Classes can't have an unfulfilled self type with unimplemented methods

trait Bar { def bar: Int }
class Foo { self : Bar => }

2 |class Foo { self : Bar => }
  |      ^
  |   class Foo needs to be abstract, since def bar: => Int is not defined 
one error found

It is allowed in Scalac

[Blaisorblade]

So there is a real use case

To clarify: I mean, one could just require that the class is marked abstract and support the same use cases.

[griggt]

FWIW, this compiles without error since #8332, both with and without -language:Scala2.