[nongnu] elpa/undo-fu-session fddcc75a58 01/53: Initial commit.

[ELPA Syncer]

branch: elpa/undo-fu-session
commit fddcc75a582aeccdd01f42016ce2195d9d029147
Author: Campbell Barton <ideasman42@gmail.com>
Commit: Campbell Barton <ideasman42@gmail.com>

    Initial commit.
---
 .elisp-autofmt          |   0
 LICENSE                 | 674 ++++++++++++++++++++++++++++++++++++++++++++++++
 readme.rst              | 102 ++++++++
 undo-fu-session-test.el |  63 +++++
 undo-fu-session.el      | 496 +++++++++++++++++++++++++++++++++++
 5 files changed, 1335 insertions(+)

diff --git a/.elisp-autofmt b/.elisp-autofmt
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000000..f288702d2f
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,674 @@
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+
+  15. Disclaimer of Warranty.
+
+  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
+APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program 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 3 of the License, or
+    (at your option) any later version.
+
+    This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/readme.rst b/readme.rst
new file mode 100644
index 0000000000..3f888cd00e
--- /dev/null
+++ b/readme.rst
@@ -0,0 +1,102 @@
+###############
+Undo Fu Session
+###############
+
+Save & recover undo steps between Emacs sessions.
+
+This package writes undo/redo information upon file save which is restored
+where possible when the file is loaded again.
+
+The following features are supported:
+
+- Store full undo/redo history, allowing ``undo-only`` to work as expected.
+- Uses a minor-mode which can be enabled globally or buffer-local.
+- Option to store compressed.
+- Option to limit number of undo-session files stored
+  *(avoid adding files indefinitely until the user manually removes them).*
+- Fast early-exit on restore
+  *(only decode undo data if buffer length & checksum match).*
+
+
+Motivation
+==========
+
+To have a stand-alone package that stores Emacs built-in undo information for 
re-use,
+without imposing any changes to undo functionality.
+
+While this package is intended for use with `undo-fu 
<https://gitlab.com/ideasman42/emacs-undo-fu>`__,
+there are no inter-dependencies.
+
+
+Usage
+=====
+
+Typically this package is enabled globally,
+afterwards it runs automatically when saving & loading files.
+
+
+Enable (Global)
+---------------
+
+Enabling globally is most straightforward, you can then
+disable storing undo information by mode and file-name.
+
+.. code-block:: elisp
+
+   (global-undo-fu-session-mode)
+
+
+Enable (Buffer)
+---------------
+
+If you want to isolate this functionality,
+you can enable this using a mode hook for e.g.
+
+.. code-block:: elisp
+
+   ;; Only use undo-fu-session for org mode.
+   (add-hook 'org-mode-hook
+     (lambda ()
+       (undo-fu-session-mode))
+
+
+Details
+-------
+
+- Undo session information is stored in a directory,
+  with a corresponding file for each undo session.
+- Each file stores a length and checksum which is validated
+  before restoring the undo-session.
+- A mismatch with the file length or checksum will skip loading the undo 
session
+  with a message.
+
+
+Customization
+-------------
+
+``undo-fu-session-directory`` (``"undo-fu-session"`` in emacs user directory)
+   The location of stored files.
+``undo-fu-session-compression`` (``t``)
+   Store files compressed.
+``undo-fu-session-incompatible-files`` (``'()``)
+   List of regexps or functions for matching file names to ignore 
saving/recovering undo session.
+``undo-fu-session-incompatible-major-modes`` (``nil``)
+   List of major-modes in which saving undo session should not be performed.
+``undo-fu-session-file-limit`` (``nil``)
+   Number of files to store, nil to disable limiting entirely.
+
+   Enforcing removes the oldest files.
+
+
+Installation
+============
+
+The package is available in melpa as ``undo-fu-session``, here is an example 
with ``use-package``:
+
+.. code-block:: elisp
+
+   (use-package undo-fu-session
+     :config
+     (setq undo-fu-session-incompatible-files '("COMMIT_EDITMSG$" 
"git-rebase-todo$")))
+
+   (global-undo-fu-session-mode)
diff --git a/undo-fu-session-test.el b/undo-fu-session-test.el
new file mode 100644
index 0000000000..6320219a49
--- /dev/null
+++ b/undo-fu-session-test.el
@@ -0,0 +1,63 @@
+;; To test this file run:
+;; emacs --eval '(progn (add-to-list \'load-path ".") (load 
"undo-fu-session.el") (load "undo-fu-session-test.el"))' --batch
+
+(global-undo-fu-session-mode)
+
+(defmacro with-temp-dir (temp-dir &rest body)
+  `
+  (let ((,temp-dir (make-temp-file "" t)))
+    (unwind-protect
+      (progn
+        ,@body)
+      (delete-directory ,temp-dir t))))
+
+(with-temp-dir
+  ;; Don't touch the users home directory.
+  undo-fu-session-directory
+
+  (dotimes (f 100)
+    (let*
+      ( ;; While the session file wouldn't typically
+        ;; be in the same directory as the undo session data, it's harmless.
+        (filename (concat undo-fu-session-directory "/undo-fu-session-test"))
+        (filename-session (undo-fu-session--make-file-name filename)))
+      (when (file-exists-p filename)
+        (delete-file filename))
+      (when (file-exists-p filename-session)
+        (delete-file filename-session))
+      (with-current-buffer (find-file-literally filename)
+        (dotimes (_i 1000)
+          (ignore-errors
+            (cl-case
+              (random 3)
+              (0
+                (dotimes (_j 10)
+                  (insert (make-string (1+ (random 20)) (+ (random 26) 65)))))
+              (1 (newline))
+              (2 (insert "\t"))
+              (3 (forward-line))
+              (4 (forward-line -1))
+              (5 (kill-line))
+              (6 (kill-paragraph -1))
+              (7 (yank))
+              (8
+                (kill-region
+                  (+ (point-min) (random (point-max)))
+                  (+ (point-min) (random (point-max))))))))
+        (save-buffer)
+        (undo-fu-session-save)
+        (kill-buffer (current-buffer)))
+      (with-current-buffer (find-file-literally filename)
+        (undo-fu-session-recover)
+        (ignore-errors
+          (while
+            (prog1 t
+              (undo))))
+        (let ((contents (buffer-string)))
+          (set-buffer-modified-p nil)
+          (kill-buffer (current-buffer))
+          (if (string-equal contents "")
+            (message "Test succeeded #%s" f)
+            (error "Test failed #%s" f)))))))
+
+(message "Done")
diff --git a/undo-fu-session.el b/undo-fu-session.el
new file mode 100644
index 0000000000..958b91bb7e
--- /dev/null
+++ b/undo-fu-session.el
@@ -0,0 +1,496 @@
+;;; undo-fu-session.el --- Persistent undo, available between sessions -*- 
lexical-binding: t -*-
+
+;; Copyright (C) 2020  Campbell Barton
+;; Copyright (C) 2009-2015  Tomohiro Matsuyama
+
+;; Author: Campbell Barton <ideasman42@gmail.com>
+
+;; URL: https://gitlab.com/ideasman42/emacs-undo-fu-session
+;; Keywords: convenience
+;; Version: 0.1
+;; Package-Requires: ((emacs "24.1"))
+
+;; This program 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 3 of the License, or
+;; (at your option) any later version.
+
+;; This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; This extension provides a way to use undo history of
+;; individual file buffers persistently.
+;;
+;; Write the following code to your .emacs:
+;;
+;; (require 'undo-fu-session)
+;; (global-undo-fu-session-mode)
+;;
+;; Now you can record and recover undo-fu-session by typing
+;; C-x C-s (save-buffer) an C-x C-f (find-file).
+;; And then type C-/ (undo).
+
+;;; Code:
+
+;; ---------------------------------------------------------------------------
+;; Custom variables.
+
+(defgroup undo-fu-session nil
+  "Persistent undo history, stored on disk between sessions."
+  :group 'convenience)
+
+(defcustom undo-fu-session-directory
+  (locate-user-emacs-file "undo-fu-session" ".emacs-undo-fu-session")
+  "A directory being stored undo history files."
+  :group 'undo-fu-session
+  :type 'string)
+
+(defcustom undo-fu-session-compression t
+  "Store files compressed."
+  :group 'undo-fu-session
+  :type 'boolean)
+
+(defcustom undo-fu-session-incompatible-files '()
+  "List of regexps or functions for matching file names to ignore for undo 
session."
+  :group 'undo-fu-session
+  :type '(repeat (choice regexp function)))
+
+(defcustom undo-fu-session-incompatible-major-modes nil
+  "List of major-modes in which saving undo history should not be performed."
+  :type '(repeat symbol)
+  :group 'undo-fu-session)
+
+(defcustom undo-fu-session-file-limit nil
+  "Number of files to store, nil to disable limiting entirely.
+
+Enforcing removes the oldest files."
+  :type 'integer
+  :group 'undo-fu-session)
+
+
+;; ---------------------------------------------------------------------------
+;; Undo Encode/Decode Functionality
+
+(defun undo-fu-session--walk-tree (fn tree)
+  "Operate recursively on undo history, calling FN TREE."
+  (cond
+    ((consp tree)
+      (let ((value (funcall fn tree)))
+        (if (eq value tree)
+          (let*
+            (
+              (cons (cons (undo-fu-session--walk-tree fn (car tree)) nil))
+              (cur cons)
+              cdr)
+            (while tree
+              (setq cdr (cdr tree))
+              (if (consp cdr)
+                (let ((next (cons (undo-fu-session--walk-tree fn (car cdr)) 
nil)))
+                  (setcdr cur next)
+                  (setq cur next)
+                  (setq tree cdr))
+                (setcdr cur (undo-fu-session--walk-tree fn cdr))
+                (setq tree nil)))
+            cons)
+          value)))
+    ((vectorp tree)
+      (let ((value (funcall fn tree)))
+        (if (eq value tree)
+          (let*
+            (
+              (length (length tree))
+              (vector (make-vector length nil)))
+            (dotimes (i (1- length))
+              (aset vector i (undo-fu-session--walk-tree fn (aref tree i))))
+            vector)
+          value)))
+    (tree
+      (funcall fn tree))))
+
+(defun undo-fu-session--encode (tree)
+  "Encode `TREE' so that it can be stored as a file."
+  (undo-fu-session--walk-tree
+    (lambda (a)
+      (cond
+        ((markerp a)
+          (cons
+            (if (marker-insertion-type a)
+              'marker*
+              'marker)
+            (marker-position a)))
+        ((overlayp a)
+          `(overlay ,(overlay-start a) ,(overlay-end a)))
+        ((stringp a)
+          (substring-no-properties a))
+        (t
+          a)))
+    tree))
+
+(defun undo-fu-session--decode (tree)
+  "Decode `TREE' so that it can be recovered as undo history."
+  (undo-fu-session--walk-tree
+    (lambda (a)
+      (if (consp a)
+        (cond
+          ((eq (car a) 'marker)
+            (set-marker (make-marker) (cdr a)))
+          ((eq (car a) 'marker*)
+            (let ((marker (make-marker)))
+              (set-marker marker (cdr a))
+              (set-marker-insertion-type marker t)
+              marker))
+          ((eq (car a) 'overlay)
+            (let
+              (
+                (start (cadr a))
+                (end (caddr a)))
+              (if (and start end)
+                (make-overlay (cadr a) (caddr a))
+                ;; Make deleted overlay
+                (let ((overlay (make-overlay (point-min) (point-min))))
+                  (delete-overlay overlay)
+                  overlay))))
+          (t
+            a))
+        a))
+    tree))
+
+(defun undo-fu-session--next-step (list)
+  "Get the next undo step in the list.
+
+Argument LIST compatible list `buffer-undo-list'."
+  (while (car list)
+    (setq list (cdr list)))
+  (while (and list (null (car list)))
+    (setq list (cdr list)))
+  list)
+
+(defun undo-fu-session--list-to-index-map (list index index-step 
step-to-index-hash)
+  "Populate the STEP-TO-INDEX-HASH with LIST element as keys mapping to INDEX 
by INDEX-STEP."
+  (unless (eq list t)
+    (while list
+      (puthash list index step-to-index-hash)
+      (setq index (+ index index-step))
+      (setq list (undo-fu-session--next-step list)))))
+
+(defun undo-fu-session--list-from-index-map (list index index-step 
step-from-index-hash)
+  "Populate the STEP-FROM-INDEX-HASH with INDEX by INDEX-STEP as keys mapping 
to LIST elements."
+  (unless (eq list t)
+    (while list
+      (puthash index list step-from-index-hash)
+      (setq index (+ index index-step))
+      (setq list (undo-fu-session--next-step list)))))
+
+(defun undo-fu-session--equivtable-encode (equiv-table buffer-list 
pending-list)
+  "Convert the EQUIV-TABLE into an alist of buffer list indices.
+Argument BUFFER-LIST typically `undo-buffer-list'.
+Argument PENDING-LIST typically `pending-undo-list'."
+  (let
+    ( ;; Map undo-elem -> index.
+      ;; Negative indices for 'pending-list'.
+      (step-to-index-hash (make-hash-table :test 'eq))
+      (equiv-table-alist (list)))
+
+    (undo-fu-session--list-to-index-map buffer-list 0 1 step-to-index-hash)
+    (undo-fu-session--list-to-index-map pending-list -1 -1 step-to-index-hash)
+
+    (maphash
+      (lambda (key val)
+        (let
+          (
+            (key-num (gethash key step-to-index-hash))
+            (val-num
+              (if (eq t val)
+                t
+                (gethash val step-to-index-hash))))
+          (when (and key-num val-num)
+            (push (cons key-num val-num) equiv-table-alist))))
+      equiv-table)
+    equiv-table-alist))
+
+
+(defun undo-fu-session--equivtable-decode (equiv-table-alist buffer-list 
pending-list)
+  "Convert EQUIV-TABLE-ALIST into a hash compatible with `undo-equiv-table'.
+Argument BUFFER-LIST an `undo-buffer-list' compatible list.
+Argument PENDING-LIST an `pending-undo-list'. compatible list."
+
+  (let*
+    (
+      (equiv-table-length (length equiv-table-alist))
+      ;; Map index -> undo-elem.
+      ;; Negative indices for 'pending-list'.
+      (step-from-index-hash (make-hash-table :test 'eq))
+      (equiv-table-hash (make-hash-table :test 'eq :weakness t :size 
equiv-table-length)))
+
+    (unless (zerop equiv-table-length)
+
+      (undo-fu-session--list-from-index-map buffer-list 0 1 
step-from-index-hash)
+      (undo-fu-session--list-from-index-map pending-list -1 -1 
step-from-index-hash)
+
+      (dolist (item equiv-table-alist)
+        (pcase-let ((`(,key-num . ,val-num) item))
+          (let
+            (
+              (key (gethash key-num step-from-index-hash))
+              (val
+                (if (eq t val-num)
+                  t
+                  (gethash val-num step-from-index-hash))))
+            (puthash key val equiv-table-hash)))))
+    equiv-table-hash))
+
+
+;; ---------------------------------------------------------------------------
+;; Undo Session Limiting Functionality
+
+(defun undo-fu-session--file-limit-enforce ()
+  "Limit the number of session files to the `undo-fu-session-file-limit' 
newest."
+  ;; While errors are highly unlikely in this case,
+  ;; clearing old files should _never_ interfere with other operations,
+  ;; so surround with error a check & error message.
+  (condition-case err_1
+    (when (file-directory-p undo-fu-session-directory)
+      (dolist
+        (file-with-attrs
+          (nthcdr ;; Skip new files, removing old.
+            undo-fu-session-file-limit
+            (sort ;; Sort new files first.
+              (delq
+                nil ;; Non-file.
+                (mapcar
+                  #'
+                  (lambda (x)
+                    (unless (nth 1 x)
+                      x))
+                  (directory-files-and-attributes undo-fu-session-directory t 
nil t)))
+              (lambda (x y) (time-less-p (nth 6 y) (nth 6 x))))))
+        (let ((file (car file-with-attrs)))
+          (condition-case err_2
+            (delete-file file)
+            (error (message "Undo-Fu-Session error deleting '%s' for '%s'" 
err_2 file))))))
+    (error (message "Undo-Fu-Session error limiting files '%s'" err_1))))
+
+;; ---------------------------------------------------------------------------
+;; Undo Save/Restore Functionality
+
+(defun undo-fu-session--make-file-name (filename)
+  "Take the path FILENAME and return a name base on this."
+  (concat
+    (expand-file-name
+      (url-hexify-string (convert-standard-filename (expand-file-name 
filename)))
+      undo-fu-session-directory)
+    (if undo-fu-session-compression
+      ".gz"
+      ".el")))
+
+(defun undo-fu-session--match-file-name (filename test-files)
+  "Return t if FILENAME match any item in TEST-FILES."
+  (catch 'found
+    (dolist (matcher test-files)
+      (when
+        (if (stringp matcher)
+          (string-match matcher filename)
+          (funcall matcher filename))
+        (throw 'found t)))))
+
+(defun undo-fu-session--recover-buffer-p (buffer)
+  "Return t if undo history of BUFFER should be recovered."
+  (let
+    (
+      (filename (buffer-file-name buffer))
+      (test-files undo-fu-session-incompatible-files)
+      (test-modes undo-fu-session-incompatible-major-modes))
+    (cond
+      ((null filename)
+        nil)
+      ((and test-files (undo-fu-session--match-file-name filename test-files))
+        nil)
+      ((and test-modes (memq (buffer-local-value 'major-mode buffer) 
test-modes))
+        nil)
+      (t
+        t))))
+
+(defun undo-fu-session--save-impl ()
+  "Internal save logic, resulting in t on success."
+  (let
+    (
+      (buffer (current-buffer))
+      (filename (buffer-file-name))
+      (undo-file nil)
+      (content-header nil)
+      (content-data nil)
+
+      ;; Quiet compression messages for 'with-auto-compression-mode'.
+      (jka-compr-verbose nil))
+
+    (catch 'exit
+      ;; No need for a message, exit silently since there is nothing to do.
+      (unless (undo-fu-session--recover-buffer-p buffer)
+        (throw 'exit nil))
+
+      (unless (or (consp buffer-undo-list) (consp pending-undo-list))
+        (throw 'exit nil))
+
+      (setq content-header `((buffer-size . ,(buffer-size)) (buffer-checksum . 
,(sha1 buffer))))
+      (setq content-data
+        `
+        ((emacs-pending-undo-list . ,(undo-fu-session--encode 
pending-undo-list))
+          (emacs-buffer-undo-list . ,(undo-fu-session--encode 
buffer-undo-list))
+          (emacs-undo-equiv-table
+            .
+            ,
+            (undo-fu-session--equivtable-encode
+              undo-equiv-table
+              buffer-undo-list
+              pending-undo-list)))))
+
+    (when content-data
+      (setq undo-file (undo-fu-session--make-file-name filename))
+
+      ;; Only enforce the file limit when saving new files,
+      ;; this avoids scanning the undo session directory on every successive 
save.
+      (when undo-fu-session-file-limit
+        (unless (file-exists-p undo-file)
+          (undo-fu-session--file-limit-enforce)))
+
+      (with-auto-compression-mode
+        (with-temp-buffer
+          (prin1 content-header (current-buffer))
+          (write-char ?\n (current-buffer))
+          (prin1 content-data (current-buffer))
+          (write-region nil nil undo-file nil 0)
+          t)))))
+
+(defun undo-fu-session-save-safe ()
+  "Public save function, typically called by `before-save-hook'."
+  (when (bound-and-true-p undo-fu-session-mode)
+    (condition-case err
+      (undo-fu-session--save-impl)
+      (error (message "Undo-Fu-Session can not save undo history: %s" err)))))
+
+(defun undo-fu-session-save ()
+  "Save undo history."
+  (interactive)
+  (undo-fu-session-save-safe))
+
+(defun undo-fu-session--recover-impl ()
+  "Internal restore logic, resulting in t on success."
+  (let
+    (
+      (buffer (current-buffer))
+      (filename (buffer-file-name))
+      (undo-file nil)
+      (content-header nil)
+      (content-data nil)
+
+      ;; Quiet compression messages for 'with-auto-compression-mode'.
+      (jka-compr-verbose nil))
+
+    (catch 'exit
+      ;; No need for a message, exit silently since there is nothing to do.
+      (unless (undo-fu-session--recover-buffer-p buffer)
+        (throw 'exit nil))
+
+      (setq undo-file (undo-fu-session--make-file-name filename))
+
+      (unless (file-exists-p undo-file)
+        (throw 'exit nil))
+
+      (with-auto-compression-mode
+        (with-temp-buffer
+          (insert-file-contents undo-file)
+          (goto-char (point-min))
+          (setq content-header (read (current-buffer)))
+
+          (unless (eq (buffer-size buffer) (assoc-default 'buffer-size 
content-header))
+            (message "File length doesn't match, so undo history will be 
discarded.")
+            (throw 'exit nil))
+
+          (unless (string-equal (sha1 buffer) (assoc-default 'buffer-checksum 
content-header))
+            (message "File checksum doesn't match, so undo history will be 
discarded.")
+            (throw 'exit nil))
+
+          ;; No errors... decode all undo data.
+          (setq content-data (read (current-buffer))))))
+
+    (when content-data
+      (let*
+        (
+          (emacs-pending-undo-list
+            (undo-fu-session--decode (assoc-default 'emacs-pending-undo-list 
content-data #'eq t)))
+          (emacs-buffer-undo-list
+            (undo-fu-session--decode (assoc-default 'emacs-buffer-undo-list 
content-data #'eq t)))
+          (emacs-undo-equiv-table
+            (undo-fu-session--equivtable-decode
+              (assoc-default 'emacs-undo-equiv-table content-data #'eq '())
+              emacs-buffer-undo-list
+              emacs-pending-undo-list)))
+
+        ;; Assign undo data to the current buffer.
+        (setq pending-undo-list emacs-pending-undo-list)
+        (setq buffer-undo-list emacs-buffer-undo-list)
+        (if (hash-table-p emacs-undo-equiv-table)
+          (setq undo-equiv-table emacs-undo-equiv-table)
+          (clrhash undo-equiv-table))
+        t))))
+
+(defun undo-fu-session-recover-safe ()
+  "Public restore function, typically called by `find-file-hook'."
+  (when (bound-and-true-p undo-fu-session-mode)
+    (condition-case err
+      (undo-fu-session--recover-impl)
+      (error (message "Undo-Fu-Session can not recover undo history: %s" 
err)))))
+
+(defun undo-fu-session-recover ()
+  "Recover undo history."
+  (interactive)
+  (undo-fu-session-recover-safe))
+
+;; ---------------------------------------------------------------------------
+;; Define Minor Mode
+;;
+;; Developer note, use global hooks since these run before buffers are loaded.
+;; Each function checks if the local mode is active before operating.
+
+(defun undo-fu-session-mode-enable ()
+  "Turn on 'undo-fu-session-mode' for the current buffer."
+  (unless (file-directory-p undo-fu-session-directory)
+    (make-directory undo-fu-session-directory t))
+  (add-hook 'before-save-hook #'undo-fu-session-save-safe)
+  (add-hook 'find-file-hook #'undo-fu-session-recover-safe))
+
+(defun undo-fu-session-mode-disable ()
+  "Turn off 'undo-fu-session-mode' for the current buffer."
+  (remove-hook 'before-save-hook #'undo-fu-session-save-safe t)
+  (remove-hook 'find-file-hook #'undo-fu-session-recover-safe t))
+
+(defun undo-fu-session-mode-turn-on ()
+  "Enable command `undo-fu-session-mode'."
+  (undo-fu-session-mode 1))
+
+;;;###autoload
+(define-minor-mode undo-fu-session-mode
+  "Toggle saving the undo history in the current buffer (Undo-Fu Session 
Mode).."
+  :global nil
+
+  (cond
+    (undo-fu-session-mode
+      (undo-fu-session-mode-enable))
+    (t
+      (undo-fu-session-mode-disable))))
+
+;;;###autoload
+(define-globalized-minor-mode
+  global-undo-fu-session-mode
+  undo-fu-session-mode
+  undo-fu-session-mode-turn-on)
+
+(provide 'undo-fu-session)
+;;; undo-fu-session.el ends here