Do subtyping between self types with captured type in special way

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

@@ -44,6 +44,12 @@ interface ClassicTypeSystemContext : TypeSystemInferenceExtensionContext, TypeSy
         return declarationDescriptor?.classId?.isLocal == true
     }
 
+    override val TypeVariableTypeConstructorMarker.typeParameter: TypeParameterMarker?
+        get() {
+            require(this is NewTypeVariableConstructor, this::errorMessage)
+            return this.originalTypeParameter
+        }
+
     override fun SimpleTypeMarker.possibleIntegerTypes(): Collection<KotlinTypeMarker> {
         val typeConstructor = typeConstructor()
         require(typeConstructor is IntegerLiteralTypeConstructor, this::errorMessage)
@@ -212,6 +218,13 @@ interface ClassicTypeSystemContext : TypeSystemInferenceExtensionContext, TypeSy
         return this.typeConstructor
     }
 
+    override fun TypeParameterMarker.doesFormSelfType(selfConstructor: TypeConstructorMarker): Boolean {
+        require(this is TypeParameterDescriptor, this::errorMessage)
+        require(selfConstructor is TypeConstructor, this::errorMessage)
+
+        return doesTypeParameterFormSelfType(this, selfConstructor)
+    }
+
     override fun areEqualTypeConstructors(c1: TypeConstructorMarker, c2: TypeConstructorMarker): Boolean {
         require(c1 is TypeConstructor, c1::errorMessage)
         require(c2 is TypeConstructor, c2::errorMessage)

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

@@ -17,9 +17,11 @@
 package org.jetbrains.kotlin.types.checker
 
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
+import org.jetbrains.kotlin.descriptors.TypeParameterDescriptor
 import org.jetbrains.kotlin.renderer.DescriptorRenderer
 import org.jetbrains.kotlin.resolve.calls.inference.wrapWithCapturingSubstitution
 import org.jetbrains.kotlin.types.*
+import org.jetbrains.kotlin.types.typeUtil.contains
 import org.jetbrains.kotlin.types.typesApproximation.approximateCapturedTypes
 import java.util.*
 
@@ -101,4 +103,11 @@ private fun TypeConstructor.debugInfo() = buildString {
     }
 }
 
-interface NewTypeVariableConstructor
+interface NewTypeVariableConstructor {
+    val originalTypeParameter: TypeParameterDescriptor?
+}
+
+fun doesTypeParameterFormSelfType(typeParameter: TypeParameterDescriptor, selfConstructor: TypeConstructor) =
+    typeParameter.upperBounds.any { upperBound ->
+        upperBound.contains { it.constructor == typeParameter.typeConstructor } && upperBound.constructor == selfConstructor
+    }