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9.12 Elaboration Circularities

If the binder cannot find an acceptable elaboration order, it outputs detailed diagnostics describing an `elaboration circularity'. 

package Server is
   function Func return Integer;
end Server;

with Client;
package body Server is
   function Func return Integer is
   begin
      ...
   end Func;
end Server;

with Server;
package Client is
   Val : constant Integer := Server.Func;
end Client;

with Client;
procedure Main is begin null; end Main;

error: elaboration circularity detected
info:    "server (body)" must be elaborated before "client (spec)"
info:       reason: implicit Elaborate_All in unit "client (spec)"
info:       recompile "client (spec)" with -gnatel for full details
info:          "server (body)"
info:             must be elaborated along with its spec:
info:          "server (spec)"
info:             which is withed by:
info:          "client (spec)"
info:    "client (spec)" must be elaborated before "server (body)"
info:       reason: with clause

In the example above, Client must be elaborated prior to Main by virtue of a `with' clause. The elaboration of Client invokes Server.Func, and static model generates an implicit Elaborate_All pragma for Server. The pragma implies that both the spec and body of Server, along with any units they `with', must be elaborated prior to Client. However, Server’s body `with's Client, implying that Client must be elaborated prior to Server. The end result is that Client must be elaborated prior to Client, and this leads to a circularity.