Is it possible to retain outline overlay when switching modes

Question

I want to switch between org-mode and c++-mode on top of a single file. I use org-mode syntax inside c++ comment blocks. In Org-mode I have foldable sections while in c++-mode I use hide/show for blocks. When switching mode the outline overlay is reset and everything is made visible. Is it possible to somehow prevent this and retain the visibility state?

Answer 1

I ended up using https://github.com/ShingoFukuyama/ov.el and syncing org-mode and c++-mode overlays. When switching between modes I replicate the other buffer's invisible overlays. This is done on every mode switch: (add-hook 'multi-select-mode-hook 'sync-buffer-overlays)

(require 'ov)

(defun get-org-buffer ()
  (cdr (assoc 'org-mode  multi-indirect-buffers-alist)))
(defun get-c++-buffer ()
  (cdr (assoc 'c++-mode  multi-indirect-buffers-alist)))

;; exclude the overlays marked with `ismultimode' from overlay list of buffer `buf'                                                                                                                                                                                       
(defun get-real-ov (buf)
  (let ((org-ov))
    (with-current-buffer buf
      (setq org-ov (seq-remove (lambda (x) (ov-val x 'ismultimode )) (ov-all))))
    org-ov))

;; remove all overlays marked with `ismultimode' from buffer                                                                                                                                                                                                              
(defun clean-intermediate-overlays (buf)
  (with-current-buffer buf
      (dolist (e (ov-all))
        (if (ov-val e 'ismultimode )
            (ov-reset e)))))

(defun sync-buffer-overlays ()
  (interactive)
  (let ((org-buf (get-org-buffer))
        (c++-buf (get-c++-buffer))
        (org-ov)
        (c++-ov)
        )

    (clean-intermediate-overlays c++-buf)
    (clean-intermediate-overlays org-buf)

    (setq org-ov (get-real-ov org-buf))
    (with-current-buffer c++-buf
      (dolist (e org-ov)
        (let ((beg (ov-beg e))
              (end (ov-end e)))
          (ov beg end '(invisible hs ismultimode t)))
        ))

    (setq c++-ov (get-real-ov c++-buf))
    (with-current-buffer org-buf
      (dolist (e c++-ov)
        (let ((beg (ov-beg e))
              (end (ov-end e)))
          (ov beg end '(invisible outline ismultimode t)))
        ))
    )
  )