title: Cannot export packages in systemverilog
body: <p>I've tried to make a big package that exports sub packages for not to make any dependency in test files when new sub package is added. For this, I just simply did as in following but got a compile error, it seems export does not work properly as described in LRM. Is there any missing points in my code?</p>
  
  <pre><code>package sub_pkg_A;
    ..
  endpackage
  
  package sub_pkg_B;
    ..
  endpackage
  
  // just import and export
  package top_pkg;
     import sub_pkg_A::*;
     import sub_pkg_B::*;
     export sub_pkg_A::*;
     export sub_pkg_B::*;
  endpackage
  
  // test file
  module my_test;
      import top_pkg::*;
      ..
  endmodule
  </code></pre>