If you are switching over a Rails 2.3 app to Bundler with a Rails App, or you are setting up a new one, you might run into this error when you try to boot rails or run a rake task, thankfully the solution is simple.

The problem is that in your Gemfile, you are trying to load a gem that requires the Rails stack to be in place. If you check out the Bundler docs for Rails 2.3 you will see a :plugins group option. This group provides a way to load up gem plugins that require the Rails stack.

If you are not sure which gem is requiring the Rails stack before Rails is loaded and thus blowing out bundler, you can run rake -T as usual, you will get something like this:

 $ rake -T --trace
(in /Users/mikel/Code/railsplugins)
rake aborted!
uninitialized constant ActionController
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@railsplugins/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:443:in `load_missing_constant'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@railsplugins/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:80:in `const_missing'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@railsplugins/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:92:in `const_missing'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@railsplugins/gems/behavior-0.2.0/lib/behavior.rb:80
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@railsplugins/gems/bundler-0.9.14/lib/bundler/runtime.rb:45:in `require'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@railsplugins/gems/bundler-0.9.14/lib/bundler/runtime.rb:45:in `require'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@railsplugins/gems/bundler-0.9.14/lib/bundler/runtime.rb:40:in `each'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@railsplugins/gems/bundler-0.9.14/lib/bundler/runtime.rb:40:in `require'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@railsplugins/gems/bundler-0.9.14/lib/bundler/runtime.rb:39:in `each'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@railsplugins/gems/bundler-0.9.14/lib/bundler/runtime.rb:39:in `require'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@railsplugins/gems/bundler-0.9.14/lib/bundler.rb:75:in `require'
/Users/mikel/Code/railsplugins/config/../config/preinitializer.rb:20
/Users/mikel/Code/railsplugins/config/boot.rb:28:in `load'
/Users/mikel/Code/railsplugins/config/boot.rb:28:in `preinitialize'
/Users/mikel/Code/railsplugins/config/boot.rb:10:in `boot!'
/Users/mikel/Code/railsplugins/config/boot.rb:128
/Users/mikel/.rvm/rubies/ruby-1.8.7-p249/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
/Users/mikel/.rvm/rubies/ruby-1.8.7-p249/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `require'
/Users/mikel/Code/railsplugins/Rakefile:4
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@global/gems/rake-0.8.7/lib/rake.rb:2383:in `load'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@global/gems/rake-0.8.7/lib/rake.rb:2383:in `raw_load_rakefile'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@global/gems/rake-0.8.7/lib/rake.rb:2017:in `load_rakefile'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@global/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@global/gems/rake-0.8.7/lib/rake.rb:2016:in `load_rakefile'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@global/gems/rake-0.8.7/lib/rake.rb:2000:in `run'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@global/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@global/gems/rake-0.8.7/lib/rake.rb:1998:in `run'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@global/gems/rake-0.8.7/bin/rake:31
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@global/bin/rake:19:in `load'
/Users/mikel/.rvm/gems/ruby-1.8.7-p249@global/bin/rake:19

Now, inside of that trace is a single line:

/Users/mikel/.rvm/gems/ruby-1.8.7-p249@railsplugins/gems/behavior-0.2.0/lib/behavior.rb:80

And there is your clue, moving the gem requirement for behavior into the :plugins group like this:

# Gemfile

source :gemcutter

gem 'rails', '2.3.5'

gem 'mysql',            '2.8.1'

group :plugins do
  gem 'behavior',       '0.2.0'
end

Save and re run the rake task, if you are like me and had two or three of these lurking, you will have to work out which ones to put into the :plugins group yourself, the type of plugin is usually pretty obvious.

blogLater

Mikel