I recently worked with devise in a Rails application for the first time. Using Rails 3.0.3, Bundler 1.0.9 either Devise 1.1.5 or 1.2.RC I found I had to manually add dependencies for Hpricot and Ruby_parser to my Gemfile in order to run the devise:views generator. Without those to gems explicitly declared as dependencies, running the generator produced empty views under RAILS\_ROOT/app/views/devise and yielded the following errors:

$ rails g devise:views
Required dependency hpricot not found!
Run "gem install hpricot" to get it.
…

And then after adding hpricot to the Gemfile:

$ rails g devise:views
Required dependency ruby_parser not found!
    Run "gem install ruby_parser" to get it.
…

As I wasn’t relying on those gems for anything else in the application, I only added them to the development group:

# Gemfile
group :development do
  gem 'hpricot'
  gem 'ruby_parser'
end

With those dependencies declared running the generator works as expected.