>>> I can't find a standard way of doing this.  So instead of using eval-and-compile
>>> I'll try to recalculate the value explicitly when variables are customized:
>>>
>>>   (when (or (get 'char-fold-include-base  'customized-value)
>>>             (get 'char-fold-include-alist 'customized-value)
>>>             (get 'char-fold-exclude-alist 'customized-value))
>>>     (setq char-fold-table (char-fold-make-table)))
>>
>> Instead of looking at symbol property values, which can make for a
>> confusing time when setting variables outside of customize, I think it
>> would be nicer to do something like this:
>>
>>     (defcustom char-fold-include-base char-fold--include-base-default
>>       :initialize #'custom-initialize-changed
>>       :set (lambda (sym val)
>>              (set-default sym val)
>>              ;; FIXME: Maybe delay this until after-init-time,
>>              ;; to avoid redundant calls to char-fold-make-table.
>
> I tried different possible values of :initialize,
> but not custom-initialize-changed.  I'll try this now.

I see no problems other than redundant calls to char-fold-make-table
when more than one variable is customized.  char-fold.el is autoloaded
when isearch calls char-fold-to-regexp for the first time, so I'm not
sure how after-init-hook could help in this case.