emacs:rename-buffer-file

gistfile1.sls

(defun rename-buffer-file (newname &optional ok-if-already-exists)
  "rename visited file (buffer-file-name) to NEWNAME
and appropriately change buffer name (set-visited-file-name NEWNAME).
NEWNAME must be string.

Signals a `file-already-exists' error if a file NEWNAME already exists
unless optional third argument OK-IF-ALREADY-EXISTS is non-nil.
A number as third arg means request confirmation if NEWNAME already exists.
This is what happens in interactive use with M-x."
  (interactive "FRename to: \np")
  (let ((file (buffer-file-name)))
    (when file
      (message "Rename buffer file %s to %s" file newname)
      (rename-file file newname ok-if-already-exists)
      (set-visited-file-name newname))))