[Nix-dev] (haskell) a question on depending on specific version of packages

[Marc Weber]

Excerpts from Corey O'Connor's message of Sat Jan 15 11:44:22 +0100 2011:
> Using parallel 2.2.0.1 is fine for GHC 6.12. However, when using GHC
> 7, I prefer using vty with parallel 3.1.0.1. Course, depending on the
> situation, somebody might want to use vty with parallel 3.1.0.1 under
> GHC 6.12. Which leads me to wonder:

Let me tell you the ways I know about:

A1) using ~/.nixpkgs/config.nix or (nixpkgs configuration section in
nixos):
  http://www.mail-archive.com/nix-dev@cs.uu.nl/msg08052.html

A2) using override (this package only, create new name)
  vty2 = vty.override { parallel = parallel; };


A3) using system configuration:

  vty = callPackage ../development/libraries/haskell/vty {
    parallel = if (cgetConfig ["haskellPackages" "useparallel-2-2.."] ttrue) then parallel_2_2_0_1 else parallel;
  };


B) same as A3, but based on ghc version:

  vty = callPackage ../development/libraries/haskell/vty {
    # > must be encoded using builtins.lessThan
    parallel = if (builtins.versionCompare ghc.version "xxx" > "target-version")  then parallel_2_2_0_1 else parallel;
  };


C) using deepOverride (sipirit of webkit)
  webkit = ((builderDefsPackage ../development/libraries/webkit {
    inherit (gnome28) gtkdoc libsoup;
    inherit (gtkLibs) gtk atk pango glib;
    inherit freetype fontconfig gettext gperf curl
      libjpeg libtiff libpng libxml2 libxslt sqlite
      icu cairo perl intltool automake libtool
      pkgconfig autoconf bison libproxy enchant
      python ruby which flex geoclue;
    inherit (gst_all) gstreamer gstPluginsBase gstFfmpeg
      gstPluginsGood;
    inherit (xlibs) libXt renderproto libXrender;
  }).deepOverride {libsoup = gnome28.libsoup_2_31;});

  Eelco once said he dislikes this way - because it forces passing
  a different libsoup to to all packages.
  Maybe his disliking stopped when callPackages was introduced - because
  he never replied  /commented on my patch which improved deep overriding !?)
  although I asked about 3 times!
  It was about this patch (I'm still rebasing it):
  http://thread.gmane.org/gmane.linux.distributions.nixos.scm/382/focus=5041

D) use hack-nix.

  You have a "haskell-package" configuration consisting of
  - a pool of packages (most are taken from hackage, but you can add your
    own)
  - a set of attributes patching the generated stuff (eg adding c
    depnedencies, setting flags, ..)

  Then a brute force solver tries to find a valid solution for the set of
  packages you're interested in.

  Here you can easily replace packages by others in the pool or change
  cabal configurations for each build taking place.

  I haven't tried building anything using ghc-7 yet.

comments:
==========

You only want to have a closer look at B,C,D because they let you
override the package version for a different ghc version only

D) is superior to A-C because it will tell you before starting to build
that the versions you selected match (according to .cabal files) - or it
will fail.

I was told that have "dozens" of things in my mind at the same time -
and that's not always easy to follow me. So bear with me and ask if
there are any questions left.

Currently I'm talking to Andres Loeh to make him understand more about
hack-nix - so that we eventually can join efforts maintaining one way of
building packages using Nix in the future.

Marc Weber