Subject: bug#48841: fido-mode is slower than ido-mode with similar settings

From: Dmitry Gutov <[email-masked]>
Date: Sat, 5 Jun 2021 04:39:49 +0300

I'm comparing

   ido-mode
   with ido-ubiquitous-mode (for support for arbitrary completion 
tables), available at 
https://github.com/DarwinAwardWinner/ido-completing-read-plus
   with (setq ido-enable-flex-matching t), of course

versus

  fido-mode
  with
    (setq icomplete-compute-delay 0)
    (setq icomplete-show-matches-on-no-input t)
    (setq icomplete-max-delay-chars 0)

The values chosen for behavior maximally close to ido.

Try something like:

  - Start a session with personal config and a number of loaded packages 
(so that there are a lot of functions defined in obarray)
  - Type 'C-h f'
  - Type 'a', then type 'b'.
  - Delete 'b', type it again, see how quickly you can make the 
completions update.

With ido, the updates seem instant (probably due to some magic in 
ido-completing-read-plus); with fido, there is some lag. Not huge, but 
easy enough to notice.