Raises exception when respond_to called multiple times in incompatible way

Nesting respond_to calls can lead to unexpected behavior, so it should be
avoided. Currently, the first respond_to format match sets the content-type
for the resulting response. But, if a nested respond_to occurs, it is possible
to match on a different format. For example:

    respond_to do |outer_type|
      outer_type.js do
        respond_to do |inner_type|
          inner_type.html { render body: "HTML" }
        end
      end
    end

Browsers will often include */* in their Accept headers. In the above example,
such a request would result in the outer_type.js match setting the content-
type of the response to text/javascript, while the inner_type.html match will
cause the actual response to return "HTML".

This change tries to minimize potential breakage by only raising an exception
if the nested respond_to calls are in conflict with each other. So, something
like the following example would not raise an exception:

    respond_to do |outer_type|
      outer_type.js do
        respond_to do |inner_type|
          inner_type.js { render body: "JS" }
        end
      end
    end

While the above is nested, it doesn't affect the content-type of the response.

1 files changed, 34 insertions, 0 deletions

diff --git a/actionpack/test/controller/mime/respond_to_test.rb b/actionpack/test/controller/mime/respond_to_test.rb
index 771eccb29b..1163775d3c 100644
--- a/actionpack/test/controller/mime/respond_to_test.rb
+++ b/actionpack/test/controller/mime/respond_to_test.rb
@@ -102,6 +102,26 @@ class RespondToController < ActionController::Base
     end
   end
 
+  def using_conflicting_nested_js_then_html
+    respond_to do |outer_type|
+      outer_type.js do
+        respond_to do |inner_type|
+          inner_type.html { render body: "HTML" }
+        end
+      end
+    end
+  end
+
+  def using_non_conflicting_nested_js_then_js
+    respond_to do |outer_type|
+      outer_type.js do
+        respond_to do |inner_type|
+          inner_type.js { render body: "JS" }
+        end
+      end
+    end
+  end
+
   def custom_type_handling
     respond_to do |type|
       type.html { render body: "HTML"    }
@@ -430,6 +450,20 @@ class RespondToControllerTest < ActionController::TestCase
     assert_equal "<p>Hello world!</p>\n", @response.body
   end
 
+  def test_using_conflicting_nested_js_then_html
+    @request.accept = "*/*"
+    assert_raises(ActionController::RespondToMismatchError) do
+      get :using_conflicting_nested_js_then_html
+    end
+  end
+
+  def test_using_non_conflicting_nested_js_then_js
+    @request.accept = "*/*"
+    get :using_non_conflicting_nested_js_then_js
+    assert_equal "text/javascript", @response.content_type
+    assert_equal "JS", @response.body
+  end
+
   def test_with_atom_content_type
     @request.accept = ""
     @request.env["CONTENT_TYPE"] = "application/atom+xml"