1 #![warn(rust_2018_idioms, single_use_lifetimes)] 2 3 use std::{env, process::Command}; 4 main()5fn main() { 6 if is_nightly() { 7 println!("cargo:rustc-cfg=nightly"); 8 } 9 } 10 is_nightly() -> bool11fn is_nightly() -> bool { 12 env::var_os("RUSTC") 13 .and_then(|rustc| Command::new(rustc).arg("--version").output().ok()) 14 .and_then(|output| String::from_utf8(output.stdout).ok()) 15 .map_or(false, |version| version.contains("nightly") || version.contains("dev")) 16 } 17