system, home: Validate ‘services’ field value.

This guides newcomers who might stick a single (service …) form
in this field.

* gnu/services.scm (validate-service-list): New macro.
(%validate-service-list): New procedure.
* gnu/system.scm (<operating-system>)[services]: Add ‘sanitize’.
* gnu/home.scm (<home-environment>)[services]: Add ‘sanitize’.

Change-Id: I9e29bd9a078e87b627ab766fd669ba9de79f8473

gnu/home.scm

@@ -1,6 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2021 Andrew Tropin <andrew@trop.in>
-;;; Copyright © 2022 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2022, 2024 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -67,7 +67,8 @@ (define-record-type* <home-environment> home-environment
                                 this-home-environment)))
 
   (services           home-environment-user-services
-                      (default '()))
+                      (default '())
+                      (sanitize validate-service-list))
 
   (location           home-environment-location            ; <location>
                       (default (and=> (current-source-location)

gnu/services.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2015-2023 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2015-2024 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2016 Chris Marusich <cmmarusich@gmail.com>
 ;;; Copyright © 2020 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
 ;;; Copyright © 2020, 2021 Ricardo Wurmus <rekado@elephly.net>
@@ -91,6 +91,8 @@ (define-module (gnu services)
             for-home
             for-home?
 
+            validate-service-list
+
             service-error?
             missing-value-service-error?
             missing-value-service-error-type
@@ -1271,4 +1273,19 @@ (define-syntax-rule (for-home exp ...)
   (syntax-parameterize ((for-home? (identifier-syntax #t)))
     exp ...))
 
+(define-with-syntax-properties (validate-service-list (value properties))
+  (%validate-service-list value properties))
+
+(define (%validate-service-list value properties)
+  (match value
+    (((? service?) ...) value)
+    (_
+     (raise
+      (make-compound-condition
+       (condition
+        (&error-location
+         (location (source-properties->location properties))))
+       (formatted-message
+        (G_ "'services' field must contain a list of services")))))))
+
 ;;; services.scm ends here.

gnu/system.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2013-2022 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2013-2022, 2024 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2015 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2015, 2016 Alex Kost <alezost@gmail.com>
 ;;; Copyright © 2016 Chris Marusich <cmmarusich@gmail.com>
@@ -294,7 +294,8 @@ (define-record-type* <operating-system> operating-system
                                 this-operating-system)))
   (services operating-system-user-services        ; list of services
             (thunked)                     ;allow for system-dependent services
-            (default %base-services))
+            (default %base-services)
+            (sanitize validate-service-list))
 
   (pam-services operating-system-pam-services     ; list of PAM services
                 (default (base-pam-services)))