Warn about Results only used in println!()

[pgerber]

A few times now, I've come across tests where a result wasn't verified. Most often, this happens when the result is printed for debugging purposes. See sample code below or have a look at this this real-word example.

While I haven't seen it, I guess this could also be an issue outside of tests or with error!(), warn!(), etc.

I believe it would make since to emit a warning in such cases.

Sample:

some_fn() -> Result<…, …> {
    unimplemented!()
}

#[test]
fn a_test() {
    …
    let result = some_fn();
    println!("result: {:?}", result);   // This compiles with no warning because the `Result` is used by println!()
}

[apoelstra]

If you really didn't intend to do anything with the error but log it, how would you indicate that?