Gemfile

source 'https://rubygems.org'
gemspec

gem 'rake'

rails = ENV['RAILS'] || 'master'

if rails == 'master'
  arel = ENV['AREL'] || 'master'
  arel_opts =
    case arel
    when /\// # A path
      { path: arel }
    when /^v/ # A tagged version
      { git: 'git://github.com/rails/arel.git', tag: arel }
    else
      { git: 'git://github.com/rails/arel.git', branch: arel }
    end
  gem 'arel', arel_opts
end

case rails
when /\// # A path
  gem 'activerecord', path: "#{rails}/activerecord"
when /^v/ # A tagged version
  git 'git://github.com/rails/rails.git', tag: rails do
    gem 'activerecord'
  end
else
  git 'git://github.com/rails/rails.git', branch: rails do
    gem 'activerecord'
  end
end