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[OSR] Ports-like package management system
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Date: -- (:)
From: Berke Durak <berke.durak@e...>
Subject: [OSR] Ports-like package management system
Hello,

Following Markus's message, discussions with Nicolas Pouillard and
Sylvain Le Gall and others, and of course my previous work in the EDOS
project, here are some thoughts about package management systems
(PMSs) for Ocaml.

First, the PMSs of Linux distributions are perfectly adequate for end
users and administrators having to deploy and manage identical
packages accross multiple machines.  These are very complex systems
including a substantial social part.

But they are not very suitable for developers.

As Markus pointed out, developers cannot go thru a packaging step to
test the result of a change, much less wait for the fine Debian team.

One reason is that most developers, including myself, cannot be
bothered to package software for a Linux distribution, because correct
packaging is complex and requires adherence to a set of rules must be
remembered and which cannot all be checked by software.  As packaging
is not done very often, you tend to forget those rules, and that is
why we have people who package often to not forget the rules:
maintainers.  Without maintainers, we would be in a world of pain to
install any piece of non-trivial software and we are thankful to them.

But developers absolutely need to be able to work on multiple versions
of the same software component at once, patch those versions or
compile them with unusual flags, and often use the absolutely latest
unpackaged version.  And that is the second reason why the Debian or
Red Hat PMSs are not adequate.  They have a single global state per
system, which includes the installed files, and the package database,
and cannot handle multiple versions of the same package, nor multiple
compilations of the same version.  (This also applies to Gentoo.)

We thus need versions, and lots of them!  We need to base our
developer packages on a version control system, in the style of BSD
ports.  BSD ports are usually based on CVS, sometimes on Subversion.
As we are looking to increase collaboration, having a single point of
contention is a serious limitations of these centralized systems;
we'll prefer more recent "distributed" version control system.

Of available distributed VCSs with a serious user base, we have Darcs,
Mercurial and Git.

Basing a PMS for Ocaml on a VCS written in Haskell would violate the
``Trading with the Enemy'' act.  Moreover Darcs has some performance
problems of its own.

Mercurial (Hg) is written in Python extended in C for performance.  It
is quite friendly and works well under Windows.  However, its
developers are not as elite as Git's, its merging features are less
advanced and Python sux0rz.

I have been using Hg for the past few months and been quite happy with
it, but then I was mostly working alone.  Git is certainly as good as
Mercurial for that kind of usage and, as it is written in pure C, I
advocate its use.  Until someone writes a VCS in Ocaml, that is.

Let's get back to the subject.  BSD ports are also based on make,
whose main limitation, the static dependency graph, has been addressed
in ocamlbuild.  I know there is Omake, but I think it suffers from the
``Yet Another Turing-Complete Language'' syndrome.

So I am calling for a solution based on a ports-like system but based
on a distributed VCS and on an improved ocamlbuild.

Assume you are writing a program FOO and want to use a package BAR
available from bar.org.  You tell ocamlbuild by adding some tag such
as

   <mytarget.native>: require(http://bar.org/repository/)

And when you run ocamlbuild, it automatically checks out a copy of
BAR, compiles and loads its myocamlbuild.ml module which adds the
required flags.  Of course it should be possible to specify a
particular revision...  And if BAR has itself dependencies, those too
would be checked out.

Note that Git has a nice option for cloning checked out repositories
using hard links; that could be used to maintain a cache of checkouts,
for instance in the user's ~/.ocamlbuild/checkouts/ directory.

So basically I propose that we improve ocamlbuild to allow for
multiple plugin files (using dynamic loading) and use that to define a
BSD ports-like system targeted at developers.

-- 
Berke DURAK