Add a predicate for canonical file name

[Tino Calancha]

Hi,

i dont see in Emacs a predicate for a file name being canonical.
We have a predicate for absolute file names, `file-name-absolute-p'.
In some cases we might want to check if the file name is canonical.
For instance, following might fail to set point in simple.el line:
it fails when `dired-goto-file' argument is not canonical:

(let* ((dir (expand-file-name "lisp" source-directory))
       (file (expand-file-name "simple.el" dir)))
  (when (file-name-absolute-p file)
    (dired-other-window dir)
    (goto-char (point-min))
    (dired-goto-file (abbreviate-file-name file))))
    ;; (dired-goto-file file))) ; This works.


Do you think has sense to add a predicate as follows?:
If the answer is yes: where should be defined?

(defsubst myfile-name-canonical-p (filename)
  "Return non-nil if FILENAME specifies an absolute canonical file name."
  (string= filename (expand-file-name filename)))

Following is a simple comparison `file-name-absolute-p' with
`myfile-name-canonical-p':

(let ((dirs '("./foo" "../foo" "/foo//bar" "/foo/./bar" "/foo/../bar" 
"~/bar"
              "//foo/bar" "/foo/bar" "/foo/bar/" 
"/sudo:address@hidden:/foo/bar/")))
  (mapcar 'file-name-absolute-p dirs))
=> (nil nil t t t t t t t t)

(let ((dirs '("./foo" "../foo" "/foo//bar" "/foo/./bar" "/foo/../bar" 
"~/bar"
              "//foo/bar" "/foo/bar" "/foo/bar/" 
"/sudo:address@hidden:/foo/bar/")))
  (mapcar 'myfile-name-canonical-p dirs))
=> (nil nil nil nil nil nil t t t t)