You seem pretty sure, that it isn't. 

Ap

<div>-------- Ursprüngliche Nachricht --------</div><div>Von: Stefan Monnier <monnier@IRO.UMontreal.CA> </div><div>Datum:05.11.2017  16:05  (GMT+01:00) </div><div>An: emacs-devel@gnu.org </div><div>Cc: Andreas Politz <politza@hochschule-trier.de> </div><div>Betreff: Re: [Emacs-diffs] master d3233b4: Make filecache use extended completion </div><div>
</div>> +          (let* ((completion-list (completion-all-completions
> +                                   newstring file-cache-alist nil newpoint))
> +                 (base-size       (cdr (last completion-list))))
> +            (when base-size
> +              (setcdr (last completion-list) nil))
> +            (if (> (length completion-list) 1)
> +                (progn
> +                  (delete-region (- (point-max) (length string)) (point-max))
> +                  (save-excursion (insert newstring))
> +                  (forward-char newpoint)
> +                  ;; Add our own setup function to the Completions Buffer
> +                  (let ((completion-setup-hook
> +                         (append completion-setup-hook
> +                                 (list 'file-cache-completion-setup-function))))
> +                    (with-output-to-temp-buffer file-cache-completions-buffer
> +                      (display-completion-list
> +                       (completion-hilit-commonality completion-list newpoint)))))

IIRC completion-all-completions already returns hilited strings (and
done with more care than what completion-hilit-commonality can do).
So is this completion-hilit-commonality call still beneficial?


        Stefan