Testing your .emacs sanity

Here's a little snippet that came up as a Stack Overflow answer once:

(defun ora-test-emacs ()
  (interactive)
  (require 'async)
  (async-start
   (lambda () (shell-command-to-string
          "emacs --batch --eval \"
(condition-case e
    (progn
      (load \\\"~/.emacs\\\")
      (message \\\"-OK-\\\"))
  (error
   (message \\\"ERROR!\\\")
   (signal (car e) (cdr e))))\""))
   `(lambda (output)
      (if (string-match "-OK-" output)
          (when ,(called-interactively-p 'any)
            (message "All is well"))
        (switch-to-buffer-other-window "*startup error*")
        (delete-region (point-min) (point-max))
        (insert output)
        (search-backward "ERROR!")))))

This function will quietly run a batch Emacs with your current config to see if it errors out or not.

• in case that there were no start up errors, it will echo "All is well"
• when there's an error, it will pop to a *startup error* buffer with the error description

The nice thing about this is that in case of an error you have a functional Emacs to fix that error, since fixing errors with emacs -Q is quite painful.

Another approach could be to just start a new Emacs instance, and close the window in case there isn't an error. So all that the code above does is automate closing the window (sort of, since the window never opens). Still, I think it's pretty cool. And you could attach it to the after-save-hook of your .emacs, or a timer.

You could even configure Emacs to send you an email in case it notices that there will be an error on the next start up. Or add the test to before-save-hook and abort the save in case it results in an error. That's some HAL 9000 level stuff right there:

I'm sorry Dave, I'm afraid I can't do that.