evil-join amalgamates multiple joins

[panurg]

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Issue type

• Bug report

Environment

Emacs version: GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.34, cairo version 1.16.0) Operating System: NixOS 22.11 (Raccoon) Evil version: 1.15.0 Evil installation type: nixpkgs (2d10e73416ec1449ef74aeac7faf2cf8c556ff5a) + nix community emacs overlay (d17b8b8fc033debb3e75cfc44aaaf8f47d5e04fd) Graphical/Terminal: Wayland Tested in a make emacs session (see CONTRIBUTING.md): No

Prerequisite

evil-mode with undo-redo or undo-fu evil undo system

Reproduction steps

• Insert several lines of text
• Go to the first line by pressing gg
• Join lines by frequently pressing J without moving cursor or doing any other actions
• Undo joining by pressing u several times

Expected behavior

Each line join can be undone one-by-one.

Actual behavior

All line joins are undone simultaneously.

Further notes

If undo-tree is used then undo works as expected. Joins are not amalgamated if there is a delay between them.

I did not find appropriate configuration option (evil-want-fine-undo does not change behavior). I was able to fix that by monkey patching evil-join

  (defun evil--add-undo-boundaries (orig &rest r)
    "Add undo boundaries around command."
    (evil-start-undo-step)
    (apply orig r)
    (evil-end-undo-step))
  (advice-add #'evil-join :around #'evil--add-undo-boundaries)

I am not sure if this is a good fix as I am not familiar with Lisp.

[axelf4]

Caused by delete-char, which is used transitively, unconditionally calling undo-auto-amalgamate. Wow, that is a headache!

Your workaround is fine but

(advice-add #'evil-join :after (lambda (&rest _) (undo-boundary)))

does the same without any unnecessary steps, i.e. it adds an explicit undo boundary, instead of one added implicitly after each command, and that will be removed by undo-auto-amalgamate. Could also just (cl-letf (((symbol-function #'undo-auto-amalgamate) #'ignore)) ...).