1 use std::env;
2 use std::process::Command;
3 use std::str::{self, FromStr};
4
main()5 fn main(){
6 let minor = match rustc_minor_version() {
7 Some(minor) => minor,
8 None => return,
9 };
10
11 // const fn stabilized in Rust 1.31:
12 if minor >= 31 {
13 println!("cargo:rustc-cfg=bitflags_const_fn");
14 }
15 }
16
rustc_minor_version() -> Option<u32>17 fn rustc_minor_version() -> Option<u32> {
18 let rustc = match env::var_os("RUSTC") {
19 Some(rustc) => rustc,
20 None => return None,
21 };
22
23 let output = match Command::new(rustc).arg("--version").output() {
24 Ok(output) => output,
25 Err(_) => return None,
26 };
27
28 let version = match str::from_utf8(&output.stdout) {
29 Ok(version) => version,
30 Err(_) => return None,
31 };
32
33 let mut pieces = version.split('.');
34 if pieces.next() != Some("rustc 1") {
35 return None;
36 }
37
38 let next = match pieces.next() {
39 Some(next) => next,
40 None => return None,
41 };
42
43 u32::from_str(next).ok()
44 }