build.rs

extern crate rustc_version;
use rustc_version::{version_meta, Channel}

fn main() {
    // Set cfg flags depending on release channel
    match version_meta().unwrap().channel {
        Channel::Stable => {
            println!("cargo:rustc-cfg=rustc-stable");
        }
        Channel::Beta => {
            println!("cargo:rustc-cfg=rustc-beta");
        }
        Channel::Nightly => {
            println!("cargo:rustc-cfg=rustc-nightly");
        }
        Channel::Dev => {
            println!("cargo:rustc-cfg=rustc-dev");
        }
    }
}