Sprockets producing Handlebars templates from Haml

config.rb

http_path = "/"
css_dir = "public/stylesheets"
sass_dir = "sass"
images_dir = "public/images"
http_images_dir = "images"

javascripts_dir = "public/javascripts"

fonts_dir = "public/fonts"
http_fonts_dir = "fonts"

line_comments = false

config.ru

$LOAD_PATH << File.expand_path('.')

require 'rubygems'
require 'bundler/setup'
require 'haml'
require 'sass'
require 'sass/plugin/rack'
require 'compass'
require 'tilt'
require 'sprockets'
require 'hamlbars'

Compass.add_configuration(File.expand_path('config.rb'))
Compass.configure_sass_plugin!
use Sass::Plugin::Rack

map '/javascripts' do
  sprockets = Sprockets::Environment.new
  sprockets.engines.register 'hamlbars', Tilt::HamlbarsTemplate
  sprockets.paths << 'apps'
  sprockets.paths << 'vendor/javascripts'
  sprockets.static_root = 'public/javascripts'
  run sprockets
end

map '/' do
  run Rack::Directory.new('public')
end

hamlbars.rb

require 'tilt/template'

module Tilt
  class HamlbarsTemplate < Template
    JS_ESCAPE_MAP = {
      "\r\n"  => '\n',
      "\n"    => '\n',
      "\r"    => '\n',
      '"'     => '\\"',
      "'"     => "\\'" }

    self.default_mime_type = 'application/javascript'

    def self.engine_initialized?
      defined? ::Haml::Engine
    end

    def initialize_engine
      require_template_library 'haml'
    end

    def prepare
      options = @options.merge(:filename => eval_file, :line => line)
      @engine = ::Haml::Engine.new(data, options)
    end

    def evaluate(scope, locals, &block)
      template = if @engine.respond_to?(:precompiled_method_return_value, true)
        super
      else
        @engine.render(scope, locals, &block)
      end
      if basename =~ /^_/
        "Handlebars.registerPartial('#{name}', '#{template.strip.gsub(/(\r\n|[\n\r"'])/) { JS_ESCAPE_MAP[$1] }}');\n"
      else
        "App.registerTemplate('#{name}', '#{template.strip.gsub(/(\r\n|[\n\r"'])/) { JS_ESCAPE_MAP[$1] }}');\n"
      end
    end

    # Precompiled Haml source. Taken from the precompiled_with_ambles
    # method in Haml::Precompiler:
    # http://github.com/nex3/haml/blob/master/lib/haml/precompiler.rb#L111-126
    def precompiled_template(locals)
      @engine.precompiled
    end

    def precompiled_preamble(locals)
      local_assigns = super
      @engine.instance_eval do
        <<-RUBY
          begin
            extend Haml::Helpers
            _hamlout = @haml_buffer = Haml::Buffer.new(@haml_buffer, #{options_for_buffer.inspect})
            _erbout = _hamlout.buffer
            __in_erb_template = true
            _haml_locals = locals
            #{local_assigns}
        RUBY
      end
    end

    def precompiled_postamble(locals)
      @engine.instance_eval do
        <<-RUBY
            #{precompiled_method_return_value}
          ensure
            @haml_buffer = @haml_buffer.upper
          end
        RUBY
      end
    end
  end
end

module Haml
  module Helpers

    module HamlbarsExtensions
      def iterate(name, &block)
        content = capture_haml(&block)
        "{{##{name}}}#{content.strip}{{/#{name}}}"
      end
    end

    include HamlbarsExtensions
  end
end

I just started working on making sprockets support sass better. It should land in the next few days: sstephenson/sprockets#23

That's great news. Thanks for the heads up and all your excellent work.