coffee.rb

# A coffee-script filter for nanoc3
require 'open3'
require 'win32/open3' if RUBY_PLATFORM.match /win32/

class CoffeeFilter < Nanoc3::Filter
  identifier :coffee

  def run(content, params = {})
    output = ''
    command = 'coffee -s -p -l'
    Open3.popen3(command) do |stdin, stdout, stderr|
      stdin.puts content
      stdin.close
      output = stdout.read.strip
      [stdout, stderr].each { |io| io.close }
    end
    output
  end
end

config.yml

# Be sure to add your coffee extension at the end
text_extensions: [ 'css', 'erb', 'haml', 'htm', 'html', 'js', 'less', 'markdown', 'md', 'php', 'rb', 'sass', 'txt', 'coffee' ]

Rules

# Compile both coffee and js, co-mingled in the same directory
compile '/js/*' do
  case item[:extension]
    when 'coffee'
      filter :coffee
    when 'js'
      # Nothing
  end
end