root-system in debian

[cholm]

Hi Gürkan,

On 2018-10-12 10:18, Gürkan Myczko wrote:
> Hello Christian
> 
> What was the reason root-system is not in Debian any more?

First off, I am not, nor have I ever been the Debian maintainer of 
root-system (and related packages).  My contribution was to set-up the 
packaging stuff and make sure that the licenses where DFSG-compliant.

Maintenance of the packages was then assumed by the Debian Science team 
(Cc'ed).

I do not know the specific reasons why root-system was removed from 
Debian.

If I were to guess, which I will, then I would say that the version in 
Debian (5.34) was old.  The version is still being maintained (albeit 
not by the ROOT developers but by LHC experiments that still use the 
older version).   The newer version of ROOT (6+) is radically different 
from previous versions, most specifically that the hand written C++ 
parser and interpreter (CINT) was replaced by an LLVM/Clang backend.   
The new interpreter (Cling) is far better than the old one, and also 
allows usage of ROOT in Jupyter via a kernel.

All of this is not a show-stopper for Debian packaging.  In fact, most 
of the packaging scripts, etc. would still work except for a few tweaks 
here and there.

What is a little troublesome for Debian is that ROOT comes with it's own 
(hacked) LLVM/Clang to enable the interpreter Cling.   Essentially, 
Cling has to hook into somewhat deep (and non-trivial) places of Clang 
to work.   This means that building ROOT cannot rely on system 
LLVM/Clang.  Until the Cling specific hooks are merged upstream in 
Clang, that will likely always be a situation.

Whether this is a real problem for Debian, I do not know.  The ROOT 
versions of LLVM and Clang are not made public to the install system but 
are absorbed into the run-time library libCling.  Of course, there's a 
duplication of binary code (more or less), which is not great, but not a 
huge problem in this case.

> Will it return?

I don't know.  I seem to remember seeing a Git project which packaged up 
ROOT6, but now I cannot find it again.  However, the fixes should be 
fairly trivial.  The infrastructure of the build system hasn't changed 
much in ROOT6 (as compared to ROOT5), and some plugins has disappeared, 
so in that sense it would be simpler.

The best people to ask for the information on why ROOT was removed from 
Debian and whether it will return are the maintainers (Cc'ed).  I would 
personally also like to hear the answers.

Yours,

-- 
Christian Holm Christensen 
-------------------------------------------------
  Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen
  http://cern.ch/cholm, +4524618591