flake: add flake.nix

No flake.lock is added because the only input (nixpkgs) will almost
always be overridden, and currently Home Manager's testing and
verification is not flake based.

PR #1455

.github/CODEOWNERS

@@ -1,5 +1,7 @@
 *                                                     @rycee
 
+/flake.nix                                            @bqv @kisik21
+
 /modules/home-environment.nix                         @rycee
 
 /modules/misc/dconf.nix                               @gnidorah @rycee

.gitignore

@@ -1 +1,2 @@
+/flake.lock
 /result*

flake.nix

@@ -0,0 +1,21 @@
+{
+  description = "Home Manager for Nix";
+
+  outputs = { self, nixpkgs }: rec {
+    nixosModules.home-manager = import ./nixos;
+
+    lib = {
+      homeManagerConfiguration = { configuration, system, homeDirectory
+        , username
+        , pkgs ? builtins.getAttr system nixpkgs.outputs.legacyPackages
+        , check ? true }@args:
+        import ./modules {
+          inherit pkgs check;
+          configuration = { ... }: {
+            imports = [ configuration ];
+            home = { inherit homeDirectory username; };
+          };
+        };
+    };
+  };
+}