bug#64440: 30.0.50; [PATCH] Highlight on non toolkit menu bar items

[Eli Zaretskii <eliz@gnu.org>]

> From: Manuel Giraud <manuel@ledu-giraud.fr>
> Cc: luangruo@yahoo.com,  stefankangas@gmail.com,  64440@debbugs.gnu.org
> Date: Mon, 11 Sep 2023 16:59:11 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> [...]
> 
> >> Is that what you are looking for?
> >
> > This gives some of the answers, but the command 'pgrow' (defined on
> > src/.gdbinit) would have done that better, and would also show the
> > glyphs themselves.  Can you show what 'pgrow' produces in this case?
> 
> Here is what I get:
> 
> (gdb) pgrow
> TEXT: 120 glyphs
>   0    0: CHAR[F] str=0x66f834da[0] blev=0,btyp=L w=7 a+d=11+2 face=10
>   1    7: CHAR[i] str=0x66f834da[1] blev=0,btyp=L w=7 a+d=11+2 face=10
>   2   14: CHAR[l] str=0x66f834da[2] blev=0,btyp=L w=7 a+d=11+2 face=10
>   3   21: CHAR[e] str=0x66f834da[3] blev=0,btyp=L w=7 a+d=11+2 face=10
>   4   28: CHAR[ ] str=0x66f834da[-1] blev=0,btyp=B w=7 a+d=11+2 face=10
>   5   35: CHAR[E] str=0x66fede1c[0] blev=0,btyp=L w=7 a+d=11+2 face=10
>   6   42: CHAR[d] str=0x66fede1c[1] blev=0,btyp=L w=7 a+d=11+2 face=10
>   7   49: CHAR[i] str=0x66fede1c[2] blev=0,btyp=L w=7 a+d=11+2 face=10
>   8   56: CHAR[t] str=0x66fede1c[3] blev=0,btyp=L w=7 a+d=11+2 face=10
>   9   63: CHAR[ ] str=0x66fede1c[-1] blev=0,btyp=B w=7 a+d=11+2 face=10

Thanks.  That's what I imagined we have there.  So I guess considering
that a string ends where is SCHARS end is reasonable.

But note that the above means you could also detect where each item
ends by looking for the glyph whose string position is -1.  So maybe
add an assertion there that the glyph after the last character has its
position as -1, in case we could have some complications there with
double-width characters or something.