Vundo is now available on ELPA!

Vundo (visual undo) displays the undo history as a tree and lets you
move in the tree to go back to previous buffer states. To use vundo,
type M-x vundo RET in the buffer you want to undo. An undo tree buffer
should pop up. To move around, type:

  f   to go forward
  b   to go backward

  n   to go to the node below when at a branch point
  p   to go to the node above

  a   to go back to the last branching point
  w   to go forward to the next branching point
  e   to go forward to the end/tip of the branch
  l   to go to the last saved node
  r   to go to the next saved node

  m   to mark the current node for diff
  u   to unmark the marked node
  d   to show a diff between the marked (or parent) and current nodes

  q   to quit, you can also type C-g

  C-c C-s (or whatever binding you used for save-buffer)
      to save the buffer at the current undo state

n/p may need some more explanation. In the following tree, n/p can
move between A and B because they share a parent (thus at a branching
point), but not C and D. To make it clear, branches you can switch
between are highlighted with bold face.

         A  C
    ──○━━○──○──○──○
      ┃  ↕︎
      ┗━━○──○──○
         B  D

By default, you need to press RET to “commit” your change and return
to the buffer.  If instead you quit with q or C-g, the changes made by
vundo are rolled back. You can set ‘vundo-roll-back-on-quit’ to nil to
disable rolling back.

You might see some green nodes in the tree, those are the buffer
states that have been saved to disk; the last saved node is emphasized
in bold. You can type "l" to jump to the last saved node.

Note: vundo.el requires Emacs 28.

Customizable faces:

- vundo-default
- vundo-node
- vundo-stem
- vundo-highlight
- vundo-saved
- vundo-last-saved

If you want to use prettier Unicode characters to draw the tree like
this:

    ○──○──○
    │  └──●
    ├──○
    └──○

set vundo-glyph-alist by

    (setq vundo-glyph-alist vundo-unicode-symbols)

Your default font needs to contain these Unicode characters, otherwise
they look terrible and don’t align. You can find a font that covers
these characters (eg, Symbola, Unifont), and set ‘vundo-default’ face
to use that font:

    (set-face-attribute 'vundo-default nil :family "Symbola")

Diff:

Vundo uses Emacs' facilities to provide diffs among arbitrary undo
states: just (m)ark and (d)iff.  By default, vundo's diff window is
buried when vundo quits; see `vundo-diff-quit' for other options.

Terminal users may encounter unwanted control characters in the diff
output.  Emacs colors diff buffers itself, so this can be remedied by
instructing diff not to print color codes:

    (setq diff-switches "-u --color=never")

Comparing to undo-tree:

Vundo doesn’t need to be turned on all the time nor replace the undo
commands like undo-tree does. Vundo displays the tree horizontally,
whereas undo-tree displays a tree vertically.  Diff is provided
on-demand between any nodes.

Tests:

You can run tests by loading test/vundo-test.el and M-x ert RET t RET
to run those tests interactively, or use the following batch command:

     emacs --batch \
           -l vundo.el \
           -l test/vundo-test.el \
           -f ert-run-tests-batch-and-exit


Changelog (full changelog in NEWS.txt):

<2023-02-16 Fri>: Version 2.3.0: navigate among all saved nodes.
Automatically bury the vundo-diff window when vundo quits.

<2023-12-17 Sun>: Version 2.2.0: vundo-diff introduced, supporting
on-demand diff to parent or any marked node.  Improved tree draw
speed.

<2022-04-04 Mon>: Version 1.0.0

<2022-03-29 Tue>: vundo--mode and vundo--mode-map are now vundo-mode
and vundo-mode-map. A new custom option vundo-compact-display is added.

<2022-03-23 Wed>: UI now defaults to ASCII mode. ASCII mode also draws
differently now, it now draws

    o--o--o     instead of      o--o--o
    |  `--x                     |  +--*
    |--o                        |--o
    `--o                        +--o

<2021-11-26 Fri>: Variable vundo-translate-alist changed to
vundo-glyph-alist and has different value now.