Curly underlines not working in Zellij

[paride]

Basic information

zellij --version: 0.29.1
stty size: 24 80
uname -av: Linux stramonio 5.19.0-9-generic #9-Ubuntu SMP PREEMPT_DYNAMIC Mon Jul 4 13:18:59 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

Further information

Several terminals support "curly underlines" or "undercurls", which are used by editors like Neovim to highlight spelling errors and similar. See https://evantravers.com/articles/2021/02/05/curly-underlines-in-kitty-tmux-neovim/ for a good coverage on the feature.

Terminal support for undercurls can be tested via:

printf '\e[4:3mUnderlined\n

I tested it with gnome-terminal an Tilix, this is the output:

However from within zellij (same terminal, same shell) no underline is produced:

In both cases I have

paride@stramonio:~$ echo $TERM
xterm-256color
paride@stramonio:~$ echo $VTE_VERSION
6800

so I'm not sure of where the undercurl capability is getting lost.

[fralcow]

I took a look at this bug, looks like the '\e[4:3mSomeText\n' does not work indeed, specifically the I '\e[4:3' part, since it's a combination of italic (code 3) and underscore (code 4) ansi parameters, hence /zellij/zellij-server/src/panes/terminal_character.rs throws an error, since it only matches vectors of len 1, and here it receives [4, 3] :
WARN |zellij_server::panes::ter| 2022-09-17 12:54:18.299 [screen ] [zellij-server/src/panes/terminal_character.rs:396]: unhandled csi m code [4, 3]

Interestingly enough, just the underscored text works just fine: printf '\e[4mUnderlined\n' . Vim, however, uses code [4, 3] to format underlined characters.

I can try adding this [4, 3] parameter as one of the match cases to print characters as just underlined, but not sure how hacky of a solution this is. I'll try looking into the curly underscore stuff and see if it can be used.

[sploders101]

I added this in #2018
It looks like the escape sequences use sub-parameters (please excuse my ignorance on jargon; I don't have a lot of experience with terminal emulator code), using : instead of ;, and the match statement appears to handle this using two-dimensional iterators. I added it to the match statement and passed it through to the Display implementation and it seems to work well.

[gam-phon]

@imsnif what is the current progress on this?

[gmr458]

any update on this?

[zicklag]

Looks like there's been some great progress in #2730! 🎉

[steakhutzeee]

Hi, I'm using WSL2 in Windows Terminal and was able to see undercurls in Neovim with tmux by setting:

set -as terminal-overrides ',*:Smulx=\E[4::%p1%dm'
set -as terminal-overrides ',*:Setulc=\E[58::2::%p1%{65536}%/%d::%p1%{256}%/%{255}%&%d::%p1%{255}%&%d%;m'

I see undercurls are enabled in Zellij config but they are not working. What do you suggest?