Xref: utzoo comp.emacs:4439 gnu.emacs:87 gnu.emacs.bug:108
Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!rutgers!aramis.rutgers.edu!porthos.rutgers.edu!gaynor
From: gaynor@porthos.rutgers.edu (Silver)
Newsgroups: comp.emacs,gnu.emacs,gnu.emacs.bug
Subject: symbolic links & GNU Emacs
Keywords: breaking symbolic links
Message-ID: <Oct.19.04.46.36.1988.22562@porthos.rutgers.edu>
Date: 19 Oct 88 08:46:37 GMT
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 65


I got burned by breaking a symbolic link chain, by the way GNU Emacs saves
files.  I edited a link, not realizing that it wasn't the file I had intended
to edit.  When I went to save the file, emacs did it's usual antics of moving
the previous contents to the backup file, and saved the buffer into a newly
created file.  So, to avoid getting nuked in the future, I wrote a quickie
which (query) resolves links when a file is found.  I didn't sit around and
test it for hours, but it worked on all of the nastiest cases I could think of
in half an hour.  It is not armed to the teeth with features; the only effect
of installing it is the addition of a find-file hook and a tweek to
basic-save-buffer.  I think things should be done in a similar fashion by
default, which is why you are seeing this on gnu.emacs.bug.  I'd appreciate
hearing your comments if you have any.

Regards, [Ag] gaynor@rutgers.edu

--------------------------------- symlink.el ----------------------------------
;; GNU, it's yours if you want it.  [Ag] gaynor@rutgers.edu


(provide 'symlink)


(defvar buffer-symlink-name nil
"Set to the name of the file at which a symbolic link chain should be broken
when performing a basic-save-buffer.")


(setq find-file-hooks
      (cons 'find-file-symlink-hook
	    find-file-hooks))


(defun find-file-symlink-hook ()
"find-file hook which assigns buffer-symlink-name upon reading a file.
Interactively walks through a symlink chain until user chooses to break the
chain."
  (set (make-local-variable 'buffer-symlink-name)
       (resolve-symlink-name buffer-file-name)))


(defun resolve-symlink-name (file-name &optional quiet)
  (let ((symlink-name file-name)
	(sln (file-symlink-p file-name)))
    (while (and sln
		(or quiet
		    (y-or-n-p (format "Follow symlink %s to %s? "
				      symlink-name sln))))
      (setq symlink-name (expand-file-name sln)
	    sln (file-symlink-p sln)))
    symlink-name))


;; Redefine basic-save-buffer to give precedence to buffer-symlink-name if it
;; is non-nil.
(let ((bsb (symbol-function 'basic-save-buffer)))
  (fset 'basic-save-buffer
	 (list (car (nthcdr 0 bsb)) ;; lambda
	       (car (nthcdr 1 bsb)) ;; arguments
	       (car (nthcdr 2 bsb)) ;; documentation
	       (car (nthcdr 3 bsb)) ;; interactive
	       (append '(let ((buffer-file-name (or buffer-symlink-name
						    buffer-file-name))
			      (real-buffer-file-name buffer-file-name)))
		       (nthcdr 4 bsb))))) ;; body of basic-save-buffer