An invalid meta-item was used inside an attribute.
Erroneous code example:
#![allow(unused)]
#![feature(staged_api)]
#![allow(internal_features)]
#![stable(since = "1.0.0", feature = "test")]
fn main() {
#[deprecated(note)]
#[unstable(feature = "deprecated_fn", issue = "123")]
fn deprecated() {}
#[unstable(feature = "unstable_struct", issue)]
struct Unstable;
#[rustc_const_unstable(feature)]
const fn unstable_fn() {}
#[stable(feature = "stable_struct", since)]
struct Stable;
#[rustc_const_stable(feature)]
const fn stable_fn() {}
}
ⓘ
Meta items are the key-value pairs inside of an attribute.
To fix these issues you need to give required key-value pairs.
#![allow(unused)]
#![feature(staged_api)]
#![allow(internal_features)]
#![stable(since = "1.0.0", feature = "test")]
fn main() {
#[deprecated(since = "1.39.0", note = "reason")]
#[unstable(feature = "deprecated_fn", issue = "123")]
fn deprecated() {}
#[unstable(feature = "unstable_struct", issue = "123")]
struct Unstable;
#[rustc_const_unstable(feature = "unstable_fn", issue = "124")]
const fn unstable_fn() {}
#[stable(feature = "stable_struct", since = "1.39.0")]
struct Stable;
#[rustc_const_stable(feature = "stable_fn", since = "1.39.0")]
const fn stable_fn() {}
}