yarn-plugin-nixify

Upgrading the plugin? See UPGRADING.md

Generates a Nix expression to build a Yarn v3 or v4 project (not using zero-install).

Provides a yarn shell alias in the Nix builder — no global Yarn v1 install needed.
A default configure-phase that runs yarn in your project. (May be all that's needed for plain JavaScript projects.)
A default install-phase that creates executables for you based on "bin" in your package.json, making your package readily installable.
Preloading of your Yarn cache into the Nix store, speeding up local nix-build.
Automatically keeps your Nix expression up-to-date as you yarn add / yarn remove dependencies.
No Nix installation required for the plugin itself, so it should be safe to add to your project even if some developers don't use Nix.

Related projects:

node2nix, yarn2nix: Both do a similar job, but as separate commands. By comparison, this plugin tries to automate the process and make things easy for Nix and non-Nix devs alike.
composer-plugin-nixify: Similar solution for PHP with Composer.

Usage

This plugin is compatible with Yarn >= 3.1.0 or >= 4.0.0. Run the following in your project folder to check:

# Check your Yarn version
yarn --version

# Upgrade to the latest version, if necessary
yarn set version berry

To then use the Nixify plugin:

# Install the plugin
yarn plugin import https://raw.githubusercontent.com/stephank/yarn-plugin-nixify/main/dist/yarn-plugin-nixify.js

# Run Yarn as usual
yarn

# Build your project with Nix
nix-build

Running yarn with this plugin enabled will generate two files:

yarn-project.nix: This file is always overwritten, and contains a basic derivation for your project.
default.nix: Only generated if it does not exist yet. This file is intended to be customized with any project-specific logic you need.

This may already build successfully! But if your project needs extra build steps or native dependencies, you may have to customize default.nix a bit. Some examples of what's possible:

{ pkgs ? import <nixpkgs> { } }:

let

  project = pkgs.callPackage ./yarn-project.nix {

    # Example of selecting a specific version of Node.js.
    nodejs = pkgs.nodejs-14_x;

  } {

    # Example of providing a different source tree.
    src = pkgs.lib.cleanSource ./.;

  };

in project.overrideAttrs (oldAttrs: {

  # If your top-level package.json doesn't set a name, you can set one here.
  name = "myproject";

  # Example of adding packages to the build environment.
  # Especially dependencies with native modules may need a Python installation.
  buildInputs = oldAttrs.buildInputs ++ [ pkgs.python3 ];

  # Example of invoking a build step in your project.
  buildPhase = ''
    yarn build
  '';

})

Settings

Some additional settings are available in .yarnrc.yml:

nixExprPath can be set to customize the path where the Nixify plugin writes yarn-project.nix. For example, if you're also using Niv in your project, you may prefer to set this to nix/yarn-project.nix.
generateDefaultNix can be set to false to disable generating a default.nix. This file is only generated if it doesn't exist yet, but this flag can be useful if you don't want a default.nix at all.
enableNixPreload can be set to false to disable preloading Yarn cache into the Nix store. This preloading is intended to speed up a local nix-build, because Nix will not have to download dependencies again. Preloading does mean another copy of dependencies on disk, even if you don't do local Nix builds, but the size is usually not an issue on modern disks.
individualNixPackaging can be set to true to create a derivation per dependency. This is useful in some cases, but can significantly slow down builds if cache is cold and preloading is not possible.
isolatedNixBuilds, see ISOLATED_BUILDS.md.
installNixBinariesForDependencies can be set to also install executables for binaries defined by dependencies. This can be useful if these need to be in $PATH for other tools, or if you're creating a workspace just to collect command-line tools.

Hacking

# In this directory:
yarn
yarn build-dev

# In your test project:
yarn plugin import /path/to/yarn-plugin-nixify/dist/yarn-plugin-nixify.dev.js

(Alternatively, add a direct reference in .yarnrc.yml. This will likely only work if the Nix sandbox is disabled.)