:empty selector with animation not working properly

https://bugs.webkit.org/show_bug.cgi?id=269051 rdar://122838142 Reviewed by Antti Koivisto. If an element is targeted by an animation, it may cause style updates with an `AnimationOnly` resolution type. When `Style::TreeResolver::resolveElement()` is called for that element, `resetStyleRelations()` is called on that element first under `Style::TreeResolver::resolveComposedTree()` while iterating through the composed tree. If an `:empty` pseudo-class rule matches that element, that call to `resetStyleRelations()` will remove the `StyleAffectedByEmpty` flag on that element, but it will not be recomputed under `resolveElement()` because when `styleForStyleable()` is called the `AnimationOnly` resolution type will mean that we clone the cached last style resolution style to return the `ResolvedStyle` value, clear of any relations. We now avoid calling `resetStyleRelations()` if the resolution type is `AnimationOnly`, ensuring that relations are preserved throughout animation updates. * LayoutTests/imported/w3c/web-platform-tests/css/css-animations/empty-pseudo-class-with-animation-expected.txt: Added. * LayoutTests/imported/w3c/web-platform-tests/css/css-animations/empty-pseudo-class-with-animation.html: Added. * Source/WebCore/style/StyleTreeResolver.cpp: (WebCore::Style::TreeResolver::resolveComposedTree): Canonical link: https://commits.webkit.org/275832@main
WebKit · Mar 8, 2024 · 319ecb9 · 319ecb9
1 parent eaa411f
commit 319ecb9
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diff --git a/.../w3c/web-platform-tests/css/css-animations/empty-pseudo-class-with-animation-expected.txt b/.../w3c/web-platform-tests/css/css-animations/empty-pseudo-class-with-animation-expected.txt
@@ -0,0 +1,3 @@
+
+PASS Setting an "animation" style property on an element does not interfere with the :empty pseudo-class.
+
diff --git a/...imported/w3c/web-platform-tests/css/css-animations/empty-pseudo-class-with-animation.html b/...imported/w3c/web-platform-tests/css/css-animations/empty-pseudo-class-with-animation.html
@@ -0,0 +1,47 @@
+<!DOCTYPE html>
+<link rel="author" href="mailto:graouts@apple.com">
+<link rel="help" href="https://drafts.csswg.org/css-animations/">
+<link rel="help" href="https://drafts.csswg.org/selectors/#the-empty-pseudo">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/css-animations/support/testcommon.js"></script>
+
+<div class="container"></div>
+
+<style>
+
+.container {
+  width: 100px;
+  height: 100px;
+  background-color: rgb(0, 255, 0);
+}
+
+.container:empty {
+  background-color: rgb(255, 0, 0);
+  animation: anim 1s;
+}
+
+@keyframes anim { }
+
+</style>
+
+<script>
+
+promise_test(async () => {
+  const container = document.querySelector(".container");
+  const computedStyle = getComputedStyle(container);
+
+  // Check that the :empty rule applies initially.
+  assert_equals(computedStyle.backgroundColor, 'rgb(255, 0, 0)',
+    'The initial background-color matches the value set by the :empty rule.');
+
+  // Await a couple of frames to let any animation-related style updates happen.
+  await waitForAnimationFrames(2);
+
+  // Append a child which should no longer let the :empty rule apply.
+  container.appendChild(document.createElement("span"));
+  assert_equals(computedStyle.backgroundColor, 'rgb(0, 255, 0)',
+    'The background-color after inserting a child into the container no longer matches the value set by the :empty rule.');
+}, 'Setting an "animation" style property on an element does not interfere with the :empty pseudo-class.');
+
+</script>
diff --git a/Source/WebCore/style/StyleTreeResolver.cpp b/Source/WebCore/style/StyleTreeResolver.cpp
@@ -999,7 +999,9 @@ void TreeResolver::resolveComposedTree()
         auto resolutionType = determineResolutionType(element, style, parent.descendantsToResolve, parent.change);
         if (resolutionType) {
             element.resetComputedStyle();
-            element.resetStyleRelations();
+
+            if (*resolutionType != ResolutionType::AnimationOnly)
+                element.resetStyleRelations();
 
             if (element.hasCustomStyleResolveCallbacks())
                 element.willRecalcStyle(parent.change);