bug#24157: 25.1.50; (princ "..." t) does not go to stderr in batch mode

[Eli Zaretskii]

> From: Clément Pit--Claudel <clement.pit@gmail.com>
> Date: Fri, 5 Aug 2016 03:11:59 -0400
> 
> This means that the only way to write to stderr without a newline is (let 
> ((cursor-in-echo-area t)) (message ...)), right? This is not ideal.

No, you also have external-debugging-output (as pointed out by
Andreas) and append-to-file.

> Also, I still think that this is an issue:
> 
>   $ emacs --batch --eval '(progn (princ "to stdout!") (message "to 
> stderr."))' > /dev/null
> 
>   to stderr.
>   $ emacs --batch --eval '(progn (message "to stderr.") (princ "to 
> stdout!"))' > /dev/null
>   to stderr.
>   $ emacs --batch --eval '(progn (princ "to stdout!") (message "to 
> stderr."))' 2> /dev/null
>   to stdout!
> 
> If I read what you sent correctly, the first two rpograms should produce the 
> same output, and the call to princ shouldn't cause 'message' to insert a 
> newline before "to stderr.", right?

No, what you see is deliberate behavior, intended to avoid mixing
output to stdout and stderr, when they are connected to the same
device.  You have redirected stdout, so the result looks surprising,
but that behavior is explicitly coded in Emacs (grep the C sources for
noninteractive_need_newline).