LibWeb: Implement the :default pseudo-class

Author: https://github.com/Gingeh
Commit: 3fe148f2d4
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4838
Reviewed-by: https://github.com/AtkinsSJ ✅

Libraries/LibWeb/HTML/HTMLFormElement.cpp

@@ -1176,13 +1176,13 @@ JS::Value HTMLFormElement::named_item_value(FlyString const& name) const
 }
 
 // https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#default-button
-FormAssociatedElement* HTMLFormElement::default_button()
+FormAssociatedElement* HTMLFormElement::default_button() const
 {
     // A form element's default button is the first submit button in tree order whose form owner is that form element.
     FormAssociatedElement* default_button = nullptr;
 
     root().for_each_in_subtree([&](auto& node) {
-        auto* form_associated_element = dynamic_cast<FormAssociatedElement*>(&node);
+        auto* form_associated_element = const_cast<FormAssociatedElement*>(dynamic_cast<FormAssociatedElement const*>(&node));
         if (!form_associated_element)
             return TraversalDecision::Continue;
 

Libraries/LibWeb/HTML/HTMLFormElement.h

@@ -102,6 +102,8 @@ public:
     String action() const;
     WebIDL::ExceptionOr<void> set_action(String const&);
 
+    FormAssociatedElement* default_button() const;
+
 private:
     HTMLFormElement(DOM::Document&, DOM::QualifiedName);
 
@@ -126,7 +128,6 @@ private:
     ErrorOr<void> mail_as_body(URL::URL parsed_action, Vector<XHR::FormDataEntry> entry_list, EncodingTypeAttributeState encoding_type, String encoding, GC::Ref<Navigable> target_navigable, Bindings::NavigationHistoryBehavior history_handling, UserNavigationInvolvement user_involvement);
     void plan_to_navigate_to(URL::URL url, Variant<Empty, String, POSTResource> post_resource, Vector<XHR::FormDataEntry> entry_list, GC::Ref<Navigable> target_navigable, Bindings::NavigationHistoryBehavior history_handling, UserNavigationInvolvement user_involvement);
 
-    FormAssociatedElement* default_button();
     size_t number_of_fields_blocking_implicit_submission() const;
 
     bool m_firing_submission_events { false };

Libraries/LibWeb/HTML/HTMLInputElement.cpp

@@ -3027,6 +3027,18 @@ bool HTMLInputElement::required_applies() const
     }
 }
 
+// https://html.spec.whatwg.org/multipage/input.html#do-not-apply
+bool HTMLInputElement::checked_applies() const
+{
+    switch (type_state()) {
+    case TypeAttributeState::Checkbox:
+    case TypeAttributeState::RadioButton:
+        return true;
+    default:
+        return false;
+    }
+}
+
 bool HTMLInputElement::has_selectable_text() const
 {
     // Potential FIXME: Date, Month, Week, Time and LocalDateAndTime are rendered as a basic text input for now,

Libraries/LibWeb/HTML/HTMLInputElement.h

@@ -220,6 +220,7 @@ public:
     bool pattern_applies() const;
     bool multiple_applies() const;
     bool required_applies() const;
+    bool checked_applies() const;
     bool has_selectable_text() const;
 
     bool supports_a_picker() const;