bug#61704: 29.0.60; Crash in get_narrowed_begv

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 22 Feb 2023 13:17:27 +0000
> From: Gregory Heytings <gregory@heytings.org>
> cc: luangruo@yahoo.com, 61704@debbugs.gnu.org
> 
> 
> >> How can len possibly be 0 at that point?  It is (in short) 
> >> window_body_width (w, WINDOW_BODY_IN_CANONICAL_CHARS) * 
> >> window_body_height (w, WINDOW_BODY_IN_CANONICAL_CHARS).  We could add a 
> >> condition in get_narrowed_len to return 1 when the result is 0, but it 
> >> could be a bug somewhere else (can a window body have a zero width 
> >> and/or height?), in which case it would be better to fix the bug there.
> >
> > I agree that we should understand how this happened (and asked a similar 
> > question), but I installed a defensive protection anyway.  It cannot do 
> > any harm.
> >
> 
> Okay.  Let's hope this will not hide another real bug.
> 
> I found a way to get such small windows: set window-min-width, 
> window-min-height, window-safe-min-width and window-safe-min-heigth to 0. 
> Of course doing that ignores the fact that the docstring of the 
> window-safe-min-* variables say that "Anything less might crash Emacs", 
> and that their values are 2 (width) and 1 (height).  Which makes me wonder 
> why these variables can be changed / exist.

Maybe Martin (CC'ed) can answer that.