nvim detects wrong background in tmux

[Bekaboo]

Problem

nvim uses light background when the terminal has dark background. This only happens in tmux (version 3.4).

Steps to reproduce

1. nvim --clean in a dark terminal
2. Notice that nvim uses light background

Expected behavior

nvim uses dark background.

Neovim version (nvim -v)

NVIM v0.10.0-dev-2503+gda2130934b

Vim (not Nvim) behaves the same?

no, vim does not automatically detects terminal background

Operating system/version

Linux 6.6.9-arch1-1

Terminal name/version

alacritty 0.13.1 (fe2a3c56)

$TERM environment variable

tmux-256color

Installation

AUR

[zeertzjq]

Cannot reproduce

[Bekaboo]

@zeertzjq Thanks for your response. I don't know how to reliably reproduce it on other machines but here's the screen recording on my end:

https://github.com/neovim/neovim/assets/76579810/ae1efa29-dd79-4002-a75f-29d3204eba18

---

I also noticed that

1. This bug only happens when nvim is launched inside a tmux session
2. This bug does not exist in version NVIM v0.10.0-dev-2363+gb76a01055f but exists in NVIM v0.10.0-dev-2503+gda2130934b

So I wonder if it is due to commit eef2aedff?

[przepompownia]

@Bekaboo It's possible that your tmux configuration can be helpful here (or full repro with it).

[Bekaboo]

@przepompownia The problem persists but I cannot seem to reliably reproduce it, sometimes nvim detects the correct background but sometimes not. In addition, my tmux config is lengthy so I am not sure whether it will be helpful, but here is the link: https://github.com/Bekaboo/dot/blob/master/.config/tmux/tmux.conf

I will report here again once I have time to reduce my tmux config and find a way to reliably reproduce the bug.