I've been looking all over the place but I can't find anything. Does anyone know how to create an Xcode 4 plugin?
As far as I know there is no official way to create Xcode 4 plugins (just like there wasn't one for v3.x).
Here is an openradar on Xcode's lack of plugin support:
Please support the ability for 3rd parties to extend Xcode via a public plugin API. Aperture, Visual Studio, Eclipse, TextMate and other applications benefit from this ability. I would like to see more advanced refactorings, code analysis (think Resharper by Jetbrains) and modeling.
Please dupe this if you want plugins!
Edit: Just stumbled upon this:
Cédric Luthi: "Xcode 4 does support user-defined plugins, see CLITool-InfoPlist for an example of a working Xcode 4 plugin. You just have to add XC4Compatible (true) in the Info.plist."
https://github.com/0xced/CLITool-InfoPlist
That being said these GitHub repos might be handy, too:
Xcode4 Plugin-API Documentation (link dead)
Xcode Plugin Template (link updated)
Further more mogenerator's Xmod plugin might be a good starting point.
(Wasn't Xcode-4 compatible yet, last time I checked, though)