[RFC] Replace Java with Go in default languages

[Jeff Law <law at redhat dot com>]

GCJ has, IMHO, moved from active development into a deep maintenance 
mode.    I suspect this is largely due to the change of focus of key 
developers to OpenJDK and other projects.  GCJ played a role in 
bootstrapping OpenJDK, both technically and politically and had OpenJDK 
not happened, I suspect GCJ would still be under active development.

The last news item related to Java was 2009 and scanning the ChangeLog 
doesn't show significant project activity (~14 changes in 2013, most of 
which look like routine maintenance in the language front-end.   There's 
even fewer changes occurring in the runtime system.

I did some benchmarking using one of my slower systems (primarily 
because my faster systems are used for real work).  It's an older quad 
machine, but should give us a reasonable feel for how expensive java is 
to the bootstrap & regression testing process.

A default languages bootstrap takes 67 minutes on that box (-j4).  The 
times were consistent to within 20 seconds.  Disabling java brings that 
time down to 51 minutes, again with a variance of around 20 seconds. 
That means roughly 25% of the time to bootstrap is Java.

I didn't measure total testing time -- just the time to test Java, where 
it clocks in at 7 minutes (again -j4, though it's clearly not doing much 
in parallel).

Clearly bootstrapping and testing Java is expensive.  It's better than a 
while back (thanks to removing the static library build), but it's still 
a significant component of the bootstrap & test cycle we all do regularly.

We discussed removing libjava extensively in 2008, but never moved 
forward.  It's not entirely clear why from reviewing the thread. 
Additionally, I think the landscape around OpenJDK is a bit different 
now than then and thus it's time to revisit.

So instead of proposing that we just remove Java from the default 
languags, I propose that we replace Java with Go.

Go uses -fnon-call-exceptions which is one of the things that was a bit 
unique about GCJ and Go appears to have a much more vibrant developer 
and user community than GCJ.  So we get the -fnon-call-exceptions 
testing we want and we're actually building a front-end that a larger 
community cares about.

A bootstrap with Go replacing Java clocks in at 56 minutes.  So we're 
still getting most of the improvement in bootstrap times.

Testing Go (compiler & runtime) takes about a minute longer than libjava 
(it's doing more in parallel, so serially Go would be considerably 
longer in testing).

Clearly switching from libjava to go would be a significant improvement 
in the bootstrap and regression test cycle.  On the box I tested we'd 
see roughly at 15% improvement and we'd still get testing of 
-fnon-call-exceptions.


Thoughts or comments?