The readValue fails for maps with inline-value-class as key

[TobseF]

Search before asking

• I searched in the issues and found nothing similar.
  Sorry, seems to be a duplicate of Cannot use value class as map key in 2.17 #777
• I searched in the issues of databind and other modules used and found nothing similar.
• I have confirmed that the problem only occurs when using Kotlin.

Describe the bug

Using a Kotlin inline-value-class a key in map breaks the Jackson serialization.
For example, it's not possible to read a map of type Map<Index, Int> where Index is a value class:

@JvmInline
value class Index(val value: Int = 0)

                       // ↱ the `map` uses a value class `Index` as key
data class FooMapKey(val map : MutableMap<Index, Int> = mutableMapOf())

Reading a JSON file with such a map fails:

val mapper = jacksonObjectMapper().registerKotlinModule()
        
val fooJson = "{ "map": { "1": 42 } }"
val readValue = mapper.readValue<FooField>(fooJson) // ⚡`Cannot find a (Map) Key deserializer `

It fails during readValue(json) with the error:

Cannot find a (Map) Key deserializer for type [simple type, class de.itscope.catalog.pricelist.ParseValueClassTest$Index]
 at [Source: REDACTED (`StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION` disabled); line: 1, column: 1]
com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot find a (Map) Key deserializer for type [simple type, class de.itscope.catalog.pricelist.ParseValueClassTest$Index]
 at [Source: REDACTED (`StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION` disabled); line: 1, column: 1]
	at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67)

It's does not belong to the input. It even fails if the map is empty:

{
  "map" : { }
}

Using a value class as map-key, helps a lot to make map access type safe and improve the readability of code.
The other way around already works — Using the value class as value. So it's possible to save this class:

data class FooMapValue(val map : MutableMap<Int, Index> = mutableMapOf())

To Reproduce

@Test
fun parseFooMapTest(){
    val mapper = jacksonObjectMapper().registerKotlinModule()

    val foo = FooMapKey().apply {
        map[Index(1)] = 42
    }
    val fooJson = mapper.writeValueAsString(foo)
    val readValue = mapper.readValue<FooMapKey>(fooJson)   // ⚡`Cannot find a (Map) Key deserializer `

    assertEquals(foo, readValue)
}

Expected behavior

The mapper.readValue<FooMapKey>(fooJson) should read the JSON and deserialize into a FooMapKey.

Versions

Kotlin: 2.0.0
Jackson-module-kotlin: 2.17.2
Jackson-databind: 2.17.2

Additional context

You can find a detailed test example for the problem here:
ParseValueClassMapTest.kt

[cowtowncoder]

Correct: for now, you need to register a key deserializer for things other than basic scalar JDK types (Strings, primitives/wrappers, Enums).

[k163377]

@TobseF
At present, key deserialisers have to be defined manually.
There are many dependencies on specific implementations, but the following work except in edge cases.
https://github.com/ProjectMapK/jackson-module-kogera/pull/224/files#diff-b03a6f91081da3aa22c53b161b0a2f6f1a0cf4ba318329907046b5f5335b17c8

By the way, if the content is a complete duplication, could you close it?