fix: unhandledrejection handling for sync throw in top level (#15279)

Fixes an edge in "unhandledrejection" event that prevent synchronous
errors being surfaced when throw from a top-level scope.

cli/tests/integration/run_tests.rs

@@ -2787,3 +2787,8 @@ itest!(unhandled_rejection {
   args: "run --check unhandled_rejection.ts",
   output: "unhandled_rejection.ts.out",
 });
+
+itest!(unhandled_rejection_sync_error {
+  args: "run --check unhandled_rejection_sync_error.ts",
+  output: "unhandled_rejection_sync_error.ts.out",
+});

cli/tests/testdata/unhandled_rejection_sync_error.ts

@@ -0,0 +1,6 @@
+globalThis.addEventListener("unhandledrejection", (e) => {
+  console.log("unhandled rejection at:", e.promise, "reason:", e.reason);
+  e.preventDefault();
+});
+
+throw new Error("boom!");

cli/tests/testdata/unhandled_rejection_sync_error.ts.out

@@ -0,0 +1,6 @@
+[WILDCARD]
+unhandled rejection at: Promise {
+  <rejected> Error: boom!
+    at file:///[WILDCARD]testdata/unhandled_rejection_sync_error.ts:6:7
+} reason: Error: boom!
+    at file:///[WILDCARD]testdata/unhandled_rejection_sync_error.ts:6:7

core/bindings.rs

@@ -363,6 +363,8 @@ pub extern "C" fn promise_reject_callback(message: v8::PromiseRejectMessage) {
       }
     }
 
+    // TODO(bartlomieju): remove this whole block, `js_uncaught_exception_cb` is
+    // not needed anymore
     if let Some(exception) = tc_scope.exception() {
       if let Some(js_uncaught_exception_cb) = js_uncaught_exception_cb {
         tc_scope.reset(); // Cancel pending exception.

core/runtime.rs

@@ -1335,7 +1335,15 @@ impl JsRuntime {
         .expect("Expected to get promise as module evaluation result");
       let promise_global = v8::Global::new(tc_scope, promise);
       let mut state = state_rc.borrow_mut();
+      {
+        let pending_mod_evaluate = state.pending_mod_evaluate.as_ref().unwrap();
+        let pending_rejection_was_already_handled = pending_mod_evaluate
+          .handled_promise_rejections
+          .contains(&promise_global);
+        if !pending_rejection_was_already_handled {
           state.pending_promise_exceptions.remove(&promise_global);
+        }
+      }
       let promise_global = v8::Global::new(tc_scope, promise);
       state.pending_mod_evaluate.as_mut().unwrap().promise =
         Some(promise_global);

runtime/js/99_main.js

@@ -602,7 +602,7 @@ delete Intl.v8BreakIterator;
       WeakMapPrototypeDelete(pendingRejectionsReasons, promise);
 
       if (!hasPendingException) {
-        return;
+        continue;
       }
 
       const event = new PromiseRejectionEvent("unhandledrejection", {
@@ -610,9 +610,21 @@ delete Intl.v8BreakIterator;
         promise,
         reason,
       });
-      globalThis.dispatchEvent(event);
 
-      // If event was not prevented we will let Rust side handle it.
+      const errorEventCb = (event) => {
+        if (event.error === reason) {
+          core.opSync("op_remove_pending_promise_exception", promise);
+        }
+      };
+      // Add a callback for "error" event - it will be dispatched
+      // if error is thrown during dispatch of "unhandledrejection"
+      // event.
+      globalThis.addEventListener("error", errorEventCb);
+      globalThis.dispatchEvent(event);
+      globalThis.removeEventListener("error", errorEventCb);
+
+      // If event was not prevented (or "unhandledrejection" listeners didn't
+      // throw) we will let Rust side handle it.
       if (event.defaultPrevented) {
         core.opSync("op_remove_pending_promise_exception", promise);
       }