[@scope] Support @scope (:host)

In CalculateActivations, we'd previously just call Element.parentElement up the ancestor chain, therefore never reach the host. Additionally, we did not propagate the original SelectorCheckerContext.scope which is needed for :host to match. This CL uses ParentOrShadowHostElement, and adds the concept of "activation ceiling" to deal with the fact that we need to look at one element *above* the current activation root when that root is a ShadowRoot. Note that :scope is supposed to be able to match "virtual" roots [1] (like a ShadowRoot), but Blink does not support this in general. This CL does not address this issue. [1] w3c/csswg-drafts#7261 Bug: 1280240 Change-Id: I2d0be103f4cd02ec576711b959e075a5118e694a Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4272396 Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org> Reviewed-by: Rune Lillesveen <futhark@chromium.org> Cr-Commit-Position: refs/heads/main@{#1108363}
web-platform-tests · Feb 22, 2023 · 1a1f712 · 1a1f712
1 parent eb3ce5b
commit 1a1f712
Showing 1 changed file with 60 additions and 0 deletions.
diff --git a/css/css-cascade/scope-shadow.html b/css/css-cascade/scope-shadow.html
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+<!DOCTYPE html>
+<title>@scope - ShadowDOM</title>
+<link rel="help" href="https://drafts.csswg.org/css-cascade-6/#scope-atrule">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/declarative-shadow-dom-polyfill.js"></script>
+
+<div id=host_plain>
+  <template shadowroot=open>
+    <style>
+      @scope (:host) {
+        .a {
+          z-index: 1;
+        }
+      }
+    </style>
+    <div class=a>
+    </div>
+  </template>
+</div>
+<script>
+  setup(() => {
+    polyfill_declarative_shadow_dom(document);
+  });
+
+  test(() => {
+    let a = host_plain.shadowRoot.querySelector('.a');
+    assert_equals(getComputedStyle(a).zIndex, '1');
+  }, '@scope can match :host');
+</script>
+
+<div id=host_functional>
+  <template shadowroot=open>
+    <style>
+      @scope (:host(div)) {
+        .a {
+          z-index: 1;
+        }
+      }
+      /* Should not match: */
+      @scope (:host(span)) {
+        .a {
+          z-index: 42;
+        }
+      }
+    </style>
+    <div class=a>
+    </div>
+  </template>
+</div>
+<script>
+  setup(() => {
+    polyfill_declarative_shadow_dom(document);
+  });
+
+  test(() => {
+    let a = host_functional.shadowRoot.querySelector('.a');
+    assert_equals(getComputedStyle(a).zIndex, '1');
+  }, '@scope can match :host(...)');
+</script>