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

[Dmitry Gutov]

On 13/08/2023 15:01, Eli Zaretskii wrote:
> > Date: Sun, 13 Aug 2023 13:48:42 +0300
> > Cc: casouri@gmail.com, itaemu@gmail.com, 64420@debbugs.gnu.org
> > From: Dmitry Gutov <dmitry@gutov.dev>
> >
> > > > So the point here would be that some "ambiguous" ones are still wider
> > > > than 1, I guess.
> > > According to Yuan, at least in his environment those characters have a
> > > width that is closer to 2 than to 1.  In which case using 2 would
> > > produce better alignment.  Of course, using string-pixel-width will
> > > produce an even better alignment.
> >
> > In GUI, that is. But if they are displayed with width 1 in terminal, we
> > better make string-width return 1 for them too.
>
> Yes.  But it turns out that how wide these characters are on TTY
> frames depends on the terminal emulator and its own options regarding
> those characters.  So some users will want the value 1 and others will
> want the value 2, depending on which terminals they use and what
> options of those terminals they like best.

That's where having the option that we just added will be beneficial. As 
opposed to, say, changing the behavior outright.

> The important part is that the Emacs's notion of the character width
> is consistent with that of the terminal.
>
> > That might be slightly worse for certain applications (like popup in
> > company), but at least the basic rendering and navigation bugs in
> > terminal will be fixed this way. And the new popup rendering for company
> > (using string-width and spacing instructions) is close to being ready
> > anyway.
>
> Yes, sure.  There's no doubt on my side that this option is useful;
> I'm just trying to collect data that would allow us to decide on the
> best default value, that's all.

Yuan seems to be saying that iTerm2, at least, defaults to showing the 
ambiguous chars at width 1 and issues a warning when the user tries to 
change that option.

gnome-terminal also has that default. I just checked on my machine 
(Ubuntu from 2022), and the description in this bug report from 2015 
also says that: https://bugzilla.gnome.org/show_bug.cgi?id=749414, so 
the default is not new.

Others are welcome to report their experience.

I've found a couple of conflicting reports regarding Microsoft Terminal, 
someone could test that too.