bug#3911: 23.1.50; get-free-disk-space relative to non-existent default-directory

[Kevin Ryde <user42@zip.com.au>]

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On a non-existent directory get-free-disk-space returns nil, eg.

    (get-free-disk-space "/no/such/dir")
    => nil

But if it's done by a relative path from a default-directory which
doesn't exist, then the answer is the space in your home directory

    (let ((default-directory "/no/such/dir"))
      (get-free-disk-space "."))
    => 3705637

I hoped the two answers would be the same.

This is with the "df"-running code in get-free-disk-space, ie. no
`file-system-info' function.

Perhaps absolutize per below with an inserted setq, the diff being just
re-indent.

(I still think the use of the home dir there is either complicated and
unnecessary, or complicated and necessary everywhere.  Or maybe better
call-process could not attempt a chdir at all if a caller doesn't care
about the current directory.  But leaving that unchanged as yet.)

2009-07-24  Kevin Ryde  <user42@zip.com.au>

	* files.el (get-free-disk-space): Absolutize the dir before
	changing default-directory, so as not to answer about a different
	directory.


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*** files.el	24 Jul 2009 07:35:37 +1000	1.1063
--- files.el	24 Jul 2009 08:07:01 +1000	
***************
*** 5394,5410 ****
        (save-match-data
  	(with-temp-buffer
  	  (when (and directory-free-space-program
! 		     (let ((default-directory
! 			     (if (and (not (file-remote-p default-directory))
! 				      (file-directory-p default-directory)
! 				      (file-readable-p default-directory))
! 				 default-directory
! 			       (expand-file-name "~/"))))
! 		       (eq (call-process directory-free-space-program
! 					 nil t nil
! 					 directory-free-space-args
! 					 dir)
! 			   0)))
  	    ;; Usual format is a header line followed by a line of
  	    ;; numbers.
  	    (goto-char (point-min))
--- 5394,5413 ----
        (save-match-data
  	(with-temp-buffer
  	  (when (and directory-free-space-program
!                      (progn
!                        ;; absolutize before changing default-directory
!                        (setq dir (expand-file-name dir))
!                        (let ((default-directory
!                                (if (and (not (file-remote-p default-directory))
!                                         (file-directory-p default-directory)
!                                         (file-readable-p default-directory))
!                                    default-directory
!                                  (expand-file-name "~/"))))
!                          (eq (call-process directory-free-space-program
!                                            nil t nil
!                                            directory-free-space-args
!                                            dir)
!                              0))))
  	    ;; Usual format is a header line followed by a line of
  	    ;; numbers.
  	    (goto-char (point-min))

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In GNU Emacs 23.1.50.4 (i586-pc-linux-gnu, GTK+ Version 2.16.4)
 of 2009-07-24 on blah.blah
configured using `configure  'CFLAGS=-O -g' '--prefix=/down/emacs/b/inst' '--with-x-toolkit=gtk''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_AU
  value of $XMODIFIERS: nil
  locale-coding-system: iso-latin-1-unix
  default-enable-multibyte-characters: t