Respect Rails.public_path when computing the path to the manifest file.

This is important when packaging JRuby apps using warbler, as the
public directory configured to be the root of the war file, rather
than underneath a directory called "public".

Author: swisener

lib/sprockets/railtie.rb

@@ -1,3 +1,5 @@
+
+
 require 'rails'
 require 'rails/railtie'
 require 'action_controller/railtie'
@@ -64,7 +66,7 @@ def configure(&block)
     config.after_initialize do |app|
       config = app.config
 
-      manifest_path = File.join(app.root, 'public', config.assets.prefix)
+      manifest_path = File.join(::Rails.public_path, config.assets.prefix)
 
       unless config.assets.version.blank?
         app.assets.version += "-#{config.assets.version}"

test/test_railtie.rb

@@ -162,4 +162,13 @@ def test_sprockets_context_helper
     assert_equal false, env.context_class.digest_assets
     assert_equal nil, env.context_class.config.asset_host
   end
+
+  def test_manifest_path_respects_rails_public_path
+    app.configure do
+      config.paths['public'] = 'test_public'
+    end
+    app.initialize!
+
+    assert_match %r{test_public/assets/manifest-.*.json}, ActionView::Base.assets_manifest.path
+  end
 end