ActiveModel::Lint variable type of #to_key's output

Hi,

The ActiveModel Lint tests do not specify whether a comliant model needs to produce a String or a Fixnum when the #to_key compliance method is called.

However ActionController is intolerant and expects a String as it calls #join on #to_key's output.

Here is the soft spot requiring a String value for key in action_controller/record_identifier.rb line 81:

def record_key_for_dom_id(record)
  record = record.to_model if record.respond_to?(:to_model)
  key = record.to_key
  key ? sanitize_dom_id(key.join('_')) : key
end

Now is ActionController rightfully intolerant and ActiveModel needs to reflect that?
Or should ActionController take non-string values into account?

This issue arose when today, I started playing with the early ActiveModel compliance that is being built into the neo4j.rb library; it produces a Fixnum.

Both using a Fixnum or a String could make sense and if neither is enforced in the Lint test you should expect either to work.

Here is a link to the Lint test.

(This is my second issue filing ever, if you want patches, failing tests or diffs then I'm going to need some pointers because I'm not sure exactly how to produce or present there things)