bug#51377: Automatically exit server when it has no remaining clients

[Jim Porter <jporterbugs@gmail.com>]

On 10/24/2021 9:32 AM, Gregory Heytings wrote:
>> I'm not sure I understand the patch; `save-buffers-kill-emacs' prompts 
>> the user to save buffers before killing Emacs, but how would that work 
>> in a daemon when there are no frames remaining?
> 
> There is one (invisible) frame remaining: the daemon frame.  And when 
> there are no other frames (graphical or non-graphical) ones, there's 
> nothing to save, save-buffer-kill-emacs just kills emacs.

I don't think this is true in general. The docstring for 
`server-save-buffers-kill-terminal' says: "If emacsclient was started 
with a list of filenames to edit, then only these files will be asked to 
be saved." As a result, some files with unsaved changes may still exist, 
so we'd want to prompt about those *before* the last frame is closed.

To see this in action:

   $ emacs -Q --daemon
   $ emacsclient foo.txt
   C-x C-f bar.txt
   ;; Make some edits
   C-x C-c
   ;; Exits immediately without prompting about saving bar.txt

If `save-buffers-kill-emacs' were called after that, the Emacs daemon 
would be killed, losing the edits to bar.txt.