[PATCH]saveplace.el: forget saved places for unreadable files

[Stephen Compall]

"Bug": save-place doesn't "garbage collect" useless saved places.

Upon looking in my `.emacs-places' file for the first time, I noticed
that I no longer had many of the files it had saved places for.
Long-gone source trees were still meticulously bookmarked in the
alist.  Theoretically, `save-place-alist' can grow indefinitely,
filling with entries that no longer refer to a file.

I feel the solution is to provide some way for users to automatically
remove useless entries in `save-place-alist'.  As all save-place users
have an interest in cleaning this up, I feel this functionality is
generally useful enough to be included with the Emacs distribution.

"Semifix": This is a patch against emacs/lisp/saveplace.el, CVS
revision 1.25.  I added an interactive function,
`save-place-forget-unreadable-files', that removes entries from
`save-place-alist' whose CARs return nil when `file-readable-p' is
applied.  In short, it forgets unreadable files.  As I can immediately
think of reasons why automatically doing this may not be desirable, I
added a customizable toggle, named same as the function, to call the
function before writing to `save-place-file' 's buffer.

Reasons this may not be desirable:

 * removable/network drives, tarballs: files with useful saved places
   may not always be present

 * file-readable-p can be slow applied to certain volumes, such as
   CD-ROM drives.  The first time I ran it, on my formerly 1000-item
   save-place-alist, emacs hung on exit while the CD-ROM spun up for
   the necessary tests

 * only one static test available: file-readable-p.  Perhaps should
   allow user-defined filtering, as is available with midnight mode,
   so users could limit saved places as they saw fit.  I suppose this
   could be done with a find-file-hook that sets `save-place'
   accordingly, but there's already one test I know of for which this
   method would be ineffective: the one this patch includes.

If anyone has interest in expanding this feature, particularly in
making the test(s?) more configurable, please share a good way to go
about that, if you please.  For that matter, any other suggestions are
welcome, of course.

This patch runs until the signature; you may also retrieve it from
http://csserver.evansville.edu/~sc87/dist/saveplace-forget.1S11.patch.
I have tested it against Emacs 21.3; however, the patch is made
against CVS revision 1.25 (in HEAD branch).

*** /mnt/cdrom/emacs-cvs/lisp/saveplace.el      2003-03-25 13:32:39.000000000 
-0600
--- /home/sirian/ide/scripts/saveplace.el       2003-07-21 15:59:39.000000000 
-0500
***************
*** 94,99 ****
--- 94,111 ----
                 (const :tag "No Limit" nil))
    :group 'save-place)
  
+ (defcustom save-place-forget-unreadable-files nil
+   "Non-nil means forget place in unreadable files.
+ 
+ The filenames in `save-place-alist' are filtered through
+ `file-readable-p'. if nil, the alist entry is removed.
+ 
+ You may do this anytime by calling the complementary function,
+ `save-place-forget-unreadable-files'.  When this option is turned on,
+ this happens automatically before saving `save-place-alist' to
+ `save-place-file'."
+   :type '(boolean) :group 'save-place)
+ 
  (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
***************
*** 138,149 ****
--- 150,185 ----
                    (cons (cons buffer-file-name position)
                          save-place-alist)))))))
  
+ (defun save-place-forget-unreadable-files ()
+   "Remove unreadable files from `save-place-alist'.
+ For each entry in the alist, if `file-readable-p' returns nil for the
+ filename, remove the entry.  Save the new alist \(as the first pair
+ may have changed\) back to `save-place-alist'."
+   (interactive)
+   ;; the following was adapted from an in-place filtering function,
+   ;; `filter-mod', used in the original.
+   (unless (null save-place-alist)     ;says it better than `when'
+     ;; first, check all except first
+     (let ((fmprev save-place-alist) (fmcur (cdr save-place-alist)))
+       (while fmcur                    ;not null
+       ;; a value is only saved when it becomes FMPREV.
+       (if (file-readable-p (caar fmcur))
+           (setq fmprev fmcur)
+         (setcdr fmprev (cdr fmcur)))
+       (setq fmcur (cdr fmcur))))
+     ;; test first pair, keep it if OK, otherwise 2nd element, which
+     ;; may be '()
+     (unless (file-readable-p (caar save-place-alist))
+       (setq save-place-alist (cdr save-place-alist)))))
+ 
  (defun save-place-alist-to-file ()
    (let ((file (expand-file-name save-place-file)))
      (save-excursion
        (message "Saving places to %s..." file)
        (set-buffer (get-buffer-create " *Saved Places*"))
        (delete-region (point-min) (point-max))
+       (when save-place-forget-unreadable-files
+       (save-place-forget-unreadable-files))
        (print save-place-alist (current-buffer))
        (let ((version-control
               (cond


--
Stephen Compall or s11 or sirian

Worrying is like rocking in a rocking chair -- It gives you something to do,
but it doesn't get you anywhere.

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