bug#59141: 28.1.90; Face :extend when all the line but trailing \n is invisible

[Eli Zaretskii <eliz@gnu.org>]

> From: Abdul-Lateef Haji-Ali <abdo.haji.ali@gmail.com>
> Cc: yantar92@posteo.net, 59141@debbugs.gnu.org, kevin.legouguec@gmail.com,
>  juri@linkov.net
> Date: Fri, 11 Nov 2022 20:17:26 +0000
> 
> >> The suggested solution is have an outline entry include the new line character (so that the whole extended lines is hidden). The displayed text after the invisible text would then be "...\n".
> > ,----
> > | * A* B
> > `----
> >
> > because the newline will be hidden
> 
> At the moment, if the new line is included in the entry then the output would be
> ,----
> | * A...* B
> `----
> 
> However, if the displayed text after the invisible text is changed to "...\n" instead of "..." (through `display` or better yet through a change to invisibility-specs as I suggested) then the output is correct.

You are basically suggesting to hide the entire buffer text and
instead display something else via display properties.  That's not
what outline modes do.

The solution to this problem is simple: don't use the :extend
attribute for these faces.  That's all.  This attribute is not
intended for what you want to achieve here.  A whole bunch of problems
automatically gets resolved if you don't use :extend.