Merge pull request #1461 from fluent/revert-1415-use-basic-object-for…

…-clean-room

Revert "Use BasicObject for cleanroom"

lib/fluent/plugin/filter_record_transformer.rb

@@ -308,10 +308,14 @@ def expand(str, placeholders, force_stringify = false)
         raise "failed to expand `#{str}` : error = #{e}"
       end
 
-      class CleanroomExpander < BasicObject
+      class CleanroomExpander
         def expand(__str_to_eval__, tag, time, record, tag_parts, tag_prefix, tag_suffix, hostname)
           instance_eval(__str_to_eval__)
         end
+
+        (Object.instance_methods).each do |m|
+          undef_method m unless m.to_s =~ /^__|respond_to_missing\?|object_id|public_methods|instance_eval|method_missing|define_singleton_method|respond_to\?|new_ostruct_member/
+        end
       end
     end
   end