This is an Emacs mode that allows you to store overlays between sessions. This is useful for storing overlays with the invisible property in hideshow and outline modes.
The goal for persistent-overlays is to maintain persistent overlays between emacs sessions. It has been tested with hideshow and outline modes on Linux, Mac OS X and Windows. However, this version should be considered beta software and it has not been previously released.
Overlays are stored in ~/.emacs-persistent-overlays by default. There are several customizable variables which allow a user to change the file naming convention and the storage location of the overlay files.
Please use describe-mode for a full description.
To enable this mode add the following to your ~/.emacs or ~/emacs.d/init.el file. This assumes that you have placed persistent-overlays.el somewhere in your load-path.
(load-library "persistent-overlays")
FWIW - this is what I use in my .emacs:
;; minor modes on by default for all programming modes
(add-to-list 'load-path "~/commonenv/emacs/Emacs-Persistent-Overlays/")
(load-library "persistent-overlays")
(when (not (< emacs-major-version 24))
(add-hook 'prog-mode-hook (lambda () (hs-minor-mode 1) (setq hs-allow-nesting t) (persistent-overlays-minor-mode 1))))
(when (not (> emacs-major-version 23))
(add-hook 'c-mode-hook (lambda () (hs-minor-mode 1) (setq hs-allow-nesting t) (persistent-overlays-minor-mode 1)))
(add-hook 'c++-mode-hook (lambda () (hs-minor-mode 1) (setq hs-allow-nesting t) (persistent-overlays-minor-mode 1)))
(add-hook 'emacs-lisp-mode-hook (lambda () (hs-minor-mode 1) (setq hs-allow-nesting t) (persistent-overlays-minor-mode 1)))
)
Enjoy
This is a minor mode to make overlays persistent by saving them to a file and subsequently loading them. By default overlays are stored in ~/.emacs-persistent-overlays with a file name that is created as a combination of the buffer name and a SHA1 hash of the file name to which they correspond. NOTE: you need to create the directory ~/.emacs-persistent-overlays.
persistent-overlays-directory may be set to indicate a different directory in which to store overlays. If persistent-overlays-use-path-name is set to t, the overlay file is named using the underscore delimited full path of the file instead of using a SHA1 hash. Overlay file names always end with .povly.
persistent-overlays-property-names specifies a list of property symbols that must exist in an overlay for it to be handled by this mode. By default it is set to a list containing the symbol 'invisible so that overlays which hide sections of a buffer are stored. This was the primary motivation for this mode.
If persistent-overlays-auto-save is t all overlays containing properties in persistent-overlays-property-names will be saved in the directory indicated by persistent-overlays-directory when the buffer is saved.
If persistent-overlays-auto-load is t existing overlays for the buffer will be loaded from persistent-overlays-directory when the buffer is loaded or when persistent-overlays-minor-mode is enabled.
If persistent-overlays-auto-merge is t existing overlays for the buffer will be loaded and merged from persistent-overlays-directory when the buffer is loaded and when persistent-overlays-minor-mode is enabled. This is the default behavior which is useful when persistent-overlays-minor-mode is enabled after having created additional overlays.
Other custom variables are persistent-overlays-store-with-user-file, persistent-overlays-store-as-hidden and persistent-overlays-disable-on-major-mode-change. Please use describe-variable for details on those variables.
NOTE: There is currently no mechanism for binding overlay files with the corresponding user files when files are moved. If you wish to retain existing stored overlays you can manually load or merge the overlays from the original overlay file after renaming the user file. You may also want to delete the original overlay file after merging to avoid having unused overlay files lying around. Each overlay file contains the full path name of the file to which it applies as its first line.
If you edit a file outside of Emacs, any stored overlays are potentially invalid due to repositioning of the text. For example, performing a git checkout of a file to restore the master version over an edited version. In this scenario, you may need to expand all hidden overlays and save to overwrite the existing overlays (or exit Emacs, delete the overlay file and restart Emacs).