bug#39564: 28.0.50; read-key function do not display the prompt if called from read-from-minibuffer

[Eli Zaretskii]

> From: Oleh Krehel <ohwoeowho@gmail.com>
> Date: Tue, 11 Feb 2020 17:17:02 +0100
> 
> Here's an updated code that works as intended on 26.3 and unexpected on 28.
> 
> (defun make-lines (n)
>   (mapconcat #'number-to-string
>              (number-sequence 0 n) "\n"))
> 
> (let ((map (make-sparse-keymap)))
>   (define-key map (kbd "C-f") (lambda ()
>                                 (interactive)
>                                 (let ((inhibit-field-text-motion t))
>                                   (goto-char (point-min)))
>                                 (message "%S"
>                                          (read-key
>                                           (concat
>                                            (make-lines 10)
>                                            "\nTest2")))
>                                 (minibuffer-keyboard-quit)))
>   (read-from-minibuffer (concat (make-lines 10) "\nTest1: ") nil map))
> 
> The idea here is that the read-key hint will occupy as much space as
> the initial read-from-minibuffer.

Thanks, but I still don't understand what should one do with this
snippet (after evaluating it) to see the problem.  Please tell more.