nixpkgs/neovim: use global statusline

Also indicate the active window with a different background

.config/nixpkgs/neovim/theme.lua

@@ -3,6 +3,46 @@ vim.o.termguicolors = true
 vim.g.sonokai_transparent_background = true
 vim.g.sonokai_disable_terminal_colors = true
 
+vim.o.laststatus = 3
+
+-- neovim has a NormalNC highlight group that applies to inactive windows but
+-- we want to apply different styles to *active* windows. The Normal highlight
+-- group is special and setting a background there applies to everything and
+-- cannot be "unset" from other groups like NormalNC.
+--
+-- What we do here is create a new highlight namespace that we apply to active
+-- windows only. We have to copy all the original highlight groups and then
+-- apply our changes. We then change the window's highlight namespace on
+-- WinEnter/WinLeave.
+local active_ns = vim.api.nvim_create_namespace('active')
+
+function init_active_ns()
+  local hls = vim.api.nvim_get_hl(0, {})
+  for k,v in ipairs(hls) do
+    vim.api.nvim_set_hl(active_ns, k, v)
+  end
+
+  local normal = vim.api.nvim_get_hl(0, { name = 'Normal' })
+  normal.ctermbg = 235
+  normal.bg = '#2c2c2c'
+
+  vim.api.nvim_set_hl(active_ns, 'Normal', normal)
+
+  vim.api.nvim_win_set_hl_ns(0, active_ns)
+end
+
+vim.api.nvim_create_autocmd('WinEnter', {
+  callback = function()
+    vim.api.nvim_win_set_hl_ns(0, active_ns)
+  end
+})
+
+vim.api.nvim_create_autocmd('WinLeave', {
+  callback = function()
+    vim.api.nvim_win_set_hl_ns(0, 0)
+  end
+})
+
 vim.api.nvim_create_autocmd('ColorScheme', {
   pattern = 'sonokai',
   callback = function()
@@ -17,6 +57,8 @@ vim.api.nvim_create_autocmd('ColorScheme', {
     vim.fn['sonokai#highlight']('MiniStatuslineModeVisual', palette.black, palette.orange)
     vim.fn['sonokai#highlight']('MiniStatuslineModeReplace', palette.black, palette.red)
     vim.fn['sonokai#highlight']('MiniStatuslineModeOther', palette.black, palette.green)
+
+    init_active_ns()
   end,
 })