[Nix-dev] Language-specific package managers

[Malcolm Matalka]

The situations you've described are basically the ones I'm in.  Luckily
the ocaml package manager I am using just does local installs the
packages in the home dir.  I actually think I have figured out why it
wasn't building packages for me before, and think I can get around it so
I can just use the ocaml package manager for fast development and once
things become static make real Nix expressions from it.

/M

Florian Friesdorf <flo at chaoflow.net> writes:

> Hi Malcolm,
>
> Malcolm Matalka <mmatalka at gmail.com> writes:
>> Thanks for the complete response Marc.
>>
>> For the mean time, the current solution I'm working on is manually
>> converting packages to Nix.  The translation is pretty straight forward
>> and I should be able to write a tool to automatically do it.  It's not
>> optimal but I have been able to get all of the packages I care about
>> into my local nixpkgs repo and will submit them to the master repo once
>> I'm satisfied with them.
>
> I like the approach of (semi-)automatically creating nix expressions.
>
> In my understanding (and I am pretty determined but happy to change it
> based on good arguments):
>
> A set of nix expressions always produces the very same output.
>
> For me this means (so far) that ad-hoc resolving dependencies within nix
> is not needed. I want to resolve dependencies ad-hoc when creating a new
> set of nix expressions, but not when I install a package via nix.
>
> Therefore the resolver belongs outside of nix.
>
> If I want to install things ad-hoc in a nix system, I need to create a
> bridge between a nix world where everything is determined and a fluent
> world where things are installed as they are available. These fluent
> things cannot reside in the nix store. Whether such dynamically managed
> things belong into /var or a user's home is another discussion.
>
> For nodejs I was quit happy that I got such a dynamic profile via:
> % npm config set prefix ~/.nodejs
>
> Now installing things "globally" end up in ~/.nodejs and the bins in
> ~/.nodejs/.bin, which I included in my path. Perfect quick and dirty
> installation of the view nodejs packages I need.
>
> For python we are aiming at something similar: generate nix expression
> and check them into git for commonly needed packages, use the rest via
> easy_install, but give the people the tool to create nix expressions for
> whatever they need.
>
> Looking forward to your ocaml work!
>
> regards
> forian
>
>> Marc Weber <marco-oweber at gmx.de> writes:
>>
>>> I created 
>>> hack-nix for Haskell, which dumps hackage. contains a brute force
>>> dependency solver
>>>
>>> nixpkgs-ruby-overlay [1] which dumps rubyforge (which is quite usable, but not perfect yet)
>>> nixpkgs-python-overlay [2] which dumps PyPi (experimental, dependency inforamtion is not complete enough)
>>> does not do backtracking, if dependencies fails its you having to to
>>> tell it "try lib-A version 2.0.0".
>>>
>>> They are special because they all work on a "dump of packages" creating
>>> .nix derivations on the fly whereas cabal2nix creates .nix files very
>>> close to what you find in nixpkgs.
>>>
>>> They all create kind of shell script you can source to augment the
>>> environment variables, so that dependencies are found.
>>> Thus you can have multiple "sets of packages" for different targen
>>> porjects within the same user account without conflicts - however you
>>> always have to load such an environment, eg by
>>>
>>>   # run bash with ruby packgaes found in environment "name"
>>>   ruby-env-name bash
>>>
>>> Known additional universes:
>>>   - perl
>>>   - java, scala (ivy, maven, sbt)
>>>   - ....
>>>
>>> There are many ideas and ways to implement such.
>>> Eg for scala/maven/ivy/... one way to think about it would be using the
>>> store as "installation place", but not using much about the nix* tools
>>> otherwise.
>>>
>>> then sbt build would just store everything in store.
>>> Other ways are creating .nix files for a target on the fly - such as
>>> sbt/ivy/mvn create-nix-derivations (which is close to what cabal2nix
>>> does).
>>>
>>> The downside is that you may have to run a tool before you can succeed
>>> with nixos-rebuild-switch, because not everything may be packaged.
>>>
>>> The perfect way would be including a SOT solver in nix, which hasn't
>>> beeen done yet - and which was not favored by Eelco in the past (maybe
>>> for good reason). Eg Eclipse plugin system works this way: the SAT
>>> solver tries to find one working set of dependencies to satisfy the
>>> setup you want - however the search space may be very big - which is why
>>> I limit the simple brute force solver used by hack-nix by passing only a
>>> subset of all packages found on hackage (latest versions & same manually
>>> selected ones).
>>>
>>> While such a generic approach may seem perfect, there are these
>>> downsides:
>>>
>>> - its harder to controls when rebuilds will take place, because small
>>>   changes in the pool may cause the solver arbitrarely choose a
>>>   different solution, otherwise its you having to force eg library-A
>>>   version should be 1.0 like thing.
>>>
>>>   and such rebuilds are bad, because its easy to loos track about which
>>>   combinations actually work, because while constrtaints are fine, they
>>>   are never complete.
>>>
>>>   Thus in any case there will be lots of maintainance effort.
>>>
>>> - its also hard and time consuming (for humans and the cpu) to evaluate
>>>   all solutions over and over again - which may not be the perfect end
>>>   user experience. Eg you do'nt want wont to wait 30secs for the
>>>   evaluation to finish just to install "gnu sed"
>>>
>>>> translation apps for all language package manager types?  Specifically I
>>>> am looking at opam, the new ocaml package manager.
>>> I never used opam.
>>>
>>> Can you copy paste a package description with dependency information so
>>> that we can get an idea about how it actually looks like?
>>>
>>> Cabal is kind of "static", but very complex.
>>> Example:
>>> http://hackage.haskell.org/packages/archive/darcs/2.8.3/darcs.cabal
>>> scroll down to "build-depends" which depend on "flags" which are
>>> automatiacally chosen depending on the ghc version available - but
>>> flags are also used to enable/disable features or test cases
>>>
>>> for python and ruby there are .py or gemspec files.
>>> The problem is that they may even run python or ruby code - thus
>>> there may be packages whos dependencies may depend on configuration
>>> options and or the system which makes it harder to to dump such info
>>> into something which can be read and used by nix.
>>>
>>> [1] ruby: http://gitorious.org/nixpkgs-ruby-overlay
>>> [2] python: http://gitorious.org/nixpkgs-python-overlay
>>>
>>> For ruby and Haskell I also have some code which can create package
>>> descriptions for dev versions of packages which then can be read by the
>>> code creating the derivations on the fly.
>>>
>>> And then there is stills the question:
>>> Is it efficient to download 40.000 package descriptions if you need only
>>> 10? The lazy behaviour of the native package managers for ruby (gem),
>>> python (eg pip) etc somehow make this question obsolete.
>>>
>>> Just think about how many perl packages there are available.
>>>
>>> Well - you don't have to download 40.000 packages, cabal2nix only dumps
>>> the the maintained packages which are selected manually.
>>> Another solution would be making nix connect to a server to access a
>>> versioned well known "dump state" about known packages. Then only those
>>> package infos could be fetched which are required to fullfill would have
>>> to be fetched.
>>>
>>> The ivy case may be not trivial cause you can configure dependencies in
>>> a transient way which means if you have A < B < C you can configure C to
>>> modify dependency A or such (I never fully had the time to learn about
>>> all features).
>>>
>>> So the topic is hot - and there is still quite some work left to be
>>> done.
>>>
>>> The cabal2nix way may work well if you need some packages only and is
>>> easy to understand and to debug.
>>>
>>> I hope I was able to shed some light into current state I know about -
>>> others may know more.
>>>
>>> Let's not forgett that eg most xorg packages are generated
>>> automatically, too. The some additional manual work is required to make
>>> everything build.
>>>
>>> There are more sub universes, such as gnome which is provides a central
>>> download folder hirarchy you could use to dump package information from.
>>> Nobody did it yet.
>>>
>>> Marc Weber
>>> _______________________________________________
>>> nix-dev mailing list
>>> nix-dev at lists.science.uu.nl
>>> http://lists.science.uu.nl/mailman/listinfo/nix-dev
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