Fix improper detection and handling of html_safe buffer in CacheHelper

actionpack/lib/action_view/helpers/cache_helper.rb

@@ -53,10 +53,10 @@ def fragment_for(name = {}, options = nil, &block) #:nodoc:
           # This dance is needed because Builder can't use capture
           pos = output_buffer.length
           yield
-          if output_buffer.is_a?(ActionView::OutputBuffer)
+          if output_buffer.html_safe?
             safe_output_buffer = output_buffer.to_str
             fragment = safe_output_buffer.slice!(pos..-1)
-            self.output_buffer = ActionView::OutputBuffer.new(safe_output_buffer)
+            self.output_buffer = output_buffer.class.new(safe_output_buffer)
           else
             fragment = output_buffer.slice!(pos..-1)
           end

actionpack/test/controller/caching_test.rb

@@ -785,3 +785,53 @@ def test_xml_formatted_fragment_caching
     assert_equal "  <p>Builder</p>\n", @store.read('views/test.host/functional_caching/formatted_fragment_cached')
   end
 end
+
+class CacheHelperOutputBufferTest < ActionController::TestCase
+
+  class MockController
+    def read_fragment(name, options)
+      return false
+    end
+
+    def write_fragment(name, fragment, options)
+      fragment
+    end
+  end
+
+  def setup
+    super
+  end
+
+  def test_output_buffer
+    output_buffer = ActionView::OutputBuffer.new
+    controller = MockController.new
+    cache_helper = Object.new
+    cache_helper.extend(ActionView::Helpers::CacheHelper)
+    cache_helper.expects(:controller).returns(controller).at_least(0)
+    cache_helper.expects(:output_buffer).returns(output_buffer).at_least(0)
+    # if the output_buffer is changed, the new one should be html_safe and of the same type
+    cache_helper.expects(:output_buffer=).with(responds_with(:html_safe?, true)).with(instance_of(output_buffer.class)).at_least(0)
+
+    assert_nothing_raised do
+      cache_helper.send :fragment_for, 'Test fragment name', 'Test fragment', &Proc.new{ nil }
+      assert output_buffer.html_safe?, "Output buffer should stay html_safe"
+    end
+  end
+
+  def test_safe_buffer
+    output_buffer = ActiveSupport::SafeBuffer.new
+    controller = MockController.new
+    cache_helper = Object.new
+    cache_helper.extend(ActionView::Helpers::CacheHelper)
+    cache_helper.expects(:controller).returns(controller).at_least(0)
+    cache_helper.expects(:output_buffer).returns(output_buffer).at_least(0)
+    # if the output_buffer is changed, the new one should be html_safe and of the same type
+    cache_helper.expects(:output_buffer=).with(responds_with(:html_safe?, true)).with(instance_of(output_buffer.class)).at_least(0)
+
+    assert_nothing_raised do
+      cache_helper.send :fragment_for, 'Test fragment name', 'Test fragment', &Proc.new{ nil }
+      assert output_buffer.html_safe?, "Output buffer should stay html_safe"
+    end
+  end
+
+end