Add KeyDeserializer for value class

based ProjectMapK/jackson-module-kogera#224

Author: k163377

src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinKeyDeserializers.kt

@@ -5,6 +5,11 @@ import com.fasterxml.jackson.core.exc.InputCoercionException
 import com.fasterxml.jackson.databind.*
 import com.fasterxml.jackson.databind.deser.std.StdKeyDeserializer
 import com.fasterxml.jackson.databind.deser.std.StdKeyDeserializers
+import com.fasterxml.jackson.databind.exc.InvalidDefinitionException
+import java.lang.reflect.Method
+import kotlin.reflect.KClass
+import kotlin.reflect.full.primaryConstructor
+import kotlin.reflect.jvm.javaMethod
 
 // The reason why key is treated as nullable is to match the tentative behavior of StdKeyDeserializer.
 // If StdKeyDeserializer is modified, need to modify this too.
@@ -65,18 +70,68 @@ internal object ULongKeyDeserializer : StdKeyDeserializer(TYPE_LONG, ULong::clas
     }
 }
 
-internal object KotlinKeyDeserializers : StdKeyDeserializers() {
-    private fun readResolve(): Any = KotlinKeyDeserializers
+// The implementation is designed to be compatible with various creators, just in case.
+internal class ValueClassKeyDeserializer<S, D : Any>(
+    private val creator: Method,
+    private val converter: ValueClassBoxConverter<S, D>
+) : KeyDeserializer() {
+    private val unboxedClass: Class<*> = creator.parameterTypes[0]
 
+    init {
+        creator.apply { if (!this.isAccessible) this.isAccessible = true }
+    }
+
+    // Based on databind error
+    // https://github.com/FasterXML/jackson-databind/blob/341f8d360a5f10b5e609d6ee0ea023bf597ce98a/src/main/java/com/fasterxml/jackson/databind/deser/DeserializerCache.java#L624
+    private fun errorMessage(boxedType: JavaType): String =
+        "Could not find (Map) Key deserializer for types wrapped in $boxedType"
+
+    override fun deserializeKey(key: String?, ctxt: DeserializationContext): Any {
+        val unboxedJavaType = ctxt.constructType(unboxedClass)
+
+        return try {
+            // findKeyDeserializer does not return null, and an exception will be thrown if not found.
+            val value = ctxt.findKeyDeserializer(unboxedJavaType, null).deserializeKey(key, ctxt)
+            @Suppress("UNCHECKED_CAST")
+            converter.convert(creator.invoke(null, value) as S)
+        } catch (e: InvalidDefinitionException) {
+            throw JsonMappingException.from(ctxt, errorMessage(ctxt.constructType(converter.boxedClass.java)), e)
+        }
+    }
+
+    companion object {
+        fun createOrNull(
+            boxedClass: KClass<*>,
+            cache: ReflectionCache
+        ): ValueClassKeyDeserializer<*, *>? {
+            // primaryConstructor.javaMethod for the value class returns constructor-impl
+            // Only primary constructor is allowed as creator, regardless of visibility.
+            // This is because it is based on the WrapsNullableValueClassBoxDeserializer.
+            // Also, as far as I could research, there was no such functionality as JsonKeyCreator,
+            // so it was not taken into account.
+            val creator = boxedClass.primaryConstructor?.javaMethod ?: return null
+            val converter = cache.getValueClassBoxConverter(creator.returnType, boxedClass)
+
+            return ValueClassKeyDeserializer(creator, converter)
+        }
+    }
+}
+
+internal class KotlinKeyDeserializers(private val cache: ReflectionCache) : StdKeyDeserializers() {
     override fun findKeyDeserializer(
         type: JavaType,
         config: DeserializationConfig?,
         beanDesc: BeanDescription?
-    ): KeyDeserializer? = when (type.rawClass) {
-        UByte::class.java -> UByteKeyDeserializer
-        UShort::class.java -> UShortKeyDeserializer
-        UInt::class.java -> UIntKeyDeserializer
-        ULong::class.java -> ULongKeyDeserializer
-        else -> null
+    ): KeyDeserializer? {
+        val rawClass = type.rawClass
+
+        return when {
+            rawClass == UByte::class.java -> UByteKeyDeserializer
+            rawClass == UShort::class.java -> UShortKeyDeserializer
+            rawClass == UInt::class.java -> UIntKeyDeserializer
+            rawClass == ULong::class.java -> ULongKeyDeserializer
+            rawClass.isUnboxableValueClass() -> ValueClassKeyDeserializer.createOrNull(rawClass.kotlin, cache)
+            else -> null
+        }
     }
 }

src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinModule.kt

@@ -130,7 +130,7 @@ class KotlinModule private constructor(
         )
 
         context.addDeserializers(KotlinDeserializers(cache, useJavaDurationConversion))
-        context.addKeyDeserializers(KotlinKeyDeserializers)
+        context.addKeyDeserializers(KotlinKeyDeserializers(cache))
         context.addSerializers(KotlinSerializers())
         context.addKeySerializers(KotlinKeySerializers())