bug#64735: 29.0.92; find invocations are ~15x slower because of ignores

[Po Lu]

Spencer Baugh <sbaugh@janestreet.com> writes:

> Not to derail too much, but find as a subprocess has one substantial
> advantage over find in Lisp: It can run in parallel with Emacs, so that
> we actually use multiple CPU cores.
>
> Between that, and the remote support part, I personally much prefer find
> to be a subprocess rather than in Lisp.  I don't think optimizing
> directory-files-recursively is a great solution.
>
> (Really it's entirely plausible that Emacs could be improved by
> *removing* directory-files-recursively, in favor of invoking find as a
> subprocess: faster, parallelized execution, and better remote support.)

find is only present in the default installations of Unix-like systems,
so it doesn't work without additional configuration on MS-Windows or
MS-DOS.  project.el and rgrep fail to work on USG Unix because they both
use `-path'.

Programs that use find should fall back to directory-file-recursively
when any of the situations above are detected.