imported/w3c/web-platform-tests/css/css-nesting/cssom.html is failing…

… in WebKit

https://bugs.webkit.org/show_bug.cgi?id=262459

Reviewed by Ryosuke Niwa.

We have an optimization in CharacterData::setData() that avoids doing some work
when the JS cannot observe it. This optimization was breaking the test.

The test sets the innerHTML of a <style> element, which ends up calling setData()
on the child Text node (as an optimization) and then takes the optimized code
path in CharacterData::setData(). The optimized code path fails to notify the
ancestors that the text has changed. However, HTMLStyleElement::childrenChanged()
has code that needs to run in such case.

As a result, I am now disabling the optimization in CharacterData::setData() if
the parent node is an HTMLStyleElement.

* LayoutTests/imported/w3c/web-platform-tests/css/css-nesting/cssom-expected.txt:
* Source/WebCore/dom/CharacterData.cpp:
(WebCore::canUseSetDataOptimization):

Canonical link: https://commits.webkit.org/268707@main

LayoutTests/imported/w3c/web-platform-tests/css/css-nesting/cssom-expected.txt

@@ -13,7 +13,7 @@ PASS Simple CSSOM manipulation of subrules 5
 PASS Simple CSSOM manipulation of subrules 6
 PASS Simple CSSOM manipulation of subrules 7
 PASS Simple CSSOM manipulation of subrules 8
-FAIL Simple CSSOM manipulation of subrules 9 assert_equals: selectorText and insertRule expected ".a {\n  color: red;\n  div & { }\n  div.b .c & { color: green; }\n  .c div.b &, div & { color: blue; }\n}" but got ".a {\n  color: olivedrab;\n  div & { }\n  div.b .c & { color: green; }\n  .c div.b &, div & { color: blue; }\n}"
+PASS Simple CSSOM manipulation of subrules 9
 PASS Simple CSSOM manipulation of subrules 10
 PASS Mutating the selectorText of outer rule invalidates inner rules
 

Source/WebCore/dom/CharacterData.cpp

@@ -27,6 +27,7 @@
 #include "ElementTraversal.h"
 #include "EventNames.h"
 #include "FrameSelection.h"
+#include "HTMLStyleElement.h"
 #include "InspectorInstrumentation.h"
 #include "MutationEvent.h"
 #include "MutationObserverInterestGroup.h"
@@ -50,7 +51,7 @@ static bool canUseSetDataOptimization(const CharacterData& node)
 {
     auto& document = node.document();
     return !document.hasListenerType(Document::ListenerType::DOMCharacterDataModified) && !document.hasMutationObserversOfType(MutationObserverOptionType::CharacterData)
-        && !document.hasListenerType(Document::ListenerType::DOMSubtreeModified);
+        && !document.hasListenerType(Document::ListenerType::DOMSubtreeModified) && !is<HTMLStyleElement>(node.parentNode());
 }
 
 void CharacterData::setData(const String& data)