RubyMine Debugger.start is not called yet

The other solutions won't work if you check in your Gemfile.lock - it will vary depending on what machine it was generated on (didn't try it, but pretty sure this is true).

Instead, I put the gem in a separate, non default section in the Gemfile:

group :debugging do
  gem 'debugger'
end

Then, in application.rb, I require it conditionally. Also, I didn't have RM_INFO, so I check RUBYLIB env var:

Bundler.require(:default, Rails.env) if defined?(Bundler)

unless ENV['RUBYLIB'] =~ /RubyMine/
  require 'debugger'
end