Warn about do end syntax in redirect option

actionpack/lib/action_dispatch/routing/redirection.rb

@@ -72,6 +72,9 @@ module Redirection
       #     "http://#{request.host_with_port}#{path}"
       #   }
       #
+      # Note that the `do end` syntax for the redirect block wouldn't work, as Ruby would pass
+      # the block to `match` instead of `redirect`. Use `{ ... }` instead.
+      #
       # The options version of redirect allows you to supply only the parts of the url which need
       # to change, it also supports interpolation of the path similar to the first example.
       #