Fix yaml serialization when using Psych.

Without these changes, I was getting SystemStackErrors when calling YAML.dump(stubbed_object) or stubbed_object.to_yaml.

To test this, you may need to reinstall ruby 1.9.2 with psych support.  On OSX with homebrew and rvm, this will do the trick:

brew install libyaml
rvm install ruby-1.9.2 --with-libyaml-dir=/usr/local

Closes rspec#36.

lib/rspec/mocks/extensions/psych.rb

@@ -0,0 +1,21 @@
+module Psych
+  class << self
+    def dump_with_mocks(object, *args)
+      return dump_without_mocks(object, *args) unless object.instance_variable_defined?(:@mock_proxy)
+
+      mp = object.instance_variable_get(:@mock_proxy)
+      return dump_without_mocks(object, *args) unless mp.is_a?(::RSpec::Mocks::Proxy)
+
+      object.send(:remove_instance_variable, :@mock_proxy)
+
+      begin
+        dump_without_mocks(object, *args)
+      ensure
+        object.instance_variable_set(:@mock_proxy,mp)
+      end
+    end
+
+    alias_method :dump_without_mocks, :dump
+    alias_method :dump, :dump_with_mocks
+  end
+end

lib/rspec/mocks/serialization.rb

@@ -1,4 +1,5 @@
 require 'rspec/mocks/extensions/marshal'
+require 'rspec/mocks/extensions/psych' if defined?(::Psych)
 
 module RSpec
   module Mocks
@@ -8,14 +9,15 @@ def self.fix_for(object)
       end
 
       module YAML
-        def to_yaml(*a)
-          return super(*a) unless instance_variable_defined?(:@mock_proxy)
+        def to_yaml(options = {})
+          return nil if defined?(::Psych) && options.respond_to?(:[]) && options[:nodump]
+          return super(options) unless instance_variable_defined?(:@mock_proxy)
 
           mp = @mock_proxy
           remove_instance_variable(:@mock_proxy)
 
           begin
-            super(*a)
+            super(options)
           ensure
             @mock_proxy = mp
           end

spec/rspec/mocks/serialization_spec.rb

@@ -53,7 +53,7 @@ def set_stub
         subject.stub(:bazz => 5)
       end
 
-      with_yaml_loaded do
+      shared_examples_for 'normal YAML serialization' do
         it 'serializes to yaml the same with and without stubbing, using #to_yaml' do
           expect { set_stub }.to_not change { subject.to_yaml }
         end
@@ -63,6 +63,24 @@ def set_stub
         end
       end
 
+      with_yaml_loaded do
+        compiled_with_psych = RbConfig::CONFIG['configure_args'] =~ /with-libyaml/
+
+        if compiled_with_psych
+          context 'using Syck as the YAML engine' do
+            before(:each) { YAML::ENGINE.yamler = 'syck' }
+            it_behaves_like 'normal YAML serialization'
+          end
+
+          context 'using Psych as the YAML engine' do
+            before(:each) { YAML::ENGINE.yamler = 'psych' }
+            it_behaves_like 'normal YAML serialization'
+          end
+        else
+          it_behaves_like 'normal YAML serialization'
+        end
+      end
+
       without_yaml_loaded do
         it 'does not add #to_yaml to the stubbed object' do
           subject.should_not respond_to(:to_yaml)