bug#12796: Optimize `ido-completing-read' for larger lists with flex matching enabled

[Stefan Monnier]

> -      (setq re (mapconcat #'regexp-quote (split-string ido-text "") ".*"))
> +      (setq re (mapconcat #'regexp-quote (split-string ido-text "" t)
> ".*"))

Sounds like a good change.  Tho:

   (mapconcat (lambda (c) (regexp-quote (string c))) ido-text ".*")

would work as well.
You could try to speed up the regexp matching some more by eliminating
backtracking (which should mostly eliminate a few pathological cases):

   (let ((first t))
     (mapconcat (lambda (c)
                  (if first
                      (progn (setq first nil) (regexp-quote (string c)))
                    (concat "[^" (string c) "]*"
                            (regexp-quote (string c)))))
                ido-text ""))

> I'm still going to see if I can make while-no-input work here, though.

Yes, that'd be very welcome.


        Stefan