mapcat/build.rs

extern crate rustc_version;
extern crate num_cpus;

use rustc_version::{version, version_meta, Channel};
use std::io::{self, Write};
use std::fs::OpenOptions;

pub const DEFAULT_CPU_FILE: &str = "./src/consts.rs";

fn write_numcpus() -> io::Result<()>
{
    let mut file = OpenOptions::new()
	.write(true)
	.create(true)
	.truncate(true)
	.open(DEFAULT_CPU_FILE)?;

    writeln!(&mut file, "pub const CPUS: usize = {};", num_cpus::get())?;
    writeln!(&mut file, "pub type PoolContainer<T> = [T; CPUS+1];")?;
    file.flush()?;
    Ok(())
}

fn main() {
    // Assert we haven't travelled back in time
    assert!(version().unwrap().major >= 1);

    // Set cfg flags depending on release channel
    match version_meta().unwrap().channel {
        Channel::Stable => {
            println!("cargo:rustc-cfg=stable");
        }
        Channel::Beta => {
            println!("cargo:rustc-cfg=beta");
        }
        Channel::Nightly => {
            println!("cargo:rustc-cfg=nightly");
        }
        Channel::Dev => {
            println!("cargo:rustc-cfg=dev");
        }
    }

    write_numcpus().expect("Failed to write comptime cpu info to source")
}