'termsync' : cursor rendering issue on zellij with floating window

[pierregoutheraud]

Problem

Hello,

I started using zellij instead of tmux recently and I noticed an annoying bug with zellij, the cursor flickering/incorrectly rendering when using any kind of floating window: there is sometimes 1 frame where the cursor is rendered somewhere else in the terminal or completely gone while the window is being rendered.

I posted a comment on zellij github (zellij-org/zellij#3208 (comment)) and the main contributor/creator is telling me that "This issue is 99% a misimplementation of CSI 2026 (synchronized renders) by ... nvim".

Is this the case?

Screen.Recording.2024-06-20.at.10.18.40.mov

Steps to reproduce

1. zellij
2. nvim --clean -u minimal.lua
3. Then try spamming the f key, you should see the cursor blinking.

I am using nvim 0.10.0 and zellij 0.40.1.
This is reproducible on Kitty 0.35.1, Alacritty 0.13.2 and Wezterm.

minimal.lua:

function open_floating_window()
  -- Get the current buffer handle
  local buf = vim.api.nvim_create_buf(false, true)

  -- Define the window options
  local opts = {
    relative = "editor",
    width = math.floor(vim.o.columns * 0.8),
    height = math.floor(vim.o.lines * 0.8),
    col = math.floor(vim.o.columns * 0.1),
    row = math.floor(vim.o.lines * 0.1),
    anchor = "NW",
    style = "minimal",
  }
  
  -- Create the window
  vim.api.nvim_open_win(buf, true, opts)
end

-- Open the window with "f" key in normal mode
vim.api.nvim_set_keymap(
  "n",
  "f",
  ":lua open_floating_window()<CR>",
  { noremap = true, silent = true }
)

Expected behavior

On zellij, the cursor should not blink and its position should always be at the start of the floating window.

Neovim version (nvim -v)

0.10.0

Vim (not Nvim) behaves the same?

Could not test floating window in vim

Operating system/version

macOS 14.3.1

Terminal name/version

Kitty 0.35.1, Alacritty 0.13.2

$TERM environment variable

xterm-kitty

Installation

homebrew

[justinmk]

"This issue is 99% a misimplementation of CSI 2026 (synchronized renders) by ... nvim".

Does the issue occur if you disable 'termsync'?

For reference:

• Synchronized Output https://gist.github.com/christianparpart/d8a62cc1ab659194337d73e399004036
• 'termsync' implemented in c651fb3

[pierregoutheraud]

@justinmk Yes, the issue still occurs but is less obvious as the cursor only flickers but stays at the same position.
With tmux or without multiplexer it does not blink/flickers.

Screen.Recording.2024-06-20.at.18.24.32.mov

This doesn't sound like a huge deal but it becomes quite annoying when you have a bunch of plugins, opening a bunch of windows as you are typing (For example autocompletion windows etc.).

[gpanders]

I posted a comment on zellij github (zellij-org/zellij#3208 (comment)) and the main contributor/creator is telling me that "This issue is 99% a misimplementation of CSI 2026 (synchronized renders) by ... nvim".

From your linked issue:

Hey, for the record: I looked at the dump and the CSI 2026 appears at the beginning and end properly (this is a dump of the whole terminal state, not just one frame - indeed the CSI 2026 serves as the definition of the frame start and end).

[pierregoutheraud]

@gpanders I was referring to one of his previous comment:

Thanks to everyone for pointing out their reproductions and experiences here, but at this point I don't think this adds anything to the discussion. This issue is 99% a misimplementation of CSI 2026 (synchronized renders) by either noice or nvim (as demonstrated by shutting them down mitigating this issue).

Are you by any chance reproducing this weird behaviour?

[clason]

Well, it would help to have a reproduction without noice. We take standards compliance very seriously.

[gpanders]

@gpanders I was referring to one of his previous comment

Yes, but I was pointing out that later in the same thread the Zellij maintainer seems to have absolved Neovim by pointing out that our implementation is correct.

[pierregoutheraud]

@gpanders I see! Indeed he is not reproducing on this config when cating my ANSI dump.
@clason I posted a minimal.lua file in my first message, this is without any plugins.

[gpanders]

Resolved in Zellij zellij-org/zellij#3208 (comment)