bug#38875: 26.2; auto-save-list-file-name still created when auto-save-default is nil

[Eli Zaretskii]

> From: João Guerra <joca.bt@gmail.com>
> Date: Thu, 2 Jan 2020 22:09:59 +0100
> Cc: 38875@debbugs.gnu.org
> 
> > > (setq auto-save-default nil)
> > >
> > > wait a bit and `~/.emacs.d/auto-save-list/.saves-<pid>-<hostname>~`
> > > will be created.
> >
> > That's exactly what I did, except that these settings were in ~/.emacs
> > and not loaded after startup.  I waited for 30 seconds, and didn't see
> > any auto-save-list file in ~/.emacs.d/.  Not sure why it happens for
> > you.
> 
> Tried yet on another platform and Emacs version and using the method
> you described and it still happened. The thing is that for some reason
> the time it takes to create the file is not consistent, sometimes it's
> 30s (auto-save-timeout) other times is 2m :s. Made a video
> https://youtu.be/metU0u2umtQ.

Apologies, you are right.

But this seems to be working as intended.  Emacs creates that
directory if it doesn't yet exist whenever it enters do-auto-save, and
it does that before it loops over all the buffers, so it cannot yet
know whether any of the buffers wants auto-saving.  It cannot refrain
from creating the directory (and the listing file inside it) based on
the value of auto-save-default alone, because that value could have
been changed half-way through a session, and some of the buffers still
want to be auto-saved.  We could perhaps make two loops over the
buffers, one before creating the directory and one after, but that
doesn't seem like an efficient way (think of sessions with many
hundreds of buffers), and since a way exists of disabling the creation
of that directory by customizing auto-save-list-file-prefix, there
doesn't seem to be a need for punishing the users who do want
auto-saving.

OK?