JsonMappingException through nested getter with generic wildcard return type

[sunchezz89]

Having the following Code, produces an Exception if i try to serialize it. Jackson v2.9.8.
Here is an Example-Project which fully reproduces the Error. Git-Project

public class Node<T extends SuperTestClass & Cloneable> extends SuperNode<Node<T>> implements Serializable {
   
    public static void main(String[] args) throws JsonProcessingException {
        Node root = new Node();
        root.children.add(new Node());

        System.out.println(new ObjectMapper().writeValueAsString(root));
    }
 
    public List<Node<T>> children;

    public Node() {
        children = new ArrayList<Node<T>>();
    }

    /**
     * The Wildcard here seems to be the Issue.
     * If we remove this full getter, everything is working as expected.
     * @return
     */
    public List<? extends SuperNode<Node<T>>> getChildren() {
        return children;
    }
}

com.fasterxml.jackson.databind.JsonMappingException: Index: 0 (through reference chain: com.test.Node["children"]->java.util.ArrayList[0])
	at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:394)
	at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:365)
	at com.fasterxml.jackson.databind.ser.std.StdSerializer.wrapAndThrow(StdSerializer.java:338)
	at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:123)
	at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serialize(IndexedListSerializer.java:79)
	at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serialize(IndexedListSerializer.java:18)
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719)
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
	at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480)
	at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:319)
	at com.fasterxml.jackson.databind.ObjectMapper._configAndWriteValue(ObjectMapper.java:3905)
	at com.fasterxml.jackson.databind.ObjectMapper.writeValueAsString(ObjectMapper.java:3219)
	at com.test.MainJackson.main(MainJackson.java:22)
Caused by: java.lang.IndexOutOfBoundsException: Index: 0
	at java.util.Collections$EmptyList.get(Collections.java:4454)
	at com.fasterxml.jackson.databind.type.TypeFactory._verifyAndResolvePlaceholders(TypeFactory.java:505)
	at com.fasterxml.jackson.databind.type.TypeFactory._resolveTypePlaceholders(TypeFactory.java:458)
	at com.fasterxml.jackson.databind.type.TypeFactory._bindingsForSubtype(TypeFactory.java:429)
	at com.fasterxml.jackson.databind.type.TypeFactory.constructSpecializedType(TypeFactory.java:401)
	at com.fasterxml.jackson.databind.cfg.MapperConfig.constructSpecializedType(MapperConfig.java:297)
	at com.fasterxml.jackson.databind.DatabindContext.constructSpecializedType(DatabindContext.java:161)
	at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:113)
	... 10 more

Please let me know if you need anything else from me.

[cowtowncoder]

Interesting. Thank you for reporting this. Definitely sounds like a bug in type resolution.

[cowtowncoder]

I can reproduce this; added failing test.

[YannLeCorse]

I'm having the same kind of issue but 1 line before, when the lists are accessed (expectedTypes contains 2 elements, actualTypes is empty)

Caused by: java.lang.IndexOutOfBoundsException: Index: 0
	at java.base/java.util.Collections$EmptyList.get(Collections.java:4481)
	at com.fasterxml.jackson.databind.type.TypeFactory._resolveTypePlaceholders(TypeFactory.java:456)
	at com.fasterxml.jackson.databind.type.TypeFactory._bindingsForSubtype(TypeFactory.java:429)
	at com.fasterxml.jackson.databind.type.TypeFactory.constructSpecializedType(TypeFactory.java:401)
	at com.fasterxml.jackson.databind.cfg.MapperConfig.constructSpecializedType(MapperConfig.java:297)
	at com.fasterxml.jackson.databind.DatabindContext.constructSpecializedType(DatabindContext.java:161)
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter._findAndAddDynamic(BeanPropertyWriter.java:893)
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:705)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719)
	... 11 more

[cowtowncoder]

Looks like what was missing was delegation of getBindings() by ResolvedRecursiveType; adding of which resolves problem we see here, and I hope a few other reports too.