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From: ytomino <aghia05@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: discriminant questions
Date: Mon, 19 Sep 2011 07:46:15 -0700 (PDT)
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Date: 2011-09-19T07:46:15-07:00
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Please look below:

procedure q1 is
   generic
      type e is private;
   package the_package_like_ada2012_vector is
      type ref (element : not null access e) is null record;
   end the_package_like_ada2012_vector;
   generic
      type e is private;
      type ref (element : not null access e) is private;
   package the_package_use_ref is
   end the_package_use_ref;
   package inst1 is new the_package_like_ada2012_vector (integer);
   package inst2 is new the_package_use_ref (integer, inst1.ref); --
error (line 13)
   -- additional from here
   type int_ref (element : not null access Integer) is null record;
   package inst3 is new the_package_use_ref (integer, int_ref); --
ok !?!?
begin
   null;
end q1;
-- q1.adb:13:65: types of actual discriminants must match formal
-- q1.adb:13:65: instantiation abandoned

I can not understand the reason that inst1 is error and inst2 is ok.
It seems bug to me.

Can someone tell me which is this bug or specified in RM?
If this is actual bug, I'd like to report it to gcc.

Quick fix for the time being: (is this fix correct?)

Index: gcc/ada/sem_ch12.adb
===================================================================
--- gcc/ada/sem_ch12.adb	(revision 178831)
+++ gcc/ada/sem_ch12.adb	(working copy)
@@ -10158,10 +10158,10 @@
                   if Ekind (Base_Type (Formal_Subt)) =
E_Anonymous_Access_Type
                     and then (Ekind (Base_Type (Etype
(Actual_Discr)))) =
                                 E_Anonymous_Access_Type
-                    and then
+                    and then Subtypes_Match (
                       Get_Instance_Of
-                        (Designated_Type (Base_Type (Formal_Subt))) =
-                           Designated_Type (Base_Type (Etype
(Actual_Discr)))
+                        (Designated_Type (Base_Type (Formal_Subt))),
+                           Designated_Type (Base_Type (Etype
(Actual_Discr))))
                   then
                      null;