Refactor TypeUtils

 = Move to core package. It was for historical reasons in transform because
   it was originally intended as a collection of type operations that were
   were useful in transform phases. But it's now used from everywhere.
 - Make a base class of Types, so that it does not need to be imported explicitly.

Author: odersky

compiler/src/dotty/tools/dotc/ast/tpd.scala

@@ -5,7 +5,6 @@ package ast
 import dotty.tools.dotc.transform.{ExplicitOuter, Erasure}
 import typer.ProtoTypes
 import transform.SymUtils.*
-import transform.TypeUtils.*
 import core.*
 import Scopes.newScope
 import util.Spans.*, Types.*, Contexts.*, Constants.*, Names.*, Flags.*, NameOps.*

compiler/src/dotty/tools/dotc/core/ConstraintHandling.scala

@@ -10,7 +10,6 @@ import Flags.*
 import config.Config
 import config.Printers.typr
 import typer.ProtoTypes.{newTypeVar, representedParamRef}
-import transform.TypeUtils.isTransparent
 import UnificationDirection.*
 import NameKinds.AvoidNameKind
 import util.SimpleIdentitySet

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -23,7 +23,6 @@ import scala.util.control.NonFatal
 import config.Config
 import reporting.*
 import collection.mutable
-import transform.TypeUtils.*
 import cc.{CapturingType, derivedCapturingType}
 
 import scala.annotation.internal.sharable

compiler/src/dotty/tools/dotc/core/TypeApplications.scala

@@ -12,7 +12,6 @@ import Names.*
 import StdNames.nme
 import Flags.{Module, Provisional}
 import dotty.tools.dotc.config.Config
-import dotty.tools.dotc.transform.TypeUtils.isErasedValueType
 
 object TypeApplications {
 

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -16,7 +16,6 @@ import TypeErasure.{erasedLub, erasedGlb}
 import TypeApplications.*
 import Variances.{Variance, variancesConform}
 import Constants.Constant
-import transform.TypeUtils.*
 import transform.SymUtils.*
 import scala.util.control.NonFatal
 import typer.ProtoTypes.constrained

compiler/src/dotty/tools/dotc/core/TypeErasure.scala

@@ -9,7 +9,6 @@ import TypeOps.makePackageObjPrefixExplicit
 import backend.sjs.JSDefinitions
 import transform.ExplicitOuter.*
 import transform.ValueClasses.*
-import transform.TypeUtils.*
 import transform.ContextFunctionResults.*
 import unpickleScala2.Scala2Erasure
 import Decorators.*
@@ -404,7 +403,6 @@ object TypeErasure {
       tp1 // After erasure, T | Nothing is just T and C | Null is just C, if C is a reference type.
     else tp1 match {
       case JavaArrayType(elem1) =>
-        import dotty.tools.dotc.transform.TypeUtils.*
         tp2 match {
           case JavaArrayType(elem2) =>
             if (elem1.isPrimitiveValueType || elem2.isPrimitiveValueType)

compiler/src/dotty/tools/dotc/transform/TypeUtils.scala renamed to compiler/src/dotty/tools/dotc/core/TypeUtils.scala

@@ -1,13 +1,12 @@
 package dotty.tools
 package dotc
-package transform
+package core
 
-import core.*
 import TypeErasure.ErasedValueType
 import Types.*, Contexts.*, Symbols.*, Flags.*, Decorators.*
 import Names.Name
 
-object TypeUtils {
+class TypeUtils {
   /** A decorator that provides methods on types
    *  that are needed in the transformer pipeline.
    */

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -43,9 +43,8 @@ import scala.annotation.internal.sharable
 import scala.annotation.threadUnsafe
 
 import dotty.tools.dotc.transform.SymUtils.*
-import dotty.tools.dotc.transform.TypeUtils.isErasedClass
 
-object Types {
+object Types extends TypeUtils {
 
   @sharable private var nextId = 0
 

compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -23,7 +23,6 @@ import Trees.*
 import TypeApplications.*
 import NameKinds.{WildcardParamName, DefaultGetterName}
 import util.Chars.isOperatorPart
-import transform.TypeUtils.*
 import transform.SymUtils.*
 import config.{Config, Feature}
 

compiler/src/dotty/tools/dotc/transform/AccessProxies.scala

@@ -9,7 +9,6 @@ import Flags.*
 import Names.*
 import NameOps.*
 import Decorators.*
-import TypeUtils.*
 import Types.*
 import util.Spans.Span
 import config.Printers.transforms