bug#33885: 27.0.50; PUA character makes emacs crash

[Eli Zaretskii]

On December 27, 2018 10:54:59 AM GMT+02:00, Werner LEMBERG <wl@gnu.org> wrote:
> 
> Loading the attached file `bug.el' (containing the single PUA
> character U+E6A3) with
> 
>   emacs -Q bug.el
> 
> causes a crash:
> 
>   xdisp.c:28955:
>     Emacs fatal error:
>       assertion failed:
>         it->ascent >= 0 && it->descent >= 0
> 
> I've also attached the output of `bt full'.


Thanks.

Do you have some custom font setup, which is supposed to display this PUA 
character?  Because on my system, there's no font for this codepoint (as I'd 
expect), and therefore Emacs displays it as "glyphless" character, showing a 
box with the character's code in hex, and that avoids the assertion violation.

So please step through x_produce_glyphs when Emacs needs to produce a glyph for 
this character, and tell how you end up with both ascent and descent values 
zero.  It isn't supposed to happen with valid fonts.