bug#65277: 29.1.50; emacsclient Dired: frame is closed/killed when opening another dir

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 65277@debbugs.gnu.org
> Date: Thu, 17 Aug 2023 22:02:16 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> 
> > Cc: 65277@debbugs.gnu.org
> > Date: Thu, 17 Aug 2023 12:44:47 +0300
> > From: Eli Zaretskii <eliz@gnu.org>
> > 
> > Thanks for testing.  Could you please test the improved patch below?
> 
> Sorry, that patch had a silly mistake.  Please use the one below
> instead:

I have now tested the last patch I sent on a GNU/Linux system with
using "emacsclient -t", and found another problem.  The updated patch
below should solve it, so p-lease try that when you have time.

With the patch below, the result of "C-x C-v" in a client
terminal/frame is that the frame stays around, and also emacsclient
doesn't exit.  However, the buffer that visits the alternate file is
not considered a "client" buffer, so "C-x #" displays an error message
saying there are no client buffers left and does nothing else, and
"C-x k" doesn't delete the client frame.  To delete the client frame
and cause emacsclient to exit, you need to type either "C-x C-c" or
"C-x 5 0".  This might be a bit surprising, but OTOH the semantics of
the client buffer after "C-x C-v" is not well defined: should the
buffer visiting the alternate file have the same client property and
share the same kill-buffer-hook?  I could argue either way.

Here's the patch to try.  If there are no objections or bugs reported
against it, I will install this on master in a week or so.

diff --git a/lisp/files.el b/lisp/files.el
index 68c0a10..3466a53 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -1998,6 +1998,8 @@ kill-buffer-hook
 Note: Be careful with let-binding this hook considering it is
 frequently used for cleanup.")
 
+(defvar find-alternate-file-dont-kill-client nil
+  "If non-nil, `server-buffer-done' should not delete the client.")
 (defun find-alternate-file (filename &optional wildcards)
   "Find file FILENAME, select its buffer, kill previous buffer.
 If the current buffer now contains an empty file that you just visited
@@ -2044,7 +2046,8 @@ find-alternate-file
     ;; save a modified buffer visiting a file.  Rather, `kill-buffer'
     ;; asks that itself.  Thus, there's no need to temporarily do
     ;; `(set-buffer-modified-p nil)' before running this hook.
-    (run-hooks 'kill-buffer-hook)
+    (let ((find-alternate-file-dont-kill-client 'dont-kill-client))
+      (run-hooks 'kill-buffer-hook))
     ;; Okay, now we can end-of-life the old buffer.
     (if (get-buffer " **lose**")
 	(kill-buffer " **lose**"))
diff --git a/lisp/server.el b/lisp/server.el
index ba7e02d..10f1559 100644
--- a/lisp/server.el
+++ b/lisp/server.el
@@ -330,6 +330,9 @@ server-with-environment
 (defun server-delete-client (proc &optional noframe)
   "Delete PROC, including its buffers, terminals and frames.
 If NOFRAME is non-nil, let the frames live.
+If NOFRAME is the symbol \\='dont-kill-client, also don't
+delete PROC or its terminals, just kill its buffers: this is
+for when `find-alternate-file' calls this via `kill-buffer-hook'.
 Updates `server-clients'."
   (server-log (concat "server-delete-client" (if noframe " noframe")) proc)
   ;; Force a new lookup of client (prevents infinite recursion).
@@ -366,23 +369,28 @@ server-delete-client
 	    (set-frame-parameter frame 'client nil)
 	    (delete-frame frame))))
 
-      (setq server-clients (delq proc server-clients))
+      (or (eq noframe 'dont-kill-client)
+          (setq server-clients (delq proc server-clients)))
 
       ;; Delete the client's tty, except on Windows (both GUI and
       ;; console), where there's only one terminal and does not make
       ;; sense to delete it, or if we are explicitly told not.
       (unless (or (eq system-type 'windows-nt)
+                  ;; 'find-alternate-file' caused the last client
+                  ;; buffer to be killed, but we will reuse the client
+                  ;; for another buffer.
+                  (eq noframe 'dont-kill-client)
                   (process-get proc 'no-delete-terminal))
 	(let ((terminal (process-get proc 'terminal)))
 	  ;; Only delete the terminal if it is non-nil.
 	  (when (and terminal (eq (terminal-live-p terminal) t))
 	    (delete-terminal terminal))))
 
-      ;; Delete the client's process.
-      (if (eq (process-status proc) 'open)
-	  (delete-process proc))
-
-      (server-log "Deleted" proc))))
+      ;; Delete the client's process (or don't).
+      (unless (eq noframe 'dont-kill-client)
+        (if (eq (process-status proc) 'open)
+	    (delete-process proc))
+        (server-log "Deleted" proc)))))
 
 (defvar server-log-time-function #'current-time-string
   "Function to generate timestamps for `server-buffer'.")
@@ -1590,7 +1598,8 @@ server-buffer-done
 		;; frames, which might change the current buffer.  We
 		;; don't want that (bug#640).
 		(save-current-buffer
-		  (server-delete-client proc))
+		  (server-delete-client proc
+                                        find-alternate-file-dont-kill-client))
 	      (server-delete-client proc))))))
     (when (and (bufferp buffer) (buffer-name buffer))
       ;; We may or may not kill this buffer;