Macro cargo_emit::rustc_cfg

macro_rules! rustc_cfg {
    ($feature:expr $(, $($args:tt)*)?) => { ... };
}

Tells Cargo to enable a $feature.

This is equivalent to:

println!("cargo:rustc-cfg=$feature");

Examples

Useful for conditionally enabling certain code to run.

if cargo.can_bench() {
    cargo_emit::rustc_cfg!("bench");
}

Then outside of build.rs:

#[cfg(bench)]
mod benches {
    // ...
}