[Ada] Overloaded indexing operations of a derived type

This patch fixes the handling of overloaded indexing operations that are
inherited by a type derived from one that carries an indexing aspect.

Source:

---
with Ada.Text_Io; use Ada.Text_Io;
with References;
procedure Main is
  A : aliased References.Iterated;

begin
  A (1) := 42;
  Put_Line ("A (1)" & References.Object_T'Image (A (1)));
  Put_Line ("A (1, 1)" & References.Object_T'Image (A (1, 1)));
end Main;
---
package body References is
  function Find (I : aliased in out Indexed; Key : Index) return Reference_T
  is
  begin
    return (Object => I.Rep (Key)'Access);
  end Find;

  function Find (I : aliased in out Indexed; Key1, Key2 : Index)
    return Reference_T
  is
  begin
    return (Object => I.Rep (Key1)'Access);
  end Find;

  function Find (I : aliased in out Iterated; C : Cursor) return Reference_T
  is
  begin
    return (Object => I.Rep (C.I)'Access);
  end Find;

  function Has_Element (Position : Cursor) return Boolean is
  begin
    return Position.Has_Element;
  end Has_Element;

  function First (Object : Iterator) return Cursor is
    Has_Elements : constant Boolean := Object.First <= Object.Last;
  begin
    if Has_Elements then
      return (Has_Element => True, I => Object.First);
    else
      return (Has_Element => False);
    end if;
  end First;

  function Next (Object : Iterator; Position : Cursor) return Cursor is
  begin
    if Position.Has_Element and then Position.I /= Index'Last then
      return (Has_Element => True, I => Position.I + 1);
    else
      return (Has_Element => False);
    end if;
  end Next;

  function Last (Object : Iterator) return Cursor is
    Has_Elements : constant Boolean := Object.First <= Object.Last;
  begin
    if Has_Elements then
      return (Has_Element => True, I => Object.Last);
    else
      return (Has_Element => False);
    end if;
  end Last;

  function Previous (Object : Iterator; Position : Cursor) return Cursor is
  begin
    if Position.Has_Element and then Position.I /= Index'First then
      return (Has_Element => True, I => Position.I - 1);
    else
      return (Has_Element => False);
    end if;
  end Previous;

  function Iterate (Container : Iterated)
     return Iterators.Reversible_Iterator'Class
  is
  begin
    return Iterator'(First => Container.Rep'First, Last => Container.Rep'Last);
  end Iterate;
end References;
---
with Ada.Iterator_Interfaces;

package References is
  type Object_T is new Integer;

  type Reference_T (Object : not null access Object_T) is private
    with Implicit_Dereference => Object;

  type Index is range 1 .. 2;

  type Array_T is array (Index) of aliased Object_T;

  type Cursor is private;

  type Indexed is tagged
    record
      Rep : Array_T;
    end record
    with Variable_Indexing => Find;

  function Find (I : aliased in out Indexed; Key : Index) return Reference_T;
  function Find (I : aliased in out Indexed; Key1, Key2 : Index)
    return Reference_T;

  function Has_Element (Position : Cursor) return Boolean;

  package Iterators is new Ada.Iterator_Interfaces (Cursor, Has_Element);

  type Iterator is new Iterators.Reversible_Iterator with
    record
      First : Index;
      Last  : Index;
    end record;

  function First (Object : Iterator) return Cursor;
  function Next (Object : Iterator; Position : Cursor) return Cursor;
  function Last (Object : Iterator) return Cursor;
  function Previous (Object : Iterator; Position : Cursor) return Cursor;

  type Iterated is new Indexed with null record with
    Default_Iterator  => Iterate,
    Iterator_Element  => Object_T;

  function Find (I : aliased in out Iterated; C : Cursor) return Reference_T;

  function Iterate
      (Container : Iterated)
       return Iterators.Reversible_Iterator'Class;

private
  type Reference_T (Object : not null access Object_T) is null record;

  type Cursor (Has_Element : Boolean := False) is
    record
      case Has_Element is
        when True =>
          I : Index;
        when False =>
          null;
      end case;
    end record;
end References;
---

Command:

   gnatmake -q main
   main

---
Output:

   A (1) 42
   A (1, 1) 42

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

2015-10-26  Ed Schonberg  <schonberg@adacore.com>

	* exp_util.ads, exp_util.adb (Find_Primitive_Operations): New
	subprogram to retrieve by name the possibly overloaded set of
	primitive operations of a type.
	* sem_ch4.adb (Try_Container_Indexing): Use
	Find_Primitive_Operations to handle overloaded indexing operations
	of a derived type.