Error code E0547

The issue value is missing in a stability attribute.

Erroneous code example:

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

#[unstable(feature = "_unstable_fn")] // invalid
fn _unstable_fn() {}

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

Run

To fix this issue, you need to provide 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 = "none"
)] // ok!
const fn _unstable_const_fn() {}

Run

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.

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