t9273.scala:2: error: class type required but ? found
  val foo: Class[_] = classOf            // error without position, line or file
                      ^
t9273.scala:3: error: not found: type X
  val foo1: Class[_] = classOf[X]        // good error, all info contained
                               ^
t9273.scala:7: error: not found: type X
  val foo4: Class[_] = Predef.classOf[X] // good error, all info contained
                                      ^
three errors found