build.rs

use std::path::Path;
use std::process::Command;
use std::{env, str};

fn command_ok(cmd: &mut Command) -> bool {
    cmd.status().ok().map_or(false, |s| s.success())
}

fn command_output(cmd: &mut Command) -> String {
    str::from_utf8(&cmd.output().unwrap().stdout)
        .unwrap()
        .trim()
        .to_string()
}

fn main() {
    if command_ok(Command::new("stack").arg("--version")) {
        let ghc_lib =
            command_output(Command::new("stack").args(&["exec", "--", "ghc", "--print-libdir"]));
        let ghc_version =
            command_output(Command::new("stack").args(&["exec", "--", "ghc", "--numeric-version"]));
        let dir_path = env::current_dir().unwrap();
        let path = dir_path.to_str().unwrap();
        let ghc_lib_path = Path::new(&ghc_lib);
        let rts_path = ghc_lib_path.join("rts");
        println!("cargo:rustc-link-search=native={}/ext_lib/", path);
        println!(
            "cargo:rustc-link-search=native={}",
            rts_path.to_str().unwrap()
        );
        println!("cargo:rustc-link-lib=dylib=ducklingffi");
        println!("cargo:rustc-link-lib=dylib=HSrts-ghc{}", ghc_version);
        println!("cargo:rustc-env=GHC_VERSION={}", ghc_version);
    } else {
        panic!("Stack was not found in the PATH")
    }
}