[[!meta date="2016-06-28 02:54"]]
[[!img media/nixos-lores.png alt="" class="noFancy" style="float: right"]]
[[!series emscripten]]
[[!tag sprint nixos linux technology usability emscripten]]
[[!summary a report about a nixos hacking sprint in the augsburger 'openlab' hackerspace.]]

# nixos-sprint

paul and me visisted the [augsburger openlab](https://openlab-augsburg.de/) last weekend, for a nice nixos sprint with profpatsch. the sprint lasted two days and we talked lots about nix/nixpkgs internals.

## nix based emscripten toolchain

we've been working on the [emscripten nix toolchain](https://github.com/NixOS/nixpkgs/pull/16208). current status is: prototype is working and we can already compile these targets:

* libz
* libxml2
* json_c
* [xmlmirror](https://gitlab.com/odfplugfest/xmlmirror)

**note:** *YAY*, this is the first nix-based emscripten toolchain which should work on nixos but also on **mac os x** and on basically **every POSIX supporting unix**!

## nixexpr grammar

[we had the idea to make the nix expression language more forgiving](https://github.com/NixOS/nix/pull/948) by having it support `;` at the end of a normal function body.

### random example: mkDerivation
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ {.bash}
  json_c_ = emscriptenStdenv.mkDerivation rec {

    name = "json_c_";
    version = "json-c-0.12-20140410";

    buildInputs = [ autoconf automake libtool pkgconfig gnumake ];

    src = fetchgit {
      url = "https://github.com/json-c/json-c";
      rev = "refs/tags/${version}";
      sha256 = "0s9h6147v2vkd4l4k3prg850n0k1mcbhwhbr09dzq97m6vi9lfdi";
    };
    postFixup = "echo postFixup";
    preFixup = "echo preFixup";
    fixupPhase = "echo fixupPhase";
  };

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

you close the scope with `};` and you always need the `;` which is not optional.

### function call
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ {.bash}
{ foo, bar } :

{
  # function body
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

you close the scope with `}` and you are not allowed to use `};`!

**note:** [with this patch](https://github.com/NixOS/nix/pull/948) you are now allowed to write either `}` (default) or `};` which is new.

## mkDerivation outputs
i finally learned that we now have the [`outputs`-feature]( https://nixos.org/nix/manual/#ssec-derivation)

this means nixos/nix now supports split packages: 

* `foo.deb` vs. 
* `foo-dev.deb` 

as ubuntu and other distros does. 

in `nixpkgs`, for instance in an `stdenv.mkDerivation` you can now use:

    outputs = [ "lib" "headers" "doc" ];

to install software into these directories! great!


# summary

nice ppl, nice room. 10/10, would hack there again! **huge thanks to Profpatsch and helpers.**