Configures Nix on GitHub Actions for the supported platforms: Linux and macOS.

Draws heavily from Install Nix Action and is intended for use with self-hosted Github Action Runners. Once the kinks are smoothed out this should be merged into cachix/install-nix-action.

By default it has no nixpkgs configured, you have to set nix_path by picking a channel or pin nixpkgs yourself (see also pinning tutorial).

• Allows specifying $NIX_PATH and channels via nix_path
• Enables flakes and nix-command experimental features by default (to disable, set experimental-features via extra_nix_config)

Create .github/workflows/test.yml in your repo with the following contents:

name: "Test"
on:
  pull_request:
  push:
jobs:
  tests:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v4
    - uses: numtide/configure-nix-action@v1
      with:
        nix_path: nixpkgs=channel:nixos-unstable
    - run: nix-build

name: "Test"
on:
  pull_request:
  push:
jobs:
  tests:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v4
    - uses: numtide/configure-nix-action@v1
      with:
        github_access_token: ${{ secrets.GITHUB_TOKEN }}
    - run: nix build
    - run: nix flake check

To install Nix from any commit, go to the corresponding installer_test action and click on "Run numtide/configure-nix-action@XX" step and expand the first line.

• extra_nix_config: append to $HOME/.config/nix/nix.conf

• github_access_token: configure Nix to pull from GitHub using the given GitHub token. This helps work around rate limit issues. Has no effect when access-tokens is also specified in extra_nix_config.

• nix_path: set NIX_PATH environment variable, for example nixpkgs=channel:nixos-unstable

- name: Print nixpkgs version
  run: nix-instantiate --eval -E '(import <nixpkgs> {}).lib.version'

With the following inputs:

- uses: numtide/configure-nix-action@vXX
  with:
    extra_nix_config: "system-features = nixos-test benchmark big-parallel kvm"

nix-env -i mypackage -f '<nixpkgs>'

- uses: numtide/configure-nix-action@v25
  with:
    extra_nix_config: |
      trusted-public-keys = nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
      substituters = https://nix-community.cachix.org https://cache.nixos.org/

Nix runs commands in a restricted environment by default, called pure mode. In pure mode, environment variables are not passed through to improve the reproducibility of the shell.

You can use the --keep / -k flag to keep certain environment variables:

- name: Run a command with nix develop
  run: nix develop --ignore-environment --keep MY_ENV_VAR --command echo $MY_ENV_VAR
  env:
    MY_ENV_VAR: "hello world"

Or you can disable pure mode entirely with the --impure flag:

nix develop --impure