Corrected usages of isNullableType/isMarkedNullable

idea/ide-common/src/org/jetbrains/jet/plugin/util/FuzzyType.kt

@@ -42,7 +42,7 @@ fun CallableDescriptor.fuzzyExtensionReceiverType(): FuzzyType? {
 
 fun FuzzyType.makeNotNullable() = FuzzyType(type.makeNotNullable(), freeParameters)
 fun FuzzyType.makeNullable() = FuzzyType(type.makeNullable(), freeParameters)
-fun FuzzyType.isNullable() = type.isMarkedNullable()
+fun FuzzyType.nullability() = type.nullability()
 
 class FuzzyType(
         val type: JetType,

idea/ide-common/src/org/jetbrains/jet/plugin/util/TypeUtils.kt

@@ -29,6 +29,7 @@ import org.jetbrains.jet.lang.types.isFlexible
 import org.jetbrains.jet.lang.types.flexibility
 import java.util.LinkedHashSet
 import org.jetbrains.jet.lang.types.isDynamic
+import org.jetbrains.jet.lang.types.isNullabilityFlexible
 
 fun JetType.makeNullable() = TypeUtils.makeNullable(this)
 fun JetType.makeNotNullable() = TypeUtils.makeNotNullable(this)
@@ -78,4 +79,18 @@ public fun JetType.getAllReferencedTypes(): Set<JetType> {
 
     addType(this)
     return types
+}
+
+public enum class TypeNullability {
+    NOT_NULL
+    NULLABLE
+    FLEXIBLE
+}
+
+public fun JetType.nullability(): TypeNullability {
+    return when {
+        isNullabilityFlexible() -> TypeNullability.FLEXIBLE
+        TypeUtils.isNullableType(this) -> TypeNullability.NULLABLE
+        else -> TypeNullability.NOT_NULL
+    }
 }

idea/ide-common/src/org/jetbrains/jet/plugin/util/extensionsUtils.kt

@@ -23,7 +23,6 @@ import org.jetbrains.jet.lang.resolve.calls.smartcasts.DataFlowInfo
 import org.jetbrains.jet.lang.resolve.scopes.JetScope
 import org.jetbrains.jet.lang.descriptors.SimpleFunctionDescriptor
 import org.jetbrains.jet.lang.resolve.calls.smartcasts.SmartCastUtils
-import org.jetbrains.jet.lang.types.TypeUtils
 import org.jetbrains.jet.lang.descriptors.DeclarationDescriptor
 
 public enum class CallType {
@@ -79,7 +78,7 @@ public fun CallableDescriptor.substituteExtensionIfCallable(
             .map {
                 var substitutor = extensionReceiverType.checkIsSuperTypeOf(it)
                 // check if we may fail due to receiver expression being nullable
-                if (substitutor == null && TypeUtils.isNullableType(it) && !TypeUtils.isNullableType(extensionReceiverType.type)) {
+                if (substitutor == null && it.nullability() == TypeNullability.NULLABLE && extensionReceiverType.nullability() == TypeNullability.NOT_NULL) {
                     substitutor = extensionReceiverType.checkIsSuperTypeOf(it.makeNotNullable())
                 }
                 substitutor