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

compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/NewCommonSuperTypeCalculator.kt

@@ -21,6 +21,7 @@ import org.jetbrains.kotlin.descriptors.annotations.Annotations
 import org.jetbrains.kotlin.types.*
 import org.jetbrains.kotlin.types.checker.*
 import org.jetbrains.kotlin.types.typeUtil.asTypeProjection
+import org.jetbrains.kotlin.types.typeUtil.canHaveUndefinedNullability
 
 object NewCommonSuperTypeCalculator {
 
@@ -61,9 +62,18 @@ object NewCommonSuperTypeCalculator {
         val notAllNotNull = types.any { !NullabilityChecker.isSubtypeOfAny(it) }
         val notNullTypes = if (notAllNotNull) types.map { it.makeNullableAsSpecified(false) } else types
 
-        val commonSuperTypes = commonSuperTypeForNotNullTypes(notNullTypes, depth)
+        val commonSuperType = commonSuperTypeForNotNullTypes(notNullTypes, depth)
+        return if (notAllNotNull)
+            refineNullabilityForUndefinedNullability(types, commonSuperType) ?: commonSuperType.makeNullableAsSpecified(true)
+        else
+            commonSuperType
+    }
 
-        return if (notAllNotNull) commonSuperTypes.makeNullableAsSpecified(true) else commonSuperTypes
+    private fun refineNullabilityForUndefinedNullability(types: List<SimpleType>, commonSuperType: SimpleType): SimpleType? {
+        if (!commonSuperType.unwrap().canHaveUndefinedNullability()) return null
+
+        val actuallyNotNull = types.all { NullabilityChecker.hasPathByNotMarkedNullableNodes(it, commonSuperType.constructor) }
+        return if (actuallyNotNull) commonSuperType else null
     }
 
     private fun List<SimpleType>.uniquify(): List<SimpleType> {

compiler/testData/diagnostics/tests/generics/commonSupertypeContravariant2.ni.txt

@@ -1,7 +1,7 @@
 package
 
-public fun foobar(/*0*/ a: A, /*1*/ b: B): In<kotlin.Nothing>?
-public fun </*0*/ T> select(/*0*/ x: T, /*1*/ y: T): T?
+public fun foobar(/*0*/ a: A, /*1*/ b: B): In<kotlin.Nothing>
+public fun </*0*/ T> select(/*0*/ x: T, /*1*/ y: T): T
 
 public final class A : In<A> {
     public constructor A()

compiler/testData/diagnostics/tests/regressions/kt7804.kt

@@ -12,7 +12,7 @@ fun <T> test(v: T): T {
         v
     }
 
-    val t: T = <!NI;DEBUG_INFO_SMARTCAST!>a<!>
+    val t: T = a
     return t
 }
 
@@ -36,7 +36,7 @@ fun <T> test3(v: T): T {
         v
     }
 
-    val t: T = <!NI;DEBUG_INFO_SMARTCAST!>a<!>
+    val t: T = a
     return t
 }
 

compiler/testData/diagnostics/tests/smartCasts/lambdaAndArgument.kt

@@ -1,5 +1,4 @@
 // !DIAGNOSTICS: -NOTHING_TO_INLINE
-// NI_EXPECTED_FILE
 
 inline fun <T> foo(t1: T, t2: T) = t1 ?: t2
 

compiler/testData/diagnostics/tests/smartCasts/lambdaAndArgument.ni.txt

@@ -1,5 +0,0 @@
-package
-
-public inline fun </*0*/ T> bar(/*0*/ l: (T) -> kotlin.Unit): T
-public inline fun </*0*/ T> foo(/*0*/ t1: T, /*1*/ t2: T): T?
-public fun use(): kotlin.Unit

compiler/testData/diagnostics/tests/smartCasts/lambdaAndArgumentFun.kt

@@ -1,5 +1,4 @@
 // !DIAGNOSTICS: -NOTHING_TO_INLINE
-// NI_EXPECTED_FILE
 // See KT-9143: smart cast on a variable nulled inside a lambda argument
 inline fun <T> foo(t1: T, t2: T) = t1 ?: t2
 

compiler/testData/diagnostics/tests/smartCasts/lambdaAndArgumentFun.ni.txt

@@ -1,5 +0,0 @@
-package
-
-public inline fun </*0*/ T> bar(/*0*/ l: (T) -> kotlin.Unit): T
-public inline fun </*0*/ T> foo(/*0*/ t1: T, /*1*/ t2: T): T?
-public fun use(): kotlin.Unit

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) {