Undo Fu

Simple, stable linear undo with redo for Emacs.

This is a light weight wrapper for Emacs built-in undo system, adding convenient undo/redo without losing access to the full undo history, allowing you to visit all previous states of the document if you need.

The changes compared Emacs undo are as follows:

• Redo will not pass the initial undo action.
• Redo will not undo (unlike Emacs redo which traverses previous undo/redo steps).
• These constraints can be temporarily disabled by pressing C-g before undo or redo.

Note that this doesn't interfere with Emacs internal undo data, which can be error prone.

Available via melpa.

Motivation

The default Emacs undo has two limitations this package aims to resolve,

• Two actions are required to initiate redo.
• It's easy to accidentally redo past the point where undo started making it inconvenient to restore the document to the point when undo began.

Usage

This package exposes the following functions:

• undo-fu-only-undo
• undo-fu-only-redo
• undo-fu-only-redo-all
• undo-fu-disable-checkpoint (only needed when undo-fu-ignore-keyboard-quit is in use).
• undo-fu-clear-all clear all undo/redo history.

Key Bindings

You will need to map these to keys yourself.

Key binding example for typical Ctrl-Z, Ctrl-Shift-Z keys:

(global-unset-key (kbd "C-z"))
(global-set-key (kbd "C-z")   'undo-fu-only-undo)
(global-set-key (kbd "C-S-z") 'undo-fu-only-redo)

Evil mode now supports undo-fu, setting evil-undo-system to 'undo-fu uses evil-modes default bindings.

Customization

undo-fu-allow-undo-in-region (nil)

This option exists for users who prefer to trade-off undo/redo functionality with the ability to limit undo to a region.

When non-nil, undoing with a selection will use undo within this region.

undo-fu-ignore-keyboard-quit (nil)

Don't use Ctrl-G (keyboard-quit) for non-linear behavior, instead, use the undo-fu-disable-checkpoint command.

This was added for users who prefer to explicitly activate this behavior. As keyboard-quit may be used for other reasons.

Details

• Holding the undo-key undoes all available actions.

• Holding the redo-key redoes all actions until the first undo performed after an edit.

• Redoing beyond this point is prevented, as you might expect since this is how undo/redo normally works, this means you can conveniently hold the redo key to reach the newest state of the document.

  If you want to keep redoing past this point you're prompted to press Ctrl-G (keyboard-quit), then you can continue to redo using Emacs default behavior until a new chain of undo/redo events is started.

Limitations

The feature undo-in-region is disabled by default.

Installation

The package is available in melpa as undo-fu.

(use-package undo-fu)

Combined with key bindings:

(use-package undo-fu
  :config
  (global-unset-key (kbd "C-z"))
  (global-set-key (kbd "C-z")   'undo-fu-only-undo)
  (global-set-key (kbd "C-S-z") 'undo-fu-only-redo))

Evil Mode

Evil mode can be configured to use undo-fu by default.

(use-package evil
  :init
  (setq evil-undo-system 'undo-fu))

(use-package undo-fu)

Hints

Undo Limits

The default undo limits for emacs are quite low _(0.15mb at time of writing)_ undo-tree for example increases these limits.

On modern systems you may wish to use much higher limits.

This example sets the limit to 64mb, 1.5x (96mb) for the strong limit and 10x (960mb) for the outer limit. Emacs uses 100x for the outer limit but this may be too high when using increased limits.

(setq undo-limit 67108864) ; 64mb.
(setq undo-strong-limit 100663296) ; 96mb.
(setq undo-outer-limit 1006632960) ; 960mb.

Other Packages

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

Undo Fu Session

This package is intended for use with undo-fu, as a way to save and restore undo sessions, even after restarting Emacs.

Undohist

This packages stores undo data between sessions, while it is compatible with undo-fu on a basic level, it doesn't store redo information (undo-fu-session is an improved alternative).

Undo Tree

This package handles undo steps as a tree by re-implementing parts of Emacs undo internals.

Undo-Fu was written to be a simpler alternative as Undo Tree had long standing unresolved bugs at the time of writing.

Vundo

This package supports navigating undo as a tree structure and works well with undo-fu & undo-fu-session, there are no inter-dependencies as both packages operate on Emacs built-in undo.