Reflection: add KType.withNullability

compiler/testData/codegen/box/reflection/mapping/types/withNullability.kt

@@ -0,0 +1,20 @@
+// WITH_REFLECT
+
+import kotlin.reflect.withNullability
+import kotlin.reflect.jvm.javaType
+import kotlin.test.assertEquals
+
+fun nonNull(): String = ""
+fun nullable(): String? = ""
+
+fun box(): String {
+    val nonNull = ::nonNull.returnType
+    val nullable = ::nullable.returnType
+
+    assertEquals(nullable.javaType, nullable.withNullability(false).javaType)
+    assertEquals(nullable.javaType, nullable.withNullability(true).javaType)
+    assertEquals(nonNull.javaType, nonNull.withNullability(false).javaType)
+    assertEquals(nullable.javaType, nonNull.withNullability(true).javaType)
+
+    return "OK"
+}

compiler/testData/codegen/box/reflection/types/withNullability.kt

@@ -0,0 +1,30 @@
+// WITH_REFLECT
+// FILE: J.java
+
+public interface J {
+    String platform();
+}
+
+// FILE: K.kt
+
+import kotlin.reflect.withNullability
+import kotlin.test.assertEquals
+
+fun nonNull(): String = ""
+fun nullable(): String? = ""
+
+fun box(): String {
+    val nonNull = ::nonNull.returnType
+    val nullable = ::nullable.returnType
+    val platform = J::platform.returnType
+
+    assertEquals(nonNull, nullable.withNullability(false))
+    assertEquals(nullable, nullable.withNullability(true))
+    assertEquals(nonNull, nonNull.withNullability(false))
+    assertEquals(nullable, nonNull.withNullability(true))
+
+    assertEquals(nonNull, platform.withNullability(false))
+    assertEquals(nullable, platform.withNullability(true))
+
+    return "OK"
+}