fix: Assume kotlin.Pair as a normal data class instead of an union

src/main/kotlin/com/github/avrokotlin/avro4k/schema/SchemaFor.kt

@@ -7,7 +7,14 @@ import com.github.avrokotlin.avro4k.RecordNaming
 import kotlinx.serialization.ExperimentalSerializationApi
 import kotlinx.serialization.InternalSerializationApi
 import kotlinx.serialization.SerializationException
-import kotlinx.serialization.descriptors.*
+import kotlinx.serialization.descriptors.PolymorphicKind
+import kotlinx.serialization.descriptors.PrimitiveKind
+import kotlinx.serialization.descriptors.SerialDescriptor
+import kotlinx.serialization.descriptors.SerialKind
+import kotlinx.serialization.descriptors.StructureKind
+import kotlinx.serialization.descriptors.capturedKClass
+import kotlinx.serialization.descriptors.elementNames
+import kotlinx.serialization.descriptors.getContextualDescriptor
 import kotlinx.serialization.modules.SerializersModule
 import kotlinx.serialization.serializerOrNull
 import org.apache.avro.Schema
@@ -63,36 +70,6 @@ class EnumSchemaFor(
    }
 }
 
-@ExperimentalSerializationApi
-class PairSchemaFor(private val descriptor: SerialDescriptor,
-                    private val configuration: AvroConfiguration,
-                    private val serializersModule: SerializersModule,
-                    private val resolvedSchemas: MutableMap<RecordNaming, Schema>
-) : SchemaFor {
-
-   override fun schema(): Schema {
-      val a = schemaFor(
-         serializersModule,
-         descriptor.getElementDescriptor(0),
-         descriptor.getElementAnnotations(0),
-         configuration,
-         resolvedSchemas
-      )
-      val b = schemaFor(
-         serializersModule,
-         descriptor.getElementDescriptor(1),
-         descriptor.getElementAnnotations(1),
-         configuration,
-         resolvedSchemas
-      )
-      return SchemaBuilder.unionOf()
-         .type(a.schema())
-         .and()
-         .type(b.schema())
-         .endUnion()
-   }
-}
-
 @ExperimentalSerializationApi
 class ListSchemaFor(private val descriptor: SerialDescriptor,
                     private val serializersModule: SerializersModule,
@@ -206,11 +183,7 @@ fun schemaFor(serializersModule: SerializersModule,
             resolvedSchemas
          )
 
-         StructureKind.CLASS, StructureKind.OBJECT -> when (descriptor.serialName) {
-            "kotlin.Pair" -> PairSchemaFor(descriptor, configuration, serializersModule, resolvedSchemas)
-            else -> ClassSchemaFor(descriptor, configuration, serializersModule, resolvedSchemas)
-         }
-
+         StructureKind.CLASS, StructureKind.OBJECT -> ClassSchemaFor(descriptor, configuration, serializersModule, resolvedSchemas)
          StructureKind.LIST -> ListSchemaFor(descriptor, serializersModule, configuration, resolvedSchemas)
          StructureKind.MAP -> MapSchemaFor(descriptor, serializersModule, configuration, resolvedSchemas)
          is PolymorphicKind -> UnionSchemaFor(descriptor, configuration, serializersModule, resolvedSchemas)
@@ -224,4 +197,4 @@ fun schemaFor(serializersModule: SerializersModule,
 // copy-paste from kotlinx serialization because it internal
 @ExperimentalSerializationApi
 internal val SerialDescriptor.unwrapValueClass: SerialDescriptor
-   get() = if (isInline) getElementDescriptor(0) else this
+   get() = if (isInline) getElementDescriptor(0) else this

src/test/kotlin/com/github/avrokotlin/avro4k/io/RecursiveIoTest.kt

@@ -8,11 +8,9 @@ import com.github.avrokotlin.avro4k.schema.Level4
 import com.github.avrokotlin.avro4k.schema.RecursiveClass
 import com.github.avrokotlin.avro4k.schema.RecursiveListItem
 import com.github.avrokotlin.avro4k.schema.RecursiveMapValue
-import com.github.avrokotlin.avro4k.schema.RecursivePair
-import io.kotest.matchers.shouldBe
 import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
 import io.kotest.matchers.types.shouldBeInstanceOf
-import org.apache.avro.generic.GenericData
 import org.apache.avro.generic.GenericRecord
 import org.apache.avro.util.Utf8
 
@@ -54,24 +52,6 @@ class RecursiveIoTest : StringSpec({
       }
    }
 
-   "read / write direct recursive pair" {
-      writeRead(RecursivePair(1, (RecursivePair(2, null) to RecursivePair(3, null))), RecursivePair.serializer())
-      writeRead(RecursivePair(1, (RecursivePair(2, null) to RecursivePair(3, null))), RecursivePair.serializer()) {
-         it["payload"] shouldBe 1
-         it["pair"].shouldBeInstanceOf<GenericData.Record>()
-         val first = (it["pair"] as GenericData.Record)["first"]
-         first.shouldBeInstanceOf<GenericRecord>()
-         first.schema shouldBe Avro.default.schema(RecursivePair.serializer())
-         first["payload"] shouldBe 2
-         first["pair"] shouldBe null
-         val second = (it["pair"] as GenericData.Record)["second"]
-         second.shouldBeInstanceOf<GenericRecord>()
-         second.schema shouldBe Avro.default.schema(RecursivePair.serializer())
-         second["payload"] shouldBe 3
-         second["pair"] shouldBe null
-      }
-   }
-
    "read / write nested recursive classes" {
       writeRead(Level1(Level2(Level3(Level4(Level1(null))))), Level1.serializer())
       writeRead(Level1(Level2(Level3(Level4(Level1(null))))), Level1.serializer()) {

src/test/kotlin/com/github/avrokotlin/avro4k/schema/RecursiveSchemaTest.kt

@@ -1,8 +1,8 @@
 package com.github.avrokotlin.avro4k.schema
 
 import com.github.avrokotlin.avro4k.Avro
-import io.kotest.matchers.shouldBe
 import io.kotest.core.spec.style.FunSpec
+import io.kotest.matchers.shouldBe
 import kotlinx.serialization.Serializable
 
 @Serializable
@@ -14,9 +14,6 @@ data class RecursiveListItem(val payload: Int, val list: List<RecursiveListItem>
 @Serializable
 data class RecursiveMapValue(val payload: Int, val map: Map<String, RecursiveMapValue>?)
 
-@Serializable
-data class RecursivePair(val payload: Int, val pair: Pair<RecursivePair, RecursivePair>?)
-
 @Serializable
 data class Level4(val level1: Level1)
 
@@ -49,12 +46,6 @@ class RecursiveSchemaTest : FunSpec({
       schema.toString(true) shouldBe expected.toString(true)
    }
 
-   test("accept direct recursive pairs") {
-      val expected = org.apache.avro.Schema.Parser().parse(this::class.java.getResourceAsStream("/recursive_pair.json"))
-      val schema = Avro.default.schema(RecursivePair.serializer())
-      schema.toString(true) shouldBe expected.toString(true)
-   }
-
    test("accept nested recursive classes") {
       val expected = org.apache.avro.Schema.Parser().parse(this::class.java.getResourceAsStream("/recursive_nested.json"))
       val schema = Avro.default.schema(Level1.serializer())