LibWeb: Fix accname computation for all aria-labelledby cases

This change ensures that:

- if an element for which an accessible name otherwise wouldn’t be
  computed is referenced in an aria-labelledby value, the accessible
  name for the element will be computed as expected.

- if an element has both an aria-label value and also an
  aria-labelledby value, the text from the aria-label value gets
  included in the computation of the element’s accessible name.

Otherwise, without this change, some elements with aria-labelledby
values will unexpectedly end up without accessible names, and some
elements with aria-label values will unexpectedly not have that
aria-label value included in the element’s accessible name.

Libraries/LibWeb/DOM/Node.cpp

@@ -2195,6 +2195,18 @@ ErrorOr<String> Node::name_or_description(NameOrDescription target, Document con
     if (is_element()) {
         auto const* element = static_cast<DOM::Element const*>(this);
         auto role = element->role_or_default();
+        bool is_referenced = false;
+        auto id = element->id();
+        if (id.has_value()) {
+            this->root().for_each_in_inclusive_subtree_of_type<HTML::HTMLElement>([&](auto& element) {
+                auto aria_data = MUST(Web::ARIA::AriaData::build_data(element));
+                if (aria_data->aria_labelled_by_or_default().contains_slow(id.value())) {
+                    is_referenced = true;
+                    return TraversalDecision::Break;
+                }
+                return TraversalDecision::Continue;
+            });
+        }
         // 2. Compute the text alternative for the current node:
         // A. If the current node is hidden and is not directly referenced by aria-labelledby or aria-describedby, nor directly referenced by a native host language text alternative element (e.g. label in HTML) or attribute, return the empty string.
         // FIXME: Check for references
@@ -2224,7 +2236,13 @@ ErrorOr<String> Node::name_or_description(NameOrDescription target, Document con
                 auto node = document.get_element_by_id(MUST(FlyString::from_utf8(id_ref)));
                 if (!node)
                     continue;
-
+                // AD-HOC: The “For each IDREF” substep in the spec doesn’t seem to explicitly require the following
+                // check for an aria-label value; but the “div group explicitly labelledby self and heading” subtest at
+                // https://wpt.fyi/results/accname/name/comp_labelledby.html won’t pass unless we do this check.
+                if (target == NameOrDescription::Name && node->aria_label().has_value() && !node->aria_label()->is_empty() && !node->aria_label()->bytes_as_string_view().is_whitespace()) {
+                    total_accumulated_text.append(' ');
+                    total_accumulated_text.append(node->aria_label().value());
+                }
                 if (visited_nodes.contains(node->unique_id()))
                     continue;
                 // a. Set the current node to the node referenced by the IDREF.
@@ -2333,7 +2351,7 @@ ErrorOr<String> Node::name_or_description(NameOrDescription target, Document con
         }
 
         // F. Otherwise, if the current node's role allows name from content, or if the current node is referenced by aria-labelledby, aria-describedby, or is a native host language text alternative element (e.g. label in HTML), or is a descendant of a native host language text alternative element:
-        if ((role.has_value() && ARIA::allows_name_from_content(role.value())) || is_descendant == IsDescendant::Yes) {
+        if ((role.has_value() && ARIA::allows_name_from_content(role.value())) || is_referenced || is_descendant == IsDescendant::Yes) {
             // i. Set the accumulated text to the empty string.
             total_accumulated_text.clear();
             // ii. Name From Generated Content: Check for CSS generated textual content associated with the current node and include

Tests/LibWeb/Text/expected/wpt-import/accname/name/comp_labelledby.txt

@@ -0,0 +1,13 @@
+Summary
+
+Harness status: OK
+
+Rerun
+
+Found 3 tests
+
+3 Pass
+Details
+Result	Test Name	MessagePass	div group explicitly labelledby heading	
+Pass	div group explicitly labelledby self and heading	
+Pass	nav with verified spaces appended between each of IDREFS	

Tests/LibWeb/Text/input/wpt-import/accname/name/comp_labelledby.html

@@ -0,0 +1,60 @@
+<!doctype html>
+<html>
+<head>
+  <title>Name Comp: Labelledby</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>
+  <script src="../../resources/testdriver-actions.js"></script>
+  <script src="../../wai-aria/scripts/aria-utils.js"></script>
+</head>
+<body>
+
+<p>Tests the <a href="https://w3c.github.io/accname/#comp_labelledby">#comp_labelledby</a> portions of the AccName <em>Name Computation</em> algorithm.</p>
+
+<!--
+
+  Some overlap with other aria-labelledby tests in:
+  - /accname/name/comp_label.html (aria-labelledby / aria-label fallback, etc.)
+  - /accname/name/comp_name_from_content.html
+  - /accname/name/shadowdom/*
+
+-->
+
+<div role="group" aria-labelledby="h" class="ex" data-expectedlabel="first heading" data-testname="div group explicitly labelledby heading">
+  <h2 id="h">first heading</h2>
+  <p>text inside div group</p>
+</div>
+
+<div role="group" aria-label="self label" id="g2" aria-labelledby="g2 h2" class="ex" data-expectedlabel="self label + first heading" data-testname="div group explicitly labelledby self and heading">
+  <h2 id="h2">+ first heading</h2>
+  <p>text inside div group</p>
+</div>
+
+<nav aria-labelledby="s1 s2 s3 s4" class="ex" data-expectedlabel="verify spaces between foreach" data-testname="nav with verified spaces appended between each of IDREFS">
+  <span id="s1">verify</span><span id="s2">spaces</span><span>FAIL IF INCLUDED</span><span id="s3">between</span><span id="s4">foreach</span>
+</nav>
+
+<!--
+
+  BLOCKED on https://github.com/w3c/accname/issues/209
+
+  Once that's resolved, it may be worthwhile to add a new ./comp_labelledby_recursion.html file,
+  so that the implementation diffs rolling in don't penalize this Interop 2024 test.
+
+  All remaining cases of https://w3c.github.io/accname/#comp_labelledby
+  - comp_labelledby_reset
+  - comp_labelledby_foreach
+  - comp_labelledby_set_current
+  - comp_labelledby_recursion
+  - comp_labelledby_append
+  - comp_labelledby_return
+
+-->
+
+<script>
+AriaUtils.verifyLabelsBySelector(".ex");
+</script>
+</body>
+</html>