Error code E0549

A deprecated attribute wasn’t paired with a stable/unstable attribute with #![feature(staged_api)] enabled.

Erroneous code example:

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

#[deprecated(
    since = "1.0.1",
    note = "explanation for deprecation"
)] // invalid
fn _deprecated_fn() {}

Run

To fix this issue, you need to add also an attribute stable or unstable. Example:

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

#[stable(since = "1.0.0", feature = "test")]
#[deprecated(
    since = "1.0.1",
    note = "explanation for deprecation"
)] // ok!
fn _deprecated_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.

Back to list of error codes