Enabled Rails asset helpers inside the Sass and Scss filters.

Closes #467

CHANGELOG.md

@@ -104,6 +104,9 @@
 
 * Add command-line option to suppress script evaluation.
 
+* It's now possible to use Rails's asset helpers inside the Sass and SCSS
+  filters.
+
 ## 3.1.6
 
 * In indented mode, don't reindent buffers that contain preserved tags, and

lib/haml/filters.rb

@@ -58,6 +58,19 @@ module Haml
       filter
     end
 
+    # Removes a filter from Haml. If the filter was removed, it returns
+    # the that was remove Module upon success, or nil on failure. If you try
+    # to redefine a filter, Haml will raise an error. Use this method first to
+    # explicitly remove the filter before redefining it.
+    # @return Module The filter module that has been removed
+    # @since 3.2.0
+    def remove_filter(name)
+      defined.delete name.downcase
+      if constants.map(&:to_s).include?(name.to_s)
+        remove_const name.to_sym
+      end
+    end
+
     # The base module for Haml filters.
     # User-defined filters should be modules including this module.
     # The name of the filter is taken by downcasing the module name.

lib/haml/railtie.rb

@@ -7,5 +7,15 @@ if defined?(ActiveSupport)
   end
 end
 
+module Haml
+  class Railtie < ::Rails::Railtie
+    initializer :haml do |app|
+      if defined?(::Sass::Rails) && app.config.assets.enabled
+        require "haml/sass_rails_filter"
+      end
+    end
+  end
+end
+
 require "haml/helpers/safe_erubis_template"
 Haml::Filters::Erb.template_class = Haml::SafeErubisTemplate

lib/haml/sass_rails_filter.rb

@@ -0,0 +1,33 @@
+module Haml
+  module Filters
+    # This is an extension of Sass::Rails's SassTemplate class that allows
+    # Rails's asset helpers to be used inside Haml Sass filter.
+    class SassRailsTemplate < ::Sass::Rails::SassTemplate
+      def render(scope=Object.new, locals={}, &block)
+        scope = ::Rails.application.assets.context_class.new(::Rails.application.assets, "/", "/")
+        super
+      end
+
+      def sass_options(scope)
+        options = super
+        options[:custom][:resolver] = ::ActionView::Base.new
+        options
+      end
+    end
+
+    # This is an extension of Sass::Rails's SassTemplate class that allows
+    # Rails's asset helpers to be used inside a Haml SCSS filter.
+    class ScssRailsTemplate < SassRailsTemplate
+      self.default_mime_type = 'text/css'
+
+      def syntax
+        :scss
+      end
+    end
+
+    remove_filter :Sass
+    remove_filter :Scss
+    register_tilt_filter "Sass", :extend => "Css", :template_class => SassRailsTemplate
+    register_tilt_filter "Scss", :extend => "Css", :template_class => ScssRailsTemplate
+  end
+end

test/filters_test.rb

@@ -7,7 +7,7 @@ class FiltersTest < MiniTest::Unit::TestCase
       Module.new {def self.name; "Foo::Bar"; end; include Haml::Filters::Base}
       assert Haml::Filters.defined.has_key? "bar"
     ensure
-      Haml::Filters.defined.delete "bar"
+      Haml::Filters.remove_filter "Bar"
     end
   end
 
@@ -19,8 +19,7 @@ class FiltersTest < MiniTest::Unit::TestCase
         end
       end
     ensure
-      Haml::Filters.defined.delete "foo"
+      Haml::Filters.remove_filter "Foo"
-      Haml::Filters.send :remove_const, :Foo
     end
   end
 
@@ -31,8 +30,7 @@ class FiltersTest < MiniTest::Unit::TestCase
         Haml::Filters.defined["textile"].template_class
       end
     ensure
-      Haml::Filters.defined.delete "textile"
+      Haml::Filters.remove_filter "Textile"
-      Haml::Filters.send :remove_const, :Textile
     end
   end
 
@@ -43,8 +41,7 @@ class FiltersTest < MiniTest::Unit::TestCase
         Haml::Filters.defined["maruku"].template_class
       end
     ensure
-      Haml::Filters.defined.delete "maruku"
+      Haml::Filters.remove_filter "Maruku"
-      Haml::Filters.send :remove_const, :Maruku
     end
   end
 
@@ -108,8 +105,7 @@ class FiltersTest < MiniTest::Unit::TestCase
       haml = ":foo"
       assert_equal "foobar\n", render(haml)
     ensure
-      Haml::Filters.defined.delete "foo"
+      Haml::Filters.remove_filter "Foo"
-      Haml::Filters.send :remove_const, :Foo
     end
   end