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Allow constructing and subclassing EventTarget #467

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merged 2 commits into from Jul 7, 2017

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@domenic domenic commented Jun 21, 2017

Closes #441. See also https://www.w3.org/Bugs/Public/show_bug.cgi?id=16487.

Tests: web-platform-tests/wpt#6306

Chrome is interested in implementing this; anyone else? @cdumez @smaug---- @travisleithead


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@domenic domenic added needs implementer interest Moving the issue forward requires implementers to express interest needs tests Moving the issue forward requires someone to write tests labels Jun 21, 2017
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smaug---- commented Jun 21, 2017

What is the current API proposal? No parent chain?
What are the use cases we try to solve?

In general I'm supportive, just need to think a bit the API so that it fulfills the most common use cases.

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domenic commented Jun 21, 2017

Yes; as noted in the pull request,

+<p class="note">In the future we could allow custom <a>get the parent</a> algorithms. Let us know
+if this would be useful for your programs. For now, all author-created {{EventTarget}}s do not
+participate in a tree structure.</p>

domenic added a commit to web-platform-tests/wpt that referenced this pull request Jun 21, 2017
@domenic domenic removed the needs tests Moving the issue forward requires someone to write tests label Jun 21, 2017
domenic added a commit to web-platform-tests/wpt that referenced this pull request Jun 22, 2017
dom.bs Outdated
@@ -944,6 +944,11 @@ and a <dfn export for=EventTarget>legacy-canceled-activation behavior</dfn> algo
are not to be used for anything else. [[!HTML]]

<dl class=domintro>
<dt><code><var>target</var> = new EventTarget();</code>
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We should link EventTarget here.

dom.bs Outdated
must run these steps:

<ol>
<li>Return a new {{EventTarget}} object, using the default <a>get the parent</a> algorithm, and
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<li><p> or maybe inline it in the previous step. It seems that you get a default get the parent and no behavior should maybe be a note as it's just a statement of fact.

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LGTM overall. I guess we still need some implementer support and tests?

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domenic commented Jun 28, 2017

Got tests, got 1 implementer support; waiting for a second.

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domenic commented Jul 6, 2017

@annevk given #441 (comment), do you think this is mergeable? (Also want to review/merge the tests.)

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annevk commented Jul 7, 2017

I confirmed on IRC that it's all good. I also reviewed the tests.

@domenic domenic merged commit c4c1c8b into master Jul 7, 2017
@domenic domenic deleted the constructible-eventtarget branch July 7, 2017 18:55
domenic added a commit to web-platform-tests/wpt that referenced this pull request Jul 7, 2017
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annevk commented Jul 8, 2017

For next time, it's worth noting the tests in the commit message I think.

Also, did any browser bugs get filed?

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domenic commented Jul 8, 2017

I was going to but then the build failed so I didn't have a spec to point them to. That should be fixed now so I can file Monday. Will update the thread then.

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domenic commented Jul 10, 2017

Re-built the spec and it's showing up now, yay. Bugs:

bertogg pushed a commit to Igalia/webkit that referenced this pull request Feb 17, 2020
https://bugs.webkit.org/show_bug.cgi?id=174313

Reviewed by Darin Adler.

LayoutTests/imported/w3c:

* web-platform-tests/WebIDL/ecmascript-binding/constructors-expected.txt:
* web-platform-tests/dom/events/Event-subclasses-constructors-expected.txt:
* web-platform-tests/dom/events/EventTarget-constructible.any-expected.txt:
* web-platform-tests/dom/events/EventTarget-constructible.any.worker-expected.txt:
* web-platform-tests/dom/events/event-global-extra.window-expected.txt:
* web-platform-tests/dom/idlharness.any.worker-expected.txt:
* web-platform-tests/dom/idlharness.window-expected.txt:

Source/WebCore:

Currently, EventTarget can't be directly constructed or be subclassed in JavaScript.
The spec for EventTarget was updated (whatwg/dom#467) to allow
constructing and subclassing EventTarget. This feature was shipped in Chrome 64 and Firefox 59.

This patch introduces EventTargetConcrete class, a user-constructable version of EventTarget,
exposed as "EventTarget" to JavaScript. We don't use EventTarget directly because it is an abstract
class and making it non-abstract is unfavorable due to size increase of EventTarget and all of its
subclasses with code that is mostly unnecessary for them, resulting in a performance decrease.

To prevent definition of specific to EventTargetConcrete `toJS` and `toJSNewlyCreated` functions,
we don't define EventTargetConcrete interface type, but rather tweak make_event_factory.pl to
default to base interface (like it does for Event).

To allow subclassing of all DOM constructors, non-custom ones replace structures of newly created
wrapper objects with ones returned by InternalFunction::createSubclassStructure. Per WebIDL spec [1],
`setSubclassStructureIfNeeded` helper uses realm of `newTarget` for default prototypes.

This approach was chosen because a) detecting [[Construct]] with callFrame->newTarget() is
unreliable outside constructor, and b) passing `newTarget` down to `createWrapper` via
`toJSNewlyCreated` is quite awkward and would result in massive code change.

[1] https://heycam.github.io/webidl/#internally-create-a-new-object-implementing-the-interface
(step 3.3.2)

Tests: fast/dom/dom-constructors.html
       imported/w3c/web-platform-tests/WebIDL/ecmascript-binding/constructors.html
       imported/w3c/web-platform-tests/dom/events/Event-subclasses-constructors.html
       imported/w3c/web-platform-tests/dom/events/EventTarget-constructible.any.html
       imported/w3c/web-platform-tests/dom/idlharness.window.html

* Headers.cmake:
* Sources.txt:
* WebCore.xcodeproj/project.pbxproj:
* bindings/js/JSDOMWrapperCache.h:
(WebCore::setSubclassStructureIfNeeded):
* bindings/js/JSEventTargetCustom.cpp:
(WebCore::toJSNewlyCreated):
* bindings/scripts/CodeGeneratorJS.pm:
(GenerateConstructorDefinition):
* bindings/scripts/InFilesCompiler.pm:
(generateInterfacesHeader):
* bindings/scripts/test/JS/*: Adjust bindings expectations.
* dom/EventTarget.cpp:
(WebCore::EventTarget::create):
* dom/EventTarget.h:
* dom/EventTarget.idl:
* dom/EventTargetConcrete.cpp: Added.
* dom/EventTargetConcrete.h: Added.
* dom/make_event_factory.pl:
(generateImplementation):

LayoutTests:

* fast/dom/dom-constructors-expected.txt:
* fast/dom/dom-constructors.html:
* platform/ios/imported/w3c/web-platform-tests/dom/events/Event-subclasses-constructors-expected.txt: Removed.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@256716 268f45cc-cd09-0410-ab3c-d52691b4dbfc
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