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

On Tue, Jan 17, 2012 at 10:18 PM, Pete Wyckoff [off-list ref] wrote:

vitor.hda@gmail.com wrote on Tue, 17 Jan 2012 00:10 +0000:

quoted

On Mon, Jan 16, 2012 at 11:41 PM, Vitor Antunes [off-list ref] wrote:

quoted

On Mon, Jan 16, 2012 at 6:57 PM, Pete Wyckoff [off-list ref] wrote:

quoted

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.

I can see now that I did not understand the "no parent" in your original
reply. What you just explained makes sense. So, let me try that and I'll
update you tomorrow.

Vitor