[view-transitions] Skip view transition when new element becomes hidden

https://bugs.webkit.org/show_bug.cgi?id=270815
rdar://124406569

Reviewed by Ryosuke Niwa.

As mandated by the spec.

* LayoutTests/TestExpectations:
* Source/WebCore/dom/ViewTransition.cpp:
(WebCore::ViewTransition::captureOldState):
(WebCore::ViewTransition::activateViewTransition):
(WebCore::ViewTransition::updatePseudoElementStyles):
* Source/WebCore/dom/ViewTransition.h:

Canonical link: https://commits.webkit.org/275956@main

LayoutTests/TestExpectations

@@ -6922,7 +6922,6 @@ imported/w3c/web-platform-tests/css/css-view-transitions/content-visibility-auto
 imported/w3c/web-platform-tests/css/css-view-transitions/content-with-transform-new-image.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-view-transitions/dialog-in-top-layer-during-transition-old.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-view-transitions/element-with-overflow.html [ ImageOnlyFailure ]
-imported/w3c/web-platform-tests/css/css-view-transitions/exit-transition-with-anonymous-layout-object.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-view-transitions/far-away-capture.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-view-transitions/fractional-box-with-overflow-children-new.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-view-transitions/massive-element-below-and-on-top-of-viewport-partially-onscreen-new.html [ ImageOnlyFailure ]

Source/WebCore/dom/ViewTransition.cpp

@@ -342,6 +342,9 @@ ExceptionOr<void> ViewTransition::captureOldState()
             if (auto name = effectiveViewTransitionName(element); !name.isNull()) {
                 if (auto check = checkDuplicateViewTransitionName(name, usedTransitionNames); check.hasException())
                     return check.releaseException();
+
+                // FIXME: Skip fragmented content.
+
                 captureElements.append(element);
             }
             return { };
@@ -493,7 +496,11 @@ void ViewTransition::activateViewTransition()
     }
 
     setupTransitionPseudoElements();
-    updatePseudoElementStyles();
+    checkFailure = updatePseudoElementStyles();
+    if (checkFailure.hasException()) {
+        skipViewTransition(checkFailure.releaseException());
+        return;
+    }
 
     m_phase = ViewTransitionPhase::Animating;
     m_ready.second->resolve();
@@ -618,15 +625,19 @@ Ref<MutableStyleProperties> ViewTransition::copyElementBaseProperties(Element& e
 }
 
 // https://drafts.csswg.org/css-view-transitions-1/#update-pseudo-element-styles
-void ViewTransition::updatePseudoElementStyles()
+ExceptionOr<void> ViewTransition::updatePseudoElementStyles()
 {
     auto& resolver = protectedDocument()->styleScope().resolver();
 
     for (auto& [name, capturedElement] : m_namedElements.map()) {
         RefPtr<MutableStyleProperties> properties;
-        if (capturedElement->newElement) {
-            CheckedPtr renderBox = dynamicDowncast<RenderBox>(capturedElement->newElement->renderer());
-            properties = copyElementBaseProperties(*capturedElement->newElement, renderBox ? renderBox->size() : LayoutSize { });
+        if (RefPtr newElement = capturedElement->newElement.get()) {
+            // FIXME: Also check fragmented content here.
+            CheckVisibilityOptions visibilityOptions { .contentVisibilityAuto = true };
+            if (!newElement->checkVisibility(visibilityOptions))
+                return Exception { ExceptionCode::InvalidStateError, "One of the transitioned elements has become hidden."_s };
+            CheckedPtr renderBox = dynamicDowncast<RenderBox>(newElement->renderer());
+            properties = copyElementBaseProperties(*newElement, renderBox ? renderBox->size() : LayoutSize { });
         } else
             properties = capturedElement->oldProperties;
 
@@ -641,6 +652,7 @@ void ViewTransition::updatePseudoElementStyles()
     }
 
     protectedDocument()->styleScope().didChangeStyleSheetContents();
+    return { };
 }
 
 }

Source/WebCore/dom/ViewTransition.h

@@ -157,7 +157,7 @@ class ViewTransition : public RefCounted<ViewTransition>, public CanMakeWeakPtr<
 
     Ref<MutableStyleProperties> copyElementBaseProperties(Element&, const LayoutSize&);
 
-    void updatePseudoElementStyles();
+    ExceptionOr<void> updatePseudoElementStyles();
     void setupDynamicStyleSheet(const AtomString&, const CapturedElement&);
 
     WeakPtr<Document, WeakPtrImplWithEventTargetData> m_document;