bug#34318: 26.1.90; Strange behavior of two line message with running shell

[martin rudalics]

>> With emacs -Q evaluate
>>
>> (message "2\n3")
>
> How do you evaluate it?  With M-:?  With C-x C-e?  With C-M-x?

Any of them.  No difference.

>> This gets me a two line message
>>
>> "1
>> 2"
>>
>> in the minibuffer.
>
> I don't see that here (with 26.1.91).

Sorry - I messed up the the numbers from two different experiments so
the report makes no sense.  Note: What matters is the _two lines vs
one line_ behavior.  I'll rephrase the report now, hopefully correct
this time:


With emacs -Q evaluate

(message "2\n3")

This gets me a two line message

"2
3"

in the minibuffer window.  Now do M-x: shell and reevaluate the form
above.  This gets me a one line message

"2\n3"

in the minibuffer window.


Reliably reproducible with today's build of Emacs 26.1.91 on GNU/Linux
with the GTK, Lucid and Motif toolkits and on Windows XP.

Two further observations:

Once the shell has been entered, exiting it and killing the *shell*
buffer does not change the behavior.

The *Messages* buffer reliably reflects the behavior.  Below see the
entire buffer with the first 5 lines after evaluating the form before
invoking shell and the final three lines after evaluating the form
after invoking shell.

-----------------------------------------------------------------
For information about GNU Emacs and the GNU system, type C-h C-a.
2
3
"2
3"
2
3
"2\n3"
-----------------------------------------------------------------

martin

PS: The scenario provided by Glenn is much simpler so let's stick to that.