bug#34448: --no-build-details means system-name is nil

bug#34448: --no-build-details means system-name is nil

[Glenn Morris]

Package: emacs
Version: 27.0.50
Severity: minor

Master at revision 2860f6cec5. If I run

emacs -Q --no-build-details

then (system-name) returns nil. I expect this switch to only affect the
values stored in the Emacs binary, not the run-time result.

I'm also not sure why --no-build-details is a run-time option (as
opposed to a build-time one).

Anyway, this breaks file-locking (cf bug#34355) and makes it impossible
to save a file.

bug#34448: --no-build-details means system-name is nil

[Lars Ingebrigtsen]

Glenn Morris <rgm@gnu.org> writes:

> emacs -Q --no-build-details
>
> then (system-name) returns nil. I expect this switch to only affect the
> values stored in the Emacs binary, not the run-time result.

Yup.  It seems like this was the intention here:

void
init_system_name (void)
{
  if (!build_details)
    {
      /* Set system-name to nil so that the build is deterministic.  */
      Vsystem_name = Qnil;
      return;
    }

which is called from

static void
init_and_cache_system_name (void)
{
  init_system_name ();
  cached_system_name = Vsystem_name;
}

which is called from

DEFUN ("system-name", Fsystem_name, Ssystem_name, 0, 0, 0,
       doc: /* Return the host name of the machine you are running on, as a string.  */)
  (void)
{
  if (EQ (Vsystem_name, cached_system_name))
    init_and_cache_system_name ();
  return Vsystem_name;

Is --no-build-details just meant to be used during builds?  If so, we
can just document that, I guess?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#34448: --no-build-details means system-name is nil

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Thu, 10 Oct 2019 00:26:53 +0200
> Cc: 34448@debbugs.gnu.org
> 
> void
> init_system_name (void)
> {
>   if (!build_details)
>     {
>       /* Set system-name to nil so that the build is deterministic.  */
>       Vsystem_name = Qnil;
>       return;
>     }
> 
> which is called from
> 
> static void
> init_and_cache_system_name (void)
> {
>   init_system_name ();
>   cached_system_name = Vsystem_name;
> }
> 
> which is called from
> 
> DEFUN ("system-name", Fsystem_name, Ssystem_name, 0, 0, 0,
>        doc: /* Return the host name of the machine you are running on, as a string.  */)
>   (void)
> {
>   if (EQ (Vsystem_name, cached_system_name))
>     init_and_cache_system_name ();
>   return Vsystem_name;
> 
> Is --no-build-details just meant to be used during builds?  If so, we
> can just document that, I guess?

Yes, documenting that would be a good compromise, I think.

bug#34448: --no-build-details means system-name is nil

[Lars Ingebrigtsen]

Eli Zaretskii <eliz@gnu.org> writes:

>> Is --no-build-details just meant to be used during builds?  If so, we
>> can just document that, I guess?
>
> Yes, documenting that would be a good compromise, I think.

I've now done this, and I'm closing this bug report.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no