From 098520de64f0ffddcaf8237bfd0dd343cc1ceb4d Mon Sep 17 00:00:00 2001
From: Mikhail Glukhikh <Mikhail.Glukhikh@jetbrains.com>
Date: Tue, 9 Aug 2016 16:41:30 +0300
Subject: [PATCH] CAST_NEVER_SUCCEEDS: do not report when casting nullable to
 nullable #KT-260 Fixed

---
 .../src/org/jetbrains/kotlin/types/CastDiagnosticsUtil.kt  | 7 +++++--
 .../testData/diagnostics/tests/cast/NullableToNullable.kt  | 7 +++++++
 .../testData/diagnostics/tests/cast/NullableToNullable.txt | 4 ++++
 .../kotlin/checkers/DiagnosticsTestGenerated.java          | 6 ++++++
 4 files changed, 22 insertions(+), 2 deletions(-)
 create mode 100644 compiler/testData/diagnostics/tests/cast/NullableToNullable.kt
 create mode 100644 compiler/testData/diagnostics/tests/cast/NullableToNullable.txt

diff --git a/compiler/frontend/src/org/jetbrains/kotlin/types/CastDiagnosticsUtil.kt b/compiler/frontend/src/org/jetbrains/kotlin/types/CastDiagnosticsUtil.kt
index cc6cc3402db..64d16cdc682 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/types/CastDiagnosticsUtil.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/types/CastDiagnosticsUtil.kt
@@ -37,9 +37,12 @@ object CastDiagnosticsUtil {
             lhsType: KotlinType,
             rhsType: KotlinType,
             platformToKotlinClassMap: PlatformToKotlinClassMap): Boolean {
-        if (KotlinBuiltIns.isNullableNothing(lhsType) && !TypeUtils.isNullableType(rhsType)) return false
+        val rhsNullable = TypeUtils.isNullableType(rhsType)
+        val lhsNullable = TypeUtils.isNullableType(lhsType)
+        if (KotlinBuiltIns.isNullableNothing(lhsType) && !rhsNullable) return false
         if (KotlinBuiltIns.isNothing(rhsType)) return false
-        if (KotlinBuiltIns.isNullableNothing(rhsType)) return TypeUtils.isNullableType(lhsType)
+        if (KotlinBuiltIns.isNullableNothing(rhsType)) return lhsNullable
+        if (lhsNullable && rhsNullable) return true
         if (lhsType.isError) return true
         if (isRelated(lhsType, rhsType, platformToKotlinClassMap)) return true
         // This is an oversimplification (which does not render the method incomplete):
diff --git a/compiler/testData/diagnostics/tests/cast/NullableToNullable.kt b/compiler/testData/diagnostics/tests/cast/NullableToNullable.kt
new file mode 100644
index 00000000000..67a064bd39f
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/cast/NullableToNullable.kt
@@ -0,0 +1,7 @@
+// From KT-13324: always succeeds
+val x = null <!USELESS_CAST!>as String?<!>
+// From KT-260: sometimes succeeds
+fun foo(a: String?): Int? {
+    val c = a as? Int?
+    return c
+}
\ No newline at end of file
diff --git a/compiler/testData/diagnostics/tests/cast/NullableToNullable.txt b/compiler/testData/diagnostics/tests/cast/NullableToNullable.txt
new file mode 100644
index 00000000000..91d2e0b0866
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/cast/NullableToNullable.txt
@@ -0,0 +1,4 @@
+package
+
+public val x: kotlin.String? = null
+public fun foo(/*0*/ a: kotlin.String?): kotlin.Int?
diff --git a/compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java b/compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java
index 3d8d3ab8eae..d4f1e8bcc95 100644
--- a/compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java
+++ b/compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java
@@ -2673,6 +2673,12 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("NullableToNullable.kt")
+            public void testNullableToNullable() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/cast/NullableToNullable.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("WhenErasedDisallowFromAny.kt")
             public void testWhenErasedDisallowFromAny() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/cast/WhenErasedDisallowFromAny.kt");