Clicking an element nested inside a checkbox/radio wrongly activates the ancestor input
https://bugs.webkit.org/show_bug.cgi?id=321247

Reviewed by Darin Adler.

WebKit's legacy-pre-activation behavior (the checkbox/radio toggle that happens before
event dispatch) was applied to the first <input> found anywhere in the event path,
including an ancestor checkbox/radio. Per the DOM specification, legacy-pre-activation
behavior must only run on the event's activation target, which is the innermost node in
the event path that has activation behavior. So when an element with its own activation
behavior (e.g. a submit/reset <button>, an <a>/<area> link, a <summary>, or a
<label><button type=button>) is nested inside a checkbox/radio, that inner element is the
activation target and the ancestor input must not be toggled or activated.

Introduce a virtual Node::hasActivationBehavior() (matching the spec concept and Blink's
HasActivationBehavior), returning true for HTMLInputElement, HTMLButtonElement,
HTMLLabelElement, and HTMLSummaryElement, and isLink() for HTMLAnchorElement (and
HTMLAreaElement via inheritance). findInputElementInEventPath() now returns the innermost
node with activation behavior, and only when that node is an <input>; otherwise no legacy
pre-activation behavior runs.

This fixes 14 subtests in Event-dispatch-single-activation-behavior.html, including the 12
that already pass in both Chrome and Firefox. The remaining failures match the ones Chrome
and/or Firefox also fail.

No new tests, rebaselined existing WPT test.

* LayoutTests/imported/w3c/web-platform-tests/dom/events/Event-dispatch-single-activation-behavior-expected.txt:
* Source/WebCore/dom/EventDispatcher.cpp:
(WebCore::findInputElementInEventPath):
* Source/WebCore/dom/Node.cpp:
(WebCore::Node::hasActivationBehavior const):
* Source/WebCore/dom/Node.h:
* Source/WebCore/html/HTMLAnchorElement.cpp:
(WebCore::HTMLAnchorElement::isSystemPreviewLink):
* Source/WebCore/html/HTMLAnchorElement.h:
* Source/WebCore/html/HTMLButtonElement.cpp:
(WebCore::HTMLButtonElement::hasActivationBehavior const):
* Source/WebCore/html/HTMLButtonElement.h:
* Source/WebCore/html/HTMLInputElement.cpp:
(WebCore::HTMLInputElement::hasActivationBehavior const):
* Source/WebCore/html/HTMLInputElement.h:
* Source/WebCore/html/HTMLLabelElement.cpp:
(WebCore::HTMLLabelElement::hasActivationBehavior const):
* Source/WebCore/html/HTMLLabelElement.h:
* Source/WebCore/html/HTMLSummaryElement.cpp:
(WebCore::HTMLSummaryElement::hasActivationBehavior const):
* Source/WebCore/html/HTMLSummaryElement.h:

Canonical link: https://commits.webkit.org/318853@main