Do not annotate Kotlin members returning platform types as @Nullable

This leads to pointless warning in Java code

compiler/backend/src/org/jetbrains/jet/codegen/AnnotationCodegen.java

@@ -34,8 +34,10 @@ import org.jetbrains.jet.lang.resolve.calls.model.ResolvedCall;
 import org.jetbrains.jet.lang.resolve.constants.*;
 import org.jetbrains.jet.lang.resolve.constants.StringValue;
 import org.jetbrains.jet.lang.resolve.name.FqName;
+import org.jetbrains.jet.lang.types.Flexibility;
 import org.jetbrains.jet.lang.types.JetType;
 import org.jetbrains.jet.lang.types.TypeUtils;
+import org.jetbrains.jet.lang.types.TypesPackage;
 import org.jetbrains.jet.lang.types.lang.KotlinBuiltIns;
 import org.jetbrains.org.objectweb.asm.*;
 
@@ -184,6 +186,14 @@ public abstract class AnnotationCodegen {
             return;
         }
 
+        if (TypesPackage.isFlexible(type)) {
+            // A flexible type whose lower bound in not-null and upper bound is nullable, should not be annotated
+            Flexibility flexibility = TypesPackage.flexibility(type);
+            if (!TypeUtils.isNullableType(flexibility.getLowerBound()) && TypeUtils.isNullableType(flexibility.getUpperBound())) {
+                return;
+            }
+        }
+
         boolean isNullableType = TypeUtils.isNullableType(type);
 
         Class<?> annotationClass = isNullableType ? Nullable.class : NotNull.class;

compiler/testData/asJava/lightClasses/nullabilityAnnotations/PlatformTypes.java

@@ -0,0 +1,11 @@
+public final class PlatformTypes implements kotlin.jvm.internal.KObject {
+    public final java.lang.String simplyPlatform() { /* compiled code */ }
+
+    @org.jetbrains.annotations.Nullable
+    public final java.util.List<java.lang.String> bothNullable() { /* compiled code */ }
+
+    @org.jetbrains.annotations.NotNull
+    public final java.util.List<java.lang.String> bothNotNull() { /* compiled code */ }
+
+    public PlatformTypes() { /* compiled code */ }
+}

compiler/testData/asJava/lightClasses/nullabilityAnnotations/PlatformTypes.kt

@@ -0,0 +1,9 @@
+// PlatformTypes
+
+import java.util.Collections
+
+class PlatformTypes {
+    fun simplyPlatform() = Collections.singletonList("")[0]
+    fun bothNullable() = Collections.emptyList<String>() ?: null
+    fun bothNotNull() = Collections.emptyList<String>()!!
+}

compiler/tests/org/jetbrains/jet/asJava/KotlinLightClassTestGenerated.java

@@ -114,6 +114,12 @@ public class KotlinLightClassTestGenerated extends AbstractKotlinLightClassTest
             doTest(fileName);
         }
 
+        @TestMetadata("PlatformTypes.kt")
+        public void testPlatformTypes() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("compiler/testData/asJava/lightClasses/nullabilityAnnotations/PlatformTypes.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("Primitives.kt")
         public void testPrimitives() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("compiler/testData/asJava/lightClasses/nullabilityAnnotations/Primitives.kt");