Bundler could not find compatible versions for gem “railties” for Rails 4.0.0

Question

I am trying to upgrade to Rails 4.0.0, and I changed the gem versions of sass-rails and coffee-rails. I need to resolve this gem conflict between rails and coffee-rails before I can upgrade to Rails 4.

When I ran bundle update this is the output I got:

$ bundle update
Updating git://github.com/pilu/web-app-theme.git
Fetching source index from https://rubygems.org/
Resolving dependencies..............
Bundler could not find compatible versions for gem "railties":
  In Gemfile:
    rails (= 4.0.0) ruby depends on
      railties (= 4.0.0) ruby

    coffee-rails (= 4.0.0) ruby depends on
      railties (4.0.0.rc2)

My Gemfile:

source 'https://rubygems.org'

gem 'rails', '4.0.0'

gem 'cancan'
gem 'client_side_validations'
gem 'devise', '~> 1.5.3'
gem 'dynamic_form'
gem 'execjs'
gem 'haml'
gem 'httparty'
gem 'jquery-rails'
gem 'mysql2'
gem 'paperclip', '~> 2.4'
gem 'prawn'
gem 'rails3-jquery-autocomplete'
gem 'rake', '0.9.2'
gem 'remotipart', '~> 1.0'
gem 'simple_datatables'
gem 'therubyracer'
gem 'validates_timeliness', '~> 3.0.2'
gem 'will_paginate', '~> 3.0'

gem 'turbolinks'
gem 'jquery-turbolinks'

gem 'noty-rails'

gem 'font-awesome-rails'

gem 'socket.io-rails'

gem 'attr_encrypted'

gem 'bullet', :group => 'development'

#temp for demo.managetherapy.com
#gem 'faker'

group :test do
  gem 'capybara'
  gem 'cucumber-rails', :require => false
  gem 'database_cleaner'
  gem 'factory_girl_rails'
#  gem 'faker'
  gem 'guard-rspec'
  gem 'selenium-webdriver', '2.7.0'
  gem 'webrat'
end

group :development, :test do
  gem 'faker'
  gem 'haml-rails'
  gem 'hpricot'
  gem 'rspec-rails'
  gem 'ruby_parser'
  #gem 'web-app-theme', '~> 0.8.0'
  gem 'web-app-theme', :git =>'git://github.com/pilu/web-app-theme.git'
end

gem 'sass-rails', '4.0.0'
gem 'compass-rails', '1.0.3'
gem 'coffee-rails', '4.0.0'
gem 'uglifier', '>= 2.1.1'
gem 'bootstrap-sass-rails'

# Use unicorn as the web server
#gem 'unicorn'

# Deploy with Capistrano
gem 'capistrano'
gem 'rvm-capistrano'

gem 'passenger'

Answer 1

Also bundle update only allows you to update one gem at a time, which is hard if you are updating to Rails 4 and a whole lot of gems have to be updated at the same time.

I solved this by deleting the Gemfile.lock and doing bundle install.

This is of course assuming you have no conflicting explicit gem version in your Gemfile to start with. So if this fails, remove version numbers from the Gemfile.