Don't take iterable path in ArrayFrom if items[@@iterator] is null

src/v8natives.js

 // Copyright 2012 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.
 
 // This file relies on the fact that the following declarations have been made
 // in runtime.js:
 // var $Object = global.Object;
 // var $Boolean = global.Boolean;
 // var $Number = global.Number;
 // var $Function = global.Function;
@@ skipping 636 matching lines @@
     %DeleteProperty(obj, p, 0);
     return true;
   } else if (should_throw) {
     throw MakeTypeError("define_disallowed", [p]);
   } else {
     return;
   }
 }
 
 
+// ES6, draft 12-24-14, section 7.3.8
+function GetMethod(obj, p) {
+  // Assert: obj is not null or undefined

[arv (Not doing code reviews), 2015/01/21 15:05:18]

Remove?

[caitp (gmail), 2015/01/21 17:21:49]

Acknowledged.

+  var func = obj[p];
+  if (IS_NULL_OR_UNDEFINED(func)) return;

[arv (Not doing code reviews), 2015/01/21 15:05:18]

return UNDEFINED;

for clarity?

[caitp (gmail), 2015/01/21 17:21:49]

Acknowledged.

+  if (IS_SPEC_FUNCTION(func)) return func;
+  throw MakeTypeError('called_non_callable', [typeof func]);

[arv (Not doing code reviews), 2015/01/21 15:05:18]

maybe update this to use the new better error message than typeof?

[caitp (gmail), 2015/01/21 17:21:49]

I had a go at it, but it will end up implicating Array.from rather than the
property itself, which is kind of weird

+}
+
+
 // Harmony proxies.
 function DefineProxyProperty(obj, p, attributes, should_throw) {
   // TODO(rossberg): adjust once there is a story for symbols vs proxies.
   if (IS_SYMBOL(p)) return false;
 
   var handler = %GetHandler(obj);
   var result = CallTrap2(handler, "defineProperty", UNDEFINED, p, attributes);
   if (!ToBoolean(result)) {
     if (should_throw) {
       throw MakeTypeError("handler_returned_false",
@@ skipping 1221 matching lines @@
   }
   if (!IS_SPEC_FUNCTION(method)) {
     throw MakeTypeError('not_iterable', [obj]);
   }
   var iterator = %_CallFunction(obj, method);
   if (!IS_SPEC_OBJECT(iterator)) {
     throw MakeTypeError('not_an_iterator', [iterator]);
   }
   return iterator;
 }