[nvim] Autocmd to highlight trailing whitespace using ErrorMsg

Additionally refactor the colors lua module into one with an init function that
init.lua can invoke.

nvim/init.lua

@@ -49,12 +49,14 @@ vim.cmd [[
 addGitTopLevelDirectoryToRuntimePath()
 
 require 'autocommands'
-require 'colors'
 require 'configuration'
 require 'diagnostics'
 require 'treesitter'
 require 'lsp'
 
+local colors = require 'colors'
+colors.init()
+
 local keys = require 'keys'
 keys.init()
 

nvim/lua/colors.lua

@@ -4,8 +4,39 @@
 -- know it can do it. This is required for most modern color themes. Apple's
 -- Terminal.app doesn't have True Color support though, so make sure it's
 -- off for that.
-vim.g.termguicolors = not vim.env.TERM_PROGRAM == "Apple_Terminal"
+--vim.g.termguicolors = not vim.env.TERM_PROGRAM == "Apple_Terminal"
 
+local function _highlight_trailing_whitespace()
+    local should_create_highlight_match = true
+
+    local group = vim.api.nvim_create_augroup("ListModeTrailingWhitespace", { clear = true })
+
+    local callback = function(env)
+        local list_mode_enabled = vim.api.nvim_get_option_value("list", { })
+        if list_mode_enabled then
+            vim.cmd [[ highlight link TrailingWhitespace ErrorMsg ]]
+            if should_create_highlight_match then
+                vim.cmd [[ match TrailingWhitespace /\v\s+$/ ]]
+                should_create_highlight_match = false
+            end
+        else
+            vim.cmd [[ highlight clear TrailingWhitespace ]]
+        end
+    end
+
+    vim.api.nvim_create_autocmd("OptionSet", {
+        pattern = "list",
+        group = group,
+        callback = callback,
+    })
+
+    vim.api.nvim_create_autocmd("BufWinEnter", {
+        group = group,
+        callback = callback,
+    })
+end
+
+local function _create_autocmds()
     local colorscheme_group = vim.api.nvim_create_augroup("ColorSchemeOverrides", { clear = true })
 
     vim.api.nvim_create_autocmd("ColorScheme", {
@@ -58,5 +89,15 @@ vim.api.nvim_create_autocmd("ColorScheme", {
         end,
         group = colorscheme_group,
     })
+end
+
+local function init_colors()
+    _highlight_trailing_whitespace()
+    _create_autocmds()
 
     vim.cmd [[ color zaibatsu ]]
+end
+
+return {
+    init = init_colors
+}