revert bd3861c580

revert Merge pull request 'Remove clanModules/*' (#4202) from remove-modules into main

Reviewed-on: https://git.clan.lol/clan/clan-core/pulls/4202

See: https://git.clan.lol/clan/clan-core/issues/4365

Not all modules are migrated.
If they are not migrated, we need to write migration docs and please display the link to the migration docs

lib/modules/inventory/frontmatter/default.nix

@@ -121,7 +121,45 @@ let
     );
 
   checkConstraints = args: (evalFrontmatter args).config.constraints.assertions;
-  getFrontmatter = _modulepath: _modulename: "clanModules are removed!";
+
+  getReadme =
+    modulepath: modulename:
+    let
+      readme = modulepath + "/README.md";
+      readmeContents =
+        if (builtins.pathExists readme) then
+          (builtins.readFile readme)
+        else
+          throw "No README.md found for module ${modulename} (expected at ${readme})";
+    in
+    readmeContents;
+
+  getFrontmatter =
+    modulepath: modulename:
+    let
+      content = getReadme modulepath modulename;
+      parts = lib.splitString "---" content;
+      # Partition the parts into the first part (the readme content) and the rest (the metadata)
+      parsed = builtins.partition ({ index, ... }: if index >= 2 then false else true) (
+        lib.filter ({ index, ... }: index != 0) (lib.imap0 (index: part: { inherit index part; }) parts)
+      );
+      meta = builtins.fromTOML (builtins.head parsed.right).part;
+    in
+    if (builtins.length parts >= 3) then
+      meta
+    else
+      throw ''
+        TOML Frontmatter not found in README.md for module ${modulename}
+
+        Please add the following to the top of your README.md:
+
+        ---
+        description = "Your description here"
+        categories = [ "Your categories here" ]
+        features = [ "inventory" ]
+        ---
+        ...rest of your README.md...
+      '';
 in
 {
   inherit