rust-clippy/tests/ui/identity_conversion.rs

#![deny(identity_conversion)]

fn test_generic<T: Copy>(val: T) -> T {
    let _ = T::from(val);
    val.into()
}

fn test_generic2<T: Copy + Into<i32> + Into<U>, U: From<T>>(val: T) {
    // ok
    let _: i32 = val.into();
    let _: U = val.into();
    let _ = U::from(val);
}

fn test_questionmark() -> Result<(), ()> {
    {
        let _: i32 = 0i32.into();
        Ok(Ok(()))
    }??;
    Ok(())
}

fn main() {
    test_generic(10i32);
    test_generic2::<i32, i32>(10i32);
    test_questionmark().unwrap();

    let _: String = "foo".into();
    let _: String = From::from("foo");
    let _ = String::from("foo");
    #[allow(identity_conversion)]
    {
        let _: String = "foo".into();
        let _ = String::from("foo");
    }

    let _: String = "foo".to_string().into();
    let _: String = From::from("foo".to_string());
    let _ = String::from("foo".to_string());
}