Completions are returning 204 No Content for external crates without `extern crate` statement

[eatsfoobars]

use rand::||;
fn main() {
    println!("Hello, world!");
}

The following snippet (with || being the cursor location) will return no completions with YCM, but works just fine with e.g. vim-racer. Adding an extern crate line above it fixes that.

std:: completions work out of the box.