I noticed that rake install installs RubyGems into $PREFIX/gems/ and not into $PREFIX/lib/ruby/gems/, such as MRI and JRuby.
$ ./configure --prefix=/usr/local/rubinius
$ rake install
$ ls /usr/local/rubinius/lib/ruby/gems
ls: cannot access /usr/local/rubinius/lib/ruby/gems: No such file or directory
$ ls /usr/local/jruby-22.214.171.124/lib/ruby/gems
$ ls /usr/local/ruby-1.9.3-p194/lib/ruby/gems
You have the option to specify the gem dir with --gemsdir.
In my opinion, there is nothing special or in fact that makes any particular sense about 'lib/ruby/gems'.
@brixen thank you for your timely response. I was more hoping that the default for the --gemdir would match that of JRuby and MRI. This would allow developers to not have to specify additional configuration options in order to get Rubinius working with rbfu, chruby (both currently expect --gemdir to be $PREFIX/lib/ruby/gems).
As a work-around for chruby, I could query RubyGems on what it's primary gem directory is. However, rbfu simply overrides GEM_PATH.