[bug#63985] [PATCH RFC 0/5] Generic INI serializer & SRFI-171 for define-configuration

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

Hello,

Bruno Victal <mirai@makinata.eu> writes:

> Introduces 'base-transducer', a SRFI-171 based transducer that can be used as a
> starting point for writing custom configuration record serializing procedures.
>
> This also fixes the symbol maybe-value serialization test case.
>
> * gnu/services/configuration.scm (empty-serializer?): New predicate.
> (base-transducer, tfilter-maybe-value): New procedure.
> (serialize-configuration): Adapt to use base-transducer.
>
> * gnu/services/telephony.scm (jami-account->alist): Use transducers to skip
> fields that are unserializable or whose field maybe-value is unset.
>
> * tests/services/configuration.scm: Remove test-expect-fail.

Pretty cool stuff!

> ---
>  gnu/services/configuration.scm   | 29 ++++++++++++++++++++++++-----
>  gnu/services/telephony.scm       | 27 +++++++++++++--------------
>  tests/services/configuration.scm |  6 +-----
>  3 files changed, 38 insertions(+), 24 deletions(-)
>
> diff --git a/gnu/services/configuration.scm b/gnu/services/configuration.scm
> index dafe72f4fe..cd2cb8318b 100644
> --- a/gnu/services/configuration.scm
> +++ b/gnu/services/configuration.scm
> @@ -42,6 +42,7 @@ (define-module (gnu services configuration)
>    #:use-module (srfi srfi-26)
>    #:use-module (srfi srfi-34)
>    #:use-module (srfi srfi-35)
> +  #:use-module (srfi srfi-171)
>    #:export (configuration-field
>              configuration-field-name
>              configuration-field-type
> @@ -59,6 +60,10 @@ (define-module (gnu services configuration)
>              define-configuration/no-serialization
>              no-serialization
>  
> +            empty-serializer?
> +            tfilter-maybe-value
> +            base-transducer
> +
>              serialize-configuration
>              define-maybe
>              define-maybe/no-serialization
> @@ -125,13 +130,27 @@ (define-record-type* <configuration-field>
>    (default-value-thunk configuration-field-default-value-thunk)
>    (documentation configuration-field-documentation))
>  
> +(define (empty-serializer? field)
> +  (eq? empty-serializer
> +       (configuration-field-serializer field)))
> +
> +(define (tfilter-maybe-value config)
> +  (tfilter (lambda (field)
> +             (let ((field-value ((configuration-field-getter field) config)))
> +               (maybe-value-set? field-value)))))
> +
> +(define (base-transducer config)
> +  (compose (tremove empty-serializer?)
> +           ;; Only serialize fields whose value isn't '%unset-marker%.
> +           (tfilter-maybe-value config)
> +           (tmap (lambda (field)
> +                   ((configuration-field-serializer field)
> +                    (configuration-field-name field)
> +                    ((configuration-field-getter field) config))))))
> +

Please add docstrings.

>  (define (serialize-configuration config fields)
>    #~(string-append
> -     #$@(map (lambda (field)
> -               ((configuration-field-serializer field)
> -                (configuration-field-name field)
> -                ((configuration-field-getter field) config)))
> -             fields)))
> +     #$@(list-transduce (base-transducer config) rcons fields)))
>

While at it, please add a docstring for this procedure as well.

>  (define-syntax-rule (id ctx parts ...)
>    "Assemble PARTS into a raw (unhygienic) identifier."
> diff --git a/gnu/services/telephony.scm b/gnu/services/telephony.scm
> index 23ccb8d403..56b7772f58 100644
> --- a/gnu/services/telephony.scm
> +++ b/gnu/services/telephony.scm
> @@ -37,6 +37,7 @@ (define-module (gnu services telephony)
>    #:use-module (srfi srfi-1)
>    #:use-module (srfi srfi-2)
>    #:use-module (srfi srfi-26)
> +  #:use-module (srfi srfi-171)
>    #:use-module (ice-9 format)
>    #:use-module (ice-9 match)
>    #:export (jami-account
> @@ -204,22 +205,20 @@ (define (jami-account->alist jami-account-object)
>        ('rendezvous-point? "Account.rendezVous")
>        ('peer-discovery? "Account.peerDiscovery")
>        ('bootstrap-hostnames "Account.hostname")
> -      ('name-server-uri "RingNS.uri")
> -      (_ #f)))
> +      ('name-server-uri "RingNS.uri")))
>  
> -  (filter-map (lambda (field)
> -                (and-let* ((name (field-name->account-detail
> +  (define jami-account-transducer
> +    (compose (tremove empty-serializer?)
> +             (tfilter-maybe-value jami-account-object)
> +             (tmap (lambda (field)
> +                     (let* ((name (field-name->account-detail
>                                    (configuration-field-name field)))
> -                           (value ((configuration-field-serializer field)
> -                                   name ((configuration-field-getter field)
> -                                         jami-account-object)))
> -                           ;; The define-maybe default serializer produces an
> -                           ;; empty string for unspecified values.
> -                           (value* (if (string-null? value)
> -                                       #f
> -                                       value)))
> -                  (cons name value*)))
> -              jami-account-fields))
> +                            (value ((configuration-field-serializer field)
> +                                    name ((configuration-field-getter field)
> +                                          jami-account-object))))
> +                       (cons name value))))))
> +
> +  (list-transduce jami-account-transducer rcons jami-account-fields))

Could you please state in a comment under "(define
jami-account-transducer" why the base transducer doesn't suffice?  It
isn't obvious to me from a casual inspection.  I guess it's because
base-transducer is not recursive?  Should it be?

>  (define (jami-account-list? val)
>    (and (list? val)
> diff --git a/tests/services/configuration.scm b/tests/services/configuration.scm
> index 8ad5907f37..40a4e74b4d 100644
> --- a/tests/services/configuration.scm
> +++ b/tests/services/configuration.scm
> @@ -337,13 +337,9 @@ (define-maybe symbol)
>  (define-configuration config-with-maybe-symbol
>    (protocol maybe-symbol ""))
>  
> -;;; Maybe symbol values are currently seen as serializable, because the
> -;;; unspecified value is '%unset-marker%, which is a symbol itself.
> -;;; TODO: Remove expected fail marker after resolution.
> -(test-expect-fail 1)
>  (test-equal "symbol maybe value serialization, unspecified"
>    ""
> -  (gexp->approximate-sexp
> +  (eval-gexp
>     (serialize-configuration (config-with-maybe-symbol)
>                              config-with-maybe-symbol-fields)))

That's nice, though I don't understand why gexp->approximate needs to be
turned into eval-gexp?

-- 
Thanks,
Maxim