Allow optional Object Id for @JsonIdentityInfo

[f0def]

Related to the #1388 and #1261

I need to use @JsonCreator to test the input arguments in the constructor. And I want to support alternate API options with or without "@id" (in some places there is recursion, and somewhere there is no).

If the way for this test to be performed without errors?

com.fasterxml.jackson.databind.exc.MismatchedInputException: No Object Id found for an instance of com.example.JsonIdentityInfoWithJsonCreatorTest$Foo, to assign to property '@id'

Tested on 2.8.3 and 2.9.0.pr4

package com.example;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonIdentityInfo;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.ObjectIdGenerators;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.Test;

import java.io.IOException;

public class JsonIdentityInfoWithJsonCreatorTest {
  @Test
  public void testJsonIdentityInfoWithJsonCreator() throws IOException {
    ObjectMapper objectMapper = new ObjectMapper();

    TypeReference typeReference = new TypeReference<Foo>() {
    };

    //no exception - ok
    objectMapper.readValue("{\"@id\": \"1\", \"name\": \"foo\"}", typeReference);

    //JsonMappingException throwed - why?
    objectMapper.readValue("{\"name\": \"foo\"}", typeReference);

    //JsonMappingException throwed - why?
    objectMapper.readValue("{\"name\": \"foo\", \"@id\": \"1\"}", typeReference);
  }

  @JsonIdentityInfo(generator = ObjectIdGenerators.IntSequenceGenerator.class)
  public static class Foo {
    @JsonCreator
    public Foo(@JsonProperty("name") String name) {
    }
  }
}

[cowtowncoder]

At this point Object Id must be present, if one is expected.

Perhaps it would be possible to have a DeserializationFeature that allows missing type id during deserialization: if so, such values would not be referencable, but would not fail.

Alternatively... maybe a better way would be to add one more property for @JsonIdentityInfo, something like requireId or just required, which would apply to that specific type.
I think I like this approach more.

I will change the title to reflect this as RFE, assuming that ability to optionally exclude Object Ids is what you would like to see, regardless of mechanism.