Subject: bug#18512: 24.3.93; tramp persistency file: incompatible with old versions? Tramp won't start!

From: Stefan Monnier <[email-masked]>
Date: Sun, 05 Oct 2014 21:11:00 -0400

>>> ! 	   (string-match-p
>>> ! 	    (format "/%s/?\\'"
>>> ! 		    (regexp-quote
>>> ! 		     (file-name-nondirectory
>>> ! 		      (directory-file-name user-emacs-directory)))) dir)
>>> (string-equal (file-name-as-directory (expand-file-name dir))
>>> (expand-file-name user-emacs-directory))
>>> (setq warned t)
>> Why not simply remove the (string-match-p "/[._]emacs\\.d/?\\'" dir) test?
> It may have been a pointless attempt to avoid statting the file-system
> unless it looked like it was going to be needed. (Does expand-file-name
> even do that?)

No, expand-file-name doesn't touch the file-system.  And neither does
file-name-as-directory.  These are just string operations.
Using file-equal-p would, OTOH.

        Stefan