LibWeb: Add activeElement attribute in ShadowRoot

Author: https://github.com/F3n67u
Commit: 66d18170c6
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/6131
Reviewed-by: https://github.com/tcl3 ✅

Libraries/LibWeb/DOM/Document.cpp

@@ -64,6 +64,7 @@
 #include <LibWeb/DOM/Document.h>
 #include <LibWeb/DOM/DocumentFragment.h>
 #include <LibWeb/DOM/DocumentObserver.h>
+#include <LibWeb/DOM/DocumentOrShadowRoot.h>
 #include <LibWeb/DOM/DocumentType.h>
 #include <LibWeb/DOM/EditingHostManager.h>
 #include <LibWeb/DOM/Element.h>
@@ -2446,43 +2447,9 @@ String const& Document::compat_mode() const
     return css1_compat;
 }
 
-// https://html.spec.whatwg.org/multipage/interaction.html#dom-documentorshadowroot-activeelement
 void Document::update_active_element()
 {
-    // 1. Let candidate be this's node document's focused area's DOM anchor.
-    Node* candidate = focused_area();
-
-    // 2. Set candidate to the result of retargeting candidate against this.
-    candidate = as<Node>(retarget(candidate, this));
-
-    // 3. If candidate's root is not this, then return null.
-    if (&candidate->root() != this) {
-        set_active_element(nullptr);
-        return;
-    }
-
-    // 4. If candidate is not a Document object, then return candidate.
-    if (!is<Document>(candidate)) {
-        set_active_element(as<Element>(candidate));
-        return;
-    }
-
-    auto* candidate_document = static_cast<Document*>(candidate);
-
-    // 5. If candidate has a body element, then return that body element.
-    if (candidate_document->body()) {
-        set_active_element(candidate_document->body());
-        return;
-    }
-
-    // 6. If candidate's document element is non-null, then return that document element.
-    if (candidate_document->document_element()) {
-        set_active_element(candidate_document->document_element());
-        return;
-    }
-
-    // 7. Return null.
-    set_active_element(nullptr);
+    set_active_element(calculate_active_element(*this));
 }
 
 void Document::set_focused_area(GC::Ptr<Node> node)

Libraries/LibWeb/DOM/Document.idl

@@ -73,7 +73,6 @@ interface Document : Node {
 
     readonly attribute USVString referrer;
 
-    readonly attribute Element? activeElement;
 
     Element? getElementById(DOMString id);
     NodeList getElementsByName([FlyString] DOMString name);

Libraries/LibWeb/DOM/DocumentOrShadowRoot.h

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2024, circl <circl.lastname@gmail.com>
+ * Copyright (c) 2025, Feng Yu <f3n67u@outlook.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/DOM/Document.h>
+#include <LibWeb/DOM/Utils.h>
+
+namespace Web::DOM {
+
+template<typename T>
+concept DocumentOrShadowRoot = OneOf<T, Document, ShadowRoot>;
+
+// https://html.spec.whatwg.org/multipage/interaction.html#dom-documentorshadowroot-activeelement
+template<DocumentOrShadowRoot T>
+GC::Ptr<Element> calculate_active_element(T& self)
+{
+    // 1. Let candidate be this's node document's focused area's DOM anchor.
+    Node* candidate = self.document().focused_area();
+
+    // 2. Set candidate to the result of retargeting candidate against this.
+    candidate = as<Node>(retarget(candidate, &self));
+
+    // 3. If candidate's root is not this, then return null.
+    if (&candidate->root() != &self)
+        return nullptr;
+
+    // 4. If candidate is not a Document object, then return candidate.
+    if (!is<Document>(candidate))
+        return as<Element>(candidate);
+
+    auto* candidate_document = as_if<Document>(candidate);
+
+    // 5. If candidate has a body element, then return that body element.
+    if (auto* body = candidate_document->body())
+        return body;
+
+    // 6. If candidate's document element is non-null, then return that document element.
+    if (auto* document_element = candidate_document->document_element())
+        return document_element;
+
+    // 7. Return null.
+    return nullptr;
+}
+
+}

Libraries/LibWeb/DOM/DocumentOrShadowRoot.idl

@@ -2,6 +2,9 @@
 
 // https://dom.spec.whatwg.org/#documentorshadowroot
 interface mixin DocumentOrShadowRoot {
+    // https://html.spec.whatwg.org/multipage/interaction.html#dom-documentorshadowroot-activeelement
+    readonly attribute Element? activeElement;
+
     // https://w3c.github.io/csswg-drafts/cssom/#extensions-to-the-document-or-shadow-root-interface
     [SameObject, ImplementedAs=style_sheets_for_bindings] readonly attribute StyleSheetList styleSheets;
     attribute any adoptedStyleSheets;

Libraries/LibWeb/DOM/ShadowRoot.cpp

@@ -7,6 +7,7 @@
 #include <LibWeb/Bindings/ShadowRootPrototype.h>
 #include <LibWeb/DOM/AdoptedStyleSheets.h>
 #include <LibWeb/DOM/Document.h>
+#include <LibWeb/DOM/DocumentOrShadowRoot.h>
 #include <LibWeb/DOM/Event.h>
 #include <LibWeb/DOM/ShadowRoot.h>
 #include <LibWeb/HTML/HTMLTemplateElement.h>
@@ -119,6 +120,11 @@ WebIDL::ExceptionOr<void> ShadowRoot::set_html_unsafe(StringView html)
     return {};
 }
 
+GC::Ptr<Element> ShadowRoot::active_element()
+{
+    return calculate_active_element(*this);
+}
+
 CSS::StyleSheetList& ShadowRoot::style_sheets()
 {
     if (!m_style_sheets)

Libraries/LibWeb/DOM/ShadowRoot.h

@@ -52,6 +52,8 @@ public:
 
     WebIDL::ExceptionOr<String> get_html(GetHTMLOptions const&) const;
 
+    GC::Ptr<Element> active_element();
+
     CSS::StyleSheetList& style_sheets();
     CSS::StyleSheetList const& style_sheets() const;
 

Tests/LibWeb/Text/expected/wpt-import/shadow-dom/focus/DocumentOrShadowRoot-activeElement.txt

@@ -0,0 +1,11 @@
+Harness status: OK
+
+Found 6 tests
+
+6 Pass
+Pass	activeElement on document & shadow root when focused element is in the shadow tree
+Pass	activeElement on document & shadow root when focused element is in the document
+Pass	activeElement on document & shadow root when focused element is slotted
+Pass	activeElement on a neighboring host when focused element is in another shadow tree
+Pass	activeElement when focused element is in a nested shadow tree
+Pass	activeElement when focused element is in a parent shadow tree

Tests/LibWeb/Text/input/wpt-import/shadow-dom/focus/DocumentOrShadowRoot-activeElement.html

@@ -0,0 +1,92 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>HTML Test: DocumentOrShadowRoot.activeElement</title>
+<script src="../../resources/testharness.js"></script>
+<script src="../../resources/testharnessreport.js"></script>
+<script src="../../resources/testdriver.js"></script>
+<script src="../../resources/testdriver-vendor.js"></script>
+<body>
+<script>
+function createChildAndFocus(focusParent) {
+  const focused = document.createElement("div");
+  focused.tabIndex = 0;
+  focusParent.appendChild(focused);
+  focused.focus();
+  return focused;
+}
+
+test(() => {
+  const host = document.createElement("div");
+  const shadowRoot = host.attachShadow({ mode: "open" });
+  document.body.appendChild(host);
+
+  const focused = createChildAndFocus(shadowRoot);
+  assert_equals(document.activeElement, host);
+  assert_equals(shadowRoot.activeElement, focused);
+}, "activeElement on document & shadow root when focused element is in the shadow tree");
+
+test(() => {
+  const host = document.createElement("div");
+  const shadowRoot = host.attachShadow({ mode: "open" });
+  document.body.appendChild(host);
+
+  const focused = createChildAndFocus(document.body);
+  assert_equals(document.activeElement, focused);
+  assert_equals(shadowRoot.activeElement, null);
+}, "activeElement on document & shadow root when focused element is in the document");
+
+test(() => {
+  const host = document.createElement("div");
+  const shadowRoot = host.attachShadow({ mode: "open" });
+  shadowRoot.appendChild(document.createElement("slot"));
+  document.body.appendChild(host);
+
+  // Child of |host|, will be slotted to the slot in |shadowRoot|.
+  const focused = createChildAndFocus(host);
+  assert_equals(document.activeElement, focused);
+  assert_equals(shadowRoot.activeElement, null);
+}, "activeElement on document & shadow root when focused element is slotted");
+
+test(() => {
+  const host = document.createElement("div");
+  const shadowRoot = host.attachShadow({ mode: "open" });
+  document.body.appendChild(host);
+  const neighborHost = document.createElement("div");
+  const neighborShadowRoot = neighborHost.attachShadow({ mode: "open" });
+  document.body.appendChild(neighborHost);
+
+  const focused = createChildAndFocus(shadowRoot);
+  assert_equals(document.activeElement, host);
+  assert_equals(shadowRoot.activeElement, focused);
+  assert_equals(neighborShadowRoot.activeElement, null);
+}, "activeElement on a neighboring host when focused element is in another shadow tree");
+
+test(() => {
+  const host = document.createElement("div");
+  const shadowRoot = host.attachShadow({ mode: "open" });
+  document.body.appendChild(host);
+  const nestedHost = document.createElement("div");
+  const nestedShadowRoot = nestedHost.attachShadow({ mode: "open" });
+  shadowRoot.appendChild(nestedHost);
+
+  const focused = createChildAndFocus(nestedShadowRoot);
+  assert_equals(document.activeElement, host);
+  assert_equals(shadowRoot.activeElement, nestedHost);
+  assert_equals(nestedShadowRoot.activeElement, focused);
+}, "activeElement when focused element is in a nested shadow tree");
+
+test(() => {
+  const host = document.createElement("div");
+  const shadowRoot = host.attachShadow({ mode: "open" });
+  document.body.appendChild(host);
+  const nestedHost = document.createElement("div");
+  const nestedShadowRoot = nestedHost.attachShadow({ mode: "open" });
+  shadowRoot.appendChild(nestedHost);
+
+  const focused = createChildAndFocus(shadowRoot);
+  assert_equals(document.activeElement, host);
+  assert_equals(shadowRoot.activeElement, focused);
+  assert_equals(nestedShadowRoot.activeElement, null);
+}, "activeElement when focused element is in a parent shadow tree");
+</script>
+</body>