1 use std::env; 2 use std::process::Command; 3 use std::str; 4 5 // The rustc-cfg strings below are *not* public API. Please let us know by 6 // opening a GitHub issue if your build environment requires some way to enable 7 // these cfgs other than by executing our build script. main()8fn main() { 9 let compiler = match rustc_version() { 10 Some(compiler) => compiler, 11 None => return, 12 }; 13 14 if compiler.minor < 36 { 15 println!("cargo:rustc-cfg=syn_omit_await_from_token_macro"); 16 } 17 18 if !compiler.nightly { 19 println!("cargo:rustc-cfg=syn_disable_nightly_tests"); 20 } 21 } 22 23 struct Compiler { 24 minor: u32, 25 nightly: bool, 26 } 27 rustc_version() -> Option<Compiler>28fn rustc_version() -> Option<Compiler> { 29 let rustc = env::var_os("RUSTC")?; 30 let output = Command::new(rustc).arg("--version").output().ok()?; 31 let version = str::from_utf8(&output.stdout).ok()?; 32 let mut pieces = version.split('.'); 33 if pieces.next() != Some("rustc 1") { 34 return None; 35 } 36 let minor = pieces.next()?.parse().ok()?; 37 let nightly = version.contains("nightly"); 38 Some(Compiler { minor, nightly }) 39 } 40