direnv-nix-action

This action will install nix with the cachix nix action and direnv to make nix based workflows easier to setup.

Example workflow

Assuming you have a nix setup with this flake

{

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };
  outputs = { self, nixpkgs, flake-utils, ... }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs { inherit system; };
      in {
        devShells = {
          # other dev shells....
          CI = pkgs.mkShell { buildInputs = [ pkgs.nodejs-16_x ]; };
        };
      });
}

and an .envrc like

if [ -z $DEV_SHELL_NAME ]; then
    use flake
else
    # running in CI
    use flake ".#${DEV_SHELL_NAME}"
fi

Then your workflow can look like

name: use nix

on: push
env:
    DEV_SHELL_NAME: CI
jobs:
  build:
    runs-on: ubuntu-latest

    steps:
    - uses: actions/checkout@v3

    - name: "Setup env"
      uses: JRMurr/direnv-nix-action@v4.1.0

    - name: use node
      run: node --version
      shell: bash

You can disable Nix installation and configure it before running direnv. For example, if you use Cachix, you can do:

name: use nix

on: push
env:
    DEV_SHELL_NAME: CI
jobs:
  build:
    runs-on: ubuntu-latest

    steps:
    - uses: actions/checkout@v3

    # Docs to use Cachix: https://nix.dev/tutorials/continuous-integration-github-actions
    - uses: cachix/install-nix-action@v17
      with:
        nix_path: nixpkgs=channel:nixos-unstable
    - uses: cachix/cachix-action@v11
      with:
        name: mycache
        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'

    - name: "Setup env"
      uses: JRMurr/direnv-nix-action@v4.1.0
      with:
        # You already installed nix, so you can disable that step
        install-nix: "false"
        # You are using Cachix cache, so no need to use Github cache too
        cache-store: "false"

    - name: use node
      run: node --version
      shell: bash