improve whitespace detection; add support for mixed indents

autoload/airline/extensions/whitespace.vim

@@ -2,10 +2,35 @@
 " vim: ts=2 sts=2 sw=2 fdm=indent
 
 function! airline#extensions#whitespace#check()
-  let w:airline_section_warning = '%{get(w:, "airline_active", 0) && search(" $", "nw")'
-        \ .'? " ".g:airline_whitespace_symbol." " : ""}'
+  if line('$') > g:airline_whitespace_max_lines
+    return ''
+  endif
+
+  let trailing = search(' $', 'nw') != 0
+  let mixed = search('^ ', 'nw') != 0 && search('^\t', 'nw') != 0
+
+  if trailing || mixed
+    let text = " ".g:airline_whitespace_symbol." "
+    if g:airline_detect_whitespace == 1
+      if trailing
+        let text .= 'trailing '
+      endif
+      if mixed
+        let text .= 'mixed-indent '
+      endif
+    endif
+    return text
+  endif
+  return ''
+endfunction!
+
+function! airline#extensions#whitespace#apply()
+  if exists('w:airline_active') && w:airline_active
+    let w:airline_section_warning = '%{airline#extensions#whitespace#check()}'
+  endif
 endfunction
 
 function! airline#extensions#whitespace#init(ext)
-  call a:ext.add_statusline_funcref(function('airline#extensions#whitespace#check'))
+  call a:ext.add_statusline_funcref(function('airline#extensions#whitespace#apply'))
 endfunction
+

doc/airline.txt

@@ -73,6 +73,13 @@ values):
   let g:airline_detect_iminsert=1
 <
 
+* enable whitespace detection
+>
+  let g:airline_detect_whitespace=0 "disabled
+  let g:airline_detect_whitespace=1 "icon and message (default)
+  let g:airline_detect_whitespace=2 "icon only
+<
+
 * change the default theme
 >
   let g:airline_theme='dark'
@@ -132,6 +139,7 @@ separators, as well as the powerline font glyths.
   let g:airline_paste_symbol = 'ρ'
   let g:airline_paste_symbol = 'Þ'
   let g:airline_paste_symbol = '∥'
+  let g:airline_whitespace_symbol = 'Ξ'
 
   " powerline symbols
   let g:airline_left_sep = ''
@@ -157,13 +165,14 @@ with the usual statusline syntax.
 
 >
   " here are the the default values
-  let g:airline_section_a      (the mode/paste indicator)
-  let g:airline_section_b      (the fugitive/lawrencium branch indicator)
-  let g:airline_section_c      (bufferline or filename)
-  let g:airline_section_gutter (syntastic, readonly flag)
-  let g:airline_section_x      (tagbar, filetype)
-  let g:airline_section_y      (fileencoding, fileformat)
-  let g:airline_section_z      (percentage, line number, column number)
+  let g:airline_section_a       (the mode/paste indicator)
+  let g:airline_section_b       (the fugitive/lawrencium branch indicator)
+  let g:airline_section_c       (bufferline or filename)
+  let g:airline_section_gutter  (syntastic, readonly flag)
+  let g:airline_section_x       (tagbar, filetype)
+  let g:airline_section_y       (fileencoding, fileformat)
+  let g:airline_section_z       (percentage, line number, column number)
+  let g:airline_section_warning (special section that only appears sometimes)
 
   " here is an example of how you could replace the branch indicator with
   " the current working directory, followed by the filename.

plugin/airline.vim

@@ -29,6 +29,7 @@ call s:check_defined('g:airline_detect_modified', 1)
 call s:check_defined('g:airline_detect_paste', 1)
 call s:check_defined('g:airline_detect_whitespace', 1)
 call s:check_defined('g:airline_whitespace_symbol', '✹')
+call s:check_defined('g:airline_whitespace_max_lines', 3000)
 call s:check_defined('g:airline_branch_prefix', exists('g:airline_powerline_fonts')?' ':'')
 call s:check_defined('g:airline_readonly_symbol', exists('g:airline_powerline_fonts')?'':'RO')
 call s:check_defined('g:airline_linecolumn_prefix', exists('g:airline_powerline_fonts')?' ':':')