Bug 1992103 - Align async modules rejection order with fulfillment order r=jonco

This patch inverts the order in which we reject promises in
AsyncModuleExecutionRejected to match AsyncModuleExecutionFulfilled:
first the promise corresponding to the leaf module (the one that throws)
is rejected, and then its ancestors.

This change was discussed at the July 2025 TC39 meeting.

Spec PR: tc39/ecma262#3695
test262: tc39/test262#4591

Differential Revision: https://phabricator.services.mozilla.com/D267210

Author: nicolo-ribaudo

js/src/vm/Modules.cpp

@@ -2507,10 +2507,10 @@ void js::AsyncModuleExecutionRejected(JSContext* cx,
   // Step 2. Assert: module.[[Status]] is evaluating-async.
   MOZ_ASSERT(module->status() == ModuleStatus::EvaluatingAsync);
 
-  // Step 3. Assert: module.[[AsyncEvaluation]] is true.
+  // Step 3. Assert: module.[[AsyncEvaluationOrder]] is an integer.
   MOZ_ASSERT(module->isAsyncEvaluating());
 
-  // Step 4. 4. Assert: module.[[EvaluationError]] is empty.
+  // Step 4. Assert: module.[[EvaluationError]] is empty.
   MOZ_ASSERT(!module->hadEvaluationError());
 
   ModuleObject::onTopLevelEvaluationFinished(module);
@@ -2521,33 +2521,34 @@ void js::AsyncModuleExecutionRejected(JSContext* cx,
   // Step 6. Set module.[[Status]] to evaluated.
   MOZ_ASSERT(module->status() == ModuleStatus::Evaluated);
 
+  // Step 7. Set module.[[AsyncEvaluationOrder]] to done.
   module->clearAsyncEvaluatingPostOrder();
 
-  // Step 7. For each Cyclic Module Record m of module.[[AsyncParentModules]],
-  //         do:
-  Rooted<ListObject*> parents(cx, module->asyncParentModules());
-  Rooted<ModuleObject*> parent(cx);
-  for (uint32_t i = 0; i < parents->length(); i++) {
-    parent = &parents->get(i).toObject().as<ModuleObject>();
-
-    // Step 7.a. Perform AsyncModuleExecutionRejected(m, error).
-    AsyncModuleExecutionRejected(cx, parent, error);
-  }
-
-  // Step 8. If module.[[TopLevelCapability]] is not empty, then:
+  // Step 9. If module.[[TopLevelCapability]] is not empty, then:
   if (module->hasTopLevelCapability()) {
-    // Step 8.a. Assert: module.[[CycleRoot]] is module.
+    // Step 9.a. Assert: module.[[CycleRoot]] is module.
     MOZ_ASSERT(module->getCycleRoot() == module);
 
-    // Step 8.b. Perform ! Call(module.[[TopLevelCapability]].[[Reject]],
+    // Step 9.b. Perform ! Call(module.[[TopLevelCapability]].[[Reject]],
     //           undefined, error).
     if (!ModuleObject::topLevelCapabilityReject(cx, module, error)) {
       // If Reject fails, there's nothing more we can do here.
       cx->clearPendingException();
     }
   }
 
-  // Step 9. Return unused.
+  // Step 10. For each Cyclic Module Record m of module.[[AsyncParentModules]],
+  //         do:
+  Rooted<ListObject*> parents(cx, module->asyncParentModules());
+  Rooted<ModuleObject*> parent(cx);
+  for (uint32_t i = 0; i < parents->length(); i++) {
+    parent = &parents->get(i).toObject().as<ModuleObject>();
+
+    // Step 10.a. Perform AsyncModuleExecutionRejected(m, error).
+    AsyncModuleExecutionRejected(cx, parent, error);
+  }
+
+  // Step 11. Return unused.
 }
 
 // https://tc39.es/proposal-import-attributes/#sec-evaluate-import-call