[rfc] bzr-colo into core

[Barry Warsaw]

On Mar 22, 2011, at 07:14 AM, Nicholas Allen wrote:

>> People working on large trees really want to have just one on-disk
>> checkout at a time, so they don't use too much disk space and so they
>> don't waste time building a new tree just to start a new branch.  

>I diagree completely. If you have a large tree or use a compiled
>language like C++ colocated branches are almost definitely what you
>don't want. You need multiple working trees so that you don't have to
>rebuild each time you switch a branch. If there's only one tree then
>when you switch the whole project will likely have to be recompiled
>again (especially if a common header file is modified because of the
>switch). This would be unacceptable for me.

I had a similar conversation with folks at Pycon.  As tempting as it is to
reduce built-time, I don't quite trust switching branches in place to cause
the right combination of recompiles.  I was not alone in my unease. ;)

>There's also something elegant about the simplicity of 1 directory = 1
>branch that I think gets lost like this. It's always clear to me which
>branch I'm working on when they are in separate directories.

I completely agree.  This is one of the most jarring adjustments for me with
the switch to Mercurial for CPython.  I'm not really sure why I'd want one
repo to contain multiple branches, and that fact that a clone gives me
everything (including branches I don't care about, e.g. Python 2.5) is
unsettling.  I am not alone in that either as many of us just do multiple
local clones to have separate directories for each mainline of development
(but then have to manually fiddle .hg/hgrc to get the push locations right).

>As long as it's just as easy to have a single branch in a directory with
>multiple trees and all the workflows that Bazaar currently supports then
>I don't mind.

I can't imagine that would go away.  I see it as a huge win for Bazaar's
model.  Still, bringing bzr-colo into the core gives folks who prefer it the
other way 'round a choice, and that *too* is one of the big wins for
Bazaar. :)

-Barry
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