From be1ecb54e6be1ee5017a1a8aeca83d9e12ad16c9 Mon Sep 17 00:00:00 2001
From: Damien George <damien@micropython.org>
Date: Tue, 7 May 2024 11:33:05 +1000
Subject: [PATCH] webassembly/api: Resolve thenables returned from
 runPythonAsync.

JavaScript semantics are such that the caller of an async function does not
need to await that function for it to run to completion.  This commit makes
that behaviour also apply to top-level async Python code run via
`runPythonAsync()`.

Signed-off-by: Damien George <damien@micropython.org>
---
 ports/webassembly/api.js                      |  6 ++++-
 .../webassembly/run_python_async_no_await.mjs | 24 +++++++++++++++++++
 .../run_python_async_no_await.mjs.exp         |  6 +++++
 3 files changed, 35 insertions(+), 1 deletion(-)
 create mode 100644 tests/ports/webassembly/run_python_async_no_await.mjs
 create mode 100644 tests/ports/webassembly/run_python_async_no_await.mjs.exp

diff --git a/ports/webassembly/api.js b/ports/webassembly/api.js
index f3245451e..c00edf575 100644
--- a/ports/webassembly/api.js
+++ b/ports/webassembly/api.js
@@ -152,7 +152,11 @@ export async function loadMicroPython(options) {
                 [buf, len, value],
             );
             Module._free(buf);
-            return proxy_convert_mp_to_js_obj_jsside_with_free(value);
+            const ret = proxy_convert_mp_to_js_obj_jsside_with_free(value);
+            if (ret instanceof PyProxyThenable) {
+                return Promise.resolve(ret);
+            }
+            return ret;
         },
         replInit() {
             Module.ccall("mp_js_repl_init", "null", ["null"]);
diff --git a/tests/ports/webassembly/run_python_async_no_await.mjs b/tests/ports/webassembly/run_python_async_no_await.mjs
new file mode 100644
index 000000000..19462d6e7
--- /dev/null
+++ b/tests/ports/webassembly/run_python_async_no_await.mjs
@@ -0,0 +1,24 @@
+// Test runPythonAsync() without await'ing it.
+
+const mp = await (await import(process.argv[2])).loadMicroPython();
+
+globalThis.p = new Promise((resolve, reject) => {
+    setTimeout(() => {
+        resolve(123);
+        console.log("setTimeout resolved");
+    }, 100);
+});
+
+console.log(1);
+
+const ret = mp.runPythonAsync(`
+import js
+print("py 1")
+print("resolved value:", await js.p)
+print("py 2")
+`);
+
+// `ret` should be a Promise.
+console.log(2, ret);
+
+// Here, the Python async code should continue to run until completed.
diff --git a/tests/ports/webassembly/run_python_async_no_await.mjs.exp b/tests/ports/webassembly/run_python_async_no_await.mjs.exp
new file mode 100644
index 000000000..1dbf7f95f
--- /dev/null
+++ b/tests/ports/webassembly/run_python_async_no_await.mjs.exp
@@ -0,0 +1,6 @@
+1
+2 Promise { <pending> }
+py 1
+setTimeout resolved
+resolved value: 123
+py 2