On Mon, Aug 02 2021, Maxim Cournoyer wrote:

> Hello again,
>
> Xinglu Chen <public@yoctocell.xyz> writes:
>
>> * gnu/services/configuration.scm (generate-documentation): If the default
>>   value of a field is a package, show the value of the ‘name’ field of the
>>   package.  This might not be the correct name in some cases though.
>
> Here also, I've edited the commit message like so:
>
>   services: configuration: Derive the default value from the package variable.
>
>   If the type of a configuration field is a package, show the name of its
>   package *variable* as the default value.
>
>   * gnu/services/configuration.scm (generate-documentation){show-default}
>   {package->symbol}: New nested procedures.  Use them to format the field
>   entries.

Thanks, I should probably re-read the manual.  :)

>> ---
>>  gnu/services/configuration.scm | 12 ++++++++++--
>>  1 file changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/gnu/services/configuration.scm b/gnu/services/configuration.scm
>> index abcbc70520..99687d065a 100644
>> --- a/gnu/services/configuration.scm
>> +++ b/gnu/services/configuration.scm
>> @@ -252,12 +252,20 @@ does not have a default value" field kind)))
>>                                          (configuration-field-default-value-thunk f)
>>                                          (lambda _ '%invalid))))
>>                           (define (show-default? val)
>> -                           (or (string? val) (number? val) (boolean? val)
>> +                           (or (string? val) (number? val) (boolean? val) (package? val)
>>                                 (and (symbol? val) (not (eq? val '%invalid)))
>>                                 (and (list? val) (and-map show-default? val))))
>> +
>> +                         (define (show-default val)
>> +                           (cond
>> +                            ((package? val)
>> +                             ;; Maybe not always correct.
>> +                             (package-name val))
>> +                            (else (str val))))
>> +
>>                           `(entry (% (heading (code ,(str field-name))
>>                                               ,@(if (show-default? default)
>> -                                                   `(" (default: " (code ,(str default)) ")")
>> +                                                   `(" (default: " (code ,(show-default default)) ")")
>>                                                     '())
>>                                               " (type: "
>>                                               ,(str field-type)
>
> I've found a (rather hacky?) way to derive a package's symbol name
> instead of using its name, which eliminates the risk of a mismatch,
> using such procedure:
>
> --8<---------------cut here---------------start------------->8---
> @@ -252,6 +254,21 @@ does not have a default value" field kind)))
>  ;; A little helper to make it easier to document all those fields.
>  (define (generate-documentation documentation documentation-name)
>    (define (str x) (object->string x))
> +
> +  (define (package->symbol package)
> +    "Return the first symbol name of a package that matches PACKAGE, else #f."
> +    (let* ((module (file-name->module-name
> +                    (location-file (package-location package))))
> +           (symbols (filter-map
> +                     identity
> +                     (module-map (lambda (symbol var)
> +                                   (and (equal? package (variable-ref var))
> +                                        symbol))
> +                                 (resolve-module module)))))
> +      (if (null? symbols)
> +          #f
> +          (first symbols))))
> +
>    (define (generate configuration-name)
>      (match (assq-ref documentation configuration-name)
>        ((fields . sub-documentation)
> @@ -270,14 +287,21 @@ does not have a default value" field kind)))
>                                    (lambda _ '%invalid))))
>                     (define (show-default? val)
>                       (or (string? val) (number? val) (boolean? val)
> +                         (package? val)
>                           (and (symbol? val) (not (eq? val '%invalid)))
>                           (and (list? val) (and-map show-default? val))))
>  
> +                   (define (show-default val)
> +                     (cond
> +                      ((package? val)
> +                       (symbol->string (package->symbol val)))
> +                      (else (str val))))
> +
>                     `(entry (% (heading
>                                 (code ,(str field-name))
>                                 ,@(if (show-default? default)
>                                       `(" (default: "
> --8<---------------cut here---------------end--------------->8---

Cool, that looks like a better way than just getting the package name.

> Tested it to generate the new Jami service documentation, and pushed as
> commit 8e1f94421873777c6bb0b83daa4f81cbacc8b3ff.
>
> I think (guix services configuration) is starting to look good!  Thanks
> to your efforts toward improving the module.

You are welcome, happy to help out.  The next step would probably be to
automatically generate the docs when invoking ‘make docs’.