with parent = null, so it is its own new
> branch, an orphan, with no parents.
>
> Now the task is to find some commit that has an identical tree to
> this temporary one.  You walk back all known p4 commits to try to
> find one that is the same.  It doesn't matter if any of those p4
> commits have other commits on top of them.
>
> At each step in the backward walk, the comparison is against the
> unchanged orphan commit.
>
> An ascii-art picture might help me.  Or even a test case.