Different dependency providers

[heyLu]

As mentioned previously (here and here, we want to be able to fetch dependencies from places other than GitHub.

I think we should support the following:

• [user/repo "version"] for GitHub and BitBucket (GitHub being the default)
• ["git://git.papill0n.org/awesome.git" :type "git"] and ["http://hg.papill0n.org/also-awesome" :type "hg"] to support git, hg and possibly others directly, on any server
• ["http://files.papill0n.org/awesome-1.0.0.tar.gz" :type "tar"]
• ["../awesome" :type "file"] for local dependencies, resolved relative to the project root directory

@kgann has suggested using multi-methods for this, seems like a good idea to me!

If you want to work on this, please say so here!

[kgann]

@heyLu I'm on it! I'll update #12 with some multi-methods and github/local files - new PR's for other providers so it doesn't get too large.

[heyLu]

@kgann Can you do all of that in a separate PR? Or even multiple PRs, depending on how big it gets?

[kgann]

@heyLu Yes, no problem.

[kgann]

I'm starting to think we will run into issues with cyclic and/or duplicate dependencies.

Consider 2 dependencies required for a project (perhaps through sub-dependencies):

[heyLy/hiccup "0.1.0"]
["git://git.github.org/heyLu/hiccup.git" :type "git"]

What do we do in this case? If we download both and place them in different paths and try to put both on the --load-path we will have some issues, right? Especially if they are conflicting versions.

What about requiring the names be present?

[heyLy/hiccup "0.1.0"]
[heyLy/hiccup "git://git.github.org/heyLu/hiccup.git" :type "git"]
[heyLu/hiccup "../my/local/hiccup" :type "file"]

This would allow us to detect cyclic dependencies as well as duplicates and abort/ignore. This is not 100% as someone could just change the name and have the duplicate dependency fetched.

Thoughts?

[mpenet]

FYI I ported clojure "dependency" lib to pixie, this could help making this happen: https://github.com/mpenet/dependency