Disable unstable feature

[CodeSandwich]

I'd like to use an unstable feature only when crate is compiled with nightly. Is it possible to annotate the #![feature(unstable_feature)] line so it's visible only for nightly compiler?

[dtolnay]

I think you would need to add a build.rs script:

#[rustversion::nightly]
fn main() {
    println!("cargo:rustc-cfg=unstable_feature");
}

#[rustversion::not(nightly)]
fn main() {}

and then do:

#![cfg_attr(unstable_feature, feature(unstable_feature))]

[WorldSEnder]

A bit nicer to read with rustversion::cfg! macro now (which isn't directly mentioned in the readme)

fn main() {
    if rustversion::cfg!(nightly) {
        println!("cargo:rustc-cfg=unstable_feature");
    }
}