Making Jammit jam with Heroku

So, you want to use Heroku and Jammit together, and you've come here of all places! I know, there's no good solution for this floating around The Interwebs, so I figured one out myself, and now I'm publishing so that you, YOU THE VIEWER, can be both shocked and amazed.

There's a nicely formatted gist right here, or you can read it inline below:

	unless Rails.env.development?
	require 'fileutils'
	output_folder = Rails.root.join("tmp", "jammit", "assets")
	FileUtils.mkdir_p(output_folder)
	# Heroku specific hack.
	Jammit::Packager.class_eval do
	def glob_files_with_heroku_hack(glob)
	paths = glob_files_without_heroku_hack(glob)
	# Heroku has a magical "public/javascripts/all.js" file. It is a Mystery.
	paths.reject { |path| path =~ /javascripts\/all.js$/ }
	end
	alias_method_chain :glob_files, :heroku_hack
	end
	Jammit.package! :output_folder => output_folder
	Rails.configuration.middleware.insert_before('Rack::Sendfile', 'Rack::Static',
	:urls => ['/assets'],
	:root => "#{Rails.root}/tmp/jammit")
	end

view raw jammit.rb hosted with ❤ by GitHub

Yes, that large hack floating around in the middle is specifically for Heroku. If you're on another cloud service that is a little less wizardly, you can drop the class_eval block entirely and you should be good to go.

If you're wondering if the resultant files will be cached by Heroku's Varnish HTTP accelerator: yes. Rack::Static will return the fetched files as Rack::File objects, which Heroku caches.

UPDATE: if it's not obvious, this needs to go into config/initializers -- so it runs once on app start up.