582966 - Harmony proxies: Object.getOwnPropertyNames(proxy) calls getOwnPropertyDescriptor trap

Status: RESOLVED WORKSFORME

(Core :: JavaScript Engine, defect, P2)

Description

[Tom Van Cutsem]

User-Agent:       Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_6_4; nl-nl) AppleWebKit/533.16 (KHTML, like Gecko) Version/5.0 Safari/533.16
Build Identifier: Tracemonkey (hg.mozilla.org/tracemonkey tip 199d64731816+ July 26, 2010)

Experimenting with Harmony proxies reveals that calling Object.getOwnPropertyNames(proxy) on a trapping proxy leads to unexpected behavior.

The following hg.ecmascript.org test cases fail:
* [ err] tostringarray-getOwnPropertyNames (TypeError: getOwnPropertyDescriptor is not a function)
* [ err] args-getOwnPropertyNames (TypeError: getOwnPropertyDescriptor is not a function)

Object.getOwnPropertyNames(proxy) calls the proxy handler's getOwnPropertyDescriptor trap for each property name returned by the getOwnPropertyNames trap. This is unexpected and should not be necessary. The above tests fail because the proxy handler does not define a getOwnPropertyDescriptor trap.

What is more: the implementation seems to call the 'getOwnPropertyDescriptor' trap in order to filter out non-enumerable properties. This seems wrong: getOwnPropertyNames should not filter out non-enumerable properties. Object.getOwnPropertyNames(proxy) should just return whatever handler.getOwnPropertyNames() returns, coerced into an array of strings.

Reproducible: Always

Steps to Reproduce:
Execute a script such as:

    var p = Proxy.create({
      getOwnPropertyNames: function() { return ["a"]; },
    });
    
    var result = Object.getOwnPropertyNames(p);
Actual Results:  
TypeError: getOwnPropertyDescriptor is not a function

Expected Results:  
The call to getOwnPropertyNames should return an array ["a"]

To run the test suite that tests the harmony proxies specification:

hg clone hg.ecmascript.org/tests/harmony/
cd proxies
./gentests > runtests.js
js runtests.js

Comment 1

[Andreas Gal :gal]

Attachment: patch

Comment 2

[Jason Orendorff [:jorendorff]]

>                 if (flags & JSITER_OWNONLY) {
>-                    if (!JSProxy::enumerateOwn(cx, pobj, proxyProps))
>+                    if (!JSProxy::getOwnPropertyNames(cx, pobj, proxyProps))
>                         return false;
>                 } else {
>                     if (!JSProxy::enumerate(cx, pobj, proxyProps))
>                         return false;
>                 }
>                for (size_t n = 0, len = proxyProps.length(); n < len; n++) {
>                    if (!Enumerate<EnumPolicy>(cx, obj, pobj, proxyProps[n], true, false, flags, ht, props))
>                        return false;
>                }
Hmm. Now we'll get all the property names, but we'll unconditionally pass true to the 'enumerable' parameter of Enumerate.

I think it is possible to get here with the JSITER_OWNONLY flag set but not JSITER_HIDDEN, and the behavior would be buggy, right?

Comment 3

[Jason Orendorff [:jorendorff]]

A test would be good, too, especially a test that

    for (k in Iterator(proxyobj, true))

reveals only properties that proxyobj says are enumerable and own.

Comment 4

[David Mandelin [:dmandelin]]

Unblocking on the assumption that full Harmony proxies spec support is not a required goal for Fx4. Correct me if I'm wrong.

Comment 5

[David Bruant]

This bug cannot be reproduces in FF4b11.

Comment 6

[Tom Van Cutsem]

Re-executed my original tests, everything works fine now.