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

[Xinglu Chen <public@yoctocell.xyz>]

[-- Attachment #1: Type: text/plain, Size: 960 bytes --]

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 ...’. :)


[-- Attachment #2: no-default-value --]
[-- Type: text/x-patch, Size: 6509 bytes --]

From 231281ebf555295e83513873293a1ad3eab884a8 Mon Sep 17 00:00:00 2001
Message-Id: <231281ebf555295e83513873293a1ad3eab884a8.1619869705.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 13:24:43 +0200
Subject: [PATCH 1/2] services: configuration: Support fields without default
 values.
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Not all fields in a configuration have a sensible default value,
e.g. ‘user.name’ in gitconfig, the user should have to set that themselves

* gnu/services/configuration.scm (configuration-missing-field): New procedure.
(define-configuration): Make default value optional.
---
 gnu/services/configuration.scm | 78 ++++++++++++++++++++++------------
 1 file changed, 51 insertions(+), 27 deletions(-)

diff --git a/gnu/services/configuration.scm b/gnu/services/configuration.scm
index 90f12a8d39..85e1ac78cb 100644
--- a/gnu/services/configuration.scm
+++ b/gnu/services/configuration.scm
@@ -2,6 +2,7 @@
 ;;; Copyright © 2015 Andy Wingo <wingo@igalia.com>
 ;;; Copyright © 2017 Mathieu Othacehe <m.othacehe@gmail.com>
 ;;; Copyright © 2017, 2018 Clément Lassieur <clement@lassieur.org>
+;;; Copyright © 2021 Xinglu Chen <public@yoctocell.xyz>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -63,6 +64,9 @@
 (define (configuration-missing-field kind field)
   (configuration-error
    (format #f "~a configuration missing required field ~a" kind field)))
+(define (configuration-no-default-value kind field)
+  (configuration-error
+   (format #f "`~a' in `~a' does not have a default value" kind field)))
 
 (define-record-type* <configuration-field>
   configuration-field make-configuration-field configuration-field?
@@ -112,7 +116,7 @@
 (define-syntax define-configuration
   (lambda (stx)
     (syntax-case stx ()
-      ((_ stem (field (field-type def) doc) ...)
+      ((_ stem (field (field-type properties ...) doc) ...)
        (with-syntax (((field-getter ...)
                       (map (lambda (field)
                              (id #'stem #'stem #'- field))
@@ -121,36 +125,56 @@
                       (map (lambda (type)
                              (id #'stem type #'?))
                            #'(field-type ...)))
+                     ((field-default ...)
+                      (map (match-lambda
+                             ((field-type default _ ...) default)
+                             ;; We get warnings about `disabled' being an
+                             ;; unbound variable unless we quote it.
+                             (_ (syntax 'disabled)))
+                           #'((field-type properties ...) ...)))
                      ((field-serializer ...)
                       (map (lambda (type)
                              (id #'stem #'serialize- type))
                            #'(field-type ...))))
-           #`(begin
-               (define-record-type* #,(id #'stem #'< #'stem #'>)
-                 #,(id #'stem #'% #'stem)
-                 #,(id #'stem #'make- #'stem)
-                 #,(id #'stem #'stem #'?)
-                 (%location #,(id #'stem #'-location)
-                            (default (and=> (current-source-location)
-                                            source-properties->location))
-                            (innate))
-                 (field field-getter (default def))
-                 ...)
-               (define #,(id #'stem #'stem #'-fields)
-                 (list (configuration-field
-                        (name 'field)
-                        (type 'field-type)
-                        (getter field-getter)
-                        (predicate field-predicate)
-                        (serializer field-serializer)
-                        (default-value-thunk (lambda () def))
-                        (documentation doc))
-                       ...))
-               (define-syntax-rule (stem arg (... ...))
-                 (let ((conf (#,(id #'stem #'% #'stem) arg (... ...))))
-                   (validate-configuration conf
-                                           #,(id #'stem #'stem #'-fields))
-                   conf))))))))
+         #`(begin
+             (define-record-type* #,(id #'stem #'< #'stem #'>)
+               #,(id #'stem #'% #'stem)
+               #,(id #'stem #'make- #'stem)
+               #,(id #'stem #'stem #'?)
+               (%location #,(id #'stem #'-location)
+                          (default (and=> (current-source-location)
+                                          source-properties->location))
+                          (innate))
+               #,@(map (lambda (name getter def)
+                         (if (equal? (syntax->datum def) (quote 'disabled))
+                             #`(#,name #,getter)
+                             #`(#,name #,getter (default #,def))))
+                       #'(field ...)
+                       #'(field-getter ...)
+                       #'(field-default ...)))
+             (define #,(id #'stem #'stem #'-fields)
+               (list (configuration-field
+                      (name 'field)
+                      (type 'field-type)
+                      (getter field-getter)
+                      (predicate field-predicate)
+                      (serializer field-serializer)
+                      ;; TODO: What if there is no default value?
+                      (default-value-thunk
+                        (lambda ()
+                          (display '#,(id #'stem #'% #'stem))
+                          (if (equal? (syntax->datum field-default)
+                                      (quote 'disabled))
+                              (configuration-no-default-value
+                               '#,(id #'stem #'% #'stem) 'field)
+                              field-default)))
+                      (documentation doc))
+                     ...))
+             (define-syntax-rule (stem arg (... ...))
+               (let ((conf (#,(id #'stem #'% #'stem) arg (... ...))))
+                 (validate-configuration conf
+                                         #,(id #'stem #'stem #'-fields))
+                 conf))))))))
 
 (define (serialize-package field-name val)
   "")
-- 
2.31.1


[-- Attachment #3: custom-serializer --]
[-- Type: text/x-patch, Size: 3020 bytes --]

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