Define append_assets_path unless it exists

Author: josh

lib/sprockets/railtie.rb

@@ -36,6 +36,17 @@ def assets
     # Returns Sprockets::Manifest for app config.
     attr_accessor :assets_manifest
   end
+
+  class Engine < Railtie
+    # Skip defining append_assets_path on Rails <= 4.2
+    unless initializers.find { |init| init.name == :append_assets_path }
+      initializer :append_assets_path, group: :all do |app|
+        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
+    end
+  end
 end
 
 module Sprockets