Comment #4 on issue 705 by [email protected]: Non-enumerable property
fails to shadow inherited enumerable property from for-in
http://code.google.com/p/v8/issues/detail?id=705
It looks like the problem is right about here:
https://github.com/v8/v8/blob/master/src/objects.cc#L5999
On each turn through the loop over prototypes, v8 is considering only
enumerable keys -- note the calls to NumberOfEnumElements() and
GetEnumElementKeys().
I think it would be necessary to maintain a map of all elements, whether
enumerable or not, and use an algorithm like this (pseudocode):
seenKeys = []
for each object in prototype chain:
visibleKeys = GetEnumElementKeys()
allKeys = GetElementKeys()
visibleKeys = Subtract(visibleKeys, seenKeys)
content = Union(content, visibleKeys)
seenKeys = Union(seenKeys, allKeys)
ES5 describes its desired result, but does not specify an algorithm:
http://www.ecma-international.org/ecma-262/5.1/#sec-12.6.4
ES6 (draft) describes an algorithm in terms of generators:
https://people.mozilla.org/~jorendorff/es6-draft.html#sec-ordinary-object-internal-methods-and-internal-slots-enumerate
Note in ES6 the use of a Set to enforce the rule that a name is only
considered once, and that higher-level nonEnumerable keys shadow
lower-level enumerable keys.
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