Support Nothing type in typeOf

The proper support will come in KT-15518, but that would be a breaking
change even for stable Kotlin without kotlin-reflect. Before that issue
is fixed, represent Nothing in types with the Void class, and use a flag
in the no-reflect implementation to remember that it's not actually the
Void class itself.

 #KT-39166 Fixed

compiler/testData/codegen/box/reflection/typeOf/noReflect/nothing_after.kt

@@ -0,0 +1,48 @@
+// !API_VERSION: LATEST
+// !USE_EXPERIMENTAL: kotlin.ExperimentalStdlibApi
+// TARGET_BACKEND: JVM
+// WITH_RUNTIME
+// FILE: box.kt
+
+package test
+
+import kotlin.reflect.KType
+import kotlin.reflect.KTypeParameter
+import kotlin.reflect.typeOf
+import kotlin.test.assertEquals
+import kotlin.test.assertNotEquals
+
+class C<V>(v: V)
+
+fun <T : Nothing?> nothingBound() =
+    (typeOf<C<T>>().arguments.single().type!!.classifier as KTypeParameter).upperBounds.single()
+
+fun check(expected: String, actual: KType) {
+    assertEquals(expected + " (Kotlin reflection is not available)", actual.toString())
+}
+
+fun box(): String {
+    check("test.C<kotlin.Nothing>", typeOf<C<Nothing>>())
+    check("test.C<kotlin.Nothing?>", typeOf<C<Nothing?>>())
+    check("kotlin.Nothing?", nothingBound<Nothing?>())
+
+    // String representation of platform types does not differ from non-nullable types in the stdlib implementation (without reflect).
+    check("test.C<kotlin.Nothing>", returnTypeOf { C(J.platformType<Nothing>()) })
+
+    // Such type's classifier is still Void::class, until KT-15518 is fixed.
+    // TODO: support a special KClass instance for Nothing (KT-15518).
+    assertEquals(Void::class, typeOf<C<Nothing>>().arguments.single().type!!.classifier)
+
+    assertNotEquals(typeOf<C<Nothing>>(), typeOf<C<Void>>())
+
+    return "OK"
+}
+
+inline fun <reified Z> returnTypeOf(block: () -> Z) =
+    typeOf<Z>()
+
+// FILE: J.java
+
+public class J {
+    public static <X> X platformType() { return null; }
+}

compiler/testData/codegen/box/reflection/typeOf/noReflect/nothing_before.kt

@@ -0,0 +1,44 @@
+// !API_VERSION: 1.5
+// !USE_EXPERIMENTAL: kotlin.ExperimentalStdlibApi
+// TARGET_BACKEND: JVM
+// WITH_RUNTIME
+// FILE: box.kt
+
+package test
+
+import kotlin.reflect.KType
+import kotlin.reflect.KTypeParameter
+import kotlin.reflect.typeOf
+import kotlin.test.assertEquals
+
+class C<V>(v: V)
+
+fun <T : Nothing?> nothingBound() =
+    (typeOf<C<T>>().arguments.single().type!!.classifier as KTypeParameter).upperBounds.single()
+
+fun check(expected: String, actual: KType) {
+    assertEquals(expected + " (Kotlin reflection is not available)", actual.toString())
+}
+
+fun box(): String {
+    check("test.C<java.lang.Void>", typeOf<C<Nothing>>())
+    check("test.C<java.lang.Void?>", typeOf<C<Nothing?>>())
+    check("java.lang.Void?", nothingBound<Nothing?>())
+
+    check("test.C<java.lang.Void>", returnTypeOf { C(J.platformType<Nothing>()) })
+
+    assertEquals(Void::class, typeOf<C<Nothing>>().arguments.single().type!!.classifier)
+
+    assertEquals(typeOf<C<Nothing>>(), typeOf<C<Void>>())
+
+    return "OK"
+}
+
+inline fun <reified Z> returnTypeOf(block: () -> Z) =
+    typeOf<Z>()
+
+// FILE: J.java
+
+public class J {
+    public static <X> X platformType() { return null; }
+}

compiler/testData/codegen/box/reflection/typeOf/nothing_after.kt

@@ -0,0 +1,47 @@
+// !API_VERSION: LATEST
+// !USE_EXPERIMENTAL: kotlin.ExperimentalStdlibApi
+// TARGET_BACKEND: JVM
+// WITH_REFLECT
+// FILE: box.kt
+
+package test
+
+import kotlin.reflect.KType
+import kotlin.reflect.KTypeParameter
+import kotlin.reflect.typeOf
+import kotlin.test.assertEquals
+import kotlin.test.assertNotEquals
+
+class C<V>(v: V)
+
+fun <T : Nothing?> nothingBound() =
+    (typeOf<C<T>>().arguments.single().type!!.classifier as KTypeParameter).upperBounds.single()
+
+fun check(expected: String, actual: KType) {
+    assertEquals(expected, actual.toString())
+}
+
+fun box(): String {
+    check("test.C<kotlin.Nothing>", typeOf<C<Nothing>>())
+    check("test.C<kotlin.Nothing?>", typeOf<C<Nothing?>>())
+    check("kotlin.Nothing?", nothingBound<Nothing?>())
+
+    check("test.C<kotlin.Nothing!>", returnTypeOf { C(J.platformType<Nothing>()) })
+
+    // Such type's classifier is still Void::class, until KT-15518 is fixed.
+    // TODO: support a special KClass instance for Nothing (KT-15518).
+    assertEquals(Void::class, typeOf<C<Nothing>>().arguments.single().type!!.classifier)
+
+    assertNotEquals(typeOf<C<Nothing>>(), typeOf<C<Void>>())
+
+    return "OK"
+}
+
+inline fun <reified Z> returnTypeOf(block: () -> Z) =
+    typeOf<Z>()
+
+// FILE: J.java
+
+public class J {
+    public static <X> X platformType() { return null; }
+}

compiler/testData/codegen/box/reflection/typeOf/nothing_before.kt

@@ -0,0 +1,44 @@
+// !API_VERSION: 1.5
+// !USE_EXPERIMENTAL: kotlin.ExperimentalStdlibApi
+// TARGET_BACKEND: JVM
+// WITH_REFLECT
+// FILE: box.kt
+
+package test
+
+import kotlin.reflect.KType
+import kotlin.reflect.KTypeParameter
+import kotlin.reflect.typeOf
+import kotlin.test.assertEquals
+
+class C<V>(v: V)
+
+fun <T : Nothing?> nothingBound() =
+    (typeOf<C<T>>().arguments.single().type!!.classifier as KTypeParameter).upperBounds.single()
+
+fun check(expected: String, actual: KType) {
+    assertEquals(expected, actual.toString())
+}
+
+fun box(): String {
+    check("test.C<java.lang.Void>", typeOf<C<Nothing>>())
+    check("test.C<java.lang.Void?>", typeOf<C<Nothing?>>())
+    check("kotlin.Nothing?", nothingBound<Nothing?>())
+
+    check("test.C<java.lang.Void>", returnTypeOf { C(J.platformType<Nothing>()) })
+
+    assertEquals(Void::class, typeOf<C<Nothing>>().arguments.single().type!!.classifier)
+
+    assertEquals(typeOf<C<Nothing>>(), typeOf<C<Void>>())
+
+    return "OK"
+}
+
+inline fun <reified Z> returnTypeOf(block: () -> Z) =
+    typeOf<Z>()
+
+// FILE: J.java
+
+public class J {
+    public static <X> X platformType() { return null; }
+}