Re: struct face question

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Date: Fri, 16 Sep 2022 13:35:45 +0800
> 
> Is it ever valid for face->fontset to be -1?

Yes, I think so.  It means there's no fontset for this face.  Which is
normal when there's no font.

> The X font backend doesn't
> support scaling fonts, so displaying the separator-line face fails to
> find a font with height 0.1, causing the following part of
> realize_gui_face to be called:
> 
>       else
> 	{
> 	  face->font = NULL;
> 	  face->fontset = -1;
> 	}
> 
> leading to face_for_char aborting from face->fontset being -1 later on.

Please show a full backtrace from the crash, and preferably also a
reproducer.  What character are we trying to display in that case?

If indeed the X font backend doesn't support that, it would perhaps
call for a different definition of the face, but I'd like to
understand the issue better before we decide how to solve it.

Thanks.