LibWeb: Support nullable EventListener parameters in WrapperGenerator

The internal C++ function will now receive a RefPtr<EventListener> for
'EventListener?' and a NonnullRefPtr<EventListener> for 'EventListener'.

Examples of this are addEventListener() and removeEventListener(), which
both have nullable callback parameters.

Userland/Libraries/LibWeb/CodeGenerators/WrapperGenerator.cpp

@@ -522,7 +522,7 @@ static void generate_to_cpp(SourceGenerator& generator, ParameterType& parameter
     else
         scoped_generator.set("return_statement", "return {};");
 
-    // FIXME: Add support for optional to all types
+    // FIXME: Add support for optional and nullable to all types
     if (parameter.type.is_string()) {
         if (!optional) {
             scoped_generator.append(R"~~~(
@@ -541,13 +541,26 @@ static void generate_to_cpp(SourceGenerator& generator, ParameterType& parameter
 )~~~");
         }
     } else if (parameter.type.name == "EventListener") {
-        scoped_generator.append(R"~~~(
+        if (parameter.type.nullable) {
+            scoped_generator.append(R"~~~(
+    RefPtr<EventListener> @cpp_name@;
+    if (!@js_name@@js_suffix@.is_null()) {
+        if (!@js_name@@js_suffix@.is_function()) {
+            vm.throw_exception<JS::TypeError>(global_object, JS::ErrorType::NotA, "Function");
+            @return_statement@
+        }
+        @cpp_name@ = adopt(*new EventListener(JS::make_handle(&@js_name@@js_suffix@.as_function())));
+    }
+)~~~");
+        } else {
+            scoped_generator.append(R"~~~(
     if (!@js_name@@js_suffix@.is_function()) {
         vm.throw_exception<JS::TypeError>(global_object, JS::ErrorType::NotA, "Function");
         @return_statement@
     }
     auto @cpp_name@ = adopt(*new EventListener(JS::make_handle(&@js_name@@js_suffix@.as_function())));
 )~~~");
+        }
     } else if (is_wrappable_type(parameter.type)) {
         scoped_generator.append(R"~~~(
     auto @cpp_name@_object = @js_name@@js_suffix@.to_object(global_object);
@@ -774,6 +787,7 @@ void generate_implementation(const IDL::Interface& interface)
 #include <LibWeb/Bindings/DocumentTypeWrapper.h>
 #include <LibWeb/Bindings/DocumentWrapper.h>
 #include <LibWeb/Bindings/EventTargetWrapperFactory.h>
+#include <LibWeb/Bindings/EventWrapperFactory.h>
 #include <LibWeb/Bindings/HTMLCanvasElementWrapper.h>
 #include <LibWeb/Bindings/HTMLHeadElementWrapper.h>
 #include <LibWeb/Bindings/HTMLImageElementWrapper.h>
@@ -1111,6 +1125,8 @@ void generate_prototype_implementation(const IDL::Interface& interface)
 #include <LibWeb/Bindings/DocumentTypeWrapper.h>
 #include <LibWeb/Bindings/DocumentWrapper.h>
 #include <LibWeb/Bindings/EventTargetWrapperFactory.h>
+#include <LibWeb/Bindings/EventWrapper.h>
+#include <LibWeb/Bindings/EventWrapperFactory.h>
 #include <LibWeb/Bindings/ExceptionOrUtils.h>
 #include <LibWeb/Bindings/HTMLCanvasElementWrapper.h>
 #include <LibWeb/Bindings/HTMLHeadElementWrapper.h>

Userland/Libraries/LibWeb/DOM/EventTarget.cpp

@@ -39,19 +39,25 @@ EventTarget::~EventTarget()
 {
 }
 
-void EventTarget::add_event_listener(const FlyString& event_name, NonnullRefPtr<EventListener> listener)
+// https://dom.spec.whatwg.org/#add-an-event-listener
+void EventTarget::add_event_listener(const FlyString& event_name, RefPtr<EventListener> listener)
 {
+    if (listener.is_null())
+        return;
     auto existing_listener = m_listeners.first_matching([&](auto& entry) {
         return entry.listener->type() == event_name && &entry.listener->function() == &listener->function() && entry.listener->capture() == listener->capture();
     });
     if (existing_listener.has_value())
         return;
     listener->set_type(event_name);
-    m_listeners.append({ event_name, move(listener) });
+    m_listeners.append({ event_name, listener.release_nonnull() });
 }
 
-void EventTarget::remove_event_listener(const FlyString& event_name, NonnullRefPtr<EventListener> listener)
+// https://dom.spec.whatwg.org/#remove-an-event-listener
+void EventTarget::remove_event_listener(const FlyString& event_name, RefPtr<EventListener> listener)
 {
+    if (listener.is_null())
+        return;
     m_listeners.remove_first_matching([&](auto& entry) {
         auto matches = entry.event_name == event_name && &entry.listener->function() == &listener->function() && entry.listener->capture() == listener->capture();
         if (matches)

Userland/Libraries/LibWeb/DOM/EventTarget.h

@@ -45,8 +45,8 @@ public:
     void ref() { ref_event_target(); }
     void unref() { unref_event_target(); }
 
-    void add_event_listener(const FlyString& event_name, NonnullRefPtr<EventListener>);
-    void remove_event_listener(const FlyString& event_name, NonnullRefPtr<EventListener>);
+    void add_event_listener(const FlyString& event_name, RefPtr<EventListener>);
+    void remove_event_listener(const FlyString& event_name, RefPtr<EventListener>);
 
     void remove_from_event_listener_list(NonnullRefPtr<EventListener>);