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).

Available via melpa.

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, 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.

(undo-fu-session-global-mode)

Enable (Buffer)

If you want to isolate this functionality, you can enable this using a mode hook for e.g.

;; Only use undo-fu-session for org mode.
(add-hook 'org-mode-hook #'undo-fu-session-mode)

Customization

undo-fu-session-directory: "undo-fu-session" in emacs user directory

The location of stored files.

undo-fu-session-linear: nil

Write linear undo history, omitting branches which were themselves undone.

Note that this only writes undo steps which would be used by undo-only.

undo-fu-session-compression: 'gz

Compression setting for stored undo data.

Valid options:

• 'bz2 BZip2.
• 'gz ZLib.
• 'xz XZ.
• 'zst Z-standard.
• nil (no compression).

After changing, run undo-fu-session-compression-update to convert existing files to the newly selected format.

undo-fu-session-file-limit: nil

Number of files to store, nil to disable limiting entirely.

Enforcing removes the oldest files.

Customization (Exclusions)

There are various methods of excluding undo-session storage, this may be done to prevent storing sensitive information or to prevent unnecessary storage of undo-session for temporary files (such as commit messages).

These exclusion options allow undo-fu-session-global-mode to be enabled. With exceptions added for cases where undo-session should not be stored.

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.

This matches derived modes so you may include a mode that other modes are derived from to avoid having to explicitly list all modes.

undo-fu-session-ignore-encrypted-files (t)

Ignore saving/recovering undo session for encrypted files (matching epa-file-name-regexp).

undo-fu-session-ignore-temp-files (t)

Ignore saving/recovering undo session for files under temporary-file-directory & undo-fu-session-temp-directories.

undo-fu-session-temp-directories ('("/tmp" "/dev/shm"))

Directories to consider temporary when undo-fu-session-ignore-temp-files is enabled.

Customization (Data Storage)

This is advanced functionality for users who prefer to define their own method of defining the file-system location of undo-fu-session data.

undo-fu-session-make-file-name-function: 'undo-fu-session-make-file-name

This function takes two arguments (filepath extension) and must return a the path where undo data is stored, ending with extension.

If you wish to store undo data next in the same directory as the file being edited this example shows how it can be achieved.

Take care, if you define paths outside of undo-fu-session-directory the following functionality

• undo-fu-session-file-limit isn't applied.
• undo-fu-session-compression-update won't update compression on existing undo data.

This example function stores undo data for ~/file.txt as ~/.#file#.undo-fu-session.gz.

(setq undo-fu-session-make-file-name-function
      (lambda (filepath extension)
        (let* ((filename (file-name-nondirectory filepath))
               (dirpath (substring filepath 0 (- (length filepath) (length filename)))))
          (concat dirpath ".#" filename "#.undo-fu-session" extension))))

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.

Installation

The package is available in melpa as undo-fu-session, here is an example with use-package:

(use-package undo-fu-session
  :config
  (setq undo-fu-session-incompatible-files '("/COMMIT_EDITMSG\\'" "/git-rebase-todo\\'")))

(undo-fu-session-global-mode)

Undo Tree

undo-tree defines it's own undo data-structures and is not compatible with undo-fu-session.

These packages cannot be used together.

Other Packages

As there are multiple packages which deal with undo, it's worth mentioning how this interacts with other packages.

Undo Fu

This package is intended for use with undo-fu-session, as a convenience wrapper over Emacs built-in undo.

Undohist

This package also stores undo data between sessions, however it doesn't store redo data making undo-only and redo-only operations fail to skip branches of undo history.

Vundo

This package supports navigating undo as a tree structure, and works with undo/redo history loaded by undo-fu-session although there are no inter-dependencies as both packages operate on Emacs built-in undo.