[view-transitions] Support style inheritance in the pseudo-element tree

https://bugs.webkit.org/show_bug.cgi?id=269808
rdar://123331760

Reviewed by Anne van Kesteren.

The style inheritance must follow the pseudo-element tree structure. This allows the different `inherit` declarations in the `viewTransitions.css` UA stylesheet to work.

This is also ergonomic for developers since they can just set the animation-duration once and have it cascade down the pseudo-element tree.

Also fix the cache to actually store the named view transition style when resolving, otherwise `TreeResolver::makeResolutionContextForPseudoElement` can't fetch it.

* LayoutTests/imported/w3c/web-platform-tests/css/css-view-transitions/style-inheritance-expected.txt: Rebaselined test.
* Source/WebCore/dom/Element.cpp:
(WebCore::Element::resolvePseudoElementStyle):
* Source/WebCore/rendering/style/RenderStyleSetters.h:
(WebCore::RenderStyle::setPseudoElementNameArgument):
* Source/WebCore/style/StyleTreeResolver.cpp:
(WebCore::Style::TreeResolver::resolveElement):
(WebCore::Style::TreeResolver::makeResolutionContextForPseudoElement):

Canonical link: https://commits.webkit.org/275121@main

LayoutTests/imported/w3c/web-platform-tests/css/css-view-transitions/style-inheritance-expected.txt

@@ -1,6 +1,3 @@
-CONSOLE MESSAGE: Unhandled Promise Rejection: Error: assert_equals: group expected "rgb(255, 0, 0)" but got "rgba(0, 0, 0, 0)"
-
-Harness Error (FAIL), message = Unhandled rejection: assert_equals: group expected "rgb(255, 0, 0)" but got "rgba(0, 0, 0, 0)"
 
 PASS style inheritance of pseudo elements
 

Source/WebCore/dom/Element.cpp

@@ -4141,8 +4141,7 @@ const RenderStyle& Element::resolvePseudoElementStyle(const Style::PseudoElement
         style->inheritFrom(*parentStyle);
         // FIXME: RenderStyle should switch to use PseudoElementIdentifier.
         style->setPseudoElementType(pseudoElementIdentifier.pseudoId);
-        if (!pseudoElementIdentifier.nameArgument.isNull())
-            style->setPseudoElementNameArgument(pseudoElementIdentifier.nameArgument);
+        style->setPseudoElementNameArgument(pseudoElementIdentifier.nameArgument);
     }
 
     auto* computedStyle = style.get();

Source/WebCore/rendering/style/RenderStyleSetters.h

@@ -471,7 +471,8 @@ inline void RenderStyle::setPseudoElementNameArgument(const AtomString& identifi
         || pseudoElementType() == PseudoId::ViewTransitionImagePair
         || pseudoElementType() == PseudoId::ViewTransitionNew
         || pseudoElementType() == PseudoId::ViewTransitionOld
-        || pseudoElementType() == PseudoId::Highlight);
+        || pseudoElementType() == PseudoId::Highlight
+        || identifier.isNull());
     SET_NESTED(m_nonInheritedData, rareData, pseudoElementNameArgument, identifier);
 }
 

Source/WebCore/style/StyleTreeResolver.cpp

@@ -296,8 +296,7 @@ auto TreeResolver::resolveElement(Element& element, const RenderStyle* existingS
             return pseudoElementChange;
         if (pseudoElementUpdate->recompositeLayer)
             update.recompositeLayer = true;
-        if (pseudoElementIdentifier.nameArgument.isNull())
-            update.style->addCachedPseudoStyle(WTFMove(pseudoElementUpdate->style));
+        update.style->addCachedPseudoStyle(WTFMove(pseudoElementUpdate->style));
         return pseudoElementUpdate->change;
     };
 
@@ -547,9 +546,26 @@ ResolutionContext TreeResolver::makeResolutionContext()
 ResolutionContext TreeResolver::makeResolutionContextForPseudoElement(const ElementUpdate& elementUpdate, const PseudoElementIdentifier& pseudoElementIdentifier)
 {
     auto parentStyle = [&]() -> const RenderStyle* {
-        if (pseudoElementIdentifier.pseudoId == PseudoId::FirstLetter) {
+        switch (pseudoElementIdentifier.pseudoId) {
+        case PseudoId::FirstLetter:
             if (auto* firstLineStyle = elementUpdate.style->getCachedPseudoStyle({ PseudoId::FirstLine }))
                 return firstLineStyle;
+            break;
+        case PseudoId::ViewTransitionGroup:
+            if (auto* viewTransitionStyle = elementUpdate.style->getCachedPseudoStyle({ PseudoId::ViewTransition }))
+                return viewTransitionStyle;
+            break;
+        case PseudoId::ViewTransitionImagePair:
+            if (auto* groupStyle = elementUpdate.style->getCachedPseudoStyle({ PseudoId::ViewTransitionGroup, pseudoElementIdentifier.nameArgument }))
+                return groupStyle;
+            break;
+        case PseudoId::ViewTransitionOld:
+        case PseudoId::ViewTransitionNew:
+            if (auto* imagePairStyle = elementUpdate.style->getCachedPseudoStyle({ PseudoId::ViewTransitionImagePair, pseudoElementIdentifier.nameArgument }))
+                return imagePairStyle;
+            break;
+        default:
+            break;
         }
         return elementUpdate.style.get();
     };