bug#53398: 29.0.50; narrow-to-region induces buffer recentering

[Eli Zaretskii <eliz@gnu.org>]

> From: Jose A Ortega Ruiz <jao@gnu.org>
> Cc: 53398@debbugs.gnu.org
> Date: Sun, 23 Jan 2022 15:42:51 +0000
> 
> just for my own understanding: are you saying that the fact that the
> minibuffer displays more than one line causes a re-centering of my
> current buffer? why is that normal? if i M-: (message "a\nb\n"), should
> i expect that my current buffer is recentered?  (it isn't).

If point is in the last N lines that would be "covered" by the
enlarged mini-window, then Emacs will recenter to keep point visible.

> (also, for the record, the message displayed by that custom set-message
> does not span more than one line, as far as i can tell.)

It does, see the continuation indicator at the right fringe.  You have
computed the alignment to span the entire screen line, but Emacs needs
one more place there to display the cursor.