Compiler quality (was: Extending discriminant types)

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

On Nov 23, 5:06 am, a...@anon.org (anon) wrote:
> What I am saying is that ALL BUG have been seen and reported by now for the
> GNAT-3.xx compilers, because of the volume of users and the amount of time
> that GNAT 3.xx series has been around.

Like I said i my earlier post, this is wrong, as has just been proven
when we discovered a previously inknown bug in GNAT 3.15p just a
couple of days ago. The bug is that GNAT 3.15p accepts T'Base for non-
scalar T, in the default (Ada 95) mode. Even 100 years from now, if a
single person still uses GNAT 3.15p, it will be possible for them to
discover a previously unknown bug.

Even an infinite amount of testing cannot prove a program to be bug-
free; it can only uncover an infinite amount of bugs. If you want to
prove a program correct, you must use formal methods, not testing.

> Also, professors may or may not call
> Adacore if they find a BUG, but they normally note the error for future
> reference.

I certainly hope professors (or any other user) don't keep their
records secret but instead report the bugs publicly, either in the
Debian bug tracking system (for GNAT 3.15p) or the GCC bugzilla (for
later versions).

> And that until 1997, all Ada compiler including the GNAT-3.xx series were
> under the control of the US's DOD and the RM and only the RM. All newer
> compilers are not under such strong arm control or limitation, rather that's
> the US gov't or the direct rules of the RM. So, you may see a more relax view
> on applying the RM, which mean that newer compiler nay have this and others
> types of an error, not found in the GNAT 3.xx series.

No, there is no "more relaxed view of the RM". The one thing that is
more relaxed is the trademark control over the name "Ada". All
versions of GNAT, in fact, undergo a constantly growing suite of tests
that includes and extends the ACATS. Every bug ever fixed has an
associated test to ensure the bug is never reintroduced. Of course,
bugs that are not yet fixed do not yet have such a test.

[...]
> Plus, the complete Ada 2005 specification compiler aka GNAT 2008, has only
> been around a few months and has yet to be fully tested by the Ada community
> which can take years.

Correct but that does not make GNAT 3.15p bug-free.

> As for GNAT 5.01 and GNAT Pro 6.01, well they were not written under the
> DOD and the RM only control. And they have not been around 10 to 14 years
> yet, for someone to say that 5.01 or 6.01 have been fully checked.

Like I said, even if you would use, say, GNAT Pro 5.01 for an infinite
amount of time, you could discover and correct an infinite number of
bugs and never be sure that the program is bug-free.

That's what first year CS students ought to learn, anyway.

--
Ludovic Brenta.