Re: Adacore and licensing (again), was: Re: State of the compiler market

[Robert Eachus <rieachus@comcast.net>]

On Wednesday, March 1, 2017 at 1:36:40 PM UTC-5, Simon Clubley wrote:
> On 2017-03-01, reinert <reinkor@gmail.com> wrote:
> >> 
> >> If you are using Adacore's free GNAT distribution instead of the FSF
> >> distribution then your resulting product will have to be open source.
> >> 
> >> Are you aware of this ?
> >> 
> >> Simon.
> >> 
> >
> > Yepp. And I assume potential users will hesitate to spend much time to learn to use something closed source from a small business :-)
> 
> Good. Given that I have had to explain this to more than one person
> over the years who simply hadn't realised this, I just wanted to be
> sure you knew.
> 
> Simon.

Don't scare people too much.  Use whatever version of GNAT (or other compiler) you want during development.  When you get ready to ship a commercial product, the version you use to compile THAT is important, consult your lawyer type stuff.  If all you distribute to your customers is source code, none of that applies.

When I was at MITRE, our group tried to keep code compiling through two different compilers during development.  Occasionally this turned out to be handy, if one compiler didn't work with a new OS release or there was a bug where we needed to wait for a compiler fix. It also let us find errors in the RM, and more interesting, thinkos, where it had to be that way in the standard, but it just seemed wrong.  For example, what happens if there are several ways to evaluate the expression in a static type declaration?  For example:

    Big: constant := 3**300 / 9**140 - 2**31; -- fits in a 32-bit integer.

But evaluating it sure doesn't.  Most compilers now have built-in bignum packages now, but you know that the compiler is not going to evaluate that the way you would.  Are there still cases where (some) compilers will reject otherwise legal programs do to (compile-time) capacity limits?  I'm sure there are, but I'm also sure that they are very hard to reach.