3 files changed, 57 insertions, 19 deletions

diff --git a/actionpack/lib/sprockets/compressors.rb b/actionpack/lib/sprockets/compressors.rb
new file mode 100644
index 0000000000..6544953df4
--- /dev/null
+++ b/actionpack/lib/sprockets/compressors.rb
@@ -0,0 +1,21 @@
+module Sprockets
+  class NullCompressor
+    def compress(content)
+      content
+    end
+  end
+
+  class LazyCompressor
+    def initialize(&block)
+      @block = block
+    end
+
+    def compressor
+      @compressor ||= @block.call || NullCompressor.new
+    end
+
+    def compress(content)
+      compressor.compress(content)
+    end
+  end
+end
\ No newline at end of file
diff --git a/actionpack/lib/sprockets/helpers/rails_helper.rb b/actionpack/lib/sprockets/helpers/rails_helper.rb
index 63820cc76c..a95e7c0649 100644
--- a/actionpack/lib/sprockets/helpers/rails_helper.rb
+++ b/actionpack/lib/sprockets/helpers/rails_helper.rb
@@ -1,4 +1,4 @@
-require "action_view/helpers"
+require "action_view"
 
 module Sprockets
   module Helpers
@@ -9,14 +9,12 @@ module Sprockets
       def asset_paths
         @asset_paths ||= begin
           config     = self.config if respond_to?(:config)
+          config   ||= Rails.application.config
           controller = self.controller if respond_to?(:controller)
-          config ||= Rails.application.config
-          if config.action_controller.present?
-            config.action_controller.default_asset_host_protocol ||= :relative
-          else
-            config.default_asset_host_protocol ||= :relative
-          end
-          RailsHelper::AssetPaths.new(config, controller)
+          paths = RailsHelper::AssetPaths.new(config, controller)
+          paths.asset_environment = asset_environment
+          paths.asset_prefix      = asset_prefix
+          paths
         end
       end
 
@@ -76,9 +74,28 @@ module Sprockets
           params[:debug_assets] == 'true'
       end
 
+      # Override to specify an alternative prefix for asset path generation.
+      # When combined with a custom +asset_environment+, this can be used to
+      # implement themes that can take advantage of the asset pipeline.
+      #
+      # If you only want to change where the assets are mounted, refer to
+      # +config.assets.prefix+ instead.
+      def asset_prefix
+        Rails.application.config.assets.prefix
+      end
+
+      # Override to specify an alternative asset environment for asset
+      # path generation. The environment should already have been mounted
+      # at the prefix returned by +asset_prefix+.
+      def asset_environment
+        Rails.application.assets
+      end
+
       class AssetPaths < ::ActionView::AssetPaths #:nodoc:
-        def compute_public_path(source, dir, ext=nil, include_host=true, protocol = nil)
-          super(source, Rails.application.config.assets.prefix, ext, include_host, protocol)
+        attr_accessor :asset_environment, :asset_prefix
+
+        def compute_public_path(source, dir, ext=nil, include_host=true, protocol=nil)
+          super(source, asset_prefix, ext, include_host, protocol)
         end
 
         # Return the filesystem path for the source
@@ -90,14 +107,14 @@ module Sprockets
           source = source.to_s
           return nil if is_uri?(source)
           source = rewrite_extension(source, nil, ext)
-          assets[source]
+          asset_environment[source]
         end
 
         def rewrite_asset_path(source, dir)
           if source[0] == ?/
             source
           else
-            assets.path(source, performing_caching?, dir)
+            asset_environment.path(source, performing_caching?, dir)
           end
         end
 
@@ -109,10 +126,6 @@ module Sprockets
           end
         end
 
-        def assets
-          Rails.application.assets
-        end
-
         # When included in Sprockets::Context, we need to ask the top-level config as the controller is not available
         def performing_caching?
           config.action_controller.present? ? config.action_controller.perform_caching : config.perform_caching
diff --git a/actionpack/lib/sprockets/railtie.rb b/actionpack/lib/sprockets/railtie.rb
index d1e97c594e..c28bdc3061 100644
--- a/actionpack/lib/sprockets/railtie.rb
+++ b/actionpack/lib/sprockets/railtie.rb
@@ -1,8 +1,12 @@
 module Sprockets
   autoload :Helpers, "sprockets/helpers"
+  autoload :LazyCompressor, "sprockets/compressors"
+  autoload :NullCompressor, "sprockets/compressors"
 
   # TODO: Get rid of config.assets.enabled
   class Railtie < ::Rails::Railtie
+    config.default_asset_host_protocol = :relative
+
     rake_tasks do
       load "sprockets/assets.rake"
     end
@@ -60,14 +64,14 @@ module Sprockets
         env.logger = Rails.logger
 
         if env.respond_to?(:cache)
-          env.cache = Rails.cache
+          env.cache = assets.cache_store || Rails.cache
         end
 
         if assets.compress
           # temporarily hardcode default JS compressor to uglify. Soon, it will work
           # the same as SCSS, where a default plugin sets the default.
-          env.js_compressor  = expand_js_compressor(assets.js_compressor || :uglifier)
-          env.css_compressor = expand_css_compressor(assets.css_compressor)
+          env.js_compressor  = LazyCompressor.new { expand_js_compressor(assets.js_compressor || :uglifier) }
+          env.css_compressor = LazyCompressor.new { expand_css_compressor(assets.css_compressor) }
         end
 
         env