Steps to upgrade an existing Rails 4.2.x app to unreleased Rails 5 edge version

Note: At the time of writing this the commands shown below were executed on Ubuntu 14.04

Updated .ruby-version by replacing 2.2.1 WITH 2.2.3. In case this file is not present, its better to create it.
Updated .ruby-gemset by replacing <MY_APP_NAME> WITH <MY_APP_NAME>-on-rails-5, where <MY_APP_NAME> represents your app's name. In case this file is not present, its better to create it.
Upgraded rvm by running command $ rvm get stable.
Installed latest stable Ruby version listed here using command: $ rvm install 2.2.3
Removed Gemfile.lock
Updated Gemfile by replacing gem 'rails', '4.2.0' WITH gem 'rails', git: 'https://github.com/rails/rails.git'
Installed bundler using command: $ gem install bundler

Ran bundle and encountered error:

```
  Bundler could not find compatible versions for gem "rack":
  In Gemfile:
    rails (>= 0) ruby depends on
      actionpack (= 5.0.0.alpha) ruby depends on
        rack (~> 2.x) ruby
  Could not find gem 'rack (~> 2.x) ruby', which is required by gem 'actionpack (= 5.0.0.alpha) ruby', in any of the sources.
```

Found following references on this error: https://github.com/rails/rails/issues/21422

Based on the reference found to get rid of the error shown above, added following to the Gemfile.

  ```
  # ================================
  # Once Rails 5 is officially released I don't think the following shall be needed. But for
  # now those are required to get rid of error reported in https://github.com/rails/rails/issues/21422
  gem 'rack', :git => 'https://github.com/rack/rack.git'
  gem 'arel', :git => 'https://github.com/rails/arel.git'
  # ================================
  ```

Reference: http://www.christopherbloom.com/2015/04/26/setting-up-a-rails-5-app-from-edge/

Ran bundle and encountered following error:

  ```
    Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

        /home/jignesh/.rvm/rubies/ruby-2.2.3/bin/ruby -r ./siteconf20151119-12203-hjmfyi.rb extconf.rb
    creating Makefile

    make "DESTDIR=" clean

    make "DESTDIR="
    compiling generator.c
    linking shared-object json/ext/generator.so
    /usr/bin/ld: cannot find -lgmp
    collect2: error: ld returned 1 exit status
    make: *** [generator.so] Error 1

    make failed, exit code 2

    Gem files will remain installed in /home/jignesh/.rvm/gems/ruby-2.2.3@<GEMSET_NAME>/gems/json-1.8.3 for inspection.
    Results logged to /home/jignesh/.rvm/gems/ruby-2.2.3@<GEMSET_NAME>/extensions/x86_64-linux/2.2.0/json-1.8.3/gem_make.out
    An error occurred while installing json (1.8.3), and Bundler cannot continue.
    Make sure that `gem install json -v '1.8.3'` succeeds before bundling.
  ```

  Found following reference on this error: http://stackoverflow.com/questions/32130649/can-not-install-json-gem-with-ruby-2-2-3-on-ubuntu

Based on the reference found to get rid of the error shown above, ran following: $ sudo apt-get install libgmp3-dev Reference: http://stackoverflow.com/a/32191707/936494
Ran bundle again and it ran successfully!

jiggneshhgohel/rails-5-edge-upgrade.markdown