Subject: Re: [bug#31788] [PATCH] tests: Honor the return value of 'start-service'.

From: Clément Lassieur <[email-masked]>
Date: Tue, 12 Jun 2018 22:03:24 +0200

Hi Ludovic,

Ludovic Courtès <[email-masked]> writes:

> Hi Clément,
>
> Clément Lassieur <[email-masked]> skribis:
>
>> Since commit dc7b3e56337ee9d8dcd8fe7d5cab71ef536d024f, 'start-service' returns
>> the Shepherd's representation of the service as a sexp, and '#f' if the
>> service fails to start.  Also, it doesn't throw an exception when the service
>> fails to start, so relying on an exception instead of relying on its return
>> value is a false positive.
>
> Looking at ‘invoke-action’ (used by ‘start-service’) in (gnu services
> herd), it seems that an exception is raised upon error:
>
>       (('reply ('version 0 x ...) ('result y) ('error error)
>                ('messages messages))
>        (for-each display-message messages)
>        (raise-shepherd-error error)
>        #f)

But that's for Shepherd errors.  When a service fails to start, it's not
a Shepherd error, so if my understanding is correct '(cont result)'
should be called.  With result being '#f'.

    (match (read sock)
      (('reply ('version 0 _ ...) ('result result) ('error #f)
               ('messages messages))
       (for-each display-message messages)
       (cont result))
      (('reply ('version 0 x ...) ('result y) ('error error)
               ('messages messages))
       (for-each display-message messages)
       (raise-shepherd-error error)
       #f)
      (x
       ;; invalid reply
       #f))