Do not add files in assets/ directories to Sprockets

railties/lib/rails/engine.rb

@@ -538,9 +538,9 @@ def load_seed
     end
 
     initializer :append_assets_path do |app|
-      app.config.assets.paths.unshift(*paths["vendor/assets"].existent)
-      app.config.assets.paths.unshift(*paths["lib/assets"].existent)
-      app.config.assets.paths.unshift(*paths["app/assets"].existent)
+      app.config.assets.paths.unshift(*paths["vendor/assets"].existent_directories)
+      app.config.assets.paths.unshift(*paths["lib/assets"].existent_directories)
+      app.config.assets.paths.unshift(*paths["app/assets"].existent_directories)
     end
 
     initializer :prepend_helpers_path do |app|

railties/lib/rails/paths.rb

@@ -193,6 +193,10 @@ def expanded
       def existent
         expanded.select { |f| File.exists?(f) }
       end
+
+      def existent_directories
+        expanded.select {|d| Dir.exists?(d) }
+      end
 
       def paths
         ActiveSupport::Deprecation.warn "paths is deprecated. Please call expand instead."

railties/test/application/assets_test.rb

@@ -86,5 +86,19 @@ def index
       assert_match "alert()", last_response.body
       assert_equal nil, last_response.headers["Set-Cookie"]
     end
+
+    test "files in any assets/ directories are not added to Sprockets" do
+      %w[app lib vendor].each do |dir|
+        app_file "#{dir}/assets/#{dir}_test.erb", "testing"
+      end
+
+      app_file "app/assets/javascripts/demo.js", "alert();"
+
+      require "#{app_path}/config/environment"
+
+      get "/assets/demo.js"
+      assert_match "alert();", last_response.body
+      assert_equal 200, last_response.status
+    end
   end
 end