Problems with asset precompile after updating to Rails 4 - ruby-on-rails

Question

I am updating a Rails application from 3.2.12 to 4.0.0.beta1. I had a few minor issues but I could get the app running and all tests passing again. The problem is when I try to precompile all the assets for deployment, I get the following error:
vagrant#precise64:/vagrant$ RAILS_ENV=production bundle exec rake assets:precompile
rake aborted!
No such file to load -- bootstrap_flash_helper
/vagrant/config/environment.rb:5:in `<top (required)>'
Tasks: TOP => environment
(See full trace by running task with --trace)
Here is my Gemfile:
source 'https://rubygems.org'
gem 'rails', '4.0.0.beta1'
gem 'pg'
gem 'github_api'
gem 'haml-rails'
gem 'jquery-rails'
gem 'simple_form', github: 'plataformatec/simple_form'
gem 'devise', github: 'plataformatec/devise', branch: 'rails4'
gem 'omniauth'
gem 'omniauth-github'
gem 'rails-backbone', '~> 0.9.10'
gem 'inherited_resources'
gem 'app_configuration'
gem 'unicorn'
gem 'foreman'
gem 'coveralls', require: false
group :assets do
gem 'sprockets-rails', github: 'rails/sprockets-rails'
gem 'coffee-rails', github: 'rails/coffee-rails'
gem 'therubyracer', platforms: :ruby
gem 'less-rails', github: 'metaskills/less-rails'
gem 'twitter-bootstrap-rails'
gem 'uglifier', '>= 1.0.3'
end
group :development do
gem 'better_errors'
gem 'binding_of_caller'
gem 'meta_request'
end
group :test, :development do
# Debugging
gem 'pry'
gem 'debugger'
gem 'debugger-pry'
gem 'pry-nav'
gem 'pry-stack_explorer'
# Testing
gem 'timecop'
gem 'rspec-rails'
gem 'shoulda-matchers'
gem 'factory_girl_rails'
gem 'faker'
# gem 'cucumber-rails', '~>1.3.0', :require => false
gem 'database_cleaner', github: 'bmabey/database_cleaner'
end
The project is open source (work in progress), here is the github repository https://github.com/wolox/mgmt
Any idea about what I missing?
Thanks

Answer 1

I had a similar issue, then I found that group :assets doesn't exist anymore. After clonning your repo, I deleted the group :assets from your Gemfile, then your assets precompiled ok!

Answer 2

The :assets group is not loaded in the production environment by default, you can change this in your config/application.rb (https://github.com/Wolox/mgmt/blob/master/config/application.rb#L7 in your repo)
The advised practice is to compile your assets in development and then push the /public/assets directory to production once you're satisfied nothing breaks.
Use this line instead, and you should be fine:
RAILS_ENV=development bundle exec rake assets:precompile