LibWeb: Implement hidden="until-found" IDL support

Follow-ups will implement the actual behaviour.

Libraries/LibWeb/HTML/HTMLElement.cpp

@@ -683,6 +683,58 @@ GC::Ptr<DOM::NodeList> HTMLElement::labels()
     return m_labels;
 }
 
+Variant<bool, double, String> HTMLElement::hidden() const
+{
+    // 1. If the hidden attribute is in the hidden until found state, then return "until-found".
+    if (get_attribute(HTML::AttributeNames::hidden) == "until-found")
+        return "until-found"_string;
+    // 2. If the hidden attribute is set, then return true.
+    if (has_attribute(HTML::AttributeNames::hidden))
+        return true;
+    // 3. Return false.
+    return false;
+}
+
+void HTMLElement::set_hidden(Variant<bool, double, String> const& given_value)
+{
+    // 1. If the given value is a string that is an ASCII case-insensitive match for "until-found", then set the hidden attribute to "until-found".
+    if (given_value.has<String>()) {
+        auto const& string = given_value.get<String>();
+        if (string.equals_ignoring_ascii_case("until-found"sv)) {
+            MUST(set_attribute(HTML::AttributeNames::hidden, "until-found"_string));
+            return;
+        }
+        // 3. Otherwise, if the given value is the empty string, then remove the hidden attribute.
+        if (string.is_empty()) {
+            remove_attribute(HTML::AttributeNames::hidden);
+            return;
+        }
+        // 4. Otherwise, if the given value is null, then remove the hidden attribute.
+        if (string.equals_ignoring_ascii_case("null"sv) || string.equals_ignoring_ascii_case("undefined"sv)) {
+            remove_attribute(HTML::AttributeNames::hidden);
+            return;
+        }
+    }
+    // 2. Otherwise, if the given value is false, then remove the hidden attribute.
+    else if (given_value.has<bool>()) {
+        if (!given_value.get<bool>()) {
+            remove_attribute(HTML::AttributeNames::hidden);
+            return;
+        }
+    }
+    // 5. Otherwise, if the given value is 0, then remove the hidden attribute.
+    // 6. Otherwise, if the given value is NaN, then remove the hidden attribute.
+    else if (given_value.has<double>()) {
+        auto const& double_value = given_value.get<double>();
+        if (double_value == 0 || isnan(double_value)) {
+            remove_attribute(HTML::AttributeNames::hidden);
+            return;
+        }
+    }
+    // 7. Otherwise, set the hidden attribute to the empty string.
+    MUST(set_attribute(HTML::AttributeNames::hidden, ""_string));
+}
+
 // https://html.spec.whatwg.org/multipage/interaction.html#dom-click
 void HTMLElement::click()
 {

Libraries/LibWeb/HTML/HTMLElement.h

@@ -95,6 +95,9 @@ public:
 
     bool cannot_navigate() const;
 
+    Variant<bool, double, String> hidden() const;
+    void set_hidden(Variant<bool, double, String> const&);
+
     void click();
 
     [[nodiscard]] String access_key_label() const;

Libraries/LibWeb/HTML/HTMLElement.idl

@@ -18,7 +18,7 @@ interface HTMLElement : Element {
     [CEReactions] attribute DOMString dir;
 
     // user interaction
-    [Reflect, CEReactions] attribute boolean hidden;
+    [CEReactions] attribute (boolean or unrestricted double or DOMString)? hidden;
     [Reflect, CEReactions] attribute boolean inert;
     undefined click();
     [Reflect=accesskey, CEReactions] attribute DOMString accessKey;

Tests/LibWeb/Text/expected/wpt-import/html/editing/the-hidden-attribute/hidden-idl.txt

@@ -0,0 +1,22 @@
+Harness status: OK
+
+Found 17 tests
+
+17 Pass
+Pass	div.hidden = false
+Pass	div.hidden = true
+Pass	div.hidden = "foo"
+Pass	div.hidden = "false"
+Pass	div.hidden = ""
+Pass	div.setAttribute('hidden', "false") should make div.hidden return true
+Pass	div.setAttribute('hidden', "foo") should make div.hidden return true
+Pass	div.hidden = "until-found"
+Pass	div.hidden = "UNTIL-FOUND"
+Pass	div.hidden = "UnTiL-FoUnD"
+Pass	div.hidden = "untıl-found"
+Pass	div.hidden = "untİl-found"
+Pass	div.hidden = null
+Pass	div.hidden = undefined
+Pass	div.hidden = 1
+Pass	div.hidden = 0
+Pass	div.hidden = NaN

Tests/LibWeb/Text/input/wpt-import/html/editing/the-hidden-attribute/hidden-idl.html

@@ -0,0 +1,49 @@
+<!DOCTYPE html>
+<link rel=author href="mailto:jarhar@chromium.org">
+<link rel=help href="https://github.com/whatwg/html/pull/7475">
+<script src="../../../resources/testharness.js"></script>
+<script src="../../../resources/testharnessreport.js"></script>
+
+<div>hello</div>
+<script>
+const div = document.querySelector('div');
+
+function runPropertyTest(assignedValue, expectedValue, expectedAttribute) {
+  test(() => {
+    div.hidden = assignedValue;
+    assert_equals(div.hidden, expectedValue,
+      `div.hidden = ${JSON.stringify(assignedValue)} should return ${JSON.stringify(expectedValue)}`);
+    assert_equals(div.getAttribute('hidden'), expectedAttribute,
+      `div.hidden = ${JSON.stringify(assignedValue)} should set the hidden attribute to ${JSON.stringify(expectedAttribute)}`);
+  }, `div.hidden = ${Number.isNaN(assignedValue) ? 'NaN' : JSON.stringify(assignedValue)}`);
+}
+
+function runAttributeTest(assignedAttribute, expectedValue) {
+  test(() => {
+    div.setAttribute('hidden', assignedAttribute);
+    assert_equals(div.hidden, expectedValue);
+  }, `div.setAttribute('hidden', ${JSON.stringify(assignedAttribute)}) should make div.hidden return ${JSON.stringify(expectedValue)}`);
+}
+
+runPropertyTest(false, false, null);
+runPropertyTest(true, true, '');
+runPropertyTest('foo', true, '');
+runPropertyTest('false', true, '');
+runPropertyTest('', false, null);
+
+runAttributeTest('false', true);
+runAttributeTest('foo', true);
+
+runPropertyTest('until-found', 'until-found', 'until-found');
+runPropertyTest('UNTIL-FOUND', 'until-found', 'until-found');
+runPropertyTest('UnTiL-FoUnD', 'until-found', 'until-found');
+runPropertyTest('unt\u0131l-found', true, '');
+runPropertyTest('unt\u0130l-found', true, '');
+
+runPropertyTest(null, false, null);
+runPropertyTest(undefined, false, null);
+
+runPropertyTest(1, true, '');
+runPropertyTest(0, false, null);
+runPropertyTest(NaN, false, null);
+</script>