[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

Saam Barati <sbarati at apple.com> changed:

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--- Comment #73 from Saam Barati <sbarati at apple.com> ---
Comment on attachment 291051
  --> https://bugs.webkit.org/attachment.cgi?id=291051
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=291051&action=review

> Source/JavaScriptCore/runtime/GenericArgumentsInlines.h:194
> +        if (optionalIndex && !thisObject->isConfigurable(optionalIndex.value()) && !descriptor.justWritablePresent())

I'm not sure this is correct here. I think you want to be following:
https://tc39.github.io/ecma262/#sec-validateandapplypropertydescriptor
more or less here, with some extra rules defined in:
https://tc39.github.io/ecma262/#sec-arguments-exotic-objects-defineownproperty-p-desc

It looks like the code below falls back to normal object storage. Why not just fall back to normal object storage in every case instead of creating the isConfigurable map?

> JSTests/stress/arguments-non-configurable.js:27
> +function tryChangeWritableOfNonConfigurableDescriptor(x) {
> +    Object.defineProperty(arguments, 0, {configurable: false});
> +    Object.defineProperty(arguments, 0, {writable: true});
> +    Object.defineProperty(arguments, 0, {writable: false});
> +}

This is the specified behavior? This goes against normal object behavior:

>>> Object.defineProperty(o, "f", {configurable: false, value: 20})
[object Object]
>>> o.f
20
>>> o.f = 40
40
>>> o.f
20
>>> Object.defineProperty(o, "f", {writable: true, value:50})
Exception: TypeError: Attempting to change writable attribute of unconfigurable property.

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