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I recently added Emacs (delete-trailing-whitespace) function to my 'before-save-hook for some programming modes, but I find it rather frustrating that it deletes whitespace from the line I am currently editing. Any suggestions as to how to fix this problem?
923
Remove trailing whitespace. To remove trailing whitespace from the entire buffer, use any of the following: ‘M-x delete-trailing-whitespace’ ( GnuEmacs version 21 or later). You can put this in ‘before-save-hook’ to ensure that your files have no trailing whitespace:
Remove whitespace at the end of the document. To remove whitespace at the end of a document, use any of the following: ‘C-x C-o’ ( ‘delete-blank-lines’) at the end of the buffer (` M-> ’).
Last updated: 2021-07-19. Deletes trailing whitespace, and also deletes trailing blank lines if delete-trailing-lines is t. (works on whole buffer or selection) Delete whitespaces that are normally considered problem.
From the commentary: “This package contains tools to do various sorts of whitespace trimming on buffer lines. The main part is WS Trim mode, which is a minor mode that automatically trims whitespace on text lines. You can control how thorough this mode should be, e.g. whether all lines or only lines you edit should be trimmed.”
This wrapper for delete-trailing-whitespace can be used to do what you want:
(defun delete-trailing-whitespace-except-current-line ()
"do delete-trailing-whitespace, except preserve whitespace of current line"
(interactive)
(let ((current-line (buffer-substring (line-beginning-position) (line-end-position)))
(backward (- (line-end-position) (point))))
(delete-trailing-whitespace)
(when (not (string-equal (buffer-substring (line-beginning-position) (line-end-position))
current-line))
(delete-region (line-beginning-position) (line-end-position))
(insert current-line)
(backward-char backward))))
Since delete-trailing-whitespace respects narrowing, one solution is to narrow the buffer to the portion before the current line and call it, then narrow to the portion after the current line and call it again:
(defun delete-trailing-whitespace-except-current-line ()
(interactive)
(let ((begin (line-beginning-position))
(end (line-end-position)))
(save-excursion
(when (< (point-min) begin)
(save-restriction
(narrow-to-region (point-min) (1- begin))
(delete-trailing-whitespace)))
(when (> (point-max) end)
(save-restriction
(narrow-to-region (1+ end) (point-max))
(delete-trailing-whitespace))))))
Put this function on your before-save-hook instead of delete-trailing-whitespace.
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