[es6] Partially implement Reflect.getOwnPropertyDescriptor.

src/builtins.cc

Index: src/builtins.cc
diff --git a/src/builtins.cc b/src/builtins.cc
index 1ed2fd125315eea8ca4af113cab5a668ad25cb3c..e7e096216feb90c7cf7cbe7fcba18f164d033b16 100644
--- a/src/builtins.cc
+++ b/src/builtins.cc
@@ -17,6 +17,7 @@
 #include "src/isolate-inl.h"
 #include "src/messages.h"
 #include "src/profiler/cpu-profiler.h"
+#include "src/property-descriptor.h"
 #include "src/prototype.h"
 #include "src/vm-state-inl.h"
 
@@ -1499,6 +1500,33 @@ BUILTIN(ReflectGet) {
 }
 
 
+// ES6 section 26.1.7 Reflect.getOwnPropertyDescriptor
+BUILTIN(ReflectGetOwnPropertyDescriptor) {
+  HandleScope scope(isolate);
+  DCHECK_EQ(3, args.length());
+  Handle<Object> target = args.at<Object>(1);
+  Handle<Object> key = args.at<Object>(2);
+
+  if (!target->IsJSReceiver()) {
+    THROW_NEW_ERROR_RETURN_FAILURE(
+        isolate, NewTypeError(MessageTemplate::kCalledOnNonObject,
+                              isolate->factory()->NewStringFromAsciiChecked(
+                                  "Reflect.getOwnPropertyDescriptor")));
+  }
+
+  Handle<Name> name;
+  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, name,
+                                     Object::ToName(isolate, key));
+
+  PropertyDescriptor desc;
+  bool found = JSReceiver::GetOwnPropertyDescriptor(
+      isolate, Handle<JSReceiver>::cast(target), name, &desc);
+  if (isolate->has_pending_exception()) return isolate->heap()->exception();
+  if (!found) return isolate->heap()->undefined_value();

[Jakob Kummerow, 2015/10/26 13:58:26]

How about folding this into PropertyDescriptor::ToObject? It would nicely mirror
step 1 "If Desc is undefined, return undefined." of the spec if that function
began with "if (this->IsEmpty()) return isolate->heap()->undefined_value();".

[neis, 2015/10/29 16:48:39]

This doesn't quite work without passing in "found" to ToObject (I don't want to
treat the empty descriptor as undefined).

Related to that, I changed ToObject slightly such that it works even for
incomplete descriptors.  There was no good reason for assuming complete inputs
(it only saved a few checks).  Please have another look.

+  return *desc.ToObject(isolate);
+}
+
+
 // ES6 section 26.1.8 Reflect.getPrototypeOf
 BUILTIN(ReflectGetPrototypeOf) {
   HandleScope scope(isolate);