Rewrite compareHK to be kind-correct

2 files changed, 13 insertions, 9 deletions

diff --git a/src/dotty/tools/dotc/core/TypeApplications.scala b/src/dotty/tools/dotc/core/TypeApplications.scala
index 66542d02d..18256b9e4 100644
--- a/src/dotty/tools/dotc/core/TypeApplications.scala
+++ b/src/dotty/tools/dotc/core/TypeApplications.scala
@@ -149,6 +149,12 @@ class TypeApplications(val self: Type) extends AnyVal {
     case _ => false
   }
 
+  /** is receiver of the form T#$apply? */
+  def isHKApply: Boolean = self match {
+    case TypeRef(_, name) => name == tpnme.hkApply
+    case _ => false
+  }
+
   /** Encode the type resulting from applying this type to given arguments */
   final def appliedTo(args: List[Type])(implicit ctx: Context): Type = /*>|>*/ track("appliedTo") /*<|<*/ {
     def matchParams(tp: Type, tparams: List[TypeSymbol], args: List[Type]): Type = args match {
diff --git a/src/dotty/tools/dotc/core/TypeComparer.scala b/src/dotty/tools/dotc/core/TypeComparer.scala
index 35e4d804b..9e86a22a7 100644
--- a/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -466,18 +466,16 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
       false
   }
 
-  /** If `projection` is of the form T # Apply where `T` is an instance of a Lambda class,
-   *  and `other` is not a type lambda projection, then convert `other` to a type lambda `U`, and
+  /** If `projection` is a hk projection T#$apply
+   *  and `other` is not a hk projection, then convert `other` to a hk projection `U`, and
    *  continue with `T <:< U` if `inOrder` is true and `U <:< T` otherwise.
    */
   def compareHK(projection: NamedType, other: Type, inOrder: Boolean) =
-    projection.name == tpnme.hkApply && { // @@@ rewrite
-      val lambda = projection.prefix.LambdaClass(forcing = true)
-      lambda.exists && !other.isLambda &&
-        other.testLifted(lambda.typeParams,
-          if (inOrder) isSubType(projection.prefix, _) else isSubType(_, projection.prefix),
-          if (inOrder) Nil else classBounds(projection.prefix))
-    }
+    projection.name == tpnme.hkApply &&
+    !other.isHKApply &&
+    other.testLifted(projection.prefix.LambdaClass(forcing = true).typeParams,
+      if (inOrder) isSubType(projection.prefix, _) else isSubType(_, projection.prefix),
+      if (inOrder) Nil else classBounds(projection.prefix))
 
   /** The class symbols bounding the type of the `Apply` member of `tp` */
   private def classBounds(tp: Type) = tp.member(tpnme.hkApply).info.classSymbols