feat(meta): Remove default values for nixpkgs version

They are considered harmful, and it simplifies the code.

hive.nix

@@ -23,17 +23,19 @@ let
   nixpkgs' = import ./meta/nixpkgs.nix;
   # All supported nixpkgs versions × systems, instanciated
   nixpkgs = nix-lib.mapSingleFuse (
-    s: nix-lib.mapSingleFuse (mkSystemNixpkgs s) nixpkgs'.versions.supported
-  ) nixpkgs'.systems.supported;
+    s: nix-lib.mapSingleFuse (mkSystemNixpkgs s) nixpkgs'.versions
+  ) nixpkgs'.systems;
 
   # Get the configured nixos version for the node,
   # defaulting to the one defined in meta/nixpkgs
-  version = node: nodes'.${node}.nixpkgs.version or nixpkgs'.versions.default;
-  systemType =
+  version = node: nodes'.${node}.nixpkgs.version;
+  system =
     node:
     nodes'.${node}.nixpkgs.system
       or (warn "${node}: Not specifying the `deployment.systemType` is deprecated!" "nixos");
 
+  nodePkgs = node: nixpkgs.${system node}.${version node};
+
   # Builds a patched version of nixpkgs, only as the source
   mkNixpkgs' =
     v:
@@ -73,11 +75,11 @@ let
   # Function to create arguments based on the node
   #
   mkArgs = node: rec {
-    lib = nixpkgs.${systemType node}.${version node}.lib // {
+    lib = nodePkgs.lib // {
       extra = nix-lib;
     };
 
-    sourcePkgs = nixpkgs.${systemType node}.${version node};
+    nodePkgs = nodePkgs node;
     meta = (import ./meta) lib;
 
     nodeMeta = meta.nodes.${node};
@@ -86,7 +88,7 @@ in
 
 {
   meta = {
-    nodeNixpkgs = nix-lib.mapSingleFuse (n: nixpkgs.${systemType n}.${version n}) nodes;
+    nodeNixpkgs = nix-lib.mapSingleFuse nodePkgs nodes;
 
     specialArgs = {
       inherit nixpkgs sources;
@@ -99,7 +101,7 @@ in
 
   registry = {
     nixos = {
-      evalConfig = args: import "${args.specialArgs.sourcePkgs.path}/nixos/lib/eval-config.nix" args;
+      evalConfig = args: import "${args.specialArgs.nodePkgs.path}/nixos/lib/eval-config.nix" args;
       defaults =
         { name, nodeMeta, ... }:
         {

meta/README.md

@@ -32,7 +32,7 @@ TODO.
 
 # Nixpkgs
 
-Machines can use different versions of NixOS, the supported and default ones are specified here.
+Machines can use different versions of NixOS, the supported ones are specified here.
 
 ## How to add a new version
 
@@ -55,7 +55,7 @@ The nodes are declared statically, several options can be configured:
 
 - `deployment`, the colmena deployment option
 - `stateVersion`, the state version of the node
-- `nixpkgs`, the version of NixOS to use
+- `nixpkgs`, the version and sytem of NixOS to use
 - `admins`, the list of administrators specific to this node, they will be given root access
 - `adminGroups`, a list of groups whose members will be added to `admins`
 - `site`, the physical location of the node

meta/nixpkgs.nix

@@ -1,25 +1,15 @@
 {
-  versions = {
-    # Default version of nixpkgs to use
-    default = "24.05";
-
+  versions = [
     # Supported nixpkgs versions
-    supported = [
     "unstable"
     "23.11"
     "24.05"
     "24.11"
   ];
-  };
-
-  systems = {
-    # Default system for our deployments
-    default = "nixos";
 
+  systems = [
     # Supported system types
-    supported = [
     "zyxel-nwa50ax"
     "nixos"
   ];
-  };
 }

meta/options.nix

@@ -141,16 +141,15 @@ in
 
               nixpkgs = {
                 version = mkOption {
-                  type = enum nixpkgs.versions.supported;
-                  inherit (nixpkgs.versions) default;
+                  type = enum nixpkgs.versions;
                   description = ''
                     Version of nixpkgs to use.
                   '';
+                  example = "unstable";
                 };
 
                 system = mkOption {
-                  type = enum nixpkgs.systems.supported;
-                  inherit (nixpkgs.systems) default;
+                  type = enum nixpkgs.systems;
                   description = ''
                     Type of system for this node, will impact how it is evaluated and deployed.
                   '';