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

[Eli Zaretskii]

> Date: Wed, 11 Dec 2019 11:24:37 +0800
> From: HaiJun Zhang <netjune@outlook.com>
> Cc: 38457@debbugs.gnu.org, juri@linkov.net
> 
> Display combination of the prompt and the message is good but may be complex 
> to implement it.

I explained in more detail how I suggested to implement thius: by
inserting the minibuffer contents before the message text.  What is
complex about that?

> What about display message transiently and then restore to prompt?
> 
> I see the doc string of minibuffer-message-timeout says: 
> 
>  How long to display an echo-area message when the minibuffer is active.
>  If the value is a number, it should be specified in seconds.
>  If the value is not a number, such messages never time out.
> 
> If minibuffer is active, the message will be displayed  for a moment(like 1s) 
> and then disappears.
> If minibuffer is not active, the message will be displayed forever. I think 
> this is simpler and also good for me.
> 
> What is the problem of this behaviour?

This is what the current code does, and the problem with that is that
some uses of 'message' don't expect the message to stay for 2 seconds,
and some expect it to stay forever.  This information is not explicit
in the call to 'message', so there's no way of communicating in down
to minibuffer-message.