[webkit-dev] Runtime setting for incomplete features

Drew Wilson atwilson at google.com
Mon Oct 5 17:46:00 PDT 2009

So, two weeks ago I sent an email on this thread stating exactly what I was
planning to do, To whit:
I do think that we ought to be returning undefined instead of null in those
cases, though, just to catch people who are accidentally using isUndefined()
utility functions from common libraries. It would not be hard to define some
kind of [mapNullToUndefined] custom attribute for the code generator.

Maciej and AP both chimed in saying that disabling enumeration (i.e.
"SharedWorker in window") would be prohibitively hard, and giving a tacit OK
to my approach (my emphasis below):

It would be pretty complicated to do that [disabling [LocalStorage in
window"] based on a runtime setting. You would need a custom getter for any
object that has properties which may appear or disappear based on settings.
This is *probably too complicated to be worth it*. Or at least, if we added
that level of code complexity I would begin to doubt the merits of
supporting runtime enabling of Web platform features.

I'm surprised to see these objections coming up now, weeks after the
original discussion, and only after my patch has landed in the tree. That
said, I agree that in an ideal world, we'd hide window.audio, shared
workers, notifications, local storage, databases, session storage and any
other runtime/platform-disabled API from enumerations - I just agree with
Maciej that this isn't a hugely important issue, since these features are
only runtime-disabled while under development and so not widely available

Regardless, I don't think we should rush out to roll all of those features
out of the tree, and I certainly don't think we should be singling out
SharedWorkers or WebSockets - if we feel strongly that this needs to be
addressed, we can update all of those features accordingly. If people with
knowledge of the internals of V8 and JSC can chime in, we can discuss how
best to approach this.


On Mon, Oct 5, 2009 at 5:04 PM, Sam Weinig <sam.weinig at gmail.com> wrote:

> Hi Folks,
> I am not happy with the way these runtime settings have been implemented so
> far as they break runtime detection using the technique we evangelize to
> developers, specifically, using the ("property" in window) method.  A
> feature that is turned off at runtime should not be detectable at all, using
> any method (including Object.keys(), object.hasOwnProperty(),
> object.propertyIsEnumerable(), for-in enumeration, etc).  I filed
> https://bugs.webkit.org/show_bug.cgi?id=29896 when the WebSocket runtime
> switching code went in and was disappointed to see similarly buggy code go
> in for SharedWorkers with out this being fixed.
> Leaving this in the tree is likely to introduce compatibility issues so I
> would recommend that we roll out these changes if they cannot be fixed in a
> timely manner.
> -Sam
> On Tue, Sep 8, 2009 at 11:47 PM, Darin Fisher <darin at chromium.org> wrote:
>> As is described in https://bugs.webkit.org/show_bug.cgi?id=28941, for
>> the Chromium project, we like to make incomplete features available
>> behind a command line flag to help facilitate testing.  I understand
>> that the norm for WebKit is to only have compile time options for new
>> / incomplete features.  In some cases, runtime settings are defined,
>> but these generally correspond to end user preferences or the needs of
>> specific embedders.
>> At any rate, I just wanted to make sure that folks were aware that
>> some settings may only exist to help facilitate Chromium's goal of
>> shipping incomplete features, disabled by default.
>> Alexey asked if there are any guidelines for when these settings may
>> be removed.  I think the main thing is that the feature has to be
>> reasonably complete and enabled by default by embedders (e.g.,
>> Chromium) that are compiling the feature.
>> Regards,
>> -Darin
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