There is no need to use instance_eval since the proc is created in the same context it is eval'ed.

actionpack/lib/action_controller/metal/redirecting.rb

@@ -88,7 +88,7 @@ def _compute_redirect_to_location(options)
           raise RedirectBackError unless refer = request.headers["Referer"]
           refer
         when Proc
-          _compute_redirect_to_location instance_eval(&options)
+          _compute_redirect_to_location options.call
         else
           url_for(options)
         end.gsub(/[\r\n]/, '')