bug#58909: 29.0.50; [WIP PATCH] Deleting the last frame of an emacsclient doesn't ask to save

[Jim Porter <jporterbugs@gmail.com>]

On 10/31/2022 12:52 PM, Eli Zaretskii wrote:
>> Date: Mon, 31 Oct 2022 12:38:04 -0700
>> From: Jim Porter <jporterbugs@gmail.com>
>> Cc: 58909@debbugs.gnu.org
>>
>> Still,
>> 'C-x C-c' still prompts in that case too. My understanding is that it
>> does so because when an application is waiting for the emacsclient to
>> finish, you can't go back from killing the terminal/client; you *can*
>> (usually) go back if you're only killing a frame.
> 
> My interpretation of why "C-x C-c" prompts is that it does the same as
> when you use it from a non-client frame.  We want the same UX in both
> cases.  "C-x 5 0" should IMO likewise produce the same behavior in
> both cases.

That's actually my goal too: I'd like to ensure that the UX for a client 
frame is as similar as possible as for a non-client frame. Since we 
disagree on what that similarity should be, I guess that means we have 
different mental models for some part of this. If it helps, I'll try to 
explain how I think of it.

 From a client frame, 'C-x C-c' prompts to save all the file-buffers 
associated with that client, and then kills the client, which kills the 
frames for that client. That's similar to 'C-x C-c' in a non-client 
setting: it kills *all* frames and prompts to save *all* file-buffers. 
So I see the client as a "sub" Emacs: it owns some frames and 
(partially) owns some buffers. Commands on the client then work on that 
subset, and only that subset. Since frames can only be owned by a single 
client, in my mind frame commands also work within that client's subset.

For frame-deletion, non-client Emacs lets you kill a single frame via 
'C-x 5 0' or clicking the X in the frame's title bar. However, if it's 
the last frame, then:

   C-x 5 0    -> Error: "Attempt to delete the sole visible or iconified 
frame"
   Clicking X -> Call 'save-buffers-kill-emacs' (see 'handle-delete-frame')

To me, that would mean that the matching UX for a client with a single 
frame (but possibly other frames for Emacs overall) is:

   C-x 5 0    -> Error
   Clicking X -> Call 'save-buffers-kill-terminal'

Signaling an error for 'C-x 5 0' seems excessively strict to me, so 
calling 'save-buffers-kill-terminal' in both cases seemed like a good 
compromise to me. Instead of getting an error, the user gets a prompt, 
but can still proceed with killing that frame if they're sure.