add flake and split evalConfig

eval-config.nix

@@ -0,0 +1,41 @@
+{ lib, system ? builtins.currentSystem or "x86_64-darwin" }:
+
+{ modules
+, inputs
+, baseModules ? import ./modules/module-list.nix
+, specialArgs ? {}
+}@args:
+
+let
+  inputsModule = {
+    _file = ./eval-config.nix;
+    config = {
+      _module.args.inputs = inputs;
+    };
+  };
+
+  pkgsModule = { config, inputs, ... }: {
+    _file = ./eval-config.nix;
+    config = {
+      _module.args.pkgs = import inputs.nixpkgs config.nixpkgs;
+      nixpkgs.system = system;
+    };
+  };
+
+  eval = lib.evalModules (builtins.removeAttrs args ["inputs"] // {
+    modules = modules ++ [ inputsModule pkgsModule ] ++ baseModules;
+    args = { inherit baseModules modules; };
+    specialArgs = { modulesPath = builtins.toString ./modules; } // specialArgs;
+  });
+
+  # Was moved in nixpkgs #82751, so both need to be handled here until 20.03 is deprecated.
+  # https://github.com/NixOS/nixpkgs/commits/dcdd232939232d04c1132b4cc242dd3dac44be8c
+  _module = eval._module or eval.config._module;
+in
+
+{
+  inherit (_module.args) pkgs;
+  inherit (eval) options config;
+
+  system = eval.config.system.build.toplevel;
+}

flake.lock

@@ -0,0 +1,25 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1602411953,
+        "narHash": "sha256-gbupmxRpoQZqL5NBQCJN2GI5G7XDEHHHYKhVwEj5+Ps=",
+        "owner": "LnL7",
+        "repo": "nixpkgs",
+        "rev": "f780534ea2d0c12e62607ff254b6b45f46653f7a",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,28 @@
+{
+  # WARNING this is very much still experimental.
+  description = "A collection of darwin modules";
+
+  outputs = { self, nixpkgs }: {
+
+    lib = {
+      # TODO handle multiple architectures.
+      evalConfig = import ./eval-config.nix { inherit (nixpkgs) lib; };
+
+      darwinSystem = { modules, inputs ? {}, ... }@args: self.lib.evalConfig (args // {
+        inputs = { inherit nixpkgs; darwin = self; } // inputs;
+        modules = modules ++ [
+        ];
+      });
+    };
+
+    darwinModules.lnl = import ./modules/examples/lnl.nix;
+    darwinModules.simple = import ./modules/examples/simple.nix;
+    darwinModules.ofborg = import ./modules/examples/ofborg.nix;
+    darwinModules.hydra = import ./modules/examples/hydra.nix;
+
+    checks.x86_64-darwin.simple = (self.lib.darwinSystem {
+      modules = [ self.darwinModules.simple ];
+    }).system;
+
+  };
+}