[jspi] Fix returning pointers from async dyncalls. (#24316)

When dyncall calls an async function it should wait for the result of
the promise to then convert the pointer.

Fixes #24307

Author: brendandahl

src/lib/libcore.js

@@ -1818,14 +1818,24 @@ addToLibrary({
     }
 #endif
     var rtn = func(...args);
-#endif
+#endif // DYNCALLS
+
+    function convert(rtn) {
 #if MEMORY64
-    return sig[0] == 'p' ? Number(rtn) : rtn;
+      return sig[0] == 'p' ? Number(rtn) : rtn;
 #elif CAN_ADDRESS_2GB
-    return sig[0] == 'p' ? rtn >>> 0 : rtn;
+      return sig[0] == 'p' ? rtn >>> 0 : rtn;
 #else
-    return rtn;
+      return rtn;
+#endif
+    }
+
+#if JSPI
+    if (promising) {
+      return rtn.then(convert);
+    }
 #endif
+    return convert(rtn);
   },
 
   $callRuntimeCallbacks__internal: true,

test/embind/embind_jspi_test.cpp

@@ -39,6 +39,11 @@ int stdFunction(const MyClass& target, int i) {
   return i + 1;
 }
 
+MyClass* asyncGetMyClass() {
+  emscripten_sleep(0);
+  return new MyClass();
+}
+
 EM_ASYNC_JS(void, jsSuspend, (), {
   await new Promise(resolve => {
     Module.unsuspendResolve = resolve;
@@ -60,6 +65,7 @@ EMSCRIPTEN_BINDINGS(xxx) {
   function("intFunc", &intFunc, async());
   function("unsuspend", &unsuspend);
   function("suspend", &suspend, async());
+  function("asyncGetMyClass", &asyncGetMyClass, allow_raw_pointers(), async());
 
   class_<MyClass>("MyClass")
     .constructor<>()
@@ -93,6 +99,9 @@ EM_ASYNC_JS(void, test, (), {
     await check(myClass.lambdaMethod(1), 2);
     await check(Module.MyClass.voidClass());
     await check(Module.MyClass.intClass(1), 2);
+    var myClassAsync = await Module.asyncGetMyClass();
+    assert(myClassAsync instanceof Module.MyClass);
+    myClassAsync.delete();
 
     setTimeout(Module.unsuspend);
     await Module.suspend();