Cross-project merges

[Andrew Bennetts]

Jelmer Vernooij wrote:
[...]
> > (I do wonder if there's a better name than "merge-into" though... there's some
> > overlap with "join" I guess.)
> Yeah, I was wondering about that. How is merge-into different from join
> and do we really need to have both in the core?

First, there's the trivial: join doesn't work with 2a either, for
similar reasons to why merge-into doesn't work.  (It expects to be able
to mutate inventory._byid).

Second, join works in terms of trees on disk.  You can't use join with a
remote branch the way you can use merge.

Third, join works with whole trees, but there are use cases for partial
merge-intos (somewhat like there are uses for partial merges).  The main
one I have in mind is to incorporate just the debian/ subdirectory of
one branch into another that doesn't have one (even if the branches are
unrelated according to bzr's history of them, due to parallel imports).

I think ideally join and merge-into (or whatever is called in the end)
would share much of their implementation internally.  As for UI... well,
as I've already said, I'm not sure :)  Starting with the UI from the
merge-into plugin seems like an ok first step, but *perhaps* the join
command should provide this functionality instead of a new command?

-Andrew.