export evaluation from default.nix and use it for docs

doc/extract-options.nix

@@ -1,31 +1,10 @@
+{ eval, lib, pkgs }:
 let
-  overlay = import ../overlay.nix;
-  pkgs = import <nixpkgs> ( {
-    overlays = [overlay];
-    config = {
-      allowUnsupportedSystem = true; # mipsel
-      permittedInsecurePackages = [
-        "python-2.7.18.6"       # kernel backports needs python <3
-      ];
-    };
-  });
-  inherit (pkgs) lib;
   inherit (lib) types;
-  modulenames =
-    builtins.attrNames
-      (lib.filterAttrsRecursive
-        (n: t:
-          (n != "arch") &&
-          ((t=="directory") ||
-           ((t=="regular") && ((builtins.match ".*\\.nix$" n) != null))))
-        (builtins.readDir ../modules));
-  modulefiles = builtins.map (n: builtins.toPath "${../modules}/${n}") modulenames;
-  eval = (lib.evalModules {
-    modules = [
-      { _module.args = { inherit pkgs; lib = pkgs.lib; }; }
-    ] ++ modulefiles;
-  });
   conf = eval.config;
+  rootDir = builtins.toPath ./..;
+  stripAnyPrefixes = lib.flip (lib.fold lib.removePrefix)
+    ["${rootDir}/"];
   optToDoc = name: opt : {
     inherit name;
     description = opt.description or null;
@@ -42,16 +21,12 @@ let
     then
       let sd = lib.attrByPath item.loc ["not found"] conf;
       in item // {
+        declarations =  map stripAnyPrefixes item.declarations;
         parameters =
           let x = lib.mapAttrsToList optToDoc sd.parameters; in x;
       }
     else
-      item;
-  o = builtins.map spliceServiceDefn
-    (pkgs.lib.optionAttrSetToDocList eval.options);
-in {
-  doc = pkgs.writeText "options.yaml" ''
-    # ${./..}
-    ${builtins.toJSON o}
-  '';
-}
+      item // { declarations =  map stripAnyPrefixes item.declarations; };
+in
+builtins.map spliceServiceDefn
+  (pkgs.lib.optionAttrSetToDocList eval.options)