nix-cache-action

A GitHub Action for caching Nix.

Usage

- name: Cache Nix
  uses: DuskSystems/nix-cache-action@${VERSION}
  with:
    key: nix-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('flake.lock', '**/*.nix') }}
    restore-keys: |
      nix-${{ runner.os }}-${{ runner.arch }}-

Why?

Efficiency

• nix-community/cache-nix-action caches the entire /nix directory.
• DeterminateSystems/magic-nix-cache caches every store path closure.
• DuskSystems/nix-cache-action caches only what can't be fetched from substituters.

As an example, a project with this Nix shell:

pkgs.mkShell {
  nativeBuildInputs = with pkgs; [
    # System
    pkg-config
  ];

  buildInputs = with pkgs; [
    # Rust
    rust-bin.stable.latest.default
    cargo-nextest
    cargo-shear

    # System
    openssl

    # Spellchecking
    typos

    # Nix
    nixfmt
  ];
}

Results in the following cache save stats:

| Action | Entries | Size | | ------------------------------------ | ------- | ------- | | nix-community/cache-nix-action | 1 | 682 MiB | | DeterminateSystems/magic-nix-cache | 200 | 523 MiB | | DuskSystems/nix-cache-action | 1 | 377 MiB |

The tradeoff is this relies on substituters being consistently available and fast to fetch from at restore time.

Compatibility

Since this action uses @actions/cache, it should be compatible with alternative GitHub Actions runners that provide their own cache backends.

License

nix-cache-action is licensed under the terms of both the MIT License and the Apache License (Version 2.0).