Jackson Databind Failing @JsonMerge with a custom Map

Continuation of https://github.com/FasterXML/jackson-databind/issues/4783.

import java.util.HashMap;
import java.util.Map;

import com.fasterxml.jackson.annotation.JsonMerge;
import com.fasterxml.jackson.databind.json.JsonMapper;

interface MyMap<K, V> extends Map<K, V> {}

class MapImpl<K, V> extends HashMap<K, V> implements MyMap<K, V> {}

class MapUtils {

    static <K, V> MyMap<K, V> createMyMap() {
        return new MapImpl<K, V>();
    }
}

class MergeMap {

    @JsonMerge // either here
    MyMap<Integer, String> map = MapUtils.createMyMap();
    @JsonMerge // or here
    public MyMap<Integer, String> getMap() {
        System.out.println("getMap");
        return map;
    }

    @Override
    public String toString() {
        return map.toString();
    }

    public static void main(String[] args) throws Exception {
        JsonMapper MAPPER = JsonMapper.builder().build();

        var merge = new MergeMap();
        merge.getMap().put(3, "ADS");
        System.out.println(merge);

        System.out.println(" == serializing --");

        var string = MAPPER.writerWithDefaultPrettyPrinter().writeValueAsString(merge);
        System.out.println(string);

        System.out.println(" == deserializing --");

        var merge2 = MAPPER.readValue(string, MergeMap.class);

        System.out.println(" == checking --");

        System.out.println(merge2);
    }
}

This fails in 2.18.2 with

getMap
{3=ADS}
 == serializing --
getMap
{
  "map" : {
    "3" : "ADS"
  }
}
 == deserializing --
Exception in thread "main" com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot find a deserializer for non-concrete Map type [map type; class example.MyMap, [simple type, class java.lang.Integer] -> [simple type, class java.lang.String]]
 at [Source: REDACTED (`StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION` disabled); line: 1, column: 1]
    at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67)
    at com.fasterxml.jackson.databind.DeserializationContext.reportBadDefinition(DeserializationContext.java:1888)
    at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:321)
    at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCacheValueDeserializer(DeserializerCache.java:284)
    at com.fasterxml.jackson.databind.deser.DeserializerCache.findValueDeserializer(DeserializerCache.java:174)
    at com.fasterxml.jackson.databind.DeserializationContext.findNonContextualValueDeserializer(DeserializationContext.java:659)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.resolve(BeanDeserializerBase.java:552)
    at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:347)
    at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCacheValueDeserializer(DeserializerCache.java:284)
    at com.fasterxml.jackson.databind.deser.DeserializerCache.findValueDeserializer(DeserializerCache.java:174)
    at com.fasterxml.jackson.databind.DeserializationContext.findRootValueDeserializer(DeserializationContext.java:669)
    at com.fasterxml.jackson.databind.ObjectMapper._findRootDeserializer(ObjectMapper.java:5048)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4918)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3860)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3828)
    at example.MergeMap.main(MergeMap.java:49)

I'm not sure where @JsonMerge should be placed - on the field or on the getter, but both failed.

Comment From: cowtowncoder

Fix from #4784 (wrt Lists) might be useful.

EDIT: indeed, just needed to apply same logic (removal of check) from Collection case.

Fixing for 2.18, to be released in 2.18.3.

Comment From: nlisker

Thanks. So does @JsonMerge go on the field or the getter, or whichever is configured to be used?

Comment From: cowtowncoder

@nlisker Should make no difference, both should work. I tend to add to getter personally fwtw. :)

Comment From: nlisker

Submitted a followup in https://github.com/FasterXML/jackson-databind/issues/4922.