Multilevel type lambdas is not supported

[newca12]

This was initially reported on the dotty gitter channel by @sorenbug but I did not find an open issue for that.

Level 1 is OK

scala> type Z = [Z[_]] => [T] => Z[T]
// defined alias type Z = [Z <: [_$109] => Any] => [T] => Z[T]

scala> val l: Z[List][Int] = List(1)
val l: Z[List][Int] = List(1)

but not level 2 and more

scala> type YZ = [Y[_]] => [Z[_]] => [T] => Y[Z[T]]
// defined alias type YZ = [Y <: [_$8] => Any] => [Z <: [_$9] => Any] => [T] => Y[Z[T]]

scala> val l: YZ[List][List][Int] = List(List(1))
1 |val l: YZ[List][List][Int] = List(List(1))
  |                              ^^^^^^^^^^^^^
  |                              Found:    List[List[Int]]
  |                              Required: YZ[List][List][Int]

[s5bug]

For context, I was originally trying to use this kind of typing to accomplish something akin to

type I = [X <: AnyKind] => X
type K = [X <: AnyKind] => [Y <: AnyKind] => X
type S = [X[_][_] <: AnyKind] => [Y[_] <: AnyKind] => [Z <: AnyKind] = X[Z][Y[Z]]