Handle kotlin / JVM erasure of types (#1295)

* Handle kotlin / JVM erasure of types

It has been observed that the Kotlin can behave
differently during reflection and return Type<Object>
where normally it would report the correct type.

Checking for erasure allows the bson-kotlin library to handle
these cases and return the expected type.

JAVA-5292

Author: rozza

bson-kotlin/src/main/kotlin/org/bson/codecs/kotlin/DataClassCodec.kt

@@ -23,12 +23,14 @@ import kotlin.reflect.KParameter
 import kotlin.reflect.KProperty1
 import kotlin.reflect.KType
 import kotlin.reflect.KTypeParameter
+import kotlin.reflect.KTypeProjection
 import kotlin.reflect.full.createType
 import kotlin.reflect.full.findAnnotation
 import kotlin.reflect.full.findAnnotations
 import kotlin.reflect.full.hasAnnotation
 import kotlin.reflect.full.primaryConstructor
 import kotlin.reflect.jvm.javaType
+import kotlin.reflect.jvm.jvmErasure
 import org.bson.BsonReader
 import org.bson.BsonType
 import org.bson.BsonWriter
@@ -199,7 +201,7 @@ internal data class DataClassCodec<T : Any>(
                     codecRegistry.getCodec(
                         kParameter,
                         (kParameter.type.classifier as KClass<Any>).javaObjectType,
-                        kParameter.type.arguments.mapNotNull { typeMap[it.type] ?: it.type?.javaType }.toList())
+                        kParameter.type.arguments.mapNotNull { typeMap[it.type] ?: computeJavaType(it) }.toList())
                 }
                 is KTypeParameter -> {
                     when (val pType = typeMap[kParameter.type] ?: kParameter.type.javaType) {
@@ -219,6 +221,13 @@ internal data class DataClassCodec<T : Any>(
                     "Could not find codec for ${kParameter.name} with type ${kParameter.type}")
         }
 
+        private fun computeJavaType(kTypeProjection: KTypeProjection): Type? {
+            val javaType: Type = kTypeProjection.type?.javaType!!
+            return if (javaType == Any::class.java) {
+                kTypeProjection.type?.jvmErasure?.javaObjectType
+            } else javaType
+        }
+
         @Suppress("UNCHECKED_CAST")
         private fun CodecRegistry.getCodec(kParameter: KParameter, clazz: Class<Any>, types: List<Type>): Codec<Any> {
             val codec =

bson-kotlin/src/test/kotlin/org/bson/codecs/kotlin/DataClassCodecProviderTest.kt

@@ -20,11 +20,22 @@ import kotlin.test.assertEquals
 import kotlin.test.assertNotNull
 import kotlin.test.assertNull
 import kotlin.test.assertTrue
+import kotlin.time.Duration
+import org.bson.BsonReader
+import org.bson.BsonWriter
+import org.bson.codecs.Codec
+import org.bson.codecs.DecoderContext
+import org.bson.codecs.EncoderContext
 import org.bson.codecs.configuration.CodecConfigurationException
+import org.bson.codecs.configuration.CodecRegistries.fromCodecs
+import org.bson.codecs.configuration.CodecRegistries.fromProviders
+import org.bson.codecs.configuration.CodecRegistries.fromRegistries
 import org.bson.codecs.kotlin.samples.DataClassParameterized
+import org.bson.codecs.kotlin.samples.DataClassWithJVMErasure
 import org.bson.codecs.kotlin.samples.DataClassWithSimpleValues
 import org.bson.conversions.Bson
 import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertDoesNotThrow
 import org.junit.jupiter.api.assertThrows
 
 class DataClassCodecProviderTest {
@@ -59,4 +70,23 @@ class DataClassCodecProviderTest {
         assertTrue { codec is DataClassCodec }
         assertEquals(DataClassWithSimpleValues::class.java, codec.encoderClass)
     }
+
+    @Test
+    fun shouldBeAbleHandleDataClassWithJVMErasure() {
+
+        class DurationCodec : Codec<Duration> {
+            override fun encode(writer: BsonWriter, value: Duration, encoderContext: EncoderContext) = TODO()
+            override fun getEncoderClass(): Class<Duration> = Duration::class.java
+            override fun decode(reader: BsonReader, decoderContext: DecoderContext): Duration = TODO()
+        }
+
+        val registry =
+            fromRegistries(
+                fromCodecs(DurationCodec()), fromProviders(DataClassCodecProvider()), Bson.DEFAULT_CODEC_REGISTRY)
+
+        val codec = assertDoesNotThrow { registry.get(DataClassWithJVMErasure::class.java) }
+        assertNotNull(codec)
+        assertTrue { codec is DataClassCodec }
+        assertEquals(DataClassWithJVMErasure::class.java, codec.encoderClass)
+    }
 }

bson-kotlin/src/test/kotlin/org/bson/codecs/kotlin/samples/DataClasses.kt

@@ -15,6 +15,7 @@
  */
 package org.bson.codecs.kotlin.samples
 
+import kotlin.time.Duration
 import org.bson.BsonDocument
 import org.bson.BsonMaxKey
 import org.bson.BsonType
@@ -159,3 +160,5 @@ data class DataClassWithFailingInit(val id: String) {
 }
 
 data class DataClassWithSequence(val value: Sequence<String>)
+
+data class DataClassWithJVMErasure(val duration: Duration, val ints: List<Int>)