Re: Proposal: diff-remove-trailing-blanks

[Vinicius Jose Latorre]

> >      (while (re-search-forward "^[+!>] .*?[ \t]+$" (point-max) t)
>
> In unified diffs, there is no white space after `+'. In other diff
> types, its seems that there is:
>
> +foo (changed or added line, unified diff)
> > foo (changed or added line, normal diff)
> ! foo (changed line, context diff)
> + foo (added line, context diff)
>
> The solution is to test the format type and adapt the regexp for it:
>
> (diff-beginning-of-hunk 'try-harder)
> (setq (diff-hunk-style))
> (case style
>     (unified (setq re ...)) ;; (+)
>     (context (setq re ...)) ;; (+! )
>     (t (setq re ...))) ;; (> )
>
> [snip]
>
> >      (if modified-buffers
> >          (let ((whitespace-style '(trailing))
> >                (whitespace-trailing-regexp "^[+!>] .*?\\([\t ]+\\)$"))
>
> Likewise.
>
> >            (whitespace-mode 1)        ; display trailing blanks in diff buffer
>
> Seeing that the diff introduces trailing whitespace is most interesting
> before removing it too. Actually, you want to highlight trailing
> withespace on the diff for knowing that you should invoke
> `diff-remove-trailing-blanks'. (A nice thing would be to automatically
> test the diff and put something on the buffer's modeline indicating that
> the diff introduces trailing whitespace. `diff-mode-hook' is handy for
> this).
>
> [snip]

Ok, so, maybe the functions below fix all of this.

(defun diff-remove-trailing-blanks ()
 "When on a buffer that contains a diff, inspects the
differences and removes trailing whitespace (spaces, tabs) from
the lines modified or introduced by this diff. Shows a message
with the name of the altered buffers, which are unsaved.  If a
file referenced on the diff has no buffer and needs to be fixed,
a buffer visiting that file is created."
 (interactive)
 (save-excursion
   ;; We assume that the diff header has no trailing whitespace.
   (let (modified-buffers white-positions)
     (goto-char (point-min))
     (while (re-search-forward "^[+!>].*?[ \t]+$" (point-max) t)
       (save-excursion
         (destructuring-bind (buf line-offset pos src dst &optional 
switched)
             (diff-find-source-location t t)
           (when line-offset
             (save-excursion
               (set-buffer buf)
               (goto-char (+ (car pos) (cdr src)))
               (beginning-of-line)
               (when (re-search-forward "\\([ \t]+\\)$" 
(line-end-position) t)
                 (unless (member buf modified-buffers)
                   (push buf modified-buffers))
                 (push buf white-positions)
                 (push (match-beginning 0) white-positions)
                 (push (match-end 0) white-positions)))))))
     (setq white-positions (nreverse white-positions))
     (while white-positions
       (save-excursion
         (set-buffer (pop white-positions))
         (delete-region (pop white-positions) (pop white-positions))))
     (if modified-buffers
         (message "Deleted trailing whitespace from: %s"
                  (mapconcat
                   #'(lambda (buf)
                       (format "`%s'" (buffer-name buf)))
                   modified-buffers
                   " "))
       (message "No fixes needed.")))))

(defun diff-show-trailing-blanks ()
 "Show trailing blanks in modified lines for diff-mode."
 (interactive)
 (let ((whitespace-style '(trailing))
       (whitespace-trailing-regexp "^[+!>].*?\\([\t ]+\\)$"))
   (whitespace-mode 1)))     ; display trailing blanks in diff buffer

(add-hook 'diff-mode-hook 'diff-show-trailing-blanks)