Error code E0546

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")] // invalid fn unstable_fn() {} #[stable(since = "1.0.0")] // invalid 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")] // ok! fn unstable_fn() {} #[stable(feature = "stable_fn", since = "1.0.0")] // ok! 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.