[Haml] Work around a bug in the Rails #cache method.

Closes gh-149

lib/haml/helpers/action_view_mods.rb

@@ -169,6 +169,22 @@ module ActionView
         alias_method :form_for_without_haml, :form_for
         alias_method :form_for, :form_for_with_haml
       end
+
+      module CacheHelper
+        # This is a workaround for a Rails 3 bug
+        # that's present at least through beta 3.
+        # Their fragment_for assumes that the block
+        # will return its contents as a string,
+        # which is not always the case.
+        # Luckily, it only makes this assumption if caching is disabled,
+        # so we only override that case.
+        def fragment_for_with_haml(*args, &block)
+          return fragment_for_without_haml(*args, &block) if controller.perform_caching
+          capture(&block)
+        end
+        alias_method :fragment_for_without_haml, :fragment_for
+        alias_method :fragment_for, :fragment_for_with_haml
+      end
     else
       module FormTagHelper
         def form_tag_with_haml(url_for_options = {}, options = {}, *parameters_for_url, &proc)

test/haml/template_test.rb

@@ -401,6 +401,17 @@ window.location.reload();
 HTML
 = update_page do |p|
   - p.reload
+HAML
+    end
+
+    def test_cache
+      @base.controller = ActionController::Base.new
+      @base.controller.perform_caching = false
+      assert_equal(<<HTML, render(<<HAML, :action_view))
+Test
+HTML
+- cache do
+  Test
 HAML
     end
   end