We’re using Vavr with Quarkus and although Quarkus supports java.util.Optional types for query parameters, I would like to be able to support Vavr’s Option type.

Reading Quarkus RestEasy Parameter Mapping a custom ParamConverterProvider can be created to return a custom ParamConverter.

import io.vavr.control.Option;
import jakarta.ws.rs.ext.ParamConverter;
import jakarta.ws.rs.ext.ParamConverterProvider;
import jakarta.ws.rs.ext.Provider;

import java.lang.annotation.Annotation;
import java.lang.reflect.Type;

@Provider
public class VavrParamConverterProvider implements ParamConverterProvider {

    @Override
    public <T> ParamConverter<T> getConverter(Class<T> rawType, Type genericType, Annotation[] annotations) {

        if (rawType.equals(Option.class)) {
            return new ParamConverter<Option<T>>() {
                @Override
                public Option<T> fromString(String value) {
                    T optionValue = ??
                    return Option.of(optionValue);
                }

                @Override
                public String toString(Option<T> option) {
                    return option.map(Object::toString).getOrElse("");
                }
            };
        }
        return null;
    }
}

The issue is: how to convert the String value to the proper type T?

Ideally I would like to use any of the other known ParamConverters but those cannot be injected. All known ParamConverters seems to be defined in the RestClientBase class, but this class is abstract and all ParamConverters are in private properties. Also the static properties are private.
Injecting a RestClientBase instance does not work.
Also injecting ParamConverterProviders does not work since that would be a cyclic dependency.

Any idea how to do this?
I cannot find the implementation for how this is done for java.util.Optional for inspiration.