[Rivet] Pythia 6420 build script

[Andy Buckley]

Alberto Ribon wrote:
>   Hi Andy,
> 
>   the idea was to abandon the hand-built build system only
>   after the green light from the experiments.
>   I have asked few times their feedback on Pythia 6419
>   built with autotools, but I did not get anything: for 
>   them, the transition to autotools has very low priority!

I would go further: for them the autotools migration has ZERO priority, 
since they have nothing to gain from it. Genser, and users like CEDAR 
with more heterogeneous deployment environments have something to gain, 
and so it's our job to get it right. Obviously, maintaining two parallel 
builds is more work for yourselves, so should be done for as short a 
time as possible. I expected the old system to be dropped with 6420, 
since there were no complaints.

In fact I would be surprised if any of the experiments tried at all to 
use the autotools build! They will only try if the autotools version is 
the only one provided, rather than an unappetising alternative in a new 
separate directory with a disturbing "ac" in the name ;) And they will 
probably say "don't change anything", if you give them the chance to 
give a free answer. That doesn't reflect technical merit or expertise, 
just conservatism... cf. the HepMC design discussions, which are now 
backfiring because the cross-section implementation is so perverse.

>   At the GENSER planning meeting, on 29 May, I am going
>   to propose to use autotools for all new versions of the
>   generators to be installed, with the possibility of 
>   quickly re-installing it with the old hand-built build
>   system in the case the experiments find problems that we
>   are not able to fix promptly.
> 
>   Let's see what will be their reply on this proposal...

This is really a technical issue about build portability, and you should 
be able to explicitly compare whether there is any difference at all by 
diffing the output of "nm libpythia6.so" or "objdump -p libpythia6.so" 
between the hand-built version and the autotools version. That's 
something for Genser to do, rather than the experiments: they will only 
give you feedback if the version that you supply causes problems... 
which is just part of the migration process between generator versions.

In the meantime, can an autotools version of 6.420 be supplied, as for 
6419? It worked well for us, hence the silence ;)

Andy