Cursor blinking within tmux stops after upgrade kitty to 0.22

[laggardkernel]

Describe the bug

Formerly, the cursor blinks normally within tmux. After upgrading kitty to 0.22.x. It doesn't blink within tmux anymore.

Envi

To Reproduce

Environments

• kitty with default config
• tmux 3.2a with following minimal config
• OS: macOS 10.14.6

# minimal tmux conf: test.conf
set-option -gs default-terminal "tmux-256color"
set-option -ga terminal-overrides ',*:Ss=\E[%p1%d q:Se=\E[5 q'

Steps to reproduce the behavior:

1. Open kitty with default config.
2. Start tmux with tmux -f ./test.conf -S ./test.socket

Then the cursor stops blinking. Downgrading kitty back to 0.21. The problem disappears.

[kovidgoyal]

This is a bug in tmux that was masked by a bug in kitty. The bug in
kitty was fixed in 0.22.0 (see #3808)

Run

kitty --dump-commands tmux

In the list of commands tmux sends kitty you will see
screen_reset_mode 12 1

This is the escape code

CSI ? 12 l

which is supposed to stop the cursor blinking, as described
here: https://invisible-island.net/xterm/ctlseqs/ctlseqs.html
(search the page for Ps = 1 2)

I dont use tmux so I cant comment on why it is doing this or how to get
it to stop doing it.

[laggardkernel]

@kovidgoyal Thanks for your reply. The clue you gave me did help.

To be frank, I know nothing about the source code of tmux. But searching 12l gives no result in the source code. One of the possible reason is that tmux is firing cnorm.

❯ infocmp xterm-kitty | grep '12l'
        clear=\E[H\E[2J, cnorm=\E[?12l\E[?25h, cr=^M,

I tried to override cnorm within tmux and my cursor blinks now.

# tmux.conf
# change \E[?12l to \E[?12h
set-option -ga terminal-overrides ',xterm-kitty:cnorm=\E[?12h\E[?25h'

Ref

Clues lead me to the current solution

• Cursor blinking discrepancy on Linux mentions cnorm and related change
• Fix so tmux correctly sends the cvvis (cursor very visible) capability, possible code why tmux send cnorm
• Change cursor shape by modifying cnorm in terminfo