"require 'capybara/rails'" gives "uninitialized constant Rack::Builder"

Question

I've been using cucumber in my app, which is a rails 2.2.2 app running in ruby 1.8.6 (upgrading isn't an option right now). Cucumber's been fine, now i'm trying to use Capybara. I've installed the capybara (1.1.1) gem and put the line require 'capybara/rails' in my features/support/env.rb file.

Now, when i run cucumber, i get this error:

Using the default profile...
uninitialized constant Rack::Builder (NameError)
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/activesupport-2.2.2/lib/active_support/dependencies.rb:445:in `load_missing_constant'
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/activesupport-2.2.2/lib/active_support/dependencies.rb:77:in `const_missing'
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/capybara-1.1.1/lib/capybara/rails.rb:4
/home/max/.rvm/rubies/ruby-1.8.6-p420/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in `gem_original_require'
/home/max/.rvm/rubies/ruby-1.8.6-p420/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in `require'
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/activesupport-2.2.2/lib/active_support/dependencies.rb:155:in `require'
/home/max/work/charanga/elearn_container/elearn/features/support/env.rb:10
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/cucumber-1.1.1/bin/../lib/cucumber/rb_support/rb_language.rb:143:in `load'
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/cucumber-1.1.1/bin/../lib/cucumber/rb_support/rb_language.rb:143:in `load_code_file'
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/cucumber-1.1.1/bin/../lib/cucumber/runtime/support_code.rb:171:in `load_file'
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/cucumber-1.1.1/bin/../lib/cucumber/runtime/support_code.rb:83:in `load_files!'
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/cucumber-1.1.1/bin/../lib/cucumber/runtime/support_code.rb:82:in `each'
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/cucumber-1.1.1/bin/../lib/cucumber/runtime/support_code.rb:82:in `load_files!'
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/cucumber-1.1.1/bin/../lib/cucumber/runtime.rb:137:in `load_step_definitions'
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/cucumber-1.1.1/bin/../lib/cucumber/runtime.rb:39:in `run!'
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/cucumber-1.1.1/bin/../lib/cucumber/cli/main.rb:43:in `execute!'
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/cucumber-1.1.1/bin/../lib/cucumber/cli/main.rb:20:in `execute'
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/cucumber-1.1.1/bin/cucumber:14
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/bin/cucumber:19:in `load'
/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/bin/cucumber:19

Here's the erroring file:

#/home/max/.rvm/gems/ruby-1.8.6-p420@elearning-resource/gems/capybara-1.1.1/lib/capybara/rails.rb
require 'capybara'
require 'capybara/dsl'

Capybara.app = Rack::Builder.new do
  map "/" do
    if Rails.version.to_f >= 3.0
      run Rails.application  
    else # Rails 2
      use Rails::Rack::Static
      run ActionController::Dispatcher.new
    end
  end
end.to_app

Capybara.asset_root = Rails.root.join('public')
Capybara.save_and_open_page_path = Rails.root.join('tmp/capybara')

So, line 4 is creating the error with the Rack::Builder.new line. But, why? Any ideas? I have the Rack gem installed already.

thanks, max

Answer 1

Try adding require 'rack/builder' before the require 'capybara/rails'in features/support/env.rb. Rails versions lower than 2.3 don't use Rack internally and thus Rack::Builder will not be loaded like capybara seems to be assuming.