bugGNU Screen - Bugs: bug #63634, GNU Screen should use wcwdith() in...

 
 

bug #63634: GNU Screen should use wcwdith() in utf8_isdouble() instead of hard-coded tables

Submitter:  Vincent Lefèvre <vinc17>
Submitted:  Mon 09 Jan 2023 11:17:13 AM UTC
   
 
Category:  Feature Request Severity:  3 - Normal
Priority:  * 5 - Normal Status:  Ready For Test
Privacy:  Public Assigned to:  None
Open/Closed:  Open Release:  None
Fixed Release:  None Planned Release:  5.0.0
Work Required:  None
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Mon 07 Aug 2023 08:37:23 AM UTC, comment #3: 

Here's the encoding.diff patch for master. It solves the issue I reported yesterday.

(file #55015)

Vincent Lefèvre <vinc17>
Sun 06 Aug 2023 10:43:27 AM UTC, comment #2: 

Yes, this was for screen-v4.

Concerning master, I cannot reproduce the display issue with my testcase using Mutt, perhaps because the way the display is managed is different in master. But I eventually managed to trigger a display issue in another way: run "screen zsh -f", then enter the wide character several times and go on after the end of the line is reached (since the character isn't available on my keyboard, I do this by pasting it, but this shouldn't matter). When the character is recognized as wide, e.g. U+26FA TENT, everything works fine (possibly except a white rectangle on the last column, depending on the parity of the number of columns, but this is another issue): the characters appear on the second line as expected. But when the character is not recognized as wide, e.g. U+1FAF6 HEART HANDS (the one I used in my testcase with Mutt), the first character after the end of line is reached is displayed on the second line, but the next ones are displayed on the first line again (erasing the prompt at the same time). I'm going to look at the patch and check that this makes this display bug disappear.

Vincent Lefèvre <vinc17>
Thu 03 Aug 2023 10:56:25 AM UTC, comment #1: 

Hi Vincent,
thank you for link to other bug tracking system, but can you attach a patch here (so that everyone can see, review and test it) please?

You're talking about 'screen-v4' branch, right? Can you provide a patch for 'master'?

I like your idea. Just want to be sure that patch doesn't broke anything on other systems.

Alexander Naumov <anaumov>
Group administrator
Mon 09 Jan 2023 11:17:13 AM UTC, original submission:  

In the utf8_isdouble() function of encoding.c, GNU Screen uses hard-coded tables, which become incomplete when Unicode evolves in the C library. This yields major display issues, such as shifted text in Mutt (based on ncurses), with the risk to lose data in this case if one doesn't notice the text shift:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1027733

Instead of hard-coded tables, GNU Screen should use the standard wcwdith() function (as done in Debian to fix the above bug), which will ensure consistency with other software that already uses it (the real terminal and perhaps libraries like ncurses). If you think that hard-coded tables are still useful, they could be enabled via an option, a bit like what cjkwidth currently does (introduced for bug #16666 "Support for UAX#11 East Asian Ambiguous characters"). BTW, I don't know whether the cjkwidth feature should be kept, but it is likely to have issues with curses applications.

Vincent Lefèvre <vinc17>

 

(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

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Attached Files
file #55015:  encoding.diff added by vinc17 (3KiB - text/x-patch)

 

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    Follow 5 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2023-08-10 anaumov StatusConfirmed Ready For Test
        Planned ReleaseNone 5.0.0
    2023-08-07 vinc17 Attached File- Added encoding.diff, #55015
    2023-08-03 anaumov CategoryNone Feature Request
        StatusNone Confirmed

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