Added isAllowedTypeVariable inside KotlinTypeChecker

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

@@ -177,8 +177,12 @@ object NewKotlinTypeChecker : KotlinTypeChecker {
         }
 
     private fun TypeCheckerContext.isSubtypeOfForSingleClassifierType(subType: SimpleType, superType: SimpleType): Boolean {
-        assert(subType.isSingleClassifierType || subType.isIntersectionType) { "Not singleClassifierType and not intersection subType: $subType" }
+        assert(subType.isSingleClassifierType || subType.isIntersectionType || subType.isAllowedTypeVariable) {
-        assert(superType.isSingleClassifierType) { "Not singleClassifierType superType: $superType" }
+            "Not singleClassifierType and not intersection subType: $subType"
+        }
+        assert(superType.isSingleClassifierType || superType.isAllowedTypeVariable) {
+            "Not singleClassifierType superType: $superType"
+        }
 
         if (!NullabilityChecker.isPossibleSubtype(this, subType, superType)) return false
 
@@ -342,8 +346,12 @@ object NullabilityChecker {
 
     private fun TypeCheckerContext.runIsPossibleSubtype(subType: SimpleType, superType: SimpleType): Boolean {
         // it makes for case String? & Any <: String
-        assert(subType.isIntersectionType || subType.isSingleClassifierType) {"Not singleClassifierType superType: $superType"}
+        assert(subType.isIntersectionType || subType.isSingleClassifierType || subType.isAllowedTypeVariable) {
-        assert(superType.isSingleClassifierType) {"Not singleClassifierType superType: $superType"}
+            "Not singleClassifierType superType: $superType"
+        }
+        assert(superType.isSingleClassifierType || subType.isAllowedTypeVariable) {
+            "Not singleClassifierType superType: $superType"
+        }
 
         // superType is actually nullable
         if (superType.isMarkedNullable) return true

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

@@ -20,7 +20,7 @@ import org.jetbrains.kotlin.types.*
 import org.jetbrains.kotlin.utils.SmartSet
 import java.util.*
 
-open class TypeCheckerContext(val errorTypeEqualsToAnything: Boolean) {
+open class TypeCheckerContext(val errorTypeEqualsToAnything: Boolean, val allowedTypeVariable: Boolean = true) {
     protected var argumentsDepth = 0
 
     private var supertypesLocked = false
@@ -116,4 +116,6 @@ open class TypeCheckerContext(val errorTypeEqualsToAnything: Boolean) {
                     substitutor.safeSubstitute(type.lowerIfFlexible(), Variance.INVARIANT).asSimpleType()
         }
     }
+
+    val UnwrappedType.isAllowedTypeVariable: Boolean get() = allowedTypeVariable && constructor is NewTypeVariableConstructor
 }

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

@@ -100,3 +100,5 @@ private fun TypeConstructor.debugInfo() = buildString {
         declarationDescriptor = declarationDescriptor.containingDeclaration
     }
 }
+
+interface NewTypeVariableConstructor