bug#38384: (next|previous)-buffer silent about not switching

[Eli Zaretskii]

> From: Juanma Barranquero <lekktu@gmail.com>
> Date: Tue, 26 Nov 2019 16:54:56 +0100
> Cc: 38384@debbugs.gnu.org
> 
> > Could that disrupt noninteractive calls?
> 
> Yes, that's why added the notice in NEWS in the "Incompatible Lisp Changes".

Then how about signaling user-error only in interactive calls?

> But, on one hand, programs should perhaps be using 
> switch-to-(prev|next)-buffer. AFAICS, next-buffer and
> previous-buffer aren't even documented in the Elisp manual (they are briefly 
> mentioned in the Emacs
> manual).
> 
>  And on the other, if code is using (next|prev)-buffer, silently getting the 
> same buffer is likely a subtle bug
> anyway. At least now they get notice.

IMO, if we can improve the diagnostics only in interactive
invocations, we have all the advantages without any disadvantages (and
can move this out of the "incompatible changes" section).