652803 - [Harmony proxies] recursive fixing doesn't throw

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect, P2)

Description

[Tom Van Cutsem]

Recursively fixing a Harmony proxy should be short-circuited by throwing a TypeError, to safeguard against infinite loops. For instance:

    var proxy = Proxy.create({
      fix: function() {
        Object.preventExtensions(proxy); // triggers 'fix()' recursively
        return {};
      }
    });
    Object.preventExtensions(proxy); // triggers 'fix'

Result: InternalError: too much recursion
Expected: a TypeError

We reached consensus on this behavior in a TC39 meeting last year. Admittedly,
it's well hidden on the semantics page:
<http://wiki.ecmascript.org/doku.php?id=harmony:proxies_semantics>

"Note: recursive fixing should be disallowed. If fix() is called on a proxy
handler while the same proxy is already being fixed (an earlier call to fix()
is already on the stack), a TypeError should be thrown. "

Comment 1

[Josh Matthews [:jdm]]

Attachment: Potential fix

So it looks like the code to do this properly is already present, but in the wrong spot. I have no way of accessing tryserver or a recent tree, so this patch may not apply or be correct. If someone (gal?) could try applying it and see if it solves the problem, I would be mighty appreciative.

Comment 2

[Brendan Eich [:brendan]]

Andreas, want to own this till Josh returns?

/be

Comment 3

[Josh Matthews [:jdm]]

Attachment: Check proxy operations before fixing object.

Tested; this works correctly.

Comment 4

[Andreas Gal :gal]

Comment on attachment 530403 [details] [diff] [review]
Check proxy operations before fixing object.

Nice patch. Thanks!

Comment 5

[Igor Bukanov]

We need a regression test for this bug. http://hg.mozilla.org/tracemonkey/rev/6855db79531d does not include one.

Comment 6

[Chris Leary [:cdleary] (not checking bugmail)]

cdleary-bot mozilla-central merge info:
http://hg.mozilla.org/mozilla-central/rev/6855db79531d
Note: not marking as fixed because fixed-in-tracemonkey is not present on the whiteboard.