Exit Emacs Calendar without having to save the diary file

Question

When I create appointments in Emacs diary via the calendar, I have to save changes to the diary file before being able to exit the calendar. I have tried to set up Emacs to automatically save the diary file once changes have been made with this code:

(add-hook 'diary-mode-hook
          (lambda ()
            (add-hook 'auto-save-hook 'diary-show-all-entries nil t)
            (auto-save-mode)))

However, hitting q in calendar still prompts me with these words:

Diary modified; do you really want to exit the calendar? (y or n) 

This from calendar.el:

(defun calendar-exit (&optional kill)
  "Get out of the calendar window and hide it and related buffers."
  (interactive "P")
  (let ((diary-buffer (get-file-buffer diary-file))
        (calendar-buffers (calendar-buffer-list)))
    (when (or (not diary-buffer)
              (not (buffer-modified-p diary-buffer))
              (yes-or-no-p
               "Diary modified; do you really want to exit the calendar? "))
      (if (and calendar-setup (display-multi-frame-p))
          ;; FIXME: replace this cruft with the `quit-restore' window property
          (dolist (w (window-list-1 nil nil t))
            (if (and (memq (window-buffer w) calendar-buffers)
                     (window-dedicated-p w))
                (if (eq (window-deletable-p w) 'frame)
            (if calendar-remove-frame-by-deleting
            (delete-frame (window-frame w))
              (iconify-frame (window-frame w)))
          (quit-window kill w))))
        (dolist (b calendar-buffers)
          (quit-windows-on b kill))))))

I would like to be able to save the diary file automatically and exit calendar without confirmation.

Answer 1

Here's a (lightly tested) implementation along the lines in the comments:

(defun my/save-diary-before-calendar-exit (_)
   (let ((diary-buffer (get-file-buffer diary-file)))
        (or (not diary-buffer)
            (not (buffer-modified-p diary-buffer))
            (with-current-buffer diary-buffer (save-buffer)))))

(advice-add 'calendar-exit :before #'my/save-diary-before-calendar-exit)

The tests are cribbed from calendar-exit itself: get the buffer of the diary file and if the buffer exists and is modified, save it.

If you want to make this permanent, you need to add the code above to your init file.

And if at any point you want to remove the advice, say:

(advice-remove 'calendar-exit #'my/save-diary-before-calendar-exit)