[bug#69591] [PATCH] services: shepherd: Support “free-form” services.

[Ludovic Courtès]

Hi Maxim,

(Cc’ing 71739, which is actually the right one.  :-))

Maxim Cournoyer <maxim.cournoyer@gmail.com> skribis:

> Ludovic Courtès <ludo@gnu.org> writes:

[...]

>> +@item @code{free-form} (default: @code{#f})
>> +When set, this field replaces the @code{start}, @code{stop}, and
>> +@code{actions} fields.  It is meant to be used when the service
>> +definition comes from some other source, typically the service
>> +collection provided by the Shepherd proper (@pxref{Service Collection,,,
>> +shepherd, The GNU Shepherd Manual}).
>> +
>> +@cindex REPL service, for shepherd
>> +For example, the snippet below defines a service for the Shepherd's
>> +built-in @acronym{REPL, read-eval-print loop} service (@pxref{REPL
>> +Service,,, shepherd, The GNU Shepherd Manual}):
>> +
>> +@lisp
>> +(shepherd-service
>> +  (provision '(repl))
>> +  (modules '((shepherd service repl)))
>> +  (free-form #~(repl-service)))
>> +@end lisp

[...]

> Hm, if free-form is expected to be a built-in procedure provided by
> Shepherd, should we call it 'built-in' instead of 'free-form' ?

I view it as something more generic: it’s typically, but not just, for
when the service comes from a procedure defined in the Shepherd itself.

Other use case is when as a service author you need more freedom that
what you get with the ‘start’ and ‘stop’ fields, like:

  (shepherd-service
    ;; …
    (free-from #~(let ((whatever (spawn-fiber …)))
                   (service '(foo) #:start …))))

It’s probably going to be a relatively marginal use case, but it’s good
to have that extra level of flexibility.

WDYT?

Thanks!

Ludo’.