How do I debug a rails 3 gem?

I have created a gem/engine based on this tutorial:

http://www.themodestrubyist.com/2010/03/05/rails-3-plugins---part-2---writing-an-engine/

However, I am getting an error when trying to use the gem in a newly created application. I am getting a "Routing Error - undefined method `sub' for nil:NilClass" when trying to access the application.

The only thing I can see in the log file is the same error. No stack trace/debug trace, so it is difficult to figure out where the error is coming from. Ideally I would like to get see the stack trace "from the gem", but it appears that rails does not debug errors originating from outside the a开发者_运维知识库pplication?

I'm using rvm, ruby 1.9.2, rails 3.0.1.

Here is my config/routes.rb file from the gem, although I do not think this is a routing error as the debug message suggests..

Rails.application.routes.draw do
    resources :pictures, :controller => 'morph/pictures'
end

Any suggestions?

If you uncomment

Rails.backtrace_cleaner.remove_silencers!

in config/initializers/backtrace_silencers.rb it will display a more complete stacktrace. It worked for me.

Is there a backtrace in your console?

If you're unable to find any additional output, then you could put a 'debugger' statement somewhere near the start of your app and step through the source code until the error appears.

You can do the same with the gem/plugin source, too.

Edit: It appears the author has a link to demo code at the bottom of the article. That might also be useful.