A.scala

class A {
  //def foo: Int = 153
}

class A2

B.scala

class B extends A2

1. compile
2. Uncomment line in A.scala
3. compile. Both sources are recompiled because we have dependency introduced by inheritance between B.scala and A.scala. Name hashing is disabled for dependencies introduced by inheritance and incremental compiler track dependencies at source level so it cannot determine that change happened to A that B doesn't inherit from.