Bug 154475 – Builtins that should not rely on iteration do.

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Mark S. Miller]

Created attachment 271806 [details]
Open this web page in Safari and Webkit Nightly, and open the console

Now that the latest WebKit seems to mostly work again on the SES selftest page
https://rawgit.com/tvcutsem/es-lab/master/src/ses/contract.html
I was seeing some new failures. But this time I was able to debug (thanks!)
and isolate the problem.

The new problem is that the builtins used by
http://wiki.ecmascript.org/doku.php?id=conventions:safe_meta_programming
all of which redate ES6 now depend on iterator.next behavior in violation of the ES6 spec.
You can see it yourself by opening the badbind.html in Safari and Webkit Nightly, opening
the console, and seeing what's there. Works fine on Safari and on every other browser I
tested. Fails on the latest WebKit nightly.

Note that I'll be updating the SES selftest page to stop removing .next, because of this
bug, so the SES selftest page will stop being a good test.

[Mark S. Miller]

Created attachment 271807 [details]
Screenshot showing Safari working and WebKit failing the badbind.html test for this bug

[Keith Miller]

I think this is because of my patch (http://trac.webkit.org/changeset/196734). I didn't realize that arguments iterator was observable from outside it's scope. Working on this now.

[Mark S. Miller]

Although this specific test passes on all other browsers, note that Chrome50 Canary has a similar but different problem: 
https://bugs.chromium.org/p/v8/issues/detail?id=4769

[Keith Miller]

Created attachment 271926 [details]
Patch

[Keith Miller]

Created attachment 271931 [details]
Benchmark results

[Geoffrey Garen]

Comment on attachment 271926 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=271926&action=review

r=me

> Source/JavaScriptCore/builtins/FunctionPrototype.js:33
> +        @putByValDirect(argumentValues, i-1, arguments[i]);

Spacing around - 1.

[WebKit Commit Bot]

Comment on attachment 271926 [details]
Patch

Clearing flags on attachment: 271926

Committed r196949: <http://trac.webkit.org/changeset/196949>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.