Re: GNAT GPL 2013 bug?

[Adam Beneschan <adambeneschan@aol.com>]

On Friday, August 9, 2013 11:25:57 AM UTC-7, Simon Wright wrote:

> 
> > On Friday, August 9, 2013 9:11:35 AM UTC-7, Simon Wright wrote:
> 
> >> > In some of the examples in your later post (like the one where Q is
> >> > private and the full type is a tagged record), there isn't a problem
> >> > either, since the procedure isn't dispatching.
> 
> >> So when GNAT says, at the procedure call, that a null value isn't
> >> allowed and that CE will be raised, it's wrong?
> 
> > I just tried it on a case with "type Q is private" [not tagged] and a
> > full definition "type Q is tagged null record", and I didn't get a
> > warning.  In the example you posted, GNAT is correct to display a
> > warning, but your procedure *is* dispatching, and this situation isn't
> > the same as the part of my post that you quoted.
> 
> I was talking about a slightly different case, corresponding to yours I
> think:
> 
>    package Dmitry is
>       type Q is private;
>       procedure P (X : access Q) is null;
>    private
>       type Q is tagged null record;
>    end Dmitry;
> 
>    with Dmitry; use Dmitry;
>    procedure Test_Dmitry is
>       Y : access Q;
>    begin
>       P (Y);                  ------ dmitry.ada:11
>    end Test_Dmitry;
> 
> and get (GCC 4.8.1 and GNAT GPL 2013):
> 
> gnatmake test_dmitry.adb  -gnat12 -f
> gcc -c -gnat12 test_dmitry.adb
> dmitry.ada:9:04: warning: variable "Y" is read but never assigned
> dmitry.ada:11:07: warning: null value not allowed here
> dmitry.ada:11:07: warning: "Constraint_Error" will be raised at run time
> gcc -c -gnat12 dmitry.ads
> gnatbind -x test_dmitry.ali
> gnatlink test_dmitry.ali

OK, that's essentially the same Ada code I was testing.  However, I was using an older version of GNAT when I tried it and didn't get a warning.  Later versions do give a warning.  

Offhand, I do think GNAT is wrong, and that P is not a dispatching procedure.  However, the language rules get a bit murky at times when untagged private types are completed with tagged types, and sometimes the rules have had to be changed because they didn't cover this case adequately.  I'll have to dig a bit further.

                                  -- Adam