feat(docs): modules docgen

docs/docgen.nix

@@ -2,6 +2,7 @@
   stdenvNoCC,
   mdbook,
   nixdoc,
+  nixosOptionsDoc,
   lib,
   excluded ? [
     ".*flake\\.nix$"
@@ -45,8 +46,9 @@ stdenvNoCC.mkDerivation {
               docs = 0;
               flake = 1;
               devShells = 2;
-              hosts = 3;
-              users = 4;
+              modules = 3;
+              hosts = 4;
+              users = 5;
             };
             order = orderMap.${lib.head (lib.splitString "/" (relPath file))};
 
@@ -66,6 +68,18 @@ stdenvNoCC.mkDerivation {
               in
               if dirPart == "." then 0 else lib.length (lib.splitString "/" dirPart);
             indent = lib.concatStringsSep "" (lib.genList (x: "    ") depth);
+
+            isModule = (r: lib.hasPrefix "modules/os" r || lib.hasPrefix "modules/home" r) relPath;
+            modulesEval = lib.evalModules {
+              modules = [
+                file
+                { _module.check = false; }
+              ];
+            };
+            moduleOptionsDoc =
+              (nixosOptionsDoc {
+                options = lib.removeAttrs modulesEval.options [ "_module" ];
+              }).optionsCommonMark;
           in
           {
             script = ''
@@ -76,6 +90,12 @@ stdenvNoCC.mkDerivation {
                 --description "${title}" \
                 --anchor-prefix "" \
                 --file "${file}" > "src/${mdPath}"
+            ''
+            + lib.optionalString isModule ''
+              {
+                echo
+                cat ${moduleOptionsDoc}
+              } >> src/${mdPath}
             '';
             summaryLine = "${indent}- [${title}](${mdPath})";
             sortKey = toString order + mdPath;