Magit extensions

Magit is a great emacs tool to help doing everyday's operations on Git repositories. In particular, I really like the contextual approach, that splits the global status in sections, meaning that the same high-level command can have subtle semantics differences when applied to different objects. As an example, the high-level `magit-discard-item' function obviously takes different steps when applied to an untracked file or to a staged hunk, or even to an entire branch.

The only disadvantage I see in the current implementation is the lack of modularity in it: a heavy use of (really nice, btw) macros makes it mandatory to have the complete set of features available when magit is loaded, so that the generated code is complete.

Still, Git has lots of contributed helpers, which means the only stable way of using them with Magit is to have them integrated upstream, which is not always possible (take the example of custom helpers that cannot be distributed) or does not even make sense (those helpers could be entirely bound to some specificities of a project).

I've been working on an attempt to make Magit more modular, by allowing the registration of so-called “extensions”. See code here: http://github.com/sigma/magit/tree/extensions

As a POC, I've extracted 2 features from the mainstream Magit, and converted them to extensions: those are magit-svn and magit-topgit. The way I see things, those 2 features are exactly the kind I'd like to add to magit for my daily work but that would not necessarily make sense as part of the core project. As far as I know, the current behavior when those 2 extensions are loaded is exactly the same as the regular upstream version (including placement of the various sections)

The current code allows you to:

• define new kind of sections (for example a “topic” kind)
• define how and where to display them (for example, right after the core “stashes” section)
• hook new behavior for existing commands for those new sections (for example a way to discard such an item)
• define new top-level commands, and associate menus

I tried to stay very close from the Magit way of doing things, and in particular the way you express things in extensions is exactly the same as what you do in the core code. Once again, tricky macros are at play to make the code look the same.

What I'd like to see in the future (though I don't have much time to do it right now :():

• new extensions, to ease my daily life.
  • a magit-p4 (perforce integration),
  • maybe a magit-stgit (stgit in place of topgit for topic branches)
  • something to integrate with VMware's ReviewBoard
• code stabilization, and official proposal upstream (if there is an interest in this)
• a way to activate those extensions on a per-project basis (I use both git-svn and git-p4 but never at the same time. same for topgit vs stgit)

An example being worth a thousand words, here is how to code the magit-topic extension. If you know the Magit code base, you should feel nearly at home.

Feel free to tell me what you think, any comment or advice is highly welcome !