let rustc = env::var_os("RUSTC").unwrap_or(OsString::from("rustc"));

let output = Command::new(&rustc)

.arg("--version")

.output()

.unwrap()

.stdout;

let version = String::from_utf8(output).unwrap();

// If we're using nightly Rust, then we can enable vector optimizations.

// Note that these aren't actually activated unless the `unstable` feature

// is enabled.

//

// We also don't activate these if we've explicitly disabled auto

// optimizations. Disabling auto optimizations is intended for use in

// tests, so that we can reliably test fallback implementations.

if env::var_os("CARGO_CFG_REGEX_DISABLE_AUTO_OPTIMIZATIONS").is_none() {

if version.contains("nightly") {

println!("cargo:rustc-cfg=regex_runtime_teddy_ssse3");

println!("cargo:rustc-cfg=regex_runtime_teddy_avx2");

}

}