I know that package variables will cause ORA-4068 error messages when another user tries to re-compile the package body that is already in use. I know why I am getting these errors, I need to know how I can detect these errors before the user compiles a package body.
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For example, a user creates a package:
session1 > l
1 create or replace package foo
2 is
3 function bar return varchar2;
4* end foo;
session1 > /

Package created.

Then, in the same session, the user creates the package body:
session1 > l
1 create or replace package body foo
2 is
3 v2 varchar2(80);
4 function bar return varchar2
5 is
6 ver varchar2(80);
7 begin
8 v2:='this is a package variable.';
9 ver := v2;
10 return ver;
11 end bar;
12* end foo;
session1 > /

Package body created.

Then the user executes the package:
session1 > set serveroutput on
session1 > exec dbms_output.put_line(foo.bar);
this is a package variable.

PL/SQL procedure successfully completed.

Now another sqlplus session is started in window#2 as the same user and he executes the package:
session2 > set serveroutput on
session2 > exec dbms_output.put_line(foo.bar);
this is a package variable.

PL/SQL procedure successfully completed.

Now, the user needs to recompile the body of foo. If he recompiles the package in session1, an ORA-4068 error will be generated in session2. Before the first session recompiles the package body, I want to be able to find out if he will generate an ORA-4068 error for any other users using that package.