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developing software using nixos

23 Mar 2012

#motivation i’ve just finished a wiki page on how to develop arbitrary software on nixos [1] (thanks to viric!). as this is fundamentally different to all other linux and non linux operating systems i think this is worth a posting about this subject in my blog.

the interesting aspect is that nix/nixos provides such a development environment per project so one is not forced to pollute the system environment with the ongoing changes which always lead to horrible side effects as regression (you know when old habits stop working as a tiny update of libX breaks tool Z).

the way it is used is covered by [1] already.

a slightly more complex example

config.nix

     1  {
     2    packageOverrides = pkgs : with pkgs; rec {
     3      # example environment from viric
     4      sdlEnv = pkgs.myEnvFun {
     5        name = "sdl";
     6        buildInputs = [ stdenv doxygen SDL SDL_image SDL_ttf SDL_gfx cmake SDL_net pkgconfig ];
     7      };
     8
     9      # a custom library NOT included in nixpkgs (maybe later it is but assume for this example it is not)
    10      libnoise = callPackage ./libnoise.nix {};
    11
    12      # this is the needed environment for development of my spring random map generator
    13      # type 'load-srmg-env' to load it after installing it using 'nix-env -i env-srmg'
    14      srmgEnv = pkgs.myEnvFun {
    15        name = "srmg";
    16        buildInputs = [ stdenv doxygen cmake libnoise qt4 ];
    17      };
    18    };
    19  }

in the ~/.nixpkgs/config.nix expression i added a custom library which is then available with nix-env, this way it can be installed using (nix-env -i libnoise).

the interesting point is that line 2 contains the rec keyword indicating that all 3 attributes in the attribute set (line 2 to 18) may recursively reference each other. this is required as the the srmgEnv on line 14 where the buildInputs lists libnoise.

the libnoise expression is outsourced (line 10) into the file libnoise.nix (listed below).

libnoise.nix

     1  {stdenv, doxygen, fetchgit, cmake}:
     2
     3  stdenv.mkDerivation rec {
     4    name = "libnoise-1.0.0";
     5
     6    # i also change bits in the library and therefore i like to have it local
     7    # in case i change anything this needs to be done to reflect the change
     8    # 1. make the change 
     9    # 2. use 'git add file_which_has_changed'
    10    # 3. use 'git commit'
    11    # 4. use 'git log' to find the most recent rev
    12    # 5. paste the copied rev in the rev field below
    13    # 6. reinstall the libnoise 
    14    src = fetchgit {
    15      url = /home/joachim/Desktop/projects/libnoise;
    16      rev = "8b5b89b7241a112dfe0b387f7589ea9a2df00b02";
    17      sha256 = "";
    18    };
    19
    20    buildInputs = [ cmake doxygen ];
    21
    22    meta = {
    23      description = "libnoise";
    24      homepage = "http://www.github.com/qknight/libnoise";
    25      license = "LGPL2";
    26      maintainers = with stdenv.lib.maintainers; [qknight];
    27    };
    28  }
    29

the libnoise.nix file is interesting as it references a local git repository. it also lists what to do in order to alter the package.

once the srmg-env is installed (nix-env -i env-srmg) it can be used using: load-srmg-env. as mentioned in [1] this environment will then behave as if one had used ubuntu linux and then installed all the required libraryies.

future

as i noted in [1] nix will soon get a toggle (nix-build –run-env ‘’ -A xterm, see [2]) which will clone the environment of virtually any sourceScription on the system. this means one can hack on any software easily by injecting code into the build chain on an arbitrary position - still, this changes won’t be persistent, meaning:

still it is one step towards the concept of the midstream platform (mentioned in my diploma thesis) and is a great way to test a quick hack.

update: 23.5.2012

another interesting potential property is that tools like kdevelop could be patched to automatically see all the include paths of a complete project and therefore are able to provide automatic code completion without having too much manual effort.

kdevelop can do that already! when importing the project’s ‘CMakeLists.txt’, kdevelop reads the ‘found’ entries and therefore collects all the library paths!

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