adding flake to 18.03

flake.nix

@@ -0,0 +1,48 @@
+# Experimental flake interface to Nixpkgs.
+# See https://github.com/NixOS/rfcs/pull/49 for details.
+{
+  description = "A collection of packages for the Nix package manager";
+
+  outputs = { self }:
+    let
+
+      jobs = import ./pkgs/top-level/release.nix {
+        nixpkgs = self;
+      };
+
+      lib = import ./lib;
+
+      systems = [ "x86_64-linux" "i686-linux" "x86_64-darwin" "aarch64-linux" ];
+
+      forAllSystems = f: lib.genAttrs systems (system: f system);
+
+    in
+    {
+      lib = lib // {
+        nixosSystem = { modules, ... } @ args:
+          import ./nixos/lib/eval-config.nix (args // {
+            modules = modules ++
+              [ { system.nixos.versionSuffix =
+                    ".${lib.substring 0 8 (self.lastModifiedDate or self.lastModified)}.${self.shortRev or "dirty"}";
+                  system.nixos.revision = lib.mkIf (self ? rev) self.rev;
+                }
+              ];
+          });
+      };
+
+      checks.x86_64-linux.tarball = jobs.tarball;
+
+      htmlDocs = {
+        nixpkgsManual = jobs.manual;
+        nixosManual = (import ./nixos/release-small.nix {
+          nixpkgs = self;
+        }).nixos.manual.x86_64-linux;
+      };
+
+      legacyPackages = forAllSystems (system: import ./. { inherit system; });
+
+      nixosModules = {
+        notDetected = import ./nixos/modules/installer/scan/not-detected.nix;
+      };
+    };
+}