LibWeb: Propagate input/textarea selection update to document selection

Calling `.setSelectionRange()` or `.select()` now updates the document
selection as well, visualizing the text selection.

Userland/Libraries/LibWeb/HTML/FormAssociatedElement.cpp

@@ -411,15 +411,22 @@ void FormAssociatedElement::set_the_selection_range(Optional<WebIDL::UnsignedLon
     //    extent or direction), then queue an element task on the user interaction task source
     //    given the element to fire an event named select at the element, with the bubbles attribute
     //    initialized to true.
+    if (was_modified) {
+        auto& html_element = form_associated_element_to_html_element();
+
         // AD-HOC: If there is no selection, we do not fire the event. This seems to correspond to how
         //         other browsers behave.
-    if (was_modified && m_selection_start != m_selection_end) {
-        auto& html_element = form_associated_element_to_html_element();
+        if (m_selection_start != m_selection_end) {
             html_element.queue_an_element_task(Task::Source::UserInteraction, [&html_element] {
                 auto select_event = DOM::Event::create(html_element.realm(), EventNames::select, { .bubbles = true });
                 static_cast<DOM::EventTarget*>(&html_element)->dispatch_event(select_event);
             });
         }
+
+        // AD-HOC: Notify the element that the selection was changed, so it can perform
+        //         element-specific updates.
+        selection_was_changed();
+    }
 }
 
 }

Userland/Libraries/LibWeb/HTML/FormAssociatedElement.h

@@ -137,6 +137,8 @@ protected:
     // https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#concept-textarea/input-relevant-value
     void relevant_value_was_changed(JS::GCPtr<DOM::Text>);
 
+    virtual void selection_was_changed() { }
+
 private:
     void reset_form_owner();
 

Userland/Libraries/LibWeb/HTML/HTMLInputElement.cpp

@@ -45,6 +45,7 @@
 #include <LibWeb/MimeSniff/Resource.h>
 #include <LibWeb/Namespace.h>
 #include <LibWeb/Page/Page.h>
+#include <LibWeb/Selection/Selection.h>
 #include <LibWeb/UIEvents/EventNames.h>
 #include <LibWeb/UIEvents/MouseEvent.h>
 #include <LibWeb/WebIDL/DOMException.h>
@@ -2353,4 +2354,13 @@ HTMLInputElement::ValueAttributeMode HTMLInputElement::value_attribute_mode() co
     VERIFY_NOT_REACHED();
 }
 
+void HTMLInputElement::selection_was_changed()
+{
+    auto selection = document().get_selection();
+    if (!selection || selection->range_count() == 0)
+        return;
+
+    MUST(selection->set_base_and_extent(*m_text_node, selection_start().value(), *m_text_node, selection_end().value()));
+}
+
 }

Userland/Libraries/LibWeb/HTML/HTMLInputElement.h

@@ -199,6 +199,9 @@ public:
     bool select_applies() const;
     bool selection_or_range_applies() const;
 
+protected:
+    void selection_was_changed() override;
+
 private:
     HTMLInputElement(DOM::Document&, DOM::QualifiedName);
 

Userland/Libraries/LibWeb/HTML/HTMLTextAreaElement.cpp

@@ -22,6 +22,7 @@
 #include <LibWeb/HTML/Numbers.h>
 #include <LibWeb/Infra/Strings.h>
 #include <LibWeb/Namespace.h>
+#include <LibWeb/Selection/Selection.h>
 
 namespace Web::HTML {
 
@@ -452,4 +453,13 @@ void HTMLTextAreaElement::queue_firing_input_event()
     });
 }
 
+void HTMLTextAreaElement::selection_was_changed()
+{
+    auto selection = document().get_selection();
+    if (!selection || selection->range_count() == 0)
+        return;
+
+    MUST(selection->set_base_and_extent(*m_text_node, selection_start().value(), *m_text_node, selection_end().value()));
+}
+
 }

Userland/Libraries/LibWeb/HTML/HTMLTextAreaElement.h

@@ -114,6 +114,9 @@ public:
     String selection_direction_binding() const;
     void set_selection_direction_binding(String direction);
 
+protected:
+    void selection_was_changed() override;
+
 private:
     HTMLTextAreaElement(DOM::Document&, DOM::QualifiedName);