An invalid meta-item was used inside an attribute.
Erroneous code example:
#![feature(staged_api)]
#![stable(since = "1.0.0", feature = "test")]
#[deprecated(note)] // error!
#[unstable(feature = "deprecated_fn", issue = "123")]
fn deprecated() {}
#[unstable(feature = "unstable_struct", issue)] // error!
struct Unstable;
#[rustc_const_unstable(feature)] // error!
const fn unstable_fn() {}
#[stable(feature = "stable_struct", since)] // error!
struct Stable;
#[rustc_const_stable(feature)] // error!
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.
#![feature(staged_api)]
#![stable(since = "1.0.0", feature = "test")]
#[deprecated(since = "1.39.0", note = "reason")] // ok!
#[unstable(feature = "deprecated_fn", issue = "123")]
fn deprecated() {}
#[unstable(feature = "unstable_struct", issue = "123")] // ok!
struct Unstable;
#[rustc_const_unstable(feature = "unstable_fn", issue = "124")] // ok!
const fn unstable_fn() {}
#[stable(feature = "stable_struct", since = "1.39.0")] // ok!
struct Stable;
#[rustc_const_stable(feature = "stable_fn", since = "1.39.0")] // ok!
const fn stable_fn() {}