Nix for devs

This is collection of recipes focused on nix-shell to make setting up project environments easy. Pragmatism and low project impact are prioritized: it's not a goal to change a nodejs project to use nix instead of npm, but it is a goal to run npm projects without having to install any OS dependencies (including nodejs itself!). nix-ops and other super-cool nix tech are completely out of scope.

Every solution should work today. If something is broken, open an issue!. If there is a better solution that will be supported by nix soon, we wait until it's released before mentioning it here (but don't hesitate to open a tracking issue!).

Maybe in the best case, this document can be a kind of gateway to nix and nixos. I keep telling my developer friends about the cool things I do with nix, but I have to add huge warnings about how much time it's taken me to get to my current level of productivity. I'm annoyingly aware of the amount of trivia I'm carying in my head (though I still feel like a beginner!), and I constantly go back to old projects to look up what I did last time to fix problems. I frequently find myself running into hard-to-google issues. So, I'm finally writing it all down, for myself as much as for my friends :)

Work-in-progress

Current state: rough sketches and todos. Pull requests welcome!

nix-shell

TODO

Run stuff without installing anything

Stuff I used to do with docker. TODO :)

Node.js

shell.nix

with import <nixpkgs> {};

stdenv.mkDerivation {
    name = "node";
    buildInputs = [
        nodejs
    ];
    shellHook = ''
        export PATH="$PWD/node_modules/.bin/:$PATH"
    '';
}

The nodejs build input sets up node and npm in the shell. The shell hook adds the .bin/ folder to your PATH, so you can install node command-line tools like grunt with npm without the -g flag. Finally, it automatically installs any dependencies found in package.json, if one exists. If you prefer to run npm install manually inside the shell, just delete that line from shellHook.

npm run <...> shortcut

It's handy to have an alias run for npm run, which makes the following two commands equivalent:

$ npm run watch:test
$ run watch:test

You can add this to shellHook:

    alias run='npm run'

Newer nodejs

shell.nix

with import <nixpkgs> {};

stdenv.mkDerivation {
    name = "node";
    buildInputs = [
        nodejs-8_x
    ];
    shellHook = ''
        export PATH="$PWD/node_modules/.bin/:$PATH"
    '';
}

Node versions are published as -_x, so etg., nodejs-7_x and nodejs-6_x are also valid.

View available npm scripts

I use jq to quickly get a summary of all scripts defined in a package's package.json file:

shell.nix

with import <nixpkgs> {};

stdenv.mkDerivation {
    name = "node";
    buildInputs = [
        jq
        nodejs
    ];
    shellHook = ''
        export PATH="$PWD/node_modules/.bin/:$PATH"
        alias scripts='jq ".scripts" package.json'
    '';
}

This sets up an alias called scripts. Example output:

$ scripts
{
  "build": "babel --ignore __tests__,story.js -d lib/ src/",
  "lint": "eslint *.js src/ storybook/",
  "start": "start-storybook -p 9001 -c ./storybook/web",
  "test": "jest --roots src --silent",
  "test:watch": "jest --roots src --watch"
}

React native

shell.nix

with import <nixpkgs> {};

let
  jdk = openjdk;
  node = nodejs-8_x;
  sdk = androidenv.androidsdk {
    platformVersions = [ "23" ];
    abiVersions = [ "x86" ];
    useGoogleAPIs = true;
    useExtraSupportLibs = false;
    useGooglePlayServices = false;
  };
  unpatched-sdk =
    let version = "3859397";
    in stdenv.mkDerivation {
      name = "unpatched-sdk";
      src = fetchzip {
        url = "https://dl.google.com/android/repository/sdk-tools-linux-${version}.zip";
        sha256 = "03vh2w1i7sjgsh91bpw40ryhwmz46rv8b9mp7xzg89zs18021plr";
      };
      installPhase = ''
        mkdir -p $out
        cp -r * $out/
      '';
      dontPatchELF = true;
    };
  run-android = pkgs.buildFHSUserEnv {
    name = "run-android";
    targetPkgs = (pkgs: [
      node
    ]);
    profile = ''
      export JAVA_HOME=${jdk.home}
      export ANDROID_HOME=$PWD/.android
      export PATH=$PWD/node_modules/.bin:$PATH
    '';
    runScript = "react-native run-android";
  };
in
  stdenv.mkDerivation {
    name = "react-native-android";
    nativeBuildInputs = [
      run-android
    ];
    buildInputs = [
      coreutils
      node
      sdk
      unpatched-sdk
    ];
    shellHook = ''
      export JAVA_HOME=${jdk}
      export ANDROID_HOME=$PWD/.android/sdk
      export PATH="$ANDROID_HOME/bin:$PWD/node_modules/.bin:$PATH"

      if ! test -d .android ; then
        echo doing hacky setup stuff:

        echo "=> pull the sdk out of the nix store and into a writeable directory"
        mkdir -p .android/sdk
        cp -r ${unpatched-sdk}/* .android/sdk/

        echo "=> don't track the sdk directory"
        echo .android/ >> .gitignore

        echo "=> get react-native-cli in here"
        npm install --no-save react-native-cli

        echo "=> set up react-native plugins... need an FHS env for... reasons."
        cd .android/sdk
          $PWD/bin/sdkmanager --update
          echo "=> installing platform stuff (you'll need to accept a license in a second)..."
          $PWD/bin/sdkmanager "platforms;android-23" "build-tools;23.0.1" "add-ons;addon-google_apis-google-23"
        cd ../../
      fi;
    '';
  }

This one is super-hacky and requires usage instructions :( also probably only works on linux :/

1. Enter the environment

$ nix-shell
[...lots of console spam the first time]
[nix-shell:]$

2. If you don't have an avd set up, make one

[nix-shell:]$ android create avd -t android-23 -b x86 -d "Nexus 5" -n nexus

That command seeme to create slightly screwy avds. I ran $ android avd and then hit edit and save without any changes on mine, which seems to fix it :/

3. Start the JS server and emulator

Both commands block: either background then (add & at the end) to run in the same terminal, or open a terminal for each

[nix-shell:]$ npm start
[nix-shell:]$ emulator -avd nexus

4. Run it!

[nix-shell:]$ run-android

Note that this run-android is provided by shell.nix, and wraps the call to react-native-cli's react-native run-android command in the FHS environment so that the build works.

Python

shell.nix

with import <nixpkgs> {};
with pkgs.python27Packages;

stdenv.mkDerivation {
  name = "python";

  buildInputs = [
    pip
    python27Full
    virtualenv
  ];

  shellHook = ''
    SOURCE_DATE_EPOCH=$(date +%s)  # so that we can use python wheels
    YELLOW='\033[1;33m'
    NC="$(printf '\033[0m')"

    echo -e "''${YELLOW}Creating python environment...''${NC}"
    virtualenv --no-setuptools venv > /dev/null
    export PATH=$PWD/venv/bin:$PATH > /dev/null
    pip install -r requirements.txt > /dev/null
  '';
}

This expression sets up a python 2 environment, and installs any dependencies from requirements.txt with pip in a virtualenv.

OS library dependencies

There is a LD_LIBRARY_PATH attribute for nix packages that can help python dependencies find the libraries they may need to complete installation. You generally need to format two pieces of information together: the path to the dependency in the nix store, and /lib.

Usually this means you just need LD_LIBRARY_PATH=${<NAME>}/lib. However, sometimes nix packages divide up their outputs, with the /lib folder and its contents at their own path in the nix store. Usually, the output with lib// is called out, and can be used like LD_LIBRARY_PATH=${<NAME>.out}/lib.

If you need to put more than on dependency into LD_LIBRARY_PATH, separate them with a colon :, like for $PATH.

geos and gdal

shell.nix

with import <nixpkgs> {};
with pkgs.python27Packages;

stdenv.mkDerivation {
  name = "python";

  buildInputs = [
    gdal
    geos
    pip
    python27Full
    virtualenv
  ];
  
  LD_LIBRARY_PATH="${geos}/lib:${gdal}/lib";

  shellHook = ''
    SOURCE_DATE_EPOCH=$(date +%s)  # so that we can use python wheels
    YELLOW='\033[1;33m'
    NC="$(printf '\033[0m')"

    echo -e "''${YELLOW}Creating python environment...''${NC}"
    virtualenv --no-setuptools venv > /dev/null
    export PATH=$PWD/venv/bin:$PATH > /dev/null
    pip install -r requirements.txt > /dev/null
  '';
}

zlib

TODO

sqlite3

TODO

---

also, http://nixos.org/nixpkgs/manual/#using-python

Rust

TODO: mozilla nix overlay for nightly

shell.nix

with import <nixpkgs> {};

stdenv.mkDerivation {
    name = "rust";
    buildInputs = [
        rustChannels.nightly.cargo
        rustChannels.nightly.rust
    ];
}

OpenSSL

shell.nix

with import <nixpkgs> {};

stdenv.mkDerivation {
    name = "rust";
    buildInputs = [
        openssl
        rustChannels.nightly.cargo
        rustChannels.nightly.rust
    ];
    shellHook = ''
        export OPENSSL_DIR="${openssl.dev}"
        export OPENSSL_LIB_DIR="${openssl.out}/lib"
    '';
}

diesel

shell.nix

with import <nixpkgs> {};

stdenv.mkDerivation {
    name = "rust";
    buildInputs = [
        postgresql
        rustChannels.nightly.cargo
        rustChannels.nightly.rust
    ];
    shellHook = ''
        export OPENSSL_DIR="${openssl.dev}"
        export OPENSSL_LIB_DIR="${openssl.out}/lib"
        export PATH="$PWD/bin:$PATH"
        export DATABASE_URL="postgres://postgres@localhost/db"
        if ! type diesel > /dev/null 2> /dev/null; then
          cargo install diesel_cli --no-default-features --features postgres --root $PWD
        fi
        diesel setup
    '';
}

TODO: talk about running postgres in a nix-shell, and don't hard-code DATABASE_URL in such an ugly way

cargo.toml

[dependencies.diesel]
version = "0.11"
features = ["postgres"]

[dependencies.diesel_codegen]
version = "0.11"
features = ["postgres"]

.gitignore

bin/