bug#38457: 27.0.50; dabbrev-expand regression due to message change

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Cc: 38457@debbugs.gnu.org
> Date: Thu, 19 Dec 2019 02:12:09 +0200
> 
> >> 0. emacs -Q
> >> 1. M-x   ;; activate the minibuffer
> >> 2. C-x o ;; switch back to *scratch*
> >> 3. Eval in *scratch* buffer:
> >>
> >>    (window-live-p (active-minibuffer-window))
> >>    => t
> >
> > OK, but the minibuffer is still active in this case, and leaving it
> > unobscured is still an advantage, right?
> 
> It never occurred to me that someone might want to see the minibuffer
> unobscured when the minibuffer is not the current buffer.

I think leaving "M-x" (or any other prompt) unobscured in this
situation is a nice benefit, and if it simplifies the code, it's even
more desirable.

> >> +(defun set-minibuffer-message (message)
> >> +  "Temporarily display MESSAGE at the end of the minibuffer.
> >> +The text is displayed for `minibuffer-message-wait' seconds,
> >> +or until the next input event arrives, whichever comes first.
> >
> > This text needs to be updated to refer to minibuffer-message-wait's
> > effect on what it does.
> 
> While thinking again about 'minibuffer-message-wait' I realized that
> maybe we need two customizable variables:
> 
> 1. minibuffer-message-clear-after-input
> 2. minibuffer-message-clear-after-timeout
> 
> because users might prefer customization of these behaviors separately.
> Here are all possible combinations (2 is an example of number of seconds,
> 0 means no timeout):
> 
> after-input=nil after-timeout=0 - never clear the message
> after-input=t   after-timeout=2 - clear either on input or after timeout
> after-input=t   after-timeout=0 - clear only when input is available:
>                                   this has an advantage that user has control 
> when
>                                   wants to clear message immediately on 
> keypress;
> after-input=nil after-timeout=2 - clear only after timeout, not on input:
>                                   this has an advantage that user will never 
> miss
>                                   a message while typing in the minibuffer,
>                                   the message will stay for the specified 
> number
>                                   of seconds regardless of input,
>                                   so user will have a chance to read it
> 
> Do all these variants make sense?

I would never want to use variants 1 and 4, but if someone wants them,
I won't object as long as the default for Emacs 27 is as in the 2nd
variant.

Thanks.