Call a specified function in intrinsic if polymorphic serializer is provided for interface.

This prioritizes module contents over default polymorphic serializer.

See https://github.com/Kotlin/kotlinx.serialization/issues/2060 and https://github.com/Kotlin/kotlinx.serialization/pull/2565

plugins/kotlinx-serialization/testData/boxIr/intrinsicsPolymorphicPriority.kt

@@ -0,0 +1,83 @@
+// TARGET_BACKEND: JVM_IR
+
+// WITH_STDLIB
+
+// FILE: stub.kt
+
+@file:JvmName("SerializersKt")
+
+package kotlinx.serialization
+
+import kotlin.reflect.KClass
+import kotlinx.serialization.modules.*
+
+// Copy of runtime function from kotlinx-serialization 1.7.0
+fun moduleThenPolymorphic(module: SerializersModule, kClass: KClass<*>): KSerializer<*> {
+    return module.getContextual(kClass) ?: PolymorphicSerializer(kClass)
+}
+
+fun moduleThenPolymorphic(module: SerializersModule, kClass: KClass<*>, argSerializers: Array<KSerializer<*>>): KSerializer<*> {
+    return module.getContextual(kClass, argSerializers.asList()) ?: PolymorphicSerializer(kClass)
+}
+
+// FILE: test.kt
+
+package a
+
+import kotlinx.serialization.*
+import kotlinx.serialization.descriptors.*
+import kotlinx.serialization.encoding.*
+import kotlinx.serialization.modules.*
+import kotlin.reflect.KClass
+import kotlin.test.*
+
+interface IApiError {
+    val code: Int
+}
+
+object MyApiErrorSerializer : KSerializer<IApiError> {
+    override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("IApiError", PrimitiveKind.INT)
+
+    override fun serialize(encoder: Encoder, value: IApiError) {
+        TODO()
+    }
+
+    override fun deserialize(decoder: Decoder): IApiError {
+        TODO()
+    }
+}
+
+interface Parametrized<T> {
+    val param: List<T>
+}
+
+class PSer<T>(val tSer: KSerializer<T>) : KSerializer<Parametrized<T>> {
+    override val descriptor: SerialDescriptor
+        get() = buildClassSerialDescriptor("PSer<${tSer.descriptor.serialName}>")
+
+    override fun serialize(encoder: Encoder, value: Parametrized<T>) {
+        TODO("Not yet implemented")
+    }
+
+    override fun deserialize(decoder: Decoder): Parametrized<T> {
+        TODO("Not yet implemented")
+    }
+}
+
+fun testParametrized() {
+    val md = SerializersModule {
+        contextual(Parametrized::class) { PSer(it[0]) }
+    }
+    assertEquals("PSer<kotlin.String>", md.serializer<Parametrized<String>>().descriptor.serialName)
+}
+
+fun box(): String {
+    val module = serializersModuleOf(IApiError::class, MyApiErrorSerializer)
+    assertSame(MyApiErrorSerializer, module.serializer<IApiError>() as KSerializer<IApiError>)
+    assertEquals(
+        MyApiErrorSerializer.descriptor,
+        module.serializer<List<IApiError>>().descriptor.elementDescriptors.first()
+    )
+    testParametrized()
+    return "OK"
+}