Automatically generate nix file from compose yaml

[joshhunt]

New to nix and compose2nix in general, and really interested in using compose2nix to manage a bunch of services.

My goal is to have docker-compose.yml be the file that's committed, and have nix run compose2nix to generate the output when building the system. I tried this:

compose2nix.nix:

{ pkgs }:

pkgs.runCommand "compose2nix-output" { } ''
  mkdir -p $out
  ${pkgs.compose2nix}/bin/compose2nix \
    --inputs ${./docker-compose.yml} \
    --output $out/generated.nix \
    --runtime docker
''

docker.nix:

{ pkgs, lib, ... }:

let
  composeGeneratedDrv = import ./compose2nix.nix { inherit pkgs; };
  composeModulePath = "${composeGeneratedDrv}/generated.nix";
in
{
  imports = [ composeModulePath ];

  virtualisation.docker = {
    enable = true;
    daemon.settings.dns = [ "127.0.0.1" ];
  };
}

However this proves difficult to get working (maybe because I'm using flakes to manage the system config?), giving me and infinite recursion error:

… while evaluating the module argument `pkgs' in "/nix/store/zkfsayxwfb5sp32cw30yvlagxib3mshw-source/services/docker":

… noting that argument `pkgs` is not externally provided, so querying `_module.args` instead, requiring `config`

… if you get an infinite recursion here, you probably reference `config` in `imports`. If you are trying to achieve a conditional import behavior dependent on `config`, consider importing unconditionally, and using `mkEnableOption` and `mkIf` to control its effect.

I think I understand this - nix cannot resolve the imports because to do that it needs pkgs (or config?), which needs to resolve the imports to determine.

I think chatgpt initially lead me astray - is something like this possible? I'm trying to have a simple and 'pure' workflow where the thing I author is the docker-compose.yml file, and then the nix version of it is automatically generated from there.

[aksiksi]

There is an open PR that’s trying to implement this: #94

But in general, it is not straightforward because it interacts with a Nix feature called IFD (import from derivation). https://nix.dev/manual/nix/2.26/language/import-from-derivation