[Ada] Misleading warnings on non-overriding predefined control operations

[Arnaud Charlet <charlet at adacore dot com>]

Inherited predefined operations on controlled types are handled in a
non-standard way in the compiler, because in some cases they must remain
callable by the generated code even if not directly visible. This results
in confusing warning messages when user-defined control operations are not
overriding and their declarations carry explicit overriding indicators.
This patch removes the warnings when indicators are present, and sets the
visibility of hidden inherited operations correctly.

Compiling derived.ads below must yield:

derived.ads:6:18: subprogram "Initialize" is not overriding
---
private with Ada.Finalization;
package Root is

  type T is tagged private;

private

  type T is new Ada.Finalization.Controlled with null record;

  overriding procedure Initialize (Ob: in out T) is null;
  overriding procedure Adjust     (Ob: in out T) is null;
  overriding procedure Finalize   (Ob: in out T) is null;

end Root;
---
with Root;

package Derived is

  type D is new Root.T with null record;
      overriding procedure Initialize (Ob: in out D);  -- wrong
  not overriding procedure Adjust     (Ob: in out D);  -- OK
end Derived;

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

2009-11-30  Ed Schonberg  <schonberg@adacore.com>

	* sem_ch3.adb (Derive_Subprogram): Indicate that an inherited
	predefined control operation is hidden if the parent type is not
	visibly controlled.
	* sem_ch6.adb (Check_Overriding_Indicator): Do not report error if
	overridden operation is not visible, as may be the case with predefined
	control operations.
	* sem_disp.adb (Check_Dispatching_Operation): Do not emit warning on
	non-overriding control operation when type is not visibly controlled,
	if the subprogram has an explicit overriding indicator.
	* sem_util.ads, sem_util.adb (Is_Visibly_Controlled): Moved here from
	sem_disp.adb.

Attachment: difs
Description: Text document