bug#6651: Better fix

[Reuben Thomas]

I recently found that my previous suggested workaround for using
whitespace-mode's autocorrection without display is flawed, as it
doesn't deal with local variables. This means that for example one's
settings for tabs vs spaces can be ignored.

Here's a fuller solution, which has two advantages: first, the local
variables now work, and secondly, the workaround of explicitly setting
write-file-functions is no longer needed. Instead, this version of the
workaround disables whitespace-mode display altogether, by simply
redefining whitespace-mode-{on,off}.

It could therefore form the basis of a refactoring that allows display
mode to be separated from correction mode.

Code follows (for .emacs or equivalent):

(require 'whitespace)

;; Versions of whitespace functions that don't turn visualisation on
(defun whitespace-turn-on ()
  "Turn on whitespace correction."
  ;; prepare local hooks
  (add-hook 'write-file-functions 'whitespace-write-file-hook nil t)
  ;; create whitespace local buffer environment
  (set (make-local-variable 'whitespace-font-lock-mode) nil)
  (set (make-local-variable 'whitespace-font-lock) nil)
  (set (make-local-variable 'whitespace-font-lock-keywords) nil)
  (set (make-local-variable 'whitespace-display-table) nil)
  (set (make-local-variable 'whitespace-display-table-was-local) nil)
  (set (make-local-variable 'whitespace-active-style)
       (if (listp whitespace-style)
           whitespace-style
         (list whitespace-style)))
  (set (make-local-variable 'whitespace-indent-tabs-mode)
       indent-tabs-mode)
  (set (make-local-variable 'whitespace-tab-width)
       tab-width))
(defun whitespace-turn-off ()
  "Turn off whitespace correction."
  (remove-hook 'write-file-functions 'whitespace-write-file-hook t))

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