Cloning a form doesn't preserve changed values of its HTMLInputElement children.

[pshaughn]

WPT html/semantics/forms/the-input-element/clone.html has a form with value and checked content attributes on many input children. It sets .value on the children, then calls cloneNode on the form. It gets back a clone, but the clone's children's values match the original values from their content attributes, not the updated values that were set by the script.

[jdm]

Node::clone's handling of elements doesn't include the concept of "cloning steps" (ie. step 5 of the algorithm), which includes specific steps for input elements (https://html.spec.whatwg.org/multipage/input.html#the-input-element%3Aconcept-node-clone-ext).

servo/components/script/dom/node.rs

Lines 2146 to 2160 in 8002c6b

	NodeTypeId::Element(..) => {
	let element = node.downcast::<Element>().unwrap();
	let name = QualName {
	prefix: element.prefix().as_ref().map(|p| Prefix::from(&**p)),
	ns: element.namespace().clone(),
	local: element.local_name().clone(),
	};
	let element = Element::create(
	name,
	element.get_is(),
	&document,
	ElementCreator::ScriptCreated,
	CustomElementCreationMode::Asynchronous,
	);
	DomRoot::upcast::<Node>(element)

We should probably extend the VirtualMethods trait to incorporate cloning steps.

[teapotd]

VirtualMethods trait already has cloning_steps method and Node::clone includes step 5:

servo/components/script/dom/node.rs

Lines 2196 to 2197 in 44b3e8b

	// Step 5: cloning steps.
	vtable_for(&node).cloning_steps(&copy, maybe_doc, clone_children);

It suffices to implement cloning_steps for HTMLInputElement. I'd like to claim this one.

@highfive assign me

[highfive]

Hey @teapotd! Thanks for your interest in working on this issue. It's now assigned to you!