Use system ruby

Author: Orion Henry

lib/language_pack/ruby.rb

@@ -252,6 +252,28 @@ def setup_profiled
   # install the vendored ruby
   # @return [Boolean] true if it installs the vendored ruby and false otherwise
   def install_ruby
+    if system_ruby
+      install_system_ruby system_ruby
+    else
+      install_ruby_orig
+    end
+  end
+
+  def install_system_ruby(ruby)
+    instrument 'ruby.install_system_ruby' do
+      dir = File.dirname(ruby)
+      file = File.basename(ruby)
+
+      install_symlink("ruby", "#{dir}/#{file}")
+      install_symlink("gem",  "#{dir}/#{file.gsub("ruby","gem")}")
+      install_symlink("ri",   "#{dir}/#{file.gsub("ruby","ri")}")
+      install_symlink("rdoc", "#{dir}/#{file.gsub("ruby","rdoc")}")
+
+      ENV["PATH"] = "#{File.expand_path("bin")}:#{ENV["PATH"]}"
+    end
+  end
+
+  def install_ruby_orig
     instrument 'ruby.install_ruby' do
       return false unless ruby_version
 
@@ -416,14 +438,26 @@ def install_binary(name)
     end
   end
 
+  def install_symlink(name, file)
+    bin_dir = "bin"
+    FileUtils.mkdir_p bin_dir
+    Dir.chdir(bin_dir) do |dir|
+      File.symlink(file,name) unless File.exists?(name)
+    end
+  end
+
   # removes a binary from the slug
   # @param [String] relative path of the binary on the slug
   def uninstall_binary(path)
     FileUtils.rm File.join('bin', File.basename(path)), :force => true
   end
 
+  def system_ruby
+    ENV["SYSTEM_RUBY"]
+  end
+
   def load_default_cache?
-    new_app? && ruby_version.default?
+    new_app? && ruby_version.default? && !system_ruby
   end
 
   # loads a default bundler cache for new apps to speed up initial bundle installs