Understanding Rust Error E0546: Missing Feature Value in Stability Attribute
Introduction to Rust Error E0546
Rust Error E0546 occurs when the feature value is missing in a stability attribute. This error is raised when using unstable functions or methods without specifying the required feature field inside the 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() {}
}
In the erroneous code example, the unstable function 'unstable_fn' and the stable function 'stable_fn' have incomplete attribute parameters, causing Rust Error E0546.
Fixing Rust Error E0546
To fix Rust Error E0546, you need to provide the missing feature field inside the stability attribute. The corrected code example is shown below:
#![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() {}
}
By providing the feature field to both the unstable and stable attributes, the Rust Error E0546 is resolved.
Additional Resources
To learn more about Rust stability attributes and nightly Rust, refer to the following resources: - How Rust is Made and 'Nightly Rust': https://doc.rust-lang.org/book/appendix-07-nightly-rust.html - Rustc Dev Guide: Stability Attributes: https://rustc-dev-guide.rust-lang.org/stability.html