Emacs hashtags (#tagsLikeThisOne) autocompletion

Question

I hashtag notes that I take with Emacs while I read books, articles, etc - humanities, mostly. I would like to know if Emacs can automatically build a list of hashtags that I enter (in a separate file, probably)? Also, can Emacs - reading from this hypothetical list - offer an incremental (or tab) autocompletion when I start to type the hashtag. I need this feature in order to have a consistent tagging.

Thanx!

Answer 1

You can use the Exuberant ctags to generate the TAGS file. For instance, if your notes are in Org mode, you can do this:

(require 'org-ctags)
(setq org-ctags-path-to-ctags "/path/to/ctags")

;; Regular expression for the hashtags.
;; Nnote that this would remove the existing definition and effectively disable 
;; the standard use of org-ctags which is to tag <<links>>. If you want to preserve old
;; behavior you need to combine the two regexes.
(setq org-ctags-tag-regexp "/(#[^+]+)/\\1/d,definition/")

(org-ctags-create-tags "directory")

Now you can use org-ctags-find-tag-interactive to search the tags which claims to have autocompletion:

(add-hook 'org-mode-hook
    (lambda ()
      (define-key org-mode-map "\C-co" 'org-ctags-find-tag-interactive)))

but I prefer Helm completion, so I just do M-x helm-etags-select. You can also ignore the org-ctags and build the TAGS yourself:

 ctags --langdef=orgmode --langmap=orgmode:.org
       --regex-orgmode="/(#[^+]+)/\1/d,definition/"
       -f /your/path/TAGS -e -R /your/path/*.org

(or create a convenience emacs function that does that for you).

Answer 2

An alternative: You can bookmark such notes. And if you use Bookmark+ then you can tag bookmarks.

You can use as many tags as you like for a bookmark, and the tags can be any strings (they can even have associated Lisp values). Bookmarks (tagged or not) are not visible in the bookmarked text, by default. But (with Bookmark+) you can have them be highlighted in various ways.