Emacs Lisp: Rename both current buffer and file it is visiting.

rename-buffer-and-file.el

;; Language: Emacs Lisp (elisp)
;; Description: Rename both current buffer and file it is visiting.
;; Author: James Cherti
;; License: MIT
;; URL: https://gist.github.com/jamescherti/fc1054ce24606c4574cfa41d1ed67412

(defun rename-buffer-and-file ()
  "Rename both current buffer and file it is visiting."
  (interactive)
  (let* ((bufname (buffer-name))
         (filename (buffer-file-name))
         (basename (file-name-nondirectory filename)))
    (unless filename
      (error "The buffer with the name '%s' is not visiting a file." bufname))
    (unless (file-exists-p filename)
      (error "The file '%s' cannot be found on the disk." filename))
    (let ((new-basename (read-string "New name: " basename)))
      (when (not (string= basename new-basename))
        (save-buffer)
        (rename-file filename new-basename 1)
        (set-visited-file-name new-basename)))))