[Ada] Spurious error with predicate and class-wide object

[Pierre-Marie de Rodat <derodat at adacore dot com>]

This patch removes a spurious error on a call to a function that applies
to a predicated tagged type, when the actual in the call is class-wide.
The argument must be converted to be type-specific, given that the predicate
function is not dispatching and cannot accept a class-wide actual.

Executing:

   gnatmake -q -gnata main
   main

must yield:

   Predicate checked
   Predicate checked
   Predicate checked
   Predicate checked
   Predicate checked
   Predicate checked

---
with Predicate_Ints; use Predicate_Ints;
procedure Main is
  Thing1 : Int := (0, 100, 50);
  Thing2 : Approx_Int := (0, 100, 50, 13);
begin
  Call_Bump (Thing1);
  Call_Bump (Thing2);
end;
---
package Predicate_Ints is

   type Int is tagged record
      Min, Max, Value : Integer;
   end record
     with Predicate => Value in Min .. Max and then Checked;

   procedure Bump (Arg : in out Int);
   procedure Call_Bump (Arg : in out Int'Class);

   function Checked  return Boolean;

   type Approx_Int is new Int with record
      Precision : Natural;
   end record;

end Predicate_Ints;
---
with Text_IO; use Text_IO;
package body Predicate_Ints is
   function Checked return Boolean is
   begin
      Put_Line ("Predicate checked");
      return True;
   end;
   
   procedure Bump (Arg : in out Int) is
   begin
      Arg.Value := Arg.Value + 1;
   end Bump;

   procedure Call_Bump (Arg : in out Int'Class) is
   begin
      Arg.Bump;
   end Call_Bump;

end Predicate_Ints;

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

2017-10-09  Ed Schonberg  <schonberg@adacore.com>

	* exp_util.adb (Make_Predicate_Call): If the type of the expression to
	which the predicate check applies is tagged, convert the expression to
	that type. This is in most cases a no-op, but is relevant if the
	expression is clas-swide, because the predicate function being invoked
	is not a primitive of the type and cannot take a class-wide actual.

Attachment: difs
Description: Text document