Using jj from Emacs

As I’m starting to use jj more and more, it’s inevitable that I’m going to want some integration between jj and Emacs. There are many packages already available that do this, including but not limited to

• jujutsu.el

• jj-mode

• vc-jj

However, I want to use this as an excuse to learn how to write my own extensions/utilities for Emacs.

emacs/init.el

(use-package alc-jj)

eshell helpers

I’m trying to use eshell more and more, it’s very cool being able to seamlessly switch between regular shell commands like cd, ls etc. and calling Emacs functions like find-file or compile!

So, after seeing this episode of Álvaro Ramírez’s Bending Emacs series I’ve been eager to find an excuse to try it out.

jj-diff

Rather than dumping the output of jj diff into the eshell window, wouldn’t it be great to redirect it to a dedicated buffer instead?

What, like this?

$ jj diff --no-pager --color never > #<buffer *jj-diff*>

Well, yes but that’s a lot to type, plus the buffer is created uses fundamental-mode it would be nice to have it automatically enable diff-mode at least. A better option would be to define my own eshell command that wrapped the underlying jj command to handle this for me.

emacs/lisp/alc-jj.el

(defun eshell/jj-diff (&rest args)
  "Eshell wrapper around 'jj diff'"
  (let ((current-dir default-directory))
    (with-current-buffer (get-buffer-create "*jj-diff*")
      ;; Ensure the command uses the current directory from where the command was invoked.
      (setq default-directory current-dir)

      ;; Clear any previous content
      (read-only-mode -1)
      (erase-buffer)

      ;; Call jj, insert output into current buffer
      (call-process "jj" nil t nil "diff" "--no-pager" "--color" "never")
      (diff-mode)

      ;; Re-enable read-only mode and show the buffer
      (read-only-mode)
      (pop-to-buffer (current-buffer)))))

emacs/lisp/alc-jj.el

(provide 'alc-jj)