Format of `nix-package-url`?

[Mr-Andersen]

So, I'd like to use specific version of Nix on my CI. I guess this should be solved with nix-package-url. But what kind of data should be hosted at this URL? Pre-built Nix? Are built Nix versions hosted anywhere?

[Montmorency]

Also trying out DetSystems github action installer and I'm a little confused by what nix-package-url should refer to? e.g. on the cachix nix installer action you specify nix_path to target a particular revision of nixpkgs. Is nix-package-url intended to be the same thing?:

e.g.

      - name: Install nix and cachix
        uses: cachix/install-nix-action@v27
        with:
           nix_path: nixpkgs=https://github.com/NixOS/nixpkgs/archive/38da06c69f821af50323d54b28d342cc3eb42891.tar.gz

I checked upstream in the installer itself but I'm still a little unclear what nix-package-url refers to e.g. a version of nix or a nixpkgs rev number or url etc?

[bigolu]

In the "Accessing other versions" section of the upstream installer, they explain how to use the --nix-package-url flag and I'm assuming the same rules apply for the nix-package-url option in this action. If so, you should be able to use a URL like the one mentioned in that section: https://releases.nixos.org/nix/nix-2.18.1/nix-2.18.1-x86_64-linux.tar.xz