Re: Change of behavior of "space" display property and face property

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Cc: "emacs-devel@gnu.org" <emacs-devel@gnu.org>
> Date: Tue, 04 Oct 2022 14:34:28 +0800
> 
> Qiantan Hong <qthong@stanford.edu> writes:
> 
> > Open an empty text file, M-: (insert #(" " 0 1 (face (:underline t) display 
> > (space :align-to right))))
> >
> > On Emacs 28, this produce a blank line with underline.
> >
> > On Emacs 29, this produce a blank line without underline. In general, 
> > “space” display 
> > seem to disregard any face property.
> >
> > Is this intended or is this a bug? “space” display respecting face property 
> > is useful for
> > typesetting. For example. I use it to display a horizontal separator under 
> > my header line.
> >
> > Best,
> > Qiantan
> 
> That is almost certainly a bug, but I cannot be certain without knowing
> what toolkit and window system you built Emacs with.

I cannot reproduce this here, on MS-Windows.  The recipe produces the
same display for me in both Emacs 28 and Emacs 29.  So if this is
reproducible on some system, it is most probably a bug in the
terminal-specific display backend.