My emacs auto delete trailing white space setup, that only operate on the region of the buffer that is show in the current window

emacs-trailing-space.el

(setq show-trailing-whitespace t)
 
(defun my-prog-nuke-trailing-whitespace ()
  (when (derived-mode-p 'prog-mode)
    (let ((win-beg (window-start))
          (win-end (window-end))
          (line-beg (line-beginning-position))
          (line-end (line-end-position)))
         (if (or (< line-beg win-start)
                 (> line-end win-end))
             (delete-trailing-whitespace win-beg win-end)
             (delete-trailing-whitespace win-beg line-beg)
             (delete-trailing-whitespace line-end win-end)))))
(add-hook 'before-save-hook 'my-prog-nuke-trailing-whitespace)

Normally i would just recommend to use the following

(defun my-prog-nuke-trailing-whitespace ()
  "Delete trailing space only in the window region."
  (when (derived-mode-p 'prog-mode)
	(delete-trailing-whitespace (window-start) (window-end))))

Unless you found yourself like me thinking while having the current line auto indented, and this little helper will delete that indentation as trailing space, which would break my train of thoughts, only to repeat this nightmare numerous time, decided to overhual it to delete all region in current window besides current line.