The latest build of RubyMine 4 (112.291) can’t debug with an rvm gemset using ruby 1.9.3 on my iMac. It complains that it is missing the necessary gems, offers to install them, downloads them and attempts to install them, and then hangs while ‘building native extensions’.

I’m sure this will all be worked out in time for release, but meanwhile here is a really easy fix: just install the ruby-debug19 gem via the command line. This, or one of its dependencies, is hanging while building native extensions when RubyMine attempts the auto-install.

rvmsudo gem install ruby-debug19

Wait for that to finish. Now when RubyMine offers to install the missing gems, it will do so without a hitch (or at least it did for me).