Delegate refineType and prepareType in TypeCheckerState to special services

This is needed to add ability to create type system independent TypeCheckerState

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

@@ -22,17 +22,20 @@ import java.util.*
  * new instance of particular [TypeCheckerState] should be created, with properly specified type system context
  */
 abstract class TypeCheckerState {
+    abstract val kotlinTypePreparator: AbstractTypePreparator
+    abstract val kotlinTypeRefiner: AbstractTypeRefiner
 
     abstract val typeSystemContext: TypeSystemContext
 
     abstract fun substitutionSupertypePolicy(type: SimpleTypeMarker): SupertypesPolicy
 
-    open fun refineType(type: KotlinTypeMarker): KotlinTypeMarker {
-        return type
+    @OptIn(TypeRefinement::class)
+    fun refineType(type: KotlinTypeMarker): KotlinTypeMarker {
+        return kotlinTypeRefiner.refineType(type)
     }
 
-    open fun prepareType(type: KotlinTypeMarker): KotlinTypeMarker {
-        return type
+    fun prepareType(type: KotlinTypeMarker): KotlinTypeMarker {
+        return kotlinTypePreparator.prepareType(type)
     }
 
     open fun customIsSubtypeOf(subType: KotlinTypeMarker, superType: KotlinTypeMarker): Boolean = true

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

@@ -7,6 +7,12 @@ package org.jetbrains.kotlin.types
 
 import org.jetbrains.kotlin.types.model.KotlinTypeMarker
 
-interface AbstractTypePreparator {
-    fun prepareType(type: KotlinTypeMarker): KotlinTypeMarker
-}
+abstract class AbstractTypePreparator {
+    abstract fun prepareType(type: KotlinTypeMarker): KotlinTypeMarker
+
+    object Default : AbstractTypePreparator() {
+        override fun prepareType(type: KotlinTypeMarker): KotlinTypeMarker {
+            return type
+        }
+    }
+}

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

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.types
+
+import org.jetbrains.kotlin.types.model.KotlinTypeMarker
+
+/**
+ * This annotation marks part of internal compiler API related to type refinement.
+ *
+ * Marking such API explicitly has two objectives:
+ * - prevent unconscious abuse of invasive API (like DelegatingSimpleType.replaceDelegate),
+ *   which shouldn't be needed by anything outside of type refinement
+ * - improve readability of classes by separating API
+ *
+ * If you're using related API outside of MPP context, it's a nice idea to consider
+ * either finding some other API or removing @TypeRefinement (and thus "publishing"
+ * API for broader use)
+ */
+@RequiresOptIn(level = RequiresOptIn.Level.ERROR)
+@Retention(AnnotationRetention.BINARY)
+@Target(AnnotationTarget.CLASS, AnnotationTarget.FUNCTION, AnnotationTarget.PROPERTY)
+annotation class TypeRefinement
+
+
+abstract class AbstractTypeRefiner {
+    @TypeRefinement
+    abstract fun refineType(type: KotlinTypeMarker): KotlinTypeMarker
+
+    object Default : AbstractTypeRefiner() {
+        @TypeRefinement
+        override fun refineType(type: KotlinTypeMarker): KotlinTypeMarker {
+            return type
+        }
+    }
+}