AI05-087 is a binding interpretation that applies to previous versions of the
language. The compiler diagnoses the error at the point of instantiation in
Ada2012 mode, and at a point of illegal use in Ada2005 mode.
the command:
gcc -c -gnat05 proc.adb
must yield:
proc.adb:18:05: instantiation error at line 13
proc.adb:18:05: assignment not available on limited type
the command:
gcc -c -gnat12 proc.adb
must yield:
proc.adb:18:45: actual for non-limited "T" cannot be a limited type
proc.adb:18:45: instantiation abandoned
proc.adb:33:06: "Store" is undefined
procedure Proc is
package Pack is
type Ifc is limited interface;
generic
type T is abstract new Ifc with private; -- T is nonlimited: 7.5(6.1/2)
procedure Classwide_Store (Target : out T'Class; Source : T'Class);
end Pack;
package body Pack is
procedure Classwide_Store (Target : out T'Class; Source : T'Class) is
begin
Target := Source;
end Classwide_Store;
end Pack;
use Pack;
procedure Store is new Classwide_Store (Ifc); -- legal? (No.)
task type Tsk;
task body Tsk is
begin
null;
end Tsk;
type Has_Task is limited new Ifc with
record
F : Tsk;
end record;
X, Y : Has_Task;
begin
Store (X, Y);
end;
Tested on x86_64-pc-linux-gnu, committed on trunk
2012-02-22 Ed Schonberg <schonb...@adacore.com>
* exp_ch5.adb (Expand_N_Assignment_Statement): Reject an
assignment to a classwide type whose type is limited, as
can happen in an instantiation in programs that run afoul or
AI05-0087.
Index: exp_ch5.adb
===================================================================
--- exp_ch5.adb (revision 184470)
+++ exp_ch5.adb (working copy)
@@ -6,7 +6,7 @@
-- --
-- B o d y --
-- --
--- Copyright (C) 1992-2011, Free Software Foundation, Inc. --
+-- Copyright (C) 1992-2012, Free Software Foundation, Inc. --
-- --
-- GNAT is free software; you can redistribute it and/or modify it under --
-- terms of the GNU General Public License as published by the Free Soft- --
@@ -28,6 +28,7 @@
with Checks; use Checks;
with Debug; use Debug;
with Einfo; use Einfo;
+with Errout; use Errout;
with Exp_Aggr; use Exp_Aggr;
with Exp_Ch6; use Exp_Ch6;
with Exp_Ch7; use Exp_Ch7;
@@ -2086,6 +2087,18 @@
and then
not Restriction_Active (No_Dispatching_Calls))
then
+ if Is_Limited_Type (Typ) then
+
+ -- This can happen in an instance when the formal is an
+ -- extension of a limited interface, and the actual is
+ -- limited. This is an error according to AI05-0087, but
+ -- is not caught at the point of instantiation in earlier
+ -- versions.
+
+ Error_Msg_N ("assignment not available on limited type", N);
+ return;
+ end if;
+
-- Fetch the primitive op _assign and proper type to call it.
-- Because of possible conflicts between private and full view,
-- fetch the proper type directly from the operation profile.
