[FIR] fix subtyping for definitely notnull types.

The current implementation doesn't consider Foo a subtype of Captured<in
Foo>!!, since AbstractTypeCheckerContext::checkSubtypeForSpecialCases
does not handle DefinitelyNotNullType cases. This PR adds handling of
DefinitelyNotNullType by looking at its original type.

^KT-42824 Fixed

core/compiler.common/src/org/jetbrains/kotlin/types/AbstractTypeChecker.kt

@@ -404,15 +404,18 @@ object AbstractTypeChecker {
 
         if (subType.isStubType() || superType.isStubType()) return isStubTypeEqualsToAnything
 
-        val superTypeCaptured = superType.asCapturedType()
+        // superType might be a definitely notNull type (see KT-42824)
+        val superOriginalType = superType.asDefinitelyNotNullType()?.original() ?: superType
+        val superTypeCaptured = superOriginalType.asCapturedType()
         val lowerType = superTypeCaptured?.lowerType()
         if (superTypeCaptured != null && lowerType != null) {
             // If superType is nullable, e.g., to check if Foo? a subtype of Captured<in Foo>?, we check the LHS, Foo?,
             // against the nullable version of the lower type of RHS. See KT-42825
-            val nullableLowerType =
-                if (superType.isMarkedNullable())
-                    lowerType.withNullability(true)
-                else lowerType
+            val nullableLowerType = if (superType.isMarkedNullable()) {
+                lowerType.withNullability(true)
+            } else {
+                if (superType.isDefinitelyNotNullType()) lowerType.makeDefinitelyNotNullOrNotNull() else lowerType
+            }
             when (getLowerCapturedTypePolicy(subType, superTypeCaptured)) {
                 CHECK_ONLY_LOWER -> return isSubtypeOf(this, subType, nullableLowerType)
                 CHECK_SUBTYPE_AND_LOWER -> if (isSubtypeOf(this, subType, nullableLowerType)) return true

core/compiler.common/src/org/jetbrains/kotlin/types/model/TypeSystemContext.kt

@@ -7,7 +7,6 @@ package org.jetbrains.kotlin.types.model
 
 import org.jetbrains.kotlin.types.AbstractTypeCheckerContext
 import org.jetbrains.kotlin.types.Variance
-import java.util.*
 import kotlin.collections.ArrayList
 import kotlin.contracts.ExperimentalContracts
 import kotlin.contracts.contract
@@ -144,9 +143,6 @@ interface TypeSystemInferenceExtensionContext : TypeSystemContext, TypeSystemBui
 
     fun KotlinTypeMarker.isBuiltinFunctionalTypeOrSubtype(): Boolean
 
-    fun KotlinTypeMarker.makeDefinitelyNotNullOrNotNull(): KotlinTypeMarker
-    fun SimpleTypeMarker.makeSimpleTypeDefinitelyNotNullOrNotNull(): SimpleTypeMarker
-
     fun createCapturedType(
         constructorProjection: TypeArgumentMarker,
         constructorSupertypes: List<KotlinTypeMarker>,
@@ -171,8 +167,6 @@ interface TypeSystemInferenceExtensionContext : TypeSystemContext, TypeSystemBui
     fun CapturedTypeMarker.typeParameter(): TypeParameterMarker?
     fun CapturedTypeMarker.withNotNullProjection(): KotlinTypeMarker
 
-    fun DefinitelyNotNullTypeMarker.original(): SimpleTypeMarker
-
     fun typeSubstitutorByTypeConstructor(map: Map<TypeConstructorMarker, KotlinTypeMarker>): TypeSubstitutorMarker
     fun createEmptySubstitutor(): TypeSubstitutorMarker
 
@@ -249,6 +243,9 @@ interface TypeSystemContext : TypeSystemOptimizationContext {
     fun KotlinTypeMarker.isCapturedType() = asSimpleType()?.asCapturedType() != null
 
     fun SimpleTypeMarker.asDefinitelyNotNullType(): DefinitelyNotNullTypeMarker?
+    fun DefinitelyNotNullTypeMarker.original(): SimpleTypeMarker
+    fun KotlinTypeMarker.makeDefinitelyNotNullOrNotNull(): KotlinTypeMarker
+    fun SimpleTypeMarker.makeSimpleTypeDefinitelyNotNullOrNotNull(): SimpleTypeMarker
     fun SimpleTypeMarker.isMarkedNullable(): Boolean
     fun KotlinTypeMarker.isMarkedNullable(): Boolean =
         this is SimpleTypeMarker && isMarkedNullable()