whitespace: add more lenient mixed whitespace algorithm

autoload/airline/extensions/whitespace.vim

@@ -30,6 +30,8 @@ function! s:check_mixed_indent()
     " count of spaces at the end of tabs should be less then tabstop value
     let t_l_s = '(^\t+ {' . &ts . ',}' . '\S)'
     return search('\v' . t_s_t . '|' . t_l_s, 'nw')
+  elseif s:indent_algo == 2
+    return search('\v(^\t* +\t\s*\S)', 'nw')
   else
     return search('\v(^\t+ +)|(^ +\t+)', 'nw')
   endif

doc/airline.txt

@@ -407,6 +407,11 @@ eclim <https://eclim.org>
   " certain number of spaces are allowed after tabs, but not in between
   " this algorithm works well for /** */ style comments in a tab-indented file
   let g:airline#extensions#whitespace#mixed_indent_algo = 1
+
+  " spaces are allowed after tabs, but not in between
+  " this algorithm works well with programming styles that use tabs for
+  " indentation and spaces for alignment
+  let g:airline#extensions#whitespace#mixed_indent_algo = 2
 <
 * customize the whitespace symbol. >
   let g:airline#extensions#whitespace#symbol = '!'