bug#33490: 27.0.50; auto-save-visited-mode clears the echo area every time the save interval is hit

[Eli Zaretskii <eliz@gnu.org>]

> From: Terje Larsen <terje.larsen@klarna.com>
> Date: Sat, 24 Nov 2018 12:56:19 +0100
> 
> M-x auto-save-visited-mode
> M-: (message "%s" "hello")
> 
> ... Wait 5 seconds ...
> 
> Now the message buffer gets cleared and you lose the message. This is
> causing usability issues when using eldoc/reading some output message as
> it continously gets cleared.
> 
> I would expect the `auto-save-visited' feature to not change the behaviour
> of the Echo Area. If you compare this to the `auto-save-mode' which
> outputs a message indicating a save, but restores the Echo Area after.
> 
> I have tracked down this to the `save-some-buffers' function or more
> specifically the `map-y-or-n-p' function that it calls. In this function
> there is a call to message like `(message "")`.

Right.  Does the patch below fix the problem?

diff --git a/lisp/emacs-lisp/map-ynp.el b/lisp/emacs-lisp/map-ynp.el
index 8260af5..93235bd 100644
--- a/lisp/emacs-lisp/map-ynp.el
+++ b/lisp/emacs-lisp/map-ynp.el
@@ -79,6 +79,7 @@ map-y-or-n-p
 
 Returns the number of actions taken."
   (let* ((actions 0)
+         (msg (current-message))
 	 user-keys mouse-event map prompt char elt def
 	 ;; Non-nil means we should use mouse menus to ask.
 	 use-menus
@@ -250,9 +251,10 @@ map-y-or-n-p
       (if delayed-switch-frame
 	  (setq unread-command-events
 		(cons delayed-switch-frame unread-command-events))))
-    ;; Clear the last prompt from the minibuffer.
+    ;; Clear the last prompt from the minibuffer, and restore the
+    ;; previous echo-area message, if any.
     (let ((message-log-max nil))
-      (message ""))
+      (message (or msg "")))
     ;; Return the number of actions that were taken.
     actions))