[rfc] bzr-colo into core

[Stephen J. Turnbull]

Congratulations on the new baby!

Neil Martinsen-Burrell writes:

 > a way to access particular head revisions by name (this is all that
 > a branch is as Stephen Turnbull has pointed out here many times)

I should note that while I still believe this is the "best" way to
think about branches, I've been forced to accept that most users (at
least for the foreseeable future) are not going to think that way.
This is visible in the Emacs experience with Bazaar, where everybody
wants editable log messages so bad they can taste it.  Similarly with
the common meme that rebasing is bad in itself because it "changes
history".  These clearly indicate that many, perhaps most, users
strongly associate a branch not just with a particular head and
implicitly with its ancestors, but explicitly with specific actual
revisions in the DAG.

And of course, that is the way that "branch" is implemented in git.
Even branch properties like default push target are associated with a
name, and therefore only indirectly (and severably!) with any actual
revisions.  But that's not true of most VCSes, and AFAIK in particular
not Bazaar.

So the bottom line is that the problem of UI design and migration is
going to be very delicate.  I agree wholeheartedly (FWIW) with:

 > I think this is a change that needs plenty of time to bake in
 > bzr.dev and maybe even a release or two before we consider making
 > it the default.

Regards,