feat: add whitespace component

README.md

@@ -733,6 +733,75 @@ sections = {
 }
 ```
 
+#### whitespace component options
+
+```lua
+sections = {
+  lualine_a = {
+    {
+      'whitespace',
+      symbols = {
+        trailing = 'trailing whitespace: ',
+        long_line = 'long line: ',
+        mixed_indent = 'mixed indent: ',
+        mixed_indent_file = 'mixed-indent file: ',
+        merge_conflict = 'merge conflict: ',
+
+        separator = ' - ', -- The separator between checks.
+      },
+
+      checks = {
+        trailing = true,          -- Whether some lines have trailing
+                                  -- whitespace.
+
+        long_line = true,         -- Whether some lines are longer than
+                                  -- &textwidth.
+
+        mixed_indent = true,      -- Whether some lines have mixed indent.
+
+        mixed_indent_file = true, -- Whether the file contains indentation that
+                                  -- doesn't match the value of expandtab.
+
+        merge_conflict = true,    -- Whether the file contains git merge
+                                  -- conflict markers.
+      }, -- Which checks to enable.
+
+      ft_checks = {
+        make = { mixed_indent = false, mixed_indent_file = false },
+        csv = { mixed_indent = false, mixed_indent_file = false },
+        mail = { trailing = false },
+      }, -- Per-filetype override for checks.
+
+      max_lines = 20000, -- Line count threshold to disable all checks.
+      timeout = 500,     -- Time before a check gives up, in milliseconds.
+
+      mixed_indent_mode = 0, -- 0: Strict (no mixed indent allowed).
+                             -- 1: Allow less than &tabstop spaces after tabs.
+                             --    This allows for comments in the form:
+                             --    /*
+                             --     *
+                             --     */
+                             -- 2: Allow spaces after tabs.
+                             --    This is for styles that use tabs for
+                             --    indentation, and spaces for alignment.
+
+      c_like_langs = {
+        'arduino',
+        'c',
+        'cpp',
+        'cuda',
+        'go',
+        'javascript',
+        'ld',
+        'php',
+      }, -- Filetypes for which the mixed-indent file check allows lines that
+         -- start with spaces before a *.
+         -- This is for /* */ comments as above.
+    }
+  }
+}
+```
+
 #### windows component options
 
 ```lua

lua/lualine/components/whitespace.lua

@@ -0,0 +1,185 @@
+-- Copyright (c) 2013-2021 Bailey Ling et al.
+-- Copyright (c) 2023 novenary
+-- MIT license, see LICENSE for more details.
+-- https://github.com/vim-airline/vim-airline/blob/master/autoload/airline/extensions/whitespace.vim
+
+local lualine_require = require('lualine_require')
+local utils = require('lualine.utils.utils')
+local M = lualine_require.require('lualine.component'):extend()
+
+local default_options = {
+  symbols = {
+    trailing = 'trailing whitespace: ',
+    long_line = 'long line: ',
+    mixed_indent = 'mixed indent: ',
+    mixed_indent_file = 'mixed-indent file: ',
+    merge_conflict = 'merge conflict: ',
+    separator = ' - ',
+  },
+  checks = {
+    trailing = true,
+    long_line = true,
+    mixed_indent = true,
+    mixed_indent_file = true,
+    merge_conflict = true,
+  },
+  ft_checks = {
+    make = { mixed_indent = false, mixed_indent_file = false },
+    csv = { mixed_indent = false, mixed_indent_file = false },
+    mail = { trailing = false },
+  },
+  max_lines = 20000,
+  mixed_indent_mode = 0,
+  timeout = 500,
+  c_like_langs = {
+    'arduino',
+    'c',
+    'cpp',
+    'cuda',
+    'go',
+    'javascript',
+    'ld',
+    'php',
+  },
+}
+
+local changedticks = {}
+local cache = {}
+
+local function Set(list)
+  local set = {}
+  for _, l in ipairs(list) do
+    set[l] = true
+  end
+  return set
+end
+
+function M:init(options)
+  M.super.init(self, options)
+  self.options = vim.tbl_deep_extend('keep', self.options or {}, default_options)
+  self.options.c_like_langs = Set(self.options.c_like_langs)
+  utils.define_autocmd('CursorHold,BufWritePost', "lua require'lualine.components.whitespace'.invalidate_cache()")
+end
+
+function M:search(pat)
+  return vim.fn.search(pat, 'nw', 0, self.options.timeout)
+end
+
+function M:check_trailing()
+  return self:search([[\s$]])
+end
+
+function M:check_long_line()
+  local tw = vim.bo.textwidth
+  if tw > 0 then
+    return self:search([[\%>]] .. tw .. [[v.\+]])
+  end
+end
+
+function M:check_mixed_indent()
+  local mode = self.options.mixed_indent_mode
+  local tab_space_tab = [[(^\t* +\t\s*\S)]]
+  if mode == 0 then
+    -- Strict mode: any mixed indent is rejected
+    return self:search([[\v(^\t+ +)|(^ +\t+)]])
+  elseif mode == 1 then
+    -- Reject spaces after tabs,
+    -- only if there's more than the tabstop width
+    local spaces_after_tabs = string.format([[(^\t+ {%d,}\S)]], vim.bo.tabstop)
+    return self:search([[\v]] .. tab_space_tab .. [[|]] .. spaces_after_tabs)
+  elseif mode == 2 then
+    -- Allow tabs for indentation, spaces for alignment
+    return self:search([[\v]] .. tab_space_tab)
+  else
+    error('Unknown mixed indent mode!')
+  end
+end
+
+function M:check_mixed_indent_file()
+  if vim.bo.expandtab then
+    return self:search([[\v(^\t+)]])
+  else
+    if self.options.c_like_langs[vim.bo.filetype] then
+      -- Allow comments of the form
+      -- /*
+      --  *
+      --  */
+      return self:search([[\v(^ +\*@!)]])
+    else
+      return self:search([[\v(^ +)]])
+    end
+  end
+end
+
+function M:check_merge_conflict()
+  local annotation = [[\%([0-9A-Za-z_.:]\+\)\?]]
+  local opener = [[\%(<<<<<<< ]] .. annotation .. [[\)]]
+  local separator = [[\%(=======\)]]
+  local closer = [[\%(>>>>>>> ]] .. annotation .. [[\)]]
+
+  local pat = [[^\%(]] .. opener
+
+  -- These file types use ======= as a header
+  local rst = Set { 'rst', 'markdown', 'rmd' }
+  if not rst[vim.bo.filetype] then
+    pat = pat .. [[\|]] .. separator
+  end
+
+  pat = pat .. [[\|]] .. closer .. [[\)$]]
+
+  return self:search(pat)
+end
+
+function M:do_checks()
+  local lines = vim.fn.line('$')
+  if vim.bo.readonly or not vim.bo.modifiable or lines > self.options.max_lines then
+    return {}
+  end
+
+  local ft = vim.bo.filetype
+  local checks = vim.tbl_extend('force', self.options.checks, self.options.ft_checks[ft] or {})
+
+  local res = {}
+  for k, v in pairs(checks) do
+    if v then
+      res[k] = self['check_' .. k](self)
+    end
+  end
+  return res
+end
+
+function M:do_checks_cached()
+  local bufnr = vim.api.nvim_get_current_buf()
+  local cached = cache[bufnr]
+  if cached then
+    return cached
+  end
+
+  local res = self:do_checks()
+  cache[bufnr] = res
+  return res
+end
+
+function M.invalidate_cache()
+  local bufnr = vim.api.nvim_get_current_buf()
+  local changedtick = vim.b.changedtick
+  if changedtick ~= changedticks[bufnr] then
+    changedticks[bufnr] = changedtick
+    cache[bufnr] = nil
+  end
+end
+
+function M:update_status()
+  local checks = self:do_checks_cached()
+
+  local status = {}
+  for k, v in pairs(checks) do
+    if v and v ~= 0 then
+      table.insert(status, string.format('%s%d', self.options.symbols[k], v))
+    end
+  end
+
+  return table.concat(status, self.options.symbols.separator)
+end
+
+return M