Polymorphic Deserialization loses type information when subtypes of subtypes are added

[njr-11]

Describe the bug
When trying out the new polymorphic deserialization feature that is new in JSON-B 3.0 on the Yasson 3.0.0-RC1 JSON-B provider, I noticed that it worked well in the basic scenario of a type with subtypes, but when more subtypes were added to a subtype, then the first-level subtype itself lost its @type property in the generated JSON, causing it to be unable to deserialize. In the following test output, you can see that the third list element lacks a "@type":"area" in its JSON, and then the error which goes along with that,

Converted list of locations to JSON as:
[{"@type":"area","@area":"city","name":"Some City","population":2000,"state":"Some State"},
{"@type":"area","@area":"state","name":"Some State","population":1000000,"capital":"Some Capital City"},
{"name":"North America","population":600000000}]
Apr 06, 2022 11:19:54 AM org.eclipse.yasson.internal.DeserializationContextImpl deserializeItem
SEVERE: Cannot infer a type for unmarshalling into: TestPolymorphism$Location
Exception in thread "main" jakarta.json.bind.JsonbException: Cannot infer a type for unmarshalling into: TestPolymorphism$Location
	at org.eclipse.yasson.internal.deserializer.DefaultObjectInstanceCreator.<init>(DefaultObjectInstanceCreator.java:41)
	at org.eclipse.yasson.internal.deserializer.DeserializationModelCreator.createObjectDeserializer(DeserializationModelCreator.java:251)
	at org.eclipse.yasson.internal.deserializer.DeserializationModelCreator.deserializerChainInternal(DeserializationModelCreator.java:193)
	at org.eclipse.yasson.internal.deserializer.DeserializationModelCreator.deserializerChain(DeserializationModelCreator.java:135)
	at org.eclipse.yasson.internal.deserializer.DeserializationModelCreator.createNewChain(DeserializationModelCreator.java:487)
	at org.eclipse.yasson.internal.deserializer.DeserializationModelCreator.typeProcessor(DeserializationModelCreator.java:476)
	at org.eclipse.yasson.internal.deserializer.DeserializationModelCreator.typeProcessor(DeserializationModelCreator.java:429)
	at org.eclipse.yasson.internal.deserializer.DeserializationModelCreator.createArrayDeserializer(DeserializationModelCreator.java:333)
	at org.eclipse.yasson.internal.deserializer.DeserializationModelCreator.deserializerChainInternal(DeserializationModelCreator.java:187)
	at org.eclipse.yasson.internal.deserializer.DeserializationModelCreator.deserializerChain(DeserializationModelCreator.java:135)
	at org.eclipse.yasson.internal.deserializer.DeserializationModelCreator.deserializerChain(DeserializationModelCreator.java:123)
	at org.eclipse.yasson.internal.DeserializationContextImpl.deserializeItem(DeserializationContextImpl.java:141)
	at org.eclipse.yasson.internal.DeserializationContextImpl.deserialize(DeserializationContextImpl.java:131)
	at org.eclipse.yasson.internal.JsonBinding.deserialize(JsonBinding.java:55)
	at org.eclipse.yasson.internal.JsonBinding.fromJson(JsonBinding.java:62)
	at TestPolymorphism.main(TestPolymorphism.java:69)

I found that you can work around this by awkwardly declaring the subtype to be a subtype of itself,

    @JsonbTypeInfo(key = "@area", value = {
        ...
        @JsonbSubtype(alias = "general", type = Area.class)
    })
    public static class Area implements Location {

in which case the @type gets added back in,

{"@type":"area","@area":"general","name":"North America","population":600000000}

but that should not be necessary.

To Reproduce
Run this test case:

import jakarta.json.bind.*;
import jakarta.json.bind.annotation.*;
import java.util.*;

public class TestPolymorphism {

    @JsonbTypeInfo({
        @JsonbSubtype(alias = "point", type = Point.class),
        @JsonbSubtype(alias = "area", type = Area.class)
    })
    public static interface Location {
    }

    @JsonbTypeInfo(key = "@area", value = {
        @JsonbSubtype(alias = "city", type = City.class),
        @JsonbSubtype(alias = "state", type = State.class),

        // Workaround here - It is awkward that Area must include itself
        // as a subtype of itself, but if we don't do this, Yasson also
        // omits "@type": "area" from the JSON, making it unable to
        // deserialize as a Location.class.
        // --- Comment out the following annotation to make it fail ---
        //@JsonbSubtype(alias = "general", type = Area.class)
    })
    public static class Area implements Location {
        public String name;
        public long population;
    }

    public static class City extends Area {
        public String state;
    }

    public static class State extends Area {
        public String capital;
    }

    public static class Point implements Location {
        public double x;
        public double y;
    }

    public static void main(String[] args) throws Exception {
        try (Jsonb jsonb = JsonbBuilder.create()) {
            Location[] list = new Location[3];

            City city = new City();
            city.name = "Some City";
            city.population = 2000;
            city.state = "Some State";
            list[0] = city;

            State state = new State();
            state.name = "Some State";
            state.population = 1000000;
            state.capital = "Some Capital City";
            list[1] = state;

            Area northAmerica = new Area();
            northAmerica.name = "North America";
            northAmerica.population = 600000000;
            list[2] = northAmerica;

            String json = jsonb.toJson(list);

            System.out.println("Converted list of locations to JSON as:");
            System.out.println(json);

            Location[] deserialized = jsonb.fromJson(json, Location[].class);

            City c = (City) deserialized[0];
            assertEquals(city.name, c.name);
            assertEquals(city.population, c.population);
            assertEquals(city.state, c.state);

            State s = (State) deserialized[1];
            assertEquals(state.name, s.name);
            assertEquals(state.population, s.population);
            assertEquals(state.capital, s.capital);

            Area a = (Area) deserialized[2];
            assertEquals(northAmerica.name, a.name);
            assertEquals(northAmerica.population, a.population);
        }
    }

    private static final void assertEquals(Object expected, Object observed) {
        if (!Objects.equals(expected, observed))
            throw new AssertionError("Expected " + expected + ", but observed " + observed);
    }
}

Expected behavior
The third list element of the test output JSON array (without the workaround enabled) should look like this, including @type,

{"@type":"area","name":"North America","population":600000000}

and then it would deserialize properly because the necessary type information would be found there.

System information:

• OS: Mac
• Java Version: 11

openjdk version "11.0.2" 2019-01-15
OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.2+9)
Eclipse OpenJ9 VM AdoptOpenJDK (build openj9-0.12.1, JRE 11 Mac OS X amd64-64-Bit Compressed References 20190204_123 (JIT enabled, AOT enabled)
OpenJ9   - 90dd8cb40
OMR      - d2f4534b
JCL      - 289c70b684 based on )

• Yasson Version: 3.0.0-RC1

Additional context
Add any other context about the problem here.

[Verdent]

Thank you, I will take a look at that :-)

[Verdent]

Very nice example. It was easy to see the issue. I will tune Yasson it a bit to reflect the following situations:

1. Serialized instance is type of Area -> it will contain just the type information from its parents and not area information itself
2. Serialized instance is type of Village and not present in Area configuration -> no polymorphic info included.