Allow existential types in hk types

1 files changed, 1 insertions, 28 deletions

diff --git a/src/dotty/tools/dotc/typer/Typer.scala b/src/dotty/tools/dotc/typer/Typer.scala
index 6510ba35b..745eee8f8 100644
--- a/src/dotty/tools/dotc/typer/Typer.scala
+++ b/src/dotty/tools/dotc/typer/Typer.scala
@@ -848,34 +848,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
       }
       val args1 = args.zipWithConserve(tparams)(typedArg(_, _)).asInstanceOf[List[Tree]]
       // check that arguments conform to bounds is done in phase PostTyper
-      val tree1 = assignType(cpy.AppliedTypeTree(tree)(tpt1, args1), tpt1, args1)
-      if (tree1.tpe.isHKApply)
-        for (arg @ TypeBoundsTree(_, _) <- args1)
-          ctx.error("illegal wildcard type argument; does not correspond to type parameter of a class", arg.pos)
-          // The reason for outlawing such arguments is illustrated by the following example.
-          // Say we have
-          //
-          //    type RMap[A, B] = Map[B, A]
-          //
-          // Then
-          //
-          //    Rmap[_, Int]
-          //
-          // translates to
-          //
-          //    Lambda$I { type hk$0; type hk$1 = Int; type $apply = Map[$hk1, $hk0] } # $apply
-          //
-          // Let's call the last type T. You would expect that
-          //
-          //    Map[Int, String] <: RMap[_, Int]
-          //
-          // But that's not the case given the standard subtyping rules. In fact, the rhs reduces to
-          //
-          //    Map[Int, T # $hk0]
-          //
-          // That means the second argument to `Map` is unknown and String is certainly not a subtype of it.
-          // To avoid the surprise we outlaw problematic wildcard arguments from the start.
-      tree1
+      assignType(cpy.AppliedTypeTree(tree)(tpt1, args1), tpt1, args1)
     }
   }