files.el

;;; files.el --- file input and output commands for Emacs

;; Copyright (C) 1985-1987, 1992-2013 Free Software Foundation, Inc.

;; Maintainer: FSF
;; Package: emacs

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; Defines most of Emacs's file- and directory-handling functions,
;; including basic file visiting, backup generation, link handling,
;; ITS-id version control, load- and write-hook handling, and the like.

;;; Code:

(defvar font-lock-keywords)

(defgroup backup nil
  "Backups of edited data files."
  :group 'files)

(defgroup find-file nil
  "Finding files."
  :group 'files)


(defcustom delete-auto-save-files t
  "Non-nil means delete auto-save file when a buffer is saved or killed.

Note that the auto-save file will not be deleted if the buffer is killed
when it has unsaved changes."
  :type 'boolean
  :group 'auto-save)

(defcustom directory-abbrev-alist
  nil
  "Alist of abbreviations for file directories.
A list of elements of the form (FROM . TO), each meaning to replace
FROM with TO when it appears in a directory name.  This replacement is
done when setting up the default directory of a newly visited file.

FROM is matched against directory names anchored at the first
character, so it should start with a \"\\\\`\", or, if directory
names cannot have embedded newlines, with a \"^\".

FROM and TO should be equivalent names, which refer to the
same directory.  Do not use `~' in the TO strings;
they should be ordinary absolute directory names.

Use this feature when you have directories which you normally refer to
via absolute symbolic links.  Make TO the name of the link, and FROM
the name it is linked to."
  :type '(repeat (cons :format "%v"
		       :value ("\\`" . "")
		       (regexp :tag "From")
		       (string :tag "To")))
  :group 'abbrev
  :group 'find-file)

(defcustom make-backup-files t
  "Non-nil means make a backup of a file the first time it is saved.
This can be done by renaming the file or by copying.

Renaming means that Emacs renames the existing file so that it is a
backup file, then writes the buffer into a new file.  Any other names
that the old file had will now refer to the backup file.  The new file
is owned by you and its group is defaulted.

Copying means that Emacs copies the existing file into the backup
file, then writes the buffer on top of the existing file.  Any other
names that the old file had will now refer to the new (edited) file.
The file's owner and group are unchanged.

The choice of renaming or copying is controlled by the variables
`backup-by-copying', `backup-by-copying-when-linked',
`backup-by-copying-when-mismatch' and
`backup-by-copying-when-privileged-mismatch'.  See also `backup-inhibited'."
  :type 'boolean
  :group 'backup)

;; Do this so that local variables based on the file name
;; are not overridden by the major mode.
(defvar backup-inhibited nil
  "Non-nil means don't make a backup, regardless of the other parameters.
This variable is intended for use by making it local to a buffer.
But it is local only if you make it local.")
(put 'backup-inhibited 'permanent-local t)

(defcustom backup-by-copying nil
 "Non-nil means always use copying to create backup files.
See documentation of variable `make-backup-files'."
  :type 'boolean
  :group 'backup)

(defcustom backup-by-copying-when-linked nil
 "Non-nil means use copying to create backups for files with multiple names.
This causes the alternate names to refer to the latest version as edited.
This variable is relevant only if `backup-by-copying' is nil."
  :type 'boolean
  :group 'backup)

(defcustom backup-by-copying-when-mismatch t
  "Non-nil means create backups by copying if this preserves owner or group.
Renaming may still be used (subject to control of other variables)
when it would not result in changing the owner or group of the file;
that is, for files which are owned by you and whose group matches
the default for a new file created there by you.
This variable is relevant only if `backup-by-copying' is nil."
  :version "24.1"
  :type 'boolean
  :group 'backup)
(put 'backup-by-copying-when-mismatch 'permanent-local t)

(defcustom backup-by-copying-when-privileged-mismatch 200
  "Non-nil means create backups by copying to preserve a privileged owner.
Renaming may still be used (subject to control of other variables)
when it would not result in changing the owner of the file or if the owner
has a user id greater than the value of this variable.  This is useful
when low-numbered uid's are used for special system users (such as root)
that must maintain ownership of certain files.
This variable is relevant only if `backup-by-copying' and
`backup-by-copying-when-mismatch' are nil."
  :type '(choice (const nil) integer)
  :group 'backup)

(defvar backup-enable-predicate 'normal-backup-enable-predicate
  "Predicate that looks at a file name and decides whether to make backups.
Called with an absolute file name as argument, it returns t to enable backup.")

(defcustom buffer-offer-save nil
  "Non-nil in a buffer means always offer to save buffer on exit.
Do so even if the buffer is not visiting a file.
Automatically local in all buffers."
  :type 'boolean
  :group 'backup)
(make-variable-buffer-local 'buffer-offer-save)
(put 'buffer-offer-save 'permanent-local t)

(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)

(defcustom find-file-visit-truename nil
  "Non-nil means visit a file under its truename.
The truename of a file is found by chasing all links
both at the file level and at the levels of the containing directories."
  :type 'boolean
  :group 'find-file)
(put 'find-file-visit-truename 'safe-local-variable 'booleanp)

(defcustom revert-without-query nil
  "Specify which files should be reverted without query.
The value is a list of regular expressions.
If the file name matches one of these regular expressions,
then `revert-buffer' reverts the file without querying
if the file has changed on disk and you have not edited the buffer."
  :type '(repeat regexp)
  :group 'find-file)

(defvar buffer-file-number nil
  "The device number and file number of the file visited in the current buffer.
The value is a list of the form (FILENUM DEVNUM).
This pair of numbers uniquely identifies the file.
If the buffer is visiting a new file, the value is nil.")
(make-variable-buffer-local 'buffer-file-number)
(put 'buffer-file-number 'permanent-local t)

(defvar buffer-file-numbers-unique (not (memq system-type '(windows-nt)))
  "Non-nil means that `buffer-file-number' uniquely identifies files.")

(defvar buffer-file-read-only nil
  "Non-nil if visited file was read-only when visited.")
(make-variable-buffer-local 'buffer-file-read-only)

(defcustom small-temporary-file-directory
  (if (eq system-type 'ms-dos) (getenv "TMPDIR"))
  "The directory for writing small temporary files.
If non-nil, this directory is used instead of `temporary-file-directory'
by programs that create small temporary files.  This is for systems that
have fast storage with limited space, such as a RAM disk."
  :group 'files
  :initialize 'custom-initialize-delay
  :type '(choice (const nil) directory))

;; The system null device. (Should reference NULL_DEVICE from C.)
(defvar null-device (purecopy "/dev/null") "The system null device.")

(declare-function msdos-long-file-names "msdos.c")
(declare-function w32-long-file-name "w32proc.c")
(declare-function dired-get-filename "dired" (&optional localp no-error-if-not-filep))
(declare-function dired-unmark "dired" (arg))
(declare-function dired-do-flagged-delete "dired" (&optional nomessage))
(declare-function dos-8+3-filename "dos-fns" (filename))
(declare-function dosified-file-name "dos-fns" (file-name))

(defvar file-name-invalid-regexp
  (cond ((and (eq system-type 'ms-dos) (not (msdos-long-file-names)))
	 (purecopy
	 (concat "^\\([^A-Z[-`a-z]\\|..+\\)?:\\|" ; colon except after drive
		 "[+, ;=|<>\"?*]\\|\\[\\|\\]\\|"  ; invalid characters
		 "[\000-\037]\\|"		  ; control characters
		 "\\(/\\.\\.?[^/]\\)\\|"	  ; leading dots
		 "\\(/[^/.]+\\.[^/.]*\\.\\)")))	  ; more than a single dot
	((memq system-type '(ms-dos windows-nt cygwin))
	 (purecopy
	 (concat "^\\([^A-Z[-`a-z]\\|..+\\)?:\\|" ; colon except after drive
		 "[|<>\"?*\000-\037]")))		  ; invalid characters
	(t (purecopy "[\000]")))
  "Regexp recognizing file names which aren't allowed by the filesystem.")

(defcustom file-precious-flag nil
  "Non-nil means protect against I/O errors while saving files.
Some modes set this non-nil in particular buffers.

This feature works by writing the new contents into a temporary file
and then renaming the temporary file to replace the original.
In this way, any I/O error in writing leaves the original untouched,
and there is never any instant where the file is nonexistent.

Note that this feature forces backups to be made by copying.
Yet, at the same time, saving a precious file
breaks any hard links between it and other files.

This feature is advisory: for example, if the directory in which the
file is being saved is not writable, Emacs may ignore a non-nil value
of `file-precious-flag' and write directly into the file.

See also: `break-hardlink-on-save'."
  :type 'boolean
  :group 'backup)

(defcustom break-hardlink-on-save nil
  "Non-nil means when saving a file that exists under several names
\(i.e., has multiple hardlinks), break the hardlink associated with
`buffer-file-name' and write to a new file, so that the other
instances of the file are not affected by the save.

If `buffer-file-name' refers to a symlink, do not break the symlink.

Unlike `file-precious-flag', `break-hardlink-on-save' is not advisory.
For example, if the directory in which a file is being saved is not
itself writable, then error instead of saving in some
hardlink-nonbreaking way.

See also `backup-by-copying' and `backup-by-copying-when-linked'."
  :type 'boolean
  :group 'files
  :version "23.1")

(defcustom version-control nil
  "Control use of version numbers for backup files.
When t, make numeric backup versions unconditionally.
When nil, make them for files that have some already.
The value `never' means do not make them."
  :type '(choice (const :tag "Never" never)
		 (const :tag "If existing" nil)
		 (other :tag "Always" t))
  :group 'backup
  :group 'vc)
(put 'version-control 'safe-local-variable
     (lambda (x) (or (booleanp x) (equal x 'never))))

(defcustom dired-kept-versions 2
  "When cleaning directory, number of versions to keep."
  :type 'integer
  :group 'backup
  :group 'dired)

(defcustom delete-old-versions nil
  "If t, delete excess backup versions silently.
If nil, ask confirmation.  Any other value prevents any trimming."
  :type '(choice (const :tag "Delete" t)
		 (const :tag "Ask" nil)
		 (other :tag "Leave" other))
  :group 'backup)

(defcustom kept-old-versions 2
  "Number of oldest versions to keep when a new numbered backup is made."
  :type 'integer
  :group 'backup)
(put 'kept-old-versions 'safe-local-variable 'integerp)

(defcustom kept-new-versions 2
  "Number of newest versions to keep when a new numbered backup is made.
Includes the new backup.  Must be > 0"
  :type 'integer
  :group 'backup)
(put 'kept-new-versions 'safe-local-variable 'integerp)

(defcustom require-final-newline nil
  "Whether to add a newline automatically at the end of the file.

A value of t means do this only when the file is about to be saved.
A value of `visit' means do this right after the file is visited.
A value of `visit-save' means do it at both of those times.
Any other non-nil value means ask user whether to add a newline, when saving.
A value of nil means don't add newlines.

Certain major modes set this locally to the value obtained
from `mode-require-final-newline'."
  :type '(choice (const :tag "When visiting" visit)
		 (const :tag "When saving" t)
		 (const :tag "When visiting or saving" visit-save)
		 (const :tag "Don't add newlines" nil)
		 (other :tag "Ask each time" ask))
  :group 'editing-basics)

(defcustom mode-require-final-newline t
  "Whether to add a newline at end of file, in certain major modes.
Those modes set `require-final-newline' to this value when you enable them.
They do so because they are often used for files that are supposed
to end in newlines, and the question is how to arrange that.

A value of t means do this only when the file is about to be saved.
A value of `visit' means do this right after the file is visited.
A value of `visit-save' means do it at both of those times.
Any other non-nil value means ask user whether to add a newline, when saving.

A value of nil means do not add newlines.  That is a risky choice in this
variable since this value is used for modes for files that ought to have
final newlines.  So if you set this to nil, you must explicitly check and
add a final newline, whenever you save a file that really needs one."
  :type '(choice (const :tag "When visiting" visit)
		 (const :tag "When saving" t)
		 (const :tag "When visiting or saving" visit-save)
		 (const :tag "Don't add newlines" nil)
		 (other :tag "Ask each time" ask))
  :group 'editing-basics
  :version "22.1")

(defcustom auto-save-default t
  "Non-nil says by default do auto-saving of every file-visiting buffer."
  :type 'boolean
  :group 'auto-save)

(defcustom auto-save-file-name-transforms
  `(("\\`/[^/]*:\\([^/]*/\\)*\\([^/]*\\)\\'"
     ;; Don't put "\\2" inside expand-file-name, since it will be
     ;; transformed to "/2" on DOS/Windows.
     ,(concat temporary-file-directory "\\2") t))
  "Transforms to apply to buffer file name before making auto-save file name.
Each transform is a list (REGEXP REPLACEMENT UNIQUIFY):
REGEXP is a regular expression to match against the file name.
If it matches, `replace-match' is used to replace the
matching part with REPLACEMENT.
If the optional element UNIQUIFY is non-nil, the auto-save file name is
constructed by taking the directory part of the replaced file-name,
concatenated with the buffer file name with all directory separators
changed to `!' to prevent clashes.  This will not work
correctly if your filesystem truncates the resulting name.

All the transforms in the list are tried, in the order they are listed.
When one transform applies, its result is final;
no further transforms are tried.

The default value is set up to put the auto-save file into the
temporary directory (see the variable `temporary-file-directory') for
editing a remote file.

On MS-DOS filesystems without long names this variable is always
ignored."
  :group 'auto-save
  :type '(repeat (list (string :tag "Regexp") (string :tag "Replacement")
					   (boolean :tag "Uniquify")))
  :initialize 'custom-initialize-delay
  :version "21.1")

(defcustom save-abbrevs t
  "Non-nil means save word abbrevs too when files are saved.
If `silently', don't ask the user before saving."
  :type '(choice (const t) (const nil) (const silently))
  :group 'abbrev)

(defcustom find-file-run-dired t
  "Non-nil means allow `find-file' to visit directories.
To visit the directory, `find-file' runs `find-directory-functions'."
  :type 'boolean
  :group 'find-file)

(defcustom find-directory-functions '(cvs-dired-noselect dired-noselect)
  "List of functions to try in sequence to visit a directory.
Each function is called with the directory name as the sole argument
and should return either a buffer or nil."
  :type '(hook :options (cvs-dired-noselect dired-noselect))
  :group 'find-file)

;; FIXME: also add a hook for `(thing-at-point 'filename)'
(defcustom file-name-at-point-functions '(ffap-guess-file-name-at-point)
  "List of functions to try in sequence to get a file name at point.
Each function should return either nil or a file name found at the
location of point in the current buffer."
  :type '(hook :options (ffap-guess-file-name-at-point))
  :group 'find-file)

;;;It is not useful to make this a local variable.
;;;(put 'find-file-not-found-hooks 'permanent-local t)
(define-obsolete-variable-alias 'find-file-not-found-hooks
    'find-file-not-found-functions "22.1")
(defvar find-file-not-found-functions nil
  "List of functions to be called for `find-file' on nonexistent file.
These functions are called as soon as the error is detected.
Variable `buffer-file-name' is already set up.
The functions are called in the order given until one of them returns non-nil.")

;;;It is not useful to make this a local variable.
;;;(put 'find-file-hooks 'permanent-local t)
(define-obsolete-variable-alias 'find-file-hooks 'find-file-hook "22.1")
(defcustom find-file-hook nil
  "List of functions to be called after a buffer is loaded from a file.
The buffer's local variables (if any) will have been processed before the
functions are called."
  :group 'find-file
  :type 'hook
  :options '(auto-insert)
  :version "22.1")

(define-obsolete-variable-alias 'write-file-hooks 'write-file-functions "22.1")
(defvar write-file-functions nil
  "List of functions to be called before writing out a buffer to a file.
If one of them returns non-nil, the file is considered already written
and the rest are not called.
These hooks are considered to pertain to the visited file.
So any buffer-local binding of this variable is discarded if you change
the visited file name with \\[set-visited-file-name], but not when you
change the major mode.

This hook is not run if any of the functions in
`write-contents-functions' returns non-nil.  Both hooks pertain
to how to save a buffer to file, for instance, choosing a suitable
coding system and setting mode bits.  (See Info
node `(elisp)Saving Buffers'.)  To perform various checks or
updates before the buffer is saved, use `before-save-hook'.")
(put 'write-file-functions 'permanent-local t)

(defvar local-write-file-hooks nil)
(make-variable-buffer-local 'local-write-file-hooks)
(put 'local-write-file-hooks 'permanent-local t)
(make-obsolete-variable 'local-write-file-hooks 'write-file-functions "22.1")

(define-obsolete-variable-alias 'write-contents-hooks
    'write-contents-functions "22.1")
(defvar write-contents-functions nil
  "List of functions to be called before writing out a buffer to a file.
If one of them returns non-nil, the file is considered already written
and the rest are not called and neither are the functions in
`write-file-functions'.

This variable is meant to be used for hooks that pertain to the
buffer's contents, not to the particular visited file; thus,
`set-visited-file-name' does not clear this variable; but changing the
major mode does clear it.

For hooks that _do_ pertain to the particular visited file, use
`write-file-functions'.  Both this variable and
`write-file-functions' relate to how a buffer is saved to file.
To perform various checks or updates before the buffer is saved,
use `before-save-hook'.")
(make-variable-buffer-local 'write-contents-functions)

(defcustom enable-local-variables t
  "Control use of local variables in files you visit.
The value can be t, nil, :safe, :all, or something else.

A value of t means file local variables specifications are obeyed
if all the specified variable values are safe; if any values are
not safe, Emacs queries you, once, whether to set them all.
\(When you say yes to certain values, they are remembered as safe.)

:safe means set the safe variables, and ignore the rest.
:all means set all variables, whether safe or not.
 (Don't set it permanently to :all.)
A value of nil means always ignore the file local variables.

Any other value means always query you once whether to set them all.
\(When you say yes to certain values, they are remembered as safe, but
this has no effect when `enable-local-variables' is \"something else\".)

This variable also controls use of major modes specified in
a -*- line.

The command \\[normal-mode], when used interactively,
always obeys file local variable specifications and the -*- line,
and ignores this variable."
  :risky t
  :type '(choice (const :tag "Query Unsafe" t)
		 (const :tag "Safe Only" :safe)
		 (const :tag "Do all" :all)
		 (const :tag "Ignore" nil)
		 (other :tag "Query" other))
  :group 'find-file)

(defvar enable-dir-local-variables t
  "Non-nil means enable use of directory-local variables.
Some modes may wish to set this to nil to prevent directory-local
settings being applied, but still respect file-local ones.")

;; This is an odd variable IMO.
;; You might wonder why it is needed, when we could just do:
;; (set (make-local-variable 'enable-local-variables) nil)
;; These two are not precisely the same.
;; Setting this variable does not cause -*- mode settings to be
;; ignored, whereas setting enable-local-variables does.
;; Only three places in Emacs use this variable: tar and arc modes,
;; and rmail.  The first two don't need it.  They already use
;; inhibit-local-variables-regexps, which is probably enough, and
;; could also just set enable-local-variables locally to nil.
;; Them setting it has the side-effect that dir-locals cannot apply to
;; eg tar files (?).  FIXME Is this appropriate?
;; AFAICS, rmail is the only thing that needs this, and the only
;; reason it uses it is for BABYL files (which are obsolete).
;; These contain "-*- rmail -*-" in the first line, which rmail wants
;; to respect, so that find-file on a BABYL file will switch to
;; rmail-mode automatically (this is nice, but hardly essential,
;; since most people are used to explicitly running a command to
;; access their mail; M-x gnus etc).  Rmail files may happen to
;; contain Local Variables sections in messages, which Rmail wants to
;; ignore.  So AFAICS the only reason this variable exists is for a
;; minor convenience feature for handling of an obsolete Rmail file format.
(defvar local-enable-local-variables t
  "Like `enable-local-variables' but meant for buffer-local bindings.
The meaningful values are nil and non-nil.  The default is non-nil.
If a major mode sets this to nil, buffer-locally, then any local
variables list in a file visited in that mode will be ignored.

This variable does not affect the use of major modes specified
in a -*- line.")

(defcustom enable-local-eval 'maybe
  "Control processing of the \"variable\" `eval' in a file's local variables.
The value can be t, nil or something else.
A value of t means obey `eval' variables.
A value of nil means ignore them; anything else means query."
  :risky t
  :type '(choice (const :tag "Obey" t)
		 (const :tag "Ignore" nil)
		 (other :tag "Query" other))
  :group 'find-file)

;; Avoid losing in versions where CLASH_DETECTION is disabled.
(or (fboundp 'lock-buffer)
    (defalias 'lock-buffer 'ignore))
(or (fboundp 'unlock-buffer)
    (defalias 'unlock-buffer 'ignore))
(or (fboundp 'file-locked-p)
    (defalias 'file-locked-p 'ignore))

(defcustom view-read-only nil
  "Non-nil means buffers visiting files read-only do so in view mode.
In fact, this means that all read-only buffers normally have
View mode enabled, including buffers that are read-only because
you visit a file you cannot alter, and buffers you make read-only
using \\[toggle-read-only]."
  :type 'boolean
  :group 'view)

(defvar file-name-history nil
  "History list of file names entered in the minibuffer.

Maximum length of the history list is determined by the value
of `history-length', which see.")

(put 'ange-ftp-completion-hook-function 'safe-magic t)
(defun ange-ftp-completion-hook-function (op &rest args)
  "Provides support for ange-ftp host name completion.
Runs the usual ange-ftp hook, but only for completion operations."
  ;; Having this here avoids the need to load ange-ftp when it's not
  ;; really in use.
  (if (memq op '(file-name-completion file-name-all-completions))
      (apply 'ange-ftp-hook-function op args)
    (let ((inhibit-file-name-handlers
	   (cons 'ange-ftp-completion-hook-function
		 (and (eq inhibit-file-name-operation op)
		      inhibit-file-name-handlers)))
	  (inhibit-file-name-operation op))
      (apply op args))))

(declare-function dos-convert-standard-filename "dos-fns.el" (filename))
(declare-function w32-convert-standard-filename "w32-fns.el" (filename))

(defun convert-standard-filename (filename)
  "Convert a standard file's name to something suitable for the OS.
This means to guarantee valid names and perhaps to canonicalize
certain patterns.

FILENAME should be an absolute file name since the conversion rules
sometimes vary depending on the position in the file name.  E.g. c:/foo
is a valid DOS file name, but c:/bar/c:/foo is not.

This function's standard definition is trivial; it just returns
the argument.  However, on Windows and DOS, replace invalid
characters.  On DOS, make sure to obey the 8.3 limitations.
In the native Windows build, turn Cygwin names into native names,
and also turn slashes into backslashes if the shell requires it (see
`w32-shell-dos-semantics').

See Info node `(elisp)Standard File Names' for more details."
  (cond
   ((eq system-type 'cygwin)
    (let ((name (copy-sequence filename))
	  (start 0))
      ;; Replace invalid filename characters with !
      (while (string-match "[?*:<>|\"\000-\037]" name start)
	(aset name (match-beginning 0) ?!)
	(setq start (match-end 0)))
      name))
   ((eq system-type 'windows-nt)
    (w32-convert-standard-filename filename))
   ((eq system-type 'ms-dos)
    (dos-convert-standard-filename filename))
   (t filename)))

(defun read-directory-name (prompt &optional dir default-dirname mustmatch initial)
  "Read directory name, prompting with PROMPT and completing in directory DIR.
Value is not expanded---you must call `expand-file-name' yourself.
Default name to DEFAULT-DIRNAME if user exits with the same
non-empty string that was inserted by this function.
 (If DEFAULT-DIRNAME is omitted, DIR combined with INITIAL is used,
  or just DIR if INITIAL is nil.)
If the user exits with an empty minibuffer, this function returns
an empty string.  (This can only happen if the user erased the
pre-inserted contents or if `insert-default-directory' is nil.)
Fourth arg MUSTMATCH non-nil means require existing directory's name.
 Non-nil and non-t means also require confirmation after completion.
Fifth arg INITIAL specifies text to start with.
DIR should be an absolute directory name.  It defaults to
the value of `default-directory'."
  (unless dir
    (setq dir default-directory))
  (read-file-name prompt dir (or default-dirname
				 (if initial (expand-file-name initial dir)
				   dir))
		  mustmatch initial
		  'file-directory-p))


(defun pwd ()
  "Show the current default directory."
  (interactive nil)
  (message "Directory %s" default-directory))

(defvar cd-path nil
  "Value of the CDPATH environment variable, as a list.
Not actually set up until the first time you use it.")

(defun parse-colon-path (search-path)
  "Explode a search path into a list of directory names.
Directories are separated by `path-separator' (which is colon in
GNU and Unix systems).  Substitute environment variables into the
resulting list of directory names.  For an empty path element (i.e.,
a leading or trailing separator, or two adjacent separators), return
nil (meaning `default-directory') as the associated list element."
  (when (stringp search-path)
    (mapcar (lambda (f)
	      (if (equal "" f) nil
		(substitute-in-file-name (file-name-as-directory f))))
	    (split-string search-path path-separator))))

(defun cd-absolute (dir)
  "Change current directory to given absolute file name DIR."
  ;; Put the name into directory syntax now,
  ;; because otherwise expand-file-name may give some bad results.
  (setq dir (file-name-as-directory dir))
  ;; We used to additionally call abbreviate-file-name here, for an
  ;; unknown reason.  Problem is that most buffers are setup
  ;; without going through cd-absolute and don't call
  ;; abbreviate-file-name on their default-directory, so the few that
  ;; do end up using a superficially different directory.
  (setq dir (expand-file-name dir))
  (if (not (file-directory-p dir))
      (if (file-exists-p dir)
	  (error "%s is not a directory" dir)
	(error "%s: no such directory" dir))
    (unless (file-executable-p dir)
      (error "Cannot cd to %s:  Permission denied" dir))
    (setq default-directory dir)
    (setq list-buffers-directory dir)))

(defun cd (dir)
  "Make DIR become the current buffer's default directory.
If your environment includes a `CDPATH' variable, try each one of
that list of directories (separated by occurrences of
`path-separator') when resolving a relative directory name.
The path separator is colon in GNU and GNU-like systems."
  (interactive
   (list
    ;; FIXME: There's a subtle bug in the completion below.  Seems linked
    ;; to a fundamental difficulty of implementing `predicate' correctly.
    ;; The manifestation is that TAB may list non-directories in the case where
    ;; those files also correspond to valid directories (if your cd-path is (A/
    ;; B/) and you have A/a a file and B/a a directory, then both `a' and `a/'
    ;; will be listed as valid completions).
    ;; This is because `a' (listed because of A/a) is indeed a valid choice
    ;; (which will lead to the use of B/a).
    (minibuffer-with-setup-hook
        (lambda ()
          (setq minibuffer-completion-table
                (apply-partially #'locate-file-completion-table
                                 cd-path nil))
          (setq minibuffer-completion-predicate
                (lambda (dir)
                  (locate-file dir cd-path nil
                               (lambda (f) (and (file-directory-p f) 'dir-ok))))))
      (unless cd-path
        (setq cd-path (or (parse-colon-path (getenv "CDPATH"))
                          (list "./"))))
      (read-directory-name "Change default directory: "
                           default-directory default-directory
                           t))))
  (unless cd-path
    (setq cd-path (or (parse-colon-path (getenv "CDPATH"))
                      (list "./"))))
  (cd-absolute
   (or (locate-file dir cd-path nil
                    (lambda (f) (and (file-directory-p f) 'dir-ok)))
       (error "No such directory found via CDPATH environment variable"))))

(defun load-file (file)
  "Load the Lisp file named FILE."
  ;; This is a case where .elc makes a lot of sense.
  (interactive (list (let ((completion-ignored-extensions
			    (remove ".elc" completion-ignored-extensions)))
		       (read-file-name "Load file: " nil nil 'lambda))))
  (load (expand-file-name file) nil nil t))

(defun locate-file (filename path &optional suffixes predicate)
  "Search for FILENAME through PATH.
If found, return the absolute file name of FILENAME, with its suffixes;
otherwise return nil.
PATH should be a list of directories to look in, like the lists in
`exec-path' or `load-path'.
If SUFFIXES is non-nil, it should be a list of suffixes to append to
file name when searching.  If SUFFIXES is nil, it is equivalent to '(\"\").
Use '(\"/\") to disable PATH search, but still try the suffixes in SUFFIXES.
If non-nil, PREDICATE is used instead of `file-readable-p'.

This function will normally skip directories, so if you want it to find
directories, make sure the PREDICATE function returns `dir-ok' for them.

PREDICATE can also be an integer to pass to the `access' system call,
in which case file-name handlers are ignored.  This usage is deprecated.
For compatibility, PREDICATE can also be one of the symbols
`executable', `readable', `writable', or `exists', or a list of
one or more of those symbols."
  (if (and predicate (symbolp predicate) (not (functionp predicate)))
      (setq predicate (list predicate)))
  (when (and (consp predicate) (not (functionp predicate)))
    (setq predicate
	  (logior (if (memq 'executable predicate) 1 0)
		  (if (memq 'writable predicate) 2 0)
		  (if (memq 'readable predicate) 4 0))))
  (locate-file-internal filename path suffixes predicate))

(defun locate-file-completion-table (dirs suffixes string pred action)
  "Do completion for file names passed to `locate-file'."
  (cond
   ((file-name-absolute-p string)
    ;; FIXME: maybe we should use completion-file-name-table instead,
    ;; tho at least for `load', the arg is passed through
    ;; substitute-in-file-name for historical reasons.
    (read-file-name-internal string pred action))
   ((eq (car-safe action) 'boundaries)
    (let ((suffix (cdr action)))
      `(boundaries
        ,(length (file-name-directory string))
        ,@(let ((x (file-name-directory suffix)))
            (if x (1- (length x)) (length suffix))))))
   (t
    (let ((names '())
          ;; If we have files like "foo.el" and "foo.elc", we could load one of
          ;; them with "foo.el", "foo.elc", or "foo", where just "foo" is the
          ;; preferred way.  So if we list all 3, that gives a lot of redundant
          ;; entries for the poor soul looking just for "foo".  OTOH, sometimes
          ;; the user does want to pay attention to the extension.  We try to
          ;; diffuse this tension by stripping the suffix, except when the
          ;; result is a single element (i.e. usually we only list "foo" unless
          ;; it's the only remaining element in the list, in which case we do
          ;; list "foo", "foo.elc" and "foo.el").
          (fullnames '())
	  (suffix (concat (regexp-opt suffixes t) "\\'"))
	  (string-dir (file-name-directory string))
          (string-file (file-name-nondirectory string)))
      (dolist (dir dirs)
        (unless dir
          (setq dir default-directory))
        (if string-dir (setq dir (expand-file-name string-dir dir)))
        (when (file-directory-p dir)
          (dolist (file (file-name-all-completions
                         string-file dir))
            (if (not (string-match suffix file))
                (push file names)
              (push file fullnames)
              (push (substring file 0 (match-beginning 0)) names)))))
      ;; Switching from names to names+fullnames creates a non-monotonicity
      ;; which can cause problems with things like partial-completion.
      ;; To minimize the problem, filter out completion-regexp-list, so that
      ;; M-x load-library RET t/x.e TAB finds some files.  Also remove elements
      ;; from `names' which only matched `string' when they still had
      ;; their suffix.
      (setq names (all-completions string names))
      ;; Remove duplicates of the first element, so that we can easily check
      ;; if `names' really only contains a single element.
      (when (cdr names) (setcdr names (delete (car names) (cdr names))))
      (unless (cdr names)
        ;; There's no more than one matching non-suffixed element, so expand
        ;; the list by adding the suffixed elements as well.
        (setq names (nconc names fullnames)))
      (completion-table-with-context
       string-dir names string-file pred action)))))

(defun locate-file-completion (string path-and-suffixes action)
  "Do completion for file names passed to `locate-file'.
PATH-AND-SUFFIXES is a pair of lists, (DIRECTORIES . SUFFIXES)."
  (declare (obsolete locate-file-completion-table "23.1"))
  (locate-file-completion-table (car path-and-suffixes)
                                (cdr path-and-suffixes)
                                string nil action))

(defvar locate-dominating-stop-dir-regexp
  (purecopy "\\`\\(?:[\\/][\\/][^\\/]+[\\/]\\|/\\(?:net\\|afs\\|\\.\\.\\.\\)/\\)\\'")
  "Regexp of directory names which stop the search in `locate-dominating-file'.
Any directory whose name matches this regexp will be treated like
a kind of root directory by `locate-dominating-file' which will stop its search
when it bumps into it.
The default regexp prevents fruitless and time-consuming attempts to find
special files in directories in which filenames are interpreted as hostnames,
or mount points potentially requiring authentication as a different user.")

;; (defun locate-dominating-files (file regexp)
;;   "Look up the directory hierarchy from FILE for a file matching REGEXP.
;; Stop at the first parent where a matching file is found and return the list
;; of files that that match in this directory."
;;   (catch 'found
;;     ;; `user' is not initialized yet because `file' may not exist, so we may
;;     ;; have to walk up part of the hierarchy before we find the "initial UID".
;;     (let ((user nil)
;;           ;; Abbreviate, so as to stop when we cross ~/.
;;           (dir (abbreviate-file-name (file-name-as-directory file)))
;;           files)
;;       (while (and dir
;;                   ;; As a heuristic, we stop looking up the hierarchy of
;;                   ;; directories as soon as we find a directory belonging to
;;                   ;; another user.  This should save us from looking in
;;                   ;; things like /net and /afs.  This assumes that all the
;;                   ;; files inside a project belong to the same user.
;;                   (let ((prev-user user))
;;                     (setq user (nth 2 (file-attributes dir)))
;;                     (or (null prev-user) (equal user prev-user))))
;;         (if (setq files (condition-case nil
;; 			    (directory-files dir 'full regexp 'nosort)
;; 			  (error nil)))
;;             (throw 'found files)
;;           (if (equal dir
;;                      (setq dir (file-name-directory
;;                                 (directory-file-name dir))))
;;               (setq dir nil))))
;;       nil)))