Re: Proposal: diff-remove-trailing-blanks

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

>>>> What relevant things would you like to see (or to be done) in a diff buffer?
>>>>     
>>> Here, we are interested on parts of the buffer, we don't care much about
>>> trailing whitespace out of the diff part that shows changed lines. That
>>> is, we are not interested on trailing whitespace on context lines, nor
>>> on those that are artifacts of diff-mode.
>>>   
>> Hummm, I'm confused, the original mail said:
>>
>>  "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."
>>
>>
>> So, I thought it was to remove trailing whitespaces from a diff buffer.
>
> The "removing" part is accomplished by my function. We are discussing
> the "displaying" part, which shows to the user that there is trailing
> whitespace to be removed.
>
> But I'm afraid I confused things out relating `show-trailing-whitespace'
> to whitespace-mode'.

Well, both parts, the "removing" part and the "displaying" part, related 
with trailing whitespaces can be done by whitespace-mode.

Does the following function do the job?

(defun diff-remove-trailing-blanks ()
  "When on a buffer that contains a diff, inspects the
differences and removes trailing whitespace (spaces, tabs).
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)
  (goto-char (point-min))
  ;; We assume that the diff header has no trailing whitespace.
  (let (modified-buffers)
    (while (re-search-forward "^[+!>].*[ \t]+$" (point-max) t)
      (save-excursion
    (destructuring-bind (buf line-offset pos src dst &optional switched)
            (diff-find-source-location t t)
          (unless (member buf modified-buffers)
            (when line-offset
              (set-buffer buf)
              (when (re-search-forward "\\([ \t]+\\)$" (point-max) t)
                (push buf modified-buffers)
                (let ((whitespace-style '(trailing)))
                  (whitespace-cleanup)))))))) ; cleanup trailing blanks 
in buf
    (if modified-buffers
        (let ((bufs (mapconcat #(lambda (buf)
                                  (format "`%s'" (buffer-name buf)))
                               modified-buffers
                               " "))
              (whitespace-style '(trailing)))
          (whitespace-mode)           ; display trailing blanks in diff 
buffer
          (message "Deleted trailing whitespace from: %s" bufs))
      (message "No fixes needed."))))


>> What are the relevant parts of the buffer?
>
> Those that correspond to added or modified lines in the diff.

So, should lines beginning with +, - and ! have a face to display the 
change?