This is my first time participating in a discussion, so I thought I would start off with an easy on to get my feet wet: Reading this I am not familiar with what "MOP" is?
Thank you, Rob ------ FYI: If you have any prayer requests, add them to your reply and I will be sure to pray for the needs you have. Rob Simpson @pertrai1 robesimpson.com *Love is patient, love is kind. It does not envy, it does not boast, it is not proud. It does not dishonor others, it is not self-seeking, it is not easily angered, it keeps no record of wrongs. Love does not delight in evil but rejoices with the truth. It always protects, always trusts, always hopes, always perseveres. Love never fails. - 1 Corinthians 13:4-8a NIV * On Wed, Aug 10, 2016 at 4:50 AM, Tom Van Cutsem <[email protected]> wrote: > Thanks Claude for your careful review, and for trying to articulate a more > general principle behind the invariant checks. The lack of such crisp > principles makes it (too) difficult to verify whether all necessary checks > are in place. > > To clarify, in the case of "update" MOP operations such as defineProperty > and deleteProperty, your "state B" (the observable state of the target), > presumably is the state of the target *after* the proxy trap has executed, > i.e. state B should already reflect the update. > > Both the original issue and your new test case with deleteProperty are > cases where the proxy pretends to have altered the target but has in fact > not. In a later interaction, the proxy reverts to the original state. This > violates a client's expectations about when state transitions occur. > > Interestingly, the opposite problem, where a proxy does alter the target > as requested, but then reports that the update failed, is allowed, even > though this technically also violates a client's expectations about what > state transitions have occurred. But a failed update leads to a TypeError > anyway. > > At this point, we should probably iron out the details of the fix in a > GitHub issue or on bugs.ecmascript.org. > > Cheers, > Tom > > 2016-08-09 14:44 GMT+02:00 Claude Pache <[email protected]>: > >> Given a Proxy that pretends to be in state A while its target is >> observably in state B, and assuming that the target satisfies the >> Invariants of the Essential Internal Methods [6.1.7.3], I claim that, in >> order to force the Proxy to satisfy those Invariants, it is necessary and >> sufficient to check that the two following conditions hold: >> >> * it is legal for an object to pass from state A to state B; and, >> * it is legal for an object to pass from state B to state A. >> >> [6.1.7.3]: https://tc39.github.io/ecma262/#sec-invariants-of-the- >> essential-internal-methods >> >> >> Because I am too lazy to write the proof just now, I cowardly leave it as >> an exercice to the reader. Meanwhile, that principle may be used to audit >> the robustness of the Proxy specification. I have found the following bug >> in Proxy.[[Delete]]() by applying the above principle to: >> >> * state A: nonexistent property on a nonextensible object; >> * state B: existent own property on a nonextensible object. >> >> Resurrection of a successfully deleted property on a nonextensible object: >> >> ```js >> var target = Object.preventExtensions({ x: 1 }) >> var proxy = new Proxy(target, { >> deleteProperty() { return true } >> }) >> >> Object.isExtensible(proxy) // false >> delete proxy.x // true >> proxy.hasOwnProperty('x') // true >> ``` >> >> After a first scan, I haven't found other bugs in the essential methods >> of Proxy, than that one and the missing nonconfigurable-but-writable check >> in [[GetOwnPropertyDescriptor]] and [[DefineOwnProperty]] already mentioned >> in that thread. >> >> I plan to propose a minimal patch (i.e., just adding the missing checks) >> in a few days. >> >> —Claude >> >> >> > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > >
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