Crazy infinite paths

[samuelgruetter]

Converting #161 (comment) into an issue so that it doesn't get lost:

Here's a example involving infinite paths which does not yet work:

object infpaths3 {

  object a {
    trait T { t =>
      type M <: t.g.N
      type T <: a.T
      val f: t.T

      trait U { u =>
        type N <: t.f.M
        type U <: a.x.g.U
        val f: u.U
      }
      val g: t.U
    }
    val x: a.T = ???
  }

}

It detects a cycle and outputs

$ sbt "run examples/infpaths3.scala"
[error] examples/infpaths3.scala:5: error: illegal cyclic reference: upper bound T.this.g.N of type M refers back to the type itself
[error]       type M <: t.g.N
[error]              ^

but after outputting this, dotty runs into an infinite loop.