Understanding Rust Error E0544: Multiple Stability Attributes
What is Rust Error E0544?
Rust Error E0544 occurs when multiple stability attributes are declared on the same item. Stability attributes in Rust, such as #[stable], #[unstable], or #[rustc_deprecated], serve as an indicator of the API stability, backward compatibility commitment, and maintenance status. Assigning multiple stability attributes to the same item results in ambiguity.
Erroneous Code Example
#![allow(unused)]
#![feature(staged_api)]
#![stable(since = "1.0.0", feature = "rust1")]
fn main() {
#[stable(feature = "rust1", since = "1.0.0")]
#[stable(feature = "test", since = "2.0.0")] // invalid
fn foo() {}
}In the code above, two stable attributes with different features and versions are declared on the same item (the function 'foo'). This is not permitted, and Rust shows E0544 error.
How to Fix Rust Error E0544
To resolve the E0544 error, ensure that each item has at most one stability attribute. If multiple stability attributes are required, combine the features appropriately.
Corrected Code Example
#![allow(unused)]
#![feature(staged_api)]
#![stable(since = "1.0.0", feature = "rust1")]
fn main() {
#[stable(feature = "test", since = "2.0.0")] // ok!
fn foo() {}
}In the corrected example, the function 'foo' has only one stability attribute, #[stable(feature = "test", since = "2.0.0")]. The E0544 error is resolved, and the code will compile without issues.