Monkey patch Sprockets so that non-digest assets will be generated when ENV['SPROCKETS_NON_DIGEST'] is present

commands.sh

# Run locally
$ SPROCKETS_NON_DIGEST=true RAILS_ENV=production rake assets:precompile

# Heroku setup
$ heroku labs:enable user-env-compile
$ heroku config:add SPROCKETS_NON_DIGEST=true

sprockets-patch.rb

raise("Sprockets monkey patch for v 2.10.0. Check before moving on") unless Sprockets::VERSION == "2.10.0"

module Sprockets
  class Manifest
    def compile(*args)
      unless environment
        raise Error, "manifest requires environment for compilation"
      end

      paths = environment.each_logical_path(*args).to_a +
        args.flatten.select { |fn| Pathname.new(fn).absolute? if fn.is_a?(String)}

      paths.each do |path|
        if asset = find_asset(path)
          files[asset.digest_path] = {
            'logical_path' => asset.logical_path,
            'mtime'        => asset.mtime.iso8601,
            'size'         => asset.bytesize,
            'digest'       => asset.digest
          }
          logical_path = asset.logical_path
          assets[asset.logical_path] = asset.digest_path

          target = File.join(dir, asset.digest_path)

          if File.exist?(target)
            logger.debug "Skipping #{target}, already exists"
          else
            logger.info "Writing #{target}"
            asset.write_to target
            asset.write_to "#{target}.gz" if asset.is_a?(BundledAsset)
          end

          if ENV['SPROCKETS_NON_DIGEST']
            logical_target = File.join(dir, logical_path)
            logger.info "Writing #{logical_target}"
            asset.write_to logical_target
            asset.write_to "#{logical_target}.gz" if asset.is_a?(BundledAsset)
          end

          save
          asset
        end
      end
    end
  end
end

sprockets 4.0 is under active development. Maybe it's time for a new PR there