🚀 go-pugleaf

Your compiler does the right thing.  A subtype declaration does not
derive any operations (read "enumeration literals").  If you change
the assignment in package B to y := st_2 or y := B.st_2 you will see
that the literals aren't locally defined in B, therefore they can't be
made available anywhere else through the use of a "with B".

Note that if you must do this, and a derived type won't do what you want,
you can use renaming declarations:

  package fruit_mgr is
    type fruit is (apple, banana, cherry);
  end fruit_mgt;

  with fruit_mgr;
  package pseudo_fruit_mgr is
    subtype fruit is fruit_mgr.fruit;
    function apple return fruit renames fruit_mgr.fruit;
    function banana return fruit renames fruit_mgr.banana;
    function cherry return fruit renames fruit_mgr.cherry;
  end pseude_fruit_mgr;

You can, of course, just declare constants of type pseudo_fruit_mgr.fruit
instead:

    apple: constant fruit := fruit_mgr.apple;

but this method does not preserve the semantics of enumeration literals,
particularly with reference to overloading.