Fail to deserialize local Records

[DasBrain]

Reproducer:

record NestedRecord(@JsonProperty("foo")String foo) {
    @JsonCreator
    public NestedRecord(@JsonProperty("foo") String foo) {
        this.foo = foo;
    }
}

public static void main(String[] args) throws Throwable {
    String json = "{\"foo\":\"bar\"}";
    ObjectMapper mapper = new ObjectMapper();
    System.out.println(mapper.readValue(json, NestedRecord.class));
    
    
    record LocalRecord(@JsonProperty("foo") String foo) {
        @JsonCreator 
        public LocalRecord(@JsonProperty("foo") String foo) {
            this.foo = foo;
        }
    }
    System.out.println(mapper.readValue(json, LocalRecord.class));
}

Jackson fails with the following error message:

NestedRecord[foo=bar]
Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Cannot deserialize Class test.TestMain$1LocalRecord (of type local/anonymous) as a Bean
 at [Source: (String)"{"foo":"bar"}"; line: 1, column: 1]
    at [email protected]/com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:309)
    at [email protected]/com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:268)
    at [email protected]/com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCacheValueDeserializer(DeserializerCache.java:244)
    at [email protected]/com.fasterxml.jackson.databind.deser.DeserializerCache.findValueDeserializer(DeserializerCache.java:142)
    at [email protected]/com.fasterxml.jackson.databind.DeserializationContext.findRootValueDeserializer(DeserializationContext.java:491)
    at [email protected]/com.fasterxml.jackson.databind.ObjectMapper._findRootDeserializer(ObjectMapper.java:4669)
    at [email protected]/com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4478)
    at [email protected]/com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3434)
    at [email protected]/com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3402)
    at test/.test.TestMain.main(TestMain.java:37)
Caused by: java.lang.IllegalArgumentException: Cannot deserialize Class test.TestMain$1LocalRecord (of type local/anonymous) as a Bean
    at [email protected]/com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.isPotentialBeanType(BeanDeserializerFactory.java:883)
    at [email protected]/com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.createBeanDeserializer(BeanDeserializerFactory.java:137)
    at [email protected]/com.fasterxml.jackson.databind.deser.DeserializerCache._createDeserializer2(DeserializerCache.java:414)
    at [email protected]/com.fasterxml.jackson.databind.deser.DeserializerCache._createDeserializer(DeserializerCache.java:349)
    at [email protected]/com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:264)
    ... 8 more

It seems to identify the local record as a local class, which is incorrect according to JLS § 14.3:

... A local record is not a local class.

[cowtowncoder]

Ok. Not quite sure what would be usable heuristics on JDK 7 to figure out this specific case: inner classes that are not static are considered problematic (since they expect "hidden this parameter" to be passed). Since Jackson can not use JDK functionality for detecting Record identifying aspects, it would have to be based on something else that differs between records and non-static inner classes.

As a work-around, is it possible to mark records as static (even if it makes no difference).

[DasBrain]

Records are implicitly static. So Modifier.isStatic(type.getModifiers()) returns true on them.
This is not true for local classes, as they can not be static (yet).

In com.fasterxml.jackson.databind.util.ClassUtil, change Line 130 to:

if (!Modifier.isStatic(type.getModifiers()) && hasEnclosingMethod(type)) {

Also note that Jackson CAN deserialize a record declared inside a class, it just can not deserialize local records.

[cowtowncoder]

Makes sense wrt static, was just guessing on what might be happening based on symptoms (although exception message in desc should actually have pointed me in right direction).

Quick question: line 130 on which branch? Or more importantly, in which method? isNonStaticInnerClass? If so, that'd make sense, check was probably meant to check for enclosing method

[DasBrain]

master branch. I did link the corresponding line.

[cowtowncoder]

Thank you.