Re: Proposal: diff-remove-trailing-blanks

[Vinicius Jose Latorre <viniciusjl@ig.com.br>]

>>      (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)