bug#12769: 24.2; Files won't save on Macintosh/Mountain Lion

[martin rudalics <rudalics@gmx.at>]

 > I tracked the problem down to the following (in red):
 > (setq-default indent-tabs-mode nil)
 > (add-hook 'write-file-hooks
 >   (lambda ()
 >     (if (not indent-tabs-mode)
 >       (untabify (point-min) (point-max))
 >       (delete-trailing-whitespace))))

 > So, is this a bug or is the untabify command no longer supported?  If
 > it's now a bug, this should now be reproducible.  If it's an obsolete
 > package, do you have any suggestions for a replacement?

Properly indented, the `add-hook' form above here appears as

(add-hook 'write-file-hooks
           (lambda ()
             (if (not indent-tabs-mode)
                 (untabify (point-min) (point-max))
               (delete-trailing-whitespace))))

so if `indent-tabs-mode' is on, you delete trailing whitespace and if
it's off, you untabify.  Is this what you really want?

Anyway, the problem seems that `untabify' returns non-nil and according
to the doc-string of `write-file-hooks' we know that this is a

   List of functions to be called before writing out a buffer to a file.
   If one of them returns non-nil, the file is considered already written
   and the rest are not called.

which is slightly ambiguous: One might think that if one of them returns
non-nil Emacs will "not call the rest" but nevertheless save the buffer
to its file.

In your case writing the file is aborted because `untabify' returns the
"current column `move-to-column' moved to" (whatever that is it seems to
be non-nil).  So maybe we should modify the return value of `untabify'
(like in `delete-trailing-whitespace') or you should use

(add-hook 'write-file-hooks
           (lambda ()
             (if (not indent-tabs-mode)
                 (progn
                   (untabify (point-min) (point-max))
                   nil)
               (delete-trailing-whitespace))))

still modulo your real intentions of what that lambda is supposed to do.

martin