Error code E0547
The issue
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(feature = "_unstable_fn")] // invalid fn _unstable_fn() {} #[rustc_const_unstable(feature = "_unstable_const_fn")] // invalid const fn _unstable_const_fn() {} }
To fix this issue, you need to provide the issue
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")] // ok! fn _unstable_fn() {} #[rustc_const_unstable( feature = "_unstable_const_fn", issue = "none" )] // ok! const fn _unstable_const_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.