source "http://rubygems.org" gemspec gem 'rake' rails = ENV['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 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