bug#73592: 30.0.91; delayed output with completion preview mode

[Eshel Yaron via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Christopher Howard <christopher@librehacker.com> writes:

> Here is the memory profile report, focusing on the completion-preview functions:
>
[...]
>
> And here is the CPU report:
>
> ```
>         1318  53% + command-execute
>          932  37%   Automatic GC
>          200   8% - completion-preview--post-command
>          200   8%  - completion-preview--show
>          200   8%   - completion-preview--try-update
>          200   8%    - completion-preview--update
>          200   8%     - run-hook-wrapped
>          200   8%      - completion-preview--capf-wrapper
>          184   7%       - completion-preview--try-table
>          180   7%        - completion-all-completions
>          180   7%         - completion--nth-completion
>           92   3%          - #<byte-code-function 080>
>           92   3%           - completion--twq-all
>           92   3%            - mapcar
>           88   3%             - #<byte-code-function 011>
>           80   3%              - comint-quote-filename
>           80   3%               - regexp-opt-charset
>           24   0%                - map-char-table
>           16   0%                 - #<byte-code-function 43C>
>           16   0%                    format
>            4   0%                  format
>           88   3%          - seq-some
>           88   3%           - seq-do
>           88   3%            - mapc
>           88   3%             - #<byte-code-function 0BE>
>           88   3%              - #<byte-code-function 0AF>
>           88   3%               - completion-basic-all-completions
>           88   3%                - completion-pcm--all-completions
>           88   3%                 - all-completions
>           88   3%                  - #<byte-code-function 3C8>
>           88   3%                   - #<byte-code-function 3E2>
>           68   2%                      all-completions
>           12   0%                      file-name-all-completions
>            8   0%                    - pcomplete-uniquify-list
>            8   0%                     - sort
>            4   0%                        #<primitive-function string-lessp>
>            4   0%        + minibuffer--sort-by-length-alpha
>           16   0%       + pcomplete-completions-at-point
>           28   1% + redisplay_internal (C function)
>            4   0% + timer-event-handler
>            0   0%   ...
> ```

Thanks, I get a similar profile, but no perceivable delay, so I'm not
sure it helps us pin down the problem that you're seeing.  

The fact that you don't see a delay with emacs -Q is a good lead, please
try to create a minimal configuration that reproduces this for you and
we can investigate from there.

If anybody else experiences such issues (significant delay after typing
a character before it appears), please let us know.


Thanks,

Eshel