ES6 Unscopables

src/unscopables.h

+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_UNSCOPABLES_H_
+#define V8_UNSCOPABLES_H_
+
+#include "src/isolate.h"
+#include "src/lookup.h"
+#include "src/objects.h"
+#include "src/prototype.h"
+
+namespace v8 {
+namespace internal {
+
+
+static bool BlockedByUnscopables(LookupIterator* it) {
+  Isolate* isolate = it->isolate();
+  Handle<Symbol> unscopables_symbol(
+      isolate->native_context()->unscopables_symbol(), isolate);
+
+  // TODO(arv): This should be GetNonHiddenHolder
+  Handle<JSReceiver> object = it->GetHolder<JSReceiver>();
+  if (!JSReceiver::HasOwnProperty(object, unscopables_symbol)) return false;
+  Handle<Object> unscopables;
+  MaybeHandle<Object> maybe_unscopables =
+      Object::GetProperty(object, unscopables_symbol);
+  if (!maybe_unscopables.ToHandle(&unscopables)) return false;

[Toon Verwaest, 2014/07/25 10:09:41]

Maybe add a comment here saying that you return false to flag a failure? OTOH,
what about returning a Maybe<bool> and using that to indicate that you may have
a failure rather than just a result?

+  if (!unscopables->IsSpecObject()) return false;
+  return JSReceiver::HasOwnProperty(Handle<JSReceiver>::cast(unscopables),

[Toon Verwaest, 2014/07/25 10:09:41]

This HasOwnProperty can cause an exception at least in the case where the
unscopables is a JSProxy. I wouldn't rely on the returned bool to indicate
whether there is an exception. Check has_pending_exception() instead. (See my
comment below)

+                                    it->name());
+}
+
+
+/**
+ * Lookups a property in an object environment, taking the unscopables into
+ * account. This is used For HasBinding and GetBindingValue spec algorithms for
+ * ObjectEnvironment.
+ */
+static PropertyAttributes UnscopableLookup(LookupIterator* it) {
+  PropertyAttributes attrs;
+  while ((attrs = JSReceiver::GetPropertyAttributes(it)) != ABSENT) {

[Toon Verwaest, 2014/07/25 10:09:41]

At least GetPropertyAttributesWithHandler will return NONE (in at least some
cases) if GetPropertyAttributes causes an exception to be thrown while getting
the attributes. GetPropertyAttributes currently has no other way of flagging
that it may fail. The client has to check for has_pending_exception(), and
manually propagate the exception up if so.

(This is obviously very error-prone; and making this explicit is on our TODO
list).

+    if (!BlockedByUnscopables(it)) {
+      return attrs;
+    }
+    it->Next();
+  }
+
+  return ABSENT;
+}
+}
+
+}  // namespace v8::internal
+
+#endif  // V8_UNSCOPABLES_H_