LibWeb: Add select selected options collection getter

Tests/LibWeb/Text/expected/select.txt

@@ -14,3 +14,4 @@
 14. "5 5"
 15. 8
 16. 10
+17. "2"

Tests/LibWeb/Text/input/select.html

@@ -168,5 +168,18 @@
             select.options.remove(11);
             return select.length;
         });
+
+        // 17. Get selected selected options
+        testPart(() => {
+            const select = document.createElement('select');
+            for (let i = 0; i < 10; i++) {
+                const option = document.createElement('option');
+                option.textContent = i;
+                if (i == 5) option.selected = true;
+                select.appendChild(option);
+            }
+            select.options[2].selected = true;
+            return select.selectedOptions[0].textContent;
+        });
     });
 </script>

Userland/Libraries/LibWeb/HTML/HTMLSelectElement.cpp

@@ -45,6 +45,7 @@ void HTMLSelectElement::visit_edges(Cell::Visitor& visitor)
 {
     Base::visit_edges(visitor);
     visitor.visit(m_options);
+    visitor.visit(m_selected_options);
     visitor.visit(m_inner_text_element);
     visitor.visit(m_chevron_icon_element);
 
@@ -146,6 +147,23 @@ void HTMLSelectElement::remove(WebIDL::Long index)
     const_cast<HTMLOptionsCollection&>(*options()).remove(index);
 }
 
+// https://html.spec.whatwg.org/multipage/form-elements.html#dom-select-selectedoptions
+JS::NonnullGCPtr<DOM::HTMLCollection> HTMLSelectElement::selected_options()
+{
+    // The selectedOptions IDL attribute must return an HTMLCollection rooted at the select node,
+    // whose filter matches the elements in the list of options that have their selectedness set to true.
+    if (!m_selected_options) {
+        m_selected_options = DOM::HTMLCollection::create(*this, DOM::HTMLCollection::Scope::Descendants, [](Element const& element) {
+            if (is<HTML::HTMLOptionElement>(element)) {
+                auto const& option_element = verify_cast<HTMLOptionElement>(element);
+                return option_element.selected();
+            }
+            return false;
+        });
+    }
+    return *m_selected_options;
+}
+
 // https://html.spec.whatwg.org/multipage/form-elements.html#concept-select-option-list
 Vector<JS::Handle<HTMLOptionElement>> HTMLSelectElement::list_of_options() const
 {
@@ -181,12 +199,12 @@ void HTMLSelectElement::reset_algorithm()
 }
 
 // https://html.spec.whatwg.org/multipage/form-elements.html#dom-select-selectedindex
-int HTMLSelectElement::selected_index() const
+WebIDL::Long HTMLSelectElement::selected_index() const
 {
     // The selectedIndex IDL attribute, on getting, must return the index of the first option element in the list of options
     // in tree order that has its selectedness set to true, if any. If there isn't one, then it must return −1.
 
-    int index = 0;
+    WebIDL::Long index = 0;
     for (auto const& option_element : list_of_options()) {
         if (option_element->selected())
             return index;
@@ -195,7 +213,7 @@ int HTMLSelectElement::selected_index() const
     return -1;
 }
 
-void HTMLSelectElement::set_selected_index(int index)
+void HTMLSelectElement::set_selected_index(WebIDL::Long index)
 {
     // On setting, the selectedIndex attribute must set the selectedness of all the option elements in the list of options to false,
     // and then the option element in the list of options whose index is the given new value,

Userland/Libraries/LibWeb/HTML/HTMLSelectElement.h

@@ -42,8 +42,10 @@ public:
     void remove();
     void remove(WebIDL::Long);
 
-    int selected_index() const;
-    void set_selected_index(int);
+    JS::NonnullGCPtr<DOM::HTMLCollection> selected_options();
+
+    WebIDL::Long selected_index() const;
+    void set_selected_index(WebIDL::Long);
 
     virtual String value() const override;
     WebIDL::ExceptionOr<void> set_value(String const&);
@@ -104,6 +106,7 @@ private:
     void queue_input_and_change_events();
 
     JS::GCPtr<HTMLOptionsCollection> m_options;
+    JS::GCPtr<DOM::HTMLCollection> m_selected_options;
     bool m_is_open { false };
     Vector<SelectItem> m_select_items;
     JS::GCPtr<DOM::Element> m_inner_text_element;

Userland/Libraries/LibWeb/HTML/HTMLSelectElement.idl

@@ -28,7 +28,7 @@ interface HTMLSelectElement : HTMLElement {
     [CEReactions] undefined remove(long index);
     // FIXME: [CEReactions] setter undefined (unsigned long index, HTMLOptionElement? option);
 
-    // FIXME: [SameObject] readonly attribute HTMLCollection selectedOptions;
+    [SameObject] readonly attribute HTMLCollection selectedOptions;
     attribute long selectedIndex;
     attribute DOMString value;