LibWeb: Implement the [PutForwards] IDL extended attribute

For example, consider the attribute:

    interface Element {
        [PutForwards=value] readonly attribute DOMTokenList classList;
    }

When `classList` is set, we should instead set the attribute `value` on
the `classList` attribute of the Element interface.

Meta/Lagom/Tools/CodeGenerators/LibWeb/BindingsGenerator/IDLGenerators.cpp

@@ -2178,7 +2178,7 @@ static void generate_prototype_or_global_mixin_declarations(IDL::Interface const
     JS_DECLARE_NATIVE_FUNCTION(@attribute.name:snakecase@_getter);
 )~~~");
 
-        if (!attribute.readonly || attribute.extended_attributes.contains("Replaceable"sv)) {
+        if (!attribute.readonly || attribute.extended_attributes.contains("Replaceable"sv) || attribute.extended_attributes.contains("PutForwards"sv)) {
             attribute_generator.append(R"~~~(
     JS_DECLARE_NATIVE_FUNCTION(@attribute.name:snakecase@_setter);
 )~~~");
@@ -2300,7 +2300,7 @@ JS::ThrowCompletionOr<void> @class_name@::initialize(JS::Realm& realm)
         attribute_generator.set("attribute.name", attribute.name);
         attribute_generator.set("attribute.getter_callback", attribute.getter_callback_name);
 
-        if (!attribute.readonly || attribute.extended_attributes.contains("Replaceable"sv))
+        if (!attribute.readonly || attribute.extended_attributes.contains("Replaceable"sv) || attribute.extended_attributes.contains("PutForwards"sv))
             attribute_generator.set("attribute.setter_callback", attribute.setter_callback_name);
         else
             attribute_generator.set("attribute.setter_callback", "nullptr");
@@ -2540,6 +2540,22 @@ JS_DEFINE_NATIVE_FUNCTION(@class_name@::@attribute.setter_callback@)
     TRY(this_value.as_object().internal_define_own_property("@attribute.name@", JS::PropertyDescriptor { .value = vm.argument(0), .writable = true }));
     return JS::js_undefined();
 }
+)~~~");
+        } else if (auto put_forwards_identifier = attribute.extended_attributes.get("PutForwards"sv); put_forwards_identifier.has_value()) {
+            attribute_generator.set("attribute.name", attribute.name.to_snakecase());
+            attribute_generator.set("put_forwards_identifier"sv, *put_forwards_identifier);
+
+            attribute_generator.append(R"~~~(
+JS_DEFINE_NATIVE_FUNCTION(@class_name@::@attribute.setter_callback@)
+{
+    auto* impl = TRY(impl_from(vm));
+    auto value = vm.argument(0);
+
+    auto receiver = TRY(throw_dom_exception_if_needed(vm, [&]() { return impl->@attribute.name@(); }));
+    TRY(receiver->set(JS::PropertyKey { "@put_forwards_identifier@" }, value, JS::Object::ShouldThrowExceptions::Yes));
+
+    return JS::js_undefined();
+}
 )~~~");
         }
     }

Userland/Libraries/LibWeb/HTML/Window.cpp

@@ -756,10 +756,6 @@ WebIDL::ExceptionOr<void> Window::initialize_web_interfaces(Badge<WindowEnvironm
     create_method_property("CSS", MUST_OR_THROW_OOM(heap().allocate<Bindings::CSSNamespace>(realm, realm)));
     create_method_property("WebAssembly", MUST_OR_THROW_OOM(heap().allocate<Bindings::WebAssemblyObject>(realm, realm)));
 
-    // FIXME: Implement codegen for readonly properties with [PutForwards]
-    auto& location_accessor = storage_get("location")->value.as_accessor();
-    location_accessor.set_setter(JS::NativeFunction::create(realm, location_setter, 1, "location", &realm, {}, "set"sv));
-
     return {};
 }
 
@@ -770,29 +766,6 @@ JS::ThrowCompletionOr<bool> Window::internal_set_prototype_of(JS::Object* protot
     return set_immutable_prototype(prototype);
 }
 
-static JS::ThrowCompletionOr<Window*> impl_from(JS::VM& vm)
-{
-    // Since this is a non built-in function we must treat it as non-strict mode
-    // this means that a nullish this_value should be converted to the
-    // global_object. Generally this does not matter as we try to convert the
-    // this_value to a specific object type in the bindings. But since window is
-    // the global object we make an exception here.
-    // This allows calls like `setTimeout(f, 10)` to work.
-    auto this_value = vm.this_value();
-    if (this_value.is_nullish())
-        this_value = &vm.current_realm()->global_object();
-
-    auto* this_object = MUST(this_value.to_object(vm));
-
-    if (is<WindowProxy>(*this_object))
-        return static_cast<WindowProxy*>(this_object)->window().ptr();
-
-    if (is<Window>(*this_object))
-        return static_cast<Window*>(this_object);
-
-    return vm.throw_completion<JS::TypeError>(JS::ErrorType::NotAnObjectOfType, "Window");
-}
-
 // https://html.spec.whatwg.org/multipage/window-object.html#dom-window
 JS::NonnullGCPtr<WindowProxy> Window::window() const
 {
@@ -1371,12 +1344,4 @@ size_t Window::document_tree_child_browsing_context_count() const
     return this_browsing_context->document_tree_child_browsing_context_count();
 }
 
-JS_DEFINE_NATIVE_FUNCTION(Window::location_setter)
-{
-    auto* impl = TRY(impl_from(vm));
-    auto location = TRY(Bindings::throw_dom_exception_if_needed(vm, [&] { return impl->location(); }));
-    TRY(location->set(JS::PropertyKey("href"), vm.argument(0), JS::Object::ShouldThrowExceptions::Yes));
-    return JS::js_undefined();
-}
-
 }

Userland/Libraries/LibWeb/HTML/Window.h

@@ -233,8 +233,6 @@ private:
 
     // [[CrossOriginPropertyDescriptorMap]], https://html.spec.whatwg.org/multipage/browsers.html#crossoriginpropertydescriptormap
     CrossOriginPropertyDescriptorMap m_cross_origin_property_descriptor_map;
-
-    JS_DECLARE_NATIVE_FUNCTION(location_setter);
 };
 
 void run_animation_frame_callbacks(DOM::Document&, double now);