Allow asset url config to be undefined

actionpack/lib/action_view/helpers/asset_url_helper.rb

@@ -135,7 +135,9 @@ module ActionView
           source = compute_asset_path(source, options)
         end
 
-        if relative_url_root = config.relative_url_root || asset_request.try(:script_name)
+        relative_url_root = (defined?(config.relative_url_root) && config.relative_url_root) ||
+          (asset_request && asset_request.script_name)
+        if relative_url_root
           source = "#{relative_url_root}#{source}" unless source.starts_with?("#{relative_url_root}/")
         end
 
@@ -180,7 +182,7 @@ module ActionView
       # (proc or otherwise).
       def compute_asset_host(source = "", options = {})
         request = asset_request
-        host = config.asset_host
+        host = config.asset_host if defined? config.asset_host
         host ||= request.base_url if request && options[:protocol] == :request
         return unless host
 

actionpack/test/template/asset_tag_helper_test.rb

@@ -733,3 +733,44 @@ class AssetUrlHelperControllerTest < ActionView::TestCase
     assert_equal "http://www.example.com/foo", @controller.asset_url("foo")
   end
 end
+
+class AssetUrlHelperEmptyModuleTest < ActionView::TestCase
+  tests ActionView::Helpers::AssetUrlHelper
+
+  def setup
+    super
+
+    @module = Module.new
+    @module.extend ActionView::Helpers::AssetUrlHelper
+  end
+
+  def test_asset_path
+    assert_equal "/foo", @module.asset_path("foo")
+  end
+
+  def test_asset_url
+    assert_equal "/foo", @module.asset_url("foo")
+  end
+
+  def test_asset_url_with_request
+    @module.instance_eval do
+      def request
+        Struct.new(:base_url, :script_name).new("http://www.example.com", nil)
+      end
+    end
+
+    assert @module.request
+    assert_equal "http://www.example.com/foo", @module.asset_url("foo")
+  end
+
+  def test_asset_url_with_config_asset_host
+    @module.instance_eval do
+      def config
+        Struct.new(:asset_host).new("http://www.example.com")
+      end
+    end
+
+    assert @module.config.asset_host
+    assert_equal "http://www.example.com/foo", @module.asset_url("foo")
+  end
+end