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bug#56799: [PATCH 2/5] services: configuration: Add %unset-value exporte
From: |
Attila Lendvai |
Subject: |
bug#56799: [PATCH 2/5] services: configuration: Add %unset-value exported variable. |
Date: |
Wed, 24 Aug 2022 14:40:39 +0200 |
* gnu/services/configuration.scm (%unset-value): New variable.
(normalize-field-type+def): Use it.
(maybe-value-unset?): Use it.
---
gnu/services/configuration.scm | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/gnu/services/configuration.scm b/gnu/services/configuration.scm
index e2c4fe9998..a9426066b9 100644
--- a/gnu/services/configuration.scm
+++ b/gnu/services/configuration.scm
@@ -57,6 +57,7 @@ (define-module (gnu services configuration)
serialize-configuration
define-maybe
define-maybe/no-serialization
+ %unset-value
maybe-value-set?
generate-documentation
configuration->documentation
@@ -172,10 +173,10 @@ (define (normalize-field-type+def s)
(values #'(field-type def)))
((field-type)
(identifier? #'field-type)
- (values #'(field-type 'unset)))
+ (values #'(field-type %unset-value)))
(field-type
(identifier? #'field-type)
- (values #'(field-type 'unset)))))
+ (values #'(field-type %unset-value)))))
(define (define-configuration-helper serialize? serializer-prefix syn)
(syntax-case syn ()
@@ -301,9 +302,18 @@ (define-configuration stem (field field-type+def
(define (empty-serializer field-name val) "")
(define serialize-package empty-serializer)
+;; Ideally this should be an implementation detail, but we export it
+;; to provide a simpler API that enables unsetting a configuration
+;; field that has a maybe type, but also a default value.
+;;
+;; An example use-case would be something like a network application
+;; that uses a default port, but the field can explicitly be unset to
+;; request a random port at startup.
+(define %unset-value 'unset)
+
(define (maybe-value-set? value)
"Predicate to check whether a 'maybe' value was explicitly provided."
- (not (eq? 'unset value)))
+ (not (eq? %unset-value value)))
;; A little helper to make it easier to document all those fields.
(define (generate-documentation documentation documentation-name)
--
2.35.1