Private fields

src/runtime/runtime-classes.cc

Index: src/runtime/runtime-classes.cc
diff --git a/src/runtime/runtime-classes.cc b/src/runtime/runtime-classes.cc
index 5448159513bda41508a1c8cd1f72e859be74197a..532c88edda5e49aa6b973d6fbbf49f6781435c90 100644
--- a/src/runtime/runtime-classes.cc
+++ b/src/runtime/runtime-classes.cc
@@ -75,6 +75,27 @@ RUNTIME_FUNCTION(Runtime_ThrowIfStaticPrototype) {
   return *name;
 }
 
+RUNTIME_FUNCTION(Runtime_ThrowIfMissingPrivateField) {
+  // TODO(bakkot) it would be better if this were done as part of the property
+  // lookup, instead of prior to it.
+  // Currently the parser emits code which looks like
+  // %ThrowIfMissingPrivateField(x, field)[field]
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 2);
+  CONVERT_ARG_HANDLE_CHECKED(Object, object, 0);
+  CONVERT_ARG_HANDLE_CHECKED(Symbol, name, 1);
+  DCHECK(name->is_private());
+
+  if (!object->IsJSReceiver() ||
+      !JSReceiver::HasOwnProperty(Handle<JSReceiver>::cast(object), name)
+           .FromMaybe(false)) {  // Note that this does not trigger proxy traps
+                                 // when name is a private symbol.
+    THROW_NEW_ERROR_RETURN_FAILURE(
+        isolate, NewTypeError(MessageTemplate::kMissingPrivateField));
+  }
+  return *object;  // This is used; after calling this method the field is
+                   // immediately accessed.
+}
 
 RUNTIME_FUNCTION(Runtime_HomeObjectSymbol) {
   DCHECK(args.length() == 0);