1 use std::env; 2 use std::process::Command; 3 use std::str; 4 main()5fn main() { 6 println!("cargo:rerun-if-changed=build.rs"); 7 8 let version = match rustc_version() { 9 Some(version) => version, 10 None => return, 11 }; 12 13 if version.minor < 54 { 14 // https://github.com/rust-lang/rust/pull/84717 15 println!("cargo:rustc-cfg=no_literal_fromstr"); 16 } 17 } 18 19 struct RustcVersion { 20 minor: u32, 21 } 22 rustc_version() -> Option<RustcVersion>23fn rustc_version() -> Option<RustcVersion> { 24 let rustc = env::var_os("RUSTC")?; 25 let output = Command::new(rustc).arg("--version").output().ok()?; 26 let version = str::from_utf8(&output.stdout).ok()?; 27 let mut pieces = version.split('.'); 28 if pieces.next() != Some("rustc 1") { 29 return None; 30 } 31 let minor = pieces.next()?.parse().ok()?; 32 Some(RustcVersion { minor }) 33 } 34