[Webkit-unassigned] [Bug 202139] Object spread ({ ... } syntax): object key order is modified

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=202139

Alexey Shvayka <shvaikalesh at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |shvaikalesh at gmail.com
         Resolution|---                         |DUPLICATE

--- Comment #6 from Alexey Shvayka <shvaikalesh at gmail.com> ---
(In reply to Kevin Gibbons from comment #2)
> which is the bug: it changes the order in which properties appear to have
> been added to the object, which is observable with Reflect.ownKeys. I don't
> know why it does that delete.

Thank you Kevin for super-detailed investigation!

r264574 replaces deleteProperty() calls in validateAndApplyPropertyDescriptor() with attribute-change transition, fixing the object spread order and the following test cases:

(In reply to Kevin Gibbons from comment #3)
> Also, note that any fix to this will require making all of
> 
> Reflect.ownKeys(Object.defineProperty({ a: 0, b: 0 }, 'a', { enumerable:
> false }))
> Reflect.ownKeys(Object.defineProperty({ a: 0, b: 0 }, 'a', { get: () => 0 }))
> Reflect.ownKeys(Object.defineProperty(Object.create(null, { a: { get: () =>
> {}, configurable: true }, b: { get: () => {}, configurable: true } }), 'a',
> { value: 1 }))
> Reflect.ownKeys(Object.defineProperty(Object.create(null, { a: { get: () =>
> {}, configurable: true }, b: { get: () => {}, configurable: true } }), 'a',
> { get: () => {} }))
> 
> return `["a","b"]` as well. (There are four distinct deleteProperty calls in validateAndApplyPropertyDescriptor, each of which needs to be avoided to preserve property enumeration order.)

Test262 coverage: https://github.com/tc39/test262/pull/2516.

*** This bug has been marked as a duplicate of bug 142933 ***

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