[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/lua/colors.lua

@@ -4,59 +4,100 @@
 -- 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 colorscheme_group = vim.api.nvim_create_augroup("ColorSchemeOverrides", { clear = true })
+local function _highlight_trailing_whitespace()
+    local should_create_highlight_match = true
 
-vim.api.nvim_create_autocmd("ColorScheme", {
-    callback = function()
-        vim.cmd [[
-            hi! ColorColumn cterm=NONE ctermbg=233
-            hi! CursorColumn cterm=NONE ctermbg=233
-            hi! CursorLine cterm=NONE ctermbg=233
-            hi! CursorLineNr cterm=bold ctermfg=White ctermbg=233
-            hi! LineNr ctermfg=DarkGray ctermbg=233
-        ]]
-    end,
-    group = colorscheme_group,
-})
+    local group = vim.api.nvim_create_augroup("ListModeTrailingWhitespace", { clear = true })
 
-vim.api.nvim_create_autocmd("ColorScheme", {
-    pattern = "default",
-    callback = function()
-        vim.cmd [[ hi! NormalFloat ctermfg=8 ]]
-    end,
-    group = colorscheme_group,
-})
+    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("ColorScheme", {
-    pattern = "dracula",
-    callback = function()
-        vim.cmd [[ highlight CursorLineNr guibg=#44475a ]]
-    end,
-    group = colorscheme_group,
-})
+    vim.api.nvim_create_autocmd("OptionSet", {
+        pattern = "list",
+        group = group,
+        callback = callback,
+    })
 
-vim.api.nvim_create_autocmd("ColorScheme", {
-    pattern = "witchhazel",
-    callback = function()
-        vim.cmd [[
-            hi! default link LineNr CursorLineNr
-            hi! default link CursorLineNr CursorLine
-        ]]
-    end,
-    group = colorscheme_group,
-})
+    vim.api.nvim_create_autocmd("BufWinEnter", {
+        group = group,
+        callback = callback,
+    })
+end
 
-vim.api.nvim_create_autocmd("ColorScheme", {
-    pattern = "zaibatsu",
-    callback = function()
-        vim.cmd [[
-            hi! Pmenu ctermbg=8
-            hi! VertSplit ctermbg=8
-        ]]
-    end,
-    group = colorscheme_group,
-})
+local function _create_autocmds()
+    local colorscheme_group = vim.api.nvim_create_augroup("ColorSchemeOverrides", { clear = true })
 
-vim.cmd [[ color zaibatsu ]]
+    vim.api.nvim_create_autocmd("ColorScheme", {
+        callback = function()
+            vim.cmd [[
+                hi! ColorColumn cterm=NONE ctermbg=233
+                hi! CursorColumn cterm=NONE ctermbg=233
+                hi! CursorLine cterm=NONE ctermbg=233
+                hi! CursorLineNr cterm=bold ctermfg=White ctermbg=233
+                hi! LineNr ctermfg=DarkGray ctermbg=233
+            ]]
+        end,
+        group = colorscheme_group,
+    })
+
+    vim.api.nvim_create_autocmd("ColorScheme", {
+        pattern = "default",
+        callback = function()
+            vim.cmd [[ hi! NormalFloat ctermfg=8 ]]
+        end,
+        group = colorscheme_group,
+    })
+
+    vim.api.nvim_create_autocmd("ColorScheme", {
+        pattern = "dracula",
+        callback = function()
+            vim.cmd [[ highlight CursorLineNr guibg=#44475a ]]
+        end,
+        group = colorscheme_group,
+    })
+
+    vim.api.nvim_create_autocmd("ColorScheme", {
+        pattern = "witchhazel",
+        callback = function()
+            vim.cmd [[
+                hi! default link LineNr CursorLineNr
+                hi! default link CursorLineNr CursorLine
+            ]]
+        end,
+        group = colorscheme_group,
+    })
+
+    vim.api.nvim_create_autocmd("ColorScheme", {
+        pattern = "zaibatsu",
+        callback = function()
+            vim.cmd [[
+                hi! Pmenu ctermbg=8
+                hi! VertSplit ctermbg=8
+            ]]
+        end,
+        group = colorscheme_group,
+    })
+end
+
+local function init_colors()
+    _highlight_trailing_whitespace()
+    _create_autocmds()
+
+    vim.cmd [[ color zaibatsu ]]
+end
+
+return {
+    init = init_colors
+}