GNU bug report logs - #76852
30.1; Regression in whitespace-mode causes display issue under terminal

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Package: emacs; Reported by: 张海 <dreaming.in.code.zh@HIDDEN>; Done: Eli Zaretskii <eliz@HIDDEN>; Maintainer for emacs is bug-gnu-emacs@HIDDEN.

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Date: Sat, 29 Mar 2025 14:19:54 +0300
Message-Id: <86zfh46q3p.fsf@HIDDEN>
From: Eli Zaretskii <eliz@HIDDEN>
To: dreaming.in.code.zh@HIDDEN
In-Reply-To: <86y0x6wm94.fsf@HIDDEN> (message from Eli Zaretskii on Sat, 15
 Mar 2025 13:45:27 +0200)
Subject: Re: bug#76852: 30.1;
 Regression in whitespace-mode causes display issue under terminal
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> Cc: 76852 <at> debbugs.gnu.org
> Date: Sat, 15 Mar 2025 13:45:27 +0200
> From: Eli Zaretskii <eliz@HIDDEN>
> 
> > Cc: 76852 <at> debbugs.gnu.org
> > Date: Thu, 13 Mar 2025 16:11:35 +0200
> > From: Eli Zaretskii <eliz@HIDDEN>
> > 
> > > From: 张海 <dreaming.in.code.zh@HIDDEN>
> > > Date: Thu, 13 Mar 2025 02:32:33 -0700
> > > Cc: 76852 <at> debbugs.gnu.org
> > > 
> > > > Currently, the two solution I'm pondering are:
> > > >
> > > >   . remove from the list of ambiguous-width characters some of the
> > > >     characters with low Unicode codepoints, including the 2 characters
> > > >     used by whitespace-mode, on the assumption that these characters
> > > >     are unlikely to be full-width in fonts used by Emacs users in CJK
> > > >     locales
> > > 
> > > I wonder how emacs 29.4 dealt with this - did it also have a special
> > > list of characters that it treats as half-width, while the rest are
> > > treated as full-width like what was in the announcement?
> > 
> > Emacs 29 didn't have the notion of ambiguous-width characters.  Each
> > character was either a half-width or a full-width.  And the characters
> > used by whitespace-mode were half-width.
> > 
> > > >   . change the default of cjk-ambiguous-chars-are-wide to nil, on
> > > >     the assumption that most users in CJK locales use fonts where
> > > >     these characters have half-width glyphs
> > > 
> > > I think this might be a good option because both TTY and some popular
> > > terminal emulators like gnome-terminal, gnome-console and foot ship
> > > with the ambiguous CJK characters defaulted to half width.
> > 
> > Yes, but are we sure that users in CJK locales don't customize
> > terminal emulators to default the ambiguous-width characters to
> > full-width?  If many users do that, then Emacs should cater to the
> > majority.
> > 
> > > > Thanks.  Let me think a bit more about what would be the best
> > > > solution.  But could you tell which font you used that has full-width
> > > > glyphs for these characters?  Is it unusual to use that font for
> > > > terminal emulators in CJK locales?
> > > 
> > > The fonts I'm using, and most Chinese Linux users may be using (to my
> > > understanding), are:
> > > - WenQuanYi (WQY) fonts
> > > - Noto (i.e. Source Han, a different branding) fonts
> > > See also https://wiki.archlinux.org/title/Localization/Chinese
> > > 
> > > The WenQuanYi fonts have a much longer history and the middle dot is
> > > always half width in them (checked just now). I'm currently using
> > > WenQuanYi Micro Hei.
> > > 
> > > The Noto/Source Han fonts are relatively new and have an interesting
> > > situation where the Noto Sans CJK SC/TC have the middle dot as full
> > > width but Noto Sans CJK JP/KR have it as half width.
> > > 
> > > Some Microsoft proprietary system-default fonts for Chinese
> > > characters, e.g. SimSun and SimHei, also have the middle dot as full
> > > width, but I guess few Linux users would be using it.
> > > 
> > > I should also mention that some CJK users prepend an English font
> > > before their CJK font for usage in UI/terminal, because English fonts
> > > usually contain better quality glyphs for latin letters than the ones
> > > embedded in CJK fonts - essentially they only use the CJK-only part of
> > > the CJK fonts. So the middle dot will always be half width for them.
> > > 
> > > > I'm wondering why we didn't hear
> > > > by now complaints from CJK users about the effects of
> > > > cjk-ambiguous-chars-are-wide other than on whitespace-mode.  Maybe the
> > > > other ambiguous-width characters are seldom used in practice?  Or
> > > > maybe too little time has passed since Emacs 30 was released?
> > > 
> > > I think it could be both:
> > > 
> > > 1. Emacs 30 is still new-ish, e.g. it landed in Arch Linux stable on
> > > Feb 25, only two weeks ago
> > > 
> > > 2. Not a lot of CJK users set a CJK locale ($LANG) for their terminal
> > > - they usually set it for the DE but not necessarily in
> > > /etc/locale.conf for the entire environment, because that means
> > > localized messages won't appear properly under TTY with its default
> > > font. I did that because I would manually set LANG if I actually have
> > > to use TTY instead of a terminal emulator some day.
> > 
> > Thanks for the info, I will think about this some more.
> 
> I eventually decided to go with the more conservative approach of
> removing the two characters used by whitespace-mode from the list of
> ambiguous-width characters.
> 
> This change is not installed on the emacs-30 branch, so the next Emacs
> release should have this problem fixed.

The above should have said "This change is now installed on the
emacs-30 branch".

No further comments, so I presume the fix is okay, and I'm closing
this bug.

Notification sent to 张海 <dreaming.in.code.zh@HIDDEN>:
bug acknowledged by developer. Full text available.

Reply sent to Eli Zaretskii <eliz@HIDDEN>:
You have taken responsibility. Full text available.