Error code E0426

An undeclared label was used.

Erroneous code example:

#![allow(unused)]
fn main() {
loop {
    break 'a; // error: use of undeclared label `'a`
}
}
ⓘ

Please verify you spelled or declared the label correctly. Example:

#![allow(unused)]
fn main() {
'a: loop {
    break 'a; // ok!
}
}