When I open the Gemfile inside RubyMine I can Ctrl+Click on every one of the gems and RubyMine will take me to the gem's source files. Except 'rails'..
In my current project it's
gem 'rails', '3.2.13.rc2'
And I also can't see rails in the 'External Libraries' section.
Any idea how to solve this?
With the helpful information in @zrl3dx's answer I did the following:
Going to some external library in RubyMine to see where it's looking for source files. In my case it was in
~/.rvm/gems/ruby-2.0.0-p247/gems
Then I copied the railties directory to the rails directory
rmdir rails-3.2.13.rc2
cp -a railties-3.2.13.rc2 rails-3.2.13.rc2
Then RubyMine automatically detected the source code and I can happily Ctrl+Click once again :)