WIP [esnext] implement async iteration proposal

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 23bcd150a801325191373928bf7076cce97ec28c..e296d39f981473ab8ca2dd35664b75c10a5a9ca0 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -2761,6 +2761,14 @@ void JSObject::JSObjectShortPrint(StringStream* accumulator) {
       accumulator->Add("<JS Generator>");
       break;
     }
+    case JS_ASYNC_GENERATOR_OBJECT_TYPE: {
+      accumulator->Add("<JS AsyncGenerator>");
+      break;
+    }
+    case JS_ASYNC_FROM_SYNC_ITERATOR_TYPE: {
+      accumulator->Add("<JS AsyncFromSyncIterator>");
+      break;
+    }
     // All other JSObjects are rather similar to each other (JSObject,
     // JSGlobalProxy, JSGlobalObject, JSUndetectable, JSValue).
     default: {
@@ -8645,7 +8653,8 @@ Handle<Map> Map::CopyInitialMap(Handle<Map> map, int instance_size,
   DCHECK(*map == JSFunction::cast(constructor)->initial_map() ||
          *map == *isolate->strict_function_map() ||
          *map == *isolate->generator_function_map() ||
-         *map == *isolate->async_function_map());
+         *map == *isolate->async_function_map() ||
+         *map == *isolate->async_generator_function_map());
 #endif
   // Initial maps must always own their descriptors and it's descriptor array
   // does not contain descriptors that do not belong to the map.
@@ -12638,6 +12647,8 @@ bool CanSubclassHaveInobjectProperties(InstanceType instance_type) {
     case JS_DATE_TYPE:
     case JS_FUNCTION_TYPE:
     case JS_GENERATOR_OBJECT_TYPE:
+    case JS_ASYNC_GENERATOR_OBJECT_TYPE:
+    case JS_ASYNC_FROM_SYNC_ITERATOR_TYPE:
     case JS_MAP_ITERATOR_TYPE:
     case JS_MAP_TYPE:
     case JS_MESSAGE_OBJECT_TYPE:
@@ -12711,7 +12722,9 @@ void JSFunction::EnsureHasInitialMap(Handle<JSFunction> function) {
   // suggested by the function.
   InstanceType instance_type;
   if (IsResumableFunction(function->shared()->kind())) {
-    instance_type = JS_GENERATOR_OBJECT_TYPE;
+    instance_type = IsAsyncGeneratorFunction(function->shared()->kind())
+                        ? JS_ASYNC_GENERATOR_OBJECT_TYPE
+                        : JS_GENERATOR_OBJECT_TYPE;
   } else {
     instance_type = JS_OBJECT_TYPE;
   }
@@ -19286,7 +19299,16 @@ int JSGeneratorObject::source_position() const {
   CHECK(is_suspended());
   DCHECK(function()->shared()->HasBytecodeArray());
   DCHECK(!function()->shared()->HasBaselineCode());
-  int code_offset = Smi::cast(input_or_debug_pos())->value();
+
+  int code_offset;
+  const JSAsyncGeneratorObject* async =
+      IsJSAsyncGeneratorObject() ? JSAsyncGeneratorObject::cast(this) : nullptr;
+  if (async != nullptr && async->awaited_promise()->IsJSPromise()) {
+    code_offset = Smi::cast(async->await_input())->value();
+  } else {
+    code_offset = Smi::cast(input_or_debug_pos())->value();
+  }
+
   // The stored bytecode offset is relative to a different base than what
   // is used in the source position table, hence the subtraction.
   code_offset -= BytecodeArray::kHeaderSize - kHeapObjectTag;