emacs/lisp/saveplace.el

;;; saveplace.el --- automatically save place in files.

;; Copyright (C) 1993 Free Software Foundation, Inc.

;; Author: Karl Fogel <kfogel@cs.oberlin.edu>
;; Maintainer: FSF
;; Created: July, 1993
;; Version: 1.0
;; Keywords: bookmarks, placeholders

;; This file is part of GNU Emacs.

;; GNU Emacs is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING.  If not, write to
;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

;; Automatically save place in files, so that visiting them later
;; (even during a different Emacs session) automatically moves point
;; to the saved position, when the file is first found.  Uses the
;; value of buffer-local variable save-place to determine whether to
;; save position or not.
;;
;; Don't autoload this, rather, load it, since it modifies
;; find-file-hooks and other hooks.

;; this is what I was using during testing:
;; (define-key ctl-x-map "p" 'toggle-save-place)

(defvar save-place-alist nil
  "Alist of saved places to go back to when revisiting files.
Each element looks like (FILENAME . POSITION);
visiting file FILENAME goes automatically to position POSITION
rather than the beginning of the buffer.
This alist is saved between Emacs sessions.")

(defvar save-place nil
  "*Non-nil means automatically save place in each file.
This means when you visit a file, point goes to the last place
where it was when you previously visited the same file.
This variable is automatically buffer-local.

If you wish your place in any file to always be automatically saved,
simply put this in your `~/.emacs' file:

\(setq-default save-place t\)")

(make-variable-buffer-local 'save-place)

(defvar save-place-file "~/.emacs-places"
  "*Name of the file that records `save-place-alist' value.")

(defvar save-place-loaded nil
  "Non-nil means that the `save-place-file' has been loaded.")

(defun toggle-save-place (&optional parg)
  "Toggle whether to save your place in this file between sessions.
If this mode is enabled, point is recorded when you kill the buffer
or exit Emacs.  Visiting this file again will go to that position,
even in a later Emacs session.

If called with a prefix arg, the mode is enabled if and only if
the argument is positive.

To save places automatically in all files, put this in your `.emacs' file:

\(setq-default save-place t\)"
  (interactive "P")
  (if (not buffer-file-name)
      (message 
       (format "Buffer \"%s\" not visiting a file." (buffer-name)))
    (if (and save-place (or (not parg) (<= parg 0)))
	(progn
	  (message "No place will be saved in this file.")
	  (setq save-place nil))
      (message "Place will be saved.")
      (setq save-place t))))

(defun save-place-to-alist ()
  ;; put filename and point in a cons box and then cons that onto the
  ;; front of the save-place-alist, if save-place is non-nil.
  ;; Otherwise, just delete that file from the alist.
  ;; first check to make sure alist has been loaded in from the master
  ;; file.  If not, do so, then feel free to modify the alist.  It
  ;; will be saved again when Emacs is killed.
  (or save-place-loaded (load-save-place-alist-from-file))
  (if buffer-file-name
      (progn
        (let ((cell (assoc buffer-file-name save-place-alist)))
          (if cell
              (setq save-place-alist (delq cell save-place-alist))))
        (if save-place
            (setq save-place-alist
                  (cons (cons buffer-file-name (point))
                        save-place-alist))))))

(defun save-place-alist-to-file ()
  (let ((file (expand-file-name save-place-file)))
    (save-excursion
      (message (format "Saving places to %s..." file))
      (set-buffer (get-buffer-create " *Saved Places*"))
      (delete-region (point-min) (point-max))
      (if (file-readable-p file)
          (insert-file-contents file))
      (delete-region (point-min) (point-max))
      (goto-char (point-min))
      (print save-place-alist (current-buffer))
      (write-file file)
      (kill-buffer (current-buffer))
      (message (format "Saving places to %s... done." file)))))

(defun load-save-place-alist-from-file ()
  (if (not save-place-loaded)
      (progn
        (setq save-place-loaded t)
        (let ((file (expand-file-name save-place-file)))
          ;; make sure that the alist does not get overwritten, and then
          ;; load it if it exists:
          (if (file-readable-p file)
              (save-excursion
                (message (format "Loading places from %s..."
                                 save-place-file))
                ;; don't want to use find-file because we have been
                ;; adding hooks to it.
                (set-buffer (get-buffer-create " *Saved Places*"))
                (delete-region (point-min) (point-max))
                (insert-file-contents file)
                (goto-char (point-min))
                (setq save-place-alist 
                      (car (read-from-string
                            (buffer-substring (point-min) (point-max)))))
                (kill-buffer (current-buffer))
                (message (format "Loading places from %s... done." file))
                t)
            t)
          nil))))

(defun save-places-to-alist ()
  ;; go through buffer-list, saving places to alist if save-place is
  ;; non-nil, deleting them from alist if it is nil.
  (let ((buf-list (buffer-list)))
    (while buf-list
      ;; put this into a save-excursion in case someone is counting on
      ;; another function in kill-emacs-hook to act on the last buffer
      ;; they were in:
      (save-excursion
	(set-buffer (car buf-list))
	;; save-place checks buffer-file-name too, but we can avoid
	;; overhead of function call by checking here too.
	(and buffer-file-name (save-place-to-alist))
	(setq buf-list (cdr buf-list))))))
    
(add-hook 
 'find-file-hooks
 (function
  (lambda ()
    (or save-place-loaded (load-save-place-alist-from-file))
    (let ((cell (assoc buffer-file-name save-place-alist)))
      (if cell
	  (progn
	    (goto-char (cdr cell))
	    ;; and make sure it will be saved again for later.
	    (setq save-place t)))))))

(add-hook 'kill-emacs-hook
	  (function
	   (lambda ()
	     (progn
	       (save-places-to-alist)
	       (save-place-alist-to-file)))))

(add-hook 'kill-buffer-hook 'save-place-to-alist)

(provide 'saveplace) ; why not...

;;; saveplace.el ends here