lib.modules: Add hint when using config in imports

lib/modules.nix

@@ -637,6 +637,15 @@ let
     key: f:
     args@{ config, ... }:
     let
+      importHint =
+        name:
+        if name == "config" then
+          "\n\n"
+          + ''
+            … If you get an infinite recursion here, you probably reference `config`
+              in `imports`. This is not supported; consider using mkEnableOption.''
+        else
+          "";
       # Module arguments are resolved in a strict manner when attribute set
       # deconstruction is used.  As the arguments are now defined with the
       # config._module.args option, the strictness used on the attribute
@@ -649,7 +658,7 @@ let
       # a module will resolve strictly the attributes used as argument but
       # not their values.  The values are forwarding the result of the
       # evaluation of the option.
-      context = name: ''while evaluating the module argument `${name}' in "${key}":'';
+      context = name: ''while evaluating the module argument `${name}' in "${key}":${importHint name}'';
       extraArgs = mapAttrs (
         name: _: addErrorContext (context name) (args.${name} or config._module.args.${name})
       ) (functionArgs f);