Update def and implementation of nix.package to match NixOS module

Also remove `nix.version` option since it's no longer being used
anywhere, old irrelevant `nix-info` module, and all support for
legacy `nix.profile` option.

modules/alias.nix

@@ -10,7 +10,6 @@ in
   options = {
 
     networking.networkservices = mkOption { internal = true; default = null; };
-    nix.profile = mkOption { internal = true; default = null; };
     security.enableAccessibilityAccess = mkOption { internal = true; default = null; };
     security.accessibilityPrograms = mkOption { internal = true; default = null; };
 
@@ -19,8 +18,7 @@ in
   config = {
 
     assertions =
-      [ { assertion = config.nix.profile == null; message = "nix.profile was renamed to nix.package"; }
-        { assertion = config.security.enableAccessibilityAccess == null; message = "security.enableAccessibilityAccess was removed, it's broken since 10.12 because of SIP"; }
+      [ { assertion = config.security.enableAccessibilityAccess == null; message = "security.enableAccessibilityAccess was removed, it's broken since 10.12 because of SIP"; }
         { assertion = config.system.activationScripts.extraPostActivation.text == ""; message = "system.activationScripts.extraPostActivation was renamed to system.activationScripts.postActivation"; }
         { assertion = config.system.activationScripts.extraUserPostActivation.text == ""; message = "system.activationScripts.extraUserPostActivation was renamed to system.activationScripts.postUserActivation"; }
       ];
@@ -31,8 +29,6 @@ in
 
     networking.knownNetworkServices = mkIf (config.networking.networkservices != null) config.networking.networkservices;
 
-    nix.package = mkIf (config.nix.profile != null) config.nix.profile;
-
     system.activationScripts.extraPostActivation.text = mkDefault "";
     system.activationScripts.extraUserPostActivation.text = mkDefault "";
 

modules/module-list.nix

@@ -34,7 +34,6 @@
   ./networking
   ./nix
   ./nix/nix-darwin.nix
-  ./nix/nix-info.nix
   ./nix/nixpkgs.nix
   ./environment
   ./fonts

modules/nix/default.nix

@@ -6,7 +6,7 @@ let
 
   cfg = config.nix;
 
-  isNix20 = versionAtLeast (cfg.version or "<unknown>") "1.12pre";
+  nixPackage = cfg.package.out;
 
   nixConf =
     let
@@ -61,9 +61,10 @@ let
 in
 
 {
-  imports = mapAttrsToList (oldConf: newConf:
-    mkRenamedOptionModule [ "nix" oldConf ] [ "nix" "settings" newConf ]
-  ) legacyConfMappings;
+  imports = [
+    (mkRemovedOptionModule [ "nix" "profile" ] "Use `nix.package` instead.")
+    (mkRemovedOptionModule [ "nix" "version" ] "Consider using `nix.package.version` instead.")
+  ] ++ mapAttrsToList (oldConf: newConf: mkRenamedOptionModule [ "nix" oldConf ] [ "nix" "settings" newConf ]) legacyConfMappings;
 
   ###### interface
 
@@ -72,26 +73,14 @@ in
     nix = {
 
       package = mkOption {
-        type = types.either types.package types.path;
+        type = types.package;
         default = pkgs.nix;
-        defaultText = "pkgs.nix";
-        example = literalExpression "pkgs.nixUnstable";
+        defaultText = literalExpression "pkgs.nix";
         description = ''
-          This option specifies the package or profile that contains the version of Nix to use throughout the system.
-          To keep the version of nix originally installed the default profile can be used.
-
-          eg. /nix/var/nix/profiles/default
+          This option specifies the Nix package instance to use throughout the system.
         '';
       };
 
-      # Not in NixOS module
-      version = mkOption {
-        type = types.str;
-        default = "<unknown>";
-        example = "1.11.6";
-        description = "The version of nix. Used to determine what settings to configure in nix.conf";
-      };
-
       # Not in NixOS module
       useDaemon = mkOption {
         type = types.bool;
@@ -475,14 +464,12 @@ in
       ]))
     ];
 
-
-    nix.package = mkIf (config.system.stateVersion < 3)
-      (mkDefault "/nix/var/nix/profiles/default");
-
-    nix.version = mkIf (isDerivation cfg.package) cfg.package.version or "<unknown>";
-
-    environment.systemPackages = mkIf (isDerivation cfg.package)
-      [ cfg.package ];
+    environment.systemPackages =
+      [
+        nixPackage
+        pkgs.nix-info
+      ]
+      ++ optional (config.programs.bash.enableCompletion) pkgs.nix-bash-completions;
 
     environment.etc."nix/nix.conf".source = nixConf;
 

modules/nix/nix-info.nix

@@ -1,15 +0,0 @@
-{ config, lib, pkgs, ... }:
-
-with lib;
-
-let
-  nix-info = pkgs.nix-info or null;
-in
-
-{
-  config = {
-
-    environment.systemPackages = mkIf (nix-info != null) [ nix-info ];
-
-  };
-}