Heroku throws undefined method `devise_for' - ruby-on-rails

Question

I have an app running local, and it works correctly. I've set up devise on it for OAuth with facebook.
When I push the app to Heroku I get this exception:
/app/app/controllers/users_controller.rb:2:in `<class:SessionsController>':
undefined method `devise_for'
for Users::SessionsController:Class (NoMethodError)
But I don't have this error locally.
These are the steps I took after pushing it to Heroku:
heroku run rake db:migrate
restarted heroku using heroku restart and heroku ps:restart
So the problem isn't that I still have to restart my server.
Here is my gemfile:
source 'https://rubygems.org'
gem 'rails', '3.2.12'
# Bundle edge Rails instead:
# gem 'rails', :git => 'git://github.com/rails/rails.git'
gem 'pg'
# Gems used only for assets and not required
# in production environments by default.
group :assets do
gem 'sass-rails', '~> 3.2.3'
gem 'coffee-rails', '~> 3.2.1'
# See https://github.com/sstephenson/execjs#readme for more supported runtimes
gem 'therubyracer', :platforms => :ruby
gem 'uglifier', '>= 1.0.3'
end
gem 'jquery-rails'
gem 'devise'
gem 'omniauth'
gem 'omniauth-facebook'
What could be the issue?
Edit
Here are the first lines of where the error points at:
# app/controllers/users/users_controller
class Users::SessionsController < Devise::SessionsController
devise_for :users, :controllers => { :sessions => "users/sessions" }
end

Answer 1

Did you try running this locally? devise_for should be on your routes, not in the controller see https://github.com/plataformatec/devise to make sure you have your settings correctly. You don't need to override the controller, unless you are doing something special with it. If I where you I'll try to do the least amount of change first, and incrementally change it the way you want.