fix(napi): buffer finalizer is nullable (#30514)

Fixes: https://github.com/denoland/deno/issues/30512

ext/napi/js_native_api.rs

@@ -2938,7 +2938,7 @@ fn napi_create_external_arraybuffer<'s>(
   env: &'s mut Env,
   data: *mut c_void,
   byte_length: usize,
-  finalize_cb: napi_finalize,
+  finalize_cb: Option<napi_finalize>,
   finalize_hint: *mut c_void,
   result: *mut napi_value<'s>,
 ) -> napi_status {

ext/napi/node_api.rs

@@ -319,7 +319,7 @@ fn napi_create_external_buffer<'s>(
   env: &'s mut Env,
   length: usize,
   data: *mut c_void,
-  finalize_cb: napi_finalize,
+  finalize_cb: Option<napi_finalize>,
   finalize_hint: *mut c_void,
   result: *mut napi_value<'s>,
 ) -> napi_status {

ext/napi/util.rs

@@ -25,15 +25,17 @@ pub fn get_array_buffer_ptr(ab: v8::Local<v8::ArrayBuffer>) -> *mut c_void {
 
 struct BufferFinalizer {
   env: *mut Env,
-  finalize_cb: napi_finalize,
+  finalize_cb: Option<napi_finalize>,
   finalize_data: *mut c_void,
   finalize_hint: *mut c_void,
 }
 
 impl Drop for BufferFinalizer {
   fn drop(&mut self) {
-    unsafe {
-      (self.finalize_cb)(self.env as _, self.finalize_data, self.finalize_hint);
+    if let Some(finalize_cb) = self.finalize_cb {
+      unsafe {
+        finalize_cb(self.env as _, self.finalize_data, self.finalize_hint);
+      }
     }
   }
 }
@@ -56,7 +58,7 @@ pub(crate) fn make_external_backing_store(
   data: *mut c_void,
   byte_length: usize,
   finalize_data: *mut c_void,
-  finalize_cb: napi_finalize,
+  finalize_cb: Option<napi_finalize>,
   finalize_hint: *mut c_void,
 ) -> v8::UniqueRef<v8::BackingStore> {
   let finalizer = Box::new(BufferFinalizer {

tests/napi/arraybuffer_test.js

@@ -1,6 +1,7 @@
 // Copyright 2018-2025 the Deno authors. MIT license.
 
 import { assert, assertEquals, loadTestLibrary } from "./common.js";
+import { Buffer } from "node:buffer";
 
 const typedarray = loadTestLibrary();
 
@@ -22,3 +23,8 @@ Deno.test("napi arraybuffer is detached", function () {
     assert(!typedarray.is_detached(value));
   });
 });
+
+Deno.test("napi buffer finalizer may be null", () => {
+  const buf = typedarray.test_static_external_buffer();
+  assertEquals(buf, Buffer.from([1, 2, 3]));
+});

tests/napi/src/finalizer.rs

@@ -107,6 +107,24 @@ extern "C" fn test_external_buffer(
   result
 }
 
+extern "C" fn test_static_external_buffer(
+  env: napi_env,
+  _: napi_callback_info,
+) -> napi_value {
+  let mut result = ptr::null_mut();
+  static BUF: &[u8] = &[1, 2, 3];
+  assert_napi_ok!(napi_create_external_buffer(
+    env,
+    BUF.len(),
+    BUF.as_ptr() as _,
+    None,
+    ptr::null_mut(),
+    &mut result
+  ));
+
+  result
+}
+
 extern "C" fn test_external_arraybuffer(
   env: napi_env,
   _: napi_callback_info,
@@ -136,6 +154,11 @@ pub fn init(env: napi_env, exports: napi_value) {
       "test_external_arraybuffer",
       test_external_arraybuffer
     ),
+    napi_new_property!(
+      env,
+      "test_static_external_buffer",
+      test_static_external_buffer
+    ),
   ];
 
   assert_napi_ok!(napi_define_properties(