Give assets access to asset_path during precompilation

railties/lib/rails/tasks/assets.rake

@@ -1,6 +1,9 @@
 namespace :assets do
   desc "Compile all the assets named in config.assets.precompile"
   task :precompile => :environment do
+    # Give assets access to asset_path
+    ActionView::Helpers::SprocketsHelper
+
     assets = Rails.application.config.assets.precompile
     Rails.application.assets.precompile(*assets)
   end