Issue #120: Under any_instance, modify #dup to remove the mock proxy

lib/rspec/mocks/any_instance.rb

@@ -24,6 +24,7 @@ module AnyInstance
       # @return [Recorder]
       def any_instance
         RSpec::Mocks::space.add(self)
+        modify_dup_to_remove_mock_proxy_when_invoked
         __recorder
       end
 
@@ -33,13 +34,45 @@ def rspec_verify
         super
       ensure
         __recorder.stop_all_observation!
+        restore_dup
         @__recorder = nil
       end
-
+
+      # @private
+      def rspec_reset
+        restore_dup
+        __mock_proxy.reset
+      end
+
       # @private
       def __recorder
         @__recorder ||= AnyInstance::Recorder.new(self)
       end
+
+      private
+      def modify_dup_to_remove_mock_proxy_when_invoked
+        unless self.method_defined?(:__rspec_original_dup)
+          self.class_eval do
+            def __rspec_dup
+              __remove_mock_proxy
+              __rspec_original_dup
+            end
+
+            alias_method  :__rspec_original_dup, :dup
+            alias_method  :dup, :__rspec_dup
+          end
+        end
+      end
+
+      def restore_dup
+        if self.method_defined?(:__rspec_original_dup)
+          self.class_eval do
+            alias_method  :dup, :__rspec_original_dup
+            remove_method :__rspec_original_dup
+            remove_method :__rspec_dup
+          end
+        end
+      end
     end
   end
 end

lib/rspec/mocks/methods.rb

@@ -135,6 +135,10 @@ def __mock_proxy
           mp
         end
       end
+
+      def __remove_mock_proxy
+        @mock_proxy = nil
+      end
 
       def format_chain(*chain, &blk)
         if Hash === chain.last

spec/rspec/mocks/any_instance/issue_120.rb

@@ -7,7 +7,7 @@ module Mocks
         Object.any_instance.stub(:some_method)
         o = Object.new
         o.some_method
-        o.dup.some_method
+        lambda { o.dup.some_method }.should_not raise_error(SystemStackError)
       end
     end
   end