It looks like there's a slight bug with token locations in the following rust code (from #2376)

#![allow(unused)]
fn main() {
extern "C" { fn some_func<T>(x: T); }
}

<source>:3:13: error: foreign items may not have type parameters [E0044]
    3 | extern "C" { fn some_func<T>(x: T); }
      |             ^~

We've had similar issues with location tracking before, and it might be worthwhile to adjust our lexer a bit to reduce the prevalence of these kinds of bugs