Understanding Rust Error E0705

Introduction to Rust Error E0705

Rust Error E0705 occurs when a #![feature] attribute is declared for a feature that is stable in the current edition, but not in all editions. This error is intended to help developers avoid using unstable features in their code.

Error E0705 Example

Here's an example of Rust code that triggers Error E0705:

#![allow(unused)]
#![feature(rust_2018_preview)]
#![feature(test_2018_feature)] // error: the feature

fn main() {
    // `test_2018_feature` is
    // included in the Rust 2018 edition
}

Explanation of the Example

In the erroneous code example, the feature attribute `test_2018_feature` is included in the Rust 2018 edition. However, the code is compiled with the Rust 2015 edition, causing Rust Error E0705 to be thrown.

How to Fix Error E0705

To fix Rust Error E0705, you can remove the #![feature] attribute or ensure that the feature attribute only exists in the proper edition scope.

Fixed Example

Here's a corrected version of the previous code example:

#![allow(unused)]
#![feature(rust_2018_preview)]

#[cfg(feature = "test_2018_feature")]
fn main() {
    // `test_2018_feature` is
    // included in the Rust 2018 edition
}

Summary

Rust Error E0705 is triggered when a #![feature] attribute is declared for a stable feature in the current edition, but not in other editions. To resolve this error, remove the problematic #![feature] attribute or make sure the attribute is only present within the correct edition scope.

Recommended Reading

• Rust 2018 Edition Guide