title: JRuby on Rails assets:precompile does nothing
body: <p>I have an rails application in JRuby, when I run <code>rake assets:precomile</code> it only creates a file <code>/public/assets/manifest.yml</code> with this content:</p>
  
  <pre><code>--- {}
  ...
  </code></pre>
  
  <p>None of the asstes get precompiled, but I dont get any error when I try to trace this:</p>
  
  <pre><code>tbraun@tbraun-DEBIAN:~/Dokumente/Entwicklung/RubyOnRails/Passbildkartei$ rake assets:precompile --trace
  ** Invoke environment (first_time)
  ** Execute environment
  ** Invoke assets:precompile (first_time)
  ** Execute assets:precompile
  /home/tbraun/.rvm/rubies/jruby-1.6.7.2/bin/jruby /home/tbraun/.rvm/gems/jruby-1.6.7.2/bin/rake assets:precompile:all RAILS_ENV=production RAILS_GROUPS=assets --trace
  ** Invoke environment (first_time)
  ** Execute environment
  ** Invoke assets:precompile:all (first_time)
  ** Execute assets:precompile:all
  ** Invoke assets:precompile:primary (first_time)
  ** Invoke assets:environment (first_time)
  ** Execute assets:environment
  ** Invoke environment 
  ** Invoke tmp:cache:clear (first_time)
  ** Execute tmp:cache:clear
  ** Execute assets:precompile:primary
  ** Invoke environment (first_time)
  ** Execute environment
  ** Invoke assets:precompile:nondigest (first_time)
  ** Invoke assets:environment (first_time)
  ** Execute assets:environment
  ** Invoke environment 
  ** Invoke tmp:cache:clear (first_time)
  ** Execute tmp:cache:clear
  ** Execute assets:precompile:nondigest
  </code></pre>
  
  <p>But I have some images, javascripts and stylesheets in my assets directories, I don't know what I can do to fix this.</p>
  
  <p>My JRuby version is:</p>
  
  <pre><code>jruby 1.6.7.2 (ruby-1.9.2-p312) (2012-05-01 26e08ba) (Java HotSpot(TM) 64-Bit Server VM 1.6.0_26) [linux-amd64-java]
  </code></pre>
  
  <p>And this are the gems I am using:</p>
  
  <pre><code>source 'https://rubygems.org'
  
  gem 'rails', '3.2.3'
  gem "haml", "~&gt; 3.1.4"
  gem "paperclip", "~&gt; 3.0"
  gem "will_paginate", "~&gt; 3.0.3"
  gem "devise", "~&gt; 2.1.2"
  gem "devise_ldap_authenticatable", "~&gt; 0.6.1"
  
  gem 'activerecord-jdbcsqlite3-adapter'
  gem 'activerecord-jdbcmysql-adapter'
  
  gem 'jruby-openssl'
  gem 'json'
  
  group :assets do
    gem 'sass-rails',   '~&gt; 3.2.3'
    gem 'coffee-rails', '~&gt; 3.2.1'
  
    gem 'therubyrhino'
  
    gem 'uglifier', '&gt;= 1.0.3'
    gem "haml-rails", "~&gt; 0.3.4"
  
    gem "warbler", "~&gt; 1.3.5"
  end
  
  gem 'jquery-rails'
  </code></pre>
  
  <p>Has anyone an idea how to fix this problem?</p>