Peter Verswyvelen wrote:

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

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

Shouldn't this be done by cabal, not darcs? i.e. cabal update querying a list of repositories for info about available versions (think standardised tags): cabal install can then figure out what to pull. -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited.

On Sun, 29 Mar 2009, Peter Verswyvelen wrote:

Module A requires B. When a new developer wants to get the source code, he does a "darcs get server://program/A", which gives him only the latest version of A. So he manually needs to do "darcs get server://program/B" (that B is required is usually discovered after a compilation error, talking to other developers to find out what the dependencies are, or by reading the cabal file). Furthermore it is unclear which version of A required which version of B (so you can't really roll back to old versions).

Now assume you don't have 2 modules but dozens...

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

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

There's an (unimplemented) proposal by David Roundy for darcs sub-repos that would solve this problem: you have a darcs patch type that means "depend on this patch from this other darcs repo which will be checked out in a given subdirectory". I think that solves precisely the problem you describe, and I think it should be implemented :-) Ganesh

Peter Verswyvelen writes:

Mmm, my email was indeed very unclear about my question.

A very simple example: suppose a development team is working on a program. This program consist of modules A and B. Each module has it's own Darcs repository.

Module A requires B. When a new developer wants to get the source code, he does a "darcs get server://program/A", which gives him only the latest version of A. So he manually needs to do "darcs get server://program/B" (that B is required is usually discovered after a compilation error, talking to other developers to find out what the dependencies are, or by reading the cabal file). Furthermore it is unclear which version of A required which version of B (so you can't really roll back to old versions).

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. 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. 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. The developers should actually agree upon a proper set of API's before you guys actually start building the modules separately. 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.

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?

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. -- c/* __o/* <\ * (__ */\ <

On Sun, Mar 29, 2009 at 10:26 PM, Xiao-Yong Jin 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 extensionhttp://www.selenic.com/mercurial/wiki/index.cgi/ForestExtensionfor 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.

On Mon, Mar 30, 2009 at 8:33 AM, Ketil Malde wrote:

Do one thing, and do it well. File versioning and change history: darcs. Dependency tracking and building: cabal.

Yes, that could actually work. I would just need some link between a cabal version and Darcs version (I must say I don't fully grok yet how Darcs works - my mind is still in Mercurial & Bazaar land - so "Darcs version" might not mean anything)