Example code and stacktrace from introducing a private gem with a user class with the same namespace

Devise stacktrace

.rvm/gems/ruby-1.9.2-head@quikcv/bundler/gems/devise-ea7f15917f70/lib/devise/rails/routes.rb:380:in `raise_no_devise_method_error!': Foo::User does not respond to 'devise' method. This usually means you haven't loaded your ORM file or it's being loaded too late. To fix it, be sure to require 'devise/orm/YOUR_ORM' inside 'config/initializers/devise.rb' or before your application definition in 'config/application.rb' (RuntimeError)
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/bundler/gems/devise-ea7f15917f70/lib/devise/rails/routes.rb:194:in `block in devise_for'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/bundler/gems/devise-ea7f15917f70/lib/devise/rails/routes.rb:190:in `each'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/bundler/gems/devise-ea7f15917f70/lib/devise/rails/routes.rb:190:in `devise_for'
	from /Users/baphled/Projects/QuikCV/config/routes.rb:35:in `block in <top (required)>'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/actionpack-3.1.0/lib/action_dispatch/routing/route_set.rb:257:in `instance_exec'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/actionpack-3.1.0/lib/action_dispatch/routing/route_set.rb:257:in `eval_block'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/actionpack-3.1.0/lib/action_dispatch/routing/route_set.rb:234:in `draw'
	from /Users/baphled/Projects/QuikCV/config/routes.rb:3:in `<top (required)>'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:234:in `load'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:234:in `block in load'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:225:in `load_dependency'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:234:in `load'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/railties-3.1.0/lib/rails/application/routes_reloader.rb:29:in `block in load_paths'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/railties-3.1.0/lib/rails/application/routes_reloader.rb:29:in `each'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/railties-3.1.0/lib/rails/application/routes_reloader.rb:29:in `load_paths'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/railties-3.1.0/lib/rails/application/routes_reloader.rb:13:in `reload!'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/railties-3.1.0/lib/rails/application.rb:83:in `reload_routes!'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/bundler/gems/devise-ea7f15917f70/lib/devise/rails.rb:14:in `block in <class:Engine>'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/activesupport-3.1.0/lib/active_support/lazy_load_hooks.rb:34:in `call'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/activesupport-3.1.0/lib/active_support/lazy_load_hooks.rb:34:in `execute_hook'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/activesupport-3.1.0/lib/active_support/lazy_load_hooks.rb:43:in `block in run_load_hooks'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/activesupport-3.1.0/lib/active_support/lazy_load_hooks.rb:42:in `each'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/activesupport-3.1.0/lib/active_support/lazy_load_hooks.rb:42:in `run_load_hooks'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/railties-3.1.0/lib/rails/application/finisher.rb:50:in `block in <module:Finisher>'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/railties-3.1.0/lib/rails/initializable.rb:25:in `instance_exec'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/railties-3.1.0/lib/rails/initializable.rb:25:in `run'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/railties-3.1.0/lib/rails/initializable.rb:50:in `block in run_initializers'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/railties-3.1.0/lib/rails/initializable.rb:49:in `each'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/railties-3.1.0/lib/rails/initializable.rb:49:in `run_initializers'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/railties-3.1.0/lib/rails/application.rb:92:in `initialize!'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/railties-3.1.0/lib/rails/railtie/configurable.rb:30:in `method_missing'
	from /Users/baphled/Projects/QuikCV/config/environment.rb:5:in `<top (required)>'
	from /Users/baphled/Projects/QuikCV/spec/spec_helper.rb:3:in `require'
	from /Users/baphled/Projects/QuikCV/spec/spec_helper.rb:3:in `<top (required)>'
	from /Users/baphled/Projects/QuikCV/spec/models/quik_cv/user_spec.rb:1:in `require'
	from /Users/baphled/Projects/QuikCV/spec/models/quik_cv/user_spec.rb:1:in `<top (required)>'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/rspec-core-2.6.3/lib/rspec/core/configuration.rb:419:in `load'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/rspec-core-2.6.3/lib/rspec/core/configuration.rb:419:in `block in load_spec_files'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/rspec-core-2.6.3/lib/rspec/core/configuration.rb:419:in `map'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/rspec-core-2.6.3/lib/rspec/core/configuration.rb:419:in `load_spec_files'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/rspec-core-2.6.3/lib/rspec/core/command_line.rb:18:in `run'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/rspec-core-2.6.3/lib/rspec/core/runner.rb:80:in `run_in_process'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/rspec-core-2.6.3/lib/rspec/core/runner.rb:69:in `run'
	from /Users/baphled/.rvm/gems/ruby-1.9.2-head@quikcv/gems/rspec-core-2.6.3/lib/rspec/core/runner.rb:11:in `block in autorun'

gem_user.rb

# vendor/private/gems/business_logic/foo/user.rb
module Foo
  class User
    include Mongoid::Document
    include Mongoid::TimeStamps

    field :username
    field :email
  end
end

user.rb

# app/models/foo/user.rb
module Foo
  class User
    include Mongoid::Document
    include Mongoid::TimeStamps

    devise :database_authenticatable, :registerable, :token_authenticatable,
      :recoverable, :rememberable, :trackable, :validatable, :omniauthable
  end
end