Re: [PATCH 2/2] Add a 'source' decorator for commits

On Tue, Oct 28, 2008 at 01:11:16PM +0000, Pierre Habouzit wrote:

On Tue, Oct 28, 2008 at 05:45:40AM +0000, Jeff King wrote:

quoted

On Mon, Oct 27, 2008 at 01:07:10PM -0700, Linus Torvalds wrote:

quoted

Of course, if the commit is reachable through multiple sources (which is
common), our particular choice of "first" reachable is entirely random
and depends on the particular path we happened to follow.

Hmm. It would be nice to keep even a simple counter to get a "distance"
from the ref and choose the one with the smallest distance (I think we
can get away without the complex rules that git-describe uses, since we
are not interested in describing the full commit, but rather finding a
"likely" branch).

However, that would require making multiple passes over the commit
graph, which might impact the startup speed.

Actually I tried to do that (and you meant name-rev --contains rather
than describe actually ;p), and I stopped because it's too slow. I
believe the proper way to do that is to help git-log knowing which are
the short (topic) branches, and to crawl incrementally using a
date-based hack. This would basically work a bit like this. Let's
imaging you want to crawl "next" in git and know which topics from pu
are in it. You would say e.g.:

git-log --topics=*/* next (as pretty much every */* is a topic branch
for git.git).


Then one has to know which are the heads of every topic branches first,
then crawl next the usual way, except that when you arrive to a point
that is a topic branch head, you don't look that way. You remember the
date of that point, and continue to crawl "next" a bit further so that
you can start annotating the topic's commits you've stumbled upon. And
you do that, you look at jd/topic (as in John Doe topic branch) and mark
all the commits as being from jd/topic, until you either go back to some
commit from next, or your current commit date is younger than your
current "next" crawling front. In the former case, you're done with that
topic, in the latter you must continue to preprocess "next" a bit more.

My description is clumsy, as we probably sometimes want to crawl topics
that aren't merged either like in git-log --topics=*/* --all.  But we
just have to mark the current "front" of the walk, and have it sorted
between things that are part of topic heads and the thing that are not.
We don't even need to decorate the things that are _not_ part of the
topics at all I'd say, because that's where you definitely need distance
based algorithms and multiple passes to yield correct results.

Whereas for the specific case of topic branches, which is what people
want (see Ingo's mails on the subject a week or so ago), the algorithm I
propose is, I guess, mostly O(n + m) in the number of walked commits (n)
and references (m). IOW fast.


-- 
·O·  Pierre Habouzit
··O                                                madcoder@debian.org
OOO                                                http://www.madism.org