[Haml] Fix some Rails 3 compatibility.

doc-src/HAML_CHANGELOG.md

@@ -11,6 +11,9 @@
 * Calls to `defined?` shouldn't interfere with Rails' autoloading
   in very old versions (1.2.x).
 
+* Fix a bug where calls to ActionView's `render` method
+  with blocks and layouts wouldn't work under the Rails 3.0 beta.
+
 ## 2.2.19
 
 [Tagged on GitHub](http://github.com/nex3/haml/commit/2.2.19).

lib/haml/helpers.rb

@@ -519,12 +519,12 @@ END
     # @yield A block in which the given buffer should be used
     def with_haml_buffer(buffer)
       @haml_buffer, old_buffer = buffer, @haml_buffer
-      old_buffer.active, was_active = false, old_buffer.active? if old_buffer
-      @haml_buffer.active = true
+      old_buffer.active, old_was_active = false, old_buffer.active? if old_buffer
+      @haml_buffer.active, was_active = true, @haml_buffer.active?
       yield
     ensure
-      @haml_buffer.active = false
-      old_buffer.active = was_active if old_buffer
+      @haml_buffer.active = was_active
+      old_buffer.active = old_was_active if old_buffer
       @haml_buffer = old_buffer
     end