;; Improvements:
;; - Link back to the task?
;; - Make it possible to have your note on another page?
(defun sacha/planner-create-note-from-task ()
  "Create a note based on the current task."
  (interactive)
  (let* ((task-info (planner-current-task-info))
         note-num)
    (when task-info
      (setq note-num (planner-create-note (planner-page-name)))
      (save-excursion
        (save-window-excursion
          (when (planner-find-task task-info)
            (planner-edit-task-description
             (concat (planner-task-description task-info) " "
                     (planner-make-link
                      (concat (planner-page-name) "#"
                              (number-to-string note-num))
                      "..."))))))
      (insert (planner-task-description task-info) "\n\n"))))

;; I use F9 p to go to today's page, anyway.
(define-key planner-mode-map (kbd "C-c C-n") 'sacha/planner-create-note-from-task)

../emacs/planner-config.el