Re: Ada policy

[Robert Dewar <dewar@gnat.com>]

Joe Buck wrote:

> What bothers me (and what prevents me from doing testing of Ada) is not
> that GNAT won't compile with proprietary Ada compilers, but that a
> specific release of GNAT will only compile with certain very specific
> other releases of GNAT, and that this changes all the time.  That makes it
> very hard to build.

This really is not the case, there has been no change in the set of
GNAT compilers that can be used to start a build for over four years.
Any version 3.13 or later should work fine.

> If GNAT relies on extensions, and the extensions that it relies on
> constantly change, it makes life very difficult for builders and testers.

That's simply not the case, there have been no such changes for four
years. If you have found life "very difficult", I don't see that it can
be because of constant changes which have not in fact occurred. Could
you try to be more specific about your particular experiences. Perhaps
there are completely unrelated problems that should be addressed.

> One way to avoid this, it seems, would be to try to use only standard Ada.
> This would permit other Ada compilers to compile GNAT, but that's not the
> point; the point is to lessen the bootstrap problem.  You have chosen
> otherwise, and I don't know enough to say with any confidence whether this
> is a mistake, just that there is a price for it.

We have no reports of bootstrap problems arising from inability to use
earlier versions of GNAT. We did have a couple of reports of difficulties
from trying to use incompatible versions of C and Ada (which had to do
not with extensions or anything like that, but rather with different
models for handling of exceptions).

I am not sure that using only standard Ada would in fact help much, since
in the past, the problems have come from bugs in earlier versions of GNAT.
That's a long time in the past now (over four years as per the above). I
don't know for sure that the current GNAT will not build with 3.12, since
we don't test with versions that early. Note that the set of compilers
that can be used includes all FSF versions.