From 687698da9a9a0fc193d89c2a131d52576449af71 Mon Sep 17 00:00:00 2001
From: Mikhail Glukhikh <Mikhail.Glukhikh@jetbrains.com>
Date: Tue, 9 Aug 2016 16:48:11 +0300
Subject: [PATCH] Do not report USELESS_CAST when casting null to nullable
 (special case)

---
 .../kotlin/types/expressions/BasicExpressionTypingVisitor.java  | 1 +
 compiler/testData/diagnostics/tests/cast/NullableToNullable.kt  | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/BasicExpressionTypingVisitor.java b/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/BasicExpressionTypingVisitor.java
index ab5db78f9f1..74c323bbde7 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/BasicExpressionTypingVisitor.java
+++ b/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/BasicExpressionTypingVisitor.java
@@ -331,6 +331,7 @@ public class BasicExpressionTypingVisitor extends ExpressionTypingVisitor {
     }
 
     private static boolean isUpcast(KotlinType candidateType, KotlinType targetType, KotlinTypeChecker typeChecker) {
+        if (KotlinBuiltIns.isNullableNothing(candidateType)) return false;
         if (!typeChecker.isSubtypeOf(candidateType, targetType)) return false;
 
         if (isFunctionType(candidateType) && isFunctionType(targetType)) {
diff --git a/compiler/testData/diagnostics/tests/cast/NullableToNullable.kt b/compiler/testData/diagnostics/tests/cast/NullableToNullable.kt
index 67a064bd39f..cd76ae9a3c2 100644
--- a/compiler/testData/diagnostics/tests/cast/NullableToNullable.kt
+++ b/compiler/testData/diagnostics/tests/cast/NullableToNullable.kt
@@ -1,5 +1,5 @@
 // From KT-13324: always succeeds
-val x = null <!USELESS_CAST!>as String?<!>
+val x = null as String?
 // From KT-260: sometimes succeeds
 fun foo(a: String?): Int? {
     val c = a as? Int?