Weird error with Dynamic_Predicate

[mockturtle <framefritti@gmail.com>]

Dear all,
I am experiencing an error that is making me crazy and I was wondering if someone can help.

Some background: I want to define a type that represents an "identifier."  The identifier can assume two forms: 
 - qualified (es. namespace.foo)
 - not qualified (es. foo)

The two components (namespace and name) have the usual syntax (letters, digits and underscore).  Note that there are at most two components.  I want to use the aspect Dynamic_Predicate to enforce (and document) the right syntax.

You can find prova.ads and prova.adb at the end of this message.  I am using GPS 5.2.1 (20130102) and when I try to compile I get the obscure message

  29:32 error: conversion to incomplete type
  29:32 confused by earlier errors, bailing out

on >> prova.ads <<.  If I try to do "check semantic" on prova.ads and prova.adb, everything is fine.  


Any ideas?  Is it a compiler bug or am I doing something wrong?  Updating the compiler in this moment it would be a little pain for me (for several reasons), so I would like to be sure that I am not doing some subtle error before trying the update path.

Thank you in advance 

Riccardo



--- prova.ads ---
with Ada.Characters.Handling;     use Ada.Characters.Handling;
with Ada.Strings.Fixed;

package Prova is
   type Identifier_Name is new
     String
       with Dynamic_Predicate =>
         ((for all I in Identifier_Name'Range =>
             Is_Alphanumeric (Identifier_Name (I))
           or Identifier_Name (I) = '_'
           or Identifier_Name (I) = '.')
          and
            (not (Identifier_Name (Identifier_Name'First) in '0' .. '9'))
          and
            (Identifier_Name (Identifier_Name'First) /= '.')
          and
            Ada.Strings.Fixed.Count (String (Identifier_Name), ".") <= 1);

   function Is_Qualified (Item : Identifier_Name) return Boolean
     is (Ada.Strings.Fixed.Count (String (Item), ".") = 1);

   subtype Namespace_Identifier is Identifier_Name
   with Dynamic_Predicate => not Is_Qualified (Namespace_Identifier);

   subtype Full_Identifier is Identifier_Name
   with Dynamic_Predicate => Is_Qualified (Full_Identifier);


   function Extract_Namespace (Nome : Full_Identifier)
                               return Namespace_Identifier;

end Prova;

--- prova.adb --- 

package body Prova is


   -----------------------
   -- Extract_Namespace --
   -----------------------

   function Extract_Namespace (Nome : Full_Identifier)
                               return Namespace_Identifier
   is
      Idx : Natural := Ada.Strings.Fixed.Index (String (Nome), ".");
   begin
      return Namespace_Identifier (Nome (Nome'First .. Idx - 1));
   end Extract_Namespace;

end Prova;
----