# Error code E0546

The `feature` value is missing in a stability attribute.

Erroneous code example:

    #![allow(unused)]
    #![feature(staged_api)]
    #![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)]
    #![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.