Error code E0545

The issue value is incorrect in a stability attribute.

Erroneous code example:

#![allow(unused)]
#![feature(staged_api)]
#![stable(since = "1.0.0", feature = "test")]

fn main() {
#[unstable(feature = "_unstable_fn", issue = "0")] // invalid
fn _unstable_fn() {}

#[rustc_const_unstable(feature = "_unstable_const_fn", issue = "0")] // invalid
const fn _unstable_const_fn() {}
}

To fix this issue, you need to provide a correct value in the issue field. Example:

#![allow(unused)]
#![feature(staged_api)]
#![stable(since = "1.0.0", feature = "test")]

fn main() {
#[unstable(feature = "_unstable_fn", issue = "none")] // ok!
fn _unstable_fn() {}

#[rustc_const_unstable(feature = "_unstable_const_fn", issue = "1")] // ok!
const fn _unstable_const_fn() {}
}

See the How Rust is Made and “Nightly Rust” appendix of the Book and the Stability attributes section of the Rustc Dev Guide for more details.