bug#60015: 29.0.60; multi-line messages truncated in non-selected minibuffer

[Juri Linkov <juri@linkov.net>]

>> >> 1. (run-with-timer 5 5 'message "abc\ndef")
>> >> 2. then activate the minibuffer and switch back to the original buffer
>> >> 3. after some time observe that only the first line of the multi-line message
>> >>    is displayed in the minibuffer
>> >
>> > Doesn't happen here (I waited for 2.5 minutes).  Is the recipe
>> > complete and exact?  Does it perhaps matter how do you "switch back to
>> > the original buffer"?  (I used a mouse click.)
>>
>> It's essential to ensure that the height of the minibuffer/echo area
>> initially is not more than 1 line.
>
> That's so by default, so "emacs -Q" should ensure that.  Right?

Evaluating the first line above resizes the minibuffer,
and the timer resizes the minibuffer, so it's difficult
to find a moment when it's exactly 1 line high.
I have no idea how to simplify this test case.

>> > When the problem happens, what do you see in *Messages*?  Anything
>> > other that "abc\ndef"?
>>
>> Only the first line "abc" is displayed in the minibuffer
>> as the minibuffer message.
>
> I asked about the *Messages* buffer, not about the minibuffer.

Sorry.  The *Messages* buffer shows all lines of the multi-line string.