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

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hi Ludovic,

Ludovic Courtès <ludo@gnu.org> writes:

> Hi Maxim,
>
> Maxim Cournoyer <maxim.cournoyer@gmail.com> skribis:
>
>> I've rediscovered the little gem that is (guix services configurations),
>> and attempted to make it more generally useful by adding an option to
>> opt out of serialization (which is not well adapted for producing a list
>> of command line arguments from the configuration for example):
>
> In the meantime I saw you discuss this on #guile so maybe you’ve solved
> the issue now?

No, thank you for your reply! :-)

> If not, attached is a possible solution and example.  It’s not perfect:
> in the example, you’ll get a warning about ‘serialize-integer’ being
> unbound, which is completely harmless but suboptimal.  Not sure how to
> address that.
>
> diff --git a/gnu/services/configuration.scm b/gnu/services/configuration.scm
> index 90f12a8d39..20e1647335 100644
> --- a/gnu/services/configuration.scm
> +++ b/gnu/services/configuration.scm
> @@ -109,6 +109,9 @@
>               (define (serialize-maybe-stem field-name val)
>                 (if (stem? val) (serialize-stem field-name val) ""))))))))
>
> +(define-syntax-parameter configuration-field-serialization?
> +  (identifier-syntax #t))
> +
>  (define-syntax define-configuration
>    (lambda (stx)
>      (syntax-case stx ()
> @@ -123,7 +126,8 @@
>                             #'(field-type ...)))
>                       ((field-serializer ...)
>                        (map (lambda (type)
> -                             (id #'stem #'serialize- type))
> +                             #`(and configuration-field-serialization?
> +                                    #,(id #'stem #'serialize- type)))

I tried:

(if (syntax->datum configuration-field-serialization?)
    #,(id #'stem #'serialize- type)
    #false)

hoping to get rid of the warning, but that appears to be strictly
equivalent, resulting in the same warning.  I also don't know how to fix
that.

>                             #'(field-type ...))))
>             #`(begin
>                 (define-record-type* #,(id #'stem #'< #'stem #'>)
> @@ -152,6 +156,16 @@
>                                             #,(id #'stem #'stem #'-fields))
>                     conf))))))))
>
> +(define-syntax-rule (without-field-serialization definition)
> +  (syntax-parameterize ((configuration-field-serialization?
> +                         (identifier-syntax #f)))
> +    definition
> +    #t))
> +
> +(without-field-serialization
> +  (define-configuration foo
> +    (bar (integer 123) "doc")))
> +
>  (define (serialize-package field-name val)
>    "")


That does work, thanks!  I'm a bit uncomfortable adding more warnings to
the Guix build output; OTOH it provides value (another user recently
pointed to the same annoyance here [0]).

Maxim

[0]  https://lists.gnu.org/archive/html/guix-devel/2021-04/msg00319.html