Type override in traits/classes with self-type

[scalauser12]

reproduction steps

using Scala 2.13.3

  trait A {
    self: AnyRef =>
    type T = Nothing
    def test: T = throw new NotImplementedError
  }

  trait B extends A {
    self: AnyRef =>
    override type T = String
    override def test: T = "test"
  }

  class C extends B {
    self: AnyRef =>
  }

  val c: A = new C

problem

This code compiles despite type safety having been compromised. (It does not compile without self-types.) At runtime c.test throws java.lang.ClassCastException: java.lang.String cannot be cast to scala.runtime.Nothing$.

[SethTisue]

This regressed between 2.12 and 2.13.0 — 2.12 rejects the code. (I didn't try to figure out which milestone or RC it regressed in.)

[Jasper-M]

Regressed in 2.13.0-RC1