[Webkit-unassigned] [Bug 159398] [test262] Fixing mapped arguments object property test case

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=159398

--- Comment #80 from Caio Lima <ticaiolima at gmail.com> ---
(In reply to comment #79)
> So if we change enumerable/configurable, we still keep arguments aliased?

Yes.

> Only changing writable makes it not aliased?

No. It also happens if you use non Data Descriptor (i.e. descriptor contains accessor)

> However, if you do change
> eneumerable/configurable, you still store to JSObject's property mechanism
> just to keep a record of the descriptor? Am I understanding this correctly?

Yes. We use JSObject's to consult its descriptor. When the index is mapped, we need to get the value from mapping mechanism (now it is stored on m_overrides).

To understand the correct behavior I used these test cases: https://github.com/tc39/test262/tree/master/test/language/arguments-object/mapped

Also, https://tc39.github.io/ecma262/#sec-arguments-exotic-objects-defineownproperty-p-desc is presenting when the should stop mapping.

Here https://tc39.github.io/ecma262/#sec-arguments-exotic-objects-getownproperty-p we can check steps 5. and 6, that the desc.[[Value]] is updated from mapping when it is being mapped.

Does it make more sense now?

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