Intent to Remove: Multiple Shadow Roots with a user agent shadow root

Hayato Ito

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Oct 14, 2015, 3:27:54 AM10/14/15

to blink-dev

Primary eng (and PM) emails

hay...@chromium.org

Link to "Intent to Deprecate" thread

https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/9qDsRePDALE/7c8kOkJfLgkJ

Summary

Remove the support to call createShadowRoot for an element if it has a user agent shadow root, such as <input> element.

This "Intent to Remove: Multiple Shadow Roots with a user agent shadow root" is different from what I sent last month,"Intent to Remove: Multiple Shadow Roots" [1].

[1] https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/87KFL7xdW0k

The last month's "Intent to Remove" is to remove "Multiple Shadow Roots" in general.

e.g.

A)

var div = document.createElement("div");

var sr1 = div.createShadowRoot();

var sr2 = div.createShadowRoot(); // We no longer supports.

This time, I'm going to remove the support for only the following case:

B)

var input = document.createElement("input"); // <input> has a user agent shadow root.

var sr1 = input.createShadowRoot(); // We no longer supports.

I'm going to remove only the case B. The case A continues to work.

We have a separate UseCounter for each: ElementCreateShadowRootMultiple and ElementCreateShadowRootMultipleWithUserAgentShadowRoot. The former is inclusive of the latter.

Motivation

This feature has been a cause of code complexity. It would be great to remove the support partially ahead of removing "Multiple Shadow Roots" entirely, in terms of code health.

Compatibility Risk

Low. Blink has supported this feature since M35.

No other browser supports this feature.

Usage information from UseCounter

<=0.0001%: https://www.chromestatus.com/metrics/feature/timeline/popularity/800

For reference, the usage information for Multiple Shadow Roots (in general) is 0.0058% https://www.chromestatus.com/metrics/feature/timeline/popularity/779

OWP launch tracking bug

https://code.google.com/p/chromium/issues/detail?id=489947

Entry on the feature dashboard

https://www.chromestatus.com/features/4668884095336448