bug#44070: 28.0.50; Minibuffer display "jumps" upon minor edit

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: 44070@debbugs.gnu.org
> Date: Thu, 29 Oct 2020 13:54:01 -0400
> 
> > If we want the minibuffer behave as if scroll-conservatively was set,
> > why not simply set scroll-conservatively in each minibuffer?
> 
> That was my initial thought as well, but when I tried to implement it,
> it quickly turned into a scavenge hunt trying to find all the places
> where it needs to be set (and re-set after a kill-all-local-variables).

That's strange: don't we have a single place where we create the
minibuffer?

> How 'bout the patch below, then?

LGTM, modulo the NEWS and ELisp manual updates.

> +  DEFVAR_BOOL ("minibuffer-scroll-conservatively",
> +               minibuffer_scroll_conservatively,
> +               doc: /* Non-nil means scroll conservatively in minibuffer windows.
> +When the value is nil, scrolling in minibuffer windows obeys the
> +settings of `scroll-conservatively'.  */);

I'd say "behaves as if scroll-conservatively were set" instead of
"obeys the setting of scroll-conservatively", because the latter can
be interpreted as meaning one actually needs to set
scroll-conservatively.

> +  minibuffer_scroll_conservatively = true; /* bug#44070 */

It is IMO generally not useful to have such comments, since the Git
history will tell us that much (and then some), provided you don't
forget to mention the bug number in the log message.

Thanks.