Switch to extended Nixpkg's lib

This change makes use of the `extend` function inside `lib` to inject
a new `hm` field containing the Home Manager library functions. This
simplifies use of the Home Manager library in the modules and reduces
the risk of accidental infinite recursion.

PR #994

modules/lib/default.nix

@@ -1,6 +1,6 @@
 { lib }:
 
-{
+rec {
   dag =
     let
       d = import ./dag.nix { inherit lib; };
@@ -17,6 +17,7 @@
       };
 
   strings = import ./strings.nix { inherit lib; };
+  types = import ./types.nix { inherit dag lib; };
 
   shell = import ./shell.nix { inherit lib; };
   zsh = import ./zsh.nix { inherit lib; };

modules/lib/file-type.nix

@@ -2,12 +2,6 @@
 
 with lib;
 
-let
-
-  stringsExtra = import ./strings.nix { inherit lib; };
-
-in
-
 {
   # Constructs a type suitable for a `home.file` like option. The
   # target path may be either absolute or relative, in which case it
@@ -93,7 +87,7 @@ in
         source = mkIf (config.text != null) (
           mkDefault (pkgs.writeTextFile {
             inherit (config) executable text;
-            name = stringsExtra.storeFileName name;
+            name = hm.strings.storeFileName name;
           })
         );
       };

modules/lib/stdlib-extended.nix

@@ -0,0 +1,11 @@
+# Just a convenience function that returns the given Nixpkgs standard
+# library extended with the HM library.
+
+nixpkgsLib:
+
+let
+  mkHmLib = import ./.;
+in
+  nixpkgsLib.extend (self: super: {
+    hm = mkHmLib { lib = super; };
+  })

modules/lib/types.nix

@@ -4,7 +4,6 @@ with lib;
 
 let
 
-  hmLib = import ./default.nix { inherit lib; };
   typesDag = import ./types-dag.nix { inherit dag lib; };
 
 in