fix: pass previousRealm to AsyncGeneratorCompleteStep in AsyncGeneratorYield

core/engine/src/tests/async_generator.rs

@@ -1,5 +1,5 @@
 use crate::{
-    Context, JsValue, TestAction, builtins::promise::PromiseState, object::JsPromise,
+    Context, JsValue, Source, TestAction, builtins::promise::PromiseState, object::JsPromise,
     run_test_actions,
 };
 use boa_macros::js_str;
@@ -120,3 +120,77 @@ fn return_on_then_queue() {
         TestAction::assert_eq("count", JsValue::from(2)),
     ]);
 }
+
+#[test]
+fn cross_realm_async_generator_yield() {
+    // Exercises AsyncGeneratorYield spec steps 6-8 (previousRealm handling)
+    // by creating a generator in one realm and consuming it from another.
+    // Per spec, previousRealm is the realm of the second-to-top execution
+    // context (the `next()` / AwaitFulfilled handler), which has the same
+    // realm as the generator. The iter result prototype should match the
+    // generator realm's Object.prototype.
+    let mut context = Context::default();
+
+    let generator_realm = context.create_realm().unwrap();
+
+    let old_realm = context.enter_realm(generator_realm.clone());
+    let generator = context
+        .eval(Source::from_bytes(
+            b"(async function* g() { yield 42; yield 99; })()",
+        ))
+        .unwrap();
+    context.enter_realm(old_realm);
+
+    // Grab Object.prototype from the generator's realm (previousRealm per spec).
+    let gen_realm_object_proto = generator_realm
+        .intrinsics()
+        .constructors()
+        .object()
+        .prototype();
+
+    let next_fn = generator
+        .as_object()
+        .unwrap()
+        .get(js_str!("next"), &mut context)
+        .unwrap();
+
+    let call_next = |ctx: &mut Context| -> JsValue {
+        let result = next_fn
+            .as_callable()
+            .unwrap()
+            .call(&generator, &[], ctx)
+            .unwrap();
+        ctx.run_jobs().unwrap();
+        result
+    };
+
+    // First yield: value 42
+    let first = call_next(&mut context);
+    assert_promise_iter_value(&first, &JsValue::from(42), false, &mut context);
+
+    // Verify the iter result was created in the generator's realm (previousRealm).
+    let first_promise = JsPromise::from_object(first.as_object().unwrap().clone()).unwrap();
+    let PromiseState::Fulfilled(first_result) = first_promise.state() else {
+        panic!("promise was not fulfilled");
+    };
+    assert_eq!(
+        first_result.as_object().unwrap().prototype(),
+        Some(gen_realm_object_proto.clone()),
+        "iter result prototype should be generator realm's Object.prototype"
+    );
+
+    // Second yield: value 99
+    let second = call_next(&mut context);
+    assert_promise_iter_value(&second, &JsValue::from(99), false, &mut context);
+
+    // Verify the iter result was created in the generator's realm (previousRealm).
+    let second_promise = JsPromise::from_object(second.as_object().unwrap().clone()).unwrap();
+    let PromiseState::Fulfilled(second_result) = second_promise.state() else {
+        panic!("promise was not fulfilled");
+    };
+    assert_eq!(
+        second_result.as_object().unwrap().prototype(),
+        Some(gen_realm_object_proto),
+        "iter result prototype should be generator realm's Object.prototype"
+    );
+}

core/engine/src/vm/opcode/generator/yield_stm.rs

@@ -66,13 +66,23 @@ impl AsyncGeneratorYield {
         let value = context.vm.get_register(value.into());
         let completion = Ok(value.clone());
 
-        // TODO: 6. Assert: The execution context stack has at least two elements.
-        // TODO: 7. Let previousContext be the second to top element of the execution context stack.
-        // TODO: 8. Let previousRealm be previousContext's Realm.
+        // 6. Assert: The execution context stack has at least two elements.
+        // 7. Let previousContext be the second to top element of the execution context stack.
+        // 8. Let previousRealm be previousContext's Realm.
+        let previous_realm = context
+            .vm
+            .frames
+            .get(context.vm.frames.len() - 2)
+            .map(|frame| frame.realm.clone());
+
         // 9. Perform AsyncGeneratorCompleteStep(generator, completion, false, previousRealm).
-        if let Err(err) =
-            AsyncGenerator::complete_step(&async_generator_object, completion, false, None, context)
-        {
+        if let Err(err) = AsyncGenerator::complete_step(
+            &async_generator_object,
+            completion,
+            false,
+            previous_realm,
+            context,
+        ) {
             return context.handle_error(err);
         }
 
@@ -114,8 +124,9 @@ impl AsyncGeneratorYield {
         //     a. Set generator.[[AsyncGeneratorState]] to suspended-yield.
         r#gen.data_mut().state = AsyncGeneratorState::SuspendedYield;
 
-        //     TODO: b. Remove genContext from the execution context stack and restore the execution context that is at the top of the execution context stack as the running execution context.
-        //     TODO: c. Let callerContext be the running execution context.
+        //     b. Remove genContext from the execution context stack and restore the execution context
+        //        that is at the top of the execution context stack as the running execution context.
+        //     c. Let callerContext be the running execution context.
         //     d. Resume callerContext passing undefined. If genContext is ever resumed again, let resumptionValue be the Completion Record with which it is resumed.
         //     e. Assert: If control reaches here, then genContext is the running execution context again.
         //     f. Return ? AsyncGeneratorUnwrapYieldResumption(resumptionValue).