trait Internals { this: Module =>
  val io = IO(new Bundle{ val a = Input(Bool()) })
}
class Sub extends Module with Internals
trait HasSub { this: Module with Internals =>
  val sub = Module(new Sub)
  sub.io.a := io.a
}
/* InlineInstance is mixed directly into Foo's definition. Every instance
 * of this will be inlined. */
class Foo extends Module with Internals with InlineInstance with HasSub
/* Bar will, by default, not be inlined */
class Bar extends Module with Internals with HasSub
/* The resulting instances will be:
 - Top
 - Top.x$sub
 - Top.y$sub
 - Top.z
 - Top.z.sub */
class Top extends Module with Internals {
  val x = Module(new Foo)                     // x will be inlined
  val y = Module(new Bar with InlineInstance) // y will also be inlined
  val z = Module(new Bar)                     // z will not be inlined
  Seq(x, y, z).map(_.io.a := io.a)
}