rust_src: Fix macOS

Author: ysdragon

src/rust_src/build.rs

@@ -3,9 +3,17 @@ use std::path::PathBuf;
 
 fn main() {
     let out_dir = PathBuf::from(env::var("OUT_DIR").unwrap());
-    let target_dir = PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap())
-        .join("target")
-        .join(env::var("PROFILE").unwrap_or("release".into()));
+    let manifest_dir = PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap());
+    let profile = env::var("PROFILE").unwrap_or("release".into());
+    let target = env::var("TARGET").unwrap_or_default();
+    let host = env::var("HOST").unwrap_or_default();
+
+    // For cross-compilation, cargo puts output in target/<triple>/<profile>/
+    let target_dir = if target != host && !target.is_empty() {
+        manifest_dir.join("target").join(&target).join(&profile)
+    } else {
+        manifest_dir.join("target").join(&profile)
+    };
 
     // Compile the loader .so
     // This tiny C library:
@@ -17,7 +25,6 @@ fn main() {
     std::fs::write(&loader_c, LOADER_SOURCE).unwrap();
 
     // Platform-specific loader compilation
-    let target = env::var("TARGET").unwrap_or_default();
     let is_windows = target.contains("windows");
     let is_macos = target.contains("apple") || target.contains("darwin");
 
@@ -75,6 +82,12 @@ fn main() {
     }
 
     println!("cargo:rerun-if-changed=build.rs");
+
+    // On macOS, allow undefined symbols (resolved at runtime by the loader)
+    if is_macos {
+        println!("cargo:rustc-cdylib-link-arg=-undefined");
+        println!("cargo:rustc-cdylib-link-arg=dynamic_lookup");
+    }
 }
 
 const LOADER_SOURCE: &str = r#"