fn main() { let rustc = std::env::var_os("RUSTC"); let rustc = rustc.as_ref().map(std::path::Path::new).unwrap_or_else(|| "rustc".as_ref()); let output = std::process::Command::new(rustc) .arg("--version") .output() .unwrap_or_else(|error| panic!("failed to run `{:?} --version`: {:?}", rustc, error)); assert!(output.status.success(), "{:?} -- version returned non-zero exit code", rustc); let stdout = String::from_utf8(output.stdout).expect("rustc produced non-UTF-8 output"); let version_prefix = "rustc "; if !stdout.starts_with(version_prefix) { panic!("unexpected rustc output: {}", stdout); } let version = &stdout[version_prefix.len()..]; let end = version.find(&[' ', '-'] as &[_]).unwrap_or(version.len()); let version = &version[..end]; let mut version_components = version.split('.'); let major = version_components.next().unwrap(); assert_eq!(major, "1", "unexpected Rust major version"); let minor = version_components .next() .unwrap_or("0") .parse::() .expect("invalid Rust minor version"); let msrv = std::env::var("CARGO_PKG_RUST_VERSION").unwrap(); let mut msrv = msrv.split("."); let msrv_major = msrv.next().unwrap(); assert_eq!(msrv_major, "1", "unexpected Rust major version"); let msrv_minor = msrv.next().unwrap().parse::().unwrap(); // print cfg for all interesting versions less than or equal to minor for version in msrv_minor..=minor { println!("cargo:rustc-cfg=rust_v_1_{}", version); } }