The feature
value is missing in a stability attribute.
Erroneous code example:
#![allow(unused)]
#![feature(staged_api)]
#![allow(internal_features)]
#![stable(since = "1.0.0", feature = "test")]
fn main() {
#[unstable(issue = "none")]
fn unstable_fn() {}
#[stable(since = "1.0.0")]
fn stable_fn() {}
}
ⓘ
To fix this issue, you need to provide the feature
field. Example:
#![allow(unused)]
#![feature(staged_api)]
#![allow(internal_features)]
#![stable(since = "1.0.0", feature = "test")]
fn main() {
#[unstable(feature = "unstable_fn", issue = "none")]
fn unstable_fn() {}
#[stable(feature = "stable_fn", since = "1.0.0")]
fn stable_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.