Function.name and Function.length should be configurable.

[Mark Lam]

According to https://tc39.github.io/ecma262/#sec-ecmascript-language-functions-and-classes, "Unless otherwise specified, the name property of a built-in Function object, if it exists, has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }."

[Radar WebKit Bug Importer]

<rdar://problem/24799540>

[Mark Lam]

Created attachment 272233 [details]
work in progress: changed 'name' and 'length' properties to be reified on access.

[Mark Lam]

https://tc39.github.io/ecma262/#sec-ecmascript-language-functions-and-classe also says "the length property of a built-in Function object has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }."

[Mark Lam]

Created attachment 272353 [details]
proposed patch.

[Mark Lam]

Created attachment 272354 [details]
proposed patch: rebased.

[Saam Barati]

Comment on attachment 272354 [details]
proposed patch: rebased.

View in context: https://bugs.webkit.org/attachment.cgi?id=272354&action=review

r=me with comment

> Source/JavaScriptCore/runtime/JSFunction.cpp:522
> +        if (propertyName == exec->propertyNames().length)
> +            thisObject->reifyLengthIfNeeded(exec);
> +        else if (propertyName == exec->propertyNames().name)
> +            thisObject->reifyNameIfNeeded(exec);

This code is repeated a lot. It might be worth having an inlined helper here that reifies if necessary.
You could call it reifyIfNecessary(PropertyName) or something.

[Saam Barati]

It might be worth adding some tests that will gracefully handle structure transitions
after reification.

[Saam Barati]

It's also worth adding tests that do indeed verify that
the property is configurable.

[Mark Lam]

Created attachment 272371 [details]
proposed patch 2: addressed Saam's feedback w/ new test.

[Mark Lam]

Thanks for the review.  Landed in r197205: <http://trac.webkit.org/r197205>.