Sorry for late reply, here are the benchmark stats.

The result is promising, ‘fd’ is 3x faster than ‘find’.

(benchmark 5 '(project--files-in-directory "~/Workspace/llvm-project" '(".git")))
;;=> "Elapsed time: 9.401258s (0.097027s in 1 GCs)"

(benchmark 5 '(project--files-in-directory-fd "~/Workspace/llvm-project" '(".git")))
;;=> "Elapsed time: 2.759160s (0.105133s in 1 GCs)”

Where `project--files-in-directory’ is the original version in project.el, and `project--files-in-directory-fd’ modified from the previous one for ‘fd’ use.

The definition of `project--files-in-directory-fd’ follows:

(defun project--files-in-directory-fd (dir ignores &optional files)
  (require 'find-dired)
  (require 'xref)
  (defvar find-name-arg)
  (let* ((default-directory dir)
         ;; Make sure ~/ etc. in local directory name is
         ;; expanded and not left for the shell command
         ;; to interpret.
         (localdir (file-local-name (expand-file-name dir)))
         (command (format "%s . %s %s --type f %s --print0"
                          "fd"
                          ;; In case DIR is a symlink.
                          (file-name-as-directory localdir)
                          ""
                          (if files
                              (concat (shell-quote-argument "(")
                                      " " find-name-arg " "
                                      (mapconcat
                                       #'shell-quote-argument
                                       (split-string files)
                                       (concat " -o " find-name-arg " "))
                                      " "
                                      (shell-quote-argument ")"))
                            ""))))
    (message command)
    (project--remote-file-names
     (sort (split-string (shell-command-to-string command) "\0" t)
           #'string<))))

--
Zhiwei Chen