[Ada] Spurious warnings about unused units

[Arnaud Charlet]

A prefixed call is resolved by examining the dispatch table of the controlling
object, not by visibility. The operation may be defined in another unit, and
no reference to it, or to its scope, might be created for it through the
usual Generate_Reference machinery. To prevent spurious warnings about unused
units, indicate that the operation and its scope are in fact referenced.

No simple example available.

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

2014-10-23  Ed Schonberg  <schonberg@adacore.com>

	* sem_ch4.adb (Complete_Object_Operation): Indicate that the
	scope of the operation (s) is referenced, to prevent spurious
	warnings about unused units.

-------------- next part --------------
Index: sem_ch4.adb
===================================================================
--- sem_ch4.adb	(revision 216574)
+++ sem_ch4.adb	(working copy)
@@ -7617,6 +7617,17 @@
             Rewrite (First_Actual, Obj);
          end if;
 
+         --  The operation is obtained from the dispatch table and not by
+         --  visibility, and may be declared in a unit that is not explicitly
+         --  referenced in the source, but is nevertheless required in the
+         --  context of the current unit. Indicate that operation and its scope
+         --  are referenced, to prevent spurious and misleading warnings. If
+         --  the operation is overloaded, all primitives are in the same scope
+         --  and we can use any of them.
+
+         Set_Referenced (Entity (Subprog), True);
+         Set_Referenced (Scope (Entity (Subprog)), True);
+
          Rewrite (Node_To_Replace, Call_Node);
 
          --  Propagate the interpretations collected in subprog to the new