[RFC] Revision id aliases

[Jelmer Vernooij]

On Sun, 2006-06-18 at 19:00 -0500, John Arbash Meinel wrote:
> Jelmer Vernooij wrote:
> > Another feature that would come in handy for foreign Subversion branches
> > is revision id aliasing. Are there any plans to support these in the
> > near future or are they postponed until after 1.0 ?
> What do you actually mean? That you have 2 revision_ids, but they refer
> to the same information?

> I think you are considering using aliases so you can push into
> subversion, and then have bzr believe that it is the same revision that
> I just committed. (Or more importantly, the same series of revisions).

> And I think you want aliases, because Subversion doesn't let you denote
> any sort of custom id, so you are stuck with their notation.
Yes, exactly. 

> I can say that if you were treating SVN as just another branch, you
> would actually be at the same place, where each merge generates a new
> revision id. So it isn't like bzr can't cope with each commit to SVN
> being a separate revision. As long as you make bzr think that they are
> all merges.
The problem with that is, if I understand you correctly, that you can't
use it to push from a Bazaar branch to a Subversion branch. I'm
interested in revision aliases so that I can say (locally) that a
revision id in a Subversion branch refers to the same revision I have in
my local branch so that 'bzr pull' won't complain about diverged
branches after I've pushed to the Subversion branch.

> I don't know that much has been done for revision ids. It could be done
> with a simple aliases table, but we would need to think out the
> performance implications as well. eg. I want to pull from you, and you
> have rev-ids 1,2,3,4, but I don't realize they are aliased to my
> revision ids a,b,c,d so I don't need to pull anything. I assume aliases
> can be updated after the revisions are created, so it isn't as simple as
> just pulling new revisions and noting their aliases. (If a is newly
> aliased to 1, then 1 is actually newly aliased to a as well).
I'll have a look at some of the old mailing list posts. I'm mainly
interested in having a locally updated list of revision id aliases at
the moment, for which a simple dict with mapping should do. What
specific other use cases are there for revision id aliases?

> As far as pre/post 1.0. It just depends if someone like you really wants
> them, and comes up with a reasonable solution before we decide we are at
> 1.0. We are already at 0.8. With a major performance push coming up, I
> wouldn't be surprised if we hit 1.0 fairly soon. (I don't really like to
> say any absolutes, but probably this year, and it wouldn't surprise me
> much if it was within 6 months or so).
Ah, cool - I wasn't expecting it that soon, actually. Is tagging a
showstopper for 1.0?

Cheers,

Jelmer
-- 
Jelmer Vernooij <jelmer at samba.org> - http://samba.org/~jelmer/
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