- (while (re-search-forward "[ \t][ \t][ \t]*" nil t)
- (let ((column (current-column))
- (indent-tabs-mode t))
- (delete-region (match-beginning 0) (point))
- (indent-to column))))))
+ (beginning-of-line)
+ (narrow-to-region (point) end)
+ (goto-char start)
+ (let ((indent-tabs-mode t))
+ (while (re-search-forward tabify-regexp nil t)
+ ;; The region between (match-beginning 0) and (match-end 0) is just
+ ;; spacing which we want to adjust to use TABs where possible.
+ (let ((end-col (current-column))
+ (beg-col (save-excursion (goto-char (match-beginning 0))
+ (skip-chars-forward "\t")
+ (current-column))))
+ (if (= (/ end-col tab-width) (/ beg-col tab-width))
+ ;; The spacing (after some leading TABs which we wouldn't
+ ;; want to touch anyway) does not straddle a TAB boundary,
+ ;; so it neither contains a TAB, nor will we be able to use
+ ;; a TAB here anyway: there's nothing to do.
+ nil
+ (delete-region (match-beginning 0) (point))
+ (indent-to end-col))))))))
+
+(provide 'tabify)