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 10:12:57 +0000
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> Are you sure? I am looking at `extend_face_to_end_of_line' and it looks
> >> like there is nothing preventing it from accessing it->glyph_row->glyphs
> >> array to look backwards into preceding glyphs.
> >
> > First, glyphs have only partial information about the original face
> > properties.  IOW, the produced glyph row doesn't have all the info
> > that the original text had.
> >
> > And second, I don't see how the accessibility to the glyphs is
> > relevant to the issue at hand.  Suppose the visible text of a line is:
> >
> >    aaabbbbxxx
> >
> > where each letter represents some character with different face -- you
> > want Emacs to extend face 'a' after the end of the line, not the face
> > 'x', just because the line started with characters whose face was
> > 'a'?? that's what the OP said, AFAIU.
> 
> I am also not a big fan of using the first glyph/letter in the line.
> 
> 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.