On Sun, Mar 29, 2009 at 10:26 PM, Xiao-Yong Jin <xj2106@columbia.edu> wrote:
> Now assume you don't have 2 modules but dozens...

I can't imagine such kind of situation, unless you are
really working on a very big project.  Usually, if your
project depends on other projects, mostly it should work
with stable version of other projects, but not their develop
version.  You might need some features of other projects
that is still under development, than you might have a few
repositories.  However, such situation should be well known
across all developers of your project.  And usually you guys
should agree on one particular develop version of those
dependency projects, to make sure that you guys are working
with the same set of API's.

Even if you have just two modules, manually keeping track which version used which other version feels error prone. And you need that when you want to revert to old versions (which I heard is very hard to do with Darcs anyway, but I can't confirm that, haven't tried it yet)

I don't think it is realistic to expect that for a project of medium to large size that you work only with stable versions of modules (this would exclude most packages on Hackage I guess). I understand this is the way it *should* be, but I don't think it often does. I prefer to use some unstable packages from Hackage, and contribute bugfixes or even enhancements to these packages. 
 
If those aforementioned dependency projects are just some
modules within your big projects, I think the way to go is
actually make them in the same repository.  

Yep, that's the way it's usually done. But when you have multiple teams working on different modules within the same repository, this gets annoying. 
 
I can't see the
benefit of splitting those small modules to different
repositories, apart from not letting other people know your
current developing code.  But we are using a distributed
revision control system, as darcs is, you can choose which
patch to push to the "upper stream" anyway.

So my point of view is that it is a management issue rather
than a issue of revision control system.  

Currently it mostly is a management issue, and so it often goes wrong :)
 
The developers should actually agree upon a proper set of API's before you
guys actually start building the modules separately.

In an idealized world I agree, but with modern agile software development methodologies, these APIs also evolve...
 
Another reason for such kind of RCS built-in dependency
check being impossible is that darcs are basically dealing
with a bunch of dependent patches.  Those patches only know
their dependencies within a particular repository.  You
can't logically put a dependency of an external repository
before you start pulling from that repository.

Sure, but that sounds like a current limitation, doesn't seem like this is impossible to extend.

> To me, any version control system should be able to track
>dependencies between
> repositories. Something similar like Cabal's dependency system.
>

Can you provide some examples of RCS that have such kind of
dependency system?

Mercurial had an extension for this. I'm not sure but maybe ClearCase and Accurev also support something like. A couple of years ago I also developed a version control system (closed source, private solution for customer, NTFS only) that supported dependencies between repositories ( too bad that company did not want to release the software as open source :|  )

> So my question is really, how do you solve the dependency
>tracking between
> several Darcs repositories? 

Because every source tree is a branch in darcs, you can't.

Too bad.