build.rs - external/github.com/CreepySkeleton/proc-macro-error - Git at Google

 #[rustversion::not(nightly)]
 fn check() {
     println!("cargo:rustc-cfg=use_fallback");
 }

 #[rustversion::nightly]
 fn check() {}

 fn main() {
     check()
 }
	#[rustversion::not(nightly)]
	fn check() {
	println!("cargo:rustc-cfg=use_fallback");
	}

	#[rustversion::nightly]
	fn check() {}

	fn main() {
	check()
	}