Re: Confused by y-or-n-p

[Juri Linkov]

>> > Could you please make such a change?
>>
>> Martin suggested to add the "use the old implementation" option
>> to Emacs 27.2.  Is it OK with you?
>
> Yes, thanks.

Here is the first version of the patch for master.  If generally it's OK,
then it could be backported to Emacs 27.2:

diff --git a/lisp/dired-aux.el b/lisp/dired-aux.el
index 0f68b47073..f83824a272 100644
--- a/lisp/dired-aux.el
+++ b/lisp/dired-aux.el
@@ -145,7 +145,7 @@ dired--no-subst-explain
 (defun dired--no-subst-ask (char nb-occur details)
   (let ((hilit-char (propertize (string char) 'face 'warning))
         (choices `(?y ?n ?? ,@(when details '(?^)))))
-    (read-char-from-minibuffer
+    (read-char-choice
      (format-message
       (ngettext
        "%d occurrence of `%s' will not be substituted.  Proceed? (%s) "
@@ -1380,7 +1380,7 @@ dired-query
                             (format " [Type yn!q or %s] "
                                     (key-description (vector help-char)))
                           " [Type y, n, q or !] ")))
-          (set sym (setq char (read-char-from-minibuffer prompt char-choices)))
+          (set sym (setq char (read-char-choice prompt char-choices)))
           (if (memq char '(?y ?\s ?!)) t)))))
 
 
diff --git a/lisp/files.el b/lisp/files.el
index 70d451cccf..637aaa130a 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -2141,7 +2141,7 @@ files--ask-user-about-large-file
                                       ("Yes" . ?y)
                                       ("No" . ?n)
                                       ("Open literally" . ?l)))
-                (read-char-from-minibuffer
+                (read-char-choice
                  (concat prompt " (y)es or (n)o or (l)iterally ")
                  '(?y ?Y ?n ?N ?l ?L)))))
         (cond ((memq choice '(?y ?Y)) nil)
@@ -3538,7 +3538,7 @@ hack-local-variables-confirm
                                 ", or C-v/M-v to scroll")))
               char)
          (if offer-save (push ?! exit-chars))
-         (setq char (read-char-from-minibuffer prompt exit-chars))
+         (setq char (read-char-choice prompt exit-chars))
          (when (and offer-save (= char ?!) unsafe-vars)
            (customize-push-and-save 'safe-local-variable-values unsafe-vars))
          (prog1 (memq char '(?! ?\s ?y))
diff --git a/lisp/subr.el b/lisp/subr.el
index 384dbb25cf..592c633a35 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -2626,6 +2626,10 @@ read-number
            t)))
     n))
 
+(defvar read-char-choice-use-read-key nil
+  "Prefer `read-key' when reading a character by `read-char-choice'.
+Otherwise, use the minibuffer.")
+
 (defun read-char-choice (prompt chars &optional inhibit-keyboard-quit)
   "Read and return one of CHARS, prompting for PROMPT.
 Any input that is not one of CHARS is ignored.
@@ -2636,6 +2640,8 @@ read-char-choice
 If you bind the variable `help-form' to a non-nil value
 while calling this function, then pressing `help-char'
 causes it to evaluate `help-form' and display the result."
+  (if (not read-char-choice-use-read-key)
+      (read-char-from-minibuffer prompt chars)
   (unless (consp chars)
     (error "Called `read-char-choice' without valid char choices"))
   (let (char done show-help (helpbuf " *Char Help*"))
@@ -2673,7 +2679,7 @@ read-char-choice
              (keyboard-quit))))))))
     ;; Display the question with the answer.  But without cursor-in-echo-area.
     (message "%s%s" prompt (char-to-string char))
-    char))
+    char)))
 
 (defun sit-for (seconds &optional nodisp obsolete)
   "Redisplay, then wait for SECONDS seconds.  Stop when input is available.
@@ -2920,6 +2926,10 @@ y-or-n-p-insert-other
     (minibuffer-message "Please answer y or n")
     (sit-for 2)))
 
+(defvar y-or-n-p-use-read-key nil
+  "Prefer `read-key' when answering a \"y or n\" question by `y-or-n-p'.
+Otherwise, use the minibuffer.")
+
 (defvar empty-history)
 
 (defun y-or-n-p (prompt)
@@ -2980,6 +2990,41 @@ y-or-n-p
           use-dialog-box)
       (setq prompt (funcall padded prompt t)
            answer (x-popup-dialog t `(,prompt ("Yes" . act) ("No" . skip)))))
+     (y-or-n-p-use-read-key
+      ;; ¡Beware! when I tried to edebug this code, Emacs got into a weird 
state
+      ;; where all the keys were unbound (i.e. it somehow got triggered
+      ;; within read-key, apparently).  I had to kill it.
+      (setq prompt (funcall padded prompt))
+      (while
+          (let* ((scroll-actions '(recenter scroll-up scroll-down
+                                            scroll-other-window 
scroll-other-window-down))
+                 (key
+                  (let ((cursor-in-echo-area t))
+                    (when minibuffer-auto-raise
+                      (raise-frame (window-frame (minibuffer-window))))
+                    (read-key (propertize (if (memq answer scroll-actions)
+                                              prompt
+                                            (concat "Please answer y or n.  "
+                                                    prompt))
+                                          'face 'minibuffer-prompt)))))
+            (setq answer (lookup-key query-replace-map (vector key) t))
+            (cond
+             ((memq answer '(skip act)) nil)
+             ((eq answer 'recenter)
+              (recenter) t)
+             ((eq answer 'scroll-up)
+              (ignore-errors (scroll-up-command)) t)
+             ((eq answer 'scroll-down)
+              (ignore-errors (scroll-down-command)) t)
+             ((eq answer 'scroll-other-window)
+              (ignore-errors (scroll-other-window)) t)
+             ((eq answer 'scroll-other-window-down)
+              (ignore-errors (scroll-other-window-down)) t)
+             ((or (memq answer '(exit-prefix quit)) (eq key ?\e))
+              (signal 'quit nil) t)
+             (t t)))
+        (ding)
+        (discard-input)))
      (t
       (setq prompt (funcall padded prompt))
       (let* ((empty-history '())
diff --git a/lisp/userlock.el b/lisp/userlock.el
index ec76322337..249f40e9af 100644
--- a/lisp/userlock.el
+++ b/lisp/userlock.el
@@ -159,7 +159,7 @@ ask-user-about-supersession-threat
        (message "%s" prompt)
        (error "Cannot resolve conflict in batch mode"))
       (while (null answer)
-       (setq answer (read-char-from-minibuffer prompt choices))
+       (setq answer (read-char-choice prompt choices))
        (cond ((memq answer '(?? ?\C-h))
               (ask-user-about-supersession-help)
               (setq answer nil))
diff --git a/lisp/wid-edit.el b/lisp/wid-edit.el
index 8250316bcc..bb5d26d29e 100644
--- a/lisp/wid-edit.el
+++ b/lisp/wid-edit.el
@@ -338,7 +338,7 @@ widget-choose
                                  '(display-buffer-in-direction
                                    (direction . bottom)
                                    (window-height . fit-window-to-buffer)))
-               (setq value (read-char-from-minibuffer
+               (setq value (read-char-choice
                             (format "%s: " title)
                             (mapcar #'car alist)))))
           (cdr (assoc value alist))))))