I use Emacs as my editor to compose Git commit messages. I almost never commit from the terminal with git commit -m. This approach has two advantages: I get a chance to verify what is being committed and get to compose the message using a proper editor complete with spell checking provided by flyspell mode. One thing I wish I had access to while composing commit messages is the git log. This is useful to refer to work items and encourages one to use a consistent style in the messages. This was easier in the terminal as one could do something like git log -n 3 and then commit with the -m flag.

I decided to fix this today and some tinkering later came up with a hack tp do this.

  • Git commit messages are stored in the COMMIT_EDITMSG file under .git/. So the first thing to do is to ensure that this file always gets loaded with a custom minor mode. This can be done as follows:
(add-to-list 'auto-mode-alist '("\\COMMIT_EDITMSG\\'" . load-magit-log-when-committing-mode))

The minor mode does not need to do anything. The definition would be like this:

(define-minor-mode load-magit-log-when-committing-mode
  "dummy")
  • Next step is to add a custom hook that gets run after loading the minor mode. This hook calls the function to load git logs. The code for this is:
(add-hook 'load-magit-log-when-committing-mode-hook 'show-magit-log-hook)
  • The actual function to load git logs. It calls magit-log to load the logs and then opens the original COMMIT_EDITMSG in the other frame.
(defun show-magit-log-hook ()
  (cd "..")
  (magit-log)
  (switch-to-buffer-other-window "COMMIT_EDITMSG"))

This is how Emacs looks while committing with this hack in place:

"Screenshot showing git commit log"

If you want to use this, copy the following snippet to your init.el.

;; load-magit-log-when-committing-mode
(define-minor-mode load-magit-log-when-committing-mode
  "dummy")

;; the hook
(defun show-magit-log-hook ()
  (cd "..")
  (magit-log)
  (switch-to-buffer-other-window "COMMIT_EDITMSG"))

;; add the hook
(add-hook 'load-magit-log-when-committing-mode-hook 'show-magit-log-hook)

;; load the mode for commit message
(add-to-list 'auto-mode-alist '("\\COMMIT_EDITMSG\\'" . load-magit-log-when-committing-mode))

If you have questions or comments about this blog post, you can get in touch with me on Twitter @sdqali.

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