Fix #3381: handle case of lub and glb of types with different kinds

When forming the lub and glb of two types with different numbers of type
parameters, this crashed provided neither parameter list was empty. We
now treat this analogous to the case where one of the types is a * type,
by applying both types to their parameter references.

Author: odersky

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

@@ -1427,12 +1427,13 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
   private def liftIfHK(tp1: Type, tp2: Type, op: (Type, Type) => Type, original: (Type, Type) => Type) = {
     val tparams1 = tp1.typeParams
     val tparams2 = tp2.typeParams
+    def applied(tp: Type) = tp.appliedTo(tp.typeParams.map(_.paramInfoAsSeenFrom(tp)))
     if (tparams1.isEmpty)
       if (tparams2.isEmpty) op(tp1, tp2)
-      else original(tp1, tp2.appliedTo(tp2.typeParams.map(_.paramInfoAsSeenFrom(tp2))))
+      else original(tp1, applied(tp2))
     else if (tparams2.isEmpty)
-      original(tp1.appliedTo(tp1.typeParams.map(_.paramInfoAsSeenFrom(tp1))), tp2)
-    else
+      original(applied(tp1), tp2)
+    else if (tparams1.hasSameLengthAs(tparams2))
       HKTypeLambda(
         paramNames = (HKTypeLambda.syntheticParamNames(tparams1.length), tparams1, tparams2)
           .zipped.map((pname, tparam1, tparam2) =>
@@ -1442,6 +1443,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
           tl.integrate(tparams2, tparam2.paramInfoAsSeenFrom(tp2)).bounds),
         resultTypeExp = tl =>
           original(tp1.appliedTo(tl.paramRefs), tp2.appliedTo(tl.paramRefs)))
+    else original(applied(tp1), applied(tp2))
   }
 
   /** Try to distribute `&` inside type, detect and handle conflicts

tests/pos/i3381.scala

@@ -0,0 +1,8 @@
+case class Tuple2K[X, A[_], B[_]](a: A[X], b: B[X])
+
+object Test {
+  def f[X](x: Tuple2K[X, Option, [Y] => Tuple2K[Y, Option, Option]]): Any =
+    x match {
+      case Tuple2K(_, Tuple2K(_, _)) => ???
+    }
+}