Canonical way of getting all Org tags?

[Eric Abrahamsen <eric@ericabrahamsen.net>]

Hi all,

I've got a "tags" field for contacts in EBDB (a contact management
package) where I'd like to offer completion on Org tags, so users can
tag any of their contacts using their Org tags.

Previously I was providing completion using the
`org-global-tags-completion-table' function, which Worked For Me™
because I define my tags via use in agenda files, not using
`org-tag-alist' or `org-tag-persistent-alist'. I didn't realize that
that function didn't consult those options.

What's the canonical way of getting a table of all the user's
tags, whether defined manually or used in the agenda files?

I guess I could do:

(org--tag-add-to-alist
 (org--tag-add-to-alist
  (org-global-tags-completion-table)
  org-tag-alist)
 org-tag-persistent-alist)

But that is ugly, and uses a double-dash interior function.

Any recommendations?

TIA,
Eric