Undefined identifier error with enum in the separate module

[Philippe Sigaud]

> This is the ER I have opened, if you have comments or you don't agree with
> my ideas, please comment there:
> https://d.puremagic.com/issues/show_bug.cgi?id=12059

Well, I really thought it was forbidden (as in: the code will never
work). I guess you can define foo inside module foo.d and use it
internally... So OK for your proposal.