Philip Kaludercic <philipk@posteo.net> writes:

> Mauro Aranda <maurooaranda@gmail.com> writes:
>
>>
>> I haven't watch this thread closely, but do note that creating dynamic
>> choices is quite possible, if I understand correctly what you're looking
>> for.
>>
>> If you can, take a look at the defcustom of completion-styles, in
>> minibuffer.el.  Its type uses a choice with a specialized
>> :convert-widget function to keep the choices up-to date.
>
> This might be exactly what we are looking for.  It should be possible to
> adapt `completion--update-styles-options' pretty much directly to our
> example.

Mauro, thanks for the great tip.  As Philip said, this seems to be
exactly what we need here.  Accordingly, I'm attaching an updated patch for the
`defcustom` types (the two other patches from my previous message are
not affected and remain applicable).