Bug 78525 – CSS regions enabled by default

• Status: RESOLVED
• Resolution: FIXED
• Component: CSS

[James Robinson]

CSS regions are enabled by default today, but we aren't quite ready to be exposing these to the web yet in shipping browsers (at least in Chromium).  I think we should add guards back for now while the feature is still under active development and the CSSWG is debating how this area will look.

Options:

1.) #ifdef ENABLE(). Upside: Easy, works in all platforms. Downside: this prevents the bots from running the tests by default, far more annoying for developers, greater risk of compile breakage from developers not working directly on the feature.

2.) Runtime preference. Upside: Fairly easy, allows for feature to by on in DumpRenderTree and off in shipping browsers and allows for developers working on the feature to simply flip a flag to test without requiring rebuilds. Prevents compile breakages from developers not working directly on the feature. Downside: No way to have runtime guards for the JSC bindings.

[Mihnea Ovidenie]

I would prefer to use a runtime flag for the feature instead of a compile time flag.

[James Robinson]

I agree that would be more convenient.  In IRC Dave Hyatt agreed that a runtime guard is probably the best way to go here.

Do you have some cycles to try to make this happen, Mihnea?  I probably won't be able to take this on this week.  In order to make the next Chromium release train we would want something in place in the next 3 weeks.

[Mihnea Ovidenie]

Working on it.

[Mihnea Ovidenie]

Created attachment 127400 [details]
Patch

First version of patch. It disables css regions functionality at runtime. The preference key is "WebKitCSSRegionsEnabled".
In DRT, use layoutTestController.overridePreference("WebKitCSSRegionsEnabled", "1") to enable the css regions functionality.
The css regions tests in fast/repaint will be moved to fast/regions in another patch.
The css regions tests in fast/regions are skipped and will be enabled in another patch.

[Mihnea Ovidenie]

Created attachment 127584 [details]
Patch 2

Another patch, this time the css regions are enabled by default.

[Dave Hyatt]

Comment on attachment 127584 [details]
Patch 2

r=me

[WebKit Review Bot]

Comment on attachment 127584 [details]
Patch 2

Clearing flags on attachment: 127584

Committed r108108: <http://trac.webkit.org/changeset/108108>

[WebKit Review Bot]

All reviewed patches have been landed.  Closing bug.

[Peter Beverloo]

(In reply to comment #8)
> All reviewed patches have been landed.  Closing bug.

Toggling regions during run-time will disable working of the CSS properties, but since DOM properties[1] (and perhaps element.style.webkitRegionOverflow et al as well, haven't tested that) will still be exposed this will break feature detection. Take the following script:

var element = document.createElement('div');
if (typeof(x.webkitRegionOverflow) !== 'undefined') {
    // supported!
}

While larger scripts such as Modernizr haven't yet picked up on detecting CSS Region support (supposedly since it is enabled by default and the DOM implementation is still rather new), this doesn't seem a desirable effect. Have you thought about this?

[1] http://trac.webkit.org/browser/trunk/Source/WebCore/dom/Element.idl#L137

[James Robinson]

The DOM features should be guarded by V8EnabledAtRuntime:

http://trac.webkit.org/wiki/WebKitIDL#V8EnabledAtRuntime


There's no way to guard at runtime for the JSC bindings, but I think we're OK there due to ship schedules.