nix-cache-action

A GitHub Action for caching Nix.

Usage

- name: Cache Nix
  uses: SwornSystems/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.
• SwornSystems/nix-cache-action caches only what substituters can't offer.

As an example, a project with this setup:

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	666 MiB
DeterminateSystems/magic-nix-cache	185	592 MiB
SwornSystems/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 with their own cache backends.

License

Licensed under the terms of both the MIT License and the Apache License (Version 2.0).