[JSPI] Do not automatically wrap async library functions.

In a number of places (e.g. `emscripten_async_wget_data`) library functions
use an `async` JS functions, but they do not actually want to use JSPI
wrappers. Change it so functions must explicitly use `foo__async: true` to
enable JSPI wrappers.

Fixes #20289

Author: brendandahl

ChangeLog.md

@@ -32,6 +32,10 @@ See docs/process.md for more on how version tagging works.
   for chrome, or
     emrun --browser=firefox --browser-args=-headless [..]
   for firefox. (#24537)
+- When JSPI is enabled `async` library functions are no longer automatically
+  wrapped with `WebAssembly.Suspending` functions. To automatically wrap library
+  functions for use with JSPI they must now explicitly set
+  `myLibraryFunction__async: true`.
 
 4.0.10 - 06/07/25
 -----------------

src/jsifier.mjs

@@ -534,9 +534,7 @@ function(${args}) {
       if (ASYNCIFY) {
         const original = LibraryManager.library[symbol];
         if (typeof original == 'function') {
-          isAsyncFunction =
-            LibraryManager.library[symbol + '__async'] ||
-            original.constructor.name == 'AsyncFunction';
+          isAsyncFunction = LibraryManager.library[symbol + '__async'];
         }
         if (isAsyncFunction) {
           asyncFuncs.push(symbol);

src/lib/libasync.js

@@ -559,6 +559,7 @@ addToLibrary({
 #endif
 
   _load_secondary_module__sig: 'v',
+  _load_secondary_module__async: true,
   _load_secondary_module: async function() {
     // Mark the module as loading for the wasm module (so it doesn't try to load it again).
     wasmExports['load_secondary_module_status'].value = 1;

test/test_other.py

@@ -3484,6 +3484,34 @@ def test_jspi_add_function(self):
       '-Wno-experimental']
     self.do_runf('other/test_jspi_add_function.c', 'done')
 
+  @requires_jspi
+  def test_jspi_async_function(self):
+    # Make sure async library functions are not automatically JSPI'd.
+    create_file('lib.js', r'''
+      addToLibrary({
+       foo: async function(f) { await Promise.resolve(); },
+      });
+      ''')
+    create_file('main.c', r'''
+        #include <emscripten.h>
+        extern void foo();
+        EMSCRIPTEN_KEEPALIVE void test() {
+          foo();
+        }
+      ''')
+    create_file('post.js', r'''
+        Module.onRuntimeInitialized = () => {
+          _test()
+          console.log('done');
+        };
+      ''')
+    self.emcc_args += [
+      '-sJSPI',
+      '--js-library=lib.js',
+      '-Wno-experimental',
+      '--post-js=post.js']
+    self.do_runf('main.c', 'done')
+
   @requires_dev_dependency('typescript')
   @parameterized({
     'commonjs': [['-sMODULARIZE'], ['--module', 'commonjs', '--moduleResolution', 'node']],