package P is

  procedure X (A : out Natural);
  pragma Postcondition (A >= 10);

end P;

package body P is

  procedure X (A : out Natural) is
  begin
    A := 20;
  end X;

end P;

$ gcc44 -gnatwadleG -gnatVa -gnato -gnata -gnatW8 -gnatiw -
gnaty2aAbdefhiklnprStu -c p.adb
p.ads:4:25: warning: "A" may be referenced before it has a value