I got this strange error when in my Rails application:

DEPRECATION WARNING: form was removed from Rails and is now available as a plugin. Please install it with rails plugin install git://github.com/rails/dynamic_form.git.

What ended up happening was that I forgot to pass in a local ‘form’ to a partial that was expecting it to be passed in. Rails then didn’t know how to handle the form that I was trying to set, and so it fell back to some default behavior of saying that the way I was using form was deprecated.