[Ada] Remove spurious warning on access discriminant

[Arnaud Charlet]

The generated default stream input function for a record type includes
individual declarations for each discriminant and each component, followed
by a call to the corresponding input function for the component type. If the
type is a null-excluding access type we must mark the corresponding declration
as needing no initialization, to prevent spurious warnings. This mark was
present for components, but missing for access discriminants.

See gnat.dg/access_discr2.adb

Tested on i686-pc-linux-gnu, committed on trunk

2008-08-05  Ed Schonberg  <schonberg@adacore.com>

	* exp_strm.adb (Build_Record_Or_Elementary_Input_Function): For access
	discriminants, indicate that the corresponding object declaration has
	no initialization, to prevent spurious warnings when the access type is
	null-excluding.

-------------- next part --------------
Index: exp_strm.adb
===================================================================
--- exp_strm.adb	(revision 138518)
+++ exp_strm.adb	(working copy)
@@ -1113,12 +1113,22 @@ package body Exp_Strm is
          while Present (Discr) loop
             Cn := New_External_Name ('C', J);
 
-            Append_To (Decls,
+            Decl :=
               Make_Object_Declaration (Loc,
                 Defining_Identifier => Make_Defining_Identifier (Loc, Cn),
                 Object_Definition =>
-                 New_Occurrence_Of (Etype (Discr), Loc)));
+                  New_Occurrence_Of (Etype (Discr), Loc));
+
+            --  If the this  is an access discriminant, do not perform default
+            --  initialization.  The discriminant is about to get its value
+            --  from Read, and if the type is null excluding we do not want
+            --  spurious warnings on an initial null.
+
+            if Is_Access_Type (Etype (Discr)) then
+               Set_No_Initialization (Decl);
+            end if;
 
+            Append_To (Decls, Decl);
             Append_To (Decls,
               Make_Attribute_Reference (Loc,
                 Prefix => New_Occurrence_Of (Etype (Discr), Loc),