bug#65896: 30.0.50; folding text with text properties prevents background from extending past the newline

[Eli Zaretskii]

> From: Ihor Radchenko <yantar92@posteo.net>
> Cc: look@strawberrytea.xyz, 65896@debbugs.gnu.org, kevin.legouguec@gmail.com
> Date: Fri, 22 Sep 2023 12:00:14 +0000
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> What about not extending the face unless the last 2 glyphs have eq face
> >> or we have a single glyph in a row?
> >
> > That's a backward-incompatible change, so we cannot do that.
> 
> Then, what about doing this only when :extend attribute is set to number
> 2?

That'd mean quite a few changes (since currently :extend is a boolean
attribute), but okay.

However, what is the detailed description of the behavior under this
proposal?  I mean, which 2 glyphs to consider? the last two shown on
the screen line?  If so, this will cause the same problems when these
two glyphs come from different buffer lines (due to invisibility), no?
IOW, won't that cause the same surprising effects, just in other
situations?