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

[Eli Zaretskii]

> From: SUNG TAE KIM <itaemu@gmail.com>
> Date: Fri, 14 Jul 2023 13:45:58 +0900
> 
> So, I think the proper default width value of the ambiguous width characters 
> is narrow and there must
> be options for setting width for those ambiguous width characters, but such 
> change of default value
> might cause breakage in the emacs packages which rely on the CJK language 
> environment. 
> 
> All in all, I think providing comprehensive options to change the width of 
> those ambiguous width
> characters will be desirable. 

Thanks, those are also my conclusions, as described here:

  https://debbugs.gnu.org/cgi/bugreport.cgi?bug=64420#50

By default, Emacs already treats the ellipsis as a Narrow character,
and our current idea of "context" is the value of
language-environment, when the font information is not available.
Since Emacs doesn't currently support language tags or any other
feature which would allow the language to change on a per-buffer or
per-text region basis, the best we can do to allow finer-tuned width
of these characters is some kind of user customization, which assumes
that users know better which fonts are used by Emacs and by terminal
emulators they use for the Emacs TTY frames.