Cache install Nix packages

This actions allows caching of installations done via the Nix package manager to improve workflow execution time.

Installing packages via the Nix package manager is generally quite quick. However, sometimes the packages take a long time to compile or to download from their original sources. For example, this occurs with R packages and LaTeX which are downloaded from respectively CRAN and math.utah.edu. This GitHub Action speeds up the installation by simply caching the Nix store and the symlinks to the packages in the store in the GitHub Actions cache. So, the installed packages are restored from the cache by copying back /nix/store, the symlinks to /nix/store/* and some paths for the PATH environment variable.

Inputs

key - An explicit key for restoring and saving the cache.
restore-keys - An ordered list of keys to use for restoring the cache if no cache hit occurred for key.
nix_version - Nix version, defaults to nixos-unstable.
nix_file - Nix file, defaults to default.nix.
nix_install_url - Install URL for the Nix package manager; obtain newest via https://nixos.org/nix/install.

Outputs

cache-hit - A boolean value to indicate an exact match was found for the primary key.

Example workflow

name: latex

on: push

jobs:
  build:
    runs-on: ubuntu-latest

    steps:
    - uses: actions/checkout@v4

    - name: Cache install Nix packages
      uses: rikhuijzer/cache-install@v1
      with:
        key: nix-${{ hashFiles('mypackages.nix') }}
        nix_file: 'mypackages.nix'

    - name: Calculate some things
      run: julia -e 'using MyPackage; MyPackage.calculate()'

    - name: Build LaTeX
      run: latexmk -f -pdf example.tex

    - name: Build website
      run: hugo --gc --minify

where the file mypackages.nix contains

let
  # Pinning explicitly to 20.03.
  rev = "5272327b81ed355bbed5659b8d303cf2979b6953";
  nixpkgs = fetchTarball "https://github.com/NixOS/nixpkgs/archive/${rev}.tar.gz";
  pkgs = import nixpkgs {};
  myTex = with pkgs; texlive.combine {
    inherit (texlive) scheme-medium pdfcrop;
  };
in with pkgs; [
  hugo
  julia
  myTex
]