Re: eldoc-mode suspend Emacs for about 20 seconds when point moved on `pcase`

[Stefan Monnier via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org>]

> When I move point on Elisp code where is `(pcase|`. (The | represent the point)
> This issue happened every time when I move point on `pcase`.
> Here is the profiler report of CPU and Memory:

[ Can you reproduce it on purpose in a fresh Emacs session?
  If so, please file a bug report for it.  ]

> CPU Profiler Report
> #+begin_example
>        15205  89% - timer-event-handler
>        15205  89%  - apply
>        15170  88%   - #<byte-code-function 022>
>        15170  88%    - eldoc-print-current-symbol-info
>        15170  88%     - eldoc--invoke-strategy
>        15170  88%      - eldoc-documentation-default
>        15170  88%       - run-hook-wrapped
>        15170  88%        - #<byte-code-function 0D6>
>        15170  88%         - elisp-eldoc-funcall
>        15159  88%          - apply
>        15159  88%           - elisp-get-fnsym-args-string
>        15158  88%            - documentation
>        15158  88%             - pcase--make-docstring
>        15042  88%              - help-fns-short-filename
>        15019  87%               - file-relative-name
>        14867  87%                  file-name-case-insensitive-p

Hmm...

There are several inefficiencies at the level of `pcase--make-docstring`
(designed to generate the occasional *Help* buffer rather than the
on-the-fly eldoc info) as well as `help-fns-short-filename`, but the
costly operations are not supposed to be `file-name-case-insensitive-p`.

If on some systems `file-name-case-insensitive-p` can be slow, maybe we
should add some caching mechanism to it?


        Stefan