src: use correct outer Context’s microtask queue

Fall back to using the outer context’s microtask queue, rather than
the Isolate’s default one. This would otherwise result in surprising
behavior if an embedder specified a custom microtask queue for the
main Node.js context.

PR-URL: nodejs#36482
Refs: v8/v8@4bf051d
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

Author: addaleax

src/async_wrap.cc

@@ -847,7 +847,8 @@ void AsyncWrap::EmitDestroy(Environment* env, double async_id) {
   // interrupt to get this Microtask scheduled as fast as possible.
   if (env->destroy_async_id_list()->size() == 16384) {
     env->RequestInterrupt([](Environment* env) {
-      env->isolate()->EnqueueMicrotask(
+      env->context()->GetMicrotaskQueue()->EnqueueMicrotask(
+        env->isolate(),
         [](void* arg) {
           DestroyAsyncIdsCallback(static_cast<Environment*>(arg));
         }, env);

src/node_contextify.cc

@@ -199,7 +199,9 @@ MaybeLocal<Context> ContextifyContext::CreateV8Context(
       object_template,
       {},       // global object
       {},       // deserialization callback
-      microtask_queue() ? microtask_queue().get() : nullptr);
+      microtask_queue() ?
+          microtask_queue().get() :
+          env->isolate()->GetCurrentContext()->GetMicrotaskQueue());
   if (ctx.IsEmpty()) return MaybeLocal<Context>();
   // Only partially initialize the context - the primordials are left out
   // and only initialized when necessary.

src/node_task_queue.cc

@@ -95,7 +95,8 @@ static void EnqueueMicrotask(const FunctionCallbackInfo<Value>& args) {
 
   CHECK(args[0]->IsFunction());
 
-  isolate->EnqueueMicrotask(args[0].As<Function>());
+  isolate->GetCurrentContext()->GetMicrotaskQueue()
+      ->EnqueueMicrotask(isolate, args[0].As<Function>());
 }
 
 static void RunMicrotasks(const FunctionCallbackInfo<Value>& args) {

test/cctest/test_environment.cc

@@ -649,3 +649,58 @@ TEST_F(NodeZeroIsolateTestFixture, CtrlCWithOnlySafeTerminationTest) {
   isolate->Dispose();
 }
 #endif  // _WIN32
+
+TEST_F(EnvironmentTest, NestedMicrotaskQueue) {
+  const v8::HandleScope handle_scope(isolate_);
+  const Argv argv;
+
+  std::unique_ptr<v8::MicrotaskQueue> queue = v8::MicrotaskQueue::New(isolate_);
+  v8::Local<v8::Context> context = v8::Context::New(
+      isolate_, nullptr, {}, {}, {}, queue.get());
+  node::InitializeContext(context);
+  v8::Context::Scope context_scope(context);
+
+  int callback_calls = 0;
+  v8::Local<v8::Function> must_call = v8::Function::New(
+      context,
+      [](const v8::FunctionCallbackInfo<v8::Value>& info) {
+        int* callback_calls =
+            static_cast<int*>(info.Data().As<v8::External>()->Value());
+        *callback_calls |= info[0].As<v8::Int32>()->Value();
+      },
+      v8::External::New(isolate_, static_cast<void*>(&callback_calls)))
+          .ToLocalChecked();
+  context->Global()->Set(
+      context,
+      v8::String::NewFromUtf8Literal(isolate_, "mustCall"),
+      must_call).Check();
+
+  node::IsolateData* isolate_data = node::CreateIsolateData(
+      isolate_, &NodeTestFixture::current_loop, platform.get());
+  CHECK_NE(nullptr, isolate_data);
+
+  node::Environment* env = node::CreateEnvironment(
+      isolate_data, context, {}, {});
+  CHECK_NE(nullptr, env);
+
+  node::LoadEnvironment(
+      env,
+      "Promise.resolve().then(() => mustCall(1 << 0));\n"
+      "require('vm').runInNewContext("
+      "    'Promise.resolve().then(() => mustCall(1 << 1))',"
+      "    { mustCall },"
+      "    { microtaskMode: 'afterEvaluate' }"
+      ");"
+      "require('vm').runInNewContext("
+      "    'Promise.resolve().then(() => mustCall(1 << 2))',"
+      "    { mustCall }"
+      ");").ToLocalChecked();
+  EXPECT_EQ(callback_calls, 1 << 1);
+  isolate_->PerformMicrotaskCheckpoint();
+  EXPECT_EQ(callback_calls, 1 << 1);
+  queue->PerformCheckpoint(isolate_);
+  EXPECT_EQ(callback_calls, (1 << 0) | (1 << 1) | (1 << 2));
+
+  node::FreeEnvironment(env);
+  node::FreeIsolateData(isolate_data);
+}