Correctly support nullability in type arguments for serializer<T>() intrinsic.

Nullability info should be added to TYPE_OF operation marker.

Fixes https://github.com/Kotlin/kotlinx.serialization/issues/2265

plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializationJvmIrIntrinsicSupport.kt

@@ -225,13 +225,13 @@ class SerializationJvmIrIntrinsicSupport(
      *
      * Operation detection in new compilers performed by voidMagicApiCall.
      */
-    private fun InstructionAdapter.putReifyMarkerIfNeeded(type: KotlinTypeMarker, intrinsicType: IntrinsicType): Boolean =
+    private fun InstructionAdapter.putReifyMarkerIfNeeded(type: IrType, intrinsicType: IntrinsicType): Boolean =
         with(typeSystemContext) {
             val typeDescriptor = type.typeConstructor().getTypeParameterClassifier()
             if (typeDescriptor != null) { // need further reification
                 ReifiedTypeInliner.putReifiedOperationMarkerIfNeeded(
                     typeDescriptor,
-                    false,
+                    type.isMarkedNullable(),
                     ReifiedTypeInliner.OperationKind.TYPE_OF,
                     this@putReifyMarkerIfNeeded,
                     typeSystemContext

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

@@ -0,0 +1,49 @@
+// TARGET_BACKEND: JVM_IR
+
+// WITH_STDLIB
+
+import kotlinx.serialization.*
+import kotlinx.serialization.json.*
+import kotlinx.serialization.internal.*
+import kotlinx.serialization.descriptors.*
+import kotlinx.serialization.modules.*
+import java.lang.AssertionError
+
+inline fun <reified T: Any?> listOfNullable(): KSerializer<List<T?>> = serializer<List<T?>>()
+inline fun <reified T: Any> listOfNullableWithNonNullBound(): KSerializer<List<T?>> = serializer<List<T?>>()
+inline fun <reified T> listOfNullableNoExplicitBound(): KSerializer<List<T?>> = serializer<List<T?>>()
+inline fun <reified T> listOfNullableWithCast(): KSerializer<List<Any?>> = serializer<List<T?>>() as KSerializer<List<Any?>>
+inline fun <reified T> listOfUnspecifiedNullability(): KSerializer<List<T>> = serializer<List<T>>()
+
+inline fun <reified T> getSer(module: SerializersModule): KSerializer<T> {
+    return module.serializer<T>()
+}
+
+fun check(shouldBeNullable: Boolean, descriptor: SerialDescriptor) {
+    if (shouldBeNullable == descriptor.isNullable) return
+    if (shouldBeNullable) throw java.lang.AssertionError("Should be nullable, but is not: $descriptor")
+    throw java.lang.AssertionError("Should not be nullable, but it is: $descriptor")
+}
+
+fun box(): String {
+    check(false, serializer<String>().descriptor)
+    check(true, serializer<String?>().descriptor)
+
+    check(false, serializer<List<String>>().descriptor.elementDescriptors.first())
+    check(true, serializer<List<String?>>().descriptor.elementDescriptors.first())
+    check(true, serializer<List<String>?>().descriptor)
+
+    check(true, listOfNullable<String>().descriptor.elementDescriptors.first())
+    check(true, listOfNullableNoExplicitBound<String>().descriptor.elementDescriptors.first())
+    check(true, listOfNullableWithNonNullBound<String>().descriptor.elementDescriptors.first())
+    check(true, listOfNullableWithCast<String>().descriptor.elementDescriptors.first())
+
+    check(false, listOfUnspecifiedNullability<String>().descriptor.elementDescriptors.first())
+    check(true, listOfUnspecifiedNullability<String?>().descriptor.elementDescriptors.first())
+
+    val module = EmptySerializersModule()
+    check(false, getSer<String>(module).descriptor)
+    check(true, getSer<String?>(module).descriptor)
+
+    return "OK"
+}

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

@@ -47,4 +47,4 @@ fun box(): String {
         getListSer<Box<*>>()
     }
     return "OK"
-}
+}

plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirLightTreeBlackBoxTestGenerated.java

@@ -135,6 +135,12 @@ public class SerializationFirLightTreeBlackBoxTestGenerated extends AbstractSeri
             runTest("plugins/kotlinx-serialization/testData/boxIr/intrinsicsBox.kt");
         }
 
+        @Test
+        @TestMetadata("intrinsicsNullable.kt")
+        public void testIntrinsicsNullable() throws Exception {
+            runTest("plugins/kotlinx-serialization/testData/boxIr/intrinsicsNullable.kt");
+        }
+
         @Test
         @TestMetadata("intrinsicsStarProjections.kt")
         public void testIntrinsicsStarProjections() throws Exception {

plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationIrBoxTestGenerated.java

@@ -133,6 +133,12 @@ public class SerializationIrBoxTestGenerated extends AbstractSerializationIrBoxT
         runTest("plugins/kotlinx-serialization/testData/boxIr/intrinsicsBox.kt");
     }
 
+    @Test
+    @TestMetadata("intrinsicsNullable.kt")
+    public void testIntrinsicsNullable() throws Exception {
+        runTest("plugins/kotlinx-serialization/testData/boxIr/intrinsicsNullable.kt");
+    }
+
     @Test
     @TestMetadata("intrinsicsStarProjections.kt")
     public void testIntrinsicsStarProjections() throws Exception {