[elpa] externals/undo-tree 04b1a6f 054/195: Fixed bugs in history-discarding logic.

[Stefan Monnier]

branch: externals/undo-tree
commit 04b1a6f439117455e8ba502fabda359eed8963dd
Author: Toby S. Cubitt <toby-undo-tree@dr-qubit.org>
Commit: Toby S. Cubitt <toby-undo-tree@dr-qubit.org>

    Fixed bugs in history-discarding logic.
---
 undo-tree.el | 35 ++++++++++++++++++++++++++++-------
 1 file changed, 28 insertions(+), 7 deletions(-)

diff --git a/undo-tree.el b/undo-tree.el
index 7cd22f9..b44dd5e 100644
--- a/undo-tree.el
+++ b/undo-tree.el
@@ -502,6 +502,7 @@
 ;;   is displaying it
 ;; * fixed bug in `undo-tree-switch-branch'
 ;; * general code tidying and reorganisation
+;; * fixed bugs in history-discarding logic
 ;;
 ;; Version 0.1.6
 ;; * added `undo-tree-mode-lighter' customization option to allow the
@@ -990,15 +991,16 @@ Comparison is done with 'eq."
          nil)
         ;; discard root
          (t
+          ;; make child of root into new root
+          (setq node (setf (undo-tree-root buffer-undo-tree)
+                           (car (undo-tree-node-next node))))
          ;; update undo-tree size
          (decf (undo-tree-size buffer-undo-tree)
                (+ (undo-list-byte-size (undo-tree-node-undo node))
                   (undo-list-byte-size (undo-tree-node-redo node))))
-          ;; make child of root into new root
-          (setf node (setf (undo-tree-root buffer-undo-tree)
-                           (car (undo-tree-node-next node)))
-                (undo-tree-node-undo node) nil
-                (undo-tree-node-redo node) nil)
+         ;; discard new root's undo data
+         (setf (undo-tree-node-undo node) nil
+               (undo-tree-node-redo node) nil)
           ;; if new root has branches, or new root is current node, next node
           ;; to discard is oldest leaf, otherwise it's new root
           (if (or (> (length (undo-tree-node-next node)) 1)
@@ -1050,9 +1052,28 @@ set by `undo-limit', `undo-strong-limit' and 
`undo-outer-limit'."
       ;; discard nodes until next node to discard would bring memory use
       ;; within `undo-limit'
       (while (and node
+                 ;; check first if last discard has brought us within
+                 ;; `undo-limit', in case we can avoid more expensive
+                 ;; `undo-strong-limit' calculation
+                 ;; Note: this assumes undo-strong-limit > undo-limit;
+                 ;;       if not, effectively undo-strong-limit = undo-limit
+                 (> (undo-tree-size buffer-undo-tree) undo-limit)
                   (> (- (undo-tree-size buffer-undo-tree)
-                        (undo-list-byte-size (undo-tree-node-undo node))
-                        (undo-list-byte-size (undo-tree-node-redo node)))
+                       ;; if next node to discard is root, the memory we
+                       ;; free-up comes from discarding changesets from its
+                       ;; only child...
+                       (if (eq node (undo-tree-root buffer-undo-tree))
+                           (+ (undo-list-byte-size
+                               (undo-tree-node-undo
+                                (car (undo-tree-node-next node))))
+                              (undo-list-byte-size
+                               (undo-tree-node-redo
+                                (car (undo-tree-node-next node)))))
+                         ;; ...otherwise, it comes from discarding changesets
+                         ;; from along with the node itself
+                         (+ (undo-list-byte-size (undo-tree-node-undo node))
+                            (undo-list-byte-size (undo-tree-node-redo node)))
+                         ))
                      undo-limit))
         (setq node (undo-tree-discard-node node)))