bytemuck/build.rs

use std::{
  env,
  process::Command,
  str::{self, FromStr},
};

fn main() {
  let minor = match rustc_minor_version() {
    Some(minor) => minor,
    None => return,
  };

  if minor >= 51 {
    println!("cargo:rustc-cfg=min_const_generics");
  }
}

fn rustc_minor_version() -> Option<u32> {
  let rustc = match env::var_os("RUSTC") {
    Some(rustc) => rustc,
    None => return None,
  };

  let output = match Command::new(rustc).arg("--version").output() {
    Ok(output) => output,
    Err(_) => return None,
  };

  let version = match str::from_utf8(&output.stdout) {
    Ok(version) => version,
    Err(_) => return None,
  };

  let mut pieces = version.split('.');
  if pieces.next() != Some("rustc 1") {
    return None;
  }

  let next = match pieces.next() {
    Some(next) => next,
    None => return None,
  };

  u32::from_str(next).ok()
}