FE approximator conf: simplify typeVariable/HandleAsTypeVariable

Related to KT-58618

compiler/resolution.common/src/org/jetbrains/kotlin/types/AbstractTypeApproximator.kt

@@ -375,7 +375,7 @@ abstract class AbstractTypeApproximator(
         }
 
         if (typeConstructor is TypeVariableTypeConstructorMarker) {
-            return if (shouldHandleAsTypeVariable(conf, typeConstructor)) null else type.defaultResult(toSuper)
+            return if (conf.shouldKeepTypeVariableBasedType(typeConstructor, isK2)) null else type.defaultResult(toSuper)
         }
 
         if (typeConstructor.isIntegerLiteralConstantTypeConstructor()) {
@@ -393,15 +393,6 @@ abstract class AbstractTypeApproximator(
         return approximateLocalTypes(type, conf, toSuper, depth) // simple classifier type
     }
 
-    private fun shouldHandleAsTypeVariable(
-        conf: TypeApproximatorConfiguration,
-        typeConstructorMarker: TypeVariableTypeConstructorMarker,
-    ): Boolean = when (conf.typeVariable(typeConstructorMarker)) {
-        TypeApproximatorConfiguration.HandleAsTypeVariable.ALWAYS -> true
-        TypeApproximatorConfiguration.HandleAsTypeVariable.K2_ONLY -> isK2
-        TypeApproximatorConfiguration.HandleAsTypeVariable.NEVER -> false
-    }
-
     private fun approximateDefinitelyNotNullType(
         type: DefinitelyNotNullTypeMarker,
         conf: TypeApproximatorConfiguration,

compiler/resolution.common/src/org/jetbrains/kotlin/types/TypeApproximatorConfiguration.kt

@@ -38,13 +38,15 @@ open class TypeApproximatorConfiguration {
      */
     open val anonymous = false
 
-    internal enum class HandleAsTypeVariable {
-        ALWAYS,
-        K2_ONLY,
-        NEVER
-    }
+    /**
+     * This function determines the approximator behavior if a type variable based type is encountered.
+     *
+     * @param marker type variable encountered
+     * @param isK2 true for K2 compiler, false for K1 compiler
+     * @return true if the type variable based type should be kept, false if it should be approximated
+     */
+    internal open fun shouldKeepTypeVariableBasedType(marker: TypeVariableTypeConstructorMarker, isK2: Boolean): Boolean = false
 
-    internal open val typeVariable: (TypeVariableTypeConstructorMarker) -> HandleAsTypeVariable = { HandleAsTypeVariable.NEVER }
     open fun capturedType(ctx: TypeSystemInferenceExtensionContext, type: CapturedTypeMarker): Boolean =
         true  // false means that this type we can leave as is
 
@@ -63,7 +65,7 @@ open class TypeApproximatorConfiguration {
         override val integerLiteralConstantType: Boolean get() = true
         override val intersectionTypesInContravariantPositions: Boolean get() = true
 
-        override val typeVariable: (TypeVariableTypeConstructorMarker) -> HandleAsTypeVariable get() = { HandleAsTypeVariable.K2_ONLY }
+        override fun shouldKeepTypeVariableBasedType(marker: TypeVariableTypeConstructorMarker, isK2: Boolean): Boolean = isK2
     }
 
     open class PublicDeclaration(override val localTypes: Boolean, override val anonymous: Boolean) : AllFlexibleSameValue() {
@@ -73,7 +75,7 @@ open class TypeApproximatorConfiguration {
         override val integerLiteralConstantType: Boolean get() = true
         override val intersectionTypesInContravariantPositions: Boolean get() = true
 
-        override val typeVariable: (TypeVariableTypeConstructorMarker) -> HandleAsTypeVariable get() = { HandleAsTypeVariable.K2_ONLY }
+        override fun shouldKeepTypeVariableBasedType(marker: TypeVariableTypeConstructorMarker, isK2: Boolean): Boolean = isK2
 
         object SaveAnonymousTypes : PublicDeclaration(localTypes = false, anonymous = false)
         object ApproximateAnonymousTypes : PublicDeclaration(localTypes = false, anonymous = true)
@@ -89,7 +91,7 @@ open class TypeApproximatorConfiguration {
             approximatedCapturedStatus != null && type.captureStatus(ctx) == approximatedCapturedStatus
 
         override val intersection: IntersectionStrategy get() = IntersectionStrategy.ALLOWED
-        override val typeVariable: (TypeVariableTypeConstructorMarker) -> HandleAsTypeVariable get() = { HandleAsTypeVariable.ALWAYS }
+        override fun shouldKeepTypeVariableBasedType(marker: TypeVariableTypeConstructorMarker, isK2: Boolean): Boolean = true
     }
 
     object IncorporationConfiguration : AbstractCapturedTypesApproximation(CaptureStatus.FOR_INCORPORATION)
@@ -118,7 +120,7 @@ open class TypeApproximatorConfiguration {
         override val integerLiteralConstantType: Boolean get() = true
         override val allFlexible: Boolean get() = true
         override val intersection: IntersectionStrategy get() = IntersectionStrategy.ALLOWED
-        override val typeVariable: (TypeVariableTypeConstructorMarker) -> HandleAsTypeVariable get() = { HandleAsTypeVariable.ALWAYS }
+        override fun shouldKeepTypeVariableBasedType(marker: TypeVariableTypeConstructorMarker, isK2: Boolean): Boolean = true
         override val errorType: Boolean get() = true
 
         override fun capturedType(ctx: TypeSystemInferenceExtensionContext, type: CapturedTypeMarker): Boolean = false