Subject: bug#41140: “guix system” suggests wrong module import when using “remove”

From: Ricardo Wurmus <[email-masked]>
Date: Sun, 10 May 2020 23:33:11 +0200

Ricardo Wurmus <[email-masked]> writes:

> * can we avoid this by extending modify-services to support “delete”
>   much like modify-phases, and suggesting to use that instead of
>   “remove”?

The attached patch does this.

What do you think?

-- 
Ricardo

>From 40c1208cbe9cbfa58ee385ef6ee06b775d309753 Mon Sep 17 00:00:00 2001
From: Ricardo Wurmus <[email-masked]>
Date: Sun, 10 May 2020 23:29:38 +0200
Subject: [PATCH] services: Support DELETE in MODIFY-SERVICES macro.

* gnu/services.scm (%modify-service): Add clause for DELETE syntax.
(modify-services): Use FILTER-MAP; adjust docstring.
* doc/guix.texi (System Services): Mention alternative syntax.
(X Window): Use MODIFY-SERVICES syntax.
---
 doc/guix.texi    | 13 ++++++++++---
 gnu/services.scm | 23 +++++++++++++++--------
 2 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index 14a42e7070..25274a8539 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -11230,6 +11230,14 @@ following expression returns a list that contains all the services in
         %desktop-services)
 @end lisp
 
+Alternatively, the @code{modify-services} macro can be used:
+
+@lisp
+(modify-services %desktop-services
+  (delete avahi-service-type))
+@end lisp
+
+
 @unnumberedsubsec Instantiating the System
 
 Assuming the @code{operating-system} declaration
@@ -14732,9 +14740,8 @@ and tty8.
                    (service slim-service-type (slim-configuration
                                                (display ":1")
                                                (vt "vt8")))
-                   (remove (lambda (service)
-                             (eq? (service-kind service) gdm-service-type))
-                           %desktop-services))))
+                   (modify-services %desktop-services
+                     (delete gdm-service-type)))))
 @end lisp
 
 @end defvr
diff --git a/gnu/services.scm b/gnu/services.scm
index 2e4648bf78..ac614a7317 100644
--- a/gnu/services.scm
+++ b/gnu/services.scm
@@ -1,6 +1,7 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2015, 2016, 2017, 2018, 2019, 2020 Ludovic Courtès <[email-masked]>
 ;;; Copyright © 2016 Chris Marusich <[email-masked]>
+;;; Copyright © 2020 Ricardo Wurmus <[email-masked]>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -33,7 +34,7 @@
   #:use-module (guix modules)
   #:use-module (gnu packages base)
   #:use-module (gnu packages bash)
-  #:use-module (srfi srfi-1)
+  #:use-module ((srfi srfi-1) #:hide (delete))
   #:use-module (srfi srfi-9)
   #:use-module (srfi srfi-9 gnu)
   #:use-module (srfi srfi-26)
@@ -272,7 +273,11 @@ singleton service type NAME, of which the returned service is an instance."
     (service type value)))
 
 (define-syntax %modify-service
-  (syntax-rules (=>)
+  (syntax-rules (=> delete)
+    ((_ svc (delete kind) clauses ...)
+     (if (eq? (service-kind svc) kind)
+         #f
+         (%modify-service svc clauses ...)))
     ((_ service)
      service)
     ((_ svc (kind param => exp ...) clauses ...)
@@ -302,16 +307,18 @@ TYPE.  Consider this example:
     (mingetty-service-type config =>
                            (mingetty-configuration
                             (inherit config)
-                            (motd (plain-file \"motd\" \"Hi there!\")))))
+                            (motd (plain-file \"motd\" \"Hi there!\"))))
+    (delete udev-service-type))
 
 It changes the configuration of the GUIX-SERVICE-TYPE instance, and that of
-all the MINGETTY-SERVICE-TYPE instances.
+all the MINGETTY-SERVICE-TYPE instances, and it deletes instances of the
+UDEV-SERVICE-TYPE.
 
-This is a shorthand for (map (lambda (svc) ...) %base-services)."
+This is a shorthand for (filter-map (lambda (svc) ...) %base-services)."
     ((_ services clauses ...)
-     (map (lambda (service)
-            (%modify-service service clauses ...))
-          services))))
+     (filter-map (lambda (service)
+                   (%modify-service service clauses ...))
+                 services))))
 
 
 ;;;
-- 
2.25.1