1 use autocfg::AutoCfg; 2 main()3fn main() { 4 match AutoCfg::new() { 5 Ok(ac) => { 6 // The #[track_caller] attribute was stabilized in rustc 1.46.0. 7 if ac.probe_rustc_version(1, 46) { 8 autocfg::emit("tokio_track_caller") 9 } 10 } 11 12 Err(e) => { 13 // If we couldn't detect the compiler version and features, just 14 // print a warning. This isn't a fatal error: we can still build 15 // Tokio, we just can't enable cfgs automatically. 16 println!( 17 "cargo:warning=tokio: failed to detect compiler features: {}", 18 e 19 ); 20 } 21 } 22 } 23