A GitHub action to check whether a Nix flake is properly cached. It builds a derivation and fails if anything needs building rather than fetching from a remote cache. You can permit some derivations to be built using the permit_build_derivations option.

Health warning: This action is scanning the output of nix build.

jobs:
  check:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: cachix/install-nix-action@v22
      - uses: cachix/cachix-action@v12
        with:
          name: my-cache
      - name: Check the cache
        uses: holochain/nix-cache-check@v1
        with:
          derivation: .#my-derivation

There is also a working example (as long as the build is currently passing!) in the integration test for this action.