pyo3/build.rs

use std::env;
use std::io::Write;

const CFG_KEY: &'static str = "py_sys_config";

#[cfg(feature="python27-sys")]
const PYTHONSYS_ENV_VAR: &'static str = "DEP_PYTHON27_PYTHON_FLAGS";

#[cfg(feature="python3-sys")]
const PYTHONSYS_ENV_VAR: &'static str = "DEP_PYTHON3_PYTHON_FLAGS";

fn main() {
    // python{27,3.x}-sys/build.rs passes python interpreter compile flags via 
    // environment variable (using the 'links' mechanism in the cargo.toml).
    let flags = match env::var(PYTHONSYS_ENV_VAR) {
        Ok(flags) => flags,
        Err(_) => {
            writeln!(std::io::stderr(),
                "Environment variable {} not found - this is supposed to be \
                 exported from the pythonXX-sys dependency, so the build chain is broken",
                PYTHONSYS_ENV_VAR).unwrap();
            std::process::exit(1);
        }
    };

    for f in flags.split(",") {
        // write out flags as --cfg so that the same #cfg blocks can be used
        // in rust-cpython as in the -sys libs
        let key_and_val: Vec<&str> = f.split("=").collect();
        let key = key_and_val[0];
        let val = key_and_val[1];
        if key.starts_with("FLAG") {
            println!("cargo:rustc-cfg={}=\"{}\"", CFG_KEY, &key[5..])
        } else {
            println!("cargo:rustc-cfg={}=\"{}_{}\"", CFG_KEY, &key[4..], val);
        }
    }
}