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

[Eli Zaretskii]

merge 
> From: Kévin Le Gouguec <kevin.legouguec@gmail.com>
> Cc: StrawberryTea <look@strawberrytea.xyz>,  65896@debbugs.gnu.org
> Date: Tue, 12 Sep 2023 22:51:53 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > tags 65896 wishlist
> > thanks
> 
> This seems related to bug#52587, maybe so much so that it might make
> sense to merge them?

Probably, but I'll leave this to debbugs gurus, as the two bugs have
different attributes.

> AFAIU those are two aspects of the same problem people have with
> outlines: the effective :extended background comes from the last line of
> the folded content (because that's the newline that is actually
> displayed) whereas one might expect it to come from the header line (but
> it can't, because the header line's newline is invisible).

More accurately, if the last character displayed on a line has a face
with :extend attribute non-nil, that face is extended to the edge of
the window.