Major overhaul of the nix side of things, part II.

flake.lock

@@ -121,6 +121,23 @@
         "type": "github"
       }
     },
+    "nixpkgs-nonflake": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1679437018,
+        "narHash": "sha256-vOuiDPLHSEo/7NkiWtxpHpHgoXoNmrm+wkXZ6a072Fc=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "19cf008bb18e47b6e3b4e16e32a9a4bdd4b45f7e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "nixpkgs-stable": {
       "locked": {
         "lastModified": 1678872516,
@@ -169,6 +186,7 @@
         "devshell": "devshell",
         "flake-utils": "flake-utils",
         "nixpkgs": "nixpkgs",
+        "nixpkgs-nonflake": "nixpkgs-nonflake",
         "pre-commit-hooks": "pre-commit-hooks",
         "rust-overlay": "rust-overlay",
         "treefmt-nix": "treefmt-nix"

flake.nix

@@ -1,6 +1,12 @@
 {
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    # We re-use the systemd lib from NixOS, this input allows to import the needed modules.
+    # TODO: is there a better way to do this?
+    nixpkgs-nonflake = {
+      url = "github:NixOS/nixpkgs/nixos-unstable";
+      flake = false;
+    };
     flake-utils.url = "github:numtide/flake-utils";
     devshell = {
       url = "github:numtide/devshell";
@@ -41,6 +47,7 @@
   outputs =
     { self
     , nixpkgs
+    , nixpkgs-nonflake
     , flake-utils
     , rust-overlay
     , crane
@@ -49,7 +56,9 @@
     , pre-commit-hooks
     ,
     }:
-    (flake-utils.lib.eachDefaultSystem (system:
+    (flake-utils.lib.eachSystem
+      (with flake-utils.lib.system; [ x86_64-linux aarch64-linux ])
+      (system:
       let
         pkgs = import nixpkgs {
           inherit system;
@@ -180,6 +189,7 @@
     {
       lib = import ./nix/lib.nix {
         inherit nixpkgs self;
+        nixosModules = "${nixpkgs-nonflake}/nixos";
       };
 
       systemConfigs.default = self.lib.makeSystemConfig {

nix/lib.nix

@@ -1,5 +1,6 @@
-{ nixpkgs
-, self
+{ nixpkgs      # The nixpkgs flake
+, self         # The system-manager flake
+, nixosModules # The path to the nixos modules dir from nixpkgs
 ,
 }:
 let
@@ -16,22 +17,30 @@ in
       pkgs = nixpkgs.legacyPackages.${system};
       inherit (self.packages.${system}) system-manager;
 
-      # TODO can we call lib.evalModules directly instead of building a NixOS system?
-      nixosConfig = (lib.nixosSystem {
-        inherit system;
+      # Module that sets additional module arguments
+      extraArgsModule = { lib, config, pkgs, ... }: {
+        _module.args = {
+          pkgs = nixpkgs.legacyPackages.${system};
+          utils = import "${nixosModules}/lib/utils.nix" {
+            inherit lib config pkgs;
+          };
+        };
+      };
+
+      config = (lib.evalModules {
         modules = [
+          extraArgsModule
           ./modules/system-manager.nix
         ] ++ modules;
-        specialArgs = extraSpecialArgs;
       }).config;
 
       returnIfNoAssertions = drv:
         let
-          failedAssertions = map (x: x.message) (lib.filter (x: !x.assertion) nixosConfig.assertions);
+          failedAssertions = map (x: x.message) (lib.filter (x: !x.assertion) config.assertions);
         in
         if failedAssertions != [ ]
         then throw "\nFailed assertions:\n${lib.concatStringsSep "\n" (map (x: "- ${x}") failedAssertions)}"
-        else lib.showWarnings nixosConfig.warnings drv;
+        else lib.showWarnings config.warnings drv;
 
       services =
         lib.mapAttrs'
@@ -40,7 +49,7 @@ in
               storePath =
                 ''${unit.unit}/${unitName}'';
             })
-          nixosConfig.system-manager.systemd.units;
+          config.systemd.units;
 
       servicesPath = pkgs.writeTextFile {
         name = "services";
@@ -64,7 +73,7 @@ in
 
           filteredEntries = lib.filterAttrs
             (_name: etcFile: etcFile.enable)
-            nixosConfig.system-manager.environment.etc;
+            config.environment.etc;
 
           srcDrvs = lib.mapAttrs addToStore filteredEntries;
 
@@ -131,7 +140,7 @@ in
 
           declare -a failed_assertions=()
 
-          ${mkAssertions nixosConfig.system-manager.preActivationAssertions}
+          ${mkAssertions config.system-manager.preActivationAssertions}
 
           if [ ''${#failed_assertions[@]} -ne 0 ]; then
             for failed_assertion in ''${failed_assertions[@]}; do

nix/modules/default.nix

@@ -4,7 +4,6 @@
 }:
 {
   config = {
-    system-manager = {
     environment.etc = {
       foo = {
         text = ''
@@ -78,5 +77,4 @@
             })
         );
   };
-  };
 }

nix/modules/etc.nix

@@ -3,7 +3,7 @@
 , ...
 }:
 {
-  options.system-manager = {
+  options = {
     environment.etc = lib.mkOption {
       default = { };
       example = lib.literalExpression ''
@@ -100,7 +100,6 @@
                 Changing this option takes precedence over `gid`.
               '';
             };
-
           };
 
           config = {
@@ -110,7 +109,6 @@
               in lib.mkDerivedConfig options.text (pkgs.writeText name')
             );
           };
-
         }
       ));
     };

nix/modules/system-manager.nix

@@ -8,7 +8,31 @@
     ./systemd.nix
   ];
 
-  options.system-manager = {
+  options = {
+    assertions = lib.mkOption {
+      type = lib.types.listOf lib.types.unspecified;
+      internal = true;
+      default = [ ];
+      example = [{ assertion = false; message = "you can't enable this for that reason"; }];
+      description = lib.mdDoc ''
+        This option allows modules to express conditions that must
+        hold for the evaluation of the system configuration to
+        succeed, along with associated error messages for the user.
+      '';
+    };
+
+    warnings = lib.mkOption {
+      internal = true;
+      default = [ ];
+      type = lib.types.listOf lib.types.str;
+      example = [ "The `foo' service is deprecated and will go away soon!" ];
+      description = lib.mdDoc ''
+        This option allows modules to show warnings to users during
+        the evaluation of the system configuration.
+      '';
+    };
+
+    system-manager = {
       allowAnyDistro = lib.mkEnableOption "the usage of system-manager on untested distributions";
 
       preActivationAssertions = lib.mkOption {
@@ -29,14 +53,9 @@
         default = { };
       };
     };
+  };
 
   config = {
-    # Avoid some standard NixOS assertions
-    boot = {
-      loader.grub.enable = false;
-      initrd.enable = false;
-    };
-    system.stateVersion = lib.mkDefault lib.trivial.release;
 
     system-manager.preActivationAssertions = {
       osVersion =

nix/modules/systemd.nix

@@ -6,13 +6,31 @@
 }:
 
 let
-  cfg = config.system-manager.systemd;
+  cfg = config.systemd;
 
   inherit (utils) systemdUtils;
   systemd-lib = utils.systemdUtils.lib;
 in
 {
-  options.system-manager.systemd = {
+  options.systemd = {
+
+    # TODO: this is a bit dirty.
+    # The value here gets added to the PATH of every service.
+    # We could consider copying the systemd lib from NixOS and removing the bits
+    # that are not relevant to us, like this option.
+    package = lib.mkOption {
+      type = lib.types.oneOf [ lib.types.str lib.types.path lib.types.package ];
+      default = pkgs.systemdMinimal;
+    };
+
+    globalEnvironment = lib.mkOption {
+      type = with lib.types; attrsOf (nullOr (oneOf [ str path package ]));
+      default = { };
+      example = { TZ = "CET"; };
+      description = lib.mdDoc ''
+        Environment variables passed to *all* systemd units.
+      '';
+    };
 
     units = lib.mkOption {
       description = lib.mdDoc "Definition of systemd units.";
@@ -106,7 +124,6 @@ in
   };
 
   config = {
-    system-manager = {
     systemd = {
       timers =
         lib.mapAttrs
@@ -140,7 +157,7 @@ in
       let
         allowCollisions = false;
 
-          enabledUnits = cfg.units;
+        enabledUnits = lib.filterAttrs (_: unit: unit.enable) cfg.units;
       in
       {
         "systemd/system".source = pkgs.runCommand "system-manager-units"
@@ -188,5 +205,4 @@ in
           '';
       };
   };
-  };
 }