I've been able to implement the functionality I wanted using a buffer-local
variable in an org-mode hook:
>
> (defun bl/completion-use-ido ()
>   "Set the current buffer's completing read engine to IDO."
>   (setq-local completing-read-function #'ido-completing-read))

(add-hook 'org-mode-hook 'bl/completion-use-ido)


I think that works for me, but I'm open to a better suggestion if there is
one. In any case, I think re-enabling the functionality that was removed
with the "org-completion-use-ido" function should be documented somewhere.

On Fri, Aug 24, 2018 at 9:46 PM ben lamothe <zonotope@gmail.com> wrote:

> Hi. I see from the org-mode 9.0 changelog
> <https://orgmode.org/Changes_old.html> that the "org-completion-use-ido"
> option was removed:
>
>> *Remove all options related to ido or iswitchb*
>> This includes org-completion-use-iswitchb and org-completion-use-ido.
>> Instead Org uses regular functions, e.g., completion-read so as to let
>> those libraries operate.
>
>
> However, I'm unclear from the changelog and I haven't found any other
> documentation about how to restore the functionality that this option used
> to enable. I have tried ido-completing-read-plus/ido-ubiquitous
> <https://github.com/DarwinAwardWinner/ido-completing-read-plus>, but that
> is overkill because it tries to enable ido everywhere, but I just want to
> re-enable ido for org-mode completion (mainly refile). I also run into the
> same problem if I try to set the completing read function to the one from
> ido globally.
>
> What is the best way to restore the functionality of the now removed
> "org-completion-use-ido" option?
>