fix(napi): handle return value from initializer (denoland#17502)

Fixes denoland#17349

ext/napi/lib.rs

@@ -678,7 +678,7 @@ where
  let nm = unsafe { &*nm };
  assert_eq!(nm.nm_version, 1);
  // SAFETY: we are going blind, calling the register function on the other side.
- let exports = unsafe {
+ let maybe_exports = unsafe {
  (nm.nm_register_func)(
  env_ptr,
  std::mem::transmute::<v8::Local<v8::Value>, napi_value>(
@@ -687,11 +687,20 @@ where
  )
  };
 
- // SAFETY: v8::Local is a pointer to a value and napi_value is also a pointer
- // to a value, they have the same layout
- let exports = unsafe {
- std::mem::transmute::<napi_value, v8::Local<v8::Value>>(exports)
- };
+ let exports = maybe_exports
+ .as_ref()
+ .map(|_| unsafe {
+ // SAFETY: v8::Local is a pointer to a value and napi_value is also a pointer
+ // to a value, they have the same layout
+ std::mem::transmute::<napi_value, v8::Local<v8::Value>>(
+ maybe_exports,
+ )
+ })
+ .unwrap_or_else(|| {
+ // If the module didn't return anything, we use the exports object.
+ exports.into()
+ });
+
  Ok(serde_v8::Value { v8_value: exports })
  }
  None => {
@@ -704,17 +713,29 @@ where
  exports: napi_value,
  ) -> napi_value>(b"napi_register_module_v1")
  .expect("napi_register_module_v1 not found");
- init(
+ let maybe_exports = init(
  env_ptr,
  std::mem::transmute::<v8::Local<v8::Value>, napi_value>(
  exports.into(),
  ),
- )
- };
-
- Ok(serde_v8::Value {
- v8_value: exports.into(),
- })
+ );
+
+ let exports = maybe_exports
+ .as_ref()
+ .map(|_| {
+ // SAFETY: v8::Local is a pointer to a value and napi_value is also a pointer
+ // to a value, they have the same layout
+ std::mem::transmute::<napi_value, v8::Local<v8::Value>>(
+ maybe_exports,
+ )
+ })
+ .unwrap_or_else(|| {
+ // If the module didn't return anything, we use the exports object.
+ exports.into()
+ });
+
+ Ok(serde_v8::Value { v8_value: exports })
+ }
  }
  };
  // NAPI addons can't be unloaded, so we're going to "forget" the library

test_napi/src/lib.rs

@@ -123,13 +123,20 @@ pub fn init_cleanup_hook(env: napi_env, exports: napi_value) {
 #[no_mangle]
 unsafe extern "C" fn napi_register_module_v1(
  env: napi_env,
- exports: napi_value,
+ _: napi_value,
 ) -> napi_value {
  #[cfg(windows)]
  {
  napi_sys::setup();
  }
 
+ // We create a fresh exports object and leave the passed
+ // exports object empty.
+ //
+ // https://github.com/denoland/deno/issues/17349
+ let mut exports = std::ptr::null_mut();
+ assert_napi_ok!(napi_create_object(env, &mut exports));
+
  strings::init(env, exports);
  numbers::init(env, exports);
  typedarray::init(env, exports);