GNU bug report logs - #79296
30.2; format-time-string returns wrongly encoded string in MS Windows Japanese with cp65001 beta config

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#79296: closed (30.2; format-time-string returns wrongly
 encoded string in MS Windows Japanese with cp65001 beta config)
Date: Sat, 30 Aug 2025 09:26:01 +0000

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Your message dated Sat, 30 Aug 2025 12:25:09 +0300
with message-id <863499qhze.fsf <at> gnu.org>
and subject line Re: bug#79296: 30.2; format-time-string returns wrongly encoded string in MS Windows Japanese with cp65001 beta config
has caused the debbugs.gnu.org bug report #79296,
regarding 30.2; format-time-string returns wrongly encoded string in MS Windows Japanese with cp65001 beta config
to be marked as done.

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From: Shingo Tanaka <shingo.fg8 <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 30.2; format-time-string returns wrongly encoded string in MS Windows
 Japanese with cp65001 beta config
Date: Sun, 24 Aug 2025 11:16:05 +0900

MS Windows has a utf-8 configuration with setting "Beta: Use Unicode UTF-8 for
worldwide language support" to on in its language settings.  In Japanese
environment, system coding is cp932 (MS version of Japanese SJIS) without the
setting but becomes cp65001 (utf-8) with the setting on.

Emacs looks like successfully detecting the change because locale-coding-system
gets from cp932 to cp65001 as expected, and working as expected overall.

However, I found a bug that format-time-string returns a day of the week string
encoded wrongly - with cp932 even in locale-coding-system is cp65001.

Conditions:
- Windows 11 Pro 24H2 with Japanese setting and "Beta: Use Unicode UTF-8
  for worldwide language support" on
- Emacs 30.2 (latest, https://ftp.gnu.org/gnu/emacs/windows/emacs-30/)

Here is how to reproduce.
1. Run Emacs with no-init-file
2. Go to *scratch* buffer and evaluate:
   (format-time-string "%y,%d,%m %A" (date-to-time (concat "2025,1,Jan")))
3. You will get below wrongly encoded string:
   "25,01,01 \220\205\227j\223\372"
4. evaluate:
   (decode-coding-string
    (format-time-string "%y,%d,%m %A" (date-to-time (concat "2025,1,Jan")))
    'cp932)
5. You will get below correctly decoded string:
   #("25,01,01 水曜日" 9 12 (charset cp932-2-byte))

This issue doesn't happen when "Beta: Use Unicode UTF-8 for worldwide language
support" off (locale-coding-system is cp932).

If you have any question or need further information, please let me know.

Regards,
Shingo

[Message part 3 (message/rfc822, inline)]

From: Eli Zaretskii <eliz <at> gnu.org>
To: Shingo Tanaka <shingo.fg8 <at> gmail.com>
Cc: 79296-done <at> debbugs.gnu.org, shingo.fg8 <at> gmail.com, corwin <at> bru.st,
 bruno <at> clisp.org, eggert <at> cs.ucla.edu
Subject: Re: bug#79296: 30.2;
 format-time-string returns wrongly encoded string in MS Windows
 Japanese with cp65001 beta config
Date: Sat, 30 Aug 2025 12:25:09 +0300

> Date: Wed, 27 Aug 2025 22:54:30 +0900
> From: Shingo Tanaka <shingo.fg8 <at> gmail.com>
> Cc: Eli Zaretskii <eliz <at> gnu.org>,
> 	corwin <at> bru.st,
> 	shingo.fg8 <at> gmail.com,
> 	eggert <at> cs.ucla.edu,
> 	79296 <at> debbugs.gnu.org
> 
> On Wed, 27 Aug 2025 18:05:42 +0900,
> Bruno Haible wrote:
> > 
> > For producing such binaries with only Free Software (no MSVC compiler,
> > no MSVC header files) one can use MSYS2. For a year or two already
> > it supports two target environments:
> >   - mingw-w64 with MSVCRT,
> >   - mingw-w64 with UCRT.
> > These two development environments are very similar, which means that
> > the Makefile will need very few adapations.
> 
> I've just installed MSYS2 Emacs of UCRT version and run it with no init file. 
> 
> ~> pacman -S mingw-w64-ucrt-x86_64-emacs
> ~> /ucrt64/bin/runemacs --no-init-file
> 
> And confirmed the issue I reported doesn't happen even with
> "Beta: Use Unicode UTF-8 for worldwide language support" on.
> 
> In *scratch* buffer:
> 
> (format-time-string "%y,%d,%m %A" (date-to-time (concat "2025,1,Jan")))
> "25,01,01 水曜日"
> 
> w32-system-coding-system
> cp65001
> 
> w32-multibyte-code-page
> 0
> 
> w32-ansi-code-page
> 65001
> 
> (w32-get-current-locale-id)
> 1041
> 
> (w32-get-locale-info (w32-get-current-locale-id))
> "JPN"
> 
> (w32-get-default-locale-id)
> 1041
> 
> (w32-get-locale-info (w32-get-default-locale-id))
> "JPN"
> 
> (w32-get-console-codepage)
> 65001
> 
> (w32-get-console-output-codepage)
> 65001

Thanks.  I've now added a new section to the Emacs w32 FAQ about these
issues, and I'm therefore closing this bug.

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