builder > A.scala B.scala
compiling Set(A.scala, B.scala)
Changes: Map()
builder > A.scala
compiling Set(A.scala)
Changes: Map(class A -> List(Removed(Definition(A.foo))))
invalidate B.scala because inherited method removed [Removed(Definition(A.foo))]
compiling Set(B.scala)
B.scala:2: error: method foo overrides nothing
  override def foo = 2
               ^