webassembly/proxy_c: Ensure return value of async fun is passed to JS.

Signed-off-by: Damien George <damien@micropython.org>

ports/webassembly/proxy_c.c

@@ -289,10 +289,11 @@ void proxy_c_to_js_get_dict(uint32_t c_ref, uint32_t *out) {
 
 static const mp_obj_fun_builtin_var_t resume_obj;
 
-EM_JS(void, js_then_resolve, (uint32_t * resolve, uint32_t * reject), {
+EM_JS(void, js_then_resolve, (uint32_t * ret_value, uint32_t * resolve, uint32_t * reject), {
+    const ret_value_js = proxy_convert_mp_to_js_obj_jsside(ret_value);
     const resolve_js = proxy_convert_mp_to_js_obj_jsside(resolve);
     const reject_js = proxy_convert_mp_to_js_obj_jsside(reject);
-    resolve_js(null);
+    resolve_js(ret_value_js);
 });
 
 EM_JS(void, js_then_reject, (uint32_t * resolve, uint32_t * reject), {
@@ -321,7 +322,9 @@ static mp_obj_t proxy_resume_execute(mp_obj_t self_in, mp_obj_t value, mp_obj_t
     proxy_convert_mp_to_js_obj_cside(reject, out_reject);
 
     if (ret_kind == MP_VM_RETURN_NORMAL) {
-        js_then_resolve(out_resolve, out_reject);
+        uint32_t out_ret_value[PVN];
+        proxy_convert_mp_to_js_obj_cside(ret_value, out_ret_value);
+        js_then_resolve(out_ret_value, out_resolve, out_reject);
         return mp_const_none;
     } else if (ret_kind == MP_VM_RETURN_YIELD) {
         // ret_value should be a JS thenable

tests/ports/webassembly/await_js_async_py.mjs

+// Test JavaScript await'ing on Python async functions.
+
+const mp = await (await import(process.argv[2])).loadMicroPython();
+
+globalThis.asyncTimeout = (ms) =>
+    new Promise((resolve) => setTimeout(resolve, ms));
+
+mp.runPython(`
+import js
+
+def f0():
+    print("f0 run")
+    return 1
+
+async def f1():
+    print("f1 run")
+    return 2
+
+async def f2():
+    print("f2 start")
+    await js.asyncTimeout(0)
+    print("f2 end")
+    return 3
+
+async def f3():
+    print("f3 start")
+    ret = await f2()
+    print("f3 end")
+    return ret + 1
+`);
+
+console.log("f0 return:", await mp.globals.get("f0")());
+console.log("f1 return:", await mp.globals.get("f1")());
+console.log("f2 return:", await mp.globals.get("f2")());
+console.log("f3 return:", await mp.globals.get("f3")());

tests/ports/webassembly/await_js_async_py.mjs.exp

+f0 run
+f0 return: 1
+f1 run
+f1 return: 2
+f2 start
+f2 end
+f2 return: 3
+f3 start
+f2 start
+f2 end
+f3 end
+f3 return: 4