rustler 0.20.0

Safe Rust wrappers for creating Erlang NIF functions
Documentation 
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/// Detect NIF version to build against

use std::env;
use std::process::Command;

extern crate lazy_static;
use lazy_static::lazy_static;

extern crate which;
use which::which;

lazy_static! {
    // keep this sorted by version number
    static ref NIF_VERSION: Vec<&'static str> = vec![
        "2.7", "2.8", "2.9", "2.10", "2.11", "2.12", "2.13", "2.14"
    ];
}

fn main() {
    let version = match env::var("RUSTLER_NIF_VERSION") {
        Ok(version) => version,
        Err(_) => get_version_from_erl()
    };

    activate_versions(&version);
}

fn get_version_from_erl() -> String {
    let erl = which("erl").expect("expected to find 'erl' executable");
    let args = vec![
        "-noshell",
        "-eval",
        r#"io:format("~s~n", [erlang:system_info(nif_version)]), init:stop()."#
    ];

    let version = Command::new(erl)
        .args(&args)
        .output()
        .expect("failed to execute 'erl'")
        .stdout;

    let version = String::from_utf8(version).expect("convert version to String");

    version.trim().into()
}

fn activate_versions(version: &str) {
    let index = NIF_VERSION
        .iter()
        .position(|&v| v == version)
        .expect(&format!("Erlang version {} not handled, please file a a bug report.", version));

    for i in 0..=index {
        println!("cargo:rustc-cfg=nif_version_{}", version_feature(NIF_VERSION[i]));
    }
}

fn version_feature(version: &str) -> String {
    version.replace(".", "_")
}