FasterXML / FasterXML/jackson-module-scala

Case class deserialized as Map2 for unusual path-dependent types

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Dominant language
Scala
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Description

Deserialization fails in an unexpected way in following code. No exception is thrown, however `from` field of `Container` is deserialized as `Map` instead of `XY`, the program outputs:

> Container(Map(x -> 0.0, y -> 0.0))

```scala
package my.jackpack

import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.module.scala.DefaultScalaModule
import com.fasterxml.jackson.module.scala.experimental.ScalaObjectMapper

case class XY(x: Double = 0, y: Double = 0)

trait Abstract {
type Vector2f

trait ConstructVector2f {
def apply(x: Double, y: Double): Vector2f
}
implicit val Vector2f: ConstructVector2f
}

object Concrete extends Abstract {
type Vector2f = XY
object Vector2f extends ConstructVector2f {
def apply(x: Double, y: Double) = XY(x, y)
}
}

object Abstract {
val Link: Abstract = Concrete
}

import Abstract.Link.Vector2f

case class Container(from: Vector2f)

object Main extends App {

val mapper = new ObjectMapper with ScalaObjectMapper

mapper.registerModule(DefaultScalaModule)

val input = Container(Vector2f(0,0))

val out = mapper.writeValueAsString(input)

val loaded = mapper.readValue[Container](out)

val xy: Vector2f = loaded.from

println(loaded) // prints "Container(Map(x -> 0.0, y -> 0.0))" instead of "Container(XY(0.0,0.0))"
assert(xy.isInstanceOf[XY]) // fails
}
```

This happens only if the `Vector2f` is used as `import Abstract.Link.Vector2f`. Once you change it to `Concrete.Vector2f` it works fine.

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