fix: panic in worker when closing at top level (denoland#8510)

Fixes panic occurring in worker when "self.close()" is called
at the top level, ie. worker shuts down while
module evaluation promise hasn't yet resolved.

cli/tests/immediately_close_worker.js

@@ -0,0 +1 @@
+self.close();

cli/tests/integration_tests.rs

@@ -3273,6 +3273,11 @@ itest!(ignore_require {
   exit_code: 0,
 });
 
+itest!(local_sources_not_cached_in_memory {
+  args: "run --allow-read --allow-write no_mem_cache.js",
+  output: "no_mem_cache.js.out",
+});
+
 #[test]
 fn cafile_env_fetch() {
   use deno_core::url::Url;

cli/tests/no_mem_cache.js

@@ -0,0 +1,33 @@
+const fixtureFile = await Deno.makeTempFile();
+let prefix = "file://";
+if (Deno.build.os == "windows") {
+  prefix += "/";
+}
+const fixtureUrl = new URL(`${prefix}${fixtureFile}`);
+let resolve;
+
+let p = new Promise((res) => resolve = res);
+
+await Deno.writeTextFile(fixtureUrl, `self.postMessage("hello");\n`);
+
+const workerA = new Worker(fixtureUrl.href, { type: "module" });
+workerA.onmessage = (msg) => {
+  console.log(msg.data);
+  resolve();
+};
+
+await p;
+workerA.terminate();
+
+p = new Promise((res) => resolve = res);
+
+await Deno.writeTextFile(fixtureUrl, `self.postMessage("goodbye");\n`);
+
+const workerB = new Worker(fixtureUrl.href, { type: "module" });
+workerB.onmessage = (msg) => {
+  console.log(msg.data);
+  resolve();
+};
+
+await p;
+workerB.terminate();

cli/tests/no_mem_cache.js.out

@@ -0,0 +1,2 @@
+hello
+goodbye

cli/tests/workers_test.ts

@@ -341,3 +341,19 @@ Deno.test({
     w.terminate();
   },
 });
+
+Deno.test({
+  name: "Worker immediate close",
+  fn: async function (): Promise<void> {
+    const promise = deferred();
+    const w = new Worker(
+      new URL("./immediately_close_worker.js", import.meta.url).href,
+      { type: "module" },
+    );
+    setTimeout(() => {
+      promise.resolve();
+    }, 1000);
+    await promise;
+    w.terminate();
+  },
+});

core/runtime.rs

@@ -901,9 +901,13 @@ impl JsRuntime {
     let mut receiver = self.mod_evaluate_inner(id)?;
 
     poll_fn(|cx| {
-      if let Poll::Ready(result) = receiver.poll_next_unpin(cx) {
-        debug!("received module evaluate");
-        return Poll::Ready(result.unwrap());
+      if let Poll::Ready(maybe_result) = receiver.poll_next_unpin(cx) {
+        debug!("received module evaluate {:#?}", maybe_result);
+        // If `None` is returned it means that runtime was destroyed before
+        // evaluation was complete. This can happen in Web Worker when `self.close()`
+        // is called at top level.
+        let result = maybe_result.unwrap_or(Ok(()));
+        return Poll::Ready(result);
       }
       let _r = self.poll_event_loop(cx)?;
       Poll::Pending