Generate colmena and hydraJobs outputs from the same hosts attribute set

flake.nix

@@ -10,7 +10,7 @@
 
   outputs = { self, nixpkgs, nixpkgs-unstable, nixos-generators, ... }@inputs: let
     hosts = import ./hosts.nix inputs;
-    helper = (import ./helper.nix) inputs; 
+    helper = import ./helper.nix inputs; 
   in {
     colmena = {
       meta = {

helper.nix

@@ -19,8 +19,13 @@
     system,
     modules,
     ...
-  }: 
+  }:
-  (nixpkgs.lib.filterAttrs (name: host: (builtins.substring 0 1 name) != "_") (hostNixpkgs.lib.nixosSystem {
+  let
-    inherit system modules;
+    # Filter attritubes starting with _ to avoid infinite recursion when building with hydra
-  })).config.system.build.toplevel;
+    # TODO: Why does this happen?
+    filter = name: host: (builtins.substring 0 1 name) != "_";
+  in
+    (nixpkgs.lib.filterAttrs filter (hostNixpkgs.lib.nixosSystem {
+      inherit system modules;
+    })).config.system.build.toplevel; # Builds the entire NixOS system, see: https://nixos.org/manual/nixos/stable/#sec-building-parts
 }

hosts.nix

@@ -1,23 +1,27 @@
 { nixpkgs, nixpkgs-unstable, ... }:
 let
+  # Set of environment specific modules
   environments = {
     "proxmox" = [
       ./configuration/proxmox-vm
       ./configuration/proxmox-vm/hardware-configuration.nix
     ]; 
   };
+  # 
   generateDefaults = hosts: builtins.mapAttrs (name: {
     hostNixpkgs ? nixpkgs,
     system ? "x86_64-linux",
+    # pkgs is explicitly defined so that overlays for each host can easily be created
     pkgs ? hostNixpkgs.legacyPackages.${system},
     environment ? "proxmox",
     site
   }: {
     inherit hostNixpkgs system pkgs environment site;
+    # define common and host modules and additionally add environment specific modules
     modules = [
       ./configuration/common
       ./hosts/${name}
-    ] ++ (if environments ? ${environment} then environments.${environment} else []);
+    ] ++ environments.${environment};
   }) hosts;
 in
   generateDefaults {