Add the tool "nixos-typecheck" that can check an option declaration to:

 - Enforce that an option declaration has a "defaultText" if and only if the
   type of the option derives from "package", "packageSet" or "nixpkgsConfig"
   and if a "default" attribute is defined.

 - Enforce that the value of the "example" attribute is wrapped with "literalExample"
   if the type of the option derives from "package", "packageSet" or "nixpkgsConfig".

 - Warn if a "defaultText" is defined in an option declaration if the type of
   the option does not derive from "package", "packageSet" or "nixpkgsConfig".

 - Warn if no "type" is defined in an option declaration.

1 files changed, 3 insertions, 2 deletions

diff --git a/nixos/modules/system/boot/systemd-unit-options.nix b/nixos/modules/system/boot/systemd-unit-options.nix
index d4cab93b26b8..16d0e098b8c8 100644
--- a/nixos/modules/system/boot/systemd-unit-options.nix
+++ b/nixos/modules/system/boot/systemd-unit-options.nix
@@ -17,14 +17,15 @@ in rec {
 
   unitOption = mkOptionType {
     name = "systemd option";
-    merge = loc: defs:
+    typerep = "(systemdOption)";
+    merge = _module: loc: defs:
       let
         defs' = filterOverrides defs;
         defs'' = getValues defs';
       in
         if isList (head defs'')
         then concatLists defs''
-        else mergeOneOption loc defs';
+        else mergeOneOption _module loc defs';
   };
 
   sharedOptions = {