2 files changed, 19 insertions, 4 deletions
diff --git a/actionpack/lib/action_dispatch/http/mime_type.rb b/actionpack/lib/action_dispatch/http/mime_type.rb
index 9450be838c..b9d5009683 100644
--- a/actionpack/lib/action_dispatch/http/mime_type.rb
+++ b/actionpack/lib/action_dispatch/http/mime_type.rb
@@ -45,8 +45,8 @@ module Mime
   #
   #       respond_to do |format|
   #         format.html
-  #         format.ics { render text: post.to_ics, mime_type: Mime::Type["text/calendar"]  }
-  #         format.xml { render xml: @people }
+  #         format.ics { render text: @post.to_ics, mime_type: Mime::Type["text/calendar"]  }
+  #         format.xml { render xml: @post }
   #       end
   #     end
   #   end
diff --git a/actionpack/lib/action_dispatch/http/response.rb b/actionpack/lib/action_dispatch/http/response.rb
index 2fab6be1a5..c5e18048da 100644
--- a/actionpack/lib/action_dispatch/http/response.rb
+++ b/actionpack/lib/action_dispatch/http/response.rb
@@ -1,4 +1,5 @@
 require 'active_support/core_ext/module/attribute_accessors'
+require 'active_support/deprecation'
 require 'action_dispatch/http/filter_redirect'
 require 'monitor'
 
@@ -274,12 +275,22 @@ module ActionDispatch # :nodoc:
     end
 
     # Turns the Response into a Rack-compatible array of the status, headers,
-    # and body.
+    # and body. Allows explict splatting:
+    #
+    #   status, headers, body = *response
     def to_a
       rack_response @status, @header.to_hash
     end
     alias prepare! to_a
-    alias to_ary   to_a
+
+    # Be super clear that a response object is not an Array. Defining this
+    # would make implicit splatting work, but it also makes adding responses
+    # as arrays work, and "flattening" responses, cascading to the rack body!
+    # Not sensible behavior.
+    def to_ary
+      ActiveSupport::Deprecation.warn 'ActionDispatch::Response#to_ary no longer performs implicit conversion to an Array. Please use response.to_a instead, or a splat like `status, headers, body = *response`'
+      to_a
+    end
 
     # Returns the response cookies, converted to a Hash of (name => value) pairs
     #
@@ -369,6 +380,10 @@ module ActionDispatch # :nodoc:
       def to_path
         @response.stream.to_path
       end
+
+      def to_ary
+        nil
+      end
     end
 
     def rack_response(status, header)