Variable: find-file-existing-other-name
find-file-existing-other-name is a customizable variable defined in
files.el.gz.
Value
t
Documentation
Non-nil means find a file under alternative names, in existing buffers.
This means if any existing buffer is visiting the file you want under another name, you get the existing buffer instead of a new buffer.
Probably introduced at or before Emacs version 19.20.
Source Code
;; Defined in /usr/src/emacs/lisp/files.el.gz
(defcustom find-file-existing-other-name t
"Non-nil means find a file under alternative names, in existing buffers.
This means if any existing buffer is visiting the file you want
under another name, you get the existing buffer instead of a new buffer."
:type 'boolean
:group 'find-file)