added two-stage update...

Signed-off-by: Alex A. Naanou <alex.nanou@gmail.com>

configuration.nix

@@ -11,31 +11,30 @@
 # your system.  Help is available in the configuration.nix(5) man page
 # and in the NixOS manual (accessible by running ‘nixos-help’).
 
-{ config, pkgs, ... }:
+{ config, pkgs, lib, ... }: {
-
+  imports = [ 
-## LaTeX...
+    # Include the results of the hardware scan.
-#let tex = pkg.texlive.combine {
+    ./hardware-configuration.nix
-#  inherit (pkgs.texlive) scheme-basic
+  ];
-#  kvoptions calc xargs ifthen iftex pgffor xint xinttools listofitems xkeyval
-#  etoolbox changepage pdfcomment eso-pic environ numprint trimclip xcolor
-#  pagecolor colorspace graphicx adjustbox textpos fancyvrb flowfram rotating
-#  fancyhdr pdfpages geometry;
-#  #(setq org-latex-compiler "lualatex")
-#  #(setq org-preview-latex-default-process 'dvisvgm)
-#};
-#in
 
+  config = lib.mkMerge [
+    # Base configuration...
+    #
+    # The configuration is split into two parts to allow for two stage updates to conserve space
+    # on storage-limited systems.
+    #
+    # To run a two stage update do:
+    #   $ sudo NIX_LIGHTWEIGHT=1 nixos-rebbuild switch
+    #   $ reboot
+    #   $ sudo nix-collect-garbage --delete-old
+    #   $ sudo nixos-rebbuild switch
+    #
     {
       nix.settings.experimental-features = [ 
         "nix-command" 
         "flakes"
       ];
 
-  imports = [ 
-    # Include the results of the hardware scan.
-    ./hardware-configuration.nix
-  ];
-
       # Allow unfree packages
       nixpkgs.config.allowUnfree = true;
 
@@ -359,31 +358,7 @@
         tldr
         bat
 
-    # LaTeX
-    (texlive.combine {
-      inherit (texlive) scheme-medium
-      # missing:
-      #   calc graphicx ifthen pgffor rotating trimclip xinttools 
-      kvoptions xargs ifthenx iftex xint listofitems xkeyval
-      etoolbox changepage pdfcomment eso-pic environ numprint xcolor
-      pagecolor colorspace graphics adjustbox textpos fancyvrb flowfram
-      fancyhdr pdfpages geometry 
-      anyfontsize cprotect ccicons 
-      # XXX this seems to be missing...
-      #suffix 
-      lipsum 
-      hardwrap catchfile 
-      # photobook...
-      photobook
-      # doc...
-      titlesec hypdoc doctools needspace xstring listings imakeidx  
-      latexmk;
-      #(setq org-latex-compiler "lualatex")
-      #(setq org-preview-latex-default-process 'dvisvgm)
-    })
-
         # fonts...
-    nerdfonts
         terminus_font 
 
         # GUI
@@ -443,10 +418,6 @@
         ffmpeg #ffmpegthumbnailer
         httrack
 
-    #blender
-    #krita
-
-    #texlive.combined.scheme-full 
       ];
 
       programs.geary.enable = false;
@@ -502,3 +473,45 @@
       # (e.g. man configuration.nix or on https://nixos.org/nixos/options.html).
       system.stateVersion = "23.05"; # Did you read the comment?
     }
+
+
+    # Full config...
+    (lib.mkIf (builtins.getEnv "NIX_LIGHTWEIGHT" == "") {
+      environment.systemPackages = with pkgs; [
+
+        # LaTeX
+        #texlive.combined.scheme-full 
+        (texlive.combine {
+          inherit (texlive) scheme-medium
+          # missing:
+          #   calc graphicx ifthen pgffor rotating trimclip xinttools 
+          kvoptions xargs ifthenx iftex xint listofitems xkeyval
+          etoolbox changepage pdfcomment eso-pic environ numprint xcolor
+          pagecolor colorspace graphics adjustbox textpos fancyvrb flowfram
+          fancyhdr pdfpages geometry 
+          anyfontsize cprotect ccicons 
+          # XXX this seems to be missing...
+          #suffix 
+          lipsum 
+          hardwrap catchfile 
+          # photobook...
+          photobook
+          # doc...
+          titlesec hypdoc doctools needspace xstring listings imakeidx  
+          latexmk;
+          #(setq org-latex-compiler "lualatex")
+          #(setq org-preview-latex-default-process 'dvisvgm)
+        })
+
+        # fonts...
+        nerdfonts
+
+        #blender
+        #krita
+        #gimp3
+        #gimp3-with-plugins
+
+      ];
+    }) 
+  ];
+}