typelevel-nix

In antiquity, installing sbt was sufficient to compile, test, and run most Scala projects. sbt would fetch all your JVM dependencies, and you didn't have other dependencies. There was a Scala CLR target, but it was abandoned.

Years passed, and Scala.js was born, and we were back to crossing platforms. We suddenly needed a Node installation to run our tests. More libraries are supporting Scala Native. Static site generators outside our JVM bubble have come and gone.

"Faugh," you say. "The JVM is good enough for me". Fine, but your libraries target Java 8 for broad appeal and your applications target Java 17 because it's 9 bigger, and you have to juggle multiple JVMs.

Wouldn't it be nice to have one-stop shopping for your development environment again?

nix develop to the rescue

Enter the Nix package manager. We can use nix develop to get a full, build enviroment for modern, cross-platform Scala.

For now, you'll need at least Nix 2.4 and to enable the Nix command.

The baseline

$ java -version
bash: java: command not found
$ sbt -version
bash: sbt: command not found
$ node --version
bash: node: command not found

All my apes gone.

Library shell

The one-liner nix develop github:typelevel/typelevel-nix#library gets us a full environment:

$ nix develop github:typelevel/typelevel-nix#library
🔨 Welcome to typelevel-lib-shell

[general commands]

  menu      - prints this menu
  sbt       - A build tool for Scala, Java and more
  scala-cli - Command-line tool to interact with the Scala language

[versions]

  Java - 8.0.292
  Node - 16.13.1

$ sbt -version
sbt version in this project: 1.6.1
sbt script version: 1.6.1
$ exit

Application shell

Alternatively, nix develop github:typelevel/typelevel-nix#application gives us the same, with a more contemporary JDK:

$ nix develop github:typelevel/typelevel-nix#application
🔨 Welcome to typelevel-app-shell

[general commands]

  menu      - prints this menu
  sbt       - A build tool for Scala, Java and more
  scala-cli - Command-line tool to interact with the Scala language

[versions]

  Java - 17.0.1

$ sbt -version
sbt version in this project: 1.6.1
sbt script version: 1.6.1
$ exit

Embed in your project

The typelevelShell module can be imported into your devshell.mkShell configuration:

{
  inputs = {
    typelevel-nix.url = "github:typelevel/typelevel-nix";
    nixpkgs.follows = "typelevel-nix/nixpkgs";
    flake-utils.follows = "typelevel-nix/flake-utils";
  };

  outputs = { self, nixpkgs, flake-utils, typelevel-nix }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs {
          inherit system;
          overlays = [ typelevel-nix.overlays.default ];
        };
      in
      {
        devShell = pkgs.devshell.mkShell {
          imports = [ typelevel-nix.typelevelShell ];
          name = "my-project-shell";
          typelevelShell = {
            jdk.package = pkgs.jdk8;
            sbtMicrosites = {
              enable = true;
              siteDir = ./site;
            };
          };
        };
      }
    );
}

if you don't currently have a flake.nix you can create one quickly with the following command.

# For a library (defaults to jdk8)
nix flake init -t github:typelevel/typelevel-nix#library
# For an application service (defaults to jdk23)
nix flake init -t github:typelevel/typelevel-nix#application

Don't forget to tweak the devShell.name property and customize to taste.

Extra configuration in typelevelShell:

• typelevelShell.jdk.package: the JDK package to use for sbt and the $JAVA_HOME environment. Defaults to pkgs.jdk17. If you're writing a library, you probably want pkgs.jdk8.
• typelevelShell.native.enable: provide a clang environment for scala-native. Defaults to true in the library shell, and false elsewhere.
• typelevelShell.native.libraries: a list of split-output libraries to include (dev output) and link (lib output). Defaults to [ pkgs.zlib ].
• typelevelShell.nodejs.enable: provide NodeJS. Defaults to true in the library shell, and false elsewhere.
• typelevelShell.nodejs.package: the package to use for NodeJS. Defaults to pkgs.nodejs.
• typelevelShell.sbtMicrosites.enable: enables Jekyll support for sbt-microsites. Defaults to false.
• typelevelShell.sbtMicrosites.siteDir: directory with your Gemfile, Gemfile.lock, and gemset.nix. Run bundix to create a gemset.nix, and every time you upgrade Jekyll.

Infrequently asked questions

Is this stable?

Not yet, but flake.lock makes it reproducible.

Can I use it with trusty old nix-shell?

Absolutely! The shell.nix provides a flakes-compatible shell that works with nix-shell. It selects the application shell by default, but you can be specific about it. E.g.

$ nix-shell --argstr shell library

To use it remotely, copy the content of the shell.nix in your project and point src to this repository instead. E.g.

{
  src = fetchTarball {
    url = "https://github.com/typelevel/typelevel-nix/archive/main.tar.gz";
    sha256 = "0000000000000000000000000000000000000000000000000000"; # replace hash
  };
};

Can I embed this in a project to share with my colleagues and collaborators?

Yes. You should be able to put a flake.nix so you can share with your colleagues or open source collaborators, and even provide a direnv so your $SHELL and $EDITOR do the right thing. Examples forthcoming.

Can I read .java-version from jEnv to get an appropriate JDK?

typelevelShell = {
  jdk.package = builtins.getAttr "jdk${pkgs.lib.fileContents ./.java-version}" pkgs;
}