Code:

fn main() {
    let mut r = None;
    
    let c = move || {
        let _r = r;
    };
    
    r = Some(c);
}

Results in this error:

error[E0308]: mismatched types
 --> src/main.rs:4:13
  |
4 |       let c = move || {
  |  _____________^
5 | |         let _r = r;
6 | |     };
  | |_____^ cyclic type of infinite size

This seems a bit unclear to me. What types don't match here?

There is special code in the compiler that is supposed to give a better error message, but for some reason it's not happening in this case: