When `Fields` in `Selectable` comes from type alias of named tuple. the fields are not selectable

[kavedaa]

Compiler version

3.6.4-RC1-bin-20241122-64411b6-NIGHTLY and earlier

Minimized code

import scala.language.experimental.namedTuples

class SelectableNT[A <: NamedTuple.AnyNamedTuple](val nt: A) extends Selectable:
  type Fields = A
  def selectDynamic(x: String) = ???

object Test:

  val a = (name = "foo", age = 1)

  val sa = SelectableNT(a)
  sa.name   // ok

  type B = a.type  
  val b: B = a

  val sb = SelectableNT(b)
  sb.name   // fails

Output

value name is not a member of bug.SelectableNT[(bug.Test.a : (name : String, age : Int))]

Expectation

Successful compilation

[odersky]

The problem came actually not from the fact that B is an alias, but that it is an alias of a singleton type.