Break up the git feature in its own module

nix/fg42/lib.nix

@@ -16,12 +16,31 @@
 { pkgs, ... }:
 final: prev:
 rec {
+  /*
+    Create a value to be accessable on the Elisp side as a variable.
+  */
   defVar = name: defaultValue: docstring: {
     inherit name defaultValue docstring;
   };
 
+  /*
+    Create a value to be accessable on the Elisp side as a constant.
+  */
   defConst = defVar;
 
+  /* Creates an Option attribute set for a boolean value option i.e an
+     option to be toggled on or off. The option is enabled by default:
+
+     Example:
+       mkAndEnableOption "foo"
+       => { _type = "option"; default = true; description = "Whether to enable foo."; example = true; type = { ... }; }
+  */
+  mkAndEnableOption = name: prev.mkOption {
+    default = true;
+    example = true;
+    description = "Whether to enable ${name}.";
+    type = prev.types.bool;
+  };
 
   makeFG42Drv = { pname, version, ... }@args:
     (pkgs.emacsPackages.trivialBuild args).overrideAttrs (old: {

nix/modules/default.nix

@@ -24,6 +24,7 @@ let
   modules = [
     ./editor
     ./elisp
+    ./git
   ];
 
   pkgsModule = { config, ... }: {

nix/modules/git/default.nix

@@ -22,7 +22,8 @@
 { lib, config, pkgs, makeFG42Drv, ... }:
 with lib;
 let
-  cfg = config.fg42.features;
+  cfg = config.fg42.features.git;
+
   deps =
     (with pkgs.emacsPackages; [
       magit
@@ -38,7 +39,7 @@ let
   };
 in
 {
-  options.fg42.features.git = mkEnableOption "git";
+  options.fg42.features.git.enable = mkAndEnableOption "git";
 
   config = mkIf cfg.enable {
     fg42.elispPackages = [ drv ] ++ deps;
@@ -46,5 +47,7 @@ in
     fg42.paths = (with pkgs;[
       git
     ]);
+
+    fg42.requires = [ drv.pname ];
   };
 }

nix/modules/unit/default.nix

@@ -104,7 +104,6 @@ in
 
     fg42.requires = mkOption {
       type = types.listOf types.str;
-      readOnly = true;
       description = ''
         A list of Emacs packages to preload in compile time.