LibWeb/HTML: Implement and use "optional value"

Corresponds to f3444c23ff

Also import a test.

Libraries/LibWeb/HTML/FormAssociatedElement.h

@@ -126,6 +126,7 @@ public:
     bool suffering_from_a_custom_error() const;
 
     virtual String value() const { return String {}; }
+    virtual Optional<String> optional_value() const { VERIFY_NOT_REACHED(); }
 
     virtual HTMLElement& form_associated_element_to_html_element() = 0;
     HTMLElement const& form_associated_element_to_html_element() const { return const_cast<FormAssociatedElement&>(*this).form_associated_element_to_html_element(); }

Libraries/LibWeb/HTML/HTMLButtonElement.cpp

@@ -119,9 +119,17 @@ bool HTMLButtonElement::is_submit_button() const
 // https://html.spec.whatwg.org/multipage/form-elements.html#the-button-element:concept-fe-value
 String HTMLButtonElement::value() const
 {
+    // The element's value is the value of the element's value attribute, if there is one; otherwise the empty string.
     return attribute(AttributeNames::value).value_or(String {});
 }
 
+// https://html.spec.whatwg.org/multipage/form-elements.html#the-button-element:concept-fe-optional-value
+Optional<String> HTMLButtonElement::optional_value() const
+{
+    // The element's optional value is the value of the element's value attribute, if there is one; otherwise null.
+    return attribute(AttributeNames::value);
+}
+
 bool HTMLButtonElement::has_activation_behavior() const
 {
     return true;

Libraries/LibWeb/HTML/HTMLButtonElement.h

@@ -76,6 +76,7 @@ public:
     virtual Optional<ARIA::Role> default_role() const override { return ARIA::Role::button; }
 
     virtual String value() const override;
+    virtual Optional<String> optional_value() const override;
 
     virtual bool has_activation_behavior() const override;
     virtual void activation_behavior(DOM::Event const&) override;

Libraries/LibWeb/HTML/HTMLDialogElement.cpp

@@ -492,16 +492,14 @@ void HTMLDialogElement::invoker_command_steps(DOM::Element& invoker, String& com
     // 2. If command is in the Close state and element has an open attribute,
     //    then close the dialog given element with invoker's optional value and invoker.
     if (command == "close" && has_attribute(AttributeNames::open)) {
-        // FIXME: This assumes invoker is a button.
-        auto optional_value = invoker.get_attribute(AttributeNames::value);
+        auto const optional_value = as<FormAssociatedElement>(invoker).optional_value();
         close_the_dialog(optional_value, invoker);
     }
 
     // 3. If command is in the Request Close state and element has an open attribute,
     //    then request to close the dialog element with invoker's optional value and invoker.
     if (command == "request-close" && has_attribute(AttributeNames::open)) {
-        // FIXME: This assumes invoker is a button.
-        auto optional_value = invoker.get_attribute(AttributeNames::value);
+        auto const optional_value = as<FormAssociatedElement>(invoker).optional_value();
         request_close_the_dialog(optional_value, invoker);
     }
 

Libraries/LibWeb/HTML/HTMLFormElement.cpp

@@ -225,9 +225,10 @@ WebIDL::ExceptionOr<void> HTMLFormElement::submit_form(GC::Ref<HTMLElement> subm
             }
         }
 
-        // 5. Otherwise, if submitter has a value, then set result to that value.
-        if (!result.has_value())
-            result = submitter->get_attribute_value(AttributeNames::value);
+        // 5. Otherwise, if submitter is a submit button, then set result to submitter's optional value.
+        else if (auto* form_associated_element = as_if<FormAssociatedElement>(*submitter); form_associated_element && form_associated_element->is_submit_button()) {
+            result = form_associated_element->optional_value();
+        }
 
         // 6. Close the dialog subject with result and null.
         subject->close_the_dialog(move(result), nullptr);

Libraries/LibWeb/HTML/HTMLInputElement.cpp

@@ -659,6 +659,18 @@ String HTMLInputElement::value() const
     VERIFY_NOT_REACHED();
 }
 
+Optional<String> HTMLInputElement::optional_value() const
+{
+    switch (m_type) {
+    // https://html.spec.whatwg.org/multipage/input.html#submit-button-state-(type=submit):concept-fe-optional-value
+    case TypeAttributeState::SubmitButton:
+        // The element's optional value is the value of the element's value attribute, if there is one; otherwise null.
+        return get_attribute(AttributeNames::value);
+    default:
+        VERIFY_NOT_REACHED();
+    }
+}
+
 WebIDL::ExceptionOr<void> HTMLInputElement::set_value(String const& value)
 {
     auto& realm = this->realm();

Libraries/LibWeb/HTML/HTMLInputElement.h

@@ -80,6 +80,7 @@ public:
     String default_value() const { return get_attribute_value(HTML::AttributeNames::value); }
 
     virtual String value() const override;
+    virtual Optional<String> optional_value() const override;
     WebIDL::ExceptionOr<void> set_value(String const&);
 
     // https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#concept-textarea/input-relevant-value