2 files changed, 28 insertions, 25 deletions

diff --git a/src/dotty/tools/dotc/core/Substituters.scala b/src/dotty/tools/dotc/core/Substituters.scala
index 763c3eea7..0df1ea49f 100644
--- a/src/dotty/tools/dotc/core/Substituters.scala
+++ b/src/dotty/tools/dotc/core/Substituters.scala
@@ -172,39 +172,39 @@ trait Substituters { this: Context =>
     case nil => false
   }
 
-  final class SubstBindingMap(from: BindingType, to: BindingType) extends TypeMap {
+  final class SubstBindingMap(from: BindingType, to: BindingType) extends DeepTypeMap {
     def apply(tp: Type) = subst(tp, from, to, this)
   }
 
-  final class Subst1Map(from: Symbol, to: Type) extends TypeMap {
+  final class Subst1Map(from: Symbol, to: Type) extends DeepTypeMap {
     def apply(tp: Type) = subst1(tp, from, to, this)
   }
 
-  final class Subst2Map(from1: Symbol, to1: Type, from2: Symbol, to2: Type) extends TypeMap {
+  final class Subst2Map(from1: Symbol, to1: Type, from2: Symbol, to2: Type) extends DeepTypeMap {
     def apply(tp: Type) = subst2(tp, from1, to1, from2, to2, this)
   }
 
-  final class SubstMap(from: List[Symbol], to: List[Type]) extends TypeMap {
+  final class SubstMap(from: List[Symbol], to: List[Type]) extends DeepTypeMap {
     def apply(tp: Type): Type = subst(tp, from, to, this)
   }
 
-  final class SubstSymMap(from: List[Symbol], to: List[Symbol]) extends TypeMap {
+  final class SubstSymMap(from: List[Symbol], to: List[Symbol]) extends DeepTypeMap {
     def apply(tp: Type): Type = substSym(tp, from, to, this)
   }
 
-  final class SubstThisMap(from: ClassSymbol, to: Type) extends TypeMap {
+  final class SubstThisMap(from: ClassSymbol, to: Type) extends DeepTypeMap {
     def apply(tp: Type): Type = substThis(tp, from, to, this)
   }
 
-  final class SubstRefinedThisMap(from: RefinedType, to: Type) extends TypeMap {
+  final class SubstRefinedThisMap(from: RefinedType, to: Type) extends DeepTypeMap {
     def apply(tp: Type): Type = substThis(tp, from, to, this)
   }
 
-  final class SubstParamMap(from: ParamType, to: Type) extends TypeMap {
+  final class SubstParamMap(from: ParamType, to: Type) extends DeepTypeMap {
     def apply(tp: Type) = substParam(tp, from, to, this)
   }
 
-  final class SubstParamsMap(from: BindingType, to: List[Type]) extends TypeMap {
+  final class SubstParamsMap(from: BindingType, to: List[Type]) extends DeepTypeMap {
     def apply(tp: Type) = substParams(tp, from, to, this)
   }
 }
\ No newline at end of file
diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index bfe19c859..8ef7edf24 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -1989,11 +1989,6 @@ object Types {
 
   abstract class TypeMap(implicit ctx: Context) extends (Type => Type) { thisMap =>
 
-    /** Unset by default. If set also map parents and self type of a ClassInfo.
-     *  By default, only the prefix is mapped.
-     */
-    def mapClassInfosDeeply = false
-
     def apply(tp: Type): Type
 
     /** Map this function over given type */
@@ -2028,17 +2023,8 @@ object Types {
           tp.derivedTypeBounds(this(lo), this(hi))
         }
 
-      case tp @ ClassInfo(prefix, _, _, _, _) =>
-        if (mapClassInfosDeeply) {
-          val prefix1 = this(prefix)
-          val parents1 = (tp.parents mapConserve this).asInstanceOf[List[TypeRef]]
-          val self1 = tp.self match {
-            case self: Type => this(self)
-            case _ => tp.self
-          }
-          tp.derivedClassInfo(prefix1, parents1, self1)
-        }
-        else tp.derivedClassInfo(this(prefix))
+      case tp: ClassInfo =>
+        mapClassInfo(tp)
 
       case tp: TypeVar =>
         val inst = tp.instanceOpt
@@ -2076,11 +2062,28 @@ object Types {
     def mapOver(tree: Tree): Tree =
       new TreeMapper(this).apply(tree)
 
+    /** Can be overridden. By default, only the prefix is mapped. */
+    protected def mapClassInfo(tp: ClassInfo): ClassInfo =
+      tp.derivedClassInfo(this(tp.prefix))
+
     def andThen(f: Type => Type): TypeMap = new TypeMap {
       def apply(tp: Type) = f(thisMap(tp))
     }
   }
 
+  /** A type map that maps also parents and self type of a ClassInfo */
+  abstract class DeepTypeMap(implicit ctx: Context) extends TypeMap {
+    override def mapClassInfo(tp: ClassInfo) = {
+      val prefix1 = this(tp.prefix)
+      val parents1 = (tp.parents mapConserve this).asInstanceOf[List[TypeRef]]
+      val self1 = tp.self match {
+        case self: Type => this(self)
+        case _ => tp.self
+      }
+      tp.derivedClassInfo(prefix1, parents1, self1)
+    }
+  }
+
   object IdentityTypeMap extends TypeMap()(NoContext) {
     def apply(tp: Type) = tp
   }