[bug#53663] [PATCH] gnu: services: Also accept 'undefined in maybe-foo? constructs.

[Attila Lendvai <attila@lendvai.name>]

This is a temporary bandaid until a more explicit handling of maybe types is
introduced for configurations (e.g. by using srfi-189). Until then, with this
change it becomes possible to have definitions like:

(define-maybe string (no-serialization))

(define-configuration my-configuration
  (my-field (maybe-string))
  (no-serialization))

i.e. without providing a default value for MY-FIELD.
---
 gnu/services/configuration.scm | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/gnu/services/configuration.scm b/gnu/services/configuration.scm
index 0de350a4df..c5f276eab5 100644
--- a/gnu/services/configuration.scm
+++ b/gnu/services/configuration.scm
@@ -141,7 +141,9 @@ (define (define-maybe-helper serialize? prefix syn)
                                     (id #'stem #'serialize-maybe- #'stem))))
        #`(begin
            (define (maybe-stem? val)
-             (or (eq? val 'disabled) (stem? val)))
+             (or (eq? val 'disabled)
+                 (eq? val 'undefined)
+                 (stem? val)))
            #,@(if serialize?
                   (list #'(define (serialize-maybe-stem field-name val)
                             (if (stem? val)
-- 
2.34.0