[NI] Refine nullability for CST of types with undefined nullability

core/descriptors/src/org/jetbrains/kotlin/types/SpecialTypes.kt

@@ -20,9 +20,9 @@ import org.jetbrains.kotlin.descriptors.TypeParameterDescriptor
 import org.jetbrains.kotlin.descriptors.annotations.Annotations
 import org.jetbrains.kotlin.resolve.scopes.MemberScope
 import org.jetbrains.kotlin.storage.StorageManager
-import org.jetbrains.kotlin.types.checker.NewCapturedType
 import org.jetbrains.kotlin.types.checker.NewTypeVariableConstructor
 import org.jetbrains.kotlin.types.checker.NullabilityChecker
+import org.jetbrains.kotlin.types.typeUtil.canHaveUndefinedNullability
 
 abstract class DelegatingSimpleType : SimpleType() {
     protected abstract val delegate: SimpleType
@@ -82,12 +82,7 @@ class DefinitelyNotNullType private constructor(val original: SimpleType) : Dele
         }
 
         fun makesSenseToBeDefinitelyNotNull(type: UnwrappedType): Boolean =
-                canHaveUndefinedNullability(type) && !NullabilityChecker.isSubtypeOfAny(type)
-
-        private fun canHaveUndefinedNullability(type: UnwrappedType): Boolean =
-                type.constructor is NewTypeVariableConstructor ||
-                type.constructor.declarationDescriptor is TypeParameterDescriptor ||
-                type is NewCapturedType
+                type.canHaveUndefinedNullability() && !NullabilityChecker.isSubtypeOfAny(type)
     }
 
     override val delegate: SimpleType

core/descriptors/src/org/jetbrains/kotlin/types/TypeUtils.kt

@@ -23,6 +23,8 @@ import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.calls.inference.isCaptured
 import org.jetbrains.kotlin.types.*
 import org.jetbrains.kotlin.types.checker.KotlinTypeChecker
+import org.jetbrains.kotlin.types.checker.NewCapturedType
+import org.jetbrains.kotlin.types.checker.NewTypeVariableConstructor
 import java.util.*
 
 enum class TypeNullability {
@@ -201,3 +203,8 @@ fun KotlinType.containsTypeProjectionsInTopLevelArguments(): Boolean {
     val possiblyInnerType = buildPossiblyInnerType() ?: return false
     return possiblyInnerType.arguments.any { it.isStarProjection || it.projectionKind != Variance.INVARIANT }
 }
+
+fun UnwrappedType.canHaveUndefinedNullability(): Boolean =
+        constructor is NewTypeVariableConstructor ||
+        constructor.declarationDescriptor is TypeParameterDescriptor ||
+        this is NewCapturedType

core/descriptors/src/org/jetbrains/kotlin/types/checker/NewKotlinTypeChecker.kt

@@ -398,6 +398,9 @@ object NullabilityChecker {
     fun isSubtypeOfAny(type: UnwrappedType): Boolean =
             TypeCheckerContext(false).hasNotNullSupertype(type.lowerIfFlexible(), SupertypesPolicy.LowerIfFlexible)
 
+    fun hasPathByNotMarkedNullableNodes(start: SimpleType, end: TypeConstructor) =
+            TypeCheckerContext(false).hasPathByNotMarkedNullableNodes(start, end)
+
     private fun TypeCheckerContext.runIsPossibleSubtype(subType: SimpleType, superType: SimpleType): Boolean {
         // it makes for case String? & Any <: String
         assert(subType.isIntersectionType || subType.isSingleClassifierType || subType.isAllowedTypeVariable) {