Test_2.scala:3: error: anonymous class $anon inherits conflicting members:
  macro method t in trait C of type ()Unit  and
  method t in trait A of type ()Unit
(Note: this can be resolved by declaring an override in anonymous class $anon.)
  val c2 = new C with A {}
               ^
Test_2.scala:5: error: overriding macro method t in trait C of type ()Unit;
 method t cannot override a macro
  val c4 = new C with A { override def t(): Unit = () }
                                       ^
two errors found