(Fw32_battery_status): Fix computation of %t (h:min) format.

[bpt/emacs.git] / lisp / vc.el

;;; vc.el --- drive a version-control system from within Emacs

;; Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 2000,
;;   2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
;;   Free Software Foundation, Inc.

;; Author:     FSF (see below for full credits)
;; Maintainer: Andre Spiegel <spiegel@gnu.org>
;; Keywords: tools

;; 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, 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; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.

;;; Credits:

;; VC was initially designed and implemented by Eric S. Raymond
;; <esr@thyrsus.com> in 1992.  Over the years, many other people have
;; contributed substantial amounts of work to VC.  These include:
;;
;;   Per Cederqvist <ceder@lysator.liu.se>
;;   Paul Eggert <eggert@twinsun.com>
;;   Sebastian Kremer <sk@thp.uni-koeln.de>
;;   Martin Lorentzson <martinl@gnu.org>
;;   Dave Love <fx@gnu.org>
;;   Stefan Monnier <monnier@cs.yale.edu>
;;   Thien-Thi Nguyen <ttn@gnu.org>
;;   Dan Nicolaescu <dann@ics.uci.edu>
;;   J.D. Smith <jdsmith@alum.mit.edu>
;;   Andre Spiegel <spiegel@gnu.org>
;;   Richard Stallman <rms@gnu.org>
;;
;; In July 2007 ESR returned and redesigned the mode to cope better
;; with modern version-control systems that do commits by fileset
;; rather than per individual file.
;;
;; Features in the new version:
;; * Key commands (vc-next-action = C-x v v, vc-print-log = C-x v l, vc-revert
;;   = C-x v u, vc-rollback = C-x v c, vc-diff = C-x v =, vc-update = C-x v +)
;;   now operate on filesets rather than individual files.
;; * The fileset for a command is either (a) all marked files in VC-dired
;;   mode, (b) the currently visited file if it's under version control,
;;   or (c) the current directory if the visited buffer is not under
;;   version control and a wildcarding-enable flag has been set.
;;
;; If you maintain a client of the mode or customize it in your .emacs,
;; note that some backend functions which formerly took single file arguments
;; now take a list of files.  These include: register, checkin, print-log,
;; rollback, and diff.

;;; Commentary:

;; This mode is fully documented in the Emacs user's manual.
;;
;; Supported version-control systems presently include CVS, RCS, GNU
;; Arch, Subversion, Bzr, Git, Mercurial, Meta-CVS, Monotone and SCCS
;; (or its free replacement, CSSC).
;;
;; Some features will not work with old RCS versions.  Where
;; appropriate, VC finds out which version you have, and allows or
;; disallows those features (stealing locks, for example, works only
;; from 5.6.2 onwards).
;; Even initial checkins will fail if your RCS version is so old that ci
;; doesn't understand -t-; this has been known to happen to people running
;; NExTSTEP 3.0.
;;
;; You can support the RCS -x option by customizing vc-rcs-master-templates.
;;
;; Proper function of the SCCS diff commands requires the shellscript vcdiff
;; to be installed somewhere on Emacs's path for executables.
;;
;; If your site uses the ChangeLog convention supported by Emacs, the
;; function `log-edit-comment-to-change-log' could prove a useful checkin hook,
;; although you might prefer to use C-c C-a (i.e. `log-edit-insert-changelog')
;; from the commit buffer instead or to set `log-edit-setup-invert'.
;;
;; The vc code maintains some internal state in order to reduce expensive
;; version-control operations to a minimum.  Some names are only computed
;; once.  If you perform version control operations with the backend while
;; vc's back is turned, or move/rename master files while vc is running,
;; vc may get seriously confused.  Don't do these things!
;;
;; Developer's notes on some concurrency issues are included at the end of
;; the file.
;;
;; ADDING SUPPORT FOR OTHER BACKENDS
;;
;; VC can use arbitrary version control systems as a backend.  To add
;; support for a new backend named SYS, write a library vc-sys.el that
;; contains functions of the form `vc-sys-...' (note that SYS is in lower
;; case for the function and library names).  VC will use that library if
;; you put the symbol SYS somewhere into the list of
;; `vc-handled-backends'.  Then, for example, if `vc-sys-registered'
;; returns non-nil for a file, all SYS-specific versions of VC commands
;; will be available for that file.
;;
;; VC keeps some per-file information in the form of properties (see
;; vc-file-set/getprop in vc-hooks.el).  The backend-specific functions
;; do not generally need to be aware of these properties.  For example,
;; `vc-sys-working-revision' should compute the working revision and
;; return it; it should not look it up in the property, and it needn't
;; store it there either.  However, if a backend-specific function does
;; store a value in a property, that value takes precedence over any
;; value that the generic code might want to set (check for uses of
;; the macro `with-vc-properties' in vc.el).
;;
;; In the list of functions below, each identifier needs to be prepended
;; with `vc-sys-'.  Some of the functions are mandatory (marked with a
;; `*'), others are optional (`-').
;;
;; BACKEND PROPERTIES
;;
;; * revision-granularity
;;
;;   Takes no arguments.  Returns either 'file or 'repository.  Backends
;;   that return 'file have per-file revision numbering; backends
;;   that return 'repository have per-repository revision numbering,
;;   so a revision level implicitly identifies a changeset
;;
;; STATE-QUERYING FUNCTIONS
;;
;; * registered (file)
;;
;;   Return non-nil if FILE is registered in this backend.  Both this
;;   function as well as `state' should be careful to fail gracefully
;;   in the event that the backend executable is absent.  It is
;;   preferable that this function's body is autoloaded, that way only
;;   calling vc-registered does not cause the backend to be loaded
;;   (all the vc-FOO-registered functions are called to try to find
;;   the controlling backend for FILE.
;;
;; * state (file)
;;
;;   Return the current version control state of FILE.  For a list of
;;   possible values, see `vc-state'.  This function should do a full and
;;   reliable state computation; it is usually called immediately after
;;   C-x v v.  If you want to use a faster heuristic when visiting a
;;   file, put that into `state-heuristic' below.  Note that under most
;;   VCSes this won't be called at all, dir-state or dir-stus is used instead.
;;
;; - state-heuristic (file)
;;
;;   If provided, this function is used to estimate the version control
;;   state of FILE at visiting time.  It should be considerably faster
;;   than the implementation of `state'.  For a list of possible values,
;;   see the doc string of `vc-state'.
;;
;; - dir-state (dir)
;;
;;   If provided, this function is used to find the version control
;;   state of as many files as possible in DIR, and all subdirectories
;;   of DIR, in a fast way; it is used to avoid expensive indivitual
;;   vc-state calls.  The function should not return anything, but
;;   rather store the files' states into the corresponding properties.
;;   Two properties are required: `vc-backend' and `vc-state'.  (Note:
;;   in older versions this method was not required to recurse into
;;   subdirectories.)
;;
;; - dir-status (dir update-function)
;;
;;   Produce RESULT: a list of lists of the form (FILE VC-STATE EXTRA)
;;   for the files in DIR.
;;   EXTRA can be used for backend specific information about FILE.
;;   If a command needs to be run to compute this list, it should be
;;   run asynchronously using (current-buffer) as the buffer for the
;;   command.  When RESULT is computed, it should be passed back by
;;   doing: (funcall UPDATE-FUNCTION RESULT nil).
;;   If the backend uses a process filter, hence it produces partial results,
;;   they can be passed back by doing:
;;      (funcall UPDATE-FUNCTION RESULT t)
;;   and then do a (funcall UPDATE-FUNCTION RESULT nil)
;;   when all the results have been computed.
;;   To provide more backend specific functionality for `vc-dir'
;;   the following functions might be needed: `status-extra-headers',
;;   `status-printer', `extra-status-menu' and `dir-status-files'.
;;   This function is used by `vc-dir', a replacement for
;;   `vc-dired'.  vc-dir is still under development, and is NOT
;;   feature complete.  As such, the requirements for this function
;;   might change.  This is a replacement for `dir-state'.
;;
;; - dir-status-files (dir files default-state update-function)
;;
;;   This function is identical to dir-status except that it should
;;   only report status for the specified FILES. Also it needs to
;;   report on all requested files, including up-to-date or ignored
;;   files. If not provided, the default is to consider that the files
;;   are in DEFAULT-STATE.
;;
;; - status-extra-headers (dir)
;;
;;   Return a string that will be added to the *vc-dir* buffer header.
;;
;; - status-printer (fileinfo)
;;
;;   Pretty print the `vc-dir-fileinfo' FILEINFO.
;;   If a backend needs to show more information than the default FILE
;;   and STATE in the vc-dir listing, it can store that extra
;;   information in `vc-dir-fileinfo->extra'.  This function can be
;;   used to display that extra information in the *vc-dir* buffer.
;;
;; - status-fileinfo-extra (file)
;;
;;   Compute `vc-dir-fileinfo->extra' for FILE.
;;
;; * working-revision (file)
;;
;;   Return the working revision of FILE.  This is the revision fetched
;;   by the last checkout or upate, not necessarily the same thing as the
;;   head or tip revision.  Should return "0" for a file added but not yet
;;   committed.
;;
;; - latest-on-branch-p (file)
;;
;;   Return non-nil if the working revision of FILE is the latest revision
;;   on its branch (many VCSes call this the 'tip' or 'head' revision).
;;   The default implementation always returns t, which means that
;;   working with non-current revisions is not supported by default.
;;
;; * checkout-model (files)
;;
;;   Indicate whether FILES need to be "checked out" before they can be
;;   edited.  See `vc-checkout-model' for a list of possible values.
;;
;; - workfile-unchanged-p (file)
;;
;;   Return non-nil if FILE is unchanged from the working revision.
;;   This function should do a brief comparison of FILE's contents
;;   with those of the repository master of the working revision.  If
;;   the backend does not have such a brief-comparison feature, the
;;   default implementation of this function can be used, which
;;   delegates to a full vc-BACKEND-diff.  (Note that vc-BACKEND-diff
;;   must not run asynchronously in this case, see variable
;;   `vc-disable-async-diff'.)
;;
;; - mode-line-string (file)
;;
;;   If provided, this function should return the VC-specific mode
;;   line string for FILE.  The returned string should have a
;;   `help-echo' property which is the text to be displayed as a
;;   tooltip when the mouse hovers over the VC entry on the mode-line.
;;   The default implementation deals well with all states that
;;   `vc-state' can return.
;;
;; - prettify-state-info (file)
;;
;;   Translate the `vc-state' property of FILE into a string that can be
;;   used in a human-readable buffer.  The default implementation deals well
;;   with all states that `vc-state' can return.
;;
;; STATE-CHANGING FUNCTIONS
;;
;; * create-repo (backend)
;;
;;   Create an empty repository in the current directory and initialize
;;   it so VC mode can add files to it.  For file-oriented systems, this
;;   need do no more than create a subdirectory with the right name.
;;
;; * register (files &optional rev comment)
;;
;;   Register FILES in this backend.  Optionally, an initial revision REV
;;   and an initial description of the file, COMMENT, may be specified,
;;   but it is not guaranteed that the backend will do anything with this.
;;   The implementation should pass the value of vc-register-switches
;;   to the backend command.  (Note: in older versions of VC, this
;;   command took a single file argument and not a list.)
;;
;; - init-revision (file)
;;
;;   The initial revision to use when registering FILE if one is not
;;   specified by the user.  If not provided, the variable
;;   vc-default-init-revision is used instead.
;;
;; - responsible-p (file)
;;
;;   Return non-nil if this backend considers itself "responsible" for
;;   FILE, which can also be a directory.  This function is used to find
;;   out what backend to use for registration of new files and for things
;;   like change log generation.  The default implementation always
;;   returns nil.
;;
;; - could-register (file)
;;
;;   Return non-nil if FILE could be registered under this backend.  The
;;   default implementation always returns t.
;;
;; - receive-file (file rev)
;;
;;   Let this backend "receive" a file that is already registered under
;;   another backend.  The default implementation simply calls `register'
;;   for FILE, but it can be overridden to do something more specific,
;;   e.g. keep revision numbers consistent or choose editing modes for
;;   FILE that resemble those of the other backend.
;;
;; - unregister (file)
;;
;;   Unregister FILE from this backend.  This is only needed if this
;;   backend may be used as a "more local" backend for temporary editing.
;;
;; * checkin (files rev comment)
;;
;;   Commit changes in FILES to this backend.  If REV is non-nil, that
;;   should become the new revision number (not all backends do
;;   anything with it).  COMMENT is used as a check-in comment.  The
;;   implementation should pass the value of vc-checkin-switches to
;;   the backend command.  (Note: in older versions of VC, this
;;   command took a single file argument and not a list.)
;;
;; * find-revision (file rev buffer)
;;
;;   Fetch revision REV of file FILE and put it into BUFFER.
;;   If REV is the empty string, fetch the head of the trunk.
;;   The implementation should pass the value of vc-checkout-switches
;;   to the backend command.
;;
;; * checkout (file &optional editable rev)
;;
;;   Check out revision REV of FILE into the working area.  If EDITABLE
;;   is non-nil, FILE should be writable by the user and if locking is
;;   used for FILE, a lock should also be set.  If REV is non-nil, that
;;   is the revision to check out (default is the working revision).
;;   If REV is t, that means to check out the head of the current branch;
;;   if it is the empty string, check out the head of the trunk.
;;   The implementation should pass the value of vc-checkout-switches
;;   to the backend command.
;;
;; * revert (file &optional contents-done)
;;
;;   Revert FILE back to the working revision.  If optional
;;   arg CONTENTS-DONE is non-nil, then the contents of FILE have
;;   already been reverted from a version backup, and this function
;;   only needs to update the status of FILE within the backend.
;;
;; - rollback (files)
;;
;;   Remove the tip revision of each of FILES from the repository.  If
;;   this function is not provided, trying to cancel a revision is
;;   caught as an error.  (Most backends don't provide it.)  (Also
;;   note that older versions of this backend command were called
;;   'cancel-version' and took a single file arg, not a list of
;;   files.)
;;
;; - merge (file rev1 rev2)
;;
;;   Merge the changes between REV1 and REV2 into the current working file.
;;
;; - merge-news (file)
;;
;;   Merge recent changes from the current branch into FILE.
;;
;; - steal-lock (file &optional revision)
;;
;;   Steal any lock on the working revision of FILE, or on REVISION if
;;   that is provided.  This function is only needed if locking is
;;   used for files under this backend, and if files can indeed be
;;   locked by other users.
;;
;; - modify-change-comment (files rev comment)
;;
;;   Modify the change comments associated with the files at the
;;   given revision.  This is optional, many backends do not support it.
;;
;; - mark-resolved (files)
;;
;;   Mark conflicts as resolved.  Some VC systems need to run a
;;   command to mark conflicts as resolved.
;;
;; HISTORY FUNCTIONS
;;
;; * print-log (files &optional buffer)
;;
;;   Insert the revision log for FILES into BUFFER, or the *vc* buffer
;;   if BUFFER is nil.  (Note: older versions of this function expected
;;   only a single file argument.)
;;
;; - log-view-mode ()
;;
;;   Mode to use for the output of print-log.  This defaults to
;;   `log-view-mode' and is expected to be changed (if at all) to a derived
;;   mode of `log-view-mode'.
;;
;; - show-log-entry (revision)
;;
;;   If provided, search the log entry for REVISION in the current buffer,
;;   and make sure it is displayed in the buffer's window.  The default
;;   implementation of this function works for RCS-style logs.
;;
;; - wash-log (file)
;;
;;   Remove all non-comment information from the output of print-log.
;;
;; - comment-history (file)
;;
;;   Return a string containing all log entries that were made for FILE.
;;   This is used for transferring a file from one backend to another,
;;   retaining comment information.  The default implementation of this
;;   function does this by calling print-log and then wash-log, and
;;   returning the resulting buffer contents as a string.
;;
;; - update-changelog (files)
;;
;;   Using recent log entries, create ChangeLog entries for FILES, or for
;;   all files at or below the default-directory if FILES is nil.  The
;;   default implementation runs rcs2log, which handles RCS- and
;;   CVS-style logs.
;;
;; * diff (files &optional rev1 rev2 buffer)
;;
;;   Insert the diff for FILE into BUFFER, or the *vc-diff* buffer if
;;   BUFFER is nil.  If REV1 and REV2 are non-nil, report differences
;;   from REV1 to REV2.  If REV1 is nil, use the working revision (as
;;   found in the repository) as the older revision; if REV2 is nil,
;;   use the current working-copy contents as the newer revision.  This
;;   function should pass the value of (vc-switches BACKEND 'diff) to
;;   the backend command.  It should return a status of either 0 (no
;;   differences found), or 1 (either non-empty diff or the diff is
;;   run asynchronously).
;;
;; - revision-completion-table (files)
;;
;;   Return a completion table for existing revisions of FILES.
;;   The default is to not use any completion table.
;;
;; - annotate-command (file buf &optional rev)
;;
;;   If this function is provided, it should produce an annotated display
;;   of FILE in BUF, relative to revision REV.  Annotation means each line
;;   of FILE displayed is prefixed with version information associated with
;;   its addition (deleted lines leave no history) and that the text of the
;;   file is fontified according to age.
;;
;; - annotate-time ()
;;
;;   Only required if `annotate-command' is defined for the backend.
;;   Return the time of the next line of annotation at or after point,
;;   as a floating point fractional number of days.  The helper
;;   function `vc-annotate-convert-time' may be useful for converting
;;   multi-part times as returned by `current-time' and `encode-time'
;;   to this format.  Return nil if no more lines of annotation appear
;;   in the buffer.  You can safely assume that point is placed at the
;;   beginning of each line, starting at `point-min'.  The buffer that
;;   point is placed in is the Annotate output, as defined by the
;;   relevant backend.  This function also affects how much of the line
;;   is fontified; where it leaves point is where fontification begins.
;;
;; - annotate-current-time ()
;;
;;   Only required if `annotate-command' is defined for the backend,
;;   AND you'd like the current time considered to be anything besides
;;   (vc-annotate-convert-time (current-time)) -- i.e. the current
;;   time with hours, minutes, and seconds included.  Probably safe to
;;   ignore.  Return the current-time, in units of fractional days.
;;
;; - annotate-extract-revision-at-line ()
;;
;;   Only required if `annotate-command' is defined for the backend.
;;   Invoked from a buffer in vc-annotate-mode, return the revision
;;   corresponding to the current line, or nil if there is no revision
;;   corresponding to the current line.
;;
;; SNAPSHOT SYSTEM
;;
;; - create-snapshot (dir name branchp)
;;
;;   Take a snapshot of the current state of files under DIR and name it
;;   NAME.  This should make sure that files are up-to-date before
;;   proceeding with the action.  DIR can also be a file and if BRANCHP
;;   is specified, NAME should be created as a branch and DIR should be
;;   checked out under this new branch.  The default implementation does
;;   not support branches but does a sanity check, a tree traversal and
;;   for each file calls `assign-name'.
;;
;; - assign-name (file name)
;;
;;   Give name NAME to the working revision of FILE, assuming it is
;;   up-to-date.  Only used by the default version of `create-snapshot'.
;;
;; - retrieve-snapshot (dir name update)
;;
;;   Retrieve a named snapshot of all registered files at or below DIR.
;;   If UPDATE is non-nil, then update buffers of any files in the
;;   snapshot that are currently visited.  The default implementation
;;   does a sanity check whether there aren't any uncommitted changes at
;;   or below DIR, and then performs a tree walk, using the `checkout'
;;   function to retrieve the corresponding revisions.
;;
;; MISCELLANEOUS
;;
;; - root (dir)
;;
;;   Return DIR's "root" directory, that is, a parent directory of
;;   DIR for which the same backend as used for DIR applies.  If no
;;   such parent exists, this function should return DIR.
;;
;; - make-version-backups-p (file)
;;
;;   Return non-nil if unmodified repository revisions of FILE should be
;;   backed up locally.  If this is done, VC can perform `diff' and
;;   `revert' operations itself, without calling the backend system.  The
;;   default implementation always returns nil.
;;
;; - repository-hostname (dirname)
;;
;;   Return the hostname that the backend will have to contact
;;   in order to operate on a file in DIRNAME.  If the return value
;;   is nil, it means that the repository is local.
;;   This function is used in `vc-stay-local-p' which backends can use
;;   for their convenience.
;;
;; - previous-revision (file rev)
;;
;;   Return the revision number that precedes REV for FILE, or nil if no such
;;   revision exists.
;;
;; - next-revision (file rev)
;;
;;   Return the revision number that follows REV for FILE, or nil if no such
;;   revision exists.
;;
;; - check-headers ()
;;
;;   Return non-nil if the current buffer contains any version headers.
;;
;; - clear-headers ()
;;
;;   In the current buffer, reset all version headers to their unexpanded
;;   form.  This function should be provided if the state-querying code
;;   for this backend uses the version headers to determine the state of
;;   a file.  This function will then be called whenever VC changes the
;;   version control state in such a way that the headers would give
;;   wrong information.
;;
;; - delete-file (file)
;;
;;   Delete FILE and mark it as deleted in the repository.  If this
;;   function is not provided, the command `vc-delete-file' will
;;   signal an error.
;;
;; - rename-file (old new)
;;
;;   Rename file OLD to NEW, both in the working area and in the
;;   repository.  If this function is not provided, the renaming
;;   will be done by (vc-delete-file old) and (vc-register new).
;;
;; - find-file-hook ()
;;
;;   Operation called in current buffer when opening a file.  This can
;;   be used by the backend to setup some local variables it might need.
;;
;; - find-file-not-found-hook ()
;;
;;   Operation called in current buffer when opening a non-existing file.
;;   By default, this asks the user if she wants to check out the file.
;;
;; - extra-menu ()
;;
;;   Return a menu keymap, the items in the keymap will appear at the
;;   end of the Version Control menu.  The goal is to allow backends
;;   to specify extra menu items that appear in the VC menu.  This way
;;   you can provide menu entries for functionality that is specific
;;   to your backend and which does not map to any of the VC generic
;;   concepts.
;;
;; - extra-status-menu ()
;;
;;   Return a menu keymap, the items in the keymap will appear at the
;;   end of the VC Status menu.  The goal is to allow backends to
;;   specify extra menu items that appear in the VC Status menu.  This
;;   makes it possible to provide menu entries for functionality that
;;   is specific to a backend and which does not map to any of the VC
;;   generic concepts.

;;; Todo:

;; - vc-update/vc-merge should deal with VC systems that don't
;;   update/merge on a file basis, but on a whole repository basis.
;;
;; - deal with push/pull operations.
;;
;; - "snapshots" should be renamed to "branches", and thoroughly reworked.
;;
;; - when a file is in `conflict' state, turn on smerge-mode.
;;
;; - figure out what to do with conflicts that are not caused by the
;;   file contents, but by metadata or other causes.  Example: File A
;;   gets renamed to B in one branch and to C in another and you merge
;;   the two branches.  Or you locally add file FOO and then pull a
;;   change that also adds a new file FOO, ...
;;
;; - add a generic mechanism for remembering the current branch names,
;;   display the branch name in the mode-line. Replace
;;   vc-cvs-sticky-tag with that.
;;
;; - C-x v b does switch to a different backend, but the mode line is not 
;;   adapted accordingly.  Also, it considers RCS and CVS to be the same, 
;;   which is pretty confusing.
;;
;; - vc-diff should be able to show the diff for all files in a
;;   changeset, especially for VC systems that have per repository
;;   version numbers.  log-view should take advantage of this.
;;
;; - make it easier to write logs.  Maybe C-x 4 a should add to the log
;;   buffer, if one is present, instead of adding to the ChangeLog.
;;
;; - add a mechanism for editing the underlying VCS's list of files
;;   to be ignored, when that's possible.
;;
;; - When vc-next-action calls vc-checkin it could pre-fill the
;;   *VC-log* buffer with some obvious items: the list of files that
;;   were added, the list of files that were removed.  If the diff is
;;   available, maybe it could even call something like
;;   `diff-add-change-log-entries-other-window' to create a detailed
;;   skeleton for the log...
;;
;; - a way to do repository wide log (instead of just per
;;   file/fileset) is needed.  Doing it per directory might be enough...
;;
;; - most vc-dir backends need more work.  They might need to
;;   provide custom headers, use the `extra' field and deal with all
;;   possible VC states.
;;
;; - add function that calls vc-dir to `find-directory-functions'.
;;
;; - vc-diff, vc-annotate, etc. need to deal better with unregistered
;;   files. Now that unregistered and ignored files are shown in
;;   vc-dired/vc-dir, it is possible that these commands are called
;;   for unregistered/ignored files.
;;
;; - do not default to RCS anymore when the current directory is not
;;   controlled by any VCS and the user does C-x v v
;;
;; - vc-create-snapshot and vc-retrieve-snapshot should update the
;;   buffers that might be visiting the affected files.
;;
;; - Using multiple backends needs work.  Given a CVS directory with some
;;   files checked into git (but not all), using C-x v l to get a log file
;;   from a file only present in git, and then typing RET on some log entry,
;;   vc will bombs out because it wants to see the file being in CVS.
;;   Those logs should likely use a local variable to hardware the VC they
;;   are supposed to work with.
;;
;; - Another important thing: merge all the status-like backend operations.
;;   We should remove dir-status, state, dir-state, and dir-status-files, and
;;   replace them with just `status' which takes a fileset and a continuation
;;   (like dir-status) and returns a buffer in which the process(es) are run
;;   (or nil if it worked synchronously).  Hopefully we can define the old
;;   4 operations in term of this one.
;;
;; - backends that care about vc-stay-local should try to take it into
;;   account for vc-dir.  Is this likely to be useful???
;;
;; - vc-dir listing needs a footer generated when it's done to make it obvious
;; that it has finished.
;;

;;; Code:

(require 'vc-hooks)
(require 'vc-dispatcher)
(require 'tool-bar)
(require 'ewoc)

(eval-when-compile
  (require 'dired)
  (require 'cl))

(unless (assoc 'vc-parent-buffer minor-mode-alist)
  (setq minor-mode-alist
	(cons '(vc-parent-buffer vc-parent-buffer-name)
	      minor-mode-alist)))

;; General customization

(defgroup vc nil
  "Version-control system in Emacs."
  :group 'tools)

(defcustom vc-suppress-confirm nil
  "If non-nil, treat user as expert; suppress yes-no prompts on some things."
  :type 'boolean
  :group 'vc)

(defcustom vc-initial-comment nil
  "If non-nil, prompt for initial comment when a file is registered."
  :type 'boolean
  :group 'vc)

(defcustom vc-default-init-revision "1.1"
  "A string used as the default revision number when a new file is registered.
This can be overridden by giving a prefix argument to \\[vc-register].  This
can also be overridden by a particular VC backend."
  :type 'string
  :group 'vc
  :version "20.3")

(defcustom vc-checkin-switches nil
  "A string or list of strings specifying extra switches for checkin.
These are passed to the checkin program by \\[vc-checkin]."
  :type '(choice (const :tag "None" nil)
		 (string :tag "Argument String")
		 (repeat :tag "Argument List"
			 :value ("")
			 string))
  :group 'vc)

(defcustom vc-checkout-switches nil
  "A string or list of strings specifying extra switches for checkout.
These are passed to the checkout program by \\[vc-checkout]."
  :type '(choice (const :tag "None" nil)
		 (string :tag "Argument String")
		 (repeat :tag "Argument List"
			 :value ("")
			 string))
  :group 'vc)

(defcustom vc-register-switches nil
  "A string or list of strings; extra switches for registering a file.
These are passed to the checkin program by \\[vc-register]."
  :type '(choice (const :tag "None" nil)
		 (string :tag "Argument String")
		 (repeat :tag "Argument List"
			 :value ("")
			 string))
  :group 'vc)

(defcustom vc-diff-switches nil
  "A string or list of strings specifying switches for diff under VC.
When running diff under a given BACKEND, VC concatenates the values of
`diff-switches', `vc-diff-switches', and `vc-BACKEND-diff-switches' to
get the switches for that command.  Thus, `vc-diff-switches' should
contain switches that are specific to version control, but not
specific to any particular backend."
  :type '(choice (const :tag "None" nil)
		 (string :tag "Argument String")
		 (repeat :tag "Argument List"
			 :value ("")
			 string))
  :group 'vc
  :version "21.1")

(defcustom vc-diff-knows-L nil
  "*Indicates whether diff understands the -L option.
The value is either `yes', `no', or nil.  If it is nil, VC tries
to use -L and sets this variable to remember whether it worked."
  :type '(choice (const :tag "Work out" nil) (const yes) (const no))
  :group 'vc)

(defcustom vc-allow-async-revert nil
  "Specifies whether the diff during \\[vc-revert] may be asynchronous.
Enabling this option means that you can confirm a revert operation even
if the local changes in the file have not been found and displayed yet."
  :type '(choice (const :tag "No" nil)
                 (const :tag "Yes" t))
  :group 'vc
  :version "22.1")

;;;###autoload
(defcustom vc-checkout-hook nil
  "Normal hook (list of functions) run after checking out a file.
See `run-hooks'."
  :type 'hook
  :group 'vc
  :version "21.1")

(defcustom vc-annotate-display-mode 'fullscale
  "Which mode to color the output of \\[vc-annotate] with by default."
  :type '(choice (const :tag "By Color Map Range" nil)
		 (const :tag "Scale to Oldest" scale)
		 (const :tag "Scale Oldest->Newest" fullscale)
		 (number :tag "Specify Fractional Number of Days"
			 :value "20.5"))
  :group 'vc)

;;;###autoload
(defcustom vc-checkin-hook nil
  "Normal hook (list of functions) run after commit or file checkin.
See also `log-edit-done-hook'."
  :type 'hook
  :options '(log-edit-comment-to-change-log)
  :group 'vc)

;;;###autoload
(defcustom vc-before-checkin-hook nil
  "Normal hook (list of functions) run before a commit or a file checkin.
See `run-hooks'."
  :type 'hook
  :group 'vc)

;; Annotate customization
(defcustom vc-annotate-color-map
  (if (and (tty-display-color-p) (<= (display-color-cells) 8))
      ;; A custom sorted TTY colormap
      (let* ((colors
	      (sort
	       (delq nil
		     (mapcar (lambda (x)
			       (if (not (or
					 (string-equal (car x) "white")
					 (string-equal (car x) "black") ))
				   (car x)))
			     (tty-color-alist)))
	       (lambda (a b)
		 (cond
		  ((or (string-equal a "red") (string-equal b "blue")) t)
		  ((or (string-equal b "red") (string-equal a "blue")) nil)
		  ((string-equal a "yellow") t)
		  ((string-equal b "yellow") nil)
		  ((string-equal a "cyan") t)
		  ((string-equal b "cyan") nil)
		  ((string-equal a "green") t)
		  ((string-equal b "green") nil)
		  ((string-equal a "magenta") t)
		  ((string-equal b "magenta") nil)
		  (t (string< a b))))))
	     (date 20.)
	     (delta (/ (- 360. date) (1- (length colors)))))
	(mapcar (lambda (x)
		  (prog1
		      (cons date x)
		    (setq date (+ date delta)))) colors))
    ;; Normal colormap: hue stepped from 0-240deg, value=1., saturation=0.75
    '(( 20. . "#FF3F3F")
      ( 40. . "#FF6C3F")
      ( 60. . "#FF993F")
      ( 80. . "#FFC63F")
      (100. . "#FFF33F")
      (120. . "#DDFF3F")
      (140. . "#B0FF3F")
      (160. . "#83FF3F")
      (180. . "#56FF3F")
      (200. . "#3FFF56")
      (220. . "#3FFF83")
      (240. . "#3FFFB0")
      (260. . "#3FFFDD")
      (280. . "#3FF3FF")
      (300. . "#3FC6FF")
      (320. . "#3F99FF")
      (340. . "#3F6CFF")
      (360. . "#3F3FFF")))
  "Association list of age versus color, for \\[vc-annotate].
Ages are given in units of fractional days.  Default is eighteen
steps using a twenty day increment, from red to blue.  For TTY
displays with 8 or fewer colors, the default is red to blue with
all other colors between (excluding black and white)."
  :type 'alist
  :group 'vc)

(defcustom vc-annotate-very-old-color "#3F3FFF"
  "Color for lines older than the current color range in \\[vc-annotate]]."
  :type 'string
  :group 'vc)

(defcustom vc-annotate-background "black"
  "Background color for \\[vc-annotate].
Default color is used if nil."
  :type '(choice (const :tag "Default background" nil) (color))
  :group 'vc)

(defcustom vc-annotate-menu-elements '(2 0.5 0.1 0.01)
  "Menu elements for the mode-specific menu of VC-Annotate mode.
List of factors, used to expand/compress the time scale.  See `vc-annotate'."
  :type '(repeat number)
  :group 'vc)

(defvar vc-annotate-mode-map
  (let ((m (make-sparse-keymap)))
    (define-key m "A" 'vc-annotate-revision-previous-to-line)
    (define-key m "D" 'vc-annotate-show-diff-revision-at-line)
    (define-key m "f" 'vc-annotate-find-revision-at-line)
    (define-key m "J" 'vc-annotate-revision-at-line)
    (define-key m "L" 'vc-annotate-show-log-revision-at-line)
    (define-key m "N" 'vc-annotate-next-revision)
    (define-key m "P" 'vc-annotate-prev-revision)
    (define-key m "W" 'vc-annotate-working-revision)
    (define-key m "V" 'vc-annotate-toggle-annotation-visibility)
    m)
  "Local keymap used for VC-Annotate mode.")

;; Header-insertion hair

(defcustom vc-static-header-alist
  '(("\\.c\\'" .
     "\n#ifndef lint\nstatic char vcid[] = \"\%s\";\n#endif /* lint */\n"))
  "*Associate static header string templates with file types.
A \%s in the template is replaced with the first string associated with
the file's version control type in `vc-header-alist'."
  :type '(repeat (cons :format "%v"
		       (regexp :tag "File Type")
		       (string :tag "Header String")))
  :group 'vc)

(defcustom vc-comment-alist
  '((nroff-mode ".\\\"" ""))
  "*Special comment delimiters for generating VC headers.
Add an entry in this list if you need to override the normal `comment-start'
and `comment-end' variables.  This will only be necessary if the mode language
is sensitive to blank lines."
  :type '(repeat (list :format "%v"
		       (symbol :tag "Mode")
		       (string :tag "Comment Start")
		       (string :tag "Comment End")))
  :group 'vc)

(defcustom vc-checkout-carefully (= (user-uid) 0)
  "*Non-nil means be extra-careful in checkout.
Verify that the file really is not locked
and that its contents match what the master file says."
  :type 'boolean
  :group 'vc)
(make-obsolete-variable 'vc-checkout-carefully
                        "the corresponding checks are always done now."
                        "21.1")

\f
;; Variables users don't need to see

(defvar vc-disable-async-diff nil
  "VC sets this to t locally to disable some async diff operations.
Backends that offer asynchronous diffs should respect this variable
in their implementation of vc-BACKEND-diff.")

;; File property caching

(defun vc-clear-context ()
  "Clear all cached file properties."
  (interactive)
  (fillarray vc-file-prop-obarray 0))

(defmacro with-vc-properties (files form settings)
  "Execute FORM, then maybe set per-file properties for FILES.
SETTINGS is an association list of property/value pairs.  After
executing FORM, set those properties from SETTINGS that have not yet
been updated to their corresponding values."
  (declare (debug t))
  `(let ((vc-touched-properties (list t)))
     ,form
     (dolist (file ,files)
       (dolist (setting ,settings)
         (let ((property (car setting)))
           (unless (memq property vc-touched-properties)
             (put (intern file vc-file-prop-obarray)
                  property (cdr setting))))))))

;; Two macros for elisp programming

;;;###autoload
(defmacro with-vc-file (file comment &rest body)
  "Check out a writable copy of FILE if necessary, then execute BODY.
Check in FILE with COMMENT (a string) after BODY has been executed.
FILE is passed through `expand-file-name'; BODY executed within
`save-excursion'.  If FILE is not under version control, or you are
using a locking version-control system and the file is locked by
somebody else, signal error."
  (declare (debug t) (indent 2))
  (let ((filevar (make-symbol "file")))
    `(let ((,filevar (expand-file-name ,file)))
       (or (vc-backend ,filevar)
           (error "File not under version control: `%s'" file))
       (unless (vc-editable-p ,filevar)
         (let ((state (vc-state ,filevar)))
           (if (stringp state)
               (error "`%s' is locking `%s'" state ,filevar)
             (vc-checkout ,filevar t))))
       (save-excursion
         ,@body)
       (vc-checkin (list ,filevar) nil ,comment))))

;;;###autoload
(defmacro edit-vc-file (file comment &rest body)
  "Edit FILE under version control, executing body.
Checkin with COMMENT after executing BODY.
This macro uses `with-vc-file', passing args to it.
However, before executing BODY, find FILE, and after BODY, save buffer."
  (declare (debug t) (indent 2))
  (let ((filevar (make-symbol "file")))
    `(let ((,filevar (expand-file-name ,file)))
       (with-vc-file
        ,filevar ,comment
        (set-buffer (find-file-noselect ,filevar))
        ,@body
        (save-buffer)))))

;;; Code for deducing what fileset and backend to assume

(defun vc-responsible-backend (file &optional register)
  "Return the name of a backend system that is responsible for FILE.
The optional argument REGISTER means that a backend suitable for
registration should be found.

If REGISTER is nil, then if FILE is already registered, return the
backend of FILE.  If FILE is not registered, or a directory, then the
first backend in `vc-handled-backends' that declares itself
responsible for FILE is returned.  If no backend declares itself
responsible, return the first backend.

If REGISTER is non-nil, return the first responsible backend under
which FILE is not yet registered.  If there is no such backend, return
the first backend under which FILE is not yet registered, but could
be registered."
  (when (not vc-handled-backends)
    (error "No handled backends"))
  (or (and (not (file-directory-p file)) (not register) (vc-backend file))
      (catch 'found
	;; First try: find a responsible backend.  If this is for registration,
	;; it must be a backend under which FILE is not yet registered.
	(dolist (backend vc-handled-backends)
	  (and (or (not register)
		   (not (vc-call-backend backend 'registered file)))
	       (vc-call-backend backend 'responsible-p file)
	       (throw 'found backend)))
	;; no responsible backend
	(if (not register)
	    ;; if this is not for registration, the first backend must do
	    (car vc-handled-backends)
	  ;; for registration, we need to find a new backend that
	  ;; could register FILE
	  (dolist (backend vc-handled-backends)
	    (and (not (vc-call-backend backend 'registered file))
		 (vc-call-backend backend 'could-register file)
		 (throw 'found backend)))
	  (error "No backend that could register")))))

(defun vc-expand-dirs (file-or-dir-list)
  "Expands directories in a file list specification.
Only files already under version control are noticed."
  ;; FIXME: Kill this function.
  (let ((flattened '()))
    (dolist (node file-or-dir-list)
      (vc-file-tree-walk
       node (lambda (f) (when (vc-backend f) (push f flattened)))))
    (nreverse flattened)))

(defun vc-deduce-fileset (&optional allow-directory-wildcard allow-unregistered
				    include-files-not-directories)
  "Deduce a set of files and a backend to which to apply an operation.

Return (BACKEND . FILESET).
If we're in VC-dired mode, the fileset is the list of marked files.
Otherwise, if we're looking at a buffer visiting a version-controlled file,
the fileset is a singleton containing this file.
If neither of these things is true, but ALLOW-DIRECTORY-WILDCARD is on
and we're in a dired buffer, select the current directory.
If none of these conditions is met, but ALLOW_UNREGISTERED is on and the
visited file is not registered, return a singleton fileset containing it.
If INCLUDE-FILES-NOT-DIRECTORIES then if directories are marked,
return the list of files VC files in those directories instead of
the directories themselves.
Otherwise, throw an error."
  (let (backend)
    (cond
     (vc-dired-mode
      (let ((marked (dired-map-over-marks (dired-get-filename) nil)))
	(unless marked
	  (error "No files have been selected."))
	;; All members of the fileset must have the same backend
	(setq backend (vc-backend (car marked)))
	(dolist (f (cdr marked))
	  (unless (eq (vc-backend f) backend)
	    (error "All members of a fileset must be under the same version-control system.")))
	(cons backend marked)))
     ((eq major-mode 'vc-dir-mode)
      ;; FIXME: Maybe the backend should be stored in a buffer-local
      ;; variable?
      (cons (vc-responsible-backend default-directory)
		(or
		 (if include-files-not-directories
		     (vc-dir-marked-only-files)
		   (vc-dir-marked-files))
		 (list (vc-dir-current-file)))))
     ((setq backend (vc-backend buffer-file-name))
      (cons backend (list buffer-file-name)))
     ((and vc-parent-buffer (or (buffer-file-name vc-parent-buffer)
				(with-current-buffer vc-parent-buffer
				  (or vc-dired-mode (eq major-mode 'vc-dir-mode)))))
      (progn
	(set-buffer vc-parent-buffer)
	(vc-deduce-fileset)))
     ;; This is guarded by an enabling arg so users won't potentially
     ;; shoot themselves in the foot by modifying a fileset they can't
     ;; verify by eyeball.  Allow it for nondestructive commands like
     ;; making diffs, or possibly for destructive ones that have
     ;; confirmation prompts.
     ((and allow-directory-wildcard
	   ;; I think this is a misfeature.  For now, I'll leave it in, but
	   ;; I'll disable it anywhere else than in dired buffers.  --Stef
	   (and (derived-mode-p 'dired-mode)
		(equal buffer-file-name nil)
		(equal list-buffers-directory default-directory)))
      (progn
	(message "All version-controlled files below %s selected."
		 default-directory)
	(cons
	 (vc-responsible-backend default-directory)
	 (list default-directory))))
     ;; If we're allowing unregistered fiiles and visiting one, select it.
     ((and allow-unregistered (not (vc-registered buffer-file-name)))
      (cons (vc-responsible-backend
	     (file-name-directory (buffer-file-name)))
	    (list buffer-file-name)))
     (t (error "No fileset is available here.")))))

(defun vc-ensure-vc-buffer ()
  "Make sure that the current buffer visits a version-controlled file."
  (cond
   (vc-dired-mode
    (set-buffer (find-file-noselect (dired-get-filename))))
   ((eq major-mode 'vc-dir-mode)
    (set-buffer (find-file-noselect (vc-dir-current-file))))
   (t
    (while (and vc-parent-buffer
                (buffer-live-p vc-parent-buffer)
		;; Avoid infinite looping when vc-parent-buffer and
		;; current buffer are the same buffer.
 		(not (eq vc-parent-buffer (current-buffer))))
      (set-buffer vc-parent-buffer))
    (if (not buffer-file-name)
	(error "Buffer %s is not associated with a file" (buffer-name))
      (unless (vc-backend buffer-file-name)
	(error "File %s is not under version control" buffer-file-name))))))

;;; Support for the C-x v v command.
;; This is where all the single-file-oriented code from before the fileset
;; rewrite lives.

(defsubst vc-editable-p (file)
  "Return non-nil if FILE can be edited."
  (let ((backend (vc-backend file)))
    (and backend
         (or (eq (vc-checkout-model backend (list file)) 'implicit)
             (memq (vc-state file) '(edited needs-merge conflict))))))

(defun vc-buffer-sync (&optional not-urgent)
  "Make sure the current buffer and its working file are in sync.
NOT-URGENT means it is ok to continue if the user says not to save."
  (when (buffer-modified-p)
    (if (or vc-suppress-confirm
	    (y-or-n-p (format "Buffer %s modified; save it? " (buffer-name))))
	(save-buffer)
      (unless not-urgent
	(error "Aborted")))))

(defun vc-compatible-state (p q)
  "Controls which states can be in the same commit."
  (or
   (eq p q)
   (and (member p '(edited added removed)) (member q '(edited added removed)))))

;; Here's the major entry point.

;;;###autoload
(defun vc-next-action (verbose)
  "Do the next logical version control operation on the current fileset.
This requires that all files in the fileset be in the same state.

For locking systems:
   If every file is not already registered, this registers each for version
control.
   If every file is registered and not locked by anyone, this checks out
a writable and locked file of each ready for editing.
   If every file is checked out and locked by the calling user, this
first checks to see if each file has changed since checkout.  If not,
it performs a revert on that file.
   If every file has been changed, this pops up a buffer for entry
of a log message; when the message has been entered, it checks in the
resulting changes along with the log message as change commentary.  If
the variable `vc-keep-workfiles' is non-nil (which is its default), a
read-only copy of each changed file is left in place afterwards.
   If the affected file is registered and locked by someone else, you are
given the option to steal the lock(s).

For merging systems:
   If every file is not already registered, this registers each one for version
control.  This does an add, but not a commit.
   If every file is added but not committed, each one is committed.
   If every working file is changed, but the corresponding repository file is
unchanged, this pops up a buffer for entry of a log message; when the
message has been entered, it checks in the resulting changes along
with the logmessage as change commentary.  A writable file is retained.
   If the repository file is changed, you are asked if you want to
merge in the changes into your working copy."
  (interactive "P")
  (let* ((vc-fileset (vc-deduce-fileset nil t))
	 (vc-fileset-only-files (vc-deduce-fileset nil t t))
	 (only-files (cdr vc-fileset-only-files))
         (backend (car vc-fileset))
	 (files (cdr vc-fileset))
	 (state (vc-state (car only-files)))
	 (model (vc-checkout-model backend files))
	 revision)

    ;; Verify that the fileset is homogeneous
    (dolist (file (cdr only-files))
      ;; Ignore directories, they are compatible with anything.
      (unless (file-directory-p file)
	(unless (vc-compatible-state (vc-state file) state)
	  (error "%s:%s clashes with %s:%s"
		 file (vc-state file) (car files) state))
	(unless (eq (vc-checkout-model backend (list file)) model)
	  (error "Fileset has mixed checkout models"))))
    ;; Check for buffers in the fileset not matching the on-disk contents.
    (dolist (file files)
      (let ((visited (get-file-buffer file)))
	(when visited
	  (if (or vc-dired-mode (eq major-mode 'vc-dir-mode))
	      (switch-to-buffer-other-window visited)
	    (set-buffer visited))
	  ;; Check relation of buffer and file, and make sure
	  ;; user knows what he's doing.  First, finding the file
	  ;; will check whether the file on disk is newer.
	  ;; Ignore buffer-read-only during this test, and
	  ;; preserve find-file-literally.
	  (let ((buffer-read-only (not (file-writable-p file))))
	    (find-file-noselect file nil find-file-literally))
	  (if (not (verify-visited-file-modtime (current-buffer)))
	      (if (yes-or-no-p (format "Replace %s on disk with buffer contents? " file))
		  (write-file buffer-file-name)
		(error "Aborted"))
	    ;; Now, check if we have unsaved changes.
	    (vc-buffer-sync t)
	    (when (buffer-modified-p)
	      (or (y-or-n-p (message "Use %s on disk, keeping modified buffer? " file))
		  (error "Aborted")))))))
    ;; Do the right thing
    (cond
     ((eq state 'missing)
      (error "Fileset files are missing, so cannot be operated on."))
     ;; Files aren't registered
     ((or (eq state 'unregistered)
	  (eq state 'ignored))
      (mapc (lambda (arg) (vc-register nil arg)) files))
     ;; Files are up-to-date, or need a merge and user specified a revision
     ((or (eq state 'up-to-date) (and verbose (eq state 'needs-update)))
      (cond
       (verbose
	;; go to a different revision
	(setq revision (read-string "Branch, revision, or backend to move to: "))
	(let ((vsym (intern-soft (upcase revision))))
	  (if (member vsym vc-handled-backends)
	      (dolist (file files) (vc-transfer-file file vsym))
	    (dolist (file files)
              (vc-checkout file (eq model 'implicit) revision)))))
       ((not (eq model 'implicit))
	;; check the files out
	(dolist (file files) (vc-checkout file t)))
       (t
        ;; do nothing
        (message "Fileset is up-to-date"))))
     ;; Files have local changes
     ((vc-compatible-state state 'edited)
      (let ((ready-for-commit files))
	;; If files are edited but read-only, give user a chance to correct
	(dolist (file files)
	  (unless (file-writable-p file)
	    ;; Make the file+buffer read-write.
	    (unless (y-or-n-p (format "%s is edited but read-only; make it writable and continue?" file))
	      (error "Aborted"))
	    (set-file-modes file (logior (file-modes file) 128))
	    (let ((visited (get-file-buffer file)))
	      (when visited
		(with-current-buffer visited
		  (toggle-read-only -1))))))
	;; Allow user to revert files with no changes
	(save-excursion
          (dolist (file files)
            (let ((visited (get-file-buffer file)))
              ;; For files with locking, if the file does not contain
              ;; any changes, just let go of the lock, i.e. revert.
              (when (and (not (eq model 'implicit))
			 (vc-workfile-unchanged-p file)
			 ;; If buffer is modified, that means the user just
			 ;; said no to saving it; in that case, don't revert,
			 ;; because the user might intend to save after
			 ;; finishing the log entry and committing.
			 (not (and visited (buffer-modified-p))))
		(vc-revert-file file)
		(delete file ready-for-commit)))))
	;; Remaining files need to be committed
	(if (not ready-for-commit)
	    (message "No files remain to be committed")
	  (if (not verbose)
	      (vc-checkin ready-for-commit)
	    (progn
	      (setq revision (read-string "New revision or backend: "))
	      (let ((vsym (intern (upcase revision))))
		(if (member vsym vc-handled-backends)
		    (dolist (file files) (vc-transfer-file file vsym))
		  (vc-checkin ready-for-commit revision))))))))
     ;; locked by somebody else (locking VCSes only)
     ((stringp state)
      ;; In the old days, we computed the revision once and used it on
      ;; the single file.  Then, for the 2007-2008 fileset rewrite, we
      ;; computed the revision once (incorrectly, using a free var) and
      ;; used it on all files.  To fix the free var bug, we can either
      ;; use `(car files)' or do what we do here: distribute the
      ;; revision computation among `files'.  Although this may be
      ;; tedious for those backends where a "revision" is a trans-file
      ;; concept, it is nonetheless correct for both those and (more
      ;; importantly) for those where "revision" is a per-file concept.
      ;; If the intersection of the former group and "locking VCSes" is
      ;; non-empty [I vaguely doubt it --ttn], we can reinstate the
      ;; pre-computation approach of yore.
      (dolist (file files)
        (vc-steal-lock
         file (if verbose
                  (read-string (format "%s revision to steal: " file))
                (vc-working-revision file))
         state)))
     ;; conflict
     ((eq state 'conflict)
      (vc-mark-resolved files))
     ;; needs-update
     ((eq state 'needs-update)
      (dolist (file files)
	(if (yes-or-no-p (format
			  "%s is not up-to-date.  Get latest revision? "
			  (file-name-nondirectory file)))
	    (vc-checkout file (eq model 'implicit) t)
	  (when (and (not (eq model 'implicit))
		     (yes-or-no-p "Lock this revision? "))
	    (vc-checkout file t)))))
     ;; needs-merge
     ((eq state 'needs-merge)
      (dolist (file files)
	(when (yes-or-no-p (format
			  "%s is not up-to-date.  Merge in changes now? "
			  (file-name-nondirectory file)))
	  (vc-maybe-resolve-conflicts file (vc-call merge-news file)))))

     ;; unlocked-changes
     ((eq state 'unlocked-changes)
      (dolist (file files)
	(when (not (equal buffer-file-name file))
	  (find-file-other-window file))
	(if (save-window-excursion
	      (vc-diff-internal nil (cons (car vc-fileset) (list file))
				(vc-working-revision file) nil)
	      (goto-char (point-min))
	      (let ((inhibit-read-only t))
		(insert
		 (format "Changes to %s since last lock:\n\n" file)))
	      (not (beep))
	      (yes-or-no-p (concat "File has unlocked changes.  "
				   "Claim lock retaining changes? ")))
	    (progn (vc-call steal-lock file)
		   (clear-visited-file-modtime)
		   ;; Must clear any headers here because they wouldn't
		   ;; show that the file is locked now.
		   (vc-clear-headers file)
		   (write-file buffer-file-name)
		   (vc-mode-line file))
	  (if (not (yes-or-no-p
		    "Revert to checked-in revision, instead? "))
	      (error "Checkout aborted")
	    (vc-revert-buffer-internal t t)
	    (vc-checkout file t)))))
     ;; Unknown fileset state
     (t
      (error "Fileset is in an unknown state %s" state)))))

(defun vc-create-repo (backend)
  "Create an empty repository in the current directory."
  (interactive
   (list
    (intern
     (upcase
      (completing-read
       "Create repository for: "
       (mapcar (lambda (b) (list (downcase (symbol-name b)))) vc-handled-backends)
       nil t)))))
  (vc-call-backend backend 'create-repo))

;;;###autoload
(defun vc-register (&optional set-revision fname comment)
  "Register into a version control system.
If FNAME is given register that file, otherwise register the current file.
With prefix argument SET-REVISION, allow user to specify initial revision
level.  If COMMENT is present, use that as an initial comment.

The version control system to use is found by cycling through the list
`vc-handled-backends'.  The first backend in that list which declares
itself responsible for the file (usually because other files in that
directory are already registered under that backend) will be used to
register the file.  If no backend declares itself responsible, the
first backend that could register the file is used."
  (interactive "P")
  (when (and (null fname) (null buffer-file-name)) (error "No visited file"))

  (let ((bname (if fname (get-file-buffer fname) (current-buffer))))
    (unless fname (setq fname buffer-file-name))
    (when (vc-backend fname)
      (if (vc-registered fname)
	  (error "This file is already registered")
	(unless (y-or-n-p "Previous master file has vanished.  Make a new one? ")
	  (error "Aborted"))))
    ;; Watch out for new buffers of size 0: the corresponding file
    ;; does not exist yet, even though buffer-modified-p is nil.
    (when bname
      (with-current-buffer bname
	(when (and (not (buffer-modified-p))
		 (zerop (buffer-size))
		 (not (file-exists-p buffer-file-name)))
	  (set-buffer-modified-p t))
	(vc-buffer-sync)))
    (vc-start-logentry (list fname)
		    (if set-revision
			(read-string (format "Initial revision level for %s: "
					     fname))
		      (vc-call-backend (vc-responsible-backend fname)
				       'init-revision))
		    (or comment (not vc-initial-comment))
		    nil
		    "Enter initial comment."
		    (lambda (files rev comment)
		      (dolist (file files)
			(message "Registering %s... " file)
			(let ((backend (vc-responsible-backend file t)))
			  (vc-file-clearprops file)
			  (vc-call-backend backend 'register (list file) rev comment)
			  (vc-file-setprop file 'vc-backend backend)
			  (unless vc-make-backup-files
			    (make-local-variable 'backup-inhibited)
			    (setq backup-inhibited t)))
			(message "Registering %s... done" file))))))

(defun vc-register-with (backend)
  "Register the current file with a specified back end."
  (interactive "SBackend: ")
  (when (not (member backend vc-handled-backends))
    (error "Unknown back end."))
  (let ((vc-handled-backends (list backend)))
    (call-interactively 'vc-register)))

(defun vc-checkout (file &optional writable rev)
  "Retrieve a copy of the revision REV of FILE.
If WRITABLE is non-nil, make sure the retrieved file is writable.
REV defaults to the latest revision.

After check-out, runs the normal hook `vc-checkout-hook'."
  (and writable
       (not rev)
       (vc-call make-version-backups-p file)
       (vc-up-to-date-p file)
       (vc-make-version-backup file))
  (let ((backend (vc-backend file)))
    (with-vc-properties (list file)
      (condition-case err
          (vc-call-backend backend 'checkout file writable rev)
        (file-error
         ;; Maybe the backend is not installed ;-(
         (when writable
           (let ((buf (get-file-buffer file)))
             (when buf (with-current-buffer buf (toggle-read-only -1)))))
         (signal (car err) (cdr err))))
      `((vc-state . ,(if (or (eq (vc-checkout-model backend (list file)) 'implicit)
                             (not writable))
                         (if (vc-call latest-on-branch-p file)
                             'up-to-date
                           'needs-update)
                       'edited))
        (vc-checkout-time . ,(nth 5 (file-attributes file))))))
  (vc-resynch-buffer file t t)
  (run-hooks 'vc-checkout-hook))

(defun vc-mark-resolved (files)
  (with-vc-properties
   files
   (vc-call mark-resolved files)
   ;; XXX: Is this TRTD?  Might not be.
   `((vc-state . edited))))

(defun vc-steal-lock (file rev owner)
  "Steal the lock on FILE."
  (let (file-description)
    (if rev
	(setq file-description (format "%s:%s" file rev))
      (setq file-description file))
    (when (not (yes-or-no-p (format "Steal the lock on %s from %s? "
				    file-description owner)))
      (error "Steal canceled"))
    (message "Stealing lock on %s..." file)
    (with-vc-properties
     (list file)
     (vc-call steal-lock file rev)
     `((vc-state . edited)))
    (vc-resynch-buffer file t t)
    (message "Stealing lock on %s...done" file)
    ;; Write mail after actually stealing, because if the stealing
    ;; goes wrong, we don't want to send any mail.
    (compose-mail owner (format "Stolen lock on %s" file-description))
    (setq default-directory (expand-file-name "~/"))
    (goto-char (point-max))
    (insert
     (format "I stole the lock on %s, " file-description)
     (current-time-string)
     ".\n")
    (message "Please explain why you stole the lock.  Type C-c C-c when done.")))

(defun vc-checkin (files &optional rev comment initial-contents)
  "Check in FILES.
The optional argument REV may be a string specifying the new revision
level (if nil increment the current level).  COMMENT is a comment
string; if omitted, a buffer is popped up to accept a comment.  If
INITIAL-CONTENTS is non-nil, then COMMENT is used as the initial contents
of the log entry buffer.

If `vc-keep-workfiles' is nil, FILE is deleted afterwards, provided
that the version control system supports this mode of operation.

Runs the normal hooks `vc-before-checkin-hook' and `vc-checkin-hook'."
  (when vc-before-checkin-hook
    (run-hooks 'vc-before-checkin-hook))
  (vc-start-logentry
   files rev comment initial-contents
   "Enter a change comment."
   (lambda (files rev comment)
     (message "Checking in %s..." (vc-delistify files))
     ;; "This log message intentionally left almost blank".
     ;; RCS 5.7 gripes about white-space-only comments too.
     (or (and comment (string-match "[^\t\n ]" comment))
	 (setq comment "*** empty log message ***"))
     (with-vc-properties
      files
      ;; We used to change buffers to get local value of vc-checkin-switches,
      ;; but 'the' local buffer is not a well-defined concept for filesets.
      (progn
	(vc-call checkin files rev comment)
	(mapc 'vc-delete-automatic-version-backups files))
      `((vc-state . up-to-date)
	(vc-checkout-time . ,(nth 5 (file-attributes file)))
	(vc-working-revision . nil)))
     (message "Checking in %s...done" (vc-delistify files)))
   'vc-checkin-hook))

;;; Additional entry points for examining version histories

;; (defun vc-default-diff-tree (backend dir rev1 rev2)
;;   "List differences for all registered files at and below DIR.
;; The meaning of REV1 and REV2 is the same as for `vc-revision-diff'."
;;   ;; This implementation does an explicit tree walk, and calls
;;   ;; vc-BACKEND-diff directly for each file.  An optimization
;;   ;; would be to use `vc-diff-internal', so that diffs can be local,
;;   ;; and to call it only for files that are actually changed.
;;   ;; However, this is expensive for some backends, and so it is left
;;   ;; to backend-specific implementations.
;;   (setq default-directory dir)
;;   (vc-file-tree-walk
;;    default-directory
;;    (lambda (f)
;;      (vc-exec-after
;;       `(let ((coding-system-for-read (vc-coding-system-for-diff ',f)))
;;          (message "Looking at %s" ',f)
;;          (vc-call-backend ',(vc-backend f)
;;                           'diff (list ',f) ',rev1 ',rev2))))))

(defun vc-coding-system-for-diff (file)
  "Return the coding system for reading diff output for FILE."
  (or coding-system-for-read
      ;; if we already have this file open,
      ;; use the buffer's coding system
      (let ((buf (find-buffer-visiting file)))
        (when buf (with-current-buffer buf
		    buffer-file-coding-system)))
      ;; otherwise, try to find one based on the file name
      (car (find-operation-coding-system 'insert-file-contents file))
      ;; and a final fallback
      'undecided))

(defun vc-switches (backend op)
  (let ((switches
	 (or (when backend
	       (let ((sym (vc-make-backend-sym
			   backend (intern (concat (symbol-name op)
						   "-switches")))))
		   (when (boundp sym) (symbol-value sym))))
	     (let ((sym (intern (format "vc-%s-switches" (symbol-name op)))))
	       (when (boundp sym) (symbol-value sym)))
	     (cond
	      ((eq op 'diff) diff-switches)))))
    (if (stringp switches) (list switches)
      ;; If not a list, return nil.
      ;; This is so we can set vc-diff-switches to t to override
      ;; any switches in diff-switches.
      (when (listp switches) switches))))

;; Old def for compatibility with Emacs-21.[123].
(defmacro vc-diff-switches-list (backend) `(vc-switches ',backend 'diff))
(make-obsolete 'vc-diff-switches-list 'vc-switches "22.1")

(defun vc-diff-finish (buffer messages)
  ;; The empty sync output case has already been handled, so the only
  ;; possibility of an empty output is for an async process.
  (when (buffer-live-p buffer)
    (let ((window (get-buffer-window buffer t))
          (emptyp (zerop (buffer-size buffer))))
      (with-current-buffer buffer
        (and messages emptyp
             (let ((inhibit-read-only t))
               (insert (cdr messages) ".\n")
               (message "%s" (cdr messages))))
        (goto-char (point-min))
        (when window
          (shrink-window-if-larger-than-buffer window)))
      (when (and messages (not emptyp))
        (message "%sdone" (car messages))))))

(defvar vc-diff-added-files nil
  "If non-nil, diff added files by comparing them to /dev/null.")

(defun vc-diff-internal (async vc-fileset rev1 rev2 &optional verbose)
  "Report diffs between two revisions of a fileset.
Diff output goes to the *vc-diff* buffer.  The function
returns t if the buffer had changes, nil otherwise."
  (let* ((files (cdr vc-fileset))
	 (messages (cons (format "Finding changes in %s..."
                                 (vc-delistify files))
                         (format "No changes between %s and %s"
                                 (or rev1 "working revision")
                                 (or rev2 "workfile"))))
	 ;; Set coding system based on the first file.  It's a kluge,
	 ;; but the only way to set it for each file included would
	 ;; be to call the back end separately for each file.
	 (coding-system-for-read
	  (if files (vc-coding-system-for-diff (car files)) 'undecided)))
    (vc-setup-buffer "*vc-diff*")
    (message "%s" (car messages))
    ;; Many backends don't handle well the case of a file that has been
    ;; added but not yet committed to the repo (notably CVS and Subversion).
    ;; Do that work here so the backends don't have to futz with it.  --ESR
    ;;
    ;; Actually most backends (including CVS) have options to control the
    ;; behavior since which one is better depends on the user and on the
    ;; situation).  Worse yet: this code does not handle the case where
    ;; `file' is a directory which contains added files.
    ;; I made it conditional on vc-diff-added-files but it should probably
    ;; just be removed (or copied/moved to specific backends).  --Stef.
    (when vc-diff-added-files
      (let ((filtered '()))
        (dolist (file files)
          (if (or (file-directory-p file)
                  (not (string= (vc-working-revision file) "0")))
              (push file filtered)
            ;; This file is added but not yet committed;
            ;; there is no master file to diff against.
            (if (or rev1 rev2)
                (error "No revisions of %s exist" file)
              ;; We regard this as "changed".
              ;; Diff it against /dev/null.
              (apply 'vc-do-command "*vc-diff*"
                     1 "diff" file
                     (append (vc-switches nil 'diff) '("/dev/null"))))))
        (setq files (nreverse filtered))))
    (let ((vc-disable-async-diff (not async)))
      (vc-call-backend (car vc-fileset) 'diff files rev1 rev2 "*vc-diff*"))
    (set-buffer "*vc-diff*")
    (if (and (zerop (buffer-size))
             (not (get-buffer-process (current-buffer))))
        ;; Treat this case specially so as not to pop the buffer.
        (progn
          (message "%s" (cdr messages))
          nil)
      (diff-mode)
      ;; Make the *vc-diff* buffer read only, the diff-mode key
      ;; bindings are nicer for read only buffers. pcl-cvs does the
      ;; same thing.
      (setq buffer-read-only t)
      (vc-exec-after `(vc-diff-finish ,(current-buffer) ',(when verbose
                                                            messages)))
      ;; Display the buffer, but at the end because it can change point.
      (pop-to-buffer (current-buffer))
      ;; In the async case, we return t even if there are no differences
      ;; because we don't know that yet.
      t)))

;;;###autoload
(defun vc-version-diff (files rev1 rev2)
  "Report diffs between revisions of the fileset in the repository history."
  (interactive
   (let* ((vc-fileset (vc-deduce-fileset t))
	  (files (cdr vc-fileset))
	  (first (car files))
	  (completion-table
	   (vc-call revision-completion-table files))
	  (rev1-default nil)
	  (rev2-default nil))
     (cond
      ;; someday we may be able to do revision completion on non-singleton
      ;; filesets, but not yet.
      ((/= (length files) 1)
       nil)
      ;; if it's a directory, don't supply any revision default
      ((file-directory-p first)
       nil)
      ;; if the file is not up-to-date, use working revision as older revision
      ((not (vc-up-to-date-p first))
       (setq rev1-default (vc-working-revision first)))
      ;; if the file is not locked, use last and previous revisions as defaults
      (t
       (setq rev1-default (vc-call previous-revision first
				   (vc-working-revision first)))
       (when (string= rev1-default "") (setq rev1-default nil))
       (setq rev2-default (vc-working-revision first))))
     ;; construct argument list
     (let* ((rev1-prompt (if rev1-default
			     (concat "Older revision (default "
				     rev1-default "): ")
			   "Older revision: "))
	    (rev2-prompt (concat "Newer revision (default "
				 (or rev2-default "current source") "): "))
	    (rev1 (if completion-table
		      (completing-read rev1-prompt completion-table
				       nil nil nil nil rev1-default)
		    (read-string rev1-prompt nil nil rev1-default)))
	    (rev2 (if completion-table
		      (completing-read rev2-prompt completion-table
				       nil nil nil nil rev2-default)
		    (read-string rev2-prompt nil nil rev2-default))))
       (when (string= rev1 "") (setq rev1 nil))
       (when (string= rev2 "") (setq rev2 nil))
       (list files rev1 rev2))))
  (when (and (not rev1) rev2)
    (error "Not a valid revision range."))
  (vc-diff-internal
   t (cons (car (vc-deduce-fileset t)) files) rev1 rev2 (interactive-p)))

;; (defun vc-contains-version-controlled-file (dir)
;;   "Return t if DIR contains a version-controlled file, nil otherwise."
;;   (catch 'found
;;     (mapc (lambda (f) (and (not (file-directory-p f)) (vc-backend f) (throw 'found 't))) (directory-files dir))
;;     nil))

;;;###autoload
(defun vc-diff (historic &optional not-urgent)
  "Display diffs between file revisions.
Normally this compares the currently selected fileset with their
working revisions.  With a prefix argument HISTORIC, it reads two revision
designators specifying which revisions to compare.

If no current fileset is available (that is, we are not in
VC-Dired mode and the visited file of the current buffer is not
under version control) and we're in a Dired buffer, use
the current directory.
The optional argument NOT-URGENT non-nil means it is ok to say no to
saving the buffer."
  (interactive (list current-prefix-arg t))
  (if historic
      (call-interactively 'vc-version-diff)
    (when buffer-file-name (vc-buffer-sync not-urgent))
    (vc-diff-internal t (vc-deduce-fileset t) nil nil (interactive-p))))


;;;###autoload
(defun vc-revision-other-window (rev)
  "Visit revision REV of the current file in another window.
If the current file is named `F', the revision is named `F.~REV~'.
If `F.~REV~' already exists, use it instead of checking it out again."
  (interactive
   (save-current-buffer
     (vc-ensure-vc-buffer)
     (let ((completion-table
            (vc-call revision-completion-table buffer-file-name))
           (prompt "Revision to visit (default is working revision): "))
       (list
        (if completion-table
            (completing-read prompt completion-table)
          (read-string prompt))))))
  (vc-ensure-vc-buffer)
  (let* ((file buffer-file-name)
	 (revision (if (string-equal rev "")
		      (vc-working-revision file)
		    rev)))
    (switch-to-buffer-other-window (vc-find-revision file revision))))

(defun vc-find-revision (file revision)
  "Read REVISION of FILE into a buffer and return the buffer."
  (let ((automatic-backup (vc-version-backup-file-name file revision))
	(filebuf (or (get-file-buffer file) (current-buffer)))
        (filename (vc-version-backup-file-name file revision 'manual)))
    (unless (file-exists-p filename)
      (if (file-exists-p automatic-backup)
          (rename-file automatic-backup filename nil)
	(message "Checking out %s..." filename)
	(with-current-buffer filebuf
	  (let ((failed t))
	    (unwind-protect
		(let ((coding-system-for-read 'no-conversion)
		      (coding-system-for-write 'no-conversion))
		  (with-temp-file filename
		    (let ((outbuf (current-buffer)))
		      ;; Change buffer to get local value of
		      ;; vc-checkout-switches.
		      (with-current-buffer filebuf
			(vc-call find-revision file revision outbuf))))
		  (setq failed nil))
	      (when (and failed (file-exists-p filename))
		(delete-file filename))))
	  (vc-mode-line file))
	(message "Checking out %s...done" filename)))
    (let ((result-buf (find-file-noselect filename)))
      (with-current-buffer result-buf
	;; Set the parent buffer so that things like
	;; C-x v g, C-x v l, ... etc work.
	(set (make-local-variable 'vc-parent-buffer) filebuf))
      result-buf)))

;; Header-insertion code

;;;###autoload
(defun vc-insert-headers ()
  "Insert headers into a file for use with a version control system.
Headers desired are inserted at point, and are pulled from
the variable `vc-BACKEND-header'."
  (interactive)
  (vc-ensure-vc-buffer)
  (save-excursion
    (save-restriction
      (widen)
      (when (or (not (vc-check-headers))
		(y-or-n-p "Version headers already exist.  Insert another set? "))
	(let* ((delims (cdr (assq major-mode vc-comment-alist)))
	       (comment-start-vc (or (car delims) comment-start "#"))
	       (comment-end-vc (or (car (cdr delims)) comment-end ""))
	       (hdsym (vc-make-backend-sym (vc-backend buffer-file-name)
					   'header))
	       (hdstrings (and (boundp hdsym) (symbol-value hdsym))))
	  (dolist (s hdstrings)
	    (insert comment-start-vc "\t" s "\t"
		    comment-end-vc "\n"))
	  (when vc-static-header-alist
	    (dolist (f vc-static-header-alist)
	      (when (string-match (car f) buffer-file-name)
		(insert (format (cdr f) (car hdstrings)))))))))))

(defun vc-clear-headers (&optional file)
  "Clear all version headers in the current buffer (or FILE).
The headers are reset to their non-expanded form."
  (let* ((filename (or file buffer-file-name))
	 (visited (find-buffer-visiting filename))
	 (backend (vc-backend filename)))
    (when (vc-find-backend-function backend 'clear-headers)
	(if visited
	    (let ((context (vc-buffer-context)))
	      ;; save-excursion may be able to relocate point and mark
	      ;; properly.  If it fails, vc-restore-buffer-context
	      ;; will give it a second try.
	      (save-excursion
		(vc-call-backend backend 'clear-headers))
	      (vc-restore-buffer-context context))
	  (set-buffer (find-file-noselect filename))
	  (vc-call-backend backend 'clear-headers)
	  (kill-buffer filename)))))

(defun vc-modify-change-comment (files rev oldcomment)
  "Edit the comment associated with the given files and revision."
  (vc-start-logentry
   files rev oldcomment t
   "Enter a replacement change comment."
   (lambda (files rev comment)
     (vc-call-backend
      ;; Less of a kluge than it looks like; log-view mode only passes
      ;; this function a singleton list.  Arguments left in this form in
      ;; case the more general operation ever becomes meaningful.
      (vc-responsible-backend (car files))
      'modify-change-comment files rev comment))))

;;;###autoload
(defun vc-merge ()
  "Merge changes between two revisions into the current buffer's file.
This asks for two revisions to merge from in the minibuffer.  If the
first revision is a branch number, then merge all changes from that
branch.  If the first revision is empty, merge news, i.e. recent changes
from the current branch.

See Info node `Merging'."
  (interactive)
  (vc-ensure-vc-buffer)
  (vc-buffer-sync)
  (let* ((file buffer-file-name)
	 (backend (vc-backend file))
	 (state (vc-state file))
	 first-revision second-revision status)
    (cond
     ((stringp state)	;; Locking VCses only
      (error "File is locked by %s" state))
     ((not (vc-editable-p file))
      (if (y-or-n-p
	   "File must be checked out for merging.  Check out now? ")
	  (vc-checkout file t)
	(error "Merge aborted"))))
    (setq first-revision
	  (read-string (concat "Branch or revision to merge from "
			       "(default news on current branch): ")))
    (if (string= first-revision "")
	(if (not (vc-find-backend-function backend 'merge-news))
	    (error "Sorry, merging news is not implemented for %s" backend)
	  (setq status (vc-call merge-news file)))
      (if (not (vc-find-backend-function backend 'merge))
	  (error "Sorry, merging is not implemented for %s" backend)
	(if (not (vc-branch-p first-revision))
	    (setq second-revision
		  (read-string "Second revision: "
			       (concat (vc-branch-part first-revision) ".")))
	  ;; We want to merge an entire branch.  Set revisions
	  ;; accordingly, so that vc-BACKEND-merge understands us.
	  (setq second-revision first-revision)
	  ;; first-revision must be the starting point of the branch
	  (setq first-revision (vc-branch-part first-revision)))
	(setq status (vc-call merge file first-revision second-revision))))
    (vc-maybe-resolve-conflicts file status "WORKFILE" "MERGE SOURCE")))

(defun vc-maybe-resolve-conflicts (file status &optional name-A name-B)
  (vc-resynch-buffer file t (not (buffer-modified-p)))
  (if (zerop status) (message "Merge successful")
    (smerge-mode 1)
    (message "File contains conflicts.")))

;;;###autoload
(defalias 'vc-resolve-conflicts 'smerge-ediff)

;; VC Dired hook 
;; FIXME: Remove Dired support when vc-dir is ready.

(defun vc-dired-hook ()
  "Reformat the listing according to version control.
Called by dired after any portion of a vc-dired buffer has been read in."
  (message "Getting version information... ")
  ;; if the backend supports it, get the state
  ;; of all files in this directory at once
  (let ((backend (vc-responsible-backend default-directory)))
    ;; check `backend' can really handle `default-directory'.
    (if (and (vc-call-backend backend 'responsible-p default-directory)
	     (vc-find-backend-function backend 'dir-state))
	(vc-call-backend backend 'dir-state default-directory)))
  (let (filename
	(inhibit-read-only t)
	(buffer-undo-list t))
    (goto-char (point-min))
    (while (not (eobp))
      (cond
       ;; subdir header line
       ((dired-get-subdir)
        (forward-line 1)
        ;; erase (but don't remove) the "total" line
	(delete-region (point) (line-end-position))
	(beginning-of-line)
	(forward-line 1))
       ;; file line
       ((setq filename (dired-get-filename nil t))
        (cond
         ;; subdir
         ((file-directory-p filename)
          (cond
           ((member (file-name-nondirectory filename)
                    vc-directory-exclusion-list)
            (let ((pos (point)))
              (dired-kill-tree filename)
              (goto-char pos)
              (dired-kill-line)))
           (vc-dired-terse-mode
            ;; Don't show directories in terse mode.  Don't use
            ;; dired-kill-line to remove it, because in recursive listings,
            ;; that would remove the directory contents as well.
            (delete-region (line-beginning-position)
                           (progn (forward-line 1) (point))))
           ((string-match "\\`\\.\\.?\\'" (file-name-nondirectory filename))
            (dired-kill-line))
           (t
            (vc-dired-reformat-line nil)
            (forward-line 1))))
	 ;; Try to head off calling the expensive state query -
	 ;; ignore object files, TeX intermediate files, and so forth.
	 ((vc-dired-ignorable-p filename)
	  (dired-kill-line))
         ;; Ordinary file -- call the (possibly expensive) state query
	 ;;
	 ;; First case: unregistered or unknown. (Unknown shouldn't happen here)
	 ((member (vc-state filename) '(nil unregistered))
	  (if vc-dired-terse-mode
	      (dired-kill-line)
	    (vc-dired-reformat-line "?")
	    (forward-line 1)))
	 ;; Either we're in non-terse mode or it's out of date
	 ((not (and vc-dired-terse-mode (vc-up-to-date-p filename)))
	  (vc-dired-reformat-line (vc-call prettify-state-info filename))
	  (forward-line 1))
	 ;; Remaining cases are under version control but uninteresting
	 (t
	  (dired-kill-line))))
       ;; any other line
       (t (forward-line 1))))
    (vc-dired-purge))
  (message "Getting version information... done")
  (save-restriction
    (widen)
    (cond ((eq (count-lines (point-min) (point-max)) 1)
           (goto-char (point-min))
           (message "No changes pending under %s" default-directory)))))

;; VC status implementation

(defun vc-default-status-extra-headers (backend dir)
  ;; Be loud by default to remind people to add coded to display
  ;; backend specific headers.
  ;; XXX: change this to return nil before the release.
  "Extra      : Add backend specific headers here")

(defun vc-dir-headers (backend dir)
  "Display the headers in the *VC status* buffer.
It calls the `status-extra-headers' backend method to display backend
specific headers."
  (concat
   (propertize "VC backend : " 'face 'font-lock-type-face)
   (propertize (format "%s\n" backend) 'face 'font-lock-variable-name-face)
   (propertize "Working dir: " 'face 'font-lock-type-face)
   (propertize (format "%s\n" dir) 'face 'font-lock-variable-name-face)
   (vc-call-backend backend 'status-extra-headers dir)
   "\n"))

(defun vc-default-status-printer (backend fileentry)
  "Pretty print FILEENTRY."
  ;; If you change the layout here, change vc-dir-move-to-goal-column.
  (let ((state
	 (if (vc-dir-fileinfo->directory fileentry)
	     'DIRECTORY
	   (vc-dir-fileinfo->state fileentry))))
    (insert
     (propertize
      (format "%c" (if (vc-dir-fileinfo->marked fileentry) ?* ? ))
      'face 'font-lock-type-face)
     "   "
     (propertize
      (format "%-20s" state)
      'face (cond ((eq state 'up-to-date) 'font-lock-builtin-face)
		  ((memq state '(missing conflict)) 'font-lock-warning-face)
		  (t 'font-lock-variable-name-face))
      'mouse-face 'highlight)
     " "
     (propertize
      (format "%s" (vc-dir-fileinfo->name fileentry))
      'face 'font-lock-function-name-face
      'mouse-face 'highlight))))

(defun vc-default-extra-status-menu (backend)
  nil)

;; This is used to that VC backends could add backend specific menu
;; items to vc-dir-menu-map.
(defun vc-dir-menu-map-filter (orig-binding)
  (when (and (symbolp orig-binding) (fboundp orig-binding))
    (setq orig-binding (indirect-function orig-binding)))
  (let ((ext-binding
	 (vc-call-backend (vc-responsible-backend default-directory)
			  'extra-status-menu)))
    (if (null ext-binding)
	orig-binding
      (append orig-binding
	      '("----")
	      ext-binding))))

(defun vc-dir-refresh-files (files default-state)
  "Refresh some files in the VC status buffer."
  (let ((backend (vc-responsible-backend default-directory))
        (status-buffer (current-buffer))
        (def-dir default-directory))
    (vc-set-mode-line-busy-indicator)
    ;; Call the `dir-status-file' backend function.
    ;; `dir-status-file' is supposed to be asynchronous.
    ;; It should compute the results, and then call the function
    ;; passed as an argument in order to update the vc-dir buffer
    ;; with the results.
    (unless (buffer-live-p vc-dir-process-buffer)
      (setq vc-dir-process-buffer
            (generate-new-buffer (format " *VC-%s* tmp status" backend))))
    (lexical-let ((buffer (current-buffer)))
      (with-current-buffer vc-dir-process-buffer
        (cd def-dir)
        (erase-buffer)
        (vc-call-backend
         backend 'dir-status-files def-dir files default-state
         (lambda (entries &optional more-to-come)
           ;; ENTRIES is a list of (FILE VC_STATE EXTRA) items.
           ;; If MORE-TO-COME is true, then more updates will come from
           ;; the asynchronous process.
           (with-current-buffer buffer
             (vc-dir-update entries buffer)
             (unless more-to-come
               (setq mode-line-process nil)
               ;; Remove the ones that haven't been updated at all.
               ;; Those not-updated are those whose state is nil because the
               ;; file/dir doesn't exist and isn't versioned.
               (ewoc-filter vc-ewoc
                            (lambda (info)
                              (not (vc-dir-fileinfo->needs-update info))))))))))))

(defun vc-dir-refresh ()
  "Refresh the contents of the VC status buffer.
Throw an error if another update process is in progress."
  (interactive)
  (if (vc-dir-busy)
      (error "Another update process is in progress, cannot run two at a time")
    (let ((backend (vc-responsible-backend default-directory))
	  (status-buffer (current-buffer))
	  (def-dir default-directory))
      (vc-set-mode-line-busy-indicator)
      ;; Call the `dir-status' backend function.
      ;; `dir-status' is supposed to be asynchronous.
      ;; It should compute the results, and then call the function
      ;; passed as an argument in order to update the vc-dir buffer
      ;; with the results.

      ;; Create a buffer that can be used by `dir-status' and call
      ;; `dir-status' with this buffer as the current buffer.  Use
      ;; `vc-dir-process-buffer' to remember this buffer, so that
      ;; it can be used later to kill the update process in case it
      ;; takes too long.
      (unless (buffer-live-p vc-dir-process-buffer)
        (setq vc-dir-process-buffer
              (generate-new-buffer (format " *VC-%s* tmp status" backend))))
      ;; set the needs-update flag on all entries
      (ewoc-map (lambda (info) (setf (vc-dir-fileinfo->needs-update info) t) nil)
                vc-ewoc)
      (lexical-let ((buffer (current-buffer)))
        (with-current-buffer vc-dir-process-buffer
          (cd def-dir)
          (erase-buffer)
          (vc-call-backend
           backend 'dir-status def-dir
           (lambda (entries &optional more-to-come)
             ;; ENTRIES is a list of (FILE VC_STATE EXTRA) items.
             ;; If MORE-TO-COME is true, then more updates will come from
             ;; the asynchronous process.
             (with-current-buffer buffer
               (vc-dir-update entries buffer)
               (unless more-to-come
                 (let ((remaining
                        (ewoc-collect
                         vc-ewoc 'vc-dir-fileinfo->needs-update)))
                   (if remaining
                       (vc-dir-refresh-files
                        (mapcar 'vc-dir-fileinfo->name remaining)
                        'up-to-date)
                     (setq mode-line-process nil))))))))))))

(defun vc-dir-show-fileentry (file)
  "Insert an entry for a specific file into the current VC status listing.
This is typically used if the file is up-to-date (or has been added
outside of VC) and one wants to do some operation on it."
  (interactive "fShow file: ")
  (vc-dir-update (list (list (file-relative-name file) (vc-state file))) (current-buffer)))

(defun vc-dir-hide-up-to-date ()
  "Hide up-to-date items from display."
  (interactive)
  (ewoc-filter
   vc-ewoc
   (lambda (crt) (not (eq (vc-dir-fileinfo->state crt) 'up-to-date)))))

(defun vc-dir-register ()
  "Register the marked files, or the current file if no marks."
  (interactive)
  ;; FIXME: Just pass the fileset to vc-register.
  (mapc (lambda (arg) (vc-register nil arg))
	(or (vc-dir-marked-files) (list (vc-dir-current-file)))))

(defun vc-default-status-fileinfo-extra (backend file)
  "Default absence of extra information returned for a file."
  nil)

;; FIXME: Replace these with a more efficient dispatch

(defun vc-generic-status-printer (fileentry)
  (let ((backend (vc-responsible-backend (vc-dir-fileinfo->name fileentry))))
    (vc-call-backend backend 'status-printer fileentry)))
  
(defun vc-generic-state (file)
  (let ((backend (vc-responsible-backend file)))
    (vc-call-backend backend 'state)))
  
(defun vc-generic-status-fileinfo-extra (file)
  (let ((backend (vc-responsible-backend file)))
    (vc-call-backend backend 'status-fileinfo-extra)))

(defun vc-generic-dir-headers (dir)
  (let ((backend (vc-responsible-backend dir)))
    (vc-dir-headers backend dir)))

(defun vc-make-backend-object (file-or-dir)
  (vc-create-client-object 
   "VC status"
   (let ((backend (vc-responsible-backend file-or-dir)))
     (vc-dir-headers backend file-or-dir))
   #'vc-generic-status-printer
   #'vc-generic-state
   #'vc-generic-status-fileinfo-extra
   #'vc-dir-refresh))

;;;###autoload
(defun vc-dir (dir)
  "Show the VC status for DIR."
  (interactive "DVC status for directory: ")
  (pop-to-buffer (vc-dir-prepare-status-buffer dir))
  (if (eq major-mode 'vc-dir-mode)
      (vc-dir-refresh)
    ;; Otherwise, initialize a new view using the dispatcher layer
    (progn
      ;; Build a capability object and hand it to the dispatcher initializer
      (vc-dir-mode (vc-make-backend-object dir))
      ;; Add VC-specific keybindings
      (let ((map (current-local-map)))
	(define-key map "=" 'vc-diff) ;; C-x v =
	(define-key map "a" 'vc-dir-register)
	(define-key map "+" 'vc-update) ;; C-x v +
	(define-key map "R" 'vc-revert) ;; u is taken by dispatcher unmark.
	(define-key map "A" 'vc-annotate) ;; g is taken by dispatcher referesh
	(define-key map "l" 'vc-print-log) ;; C-x v l
	(define-key map "x" 'vc-dir-hide-up-to-date)
	))))

;; Named-configuration entry points

(defun vc-snapshot-precondition (dir)
  "Scan the tree below DIR, looking for files not up-to-date.
If any file is not up-to-date, return the name of the first such file.
\(This means, neither snapshot creation nor retrieval is allowed.\)
If one or more of the files are currently visited, return `visited'.
Otherwise, return nil."
  (let ((status nil))
    (catch 'vc-locked-example
      (vc-file-tree-walk
       dir
       (lambda (f)
	 (if (not (vc-up-to-date-p f)) (throw 'vc-locked-example f)
	   (when (get-file-buffer f) (setq status 'visited)))))
      status)))

;;;###autoload
(defun vc-create-snapshot (dir name branchp)
  "Descending recursively from DIR, make a snapshot called NAME.
For each registered file, the working revision becomes part of
the named configuration.  If the prefix argument BRANCHP is
given, the snapshot is made as a new branch and the files are
checked out in that new branch."
  (interactive
   (list (read-file-name "Directory: " default-directory default-directory t)
         (read-string "New snapshot name: ")
	 current-prefix-arg))
  (message "Making %s... " (if branchp "branch" "snapshot"))
  (when (file-directory-p dir) (setq dir (file-name-as-directory dir)))
  (vc-call-backend (vc-responsible-backend dir)
		   'create-snapshot dir name branchp)
  (message "Making %s... done" (if branchp "branch" "snapshot")))

;;;###autoload
(defun vc-retrieve-snapshot (dir name)
  "Descending recursively from DIR, retrieve the snapshot called NAME.
If NAME is empty, it refers to the latest revisions.
If locking is used for the files in DIR, then there must not be any
locked files at or below DIR (but if NAME is empty, locked files are
allowed and simply skipped)."
  (interactive
   (list (read-file-name "Directory: " default-directory default-directory t)
         (read-string "Snapshot name to retrieve (default latest revisions): ")))
  (let ((update (yes-or-no-p "Update any affected buffers? "))
	(msg (if (or (not name) (string= name ""))
		 (format "Updating %s... " (abbreviate-file-name dir))
	       (format "Retrieving snapshot into %s... "
		       (abbreviate-file-name dir)))))
    (message "%s" msg)
    (vc-call-backend (vc-responsible-backend dir)
		     'retrieve-snapshot dir name update)
    (message "%s" (concat msg "done"))))

;; Miscellaneous other entry points

;;;###autoload
(defun vc-print-log (&optional working-revision)
  "List the change log of the current fileset in a window.
If WORKING-REVISION is non-nil, leave the point at that revision."
  (interactive)
  (let* ((vc-fileset (vc-deduce-fileset))
	 (files (cdr vc-fileset))
	 (backend (car vc-fileset))
	 (working-revision (or working-revision (vc-working-revision (car files)))))
    ;; Don't switch to the output buffer before running the command,
    ;; so that any buffer-local settings in the vc-controlled
    ;; buffer can be accessed by the command.
    (vc-call-backend backend 'print-log files "*vc-change-log*")
    (pop-to-buffer "*vc-change-log*")
    (vc-exec-after
     `(let ((inhibit-read-only t))
    	(vc-call-backend ',backend 'log-view-mode)
	(goto-char (point-max)) (forward-line -1)
	(while (looking-at "=*\n")
	  (delete-char (- (match-end 0) (match-beginning 0)))
	  (forward-line -1))
	(goto-char (point-min))
	(when (looking-at "[\b\t\n\v\f\r ]+")
	  (delete-char (- (match-end 0) (match-beginning 0))))
	(shrink-window-if-larger-than-buffer)
	;; move point to the log entry for the working revision
	(vc-call-backend ',backend 'show-log-entry ',working-revision)
        (setq vc-sentinel-movepoint (point))
        (set-buffer-modified-p nil)))))

;;;###autoload
(defun vc-revert ()
  "Revert working copies of the selected fileset to their repository contents.
This asks for confirmation if the buffer contents are not identical
to the working revision (except for keyword expansion)."
  (interactive)
  (let* ((vc-fileset (vc-deduce-fileset))
	 (files (cdr vc-fileset)))
    ;; If any of the files is visited by the current buffer, make
    ;; sure buffer is saved.  If the user says `no', abort since
    ;; we cannot show the changes and ask for confirmation to
    ;; discard them.
    (when (or (not files) (memq (buffer-file-name) files))
      (vc-buffer-sync nil))
    (dolist (file files)
      (let ((buf (get-file-buffer file)))
	(when (and buf (buffer-modified-p buf))
	  (error "Please kill or save all modified buffers before reverting.")))
      (when (vc-up-to-date-p file)
	(unless (yes-or-no-p (format "%s seems up-to-date.  Revert anyway? " file))
	  (error "Revert canceled"))))
    (when (vc-diff-internal vc-allow-async-revert vc-fileset nil nil)
      (unless (yes-or-no-p (format "Discard changes in %s? " (vc-delistify files)))
	(error "Revert canceled"))
      (delete-windows-on "*vc-diff*")
      (kill-buffer "*vc-diff*"))
    (dolist (file files)
      (message "Reverting %s..." (vc-delistify files))
      (vc-revert-file file)
      (message "Reverting %s...done" (vc-delistify files)))))

;;;###autoload
(defun vc-rollback ()
  "Roll back (remove) the most recent changeset committed to the repository.
This may be either a file-level or a repository-level operation,
depending on the underlying version-control system."
  (interactive)
  (let* ((vc-fileset (vc-deduce-fileset))
	 (files (cdr vc-fileset))
	 (backend (car vc-fileset))
	 (granularity (vc-call-backend backend 'revision-granularity)))
    (unless (vc-find-backend-function backend 'rollback)
      (error "Rollback is not supported in %s" backend))
    (when (and (not (eq granularity 'repository)) (/= (length files) 1))
      (error "Rollback requires a singleton fileset or repository versioning"))
    (when (not (vc-call latest-on-branch-p (car files)))
      (error "Rollback is only possible at the tip revision."))
    ;; If any of the files is visited by the current buffer, make
    ;; sure buffer is saved.  If the user says `no', abort since
    ;; we cannot show the changes and ask for confirmation to
    ;; discard them.
    (when (or (not files) (memq (buffer-file-name) files))
      (vc-buffer-sync nil))
    (dolist (file files)
      (when (buffer-modified-p (get-file-buffer file))
	(error "Please kill or save all modified buffers before rollback."))
      (when (not (vc-up-to-date-p file))
	(error "Please revert all modified workfiles before rollback.")))
    ;; Accumulate changes associated with the fileset
    (vc-setup-buffer "*vc-diff*")
    (not-modified)
    (message "Finding changes...")
    (let* ((tip (vc-working-revision (car files)))
	   (previous (vc-call previous-revision (car files) tip)))
      (vc-diff-internal nil vc-fileset previous tip))
    ;; Display changes
    (unless (yes-or-no-p "Discard these revisions? ")
      (error "Rollback canceled"))
    (delete-windows-on "*vc-diff*")
    (kill-buffer"*vc-diff*")
    ;; Do the actual reversions
    (message "Rolling back %s..." (vc-delistify files))
    (with-vc-properties
     files
     (vc-call-backend backend 'rollback files)
     `((vc-state . ,'up-to-date)
       (vc-checkout-time . , (nth 5 (file-attributes file)))
       (vc-working-revision . nil)))
    (dolist (f files) (vc-resynch-buffer f t t))
    (message "Rolling back %s...done" (vc-delistify files))))

;;;###autoload
(define-obsolete-function-alias 'vc-revert-buffer 'vc-revert "23.1")

;;;###autoload
(defun vc-update ()
  "Update the current fileset's files to their tip revisions.
For each one that contains no changes, and is not locked, then this simply
replaces the work file with the latest revision on its branch.  If the file
contains changes, and the backend supports merging news, then any recent
changes from the current branch are merged into the working file."
  (interactive)
  (let* ((vc-fileset (vc-deduce-fileset))
	 (files (cdr vc-fileset))
	 (backend (car vc-fileset)))
    (dolist (file files)
      (when (let ((buf (get-file-buffer file)))
	      (and buf (buffer-modified-p buf)))
	(error "Please kill or save all modified buffers before updating."))
      (if (vc-up-to-date-p file)
	  (vc-checkout file nil t)
	(if (eq (vc-checkout-model backend (list file)) 'locking)
	    (if (eq (vc-state file) 'edited)
		(error "%s"
		       (substitute-command-keys
			"File is locked--type \\[vc-revert] to discard changes"))
	      (error "Unexpected file state (%s) -- type %s"
		     (vc-state file)
		     (substitute-command-keys
		      "\\[vc-next-action] to correct")))
	  (if (not (vc-find-backend-function backend 'merge-news))
	      (error "Sorry, merging news is not implemented for %s"
		     backend)
	    (vc-maybe-resolve-conflicts file (vc-call merge-news file))))))))

(defun vc-version-backup-file (file &optional rev)
  "Return name of backup file for revision REV of FILE.
If version backups should be used for FILE, and there exists
such a backup for REV or the working revision of file, return
its name; otherwise return nil."
  (when (vc-call make-version-backups-p file)
    (let ((backup-file (vc-version-backup-file-name file rev)))
      (if (file-exists-p backup-file)
          backup-file
        ;; there is no automatic backup, but maybe the user made one manually
        (setq backup-file (vc-version-backup-file-name file rev 'manual))
        (when (file-exists-p backup-file)
	  backup-file)))))

(defun vc-revert-file (file)
  "Revert FILE back to the repository working revision it was based on."
  (with-vc-properties
   (list file)
   (let ((backup-file (vc-version-backup-file file)))
     (when backup-file
       (copy-file backup-file file 'ok-if-already-exists 'keep-date)
       (vc-delete-automatic-version-backups file))
     (vc-call revert file backup-file))
   `((vc-state . up-to-date)
     (vc-checkout-time . ,(nth 5 (file-attributes file)))))
  (vc-resynch-buffer file t t))

;;;###autoload
(defun vc-switch-backend (file backend)
  "Make BACKEND the current version control system for FILE.
FILE must already be registered in BACKEND.  The change is not
permanent, only for the current session.  This function only changes
VC's perspective on FILE, it does not register or unregister it.
By default, this command cycles through the registered backends.
To get a prompt, use a prefix argument."
  (interactive
   (list
    (or buffer-file-name
        (error "There is no version-controlled file in this buffer"))
    (let ((backend (vc-backend buffer-file-name))
	  (backends nil))
      (unless backend
        (error "File %s is not under version control" buffer-file-name))
      ;; Find the registered backends.
      (dolist (backend vc-handled-backends)
	(when (vc-call-backend backend 'registered buffer-file-name)
	  (push backend backends)))
      ;; Find the next backend.
      (let ((def (car (delq backend (append (memq backend backends) backends))))
	    (others (delete backend backends)))
	(cond
	 ((null others) (error "No other backend to switch to"))
	 (current-prefix-arg
	  (intern
	   (upcase
	    (completing-read
	     (format "Switch to backend [%s]: " def)
	     (mapcar (lambda (b) (list (downcase (symbol-name b)))) backends)
	     nil t nil nil (downcase (symbol-name def))))))
       (t def))))))
  (unless (eq backend (vc-backend file))
    (vc-file-clearprops file)
    (vc-file-setprop file 'vc-backend backend)
    ;; Force recomputation of the state
    (unless (vc-call-backend backend 'registered file)
      (vc-file-clearprops file)
      (error "%s is not registered in %s" file backend))
    (vc-mode-line file)))

;;;###autoload
(defun vc-transfer-file (file new-backend)
  "Transfer FILE to another version control system NEW-BACKEND.
If NEW-BACKEND has a higher precedence than FILE's current backend
\(i.e.  it comes earlier in `vc-handled-backends'), then register FILE in
NEW-BACKEND, using the revision number from the current backend as the
base level.  If NEW-BACKEND has a lower precedence than the current
backend, then commit all changes that were made under the current
backend to NEW-BACKEND, and unregister FILE from the current backend.
\(If FILE is not yet registered under NEW-BACKEND, register it.)"
  (let* ((old-backend (vc-backend file))
	 (edited (memq (vc-state file) '(edited needs-merge)))
	 (registered (vc-call-backend new-backend 'registered file))
	 (move
	  (and registered    ; Never move if not registered in new-backend yet.
	       ;; move if new-backend comes later in vc-handled-backends
	       (or (memq new-backend (memq old-backend vc-handled-backends))
		   (y-or-n-p "Final transfer? "))))
	 (comment nil))
    (when (eq old-backend new-backend)
      (error "%s is the current backend of %s" new-backend file))
    (if registered
	(set-file-modes file (logior (file-modes file) 128))
      ;; `registered' might have switched under us.
      (vc-switch-backend file old-backend)
      (let* ((rev (vc-working-revision file))
	     (modified-file (and edited (make-temp-file file)))
	     (unmodified-file (and modified-file (vc-version-backup-file file))))
	;; Go back to the base unmodified file.
	(unwind-protect
	    (progn
	      (when modified-file
		(copy-file file modified-file 'ok-if-already-exists)
		;; If we have a local copy of the unmodified file, handle that
		;; here and not in vc-revert-file because we don't want to
		;; delete that copy -- it is still useful for OLD-BACKEND.
		(if unmodified-file
		    (copy-file unmodified-file file
			       'ok-if-already-exists 'keep-date)
		  (when (y-or-n-p "Get base revision from master? ")
		    (vc-revert-file file))))
	      (vc-call-backend new-backend 'receive-file file rev))
	  (when modified-file
	    (vc-switch-backend file new-backend)
	    (unless (eq (vc-checkout-model new-backend (list file)) 'implicit)
	      (vc-checkout file t nil))
	    (rename-file modified-file file 'ok-if-already-exists)
	    (vc-file-setprop file 'vc-checkout-time nil)))))
    (when move
      (vc-switch-backend file old-backend)
      (setq comment (vc-call comment-history file))
      (vc-call unregister file))
    (vc-switch-backend file new-backend)
    (when (or move edited)
      (vc-file-setprop file 'vc-state 'edited)
      (vc-mode-line file)
      (vc-checkin file nil comment (stringp comment)))))

(defun vc-rename-master (oldmaster newfile templates)
  "Rename OLDMASTER to be the master file for NEWFILE based on TEMPLATES."
  (let* ((dir (file-name-directory (expand-file-name oldmaster)))
	 (newdir (or (file-name-directory newfile) ""))
	 (newbase (file-name-nondirectory newfile))
	 (masters
	  ;; List of potential master files for `newfile'
	  (mapcar
	   (lambda (s) (vc-possible-master s newdir newbase))
	   templates)))
    (when (or (file-symlink-p oldmaster)
	      (file-symlink-p (file-name-directory oldmaster)))
      (error "This is unsafe in the presence of symbolic links"))
    (rename-file
     oldmaster
     (catch 'found
       ;; If possible, keep the master file in the same directory.
       (dolist (f masters)
	 (when (and f (string= (file-name-directory (expand-file-name f)) dir))
	   (throw 'found f)))
       ;; If not, just use the first possible place.
       (dolist (f masters)
	 (and f (or (not (setq dir (file-name-directory f)))
		    (file-directory-p dir))
	      (throw 'found f)))
       (error "New file lacks a version control directory")))))

(defun vc-delete-file (file)
  "Delete file and mark it as such in the version control system."
  (interactive "fVC delete file: ")
  (setq file (expand-file-name file))
  (let ((buf (get-file-buffer file))
        (backend (vc-backend file)))
    (unless backend
      (error "File %s is not under version control"
             (file-name-nondirectory file)))
    (unless (vc-find-backend-function backend 'delete-file)
      (error "Deleting files under %s is not supported in VC" backend))
    (when (and buf (buffer-modified-p buf))
      (error "Please save or undo your changes before deleting %s" file))
    (let ((state (vc-state file)))
      (when (eq state 'edited)
        (error "Please commit or undo your changes before deleting %s" file))
      (when (eq state 'conflict)
        (error "Please resolve the conflicts before deleting %s" file)))
    (unless (y-or-n-p (format "Really want to delete %s? "
			      (file-name-nondirectory file)))
      (error "Abort!"))
    (unless (or (file-directory-p file) (null make-backup-files)
                (not (file-exists-p file)))
      (with-current-buffer (or buf (find-file-noselect file))
	(let ((backup-inhibited nil))
	  (backup-buffer))
	;; If we didn't have a buffer visiting the file before this
	;; command, kill the buffer created by the above
	;; `find-file-noselect' call.
	(unless buf (kill-buffer (current-buffer)))))
    (vc-call delete-file file)
    ;; If the backend hasn't deleted the file itself, let's do it for him.
    (when (file-exists-p file) (delete-file file))
    ;; Forget what VC knew about the file.
    (vc-file-clearprops file)
    (vc-resynch-buffer file buf t)))

;;;###autoload
(defun vc-rename-file (old new)
  "Rename file OLD to NEW, and rename its master file likewise."
  (interactive "fVC rename file: \nFRename to: ")
  (let ((oldbuf (get-file-buffer old)))
    (when (and oldbuf (buffer-modified-p oldbuf))
      (error "Please save files before moving them"))
    (when (get-file-buffer new)
      (error "Already editing new file name"))
    (when (file-exists-p new)
      (error "New file already exists"))
    (let ((state (vc-state old)))
      (unless (memq state '(up-to-date edited))
	(error "Please %s files before moving them"
	       (if (stringp state) "check in" "update"))))
    (vc-call rename-file old new)
    (vc-file-clearprops old)
    ;; Move the actual file (unless the backend did it already)
    (when (file-exists-p old) (rename-file old new))
    ;; ?? Renaming a file might change its contents due to keyword expansion.
    ;; We should really check out a new copy if the old copy was precisely equal
    ;; to some checked-in revision.  However, testing for this is tricky....
    (when oldbuf
      (with-current-buffer oldbuf
	(let ((buffer-read-only buffer-read-only))
	  (set-visited-file-name new))
	(vc-backend new)
	(vc-mode-line new)
	(set-buffer-modified-p nil)))))

;;;###autoload
(defun vc-update-change-log (&rest args)
  "Find change log file and add entries from recent version control logs.
Normally, find log entries for all registered files in the default
directory.

With prefix arg of \\[universal-argument], only find log entries for the current buffer's file.

With any numeric prefix arg, find log entries for all currently visited
files that are under version control.  This puts all the entries in the
log for the default directory, which may not be appropriate.

From a program, any ARGS are assumed to be filenames for which
log entries should be gathered."
  (interactive
   (cond ((consp current-prefix-arg)	;C-u
	  (list buffer-file-name))
	 (current-prefix-arg		;Numeric argument.
	  (let ((files nil)
		(buffers (buffer-list))
		file)
	    (while buffers
	      (setq file (buffer-file-name (car buffers)))
	      (and file (vc-backend file)
		   (setq files (cons file files)))
	      (setq buffers (cdr buffers)))
	    files))
	 (t
          ;; Don't supply any filenames to backend; this means
          ;; it should find all relevant files relative to
          ;; the default-directory.
	  nil)))
  (vc-call-backend (vc-responsible-backend default-directory)
                   'update-changelog args))

;;; The default back end.  Assumes RCS-like revision numbering.

(defun vc-default-revision-granularity ()
  (error "Your backend will not work with this version of VC mode."))

;; functions that operate on RCS revision numbers.  This code should
;; also be moved into the backends.  It stays for now, however, since
;; it is used in code below.
;;;###autoload
(defun vc-trunk-p (rev)
  "Return t if REV is a revision on the trunk."
  (not (eq nil (string-match "\\`[0-9]+\\.[0-9]+\\'" rev))))

(defun vc-branch-p (rev)
  "Return t if REV is a branch revision."
  (not (eq nil (string-match "\\`[0-9]+\\(\\.[0-9]+\\.[0-9]+\\)*\\'" rev))))

;;;###autoload
(defun vc-branch-part (rev)
  "Return the branch part of a revision number REV."
  (let ((index (string-match "\\.[0-9]+\\'" rev)))
    (when index
      (substring rev 0 index))))

(defun vc-minor-part (rev)
  "Return the minor revision number of a revision number REV."
  (string-match "[0-9]+\\'" rev)
  (substring rev (match-beginning 0) (match-end 0)))

(defun vc-default-previous-revision (backend file rev)
  "Return the revision number immediately preceding REV for FILE,
or nil if there is no previous revision.  This default
implementation works for MAJOR.MINOR-style revision numbers as
used by RCS and CVS."
  (let ((branch (vc-branch-part rev))
        (minor-num (string-to-number (vc-minor-part rev))))
    (when branch
      (if (> minor-num 1)
          ;; revision does probably not start a branch or release
          (concat branch "." (number-to-string (1- minor-num)))
        (if (vc-trunk-p rev)
            ;; we are at the beginning of the trunk --
            ;; don't know anything to return here
            nil
          ;; we are at the beginning of a branch --
          ;; return revision of starting point
          (vc-branch-part branch))))))

(defun vc-default-next-revision (backend file rev)
  "Return the revision number immediately following REV for FILE,
or nil if there is no next revision.  This default implementation
works for MAJOR.MINOR-style revision numbers as used by RCS
and CVS."
  (when (not (string= rev (vc-working-revision file)))
    (let ((branch (vc-branch-part rev))
	  (minor-num (string-to-number (vc-minor-part rev))))
      (concat branch "." (number-to-string (1+ minor-num))))))

(defun vc-default-responsible-p (backend file)
  "Indicate whether BACKEND is reponsible for FILE.
The default is to return nil always."
  nil)

(defun vc-default-could-register (backend file)
  "Return non-nil if BACKEND could be used to register FILE.
The default implementation returns t for all files."
  t)

(defun vc-default-latest-on-branch-p (backend file)
  "Return non-nil if FILE is the latest on its branch.
This default implementation always returns non-nil, which means that
editing non-current revisions is not supported by default."
  t)

(defun vc-default-init-revision (backend) vc-default-init-revision)

(defalias 'vc-cvs-update-changelog 'vc-update-changelog-rcs2log)
(defalias 'vc-rcs-update-changelog 'vc-update-changelog-rcs2log)
;; FIXME: This should probably be moved to vc-rcs.el and replaced in
;; vc-cvs.el by code using cvs2cl.
(defun vc-update-changelog-rcs2log (files)
  "Default implementation of update-changelog.
Uses `rcs2log' which only works for RCS and CVS."
  ;; FIXME: We (c|sh)ould add support for cvs2cl
  (let ((odefault default-directory)
	(changelog (find-change-log))
	;; Presumably not portable to non-Unixy systems, along with rcs2log:
	(tempfile (make-temp-file
		   (expand-file-name "vc"
				     (or small-temporary-file-directory
					 temporary-file-directory))))
        (login-name (or user-login-name
                        (format "uid%d" (number-to-string (user-uid)))))
	(full-name (or add-log-full-name
		       (user-full-name)
		       (user-login-name)
		       (format "uid%d" (number-to-string (user-uid)))))
	(mailing-address (or add-log-mailing-address
			     user-mail-address)))
    (find-file-other-window changelog)
    (barf-if-buffer-read-only)
    (vc-buffer-sync)
    (undo-boundary)
    (goto-char (point-min))
    (push-mark)
    (message "Computing change log entries...")
    (message "Computing change log entries... %s"
	     (unwind-protect
		 (progn
		   (setq default-directory odefault)
		   (if (eq 0 (apply 'call-process
                                    (expand-file-name "rcs2log"
                                                      exec-directory)
                                    nil (list t tempfile) nil
                                    "-c" changelog
                                    "-u" (concat login-name
                                                 "\t" full-name
                                                 "\t" mailing-address)
                                    (mapcar
                                     (lambda (f)
                                       (file-relative-name
					(expand-file-name f odefault)))
                                     files)))
                       "done"
		     (pop-to-buffer (get-buffer-create "*vc*"))
		     (erase-buffer)
		     (insert-file-contents tempfile)
		     "failed"))
	       (setq default-directory (file-name-directory changelog))
	       (delete-file tempfile)))))

(defun vc-default-find-revision (backend file rev buffer)
  "Provide the new `find-revision' op based on the old `checkout' op.
This is only for compatibility with old backends.  They should be updated
to provide the `find-revision' operation instead."
  (let ((tmpfile (make-temp-file (expand-file-name file))))
    (unwind-protect
	(progn
	  (vc-call-backend backend 'checkout file nil rev tmpfile)
	  (with-current-buffer buffer
	    (insert-file-contents-literally tmpfile)))
      (delete-file tmpfile))))

(defun vc-default-prettify-state-info (backend file)
  (let* ((state (vc-state file))
	(statestring
	 (cond
	  ((stringp state) (concat "(" state ")"))
	  ((eq state 'edited) "(modified)")
	  ((eq state 'needs-merge) "(merge)")
	  ((eq state 'needs-update) "(update)")
	  ((eq state 'added) "(added)")
	  ((eq state 'removed) "(removed)")
          ((eq state 'ignored) "(ignored)")     ;; dired-hook filters this out
          ((eq state 'unregistered) "?")
	  ((eq state 'unlocked-changes) "(stale)")
	  ((not state) "(unknown)")))
	(buffer
	 (get-file-buffer file))
	(modflag
	 (if (and buffer (buffer-modified-p buffer)) "+" "")))
    (concat statestring modflag)))

(defun vc-default-rename-file (backend old new)
  (condition-case nil
      (add-name-to-file old new)
    (error (rename-file old new)))
  (vc-delete-file old)
  (with-current-buffer (find-file-noselect new)
    (vc-register)))

(defalias 'vc-default-check-headers 'ignore)

(defun vc-default-log-view-mode (backend) (log-view-mode))

(defun vc-default-show-log-entry (backend rev)
  (with-no-warnings
   (log-view-goto-rev rev)))

(defun vc-default-comment-history (backend file)
  "Return a string with all log entries stored in BACKEND for FILE."
  (when (vc-find-backend-function backend 'print-log)
    (with-current-buffer "*vc*"
      (vc-call print-log (list file))
      (vc-call-backend backend 'wash-log)
      (buffer-string))))

(defun vc-default-receive-file (backend file rev)
  "Let BACKEND receive FILE from another version control system."
  (vc-call-backend backend 'register file rev ""))

(defun vc-default-create-snapshot (backend dir name branchp)
  (when branchp
    (error "VC backend %s does not support module branches" backend))
  (let ((result (vc-snapshot-precondition dir)))
    (if (stringp result)
	(error "File %s is not up-to-date" result)
      (vc-file-tree-walk
       dir
       (lambda (f)
	 (vc-call assign-name f name))))))

(defun vc-default-retrieve-snapshot (backend dir name update)
  (if (string= name "")
      (progn
        (vc-file-tree-walk
         dir
         (lambda (f) (and
		 (vc-up-to-date-p f)
		 (vc-error-occurred
		  (vc-call checkout f nil "")
		  (when update (vc-resynch-buffer f t t)))))))
    (let ((result (vc-snapshot-precondition dir)))
      (if (stringp result)
          (error "File %s is locked" result)
        (setq update (and (eq result 'visited) update))
        (vc-file-tree-walk
         dir
         (lambda (f) (vc-error-occurred
		 (vc-call checkout f nil name)
		 (when update (vc-resynch-buffer f t t)))))))))

(defun vc-default-revert (backend file contents-done)
  (unless contents-done
    (let ((rev (vc-working-revision file))
          (file-buffer (or (get-file-buffer file) (current-buffer))))
      (message "Checking out %s..." file)
      (let ((failed t)
            (backup-name (car (find-backup-file-name file))))
        (when backup-name
          (copy-file file backup-name 'ok-if-already-exists 'keep-date)
          (unless (file-writable-p file)
            (set-file-modes file (logior (file-modes file) 128))))
        (unwind-protect
            (let ((coding-system-for-read 'no-conversion)
                  (coding-system-for-write 'no-conversion))
              (with-temp-file file
                (let ((outbuf (current-buffer)))
                  ;; Change buffer to get local value of vc-checkout-switches.
                  (with-current-buffer file-buffer
                    (let ((default-directory (file-name-directory file)))
                      (vc-call find-revision file rev outbuf)))))
              (setq failed nil))
          (when backup-name
            (if failed
                (rename-file backup-name file 'ok-if-already-exists)
              (and (not vc-make-backup-files) (delete-file backup-name))))))
      (message "Checking out %s...done" file))))

(defalias 'vc-default-revision-completion-table 'ignore)

(defun vc-default-dir-status-files (backend dir files default-state update-function)
  (funcall update-function
           (mapcar (lambda (file) (list file default-state)) files)))

(defun vc-check-headers ()
  "Check if the current file has any headers in it."
  (interactive)
  (vc-call-backend (vc-backend buffer-file-name) 'check-headers))

;;; Annotate functionality

;; Declare globally instead of additional parameter to
;; temp-buffer-show-function (not possible to pass more than one
;; parameter).  The use of annotate-ratio is deprecated in favor of
;; annotate-mode, which replaces it with the more sensible "span-to
;; days", along with autoscaling support.
(defvar vc-annotate-ratio nil "Global variable.")

;; internal buffer-local variables
(defvar vc-annotate-backend nil)
(defvar vc-annotate-parent-file nil)
(defvar vc-annotate-parent-rev nil)
(defvar vc-annotate-parent-display-mode nil)

(defconst vc-annotate-font-lock-keywords
  ;; The fontification is done by vc-annotate-lines instead of font-lock.
  '((vc-annotate-lines)))

(define-derived-mode vc-annotate-mode fundamental-mode "Annotate"
  "Major mode for output buffers of the `vc-annotate' command.

You can use the mode-specific menu to alter the time-span of the used
colors.  See variable `vc-annotate-menu-elements' for customizing the
menu items."
  ;; Frob buffer-invisibility-spec so that if it is originally a naked t,
  ;; it will become a list, to avoid initial annotations being invisible.
  (add-to-invisibility-spec 'foo)
  (remove-from-invisibility-spec 'foo)
  (set (make-local-variable 'truncate-lines) t)
  (set (make-local-variable 'font-lock-defaults)
       '(vc-annotate-font-lock-keywords t))
  (view-mode 1))

(defun vc-annotate-toggle-annotation-visibility ()
  "Toggle whether or not the annotation is visible."
  (interactive)
  (funcall (if (memq 'vc-annotate-annotation buffer-invisibility-spec)
               'remove-from-invisibility-spec
             'add-to-invisibility-spec)
           'vc-annotate-annotation)
  (force-window-update (current-buffer)))

(defun vc-annotate-display-default (ratio)
  "Display the output of \\[vc-annotate] using the default color range.
The color range is given by `vc-annotate-color-map', scaled by RATIO.
The current time is used as the offset."
  (interactive (progn (kill-local-variable 'vc-annotate-color-map) '(1.0)))
  (message "Redisplaying annotation...")
  (vc-annotate-display ratio)
  (message "Redisplaying annotation...done"))

(defun vc-annotate-oldest-in-map (color-map)
  "Return the oldest time in the COLOR-MAP."
  ;; Since entries should be sorted, we can just use the last one.
  (caar (last color-map)))

(defun vc-annotate-get-time-set-line-props ()
  (let ((bol (point))
        (date (vc-call-backend vc-annotate-backend 'annotate-time))
        (inhibit-read-only t))
    (assert (>= (point) bol))
    (put-text-property bol (point) 'invisible 'vc-annotate-annotation)
    date))

(defun vc-annotate-display-autoscale (&optional full)
  "Highlight the output of \\[vc-annotate] using an autoscaled color map.
Autoscaling means that the map is scaled from the current time to the
oldest annotation in the buffer, or, with prefix argument FULL, to
cover the range from the oldest annotation to the newest."
  (interactive "P")
  (let ((newest 0.0)
	(oldest 999999.)		;Any CVS users at the founding of Rome?
	(current (vc-annotate-convert-time (current-time)))
	date)
    (message "Redisplaying annotation...")
    ;; Run through this file and find the oldest and newest dates annotated.
    (save-excursion
      (goto-char (point-min))
      (while (not (eobp))
        (when (setq date (vc-annotate-get-time-set-line-props))
          (when (> date newest)
	    (setq newest date))
          (when (< date oldest)
	    (setq oldest date)))
        (forward-line 1)))
    (vc-annotate-display
     (/ (- (if full newest current) oldest)
        (vc-annotate-oldest-in-map vc-annotate-color-map))
     (if full newest))
    (message "Redisplaying annotation...done \(%s\)"
	     (if full
		 (format "Spanned from %.1f to %.1f days old"
			 (- current oldest)
			 (- current newest))
	       (format "Spanned to %.1f days old" (- current oldest))))))

;; Menu -- Using easymenu.el
(easy-menu-define vc-annotate-mode-menu vc-annotate-mode-map
  "VC Annotate Display Menu"
  `("VC-Annotate"
    ["By Color Map Range" (unless (null vc-annotate-display-mode)
                 (setq vc-annotate-display-mode nil)
                 (vc-annotate-display-select))
     :style toggle :selected (null vc-annotate-display-mode)]
    ,@(let ((oldest-in-map (vc-annotate-oldest-in-map vc-annotate-color-map)))
        (mapcar (lambda (element)
                  (let ((days (* element oldest-in-map)))
                    `[,(format "Span %.1f days" days)
                      (vc-annotate-display-select nil ,days)
                      :style toggle :selected
                      (eql vc-annotate-display-mode ,days) ]))
                vc-annotate-menu-elements))
    ["Span ..."
     (vc-annotate-display-select
      nil (float (string-to-number (read-string "Span how many days? "))))]
    "--"
    ["Span to Oldest"
     (unless (eq vc-annotate-display-mode 'scale)
       (vc-annotate-display-select nil 'scale))
     :help
     "Use an autoscaled color map from the oldest annotation to the current time"
     :style toggle :selected
     (eq vc-annotate-display-mode 'scale)]
    ["Span Oldest->Newest"
     (unless (eq vc-annotate-display-mode 'fullscale)
       (vc-annotate-display-select nil 'fullscale))
     :help
     "Use an autoscaled color map from the oldest to the newest annotation"
     :style toggle :selected
     (eq vc-annotate-display-mode 'fullscale)]
    "--"
    ["Toggle annotation visibility" vc-annotate-toggle-annotation-visibility
     :help
     "Toggle whether the annotation is visible or not"]
    ["Annotate previous revision" vc-annotate-prev-revision
     :help "Visit the annotation of the revision previous to this one"]
    ["Annotate next revision" vc-annotate-next-revision
     :help "Visit the annotation of the revision after this one"]
    ["Annotate revision at line" vc-annotate-revision-at-line
     :help
     "Visit the annotation of the revision identified in the current line"]
    ["Annotate revision previous to line" vc-annotate-revision-previous-to-line
     :help "Visit the annotation of the revision before the revision at line"]
    ["Annotate latest revision" vc-annotate-working-revision
     :help "Visit the annotation of the working revision of this file"]
    ["Show log of revision at line" vc-annotate-show-log-revision-at-line
     :help "Visit the log of the revision at line"]
    ["Show diff of revision at line" vc-annotate-show-diff-revision-at-line
     :help
     "Visit the diff of the revision at line from its previous revision"]
    ["Visit revision at line" vc-annotate-find-revision-at-line
     :help "Visit the revision identified in the current line"]))

(defun vc-annotate-display-select (&optional buffer mode)
  "Highlight the output of \\[vc-annotate].
By default, the current buffer is highlighted, unless overridden by
BUFFER.  `vc-annotate-display-mode' specifies the highlighting mode to
use; you may override this using the second optional arg MODE."
  (interactive)
  (when mode (setq vc-annotate-display-mode mode))
  (pop-to-buffer (or buffer (current-buffer)))
  (cond ((null vc-annotate-display-mode)
         ;; The ratio is global, thus relative to the global color-map.
         (kill-local-variable 'vc-annotate-color-map)
	 (vc-annotate-display-default (or vc-annotate-ratio 1.0)))
        ;; One of the auto-scaling modes
	((eq vc-annotate-display-mode 'scale)
	 (vc-exec-after `(vc-annotate-display-autoscale)))
	((eq vc-annotate-display-mode 'fullscale)
	 (vc-exec-after `(vc-annotate-display-autoscale t)))
	((numberp vc-annotate-display-mode) ; A fixed number of days lookback
	 (vc-annotate-display-default
	  (/ vc-annotate-display-mode
             (vc-annotate-oldest-in-map vc-annotate-color-map))))
	(t (error "No such display mode: %s"
		  vc-annotate-display-mode))))

;;;###autoload
(defun vc-annotate (file rev &optional display-mode buf move-point-to)
  "Display the edit history of the current file using colors.

This command creates a buffer that shows, for each line of the current
file, when it was last edited and by whom.  Additionally, colors are
used to show the age of each line--blue means oldest, red means
youngest, and intermediate colors indicate intermediate ages.  By
default, the time scale stretches back one year into the past;
everything that is older than that is shown in blue.

With a prefix argument, this command asks two questions in the
minibuffer.  First, you may enter a revision number; then the buffer
displays and annotates that revision instead of the working revision
\(type RET in the minibuffer to leave that default unchanged).  Then,
you are prompted for the time span in days which the color range
should cover.  For example, a time span of 20 days means that changes
over the past 20 days are shown in red to blue, according to their
age, and everything that is older than that is shown in blue.

If MOVE-POINT-TO is given, move the point to that line.

Customization variables:

`vc-annotate-menu-elements' customizes the menu elements of the
mode-specific menu.  `vc-annotate-color-map' and
`vc-annotate-very-old-color' define the mapping of time to colors.
`vc-annotate-background' specifies the background color."
  (interactive
   (save-current-buffer
     (vc-ensure-vc-buffer)
     (list buffer-file-name
	   (let ((def (vc-working-revision buffer-file-name)))
	     (if (null current-prefix-arg) def
	       (read-string
		(format "Annotate from revision (default %s): " def)
		nil nil def)))
	   (if (null current-prefix-arg)
	       vc-annotate-display-mode
	     (float (string-to-number
		     (read-string "Annotate span days (default 20): "
				  nil nil "20")))))))
  (vc-ensure-vc-buffer)
  (setq vc-annotate-display-mode display-mode) ;Not sure why.  --Stef
  (let* ((temp-buffer-name (format "*Annotate %s (rev %s)*" (buffer-name) rev))
         (temp-buffer-show-function 'vc-annotate-display-select)
         ;; If BUF is specified, we presume the caller maintains current line,
         ;; so we don't need to do it here.  This implementation may give
         ;; strange results occasionally in the case of REV != WORKFILE-REV.
         (current-line (or move-point-to (unless buf (line-number-at-pos)))))
    (message "Annotating...")
    ;; If BUF is specified it tells in which buffer we should put the
    ;; annotations.  This is used when switching annotations to another
    ;; revision, so we should update the buffer's name.
    (when buf (with-current-buffer buf
		(rename-buffer temp-buffer-name t)
		;; In case it had to be uniquified.
		(setq temp-buffer-name (buffer-name))))
    (with-output-to-temp-buffer temp-buffer-name
      (vc-call annotate-command file (get-buffer temp-buffer-name) rev)
      ;; we must setup the mode first, and then set our local
      ;; variables before the show-function is called at the exit of
      ;; with-output-to-temp-buffer
      (with-current-buffer temp-buffer-name
        (unless (equal major-mode 'vc-annotate-mode)
	  (vc-annotate-mode))
        (set (make-local-variable 'vc-annotate-backend) (vc-backend file))
        (set (make-local-variable 'vc-annotate-parent-file) file)
        (set (make-local-variable 'vc-annotate-parent-rev) rev)
        (set (make-local-variable 'vc-annotate-parent-display-mode)
             display-mode)))

    (with-current-buffer temp-buffer-name
      (vc-exec-after
       `(progn
          ;; Ideally, we'd rather not move point if the user has already
          ;; moved it elsewhere, but really point here is not the position
          ;; of the user's cursor :-(
          (when ,current-line           ;(and (bobp))
            (goto-line ,current-line)
            (setq vc-sentinel-movepoint (point)))
          (unless (active-minibuffer-window)
            (message "Annotating... done")))))))

(defun vc-annotate-prev-revision (prefix)
  "Visit the annotation of the revision previous to this one.

With a numeric prefix argument, annotate the revision that many
revisions previous."
  (interactive "p")
  (vc-annotate-warp-revision (- 0 prefix)))

(defun vc-annotate-next-revision (prefix)
  "Visit the annotation of the revision after this one.

With a numeric prefix argument, annotate the revision that many
revisions after."
  (interactive "p")
  (vc-annotate-warp-revision prefix))

(defun vc-annotate-working-revision ()
  "Visit the annotation of the working revision of this file."
  (interactive)
  (if (not (equal major-mode 'vc-annotate-mode))
      (message "Cannot be invoked outside of a vc annotate buffer")
    (let ((warp-rev (vc-working-revision vc-annotate-parent-file)))
      (if (equal warp-rev vc-annotate-parent-rev)
	  (message "Already at revision %s" warp-rev)
	(vc-annotate-warp-revision warp-rev)))))

(defun vc-annotate-extract-revision-at-line ()
  "Extract the revision number of the current line."
  ;; This function must be invoked from a buffer in vc-annotate-mode
  (vc-call-backend vc-annotate-backend 'annotate-extract-revision-at-line))

(defun vc-annotate-revision-at-line ()
  "Visit the annotation of the revision identified in the current line."
  (interactive)
  (if (not (equal major-mode 'vc-annotate-mode))
      (message "Cannot be invoked outside of a vc annotate buffer")
    (let ((rev-at-line (vc-annotate-extract-revision-at-line)))
      (if (not rev-at-line)
	  (message "Cannot extract revision number from the current line")
	(if (equal rev-at-line vc-annotate-parent-rev)
	    (message "Already at revision %s" rev-at-line)
	  (vc-annotate-warp-revision rev-at-line))))))

(defun vc-annotate-find-revision-at-line ()
  "Visit the revision identified in the current line."
  (interactive)
  (if (not (equal major-mode 'vc-annotate-mode))
      (message "Cannot be invoked outside of a vc annotate buffer")
    (let ((rev-at-line (vc-annotate-extract-revision-at-line)))
      (if (not rev-at-line)
	  (message "Cannot extract revision number from the current line")
	(vc-revision-other-window rev-at-line)))))

(defun vc-annotate-revision-previous-to-line ()
  "Visit the annotation of the revision before the revision at line."
  (interactive)
  (if (not (equal major-mode 'vc-annotate-mode))
      (message "Cannot be invoked outside of a vc annotate buffer")
    (let ((rev-at-line (vc-annotate-extract-revision-at-line))
	  (prev-rev nil))
      (if (not rev-at-line)
	  (message "Cannot extract revision number from the current line")
	(setq prev-rev
	      (vc-call previous-revision vc-annotate-parent-file rev-at-line))
	(vc-annotate-warp-revision prev-rev)))))

(defun vc-annotate-show-log-revision-at-line ()
  "Visit the log of the revision at line."
  (interactive)
  (if (not (equal major-mode 'vc-annotate-mode))
      (message "Cannot be invoked outside of a vc annotate buffer")
    (let ((rev-at-line (vc-annotate-extract-revision-at-line)))
      (if (not rev-at-line)
	  (message "Cannot extract revision number from the current line")
	(vc-print-log rev-at-line)))))

(defun vc-annotate-show-diff-revision-at-line ()
  "Visit the diff of the revision at line from its previous revision."
  (interactive)
  (if (not (equal major-mode 'vc-annotate-mode))
      (message "Cannot be invoked outside of a vc annotate buffer")
    (let ((rev-at-line (vc-annotate-extract-revision-at-line))
	  (prev-rev nil))
      (if (not rev-at-line)
	  (message "Cannot extract revision number from the current line")
	(setq prev-rev
	      (vc-call previous-revision vc-annotate-parent-file rev-at-line))
	(if (not prev-rev)
	    (message "Cannot diff from any revision prior to %s" rev-at-line)
	  (save-window-excursion
	    (vc-diff-internal
	     nil
	     (cons (vc-backend vc-annotate-parent-file)
		   (list vc-annotate-parent-file))
	     prev-rev rev-at-line))
	  (switch-to-buffer "*vc-diff*"))))))

(defun vc-annotate-warp-revision (revspec)
  "Annotate the revision described by REVSPEC.

If REVSPEC is a positive integer, warp that many revisions
forward, if possible, otherwise echo a warning message.  If
REVSPEC is a negative integer, warp that many revisions backward,
if possible, otherwise echo a warning message.  If REVSPEC is a
string, then it describes a revision number, so warp to that
revision."
  (if (not (equal major-mode 'vc-annotate-mode))
      (message "Cannot be invoked outside of a vc annotate buffer")
    (let* ((buf (current-buffer))
	   (oldline (line-number-at-pos))
	   (revspeccopy revspec)
	   (newrev nil))
      (cond
       ((and (integerp revspec) (> revspec 0))
	(setq newrev vc-annotate-parent-rev)
	(while (and (> revspec 0) newrev)
	       (setq newrev (vc-call next-revision
				     vc-annotate-parent-file newrev))
	       (setq revspec (1- revspec)))
	(unless newrev
	  (message "Cannot increment %d revisions from revision %s"
		   revspeccopy vc-annotate-parent-rev)))
       ((and (integerp revspec) (< revspec 0))
	(setq newrev vc-annotate-parent-rev)
	(while (and (< revspec 0) newrev)
	       (setq newrev (vc-call previous-revision
				     vc-annotate-parent-file newrev))
	       (setq revspec (1+ revspec)))
	(unless newrev
	  (message "Cannot decrement %d revisions from revision %s"
		   (- 0 revspeccopy) vc-annotate-parent-rev)))
       ((stringp revspec) (setq newrev revspec))
       (t (error "Invalid argument to vc-annotate-warp-revision")))
      (when newrev
	(vc-annotate vc-annotate-parent-file newrev
                     vc-annotate-parent-display-mode
                     buf
		     ;; Pass the current line so that vc-annotate will
		     ;; place the point in the line.
		     (min oldline (progn (goto-char (point-max))
					   (forward-line -1)
					   (line-number-at-pos))))))))

(defun vc-annotate-compcar (threshold a-list)
  "Test successive cons cells of A-LIST against THRESHOLD.
Return the first cons cell with a car that is not less than THRESHOLD,
nil if no such cell exists."
 (let ((i 1)
       (tmp-cons (car a-list)))
   (while (and tmp-cons (< (car tmp-cons) threshold))
     (setq tmp-cons (car (nthcdr i a-list)))
     (setq i (+ i 1)))
   tmp-cons))				; Return the appropriate value

(defun vc-annotate-convert-time (time)
  "Convert a time value to a floating-point number of days.
The argument TIME is a list as returned by `current-time' or
`encode-time', only the first two elements of that list are considered."
  (/ (+ (* (float (car time)) (lsh 1 16)) (cadr time)) 24 3600))

(defun vc-annotate-difference (&optional offset)
  "Return the time span in days to the next annotation.
This calls the backend function annotate-time, and returns the
difference in days between the time returned and the current time,
or OFFSET if present."
   (let ((next-time (vc-annotate-get-time-set-line-props)))
     (when next-time
       (- (or offset
	      (vc-call-backend vc-annotate-backend 'annotate-current-time))
	  next-time))))

(defun vc-default-annotate-current-time (backend)
  "Return the current time, encoded as fractional days."
  (vc-annotate-convert-time (current-time)))

(defvar vc-annotate-offset nil)

(defun vc-annotate-display (ratio &optional offset)
  "Highlight `vc-annotate' output in the current buffer.
RATIO, is the expansion that should be applied to `vc-annotate-color-map'.
The annotations are relative to the current time, unless overridden by OFFSET."
  (when (/= ratio 1.0)
    (set (make-local-variable 'vc-annotate-color-map)
	 (mapcar (lambda (elem) (cons (* (car elem) ratio) (cdr elem)))
		 vc-annotate-color-map)))
  (set (make-local-variable 'vc-annotate-offset) offset)
  (font-lock-mode 1))

(defun vc-annotate-lines (limit)
  (while (< (point) limit)
    (let ((difference (vc-annotate-difference vc-annotate-offset))
          (start (point))
          (end (progn (forward-line 1) (point))))
      (when difference
        (let* ((color (or (vc-annotate-compcar difference vc-annotate-color-map)
                          (cons nil vc-annotate-very-old-color)))
               ;; substring from index 1 to remove any leading `#' in the name
               (face-name (concat "vc-annotate-face-"
                                  (if (string-equal
                                       (substring (cdr color) 0 1) "#")
                                      (substring (cdr color) 1)
                                    (cdr color))))
               ;; Make the face if not done.
               (face (or (intern-soft face-name)
                         (let ((tmp-face (make-face (intern face-name))))
                           (set-face-foreground tmp-face (cdr color))
                           (when vc-annotate-background
			     (set-face-background tmp-face
						  vc-annotate-background))
                           tmp-face))))	; Return the face
          (put-text-property start end 'face face)))))
  ;; Pretend to font-lock there were no matches.
  nil)
\f

;; Set up key bindings for use while editing log messages

(defun vc-log-edit (fileset)
  "Set up `log-edit' for use with VC on FILE."
  (setq default-directory
	(with-current-buffer vc-parent-buffer default-directory))
  (log-edit 'vc-finish-logentry
	    nil
	    `((log-edit-listfun . (lambda () ',fileset))
	      (log-edit-diff-function . (lambda () (vc-diff nil)))))
  (set (make-local-variable 'vc-log-fileset) fileset)
  (make-local-variable 'vc-log-revision)
  (set-buffer-modified-p nil)
  (setq buffer-file-name nil))

;; These things should probably be generally available

(defun vc-file-tree-walk (dirname func &rest args)
  "Walk recursively through DIRNAME.
Invoke FUNC f ARGS on each VC-managed file f underneath it."
  (vc-file-tree-walk-internal (expand-file-name dirname) func args)
  (message "Traversing directory %s...done" dirname))

(defun vc-file-tree-walk-internal (file func args)
  (if (not (file-directory-p file))
      (when (vc-backend file) (apply func file args))
    (message "Traversing directory %s..." (abbreviate-file-name file))
    (let ((dir (file-name-as-directory file)))
      (mapcar
       (lambda (f) (or
               (string-equal f ".")
               (string-equal f "..")
               (member f vc-directory-exclusion-list)
               (let ((dirf (expand-file-name f dir)))
                 (or
                  (file-symlink-p dirf) ;; Avoid possible loops.
                  (vc-file-tree-walk-internal dirf func args)))))
       (directory-files dir)))))

(provide 'vc)

;; DEVELOPER'S NOTES ON CONCURRENCY PROBLEMS IN THIS CODE
;;
;; These may be useful to anyone who has to debug or extend the package.
;; (Note that this information corresponds to versions 5.x. Some of it
;; might have been invalidated by the additions to support branching
;; and RCS keyword lookup. AS, 1995/03/24)
;;
;; A fundamental problem in VC is that there are time windows between
;; vc-next-action's computations of the file's version-control state and
;; the actions that change it.  This is a window open to lossage in a
;; multi-user environment; someone else could nip in and change the state
;; of the master during it.
;;
;; The performance problem is that rlog/prs calls are very expensive; we want
;; to avoid them as much as possible.
;;
;; ANALYSIS:
;;
;; The performance problem, it turns out, simplifies in practice to the
;; problem of making vc-state fast.  The two other functions that call
;; prs/rlog will not be so commonly used that the slowdown is a problem; one
;; makes snapshots, the other deletes the calling user's last change in the
;; master.
;;
;; The race condition implies that we have to either (a) lock the master
;; during the entire execution of vc-next-action, or (b) detect and
;; recover from errors resulting from dispatch on an out-of-date state.
;;
;; Alternative (a) appears to be infeasible.  The problem is that we can't
;; guarantee that the lock will ever be removed.  Suppose a user starts a
;; checkin, the change message buffer pops up, and the user, having wandered
;; off to do something else, simply forgets about it?
;;
;; Alternative (b), on the other hand, works well with a cheap way to speed up
;; vc-state.  Usually, if a file is registered, we can read its locked/
;; unlocked state and its current owner from its permissions.
;;
;; This shortcut will fail if someone has manually changed the workfile's
;; permissions; also if developers are munging the workfile in several
;; directories, with symlinks to a master (in this latter case, the
;; permissions shortcut will fail to detect a lock asserted from another
;; directory).
;;
;; Note that these cases correspond exactly to the errors which could happen
;; because of a competing checkin/checkout race in between two instances of
;; vc-next-action.
;;
;; For VC's purposes, a workfile/master pair may have the following states:
;;
;; A. Unregistered.  There is a workfile, there is no master.
;;
;; B. Registered and not locked by anyone.
;;
;; C. Locked by calling user and unchanged.
;;
;; D. Locked by the calling user and changed.
;;
;; E. Locked by someone other than the calling user.
;;
;; This makes for 25 states and 20 error conditions.  Here's the matrix:
;;
;; VC's idea of state
;;  |
;;  V  Actual state   RCS action              SCCS action          Effect
;;    A  B  C  D  E
;;  A .  1  2  3  4   ci -u -t-          admin -fb -i<file>      initial admin
;;  B 5  .  6  7  8   co -l              get -e                  checkout
;;  C 9  10 .  11 12  co -u              unget; get              revert
;;  D 13 14 15 .  16  ci -u -m<comment>  delta -y<comment>; get  checkin
;;  E 17 18 19 20 .   rcs -u -M -l       unget -n ; get -g       steal lock
;;
;; All commands take the master file name as a last argument (not shown).
;;
;; In the discussion below, a "self-race" is a pathological situation in
;; which VC operations are being attempted simultaneously by two or more
;; Emacsen running under the same username.
;;
;; The vc-next-action code has the following windows:
;;
;; Window P:
;;    Between the check for existence of a master file and the call to
;; admin/checkin in vc-buffer-admin (apparent state A).  This window may
;; never close if the initial-comment feature is on.
;;
;; Window Q:
;;    Between the call to vc-workfile-unchanged-p in and the immediately
;; following revert (apparent state C).
;;
;; Window R:
;;    Between the call to vc-workfile-unchanged-p in and the following
;; checkin (apparent state D).  This window may never close.
;;
;; Window S:
;;    Between the unlock and the immediately following checkout during a
;; revert operation (apparent state C).  Included in window Q.
;;
;; Window T:
;;    Between vc-state and the following checkout (apparent state B).
;;
;; Window U:
;;    Between vc-state and the following revert (apparent state C).
;; Includes windows Q and S.
;;
;; Window V:
;;    Between vc-state and the following checkin (apparent state
;; D).  This window may never be closed if the user fails to complete the
;; checkin message.  Includes window R.
;;
;; Window W:
;;    Between vc-state and the following steal-lock (apparent
;; state E).  This window may never close if the user fails to complete
;; the steal-lock message.  Includes window X.
;;
;; Window X:
;;    Between the unlock and the immediately following re-lock during a
;; steal-lock operation (apparent state E).  This window may never close
;; if the user fails to complete the steal-lock message.
;;
;; Errors:
;;
;; Apparent state A ---
;;
;; 1. File looked unregistered but is actually registered and not locked.
;;
;;    Potential cause: someone else's admin during window P, with
;; caller's admin happening before their checkout.
;;
;;    RCS: Prior to version 5.6.4, ci fails with message
;;         "no lock set by <user>".  From 5.6.4 onwards, VC uses the new
;;         ci -i option and the message is "<file>,v: already exists".
;;    SCCS: admin will fail with error (ad19).
;;
;;    We can let these errors be passed up to the user.
;;
;; 2. File looked unregistered but is actually locked by caller, unchanged.
;;
;;    Potential cause: self-race during window P.
;;
;;    RCS: Prior to version 5.6.4, reverts the file to the last saved
;;         version and unlocks it.  From 5.6.4 onwards, VC uses the new
;;         ci -i option, failing with message "<file>,v: already exists".
;;    SCCS: will fail with error (ad19).
;;
;;    Either of these consequences is acceptable.
;;
;; 3. File looked unregistered but is actually locked by caller, changed.
;;
;;    Potential cause: self-race during window P.
;;
;;    RCS: Prior to version 5.6.4, VC registers the caller's workfile as
;;         a delta with a null change comment (the -t- switch will be
;;         ignored). From 5.6.4 onwards, VC uses the new ci -i option,
;;         failing with message "<file>,v: already exists".
;;    SCCS: will fail with error (ad19).
;;
;; 4. File looked unregistered but is locked by someone else.
;;;
;;    Potential cause: someone else's admin during window P, with
;; caller's admin happening *after* their checkout.
;;
;;    RCS: Prior to version 5.6.4, ci fails with a
;;         "no lock set by <user>" message.  From 5.6.4 onwards,
;;         VC uses the new ci -i option, failing with message
;;         "<file>,v: already exists".
;;    SCCS: will fail with error (ad19).
;;
;;    We can let these errors be passed up to the user.
;;
;; Apparent state B ---
;;
;; 5. File looked registered and not locked, but is actually unregistered.
;;
;;    Potential cause: master file got nuked during window P.
;;
;;    RCS: will fail with "RCS/<file>: No such file or directory"
;;    SCCS: will fail with error ut4.
;;
;;    We can let these errors be passed up to the user.
;;
;; 6. File looked registered and not locked, but is actually locked by the
;; calling user and unchanged.
;;
;;    Potential cause: self-race during window T.
;;
;;    RCS: in the same directory as the previous workfile, co -l will fail
;; with "co error: writable foo exists; checkout aborted".  In any other
;; directory, checkout will succeed.
;;    SCCS: will fail with ge17.
;;
;;    Either of these consequences is acceptable.
;;
;; 7. File looked registered and not locked, but is actually locked by the
;; calling user and changed.
;;
;;    As case 6.
;;
;; 8. File looked registered and not locked, but is actually locked by another
;; user.
;;
;;    Potential cause: someone else checks it out during window T.
;;
;;    RCS: co error: revision 1.3 already locked by <user>
;;    SCCS: fails with ge4 (in directory) or ut7 (outside it).
;;
;;    We can let these errors be passed up to the user.
;;
;; Apparent state C ---
;;
;; 9. File looks locked by calling user and unchanged, but is unregistered.
;;
;;    As case 5.
;;
;; 10. File looks locked by calling user and unchanged, but is actually not
;; locked.
;;
;;    Potential cause: a self-race in window U, or by the revert's
;; landing during window X of some other user's steal-lock or window S
;; of another user's revert.
;;
;;    RCS: succeeds, refreshing the file from the identical version in
;; the master.
;;    SCCS: fails with error ut4 (p file nonexistent).
;;
;;    Either of these consequences is acceptable.
;;
;; 11. File is locked by calling user.  It looks unchanged, but is actually
;; changed.
;;
;;    Potential cause: the file would have to be touched by a self-race
;; during window Q.
;;
;;    The revert will succeed, removing whatever changes came with
;; the touch.  It is theoretically possible that work could be lost.
;;
;; 12. File looks like it's locked by the calling user and unchanged, but
;; it's actually locked by someone else.
;;
;;    Potential cause: a steal-lock in window V.
;;
;;    RCS: co error: revision <rev> locked by <user>; use co -r or rcs -u
;;    SCCS: fails with error un2
;;
;;    We can pass these errors up to the user.
;;
;; Apparent state D ---
;;
;; 13. File looks like it's locked by the calling user and changed, but it's
;; actually unregistered.
;;
;;    Potential cause: master file got nuked during window P.
;;
;;    RCS: Prior to version 5.6.4, checks in the user's version as an
;;         initial delta.  From 5.6.4 onwards, VC uses the new ci -j
;;         option, failing with message "no such file or directory".
;;    SCCS: will fail with error ut4.
;;
;;    This case is kind of nasty.  Under RCS prior to version 5.6.4,
;; VC may fail to detect the loss of previous version information.
;;
;; 14. File looks like it's locked by the calling user and changed, but it's
;; actually unlocked.
;;
;;    Potential cause: self-race in window V, or the checkin happening
;; during the window X of someone else's steal-lock or window S of
;; someone else's revert.
;;
;;    RCS: ci will fail with "no lock set by <user>".
;;    SCCS: delta will fail with error ut4.
;;
;; 15. File looks like it's locked by the calling user and changed, but it's
;; actually locked by the calling user and unchanged.
;;
;;    Potential cause: another self-race --- a whole checkin/checkout
;; sequence by the calling user would have to land in window R.
;;
;;    SCCS: checks in a redundant delta and leaves the file unlocked as usual.
;;    RCS: reverts to the file state as of the second user's checkin, leaving
;; the file unlocked.
;;
;;    It is theoretically possible that work could be lost under RCS.
;;
;; 16. File looks like it's locked by the calling user and changed, but it's
;; actually locked by a different user.
;;
;;    RCS: ci error: no lock set by <user>
;;    SCCS: unget will fail with error un2
;;
;;    We can pass these errors up to the user.
;;
;; Apparent state E ---
;;
;; 17. File looks like it's locked by some other user, but it's actually
;; unregistered.
;;
;;    As case 13.
;;
;; 18. File looks like it's locked by some other user, but it's actually
;; unlocked.
;;
;;    Potential cause: someone released a lock during window W.
;;
;;    RCS: The calling user will get the lock on the file.
;;    SCCS: unget -n will fail with cm4.
;;
;;    Either of these consequences will be OK.
;;
;; 19. File looks like it's locked by some other user, but it's actually
;; locked by the calling user and unchanged.
;;
;;    Potential cause: the other user relinquishing a lock followed by
;; a self-race, both in window W.
;;
;;     Under both RCS and SCCS, both unlock and lock will succeed, making
;; the sequence a no-op.
;;
;; 20. File looks like it's locked by some other user, but it's actually
;; locked by the calling user and changed.
;;
;;     As case 19.
;;
;; PROBLEM CASES:
;;
;;    In order of decreasing severity:
;;
;;    Cases 11 and 15 are the only ones that potentially lose work.
;; They would require a self-race for this to happen.
;;
;;    Case 13 in RCS loses information about previous deltas, retaining
;; only the information in the current workfile.  This can only happen
;; if the master file gets nuked in window P.
;;
;;    Case 3 in RCS and case 15 under SCCS insert a redundant delta with
;; no change comment in the master.  This would require a self-race in
;; window P or R respectively.
;;
;;    Cases 2, 10, 19 and 20 do extra work, but make no changes.
;;
;;    Unfortunately, it appears to me that no recovery is possible in these
;; cases.  They don't yield error messages, so there's no way to tell that
;; a race condition has occurred.
;;
;;    All other cases don't change either the workfile or the master, and
;; trigger command errors which the user will see.
;;
;;    Thus, there is no explicit recovery code.

;; arch-tag: ca82c1de-3091-4e26-af92-460abc6213a6
;;; vc.el ends here