How to find a bug in “.emacs” or “init.el”?

Question

Sometimes when I open Emacs, Emacs initialization fail.
That is because .emacs or init.el files have a bug. (My bugs often come from just misty

Answer 1

I'll add it's good to anticipate. The function below, coming from oremacs.com allows to check the validity of our init file (or any other file) without starting up emacs:

(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!")))))

One can even add a Travis CI test.

ps: solutions summed up on wikemacs.