Force nvim to use 16 colors

[nylen]

I'd like to force nvim to use only the basic 16 ANSI colors, regardless of what it detects in the TERM or COLORTERM environment variables or wherever else it is looking. The reason is that I plan to use the same config on multiple machines, including various combinations of tmux, SSH, etc, and I will configure the actual color values in my terminal emulator.

The following code is the only place t_colors is set that I can see, and I can't find a way to override it:

neovim/src/nvim/tui/tui.c

Lines 292 to 293 in 96059d7

	// Set 't_Co' from the result of unibilium & fix_terminfo.
	t_colors = unibi_get_num(data->ut, unibi_max_colors);

In vim you can do this using: set t_Co=16

But in nvim this seems to have no effect (or crashes, see below).

I've also tried TERM= COLORTERM= nvim which doesn't change anything, nvim is still using 256 colors.

I can actually get a segfault by playing with this also, here are the steps:

1. Launch nvim
2. Run :set t_Co=16
3. Press Ctrl+Z to suspend
4. Type fg to resume
5. Observe Segmentation fault (without Step 2 this does not happen).

[nylen]

Some missing info above, though I don't think it'll be super relevant here:

• nvim --version: NVIM v0.4.3 - Build type: RelWithDebInfo
• vim -u DEFAULTS (version: 7.x, 8.0) behaves differently? - yes, vim allows setting &t_Co at runtime
• Operating system/version: Linux 5.3.0 x86_64 (Debian-based)
• Terminal name/version: xfce4-terminal v0.8.3
• $TERM: the default value on my system is xterm-256color but multiple values attempted, see first post

[justinmk]

The reason is that I plan to use the same config on multiple machines, including various combinations of tmux, SSH, etc,

t_Co=16 isn't needed for that. You can force your N/Vim colorscheme to use ANSI color indexes:

:highlight Comment ctermfg=Red

Then changing ANSI "red" to some other color in your terminal, will color comments as such. Note that this requires :set notermguicolors.

The t_xx inner-platform is not supported. :help t_xx

5. Observe Segmentation fault (without Step 2 this does not happen).

Is set t_Co=16 required to repro that? If that happens with the development version please open a new report including a backtrace.

[nylen]

Thanks for the info. You tagged this issue as a duplicate, but I wasn't able to find anything that is really the same ("force downscaling to 16 colors") on a quick search.

I do see #5538 and #11883 which also discuss t_Co but not quite in the same way.

I will test this further and report back, including setting a 16-color scheme such as https://github.com/noahfrederick/vim-noctu or https://github.com/jeffkreeftmeijer/vim-dim, and trying to reproduce the segfault in the latest development version.

[emivespa]

@nylen you can emulate t_Co with ffi: :lua f=require"ffi" f.cdef"int t_colors" f.C.t_colors=16, credit to @ seandewar from #neovim:matrix.org