nixos/documentation: Allow the inclusion of a nixpkgs/modules directory

ci/eval/default.nix

···
           "doc"
           "lib"
           "maintainers"
+          "modules"
           "nixos"
           "pkgs"
           ".version"

nixos/lib/eval-cacheable-options.nix

···
     version = release;
     revision = "release-${release}";
     prefix = modulesPath;
+    extraSources = [ (dirOf nixosPath) ];
   };
 in
 docs.optionsNix

nixos/modules/misc/documentation.nix

···
           && (t == "directory" -> baseNameOf n != "tests")
           && (t == "file" -> hasSuffix ".nix" n)
         );
+        prefixRegex = "^" + lib.strings.escapeRegex (toString pkgs.path) + "($|/(modules|nixos)($|/.*))";
+        filteredModules = builtins.path {
+          name = "source";
+          inherit (pkgs) path;
+          filter =
+            n: t:
+            builtins.match prefixRegex n != null
+            && cleanSourceFilter n t
+            && (t == "directory" -> baseNameOf n != "tests")
+            && (t == "file" -> hasSuffix ".nix" n);
+        };
       in
       pkgs.runCommand "lazy-options.json"
-        {
+        rec {
           libPath = filter (pkgs.path + "/lib");
           pkgsLibPath = filter (pkgs.path + "/pkgs/pkgs-lib");
-          nixosPath = filter (pkgs.path + "/nixos");
+          nixosPath = filteredModules + "/nixos";
           NIX_ABORT_ON_WARN = warningsAreErrors;
           modules =
             "[ "
             + concatMapStringsSep " " (p: ''"${removePrefix "${modulesPath}/" (toString p)}"'') docModules.lazy
             + " ]";
           passAsFile = [ "modules" ];
+          disallowedReferences = [
+            filteredModules
+            libPath
+            pkgsLibPath
+          ];
         }
         ''
           export NIX_STORE_DIR=$TMPDIR/store