Re: some questions on installing Ada on Linux

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

Simon Clubley writes on comp.lang.ada:
> Therefore, as I understand it, AdaCore could stop contributing code to
> the FSF gcc branch if it chooses, provided it makes the source code
> for the binaries it actually supplies to customers available under the
> GPL.

Yes, that is correct, AFAIU, but IANAL.

You must actually make a strong distinction between the compiler and the
libraries.  The compiler is and has always been pure GPL; that does not
matter to users of the compiler as long as they don't link the compiler
into their executables.

As far as libraries are concerned, you have to distinguish between
libgnat and the other libraries (such as GtkAda, XML/Ada, etc.).
libgnat from the FSF is licensed under GPL version 3 or later with
Runtime Library Exception, just like libstdc++.  In contrast, libgnat
from GNAT GPL is pure GPL i.e. no Runtime Library Exception.  (The
"GMGPL" license disappeared long ago; see the timeline in the Debian
Policy for Ada).

The sources for libgnat are distributed together with the compiler
(gnat), so are available from the FSF.  The other libraries are
distributed separately and are not available from the FSF.  They are
available from libre.adacore.com in source only form and they are also
available from several distributions in source and binary (precompiled)
forms.

Paying customers receive the Runtime Library Exception on all libraries
but not on the compiler or on GPS, AFAICT, but again that doesn't matter
since they don't incorporate the compiler or GPS into their software
(and, in fact, few of them even distribute their software to anyone, so
the redistribution terms of the license matter very little to them).

>> I was of the understanding that they are substantially merged
>> approximately once per year.  What obstructs a wholesale merge is the
>> fact that AdaCore's GNAT lags behind 2 or 3 versions from the latest
>> stable back-end.  FSF merges the vast majority of AdaCore's evolution
>> of GNAT that does not conflict with changes in the back-end.  It is
>> bit-rot, not legalese, that naturally causes 2 source bases for GNAT.
>> The relationship is symbiotic: FSF depends on AdaCore for most of the
>> evolution of the Ada front-end, whereas AdaCore depends on FSF for
>> most of the evolution of the back-end.  AdaCore merges in a newer
>> (but still lagging) back-end version approximately once per year to
>> AdaCore's state-of-the-art front-end.  Separately, FSF merges in a
>> newer (but still lagging) GNAT front-end version approximately once
>> per year to FSF's state-of-the-art back-end.

The once-per-year merges have long been banned by the FSF.  Nowadays,
AdaCore merge their changes in small chunks, almost daily, and obey the
GCC development schedule [1].

[1] https://gcc.gnu.org/develop.html

Looking at the bottom of that page: right now GCC 4.10 is in Stage 1, so
AdaCore are busy merging almost every day from GNAT Pro into the future
GCC 4.10.  If you want examples, look for emails tagged "[Ada]" on
https://gcc.gnu.org/ml/gcc-patches/2014-06/.

Again, please read the Debian Policy for Ada :)

> Unless there's some contract I am unaware of, there's nothing to stop
> AdaCore saying that future releases to the FSF gcc codebase are done
> under the terms of the pure GPL.

Yes, the FSF can stop AdaCore because the FSF owns the copyright on GNAT
and libgnat, so only the FSF gets to decide on the licensing terms.

> They have already done this once with another product. GtkAda used to
> have a GMGPL style licence up to around GtkAda 2.4, but the public
> version of GtkAda was converted (overnight) to a pure GPL licence.
> Existing releases of GtkAda stayed under the GMGPL; new releases were
> under the pure GPL.

Here comes the big distinction between libgnat which belongs to the FSF
and the other libraries which belong to AdaCore.

-- 
Ludovic Brenta.