Match type not working unless ascribed

[nicolasstucki]

Minimized code

class Test {
  val tup: Char #: Int #: String #: TupleK = ???
  val x: String #: TupleK = (tup.tail: Int #: String #: TupleK).tail
  val y: String #: TupleK = tup.tail.tail
  val z: Unit = tup.tail.tail
}

trait TupleK

object TupleK {
  type Tail[X <: NonEmptyTupleK] <: TupleK = X match {
    case _ #: xs => xs
  }
}

trait NonEmptyTupleK extends TupleK {
  /*inline*/ def tail[This >: this.type <: NonEmptyTupleK]: TupleK.Tail[This] = ???
}

abstract class #:[+H, +T <: TupleK] extends NonEmptyTupleK

Output

-- [E008] Not Found Error: tests/run/tuples1c.scala:5:37 -----------------------
5 |  val y: String #: TupleK = tup.tail.tail
  |                            ^^^^^^^^^^^^^
  |value tail is not a member of TupleK.Tail[This] - did you mean TupleK.Tail[This].wait?
  |
  |where:    This is a type variable with constraint >: (Test.this.tup : Char #: Int #: String #: TupleK) and <: NonEmptyTupleK
-- [E008] Not Found Error: tests/run/tuples1c.scala:6:25 -----------------------
6 |  val z: Unit = tup.tail.tail
  |                ^^^^^^^^^^^^^
  |value tail is not a member of TupleK.Tail[This] - did you mean TupleK.Tail[This].wait?
  |
  |where:    This is a type variable with constraint >: (Test.this.tup : Char #: Int #: String #: TupleK) and <: NonEmptyTupleK
2 errors found

Expectation

They compile with the inline, the should also compile without it.

[nicolasstucki]

This is a blocker for #9984.