patches the generated source map with the otherwise missing filename

source_maps.rb

if Rails.env.development?
  module CoffeeScript
    class SourceMapError < StandardError; end;

    class << self

      def compile script, options
        script = script.read if script.respond_to?(:read)

        if options.key?(:no_wrap) and !options.key?(:bare)
          options[:bare] = options[:no_wrap]
        else
          options[:bare] = false
        end

        # adding source mapss option. (source maps option requires filename option.)
        options[:sourceMap] = true
        options[:filename]  = options[:pathname].basename.to_s

        ret = Source.context.call("CoffeeScript.compile", script, options)

        map_dir = Rails.root.join("public/source_maps")
        map_dir.mkpath

        basename    = options[:pathname].basename('.coffee')
        map_file    = map_dir.join "#{basename}.map"
        coffee_file = map_dir.join "#{basename}.coffee"

        # patch the generated source map with the otherwise missing filename
        source_map = JSON.load(ret["v3SourceMap"])
        source_map["sources"][0] = options[:filename]

        coffee_file.open('w') {|f| f.puts script }
        map_file.open('w')    {|f| f.puts source_map.to_json }

        comment = "//@ sourceMappingURL=/source_maps/#{map_file.basename}\n"
        return comment + ret["js"]

      end

    end
  end



  # Monkeypatch this method to include the scripts' pathname
  require 'tilt/template'

  module Tilt
    class CoffeeScriptTemplate < Template
      def evaluate(scope, locals, &block)
        @output ||= CoffeeScript.compile(data, options.merge(:pathname => scope.pathname))
      end
    end
  end
end