Add Highlight Groups For Even and Odd Lines

[austinliuigi]

Feature already in Vim?

No

Feature description

Is your feature request about something that is currently impossible or hard to do? Please describe the problem.

I think it's nice for even and odd lines to have different highlights. It lets me quickly see which number in the line-number column any particular line corresponds to, regardless of how much whitespace is in front of it. It's a nice quality of life improvement when using relative numbers.

Currently, chrisbra's "DynamicSigns" plugin implements this functionality by adding signs to each line and giving them a different highlight whether they're even or odd. However, when a file has a relatively large number of lines, this causes an extreme slowdown and becomes almost unusable. Additionally, there are times when the signs to not update automatically.

Describe the solution you'd like

A builtin option of highlighting even and odd lines differently (LineEven and LineOdd hl-groups?). Here is an image using the DynamicSigns plugin:

Additional context

I have no idea about the feasibility of this, but I'm hoping it's a feature that is reasonable to add.

The highlighting doesn't even necessarily need to be tied to the line; as long as adjacent lines have different highlights, it makes it easier to see what line number each line corresponds to.

[clason]

I don't think this needs to be in core; (extmark) signs are much more efficient in Neovim, so a (Lua) plugin still sounds like the right option here. (@lewis6991 ?)

[zeertzjq]

A problem with implementing this as highlight groups is that this behavior is not wanted for every window/buffer, so if these highlight groups are added, one needs to override more highlight groups to change the background colors of a specific window.

[lewis6991]

This appears to work:

local ns = vim.api.nvim_create_namespace('evenoddlines')

vim.api.nvim_set_decoration_provider(ns, {
  on_win = function()
  end,
  on_line = function(_, _, buf, row)
    if row % 2 == 0 then
      vim.api.nvim_buf_set_extmark(buf, ns, row, 0, {
        end_row = row + 1,
        hl_group = 'Visual',
        hl_eol = true,
        ephemeral = true
      })
    end
  end
})

I did try with line_hl_group, however that doesn't appear to work with ephemeral = true.

[notomo]

FYI https://github.com/notomo/zebrazone.nvim

[clason]

Looks like there already is a fine plugin, so I'm closing this as not needed in core.

[austinliuigi]

Thank you!

[neovim-discourse]

This issue has been mentioned on Neovim Discourse. There might be relevant details there:

https://neovim.discourse.group/t/init-lua-highlight-every-even-lines/3963/2

[justinmk]

With :help 'statuscolumn' in Nvim 0.9 there is now a more "native" way to achieve this. See also https://github.com/luukvbaal/statuscol.nvim for even more examples.