LibWeb: Implement :enabled and :disabled pseudo classes to spec

Previously we only considered an element disabled if it was an <input>
element with the disabled attribute, but there's way more elements that
apply with more nuanced disabled/enabled rules.

Userland/Libraries/LibWeb/HTML/HTMLFieldSetElement.cpp

@@ -5,6 +5,7 @@
  */
 
 #include <LibWeb/HTML/HTMLFieldSetElement.h>
+#include <LibWeb/HTML/HTMLLegendElement.h>
 #include <LibWeb/HTML/Window.h>
 
 namespace Web::HTML {
@@ -16,4 +17,25 @@ HTMLFieldSetElement::HTMLFieldSetElement(DOM::Document& document, DOM::Qualified
 }
 
 HTMLFieldSetElement::~HTMLFieldSetElement() = default;
+
+// https://html.spec.whatwg.org/multipage/form-elements.html#concept-fieldset-disabled
+bool HTMLFieldSetElement::is_disabled() const
+{
+    // A fieldset element is a disabled fieldset if it matches any of the following conditions:
+    // - Its disabled attribute is specified
+    if (has_attribute(AttributeNames::disabled))
+        return true;
+
+    // - It is a descendant of another fieldset element whose disabled attribute is specified, and is not a descendant of that fieldset element's first legend element child, if any.
+    for (auto* fieldset_ancestor = first_ancestor_of_type<HTMLFieldSetElement>(); fieldset_ancestor; fieldset_ancestor = fieldset_ancestor->first_ancestor_of_type<HTMLFieldSetElement>()) {
+        if (fieldset_ancestor->has_attribute(HTML::AttributeNames::disabled)) {
+            auto* first_legend_element_child = fieldset_ancestor->first_child_of_type<HTMLLegendElement>();
+            if (!first_legend_element_child || !is_descendant_of(*first_legend_element_child))
+                return true;
+        }
+    }
+
+    return false;
+}
+
 }

Userland/Libraries/LibWeb/HTML/HTMLFieldSetElement.h

@@ -26,6 +26,8 @@ public:
         return fieldset;
     }
 
+    bool is_disabled() const;
+
     // ^FormAssociatedElement
     // https://html.spec.whatwg.org/multipage/forms.html#category-listed
     virtual bool is_listed() const override { return true; }

Userland/Libraries/LibWeb/HTML/HTMLOptionElement.cpp

@@ -8,6 +8,7 @@
 #include <AK/StringBuilder.h>
 #include <LibWeb/DOM/Node.h>
 #include <LibWeb/DOM/Text.h>
+#include <LibWeb/HTML/HTMLOptGroupElement.h>
 #include <LibWeb/HTML/HTMLOptionElement.h>
 #include <LibWeb/HTML/HTMLScriptElement.h>
 #include <LibWeb/HTML/HTMLSelectElement.h>
@@ -156,4 +157,12 @@ void HTMLOptionElement::ask_for_a_reset()
     // FIXME: Implement this operation.
 }
 
+// https://html.spec.whatwg.org/multipage/form-elements.html#concept-option-disabled
+bool HTMLOptionElement::disabled() const
+{
+    // An option element is disabled if its disabled attribute is present or if it is a child of an optgroup element whose disabled attribute is present.
+    return has_attribute(AttributeNames::disabled)
+        || (parent() && is<HTMLOptGroupElement>(parent()) && static_cast<HTMLOptGroupElement const&>(*parent()).has_attribute(AttributeNames::disabled));
+}
+
 }

Userland/Libraries/LibWeb/HTML/HTMLOptionElement.h

@@ -28,6 +28,8 @@ public:
 
     int index() const;
 
+    bool disabled() const;
+
 private:
     friend class Bindings::OptionConstructor;
     friend class HTMLSelectElement;