[Ada] Class-wide types of private extensions of constrained types

[Arnaud Charlet <charlet at adacore dot com>]

The class-wide type of private extension is created when the partial view is
analyzed. This class-wide type is shared with the full view. If the full view
is a subtype, as is the case when the parent is a constrained discriminated
subtype, the type of the private extension must be the base type of the full
view, to prevent spurious semantic errors when the classwide equivalent type
is constructed. This expansion involves dispatching calls to Size and to
Deep_Adjust, and these are best expressed on the full view.

   x.adb must compile quietly:  
---
with P; use P;
package X is

   function Create return access Child_1_3'Class;

   type Child_Acc is access all Child_1_3'Class;

end X;
---
package body X is
   function Create return access Child_1_3'Class is
      Res : Child_Acc := new Child_1_3;
      Res2 : Child_Acc := new Child_1_3'Class'(Res.all);

   begin
      return Res2;
   end Create;
end X;
---
package P is
   type Root_1 (V : Integer) is tagged record
      null;
   end record;

   type Child_1_3 is new Root_1 (1) with private;

private
   type Child_1_3 is new Root_1 (1) with null record;
end P;

Tested on x86_64-pc-linux-gnu, committed on trunk

2010-06-18  Ed Schonberg  <schonberg@adacore.com>

	* exp_util.adb (Make_Subtype_From_Expr): If the unconstrained type is
	the class-wide type for a private extension, and the completion is a
	subtype, set the type of the class-wide type to the base type of the
	full view.

Attachment: difs
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