Change effective on 05 May 2015
When deploying a Ruby on Rails site that uses the asset pipeline, the manifest file is used to determine if the assets have been precompiled. If the assets have been checked into git then the Ruby buildpack will skip asset compilation. Sprockets 3.0 introduced a new naming convention for this manifest file. As of now Heroku supports the new manifest file generated by Sprockets 3.0.
Check out the Ruby buildpack’s changelog for more information.