bug#64420: string-width of … is 2 in CJK environments

[Dmitry Gutov]

On 02/07/2023 16:43, Eli Zaretskii wrote:
> > Since the overlay-based popup is used on both GUI and Terminal frames,
> > are you suggesting I define my own string-width like this?
> >
> > (defun company--string-width (str)
> >     (if (display-graphic-p)
> >         (ceiling (/ (string-pixel-width str)
> >                     (float (default-font-width))))
> >       (string-width str)))
> Yes, definitely.  (Actually, display-multi-font-p is better than
> display-graphic-p, but in practice they will return the same value.)

Regarding this approach, though: it seems to fail in my terminal Emacs.

Meaning, when I'm testing the feature using 'emacs -nw' (inside e.g. 
gnome-terminal), both (string-pixel-width "…") and (string-width "…") 
return 2. Whereas the character on display looks 1-character wide even 
there.

More than that, moving the cursor close to that character with C-f or 
C-b creates odd effects like the cursor jumping one position to the 
left, or a char being rendered twice at a certain position on the same 
line to the right of it (after I move the cursor there past the … char), 
in my case it's an opening paren. Nothing like that happens on the lines 
without this char, or after I switch the language env back to "English".

That happens in Emacs 29.