build.rs

use std::env;
use std::ffi::OsString;

const CFG_KEY: &str = "py_sys_config";

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

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

fn watched_var_os(key: &str) -> Option<OsString> {
    println!("cargo:rerun-if-env-changed={}", key);
    env::var_os(key)
}

fn main() {
    if cfg!(feature = "python27-sys")
        && (watched_var_os("CARGO_FEATURE_PY_LINK_MODE_DEFAULT").is_some()
            || watched_var_os("CARGO_FEATURE_PY_LINK_MODE_UNRESOLVED_STATIC").is_some())
    {
        eprintln!("Cannot use link mode control with Python 2.7");
        std::process::exit(1);
    }

    // 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(_) => {
            eprintln!(
                concat!(
                    "Environment variable {} not found - this is supposed to be ",
                    "exported from the pythonXX-sys dependency, so the build ",
                    "chain is broken"
                ),
                PYTHONSYS_ENV_VAR
            );
            std::process::exit(1);
        }
    };

    if !flags.is_empty() {
        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);
            }
        }
    }
}