config: share Nix settings for NixOS and home-manager

flake.nix

@@ -152,22 +152,6 @@
         # BOOOOOOOOOOOOO! Somebody give me a tomato!
         services.xserver.excludePackages = with pkgs; [ xterm ];
 
-        # Parallel downloads! PARALLEL DOWNLOADS! It's like Pacman 6.0 all over
-        # again.
-        nix.package = pkgs.nixUnstable;
-
-        # I want to capture the usual flakes to its exact version so we're
-        # making them available to our system. This will also prevent the
-        # annoying downloads since it always get the latest revision.
-        nix.registry =
-          lib.mapAttrs'
-            (name: flake:
-              let
-                name' = if (name == "self") then "config" else name;
-              in
-              lib.nameValuePair name' { inherit flake; })
-            inputs;
-
         # Set several paths for the traditional channels.
         nix.nixPath =
           lib.mapAttrsToList
@@ -181,33 +165,6 @@
             "/nix/var/nix/profiles/per-user/root/channels"
           ];
 
-        nix.settings = {
-          # Set several binary caches.
-          substituters = [
-            "https://nix-community.cachix.org"
-            "https://foo-dogsquared.cachix.org"
-          ];
-          trusted-public-keys = [
-            "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
-            "foo-dogsquared.cachix.org-1:/2fmqn/gLGvCs5EDeQmqwtus02TUmGy0ZlAEXqRE70E="
-          ];
-
-          # Sane config for the package manager.
-          # TODO: Remove this after nix-command and flakes has been considered stable.
-          #
-          # Since we're using flakes to make this possible, we need it. Plus, the
-          # UX of Nix CLI is becoming closer to Guix's which is a nice bonus.
-          experimental-features = [ "nix-command" "flakes" "repl-flake" ];
-          auto-optimise-store = lib.mkDefault true;
-        };
-
-        # Stallman-senpai will be disappointed.
-        nixpkgs.config.allowUnfree = true;
-
-        # Extend nixpkgs with our overlays except for the NixOS-focused modules
-        # here.
-        nixpkgs.overlays = overlays;
-
         # Please clean your temporary crap.
         boot.tmp.cleanOnBoot = lib.mkDefault true;
 
@@ -287,6 +244,52 @@
           json.enable = true;
           manpages.enable = true;
         };
+
+      nixSettingsSharedConfig = { config, lib, pkgs, ... }: {
+        # I want to capture the usual flakes to its exact version so we're
+        # making them available to our system. This will also prevent the
+        # annoying downloads since it always get the latest revision.
+        nix.registry =
+          lib.mapAttrs'
+            (name: flake:
+              let
+                name' = if (name == "self") then "config" else name;
+              in
+              lib.nameValuePair name' { inherit flake; })
+            inputs;
+
+        # Parallel downloads! PARALLEL DOWNLOADS! It's like Pacman 6.0 all over
+        # again.
+        nix.package = pkgs.nixUnstable;
+
+        # Set the configurations for the package manager.
+        nix.settings = {
+          # Set several binary caches.
+          substituters = [
+            "https://nix-community.cachix.org"
+            "https://foo-dogsquared.cachix.org"
+          ];
+          trusted-public-keys = [
+            "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+            "foo-dogsquared.cachix.org-1:/2fmqn/gLGvCs5EDeQmqwtus02TUmGy0ZlAEXqRE70E="
+          ];
+
+          # Sane config for the package manager.
+          # TODO: Remove this after nix-command and flakes has been considered
+          # stable.
+          #
+          # Since we're using flakes to make this possible, we need it. Plus, the
+          # UX of Nix CLI is becoming closer to Guix's which is a nice bonus.
+          experimental-features = [ "nix-command" "flakes" "repl-flake" ];
+          auto-optimise-store = lib.mkDefault true;
+        };
+
+        # Stallman-senpai will be disappointed.
+        nixpkgs.config.allowUnfree = true;
+
+        # Extend nixpkgs with our overlays except for the NixOS-focused modules
+        # here.
+        nixpkgs.overlays = overlays;
       };
     in
     {
@@ -316,6 +319,7 @@
                 })
 
                 hostSharedConfig
+                nixSettingsSharedConfig
                 path
               ];
             in
@@ -364,6 +368,7 @@
                 targets.genericLinux.enable = true;
               })
               userSharedConfig
+              nixSettingsSharedConfig
               path
             ];
           in