Error code E0551

An invalid meta-item was used inside an attribute.

Erroneous code example:

#![allow(unused)]
fn main() {
#[deprecated(note)] // error!
fn i_am_deprecated() {}
}
ⓘ

Meta items are the key-value pairs inside of an attribute. To fix this issue, you need to give a value to the note key. Example:

#![allow(unused)]
fn main() {
#[deprecated(note = "because")] // ok!
fn i_am_deprecated() {}
}