ValueInstantiator.canInstantiate() ignores canCreateUsingArrayDelegate()

[henryptung]

Problem

Method Javadoc doesn't match behavior. As a result, delegate collection constructors (for abstract types) don't work properly.

Tested versions

jackson-databind v2.8.7 and v2.9.2.

Location in code

https://github.com/FasterXML/jackson-databind/blob/master/src/main/java/com/fasterxml/jackson/databind/deser/ValueInstantiator.java#L70

Expected Behavior

Outputs [].

Observed Behavior

Exception in thread "main" com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `ArrayDelegateDeserializationTest$MyType` (no Creators, like default construct, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information
 at [Source: (String)"[]"; line: 1, column: 1]
	at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67)
	at com.fasterxml.jackson.databind.DeserializationContext.reportBadDefinition(DeserializationContext.java:1451)
	at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1027)
	at com.fasterxml.jackson.databind.deser.AbstractDeserializer.deserialize(AbstractDeserializer.java:265)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4001)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2992)
	at ArrayDelegateDeserializationTest.main(ArrayDelegateDeserializationTest.java:35)

Test code

import java.util.List;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonValue;
import com.fasterxml.jackson.databind.ObjectMapper;

public class ArrayDelegateDeserializationTest {

    public static class MyTypeImpl implements MyType {
        private final List<Integer> values;

        MyTypeImpl(List<Integer> values) {
            this.values = values;
        }

        @Override
        public List<Integer> getValues() {
            return values;
        }
    }

    public interface MyType {
        @JsonValue
        List<Integer> getValues();

        @JsonCreator
        static MyType of(List<Integer> values) {
            return new MyTypeImpl(values);
        }
    }


    public static void main(String[] args) throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        MyType thing = mapper.readValue("[]", MyType.class);
        System.out.println(thing.getValues());
    }

}

[henryptung]

Note: did some debugger hackery to verify that bypassing this check seems to fix the bug, so adding the missing piece of canInstantiate() should do the trick.

[cowtowncoder]

Thank you for reporting the problem. Sounds like retrofitting done to add array-delegator was missing the call.