s/bar/extra/. And I think you should make sure this compiles when the `bad` ones are removed: specifically; you'll probably need `pub` on `mod bar` and `fn foobar()`). In fact, the `bad` one should be commented out (but still in the code) so that this passes the documentation tests (you'll also need `fn main() {}` somewhere for this to pass too).

(Also, a space after `//` is Rust convention.)