Before I commit code I want to: Replace all tabs with spaces, make sure indentation is correct and delete trailing whitespace.
Here's a function that does just that (inspired by cleanup-buffer from Emacs starter kit).
(defun clean-up-buffer-or-region () "Untabifies, indents and deletes trailing whitespace from buffer or region." (interactive) (save-excursion (unless (region-active-p) (mark-whole-buffer)) (untabify (region-beginning) (region-end)) (indent-region (region-beginning) (region-end)) (save-restriction (narrow-to-region (region-beginning) (region-end)) (delete-trailing-whitespace))))
The function either operates on a region (if any region is selected) or the whole buffer.
(global-set-key (kbd "C-c n") 'clean-up-buffer-or-region)