Question: binding and forwarding modifier combos with alacritty

[shiro]

Hello,
I'm a long time tmux user and recently wanted to finally figure out how to make some modifier combos work through tmux (with alacritty as my terminal emulator).

My initial goal was the following 2 things:

• bind C-Tab and C-S-Tab to some tmux functions
• passthrough C-S-P so it works the same as outside of tmux

Both of the above didn't work out of the box, but thanks to this article, I managed to add the following into alacritty config:

key_bindings:
  - { key: Tab, mods: Control, chars: "\x1b[27;5;9~" }
  - { key: Tab, mods: Control|Shift, chars: "\x1b[27;6;9~" }
  - { key: P, mods: Control|Shift, chars: "\x1b[80;5u" }

What works

With the above, the following things started working:

• neovim outside of tmux can now bind to C-S-P (which it picked up as C-P before)
• tmux can bind to C-Tab and C-S-Tab, i.e.

bind-key -n C-Tab next-window
bind-key -n C-S-Tab previous-window

now works!

Things that don't work

• neovim inside of tmux can't bind to C-S-P as its recognized as C-P
• if I remove the previous tmux bindings, I would assume that C-Tab and C-S-Tab get passed through, which does not work at all, the input seems to get consumed

Other things I tried

I looked at the Modifier Keys wiki page, enabled some tmux options, i.e.:

set -as terminal-features "xterm-256color*:RGB:extkeys"
set -s extended-keys on

and read through the kitty protocol alacritty issue.

The face that neovim outside of tmux picks up C-S-P and tmux itself can't recognize it, means the two are handling CSI sequences differently in some way... would be great if it worked in tmux as well.

Also I don't understand why tmux can bind to C-Tab but fails to forward it if not bound.

I apologize if this has been answered somewhere, I really appreciate any help since I don't know how to make it work myself 🙇

[nicm]

tmux version? tmux logs (please press the keys and tell me what you did so I can match it to the log)?

[nicm]

No, you need to get logs like it says here https://github.com/tmux/tmux/blob/master/.github/CONTRIBUTING.md#how-do-i-get-logs-from-tmux so we can see what is going on. I'm not sure if all these keys are supported by extended keys since tmux only supports mode 1 and not mode 2.

If you only have a few keys it might be quicker to get them working by using user-keys, so something like:

set -g user-keys[100] "\e[whatever"
bind -n User100 send "\e[whatever"

[shiro]

Thanks for the pointer, here's the client and server logs with a config that only enables extended keys and does nothing else.

After that I also tried the User100 config, it doesn't seem to recognize C-S-P.

I also didn't know about the send function, that one actually allows me to forward C-Tab and C-S-Tab (manually) since they are being picked up, just not being forwarded automatically. sending \e[80;5u (C-S-P) with a binding to another key also works.

[nicm]

tmux does not support C-P, it is treated the same as C-P. It also won't work with user-keys because at the moment they are checked after extended-keys. I don't think there is a way to get this to work until we have support for the keys directly.

[shiro]

Thank you for the reply, I really appreciate it!
Is there an open issue for this that I can track, or should I open a new one?

[nicm]

Probably #2705

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