Re: [Monotone-devel] branch representation

[Zbynek Winkler]

Nathaniel Smith wrote:

> So the idea is: what if we got rid of branch certs, and put a branch
> field inside the revision object?  So each revision is uniquely,
> irrevocably, in a single branch.  So each revision is not just a
> snapshot, but a snapshot with a purpose attached.  And instead of
> automatically putting a branch cert on at commit time, you put a
> "yeah, this is good" cert on (since the rev already has a purpose
> built in, your vague affirmation of goodness can be assumed to match
> that).
>  
Hmm. I think we first need to decide what *exactly* branches are before 
evaluating ideas about changing them.

The first thing that comes to mind is

   Are branches development lines or just a way to group arbitrary 
otherwise unrelated groups of revisions?

I think that the term "branch" comes with some kind of expectation. 
Almost all VCS use the term and understanding is that it usually 
represents a development line and not a bag of things. Do not get me 
wrong, I think it is really useful to have "bag of things" but please 
let's not call them branches because it is IMHO unnecessary confusion 
for anyone who has ever used other VCS. Just look at these pictures
http://www.mozilla.org/roadmap/branching-2005-01-25.png
http://www.mozilla.org/roadmap/branching-2002-12-26.png
Everyone wants to talk about stuff like "branch point" and draw the the 
branches as lines of development. And it is just too hard when your VCS 
does not know these terms or (worse) uses them to mean something 
completely different.

> Yeah, this is a really weird idea.  It's weird enough that I have
> trouble really imagining it to evaluate it.  (And enough that I
> deserve to be hit repeatedly with a stick for bringing it up when
> we're trying to _stabilize_ things...)
>
> Anyway, this wouldn't help with things that people find
> counter-intuitive like, "this branch is discontinuous", or "this
> branch has multiple branch points", or "this branch has multiple
> heads".  It would help with the confusion about revs being in multiple
> branches, and generally reduce the weirdness we have all the time
> where we have to assume all revs have branch certs on them, and try
> and guess an appropriate branch name given a revision, and so on -- it
> seems like the code and users both want to think of branch certs as at
> least somewhat special.  I'm thinking of guess_branch, and update's
> tricky handling of branches, and netsync filtering by branch...
>  
Yes, at least I think that branches are somewhat special and that the 
general idea of grouping revisions in to a bag can be done by just an 
arbitrary cert.

> It might make doing trust stuff significantly easier.
I agree. I think it would have clearer model this way. I would really 
like the fact that you need to create a new revision when moving some 
changes between branches... because in fact, I see adding new code to a 
branch as a new development and not as attachment of some arbitrary meta 
data. It would support the "line of development" thing much better.

Zbynek

--
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Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic