nix-install-pkgs-action

A GitHub Action to install Nix packages into an ephemeral profile.

The action is particularly useful if you use a self-hosted GitHub Actions Runner on NixOS. Third-party actions frequently require certain tools to be installed which are by default not available to the runner. With this action, you can install Nix packages easily making them available to following actions.

As soon as the action terminates—no matter if successfully or unsuccessfully—the profile is purged to allow garbage collection of all installed derivations.

Usage

The action supports installing derivations from Flake packages and by evaluating a given expression. Installation happens through nix profile.

You may call this action multiple times within the same job. Following steps will reuse the profile. The path of the profile is also available with the step output nix_profile_path.

Packages

Install packages by giving a comma-separated string of packages from a flake. If no flake reference is given, nixpkgs is assumed. Example:

name: 'nix-install-pkgs-action packages'
on:
  - pull_request
  - push
jobs:
  tests:
    runs-on: self-hosted
    steps:
      - uses: actions/checkout@v4
      - uses: yaxitech/nix-install-pkgs-action@v4
        with:
          packages: "nixpkgs#hello, figlet"
      - run: |
          hello
          figlet "Hello nix-install-pkgs-action!"

When installing flakes which reference a registry entry, the action resolves them as follows:

• If the input inputs-from is given, the action invokes nix profile install --inputs-from. As a result, nixpkgs#hello will look up nixpkgs using the inputs of the flake given in inputs-from.
• inputs-from defaults to ., i.e., the current working directory of the process. If this directory (or a parent) contains a valid flake, nix profile install is invoked with this flake.
• If inputs-from is unset (i.e., ""), nix profile resolves tokens using the registry.

Expressions

On some occasions, you need to compose a custom derivation from a Nix expression, for example, to install Python 3 with specific packages. This can be done with the expr input. The action evaluates the passed string through nix profile install --expr. Within your expression, the actions provides an imported nixpkgs as pkgs using the same resolution strategy as outlined for the packages input. In the following example, pkgs references inputs.nixpkgs from the flake github:yaxitech/ragenix:

name: 'nix-install-pkgs-action expr'
on:
  - pull_request
  - push
jobs:
  tests:
    runs-on: self-hosted
    steps:
      - uses: actions/checkout@v4
      - uses: yaxitech/nix-install-pkgs-action@v4
        with:
          expr: 'pkgs.python3.withPackages(ps: with ps; [toml pyyaml])'
          inputs-from: 'github:yaxitech/ragenix'
      - run: |
          python3 ...

Within your expression, the action also introduces let bindings for a flake in the current working directory (repoFlake) and for the flake referenced by inputs-from (inputsFromFlake).

Prerequisites

This action requires a Flake-enabled Nix with support for profiles.

NixOS

{
  nix.settings.experimental-features = [ "nix-command" "flakes" ];
}

Non-NixOS

Use cachix/install-nix-action to install Nix with flake support.

Development notes

After you changed package.json, you also need to update npmDepsHash in flake.nix. You can acquire the hash by running: nix develop -c prefetch-npm-deps package-lock.json.

Some of the TypeScript tests invoke nix during test execution. That means if you invoke the tests through nix, for example as part of nix build, a nix that has the recursive-nix feature enabled is required. You can put the following snippet into your configuration.nix:

{
  nix.settings = {
    experimental-features = [ "nix-command" "flakes" "recursive-nix" ];
    system-features = [ "recursive-nix" ];
  };
}