LibWeb: Add HTMLSelectedContentElement for customizable select

Introduce the HTMLSelectedContentElement and integrate it into
<select>, <option> and HTMLParser.

See whatwg/html#10548.

There are two bugs with WPT tests which causes the third subtest
in selectedcontent.html and selectedcontent-mutations.html fail.
See whatwg/html#11882, web-platform-tests/wpt#55849.

Libraries/LibWeb/HTML/HTMLSelectElement.cpp

@@ -22,6 +22,7 @@
 #include <LibWeb/HTML/HTMLOptGroupElement.h>
 #include <LibWeb/HTML/HTMLOptionElement.h>
 #include <LibWeb/HTML/HTMLSelectElement.h>
+#include <LibWeb/HTML/HTMLSelectedContentElement.h>
 #include <LibWeb/HTML/Navigable.h>
 #include <LibWeb/HTML/Numbers.h>
 #include <LibWeb/HTML/Window.h>
@@ -290,8 +291,8 @@ void HTMLSelectElement::reset_algorithm()
 // https://html.spec.whatwg.org/multipage/form-elements.html#dom-select-selectedindex
 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.
+    // The selectedIndex getter steps are to return the index of the first option element in this's list of options
+    // in tree order that has its selectedness set to true, if any. If there isn't one, then return −1.
     update_cached_list_of_options();
 
     WebIDL::Long index = 0;
@@ -303,23 +304,41 @@ WebIDL::Long HTMLSelectElement::selected_index() const
     return -1;
 }
 
-void HTMLSelectElement::set_selected_index(WebIDL::Long index)
+// https://html.spec.whatwg.org/multipage/form-elements.html#dom-select-selectedindex
+WebIDL::ExceptionOr<void> HTMLSelectElement::set_selected_index(WebIDL::Long index)
 {
-    update_cached_list_of_options();
-    // 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,
-    // if any, must have its selectedness set to true and its dirtiness set to true.
-    for (auto& option : m_cached_list_of_options)
-        option->set_selected_internal(false);
-
+    // The selectedIndex setter steps are:
     ScopeGuard guard { [&]() { update_inner_text_element(); } };
 
-    if (index < 0 || static_cast<size_t>(index) >= m_cached_list_of_options.size())
-        return;
+    // 1. Let firstMatchingOption be null.
+    GC::Ptr<HTMLOptionElement> first_matching_option;
 
-    auto& selected_option = m_cached_list_of_options[index];
-    selected_option->set_selected_internal(true);
-    selected_option->m_dirty = true;
+    // 2. For each option of this's list of options:
+    update_cached_list_of_options();
+    WebIDL::Long current_index = 0;
+    for (auto const& option : m_cached_list_of_options) {
+        // 1. Set option's selectedness to false.
+        option->set_selected_internal(false);
+
+        // 2. If firstMatchingOption is null and option's index is equal to the given value, then
+        //    set firstMatchingOption to option.
+        if (!first_matching_option && current_index == index)
+            first_matching_option = option;
+
+        current_index++;
+    }
+
+    // 3. If firstMatchingOption is not null, then set firstMatchingOption's selectedness to true
+    //    and set firstMatchingOption's dirtiness to true.
+    if (first_matching_option) {
+        first_matching_option->set_selected_internal(true);
+        first_matching_option->m_dirty = true;
+    }
+
+    // 4. Run update a select's selectedcontent given this.
+    TRY(update_selectedcontent());
+
+    return {};
 }
 
 // https://html.spec.whatwg.org/multipage/interaction.html#dom-tabindex
@@ -393,8 +412,12 @@ Optional<ARIA::Role> HTMLSelectElement::default_role() const
     return ARIA::Role::combobox;
 }
 
+// https://html.spec.whatwg.org/multipage/form-elements.html#dom-select-value
 Utf16String HTMLSelectElement::value() const
 {
+    // The value getter steps are to return the value of the first option element in this's
+    // list of options in tree order that has its selectedness set to true, if any. If there
+    // isn't one, then return the empty string.
     update_cached_list_of_options();
     for (auto const& option_element : m_cached_list_of_options)
         if (option_element->selected())
@@ -402,29 +425,61 @@ Utf16String HTMLSelectElement::value() const
     return {};
 }
 
+// https://html.spec.whatwg.org/multipage/form-elements.html#dom-select-value
 WebIDL::ExceptionOr<void> HTMLSelectElement::set_value(Utf16String const& value)
 {
+    // The value setter steps are:
+    ScopeGuard guard { [&]() { update_inner_text_element(); } };
     update_cached_list_of_options();
-    for (auto const& option_element : list_of_options())
-        option_element->set_selected(option_element->value() == value);
-    update_inner_text_element();
+
+    // 1. Let firstMatchingOption be null.
+    GC::Ptr<HTMLOptionElement> first_matching_option;
+
+    // 2. For each option of this's list of options:
+    for (auto const& option_element : m_cached_list_of_options) {
+        // 1. Set option's selectedness to false.
+        option_element->set_selected_internal(false);
+
+        // 2. If firstMatchingOption is null and option's value is equal to the given value, then set
+        //    firstMatchingOption to option.
+        if (!first_matching_option && option_element->value() == value)
+            first_matching_option = option_element;
+    }
+
+    // 3. If firstMatchingOption is not null, then set firstMatchingOption's selectedness to true and set
+    //    firstMatchingOption's dirtiness to true.
+    if (first_matching_option) {
+        first_matching_option->set_selected_internal(true);
+        first_matching_option->m_dirty = true;
+    }
+
+    // 4. Run update a select's selectedcontent given this.
+    TRY(update_selectedcontent());
+
     return {};
 }
 
-void HTMLSelectElement::queue_input_and_change_events()
+// https://html.spec.whatwg.org/multipage/form-elements.html#send-select-update-notifications
+void HTMLSelectElement::send_select_update_notifications()
 {
-    // When the user agent is to send select update notifications, queue an element task on the user interaction task source given the select element to run these steps:
+    // To send select update notifications for a select element element, queue an element task on
+    // the user interaction task source given element to run these steps:
     queue_an_element_task(HTML::Task::Source::UserInteraction, [this] {
         // 1. Set the select element's user validity to true.
         m_user_validity = true;
 
-        // 2. Fire an event named input at the select element, with the bubbles and composed attributes initialized to true.
+        // 2. Run update a select's selectedcontent given element.
+        MUST(update_selectedcontent());
+
+        // FIXME: 3. Run clone selected option into select button given element.
+
+        // 4. Fire an event named input at element, with the bubbles and composed attributes initialized to true.
         auto input_event = DOM::Event::create(realm(), HTML::EventNames::input);
         input_event->set_bubbles(true);
         input_event->set_composed(true);
         dispatch_event(input_event);
 
-        // 3. Fire an event named change at the select element, with the bubbles attribute initialized to true.
+        // 5. Fire an event named change at element, with the bubbles attribute initialized to true.
         auto change_event = DOM::Event::create(realm(), HTML::EventNames::change);
         change_event->set_bubbles(true);
         dispatch_event(*change_event);
@@ -577,7 +632,7 @@ void HTMLSelectElement::did_select_item(Optional<u32> const& id)
     }
 
     update_inner_text_element();
-    queue_input_and_change_events();
+    send_select_update_notifications();
 }
 
 void HTMLSelectElement::form_associated_element_was_inserted()
@@ -674,37 +729,35 @@ void HTMLSelectElement::update_inner_text_element()
 }
 
 // https://html.spec.whatwg.org/multipage/form-elements.html#selectedness-setting-algorithm
+// https://whatpr.org/html/11890/form-elements.html#selectedness-setting-algorithm
 void HTMLSelectElement::update_selectedness()
 {
-    if (has_attribute(AttributeNames::multiple))
-        return;
-
+    // The selectedness setting algorithm, given a select element element, is to run the following steps:
     update_cached_list_of_options();
 
-    // If element's multiple attribute is absent, and element's display size is 1,
-    if (display_size() == 1) {
-        // and no option elements in the element's list of options have their selectedness set to true,
-        if (m_cached_number_of_selected_options == 0) {
-            // then set the selectedness of the first option element in the list of options in tree order
-            // that is not disabled, if any, to true, and return.
-            for (auto const& option_element : m_cached_list_of_options) {
-                if (!option_element->disabled()) {
-                    option_element->set_selected_internal(true);
-                    update_inner_text_element();
-                    break;
-                }
-            }
-            return;
-        }
-    }
+    // 1. Let updateSelectedcontent be false.
+    auto should_update_selectedcontent = false;
 
-    // If element's multiple attribute is absent,
-    // and two or more option elements in element's list of options have their selectedness set to true,
-    // then set the selectedness of all but the last option element with its selectedness set to true
-    // in the list of options in tree order to false.
-    if (m_cached_number_of_selected_options >= 2) {
-        // then set the selectedness of all but the last option element with its selectedness set to true
-        // in the list of options in tree order to false.
+    // 2. If element 's multiple attribute is absent, and element's display size is 1,
+    //    and no option elements in the element's list of options have their selectedness set to true, then
+    if (!has_attribute(AttributeNames::multiple) && display_size() == 1 && m_cached_number_of_selected_options == 0) {
+        // 1. Set the selectedness of the first option element in the list of options in tree order
+        //    that is not disabled, if any, to true.
+        for (auto const& option_element : m_cached_list_of_options) {
+            if (!option_element->disabled()) {
+                option_element->set_selected_internal(true);
+                break;
+            }
+        }
+
+        // 2. Set updateSelectedcontent to true.
+        should_update_selectedcontent = true;
+    }
+    // Otherwise, if element's multiple attribute is absent,
+    // and two or more option elements in element's list of options have their selectedness set to true, then:
+    else if (!has_attribute(AttributeNames::multiple) && m_cached_number_of_selected_options >= 2) {
+        // 1. Set the selectedness of all but the last option element with its selectedness set to true
+        //    in the list of options in tree order to false.
         GC::Ptr<HTML::HTMLOptionElement> last_selected_option;
         u64 last_selected_option_update_index = 0;
 
@@ -722,8 +775,16 @@ void HTMLSelectElement::update_selectedness()
             if (option_element != last_selected_option)
                 option_element->set_selected_internal(false);
         }
+
+        // 2. Set updateSelectedcontent to true.
+        should_update_selectedcontent = true;
+    }
+
+    // 4. If updateSelectedcontent is true, then run update a select's selectedcontent given element.
+    if (should_update_selectedcontent) {
+        MUST(update_selectedcontent());
+        update_inner_text_element();
     }
-    update_inner_text_element();
 }
 
 bool HTMLSelectElement::is_focusable() const
@@ -746,6 +807,88 @@ HTMLOptionElement* HTMLSelectElement::placeholder_label_option() const
     return {};
 }
 
+// https://html.spec.whatwg.org/multipage/form-elements.html#select-enabled-selectedcontent
+GC::Ptr<HTMLSelectedContentElement> HTMLSelectElement::enabled_selectedcontent() const
+{
+    // To get a select's enabled selectedcontent given a select element select:
+
+    // 1. If select has the multiple attribute, then return null.
+    if (has_attribute(AttributeNames::multiple))
+        return nullptr;
+
+    // 2. Let selectedcontent be the first selectedcontent element descendant of select in tree order if any such
+    //    element exists; otherwise return null.
+    GC::Ptr<HTMLSelectedContentElement> selectedcontent;
+    for_each_in_subtree_of_type<HTMLSelectedContentElement>([&](auto& element) {
+        selectedcontent = const_cast<HTMLSelectedContentElement*>(&element);
+        return TraversalDecision::Break;
+    });
+    if (!selectedcontent)
+        return nullptr;
+
+    // 3. If selectedcontent is disabled, then return null.
+    if (selectedcontent->disabled())
+        return nullptr;
+
+    // 4. Return selectedcontent.
+    return selectedcontent;
+}
+
+// https://html.spec.whatwg.org/multipage/form-elements.html#clear-a-select%27s-non-primary-selectedcontent-elements
+void HTMLSelectElement::clear_non_primary_selectedcontent()
+{
+    // To clear a select's non-primary selectedcontent elements, given a select element select:
+
+    // 1. Let passedFirstSelectedcontent be false.
+    bool passed_first_selectedcontent = false;
+
+    // 2. For each descendant of select's descendants in tree order that is a selectedcontent element:
+    for_each_in_subtree_of_type<HTMLSelectedContentElement>([&](auto& element) {
+        // 1. If passedFirstSelectedcontent is false, then set passedFirstSelectedcontent to true.
+        if (!passed_first_selectedcontent)
+            passed_first_selectedcontent = true;
+        // 2. Otherwise, run clear a selectedcontent given descendant.
+        else
+            element.clear_selectedcontent();
+
+        return TraversalDecision::Continue;
+    });
+}
+
+// https://html.spec.whatwg.org/multipage/form-elements.html#update-a-select%27s-selectedcontent
+WebIDL::ExceptionOr<void> HTMLSelectElement::update_selectedcontent()
+{
+    // To update a select's selectedcontent given a select element select:
+
+    // 1. Let selectedcontent be the result of get a select's enabled selectedcontent given select.
+    auto selectedcontent = enabled_selectedcontent();
+
+    // 2. If selectedcontent is null, then return.
+    if (!selectedcontent)
+        return {};
+
+    // 3. Let option be the first option in select's list of options whose selectedness is true,
+    //    if any such option exists, otherwise null.
+    update_cached_list_of_options();
+    GC::Ptr<HTML::HTMLOptionElement> option;
+    for (auto const& candidate : m_cached_list_of_options) {
+        if (candidate->selected()) {
+            option = candidate;
+            break;
+        }
+    }
+
+    // 4. If option is null, then run clear a selectedcontent given selectedcontent.
+    if (!option) {
+        selectedcontent->clear_selectedcontent();
+        return {};
+    }
+
+    // 5. Otherwise, run clone an option into a selectedcontent given option and selectedcontent.
+    TRY(option->clone_into_selectedcontent(*selectedcontent));
+    return {};
+}
+
 // https://html.spec.whatwg.org/multipage/form-elements.html#the-select-element%3Asuffering-from-being-missing
 bool HTMLSelectElement::suffering_from_being_missing() const
 {