nim-ffi/examples/nim_timer/rust_bindings/build.rs

use std::path::PathBuf;
use std::process::Command;

fn main() {
    let manifest = PathBuf::from(std::env::var("CARGO_MANIFEST_DIR").unwrap());
    let nim_src = manifest.join("../nim_timer.nim");
    let nim_src = nim_src.canonicalize().unwrap_or(manifest.join("../nim_timer.nim"));

    // Walk up to find the nim-ffi repo root (directory containing nim_src's library)
    // The repo root is where nim c should be run from (contains config.nims).
    // We assume nim_src lives somewhere under repo_root.
    // Derive repo_root as the ancestor that contains the .nimble file or config.nims.
    let mut repo_root = nim_src.clone();
    loop {
        repo_root = match repo_root.parent() {
            Some(p) => p.to_path_buf(),
            None => break,
        };
        if repo_root.join("config.nims").exists() || repo_root.join("ffi.nimble").exists() {
            break;
        }
    }

    #[cfg(target_os = "macos")]
    let lib_ext = "dylib";
    #[cfg(target_os = "linux")]
    let lib_ext = "so";

    let out_lib = repo_root.join(format!("libnimtimer.{lib_ext}"));

    let mut cmd = Command::new("nim");
    cmd.arg("c")
        .arg("--mm:orc")
        .arg("-d:chronicles_log_level=WARN")
        .arg("--app:lib")
        .arg("--noMain")
        .arg(format!("--nimMainPrefix:libnimtimer"))
        .arg(format!("-o:{}", out_lib.display()));
    cmd.arg(&nim_src).current_dir(&repo_root);

    let status = cmd.status().expect("failed to run nim compiler");
    assert!(status.success(), "Nim compilation failed");

    println!("cargo:rustc-link-search={}", repo_root.display());
    println!("cargo:rustc-link-lib=nimtimer");
    println!("cargo:rerun-if-changed={}", nim_src.display());
}