sass_with_compass.rb

# frozen_string_literal: true

require 'nanoc'

module Nanoc
  module Filters
    class SassWithCompass < Nanoc::Filter
      identifier :sass_with_compass
      type :text

      requires 'configatron', 'compass', 'sass'

      def run(content, params = {})
        define_dependencies

        render_with_sourcemap(sourcemap_uri) unless configatron.web.compress

        css, sourcemap = Sass.new(@assigns).setup_and_run(content,
                                                          configure_compass(params))

        save(sourcemap)
        css
      end

      private

      def define_dependencies
        depend_on(@assigns[:items].find_all('/**/*.{jpg,png}'))
        depend_on(@assigns[:items].find_all('/**/*.{eot,ttf}'))
      end

      def configure_compass(params)
        p = params.dup
        Compass.add_project_configuration(p.delete(:config_file))

        p.merge(Compass.sass_engine_options)
      end

      def render_with_sourcemap(uri)
        ::Sass::Engine.send(:define_method,
                            :render,
                            proc { render_with_sourcemap(uri) })
      end

      def save(sourcemap)
        return unless sourcemap
        FileUtils.mkdir_p(File.dirname(sourcemap_path), verbose: false)
        IO.write(sourcemap_path, sourcemap.to_json(css_uri: @item.path))
      end

      def sourcemap_file
        @item.path + '.map'
      end

      def sourcemap_path
        File.join(@config[:output_dir], sourcemap_file)
      end

      def sourcemap_uri
        File.basename(sourcemap_file)
      end
    end
  end
end 

usage.rb

compile '/assets/css/app.sass' do
  filter :sass_with_compass, config_file: 'compass-config.rb'
end