The issue
value is incorrect in a stability attribute.
Erroneous code example:
#![feature(staged_api)]
#![stable(since = "1.0.0", feature = "test")]
#[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() {}
RunTo fix this issue, you need to provide a correct value in the issue
field.
Example:
#![feature(staged_api)]
#![stable(since = "1.0.0", feature = "test")]
#[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() {}
RunSee 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.