Unable to register serializers due to visibility problems

[gzsombor]

Describe the bug
I need to serialize objects which contains fields, which are initialized with java.util.List.of(a,b,c,d) Kyro throws this exception:

Caused by: java.lang.IllegalArgumentException: Class is not registered: java.util.ImmutableCollections$ListN
Note: To register this class use: kryo.register(java.util.ImmutableCollections.ListN.class);

I don't want to kryo.setRegistrationRequired(false), as - in my understanding - could lead to less performance, and potential incompatibilities. However, I can't really register serializer by itself, the best that I could came up with:

        kryo.register(List.of(1, 2, 3, 4).getClass(), 14);
        kryo.register(List.of(1).getClass(), 15);
        kryo.register(List.of().getClass(), 16);
        kryo.register(List.class, new CollectionSerializer<List<Object>>() {
            {
                setAcceptsNull(false);
            }
            @Override
            protected List<Object> create (Kryo kryo, Input input, Class<? extends List<Object>> type, int size) {
                return new ArrayList<>(size);
            }

        }, 17);

It seems to be working, but having helper functions on ImmutableCollectionsSerializers, which would do this initialization would be super helpful

To Reproduce
Provide a minimal reproducible example of the problem, ideally in the form of a runnable test-case.

record X(List<String> values) {}

var kryo = new Kryo();
kryo.writeClassAndObject(output, new X(List.of("hello", "world")));

Environment:

• OS: Any
• JDK Version: 17
• Kryo Version: 5.3.0

Additional context
Add any other context about the problem here.

[theigl]

@gzsombor: I agree, registering immutable collections is quite cumbersome at the moment. I'm open to adding helper functions to ImmutableCollectionsSerializers. Do you think we should add 3 separate functions for lists, sets, and maps or a single function?

It would be great if you could provide a PR.

[theigl]

@gzsombor: I created #933 to address this issue. Is this solution OK for you?

[gzsombor]

Sorry to not sending PR, but your change looks good to me!