Get rid of build_reroute. The last thing using it was the sprockets extension, though it didn't appear to need it since removing the build_reroute call leaves tests passing, and the test site I tried still generated JS from CoffeeScript just fine.

middleman-core/lib/middleman-core/core_extensions/builder.rb

@@ -6,45 +6,7 @@ module Middleman::CoreExtensions::Builder
     # @private
     def registered(app)
       app.define_hook :after_build
-      app.extend ClassMethods
-      app.send :include, InstanceMethods
-      app.delegate :build_reroute, :to => :"self.class"
     end
     alias :included :registered
   end
-  
-  # Build Class Methods
-  module ClassMethods
-    # Get a list of callbacks which can modify a files build path
-    # Each callback takes a destination path and a request path and
-    # returns a new destination path, or false if it doesn't want to reroute.
-    # @return [Array<Proc>]
-    def build_reroute(&block)
-      @build_rerouters ||= []
-      @build_rerouters << block if block_given?
-      @build_rerouters
-    end
-  end
-  
-  # Build Instance Methods
-  module InstanceMethods
-    # Run through callbacks and get the new values
-    #
-    # @param [String] destination The current destination path of the built file
-    # @param [String] request_path The request path of the file
-    # @return [String] The new destination path
-    def reroute_builder(destination, request_path)
-      result = [destination, request_path]
-      
-      build_reroute.each do |block|
-        output = block.call(destination, request_path)
-        if output
-          result = output
-          break
-        end
-      end
-      
-      result
-    end
-  end
 end

middleman-more/lib/middleman-more/core_extensions/sprockets.rb

@@ -13,18 +13,6 @@ module Middleman::CoreExtensions::Sprockets
       app.set :js_compressor, false
       app.set :css_compressor, false
       
-      # Cut off every extension after .js (which sprockets eats up)
-      app.build_reroute do |destination, request_path|
-        if !request_path.match(/\.js\./i)
-          false
-        else
-          [
-            destination.gsub(/\.js(\..*)$/, ".js"),
-            request_path.gsub(/\.js(\..*)$/, ".js")
-          ]
-        end
-      end
-      
       # Once Middleman is setup
       app.ready do
         # Create sprockets env for JS