[elpa] externals/undo-tree d7c1b2c 118/195: "De-circle" undo-tree when saving to file, restore when loading.

[Stefan Monnier]

branch: externals/undo-tree
commit d7c1b2c3cbe53c87dcc55710ed96aedd7fbc15ad
Author: Toby S. Cubitt <toby-undo-tree@dr-qubit.org>
Commit: Toby S. Cubitt <toby-undo-tree@dr-qubit.org>

    "De-circle" undo-tree when saving to file, restore when loading.
    
    Loading large undo-trees is too slow to be usable. Removing back-links from
    the tree before saving, and restoring them when loading, speeds things up.
    
    Note that this makes the written data almost but not quite non-circular; the
    pointer to the current node is still written as a circular reference "#1".
---
 undo-tree.el | 69 +++++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 54 insertions(+), 15 deletions(-)

diff --git a/undo-tree.el b/undo-tree.el
index ee23e3e..48a1208 100644
--- a/undo-tree.el
+++ b/undo-tree.el
@@ -730,6 +730,10 @@
 ;; * install history auto-save hooks globally, otherwise
 ;;   `undo-tree-load-history-hook' doesn't run because file has already been
 ;;   loaded before `undo-tree-mode' has installed the hook function
+;; * add `undo-tree-decircle' and `undo-tree-recircle' functions to,
+;;   respecrively,  nullify and restore `previous' links in undo-tree nodes
+;; * speed up history saving and (especially) loading by "de-circling"
+;;   undo-tree data before writing to file and "re-circling" it on load
 ;;
 ;; Version 0.5.3
 ;; * modified `undo-list-transfer-to-tree' and `undo-list-pop-changeset' to
@@ -1676,6 +1680,26 @@ Comparison is done with `eq'."
      (make-symbol (format "undo-tree-id%d" num))))
 
 
+(defun undo-tree-decircle (tree)
+  ;; Nullify PREVIOUS links of undo-tree-nodes, to make undo-tree data
+  ;; structure non-circular.
+  (undo-tree-mapc
+   (lambda (node)
+     (dolist (n (undo-tree-node-next node))
+       (setf (undo-tree-node-previous n) nil)))
+   tree))
+
+
+(defun undo-tree-recircle (tree)
+  ;; Recreate PREVIOUS links of undo-tree-nodes, to restore circular undo-tree
+  ;; data structure.
+  (undo-tree-mapc
+   (lambda (node)
+     (dolist (n (undo-tree-node-next node))
+       (setf (undo-tree-node-previous n) node)))
+   tree))
+
+
 
 
 ;;; =====================================================================
@@ -3051,6 +3075,10 @@ Argument is a character, naming the register."
 
 
 
+
+;;; =====================================================================
+;;;                       Persistent storage
+
 (defun undo-tree-make-history-save-file-name (file)
   "Create the undo history file name for FILE.
 Normally this is the file's name with `.' prepended and
@@ -3081,7 +3109,7 @@ without asking for confirmation."
        (undo-tree-kill-visualizer)
       (error (undo-tree-clear-visualizer-data buffer-undo-tree)))
     (let ((buff (current-buffer))
-         (tree (copy-undo-tree buffer-undo-tree)))
+         tree)
       ;; get filename
       (unless filename
        (setq filename
@@ -3091,20 +3119,29 @@ without asking for confirmation."
       (when (or (not (file-exists-p filename))
                overwrite
                (yes-or-no-p (format "Overwrite \"%s\"? " filename)))
-       ;; discard undo-tree object pool before saving
-       (setf (undo-tree-object-pool tree) nil)
-       ;; print undo-tree to file
-       ;; NOTE: We use `with-temp-buffer' instead of `with-temp-file' to
-       ;;       allow `auto-compression-mode' to take effect, in case user
-       ;;       has overridden or advised the default
-       ;;       `undo-tree-make-history-save-file-name' to add a compressed
-       ;;       file extension.
-       (with-auto-compression-mode
-         (with-temp-buffer
-           (prin1 (sha1 buff) (current-buffer))
-           (terpri (current-buffer))
-           (let ((print-circle t)) (prin1 tree (current-buffer)))
-           (write-region nil nil filename)))))))
+       (unwind-protect
+           (progn
+             ;; transform undo-tree into non-circular structure, and make
+             ;; temporary copy
+             (undo-tree-decircle buffer-undo-tree)
+             (setq tree (copy-undo-tree buffer-undo-tree))
+             ;; discard undo-tree object pool before saving
+             (setf (undo-tree-object-pool tree) nil)
+             ;; print undo-tree to file
+             ;; NOTE: We use `with-temp-buffer' instead of `with-temp-file'
+             ;;       to allow `auto-compression-mode' to take effect, in
+             ;;       case user has overridden or advised the default
+             ;;       `undo-tree-make-history-save-file-name' to add a
+             ;;       compressed file extension.
+             (with-auto-compression-mode
+               (with-temp-buffer
+                 (prin1 (sha1 buff) (current-buffer))
+                 (terpri (current-buffer))
+                 (let ((print-circle t)) (prin1 tree (current-buffer)))
+                 (write-region nil nil filename))))
+         ;; restore circular undo-tree data structure
+         (undo-tree-recircle buffer-undo-tree))
+       ))))
 
 
 
@@ -3161,6 +3198,8 @@ signaling an error if file is not found."
       ;; initialise empty undo-tree object pool
       (setf (undo-tree-object-pool tree)
            (make-hash-table :test 'eq :weakness 'value))
+      ;; restore circular undo-tree data structure
+      (undo-tree-recircle tree)
       (setq buffer-undo-tree tree))))