Re: Add a way to disable serialization support to (guix services configuration)

[Xinglu Chen]

Hi,

On Fri, Apr 23 2021, Xinglu Chen wrote:

>> Wouldn’t it be nicer to write:
>>
>>   (define-configuration foo
>>     (bar (integer 123) "doc" no-serializer)
>>     (baz (string "") "doc"))
>>
>> where ‘bar’ wouldn’t have a serializer and ‘baz’ would?
>>
>> It’s also probably easier to implement correctly.
>
> I think that would be a good idea, maybe it could also make having a
> default value be optional, like this:
>
> #+begin_src scheme
> (define-configuration foo
>   (bar (integer) "doc" no-serializer) ;no default
>   (baz (string "default") "doc"))
> #+end_src

Since nobody seemed to show any objections, I went ahead and did
something like this myself (see the attached patches).  My macros skills
aren’t that good so I hope I didn’t make any obvious mistakes. :)

I haven’t tested it thoroughly, but at least it didn’t break anything
when I ran ‘./pre-inst-env guix home build ...’. :)

0001-services-configuration-Support-fields-without-defaul.patch
Description: no-default-value

>From 90d63a46a29a8080b7f95eabcec115c5c2c6481e Mon Sep 17 00:00:00 2001
Message-Id: 
<90d63a46a29a8080b7f95eabcec115c5c2c6481e.1619869705.git.public@yoctocell.xyz>
In-Reply-To: <cover.1619869705.git.public@yoctocell.xyz>
References: <cover.1619869705.git.public@yoctocell.xyz>
From: Xinglu Chen <public@yoctocell.xyz>
Date: Sat, 1 May 2021 13:31:27 +0200
Subject: [PATCH 2/2] services: configuration: Add ability to use custom
 serializer.
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Some configuration values should not be serialized to a configuration file,
e.g. command line options for a daemon.

* gnu/services/configuration.scm (define-configuration): Add option to use a
custom serializer.
(empty-serializer): New procedure.
(serialize-package): Alias to ‘empty-serializer’.
---
 gnu/services/configuration.scm | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/gnu/services/configuration.scm b/gnu/services/configuration.scm
index 85e1ac78cb..7024b13136 100644
--- a/gnu/services/configuration.scm
+++ b/gnu/services/configuration.scm
@@ -44,6 +44,7 @@
             define-configuration
             validate-configuration
             generate-documentation
+            empty-serializer
             serialize-package))
 
 ;;; Commentary:
@@ -116,7 +117,7 @@
 (define-syntax define-configuration
   (lambda (stx)
     (syntax-case stx ()
-      ((_ stem (field (field-type properties ...) doc) ...)
+      ((_ stem (field (field-type properties ...) doc custom-serializer ...) 
...)
        (with-syntax (((field-getter ...)
                       (map (lambda (field)
                              (id #'stem #'stem #'- field))
@@ -133,9 +134,12 @@
                              (_ (syntax 'disabled)))
                            #'((field-type properties ...) ...)))
                      ((field-serializer ...)
-                      (map (lambda (type)
-                             (id #'stem #'serialize- type))
-                           #'(field-type ...))))
+                      (map (lambda (type serializer)
+                             (match serializer
+                               (((serializer)) serializer)
+                               (_ (id #'stem #'serialize- type))))
+                           #'(field-type ...)
+                           #'((custom-serializer ...) ...))))
          #`(begin
              (define-record-type* #,(id #'stem #'< #'stem #'>)
                #,(id #'stem #'% #'stem)
@@ -176,8 +180,8 @@
                                          #,(id #'stem #'stem #'-fields))
                  conf))))))))
 
-(define (serialize-package field-name val)
-  "")
+(define (empty-serializer field-name val) "")
+(define serialize-package empty-serializer)
 
 ;; A little helper to make it easier to document all those fields.
 (define (generate-documentation documentation documentation-name)
-- 
2.31.1