Added or corrected documentation headers

[emacs.git] / lisp / emerge.el

;;; emerge.el --- merge diffs under Emacs control

;;; The author has placed this file in the public domain.

;; Author: Dale R. Worley <drw@math.mit.edu>
;; Version: 4
;; Keywords: unix, tools

;;; Commentary:

;; This package assists you in reconciling differences between pair of files.

; - Starting
; 
; To start Emerge, you must run one of four commands:
; 
;       emerge-files
;       emerge-files-with-ancestor
;       emerge-buffers
;       emerge-buffers-with-ancestor
; 
; The "files" versions prompt you for two file names (the "A" and "B"
; files), the "buffers" versions prompt you for two buffer names (the
; "A" and "B" buffers).  Emerge then runs a "diff" of the two entities
; (emerge-buffers writes the buffers into temporary files for input to
; diff) and digests the output to form a list of the differences between
; the two files.  Then three buffers are set up: two containing the
; entities (emerge-files does a find-file (C-x C-f) on the files to get
; them into buffers), and one, the "merge buffer", which contains the
; working copy of the merged file that you are constructing.  The three
; buffers are put up in a nice three-window display, showing the A and B
; buffers in the upper half and the merge buffer in the lower half.
; 
; The versions of the command that say "with-ancestor" ask for a third
; name, that of an entity which is a common ancestor from which the
; versions being merged were derived.  These commands use "diff3" to
; compare all three versions.  If one version of a difference agrees
; with the ancestor, then it is presumed that the other version is the
; "correct" version, and is said to be "preferred".
; 
; (Note that if you use emerge-files, Emerge attempts to make sure that
; file on disk and the file in the buffer are the same.  If the file on
; disk has been changed, Emerge offers to revert the buffer.  If the
; buffer has been modified, Emerge offers to save the buffer.  If the
; user declines the offer, or if the file on disk and the buffer have
; both been modified, Emerge aborts with an error message.  Emerge is
; careful to widen the buffers containing the files if they have been
; narrowed.  If you use emerge-buffers, the buffers are not widened --
; only the visible portion is used.)
; 
; During the merge, the A and B buffers are read-only, so you don't
; damage them.  (This is because the A and B versions of the differences
; are extracted from these buffers.)  When you quit the merge, the
; read-only/read-write status and modified flag on the A and B buffers
; are restored.  In addition, auto-saving of the A and B buffers is
; suppressed during the merge.  This is because Emerge modifies the A
; and B buffers to point out the text of the differences, and it would
; be useless to save these changes.  (Just before suppressing
; auto-saving, Emerge forces an auto-save.)
; 
; If you give a prefix argument to emerge-files or
; emerge-files-with-ancestor, it prompts you for another file name,
; which is the file into which the merged file is to be written when you
; exit Emerge.  The output file name defaults to the A file name.  If
; you successfully quit Emerge, the merge buffer will be written to the
; output file, and the buffers for the A, B, and ancestor buffers will
; be deleted (if they exist and are not modified).  If you abort Emerge,
; the merge buffer will not be written and the buffers will not be
; deleted.
; 
; You can have any number of merges going at once -- just don't use any
; one buffer as input to more than one merge at once, since that will
; cause the read-only/modified/auto-save status save-and-restore to
; screw up.
; 
; Beware that when Emerge starts up, it does a diff or diff3 of the
; files, which can take many minutes for long files with many
; differences.  Emacs can't do anything else until diff finishes.
; 
; If diff or diff3 produces error messages, Emerge will beep and display
; the error messages instead of the merge buffer.  There will be a
; message in the echo area giving the name of the merge buffer.  Note
; that this is really just an informational message -- you still have
; switch to the merge buffer and abort the merge to restore the
; conditions before you ran Emerge.  (Emerge considers any output line
; that does not match the regexp emerge-diff/diff3-ok-lines to be an
; error message.)
; 
; After the merge has been set up, Emerge runs the hooks in
; emerge-startup-hook.
; 
; - Merging
; 
; Once you have started the merge, you manipulate the merge buffer with
; special commands issued in the merge buffer.  You may also edit the
; buffer with ordinary Emacs commands.  Emerge keeps track of each
; difference between the A and B buffers and the corresponding section
; of the merge buffer.  Initially, all differences show the A version,
; except those for which B is preferred (because A agrees with the
; ancestor), which show the B version.  Emerge always has its attention
; focused on one particular difference, which is marked off in the three
; buffers by "vvvvvvvvvvvvvvvvvvvv" above and "^^^^^^^^^^^^^^^^^^^^"
; below.  The number of the difference is shown in the mode line.
; 
; A merge buffer can be in two modes: "fast" mode and "edit" mode.  In
; fast mode, emerge commands are single characters, and ordinary Emacs
; commands are disabled.  This makes Emerge operations fast, but
; prevents you from doing more than selecing the A or the B version of
; differences.  In edit mode, all emerge commands must be prefixed with
; C-c, and all (non-conflicting) Emacs commands are available.  This
; allows editing the merge buffer, but slows down Emerge operations.
; Edit and fast modes are indicated by "F" and "E" in the minor modes in
; the mode line.
; 
; The Emerge commands are:
; 
;       p       go to the previous difference
;       n       go to the next difference
;       a       select the A version of this difference
;       b       select the B version of this difference
;       j       go to a particular difference (prefix argument
;               specifies which difference) (0j suppresses display of
;               the flags)
;       q       quit - finish the merge*
;       f       go into fast mode
;       e       go into edit mode
;       s a     set/clear auto-advance mode*
;       s s     set/clear skip-prefers mode*
;       l       recenter (C-l) all three windows*
;       - and 0 through 9
;               prefix numeric arguments
;       d a     select the A version as the default from here down in
;               the merge buffer*
;       d b     select the B version as the default from here down in
;               the merge buffer*
;       c a     copy the A version of the difference into the kill
;               ring
;       c b     copy the B version of the difference into the kill
;               ring
;       i a     insert the A version of the difference at the point
;       i b     insert the B version of the difference at the point
;       m       put the point and mark around the difference region
;       ^       scroll-down (like M-v) the three windows*
;       v       scroll-up (like C-v) the three windows*
;       <       scroll-left (like C-x <) the three windows*
;       >       scroll-right (like C-x >) the three windows*
;       |       reset horizontal scroll on the three windows*
;       x 1     shrink the merge window to one line (use C-u l to restore it
;               to full size)
;       x a     find the difference containing a location in the A buffer*
;       x b     find the difference containing a location in the B buffer*
;       x c     combine the two versions of this difference*
;       x C     combine the two versions of this difference, using a
;               register's value as the template*
;       x d     find the difference containing a location in the merge buffer*
;       x f     show the files/buffers Emerge is operating on in Help window
;               (use C-u l to restore windows)
;       x j     join this difference with the following one
;               (C-u x j joins this difference with the previous one)
;       x l     show line numbers of points in A, B, and merge buffers
;       x m     change major mode of merge buffer*
;       x s     split this difference into two differences
;               (first position the point in all three buffers to the places
;               to split the difference)
;       x t     trim identical lines off top and bottom of difference
;               (such lines occur when the A and B versions are
;               identical but differ from the ancestor version)
;       x x     set the template for the x c command*
; 
; * - more details on these commands are given below
; 
; emerge-version is a variable giving the version number of Emerge.  It
; is also a function which displays emerge-version (when called
; interactively) or returns it (when called from a program).
; 
; - Differences and their states
; 
; A difference can have one of seven states:
; 
; A:  the difference is showing the A version.
; 
; B:  the difference is showing the B version.
; 
; default-A and default-B: the difference is showing the A or B state,
; but has never been selected by the user.  All differences start in the
; default-A state (and thus the merge buffer is a copy of the A buffer),
; except those for which one buffer or another is preferred.  When the
; user selects the difference, it changes to the A or B state.
; 
; prefer-A and prefer-B: the difference is showing the A or B state.  In
; addition, the other buffer (that is, for prefer-A, the B buffer; for
; prefer-B, the A buffer) agrees with the ancestor buffer.  Thus,
; presumably, the displayed version is the correct one.  The "a" and "b"
; commands override these states, and turn them into the A and B states.
; 
; combined: the difference is showing a combination of the A and B
; states that was constructed by the "x c" or "x C" commands.  Since
; this state is neither the A or B states, the "a" and "b" commands
; won't alter the difference unless they are given a prefix argument.
; 
; The state of the currently selected difference is shown in the mode
; line of the merge window:
; 
;       state           display
; 
;       A               A
;       B               B
;       prefer-A        A*
;       prefer-B        B*
;       combined        comb
; 
; - Select default commands (d a and d b)
; 
; The d a and d b commands change all default-A's to default-B's (or
; vice-versa) from the selected difference on down to the end of the
; file to default-A or default-B, respectively.  (Since a difference
; that has been selected can not have state default-A or default-B, it
; will never be affected by d a or d b.  This leads to the unexpected
; result that d a or d b never affects the difference selected at the
; moment, but prevents differences that you have already looked at from
; changing unexpectedly.)
; 
; If you work your way down from the top of the file, using d a and d b
; at judicious points, you can effectivly make the A version the default
; for some sections of the merge buffer and the B version the default
; for others.
; 
; - Exiting (q)
; 
; The quit command finishes the merge session by restoring the state of
; the A and B buffers and removing the markers around the currently
; selected difference.  It also disables the Emerge commands in the
; merge buffer, since executing them later could damage the contents of
; the various buffers.
; 
; The action of "q" depends on how Emerge was started and whether "q"
; was given a prefix argument.  If there was no prefix argument, it is
; considered a "successful" finish.  If there was a prefix argument, it
; is considered an "unsuccessful" finish.  In either case, you are asked
; to cofirm the exit, and the confirmation message tells which sort of
; exit you are confirming.
; 
; If Emerge was started by some other process, success/failure is
; reported to the caller.
; 
; If Emerge was started with emerge-files or emerge-files-with-ancestor,
; if a prefix argument was given to that command, then you specified a
; file into which the merge is to be written.  A successful exit writes
; the merge into the output file and then kills the A, B, and ancestor
; buffers (so they aren't lying around to confuse you, since they
; probably all have similar names).
; 
; - Auto-advance mode (s a)
; 
; If auto-advance mode is set, the "a" and "b" commands perform an "n"
; (select next difference) afterward.  When auto-advance mode is set,
; it is indicated by "A" in the minor modes in the mode line.
; "s a" with a positive argument sets auto-advance, with a non-positive
; argument clears it, and with no argument toggles it.
; 
; - Skip-prefers mode (s s)
; 
; If skip-prefers mode is set, the "n" and "p" commands skip over
; differences with states prefer-A and prefer-B.  Thus you will only see
; differences for which one version isn't presumed "correct".  When
; skip-prefers mode is set, it is indicated by "S" in the minor modes in
; the mode line.  "s s" with a positive argument sets auto-advance, with
; a non-positive argument clears it, and with no argument toggles it.
; 
; - Recenter (l)
; 
; The Emerge "l" command causes the selected difference to be brought
; into view in the three windows, or at least, whichever of the three
; merge buffers are visible at the moment.  If a prefix argument is
; given, then the original three-window display is set up before the
; difference texts are shown.
; 
; - Scrolling the text (^, v, <, >, and |)
; 
; Emerge has several commands which scroll all three windows by the same
; amount, thus allowing you to easily compare the versions of the text.
; The commands are "^" (scroll-up), "v" (scroll-down), "<"
; (scroll-left), ">" (scroll-right), and "|" (reset horizontal
; scrolling).  (Remember that Emacs names scrolling commands by the
; motion of the text with respect to the window, so C-v is called
; "scroll-up".)
; 
; If these commands (except "|") are given an argument, that is the
; number of lines or characters by which the windows are scrolled.
; Otherwise, the amount of motion is computed based on the dimensions of
; the merge buffer window -- the height of the merge buffer window
; (minus next-frame-context-lines), or half the width of the merge
; buffer window.  (The A and B version windows are assumed to be as high
; as the merge window, but half as wide.)  If the argument is just `C-u
; -', then the scrolling is half the default amount.
; 
; - Finding the difference at or near a location (x d, x a, and x b)
; 
; The "x d" command selects the difference containing the current point
; in the merge buffer.  If there is no difference containing the point,
; an error is given.  An argument can be given to the command to change
; this behavior: if the argument is positive (e.g., C-u), the next
; following difference is selected; if the argument is negative (e.g.,
; C-u -), the previous difference is selected.
; 
; The "x a" and "x b" commands select the difference containing the
; current point in the A and B buffers, respectively.  Otherwise, they
; act like the "x d" command.  Note that although the point used in the
; commands is not the merge buffer point, the commands can only be
; issued in the merge buffer, because it is the only buffer with the
; Emerge keymap.
; 
; - Combining the two versions (x c, x C, and x x)
; 
; Sometimes one wants to combine the two versions of a difference.  For
; instance, when merging two versions of a program, one wants to make
; something like this:
; 
;       #ifdef NEW
;               ...new version of code...
;       #else /* NEW */
;               ...old version of code...
;       #endif /* NEW */
; 
; The "x c" command will make such a combined version.  (Note that any
; combined version is not the same as either the A or B versions, and so
; the "a" and "b" commands will refuse to alter it unless they are given
; a prefix argument.)  The combination is made under control of a
; template, which is a character string with the following
; interpolations:
; 
;       %a      the A version of the difference
;       %b      the B version of the difference
;       %%      the character '%'
; 
; Thus, the template used above is 
; 
;       #ifdef NEW\n%b#else /* NEW */\n%a#endif /* NEW */\n
; 
; (using \n here to represent newlines).  The template is stored in the
; variable emerge-combine-versions-template, and its initial value is
; the one given above.  The template can be set (from the current
; region) by the "x x" command.  (Be careful to get the newlines in the
; template in the right places!)  ("x x" was chosen by analogy with "C-x
; x".)  ("x x" is only available in the merge buffer, of course.
; Elsewhere, M-x emerge-set-combine-versions-template can be used.)  If
; "x x" is given a prefix argument, emerge-combine-versions-template is
; localized in the merge buffer before its value is set, so the "x x"
; command's effect (and the effect of any later "x x" command in the
; merge buffer) is only on the merge buffer.
; 
; The "x C" command is like "x c", but it prompts for a character
; which is the register whose value is to be used as the template.
; This allows one to use multiple templates conveniently.
; 
; - Changing the major mode of the edit buffer (x m)
; 
; The "x m" command prompts for the name of a major-mode-setting command
; and executes it.  Ordinarily, major-mode-setting commands change the
; mode line and local keymap, so the "x m" command then resets the
; Emerge mode line and the fast or edit mode local keymap, as
; appropriate.
; 
; If you have already changed the major mode of the merge buffer and
; lost the Emerge keymap, you can use M-x emerge-set-merge-mode to
; execute this command.
; 
; Beware that "x m" accepts any command name, not just
; major-mode-setting commands.
; 
; - Writing the merge buffer manually
; 
; Emerge places a wrapper (emerge-query-and-call) on the key bindings of
; save-buffer (usually "C-x C-s") and write-file (usually "C-x C-w"), in
; order to protect the user from writing out the merge before it is
; finished.  Emerge-query-and-call asks the user if he is sure he wants
; to write out the incomplete merge.  If he answers yes, the buffer is
; written out.  The flags are suppressed while the write is being done.
; As a result of this, the displayed portions of the buffers are
; recentered (equivalent to "l").
; 
; - Running Emerge standalone
; 
; If you invoke emacs with the following arguments, you can execute
; Emerge as a standalone program:
; 
;       emacs -l emerge -f emerge-files-command file-a file-b file-out
; 
;       emacs -l emerge -f emerge-files-with-ancestor-command
;               file-a file-b file-ancestor file-out
; 
; When the user gives the "q" (quit) command, Emerge will write out the
; merge buffer in file-out and terminate Emacs.  If a prefix argument is
; given, Emacs will terminate with an unsuccessful return code (1), if
; not, it will terminate with a successful return code (0).
; 
; - Invoking Emerge remotely
; 
; If you use the Emacs client/server code that supports remote
; execution, then you can invoke Emerge remotely by executing one of the
; Lisp calls:
; 
;       (emerge-files-remote "file A" "file B" "output file")
; 
;       (emerge-files-with-ancestor-remote "file A" "file B"
;               "ancestor file" "output file")
; 
; Returning a successful/unsuccessful return code is not yet supported
; by the Emacs client/server code.
; 
; Beware that in systems of networked workstations, even though all user
; directories are shared between all the workstations, the /tmp
; directory on each workstation is not shared, so writing files into
; /tmp and then remotely invoking Emerge is not likely to work.
; 
; - Effect of merge flags on indenting code
; 
; The presence of the flags confuses the indentation code of C and
; Emacs-Lisp modes.  Starting the flag strings
; (emerge-{before,after}-flag) with '#' (for C) or ';' (for Lisp)
; prevents the indentation code from noticing the flags.  Remember to
; change the flag strings before loading Emerge, or to execute
; emerge-new-flags after changing them.  But never change the flag
; strings while a merge is being performed.
; 
; - Autoloading
; 
; The following autoloads will make all top-level Emerge files
; autoloading.  Make sure that "emerge" is in a directory on load-path.
; 
; (autoload 'emerge-files "emerge"
;         "Run Emerge on two files."
;         t)
; (autoload 'emerge-files-with-ancestor "emerge"
;         "Run Emerge on two files, giving another file as the ancestor."
;         t)
; (autoload 'emerge-buffers "emerge"
;         "Run Emerge on two buffers."
;         t)
; (autoload 'emerge-buffers-with-ancestor "emerge"
;         "Run Emerge on two buffers, giving another buffer as the ancestor."
;         t)
; (autoload 'emerge-files-command "emerge")
; (autoload 'emerge-files-with-ancestor-command "emerge")
; (autoload 'emerge-files-remote "emerge")
; (autoload 'emerge-files-with-ancestor-remote "emerge")
; 
; ================================================================

;;; Change Log:

; - Changes from version 3 to version 4
; 
; More configuration variables are marked as user options.
; 
; Code is included for an improved version of make-auto-save-file-name
; which eliminates many problems with the default version.  See the
; documentation of emerge-make-auto-save-file-name to see how to
; activate it.
; 
; Emerge now works with Gnu diff3, which can produce the groups of lines
; from the various files in the order 1, 2, 3 or 1, 3, 2.
; 
; Added x f command to show what files or buffers are being operated on.
; 
; The merge buffer now starts read-only, which being in fast mode it
; should be.
; 
; When merging buffers, Emerge writes their contents into temporary
; files in the directory $TMPDIR (if it is defined), or /tmp by default.
; 
; Added x j command to join two differences.
; 
; Added x s command to split a difference into two differences.
; 
; Added emerge-version variable and function to report the version of Emerge
; being run.
; 
; Added x t command to trim unchanged lines off top and bottom of
; difference region.
; 
; Added x d, x a, and x b commands to locate the differences at or near
; a given location in one of the buffers.
; 
; Emerge no longer tries to copy the minor modes from the A buffer to
; the merge buffer, only the major mode.
; 
; The programs executed to find the differences between versions of the file
; are no longer controlled by emerge-diff/diff3-command, but rather by:
;   emerge-diff-program       
;     Variable: *Name of the program which compares two files.
;   emerge-diff3-program              
;     Variable: *Name of the program which compares an ancestor file
;     (first argument) and two variant files (second and third arguments).
;   emerge-diff-options       
;     Variable: *Options to be passed to emerge-diff/diff3-program.
; 
; The names of the files are expanded (see expand-file-name) before being
; passed to emerge-diff/diff3-program, so diff need not invoked under a shell
; that understands '~', for instance.
; 
; If the diff/diff3 program reports errors, the user is notified and the
; errors are displayed.
; 
; The command "0j" can be used to suppress the flags from showing in the buffers.
; 
; A discussion of the effect of the merge flags on indentation of code
; has been added to the documentation.
; 
; If kill-fix.el is loaded, Emerge control variables new have their
; 'preserved' property set, so setting the major mode in the merge
; buffer doesn't destroy Emerge's state.
; 
; Added x c, x C, and x x commands to allow the A and B versions to be
; combined into #ifdef - #endif forms.
; 
; Replaced calls of "ding" to calls of "error" where appropriate.
; 
; Added x m command to allow major mode of merge buffer to be changed.
; 
; Added x 1 command to shrink the merge window to one line.
; 
; Added emerge-startup-hook to allow customization.
; 
; Fixed a bug that is activated when a remote merge request is made when
; the minibuffer window is selected.
; 
; - Changes from version 2 to version 3
; 
; The directory into which temporary files are written is now controlled
; by a user option (emerge-temp-file-prefix).
; 
; The A and B versions of the difference can be loaded into the kill
; ring with the "c a" and "c b" commands.
; 
; The A and B versions of the difference can be inserted into the merge
; buffer with the "i a" and "i b" commands.
; 
; The difference region of the merge buffer can be surrounded by the
; point and mark with the "m" command.
; 
; The three windows can be scrolled together with the "^", "v", "<",
; ">", and "|" commands.
; 
; The "s s" and "s a" commands report the state of the option in the
; echo area.  Similarly, the "f" and "e" commands report what they do in
; the echo area.
; 
; The "q" command has been revamped, and its behavior is now controlled
; by the manner in which Emerge is started.  In particular, if you wish
; to write the merge buffer into a file upon exiting, invoke
; emerge-files[-with-ancestor] with a prefix argument, and it will
; prompt you for the file name.  Then exiting will write the merge
; buffer to the file, unless "q" is given a prefix argument.
; 
; The "i a" and "i b" commands now work in fast mode.
; 
; The modifications that Emerge makes to save-buffer and write-file are
; described.
; 
; Emerge now handles merging narrowed buffers correctly.
; 
; Emerge now isn't fooled when the buffer visiting a file is not the
; same as the file on disk.

;;; Code:

;;; Macros

(defmacro emerge-eval-in-buffer (buffer &rest forms)
  "Macro to switch to BUFFER, evaluate FORMS, returns to original buffer.
Differs from `save-excursion' in that it doesn't save the point and mark."
  (` (let ((StartBuffer (current-buffer)))
    (unwind-protect
        (progn
          (set-buffer (, buffer))
          (,@ forms))
      (set-buffer StartBuffer)))))

(defmacro emerge-defvar-local (var value doc) 
  "Defines SYMBOL as an advertised variable.  
Performs a defvar, then executes `make-variable-buffer-local' on
the variable.  Also sets the 'preserved' property, so that
`kill-all-local-variables' (called by major-mode setting commands) 
won't destroy Emerge control variables."
  (` (progn
       (defvar (, var) (, value) (, doc))
       (make-variable-buffer-local '(, var))
       (put '(, var) 'preserved t))))

;; Add entries to minor-mode-alist so that emerge modes show correctly
(setq emerge-minor-modes-list '((emerge-mode " Emerge")
                                (emerge-fast-mode " F")
                                (emerge-edit-mode " E")
                                (emerge-auto-advance " A")
                                (emerge-skip-prefers " S")))
(if (not (assq 'emerge-mode minor-mode-alist))
    (setq minor-mode-alist (append emerge-minor-modes-list
                                   minor-mode-alist)))

;; We need to define this function so describe-mode can describe Emerge mode.
(defun emerge-mode ()
  "Emerge mode is used by the Emerge file-merging package.
It is entered only through one of the functions:
        `emerge-files'
        `emerge-files-with-ancestor'
        `emerge-buffers'
        `emerge-buffers-with-ancestor'
        `emerge-files-command'
        `emerge-files-with-ancestor-command'
        `emerge-files-remote'
        `emerge-files-with-ancestor-remote'

Commands:
\\{emerge-basic-keymap}
Commands must be prefixed by \\<emerge-fast-keymap>\\[emerge-basic-keymap] in 'edit' mode, but can be invoked directly
in 'fast' mode.")

(defvar emerge-version "4"
  "The version of Emerge.")

(defun emerge-version ()
  "Return string describing the version of Emerge.
When called interactively, displays the version."
  (interactive)
  (if (interactive-p)
      (message "Emerge version %s" (emerge-version))
    emerge-version))

;;; Emerge configuration variables

;; Commands that produce difference files
;; All that can be configured is the name of the programs to execute
;; (emerge-diff-program and emerge-diff3-program) and the options
;; to be provided (emerge-diff-options).  The order in which the file names
;; are given is fixed.
;; The file names are always expanded (see expand-file-name) before being
;; passed to diff, thus they need not be invoked under a shell that 
;; understands '~'.
;; The code which processes the diff/diff3 output depends on all the
;; finicky details of their output, including the somewhat strange
;; way they number lines of a file.
(defvar emerge-diff-program "diff"
  "*Name of the program which compares two files.")
(defvar emerge-diff3-program "diff3"
  "*Name of the program which compares an ancestor file (first argument)
and two variant files (second and third arguments).")
(defvar emerge-diff-options ""
  "*Options to be passed to emerge-diff/diff3-program.")
(defvar emerge-match-diff-line (let ((x "\\([0-9]+\\)\\(\\|,\\([0-9]+\\)\\)"))
                                 (concat "^" x "\\([acd]\\)" x "$"))
  "*Pattern to match lines produced by diff that describe differences (as
opposed to lines from the source files).")
(defvar emerge-diff-ok-lines
  "^\\([0-9,]+[acd][0-9,]+$\\|[<>] \\|---\\)"
  "*Regexp that matches normal output lines from  emerge-diff-program .
Lines that do not match are assumed to be error output.")
(defvar emerge-diff3-ok-lines
  "^\\([1-3]:\\|====\\|  \\)"
  "*Regexp that matches normal output lines from  emerge-diff3-program .
Lines that do not match are assumed to be error output.")

;; The flags used to mark differences in the buffers.

;; These function definitions need to be up here, because they are used
;; during loading.
(defun emerge-new-flags ()
  "Function to be called after `emerge-{before,after}-flag'.
This is called after these functions are changed to compute values that
depend on the flags."
  (setq emerge-before-flag-length (length emerge-before-flag))
  (setq emerge-before-flag-lines
        (count-matches-string emerge-before-flag "\n"))
  (setq emerge-before-flag-match (regexp-quote emerge-before-flag))
  (setq emerge-after-flag-length (length emerge-after-flag))
  (setq emerge-after-flag-lines
        (count-matches-string emerge-after-flag "\n"))
  (setq emerge-after-flag-match (regexp-quote emerge-after-flag)))
(defun count-matches-string (string regexp)
  "Return the number of matches in STRING for REGEXP."
  (let ((i 0)
        (count 0))
    (while (string-match regexp string i)
      (setq count (1+ count))
      (setq i (match-end 0)))
    count))

(defvar emerge-before-flag "vvvvvvvvvvvvvvvvvvvv\n"
  "*Flag placed above the highlighted block of code.  Must end with newline.
Must be set before Emerge is loaded, or  emerge-new-flags  must be run
after setting.")
(defvar emerge-after-flag "^^^^^^^^^^^^^^^^^^^^\n"
  "*Flag placed below the highlighted block of code.  Must end with newline.
Must be set before Emerge is loaded, or  emerge-new-flags  must be run
after setting.")

;; Calculate dependent variables
(emerge-new-flags)

(defvar emerge-min-visible-lines 3
  "*Number of lines that we want to show above and below the flags when we are
displaying a difference.")

(defvar emerge-temp-file-prefix
  (let ((env (getenv "TMPDIR"))
        d)
    (setq d (if (and env (> (length env) 0))
                env
              "/tmp"))
    (if (= (aref d (1- (length d))) ?/)
        (setq d (substring d 0 -1)))
    (concat d "/emerge"))
  "*Prefix to put on Emerge temporary file names.
Do not start with '~/' or '~user-name/'.")

(defvar emerge-temp-file-mode 384       ; u=rw only
  "*Mode for Emerge temporary files.")

(defvar emerge-combine-versions-template
  "#ifdef NEW\n%b#else /* NEW */\n%a#endif /* NEW */\n"
  "*Template for  emerge-combine-versions  to combine the two versions.
The template is inserted as a string, with the following interpolations:
        %a      the A version of the difference
        %b      the B version of the difference
        %%      the character '%'
Don't forget to end the template with a newline.
Note that this variable can be made local to a particular merge buffer by
giving a prefix argument to  emerge-set-combine-versions-template .")

;; Build keymaps

(defvar emerge-basic-keymap nil
  "Keymap of Emerge commands.
Directly available in 'fast' mode;
must be prefixed by \\<emerge-fast-keymap>\\[emerge-basic-keymap] in 'edit' mode.")

(defvar emerge-fast-keymap nil
  "Local keymap used in Emerge 'fast' mode.
Makes Emerge commands directly available.")

(defvar emerge-command-prefix "\C-c"
  "*Command prefix for Emerge commands in 'edit' mode.
Must be set before Emerge is loaded.")

;; This function sets up the fixed keymaps.  It is executed when the first
;; Emerge is done to allow the user maximum time to set up the global keymap.
(defun emerge-setup-fixed-keymaps ()
  ;; Set up the basic keymap
  (setq emerge-basic-keymap (make-keymap))
  (suppress-keymap emerge-basic-keymap) ; this sets 0..9 to digit-argument and
                                        ; - to negative-argument
  (define-key emerge-basic-keymap "p" 'emerge-previous-difference)
  (define-key emerge-basic-keymap "n" 'emerge-next-difference)
  (define-key emerge-basic-keymap "a" 'emerge-select-A)
  (define-key emerge-basic-keymap "b" 'emerge-select-B)
  (define-key emerge-basic-keymap "j" 'emerge-jump-to-difference)
  (define-key emerge-basic-keymap "q" 'emerge-quit)
  (define-key emerge-basic-keymap "f" 'emerge-fast-mode)
  (define-key emerge-basic-keymap "e" 'emerge-edit-mode)
  (define-key emerge-basic-keymap "s" nil)
  (define-key emerge-basic-keymap "sa" 'emerge-auto-advance)
  (define-key emerge-basic-keymap "ss" 'emerge-skip-prefers)
  (define-key emerge-basic-keymap "l" 'emerge-recenter)
  (define-key emerge-basic-keymap "d" nil)
  (define-key emerge-basic-keymap "da" 'emerge-default-A)
  (define-key emerge-basic-keymap "db" 'emerge-default-B)
  (define-key emerge-basic-keymap "c" nil)
  (define-key emerge-basic-keymap "ca" 'emerge-copy-as-kill-A)
  (define-key emerge-basic-keymap "cb" 'emerge-copy-as-kill-B)
  (define-key emerge-basic-keymap "i" nil)
  (define-key emerge-basic-keymap "ia" 'emerge-insert-A)
  (define-key emerge-basic-keymap "ib" 'emerge-insert-B)
  (define-key emerge-basic-keymap "m" 'emerge-mark-difference)
  (define-key emerge-basic-keymap "v" 'emerge-scroll-up)
  (define-key emerge-basic-keymap "^" 'emerge-scroll-down)
  (define-key emerge-basic-keymap "<" 'emerge-scroll-left)
  (define-key emerge-basic-keymap ">" 'emerge-scroll-right)
  (define-key emerge-basic-keymap "|" 'emerge-scroll-reset)
  (define-key emerge-basic-keymap "x" nil)
  (define-key emerge-basic-keymap "x1" 'emerge-one-line-window)
  (define-key emerge-basic-keymap "xa" 'emerge-find-difference-A)
  (define-key emerge-basic-keymap "xb" 'emerge-find-difference-B)
  (define-key emerge-basic-keymap "xc" 'emerge-combine-versions)
  (define-key emerge-basic-keymap "xC" 'emerge-combine-versions-register)
  (define-key emerge-basic-keymap "xd" 'emerge-find-difference)
  (define-key emerge-basic-keymap "xf" 'emerge-file-names)
  (define-key emerge-basic-keymap "xj" 'emerge-join-differences)
  (define-key emerge-basic-keymap "xl" 'emerge-line-numbers)
  (define-key emerge-basic-keymap "xm" 'emerge-set-merge-mode)
  (define-key emerge-basic-keymap "xs" 'emerge-split-difference)
  (define-key emerge-basic-keymap "xt" 'emerge-trim-difference)
  (define-key emerge-basic-keymap "xx" 'emerge-set-combine-versions-template)
  ;; Allow emerge-basic-keymap to be referenced indirectly
  (fset 'emerge-basic-keymap emerge-basic-keymap)
  ;; Set up the fast mode keymap
  (setq emerge-fast-keymap (copy-keymap emerge-basic-keymap))
  ;; Allow prefixed commands to work in fast mode
  (define-key emerge-fast-keymap emerge-command-prefix 'emerge-basic-keymap)
  ;; Allow emerge-fast-keymap to be referenced indirectly
  (fset 'emerge-fast-keymap emerge-fast-keymap)
  ;; Suppress write-file and save-buffer
  (emerge-shadow-key-definition 'write-file 'emerge-query-write-file
                                (current-global-map) emerge-fast-keymap)
  (emerge-shadow-key-definition 'save-buffer 'emerge-query-save-buffer
                                (current-global-map) emerge-fast-keymap))

;; Variables which control each merge.  They are local to the merge buffer.

;; Mode variables
(emerge-defvar-local emerge-mode nil
  "Indicator for emerge-mode.")
(emerge-defvar-local emerge-fast-mode nil
  "Indicator for emerge-mode fast submode.")
(emerge-defvar-local emerge-edit-mode nil
  "Indicator for emerge-mode edit submode.")
(emerge-defvar-local emerge-A-buffer nil
  "The buffer in which the A variant is stored.")
(emerge-defvar-local emerge-B-buffer nil
  "The buffer in which the B variant is stored.")
(emerge-defvar-local emerge-merge-buffer nil
  "The buffer in which the merged file is manipulated.")
(emerge-defvar-local emerge-ancestor-buffer nil
  "The buffer in which the ancestor variant is stored,
or nil if there is none.")

(defconst emerge-saved-variables
  '((buffer-modified-p set-buffer-modified-p)
    buffer-read-only
    buffer-auto-save-file-name)
  "Variables and properties of a buffer which are saved, modified and restored
during a merge.")
(defconst emerge-merging-values '(nil t nil)
  "Values to be assigned to emerge-saved-variables during a merge.")

(emerge-defvar-local emerge-A-buffer-values nil
  "Remembers emerge-saved-variables for emerge-A-buffer.")
(emerge-defvar-local emerge-B-buffer-values nil
  "Remembers emerge-saved-variables for emerge-B-buffer.")

(emerge-defvar-local emerge-difference-list nil
  "Vector of differences between the variants, and markers in the buffers to
show where they are.  Each difference is represented by a vector of seven
elements.  The first two are markers to the beginning and end of the difference
section in the A buffer, the second two are markers for the B buffer, the third
two are markers for the merge buffer, and the last element is the \"state\" of
that difference in the merge buffer.
  A section of a buffer is described by two markers, one to the beginning of
the first line of the section, and one to the beginning of the first line
after the section.  (If the section is empty, both markers point to the same
point.)  If the section is part of the selected difference, then the markers
are moved into the flags, so the user can edit the section without disturbing
the markers.
  The \"states\" are:
        A               the merge buffer currently contains the A variant
        B               the merge buffer currently contains the B variant
        default-A       the merge buffer contains the A variant by default,
                        but this difference hasn't been selected yet, so
                        change-default commands can alter it
        default-B       the merge buffer contains the B variant by default,
                        but this difference hasn't been selected yet, so
                        change-default commands can alter it
        prefer-A        in a three-file merge, the A variant is the prefered
                        choice
        prefer-B        in a three-file merge, the B variant is the prefered
                        choice")
(emerge-defvar-local emerge-current-difference -1
  "The difference that is currently selected.")
(emerge-defvar-local emerge-number-of-differences nil
  "Number of differences found.")
(emerge-defvar-local emerge-edit-keymap nil
  "The local keymap for the merge buffer, with the emerge commands defined in
it.  Used to save the local keymap during fast mode, when the local keymap is
replaced by emerge-fast-keymap.")
(emerge-defvar-local emerge-old-keymap nil
  "The original local keymap for the merge buffer.")
(emerge-defvar-local emerge-auto-advance nil
  "*If non-nil, emerge-select-A and emerge-select-B automatically advance to
the next difference.")
(emerge-defvar-local emerge-skip-prefers nil
  "*If non-nil, differences for which there is a preference are automatically
skipped.")
(emerge-defvar-local emerge-startup-hook nil
  "*Hooks to run in the merge buffer after the merge has been set up.")
(emerge-defvar-local emerge-quit-hook nil
  "Hooks to run in the merge buffer after the merge has been finished.
emerge-prefix-argument will be bound to the prefix argument of the emerge-quit
command.
This is  not  a user option, since Emerge uses it for its own processing.")
(emerge-defvar-local emerge-output-description nil
  "Describes output destination merge, for the use of `emerge-file-names'.")

;;; Setup functions for two-file mode.

(defun emerge-files-internal (file-A file-B &optional startup-hooks quit-hooks
                                     output-file)
  (let ((buffer-A (find-file-noselect file-A))
        (buffer-B (find-file-noselect file-B)))
    ;; Make sure the entire files are seen, and they reflect what is on disk
    (emerge-eval-in-buffer buffer-A
                           (widen)
                           (emerge-verify-file-buffer))
    (emerge-eval-in-buffer buffer-B
                           (widen)
                           (emerge-verify-file-buffer))
    (emerge-setup buffer-A file-A buffer-B file-B startup-hooks quit-hooks
                  output-file)))

;; Start up Emerge on two files
(defun emerge-setup (buffer-A file-A buffer-B file-B startup-hooks quit-hooks
                              output-file)
  (setq file-A (expand-file-name file-A))
  (setq file-B (expand-file-name file-B))
  (setq output-file (and output-file (expand-file-name output-file)))
  (let* ((merge-buffer-name (emerge-unique-buffer-name "*merge" "*"))
         ;; create the merge buffer from buffer A, so it inherits buffer A's
         ;; default directory, etc.
         (merge-buffer (emerge-eval-in-buffer
                        buffer-A
                        (get-buffer-create merge-buffer-name))))
    (emerge-eval-in-buffer
     merge-buffer
     (emerge-copy-modes buffer-A)
     (setq buffer-read-only nil)
     (auto-save-mode 1)
     (setq emerge-mode t)
     (setq emerge-A-buffer buffer-A)
     (setq emerge-B-buffer buffer-B)
     (setq emerge-ancestor-buffer nil)
     (setq emerge-merge-buffer merge-buffer)
     (setq emerge-output-description
           (if output-file
               (concat "Output to file: " output-file)
             (concat "Output to buffer: " (buffer-name merge-buffer))))
     (insert-buffer emerge-A-buffer)
     (emerge-set-keys)
     (setq emerge-difference-list (emerge-make-diff-list file-A file-B))
     (setq emerge-number-of-differences (length emerge-difference-list))
     (setq emerge-current-difference -1)
     (setq emerge-quit-hooks quit-hooks)
     (emerge-remember-buffer-characteristics))
    (emerge-setup-windows buffer-A buffer-B merge-buffer t)
    (emerge-eval-in-buffer merge-buffer
                           (run-hooks 'startup-hooks 'emerge-startup-hook)
                           (setq buffer-read-only t))))

;; Generate the Emerge difference list between two files
(defun emerge-make-diff-list (file-A file-B)
  (setq emerge-diff-buffer (get-buffer-create "*emerge-diff*"))
  (emerge-eval-in-buffer
   emerge-diff-buffer
   (erase-buffer)
   (shell-command
    (format "%s %s %s %s"
            emerge-diff-program emerge-diff-options file-A file-B)
    t))
  (emerge-prepare-error-list emerge-diff-ok-lines)
  (emerge-convert-diffs-to-markers
   emerge-A-buffer emerge-B-buffer emerge-merge-buffer
   (emerge-extract-diffs emerge-diff-buffer)))

(defun emerge-extract-diffs (diff-buffer)
  (let (list)
    (emerge-eval-in-buffer
     diff-buffer
     (goto-char (point-min))
     (while (re-search-forward emerge-match-diff-line nil t)
       (let* ((a-begin (string-to-int (buffer-substring (match-beginning 1)
                                                        (match-end 1))))
              (a-end  (let ((b (match-beginning 3))
                            (e (match-end 3)))
                        (if b
                            (string-to-int (buffer-substring b e))
                          a-begin)))
              (diff-type (buffer-substring (match-beginning 4) (match-end 4)))
              (b-begin (string-to-int (buffer-substring (match-beginning 5)
                                                        (match-end 5))))
              (b-end (let ((b (match-beginning 7))
                           (e (match-end 7)))
                       (if b
                           (string-to-int (buffer-substring b e))
                         b-begin))))
         ;; fix the beginning and end numbers, because diff is somewhat
         ;; strange about how it numbers lines
         (if (string-equal diff-type "a")
             (progn
               (setq b-end (1+ b-end))
               (setq a-begin (1+ a-begin))
               (setq a-end a-begin))
           (if (string-equal diff-type "d")
               (progn
                 (setq a-end (1+ a-end))
                 (setq b-begin (1+ b-begin))
                 (setq b-end b-begin))
             ;; (string-equal diff-type "c")
             (progn
               (setq a-end (1+ a-end))
               (setq b-end (1+ b-end)))))
         (setq list (cons (vector a-begin a-end
                                  b-begin b-end
                                  'default-A)
                          list)))))
    (nreverse list)))

;; Set up buffer of diff/diff3 error messages.
(defun emerge-prepare-error-list (ok-regexp)
  (setq emerge-diff-error-buffer (get-buffer-create "*emerge-diff-errors*"))
  (emerge-eval-in-buffer
   emerge-diff-error-buffer
   (erase-buffer)
   (insert-buffer emerge-diff-buffer)
   (delete-matching-lines ok-regexp)))

;;; Top-level and setup functions for three-file mode.

(defun emerge-files-with-ancestor-internal (file-A file-B file-ancestor
                                          &optional startup-hooks quit-hooks
                                          output-file)
  (let ((buffer-A (find-file-noselect file-A))
        (buffer-B (find-file-noselect file-B))
        (buffer-ancestor (find-file-noselect file-ancestor)))
    ;; Make sure the entire files are seen, and they reflect what is on disk
    (emerge-eval-in-buffer buffer-A
                           (widen)
                           (emerge-verify-file-buffer))
    (emerge-eval-in-buffer buffer-B
                           (widen)
                           (emerge-verify-file-buffer))
    (emerge-eval-in-buffer buffer-ancestor
                           (widen)
                           (emerge-verify-file-buffer))
    (emerge-setup-with-ancestor buffer-A file-A buffer-B file-B
                                buffer-ancestor file-ancestor
                                startup-hooks quit-hooks output-file)))

;; Start up Emerge on two files with an ancestor
(defun emerge-setup-with-ancestor (buffer-A file-A buffer-B file-B
                                            buffer-ancestor file-ancestor
                                            &optional startup-hooks quit-hooks
                                            output-file)
  (setq file-A (expand-file-name file-A))
  (setq file-B (expand-file-name file-B))
  (setq file-ancestor (expand-file-name file-ancestor))
  (setq output-file (and output-file (expand-file-name output-file)))
  (let* ((merge-buffer-name (emerge-unique-buffer-name "*merge" "*"))
         ;; create the merge buffer from buffer A, so it inherits buffer A's
         ;; default directory, etc.
         (merge-buffer (emerge-eval-in-buffer
                        buffer-A
                        (get-buffer-create merge-buffer-name))))
    (emerge-eval-in-buffer
     merge-buffer
     (emerge-copy-modes buffer-A)
     (setq buffer-read-only nil)
     (auto-save-mode 1)
     (setq emerge-mode t)
     (setq emerge-A-buffer buffer-A)
     (setq emerge-B-buffer buffer-B)
     (setq emerge-ancestor-buffer buffer-ancestor)
     (setq emerge-merge-buffer merge-buffer)
     (setq emerge-output-description
           (if output-file
               (concat "Output to file: " output-file)
             (concat "Output to buffer: " (buffer-name merge-buffer))))
     (insert-buffer emerge-A-buffer)
     (emerge-set-keys)
     (setq emerge-difference-list
           (emerge-make-diff3-list file-A file-B file-ancestor))
     (setq emerge-number-of-differences (length emerge-difference-list))
     (setq emerge-current-difference -1)
     (setq emerge-quit-hook quit-hooks)
     (emerge-remember-buffer-characteristics)
     (emerge-select-prefer-Bs))
    (emerge-setup-windows buffer-A buffer-B merge-buffer t)
    (emerge-eval-in-buffer merge-buffer
                           (run-hooks 'startup-hooks 'emerge-startup-hook)
                           (setq buffer-read-only t))))

;; Generate the Emerge difference list between two files with an ancestor
(defun emerge-make-diff3-list (file-A file-B file-ancestor)
  (setq emerge-diff-buffer (get-buffer-create "*emerge-diff*"))
  (emerge-eval-in-buffer
   emerge-diff-buffer
   (erase-buffer)
   (shell-command
    (format "%s %s %s %s %s"
            emerge-diff3-program emerge-diff-options
            file-ancestor file-A file-B)
    t))
  (emerge-prepare-error-list emerge-diff3-ok-lines)
  (emerge-convert-diffs-to-markers
   emerge-A-buffer emerge-B-buffer emerge-merge-buffer
   (emerge-extract-diffs3 emerge-diff-buffer)))

(defun emerge-extract-diffs3 (diff-buffer)
  (let (list)
    (emerge-eval-in-buffer
     diff-buffer
     (while (re-search-forward "^====\\(.?\\)$" nil t)
       ;; leave point after matched line
       (beginning-of-line 2)
       (let ((agreement (buffer-substring (match-beginning 1) (match-end 1))))
         ;; if the A and B files are the same, ignore the difference
         (if (not (string-equal agreement "1"))
             (setq list
                   (cons 
                    (let ((group-2 (emerge-get-diff3-group "2"))
                          (group-3 (emerge-get-diff3-group "3")))
                      (vector (car group-2) (car (cdr group-2))
                              (car group-3) (car (cdr group-3))
                              (cond ((string-equal agreement "2") 'prefer-A)
                                    ((string-equal agreement "3") 'prefer-B)
                                    (t 'default-A))))
                    list))))))
    (nreverse list)))

(defun emerge-get-diff3-group (file)
  ;; This save-excursion allows emerge-get-diff3-group to be called for the
  ;; various groups of lines (1, 2, 3) in any order, and for the lines to
  ;; appear in any order.  The reason this is necessary is that Gnu diff3
  ;; can produce the groups in the order 1, 2, 3 or 1, 3, 2.
  (save-excursion
    (re-search-forward
     (concat "^" file ":\\([0-9]+\\)\\(,\\([0-9]+\\)\\)?\\([ac]\\)$"))
    (beginning-of-line 2)
    ;; treatment depends on whether it is an "a" group or a "c" group
    (if (string-equal (buffer-substring (match-beginning 4) (match-end 4)) "c")
        ;; it is a "c" group
        (if (match-beginning 2)
            ;; it has two numbers
            (list (string-to-int
                   (buffer-substring (match-beginning 1) (match-end 1)))
                  (1+ (string-to-int
                       (buffer-substring (match-beginning 3) (match-end 3)))))
          ;; it has one number
          (let ((x (string-to-int
                    (buffer-substring (match-beginning 1) (match-end 1)))))
            (list x (1+ x))))
      ;; it is an "a" group
      (let ((x (1+ (string-to-int
                    (buffer-substring (match-beginning 1) (match-end 1))))))
        (list x x)))))

;;; Functions to start Emerge on files

;;;###autoload
(defun emerge-files (arg file-A file-B file-out &optional startup-hooks
                     quit-hooks)
  "Run Emerge on two files."
  (interactive
   (let (f)
     (list current-prefix-arg
           (setq f (read-file-name "File A to merge: " nil nil 'confirm))
           (read-file-name "File B to merge: " nil nil 'confirm)
           (and current-prefix-arg
                (read-file-name
                 (format "Output file: (default %s) " f)
                 nil f nil)))))
  (emerge-files-internal
   file-A file-B startup-hooks
   (if arg
       (cons (` (lambda () (emerge-files-exit (, file-out))))
             quit-hooks)
     quit-hooks)
   file-out))

;;;###autoload
(defun emerge-files-with-ancestor (arg file-A file-B file-ancestor file-out
                                   &optional startup-hooks quit-hooks)
  "Run Emerge on two files, giving another file as the ancestor."
  (interactive
   (let (f)
     (list current-prefix-arg
           (setq f (read-file-name "File A to merge: " nil nil 'confirm))
           (read-file-name "File B to merge: " nil nil 'confirm)
           (read-file-name "Ancestor file: " nil nil 'confirm)
           (and current-prefix-arg
                (read-file-name
                 (format "Output file: (default %s) " f)
                 nil f nil)))))
  (emerge-files-with-ancestor-internal
   file-A file-B file-ancestor startup-hooks
   (if arg
       (cons (` (lambda () (emerge-files-exit (, file-out))))
             quit-hooks)
     quit-hooks)
   file-out))

;; Write the merge buffer out in place of the file the A buffer is visiting.
(defun emerge-files-exit (file-out)
  ;; if merge was successful was given, save to disk
  (if (not emerge-prefix-argument)
      (emerge-write-and-delete file-out)))

;;; Functions to start Emerge on buffers

;;;###autoload
(defun emerge-buffers (buffer-A buffer-B &optional startup-hooks quit-hooks)
  "Run Emerge on two buffers."
  (interactive "bBuffer A to merge: \nbBuffer B to merge: ")
  (let ((emerge-file-A (emerge-make-temp-file "A"))
        (emerge-file-B (emerge-make-temp-file "B")))
    (emerge-eval-in-buffer
     buffer-A
     (write-region (point-min) (point-max) emerge-file-A nil 'no-message))
    (emerge-eval-in-buffer
     buffer-B
     (write-region (point-min) (point-max) emerge-file-B nil 'no-message))
    (emerge-setup (get-buffer buffer-A) emerge-file-A
                  (get-buffer buffer-B) emerge-file-B
                  (cons (function (lambda ()
                                    (delete-file emerge-file-A)
                                    (delete-file emerge-file-B)))
                        startup-hooks)
                  quit-hooks
                  nil)))

;;;###autoload
(defun emerge-buffers-with-ancestor (buffer-A buffer-B buffer-ancestor
                                              &optional startup-hooks
                                              quit-hooks)
  "Run Emerge on two buffers, giving another buffer as the ancestor."
  (interactive
   "bBuffer A to merge: \nbBuffer B to merge: \nbAncestor buffer: ")
  (let ((emerge-file-A (emerge-make-temp-file "A"))
        (emerge-file-B (emerge-make-temp-file "B"))
        (emerge-file-ancestor (emerge-make-temp-file "anc")))
    (emerge-eval-in-buffer
     buffer-A
     (write-region (point-min) (point-max) emerge-file-A nil 'no-message))
    (emerge-eval-in-buffer
     buffer-B
     (write-region (point-min) (point-max) emerge-file-B nil 'no-message))
    (emerge-eval-in-buffer
     buffer-ancestor
     (write-region (point-min) (point-max) emerge-file-ancestor nil
                   'no-message))
    (emerge-setup-with-ancestor (get-buffer buffer-A) emerge-file-A
                                (get-buffer buffer-B) emerge-file-B
                                (get-buffer buffer-ancestor)
                                emerge-file-ancestor
                                (cons (function (lambda ()
                                                  (delete-file emerge-file-A)
                                                  (delete-file emerge-file-B)
                                                  (delete-file
                                                   emerge-file-ancestor)))
                                      startup-hooks)
                                quit-hooks
                                nil)))

;;; Functions to start Emerge from the command line

;;;###autoload
(defun emerge-files-command ()
  (let ((file-a (nth 0 command-line-args-left))
        (file-b (nth 1 command-line-args-left))
        (file-out (nth 2 command-line-args-left)))
    (setq command-line-args-left (nthcdr 3 command-line-args-left))
    (emerge-files-internal
     file-a file-b nil
     (list (` (lambda () (emerge-command-exit (, file-out))))))))

;;;###autoload
(defun emerge-files-with-ancestor-command ()
  (let (file-a file-b file-anc file-out)
    ;; check for a -a flag, for filemerge compatibility
    (if (string= (car command-line-args-left) "-a")
        ;; arguments are "-a ancestor file-a file-b file-out"
        (progn
          (setq file-a (nth 2 command-line-args-left))
          (setq file-b (nth 3 command-line-args-left))
          (setq file-anc (nth 1 command-line-args-left))
          (setq file-out (nth 4 command-line-args-left))
          (setq command-line-args-left (nthcdr 5 command-line-args-left)))
      ;; arguments are "file-a file-b ancestor file-out"
      (setq file-a (nth 0 command-line-args-left))
      (setq file-b (nth 1 command-line-args-left))
      (setq file-anc (nth 2 command-line-args-left))
      (setq file-out (nth 3 command-line-args-left))
      (setq command-line-args-left (nthcdr 4 command-line-args-left)))
    (emerge-files-with-ancestor-internal
     file-a file-b file-anc nil
     (list (` (lambda () (emerge-command-exit (, file-out))))))))
      
(defun emerge-command-exit (file-out)
  (emerge-write-and-delete file-out)
  (kill-emacs (if emerge-prefix-argument 1 0)))

;;; Functions to start Emerge via remote request

;;;###autoload
(defun emerge-files-remote (file-a file-b file-out)
  (setq emerge-file-out file-out)
  (emerge-files-internal
   file-a file-b nil
   (list (` (lambda () (emerge-remote-exit (, file-out) '(, exit-func)))))
   file-out)
  (throw 'client-wait nil))

;;;###autoload
(defun emerge-files-with-ancestor-remote (file-a file-b file-anc file-out)
  (setq emerge-file-out file-out)
  (emerge-files-with-ancestor-internal
   file-a file-b file-anc nil
   (list (` (lambda () (emerge-remote-exit (, file-out) '(, exit-func)))))
   file-out)
  (throw 'client-wait nil))

(defun emerge-remote-exit (file-out exit-func)
  (emerge-write-and-delete file-out)
  (kill-buffer emerge-merge-buffer)
  (funcall exit-func (if emerge-prefix-argument 1 0)))

;;; Common setup routines

;; Set up the window configuration.  If POS is given, set the points to
;; the beginnings of the buffers.
(defun emerge-setup-windows (buffer-A buffer-B merge-buffer &optional pos)
  ;; Make sure we are not in the minibuffer window when we try to delete
  ;; all other windows.
  (if (eq (selected-window) (minibuffer-window))
      (other-window 1))
  (delete-other-windows)
  (switch-to-buffer merge-buffer)
  (emerge-refresh-mode-line)
  (split-window-vertically)
  (split-window-horizontally)
  (switch-to-buffer buffer-A)
  (if pos
      (goto-char (point-min)))
  (other-window 1)
  (switch-to-buffer buffer-B)
  (if pos
      (goto-char (point-min)))
  (other-window 1)
  (if pos
      (goto-char (point-min)))
  ;; If diff/diff3 reports errors, display them rather than the merge buffer.
  (if (/= 0 (emerge-eval-in-buffer emerge-diff-error-buffer (buffer-size)))
      (progn
        (ding)
        (message "Errors found in diff/diff3 output.  Merge buffer is %s."
                 (buffer-name emerge-merge-buffer))
        (switch-to-buffer emerge-diff-error-buffer))))

;; Set up the keymap in the merge buffer
(defun emerge-set-keys ()
  ;; Set up fixed keymaps if necessary
  (if (not emerge-basic-keymap)
      (emerge-setup-fixed-keymaps))
  ;; Save the old local map
  (setq emerge-old-keymap (current-local-map))
  ;; Construct the edit keymap
  (setq emerge-edit-keymap (if emerge-old-keymap
                               (copy-keymap emerge-old-keymap)
                             (make-sparse-keymap)))
  ;; Install the Emerge commands
  (emerge-force-define-key emerge-edit-keymap emerge-command-prefix
                           'emerge-basic-keymap)
  ;; Suppress write-file and save-buffer
  (emerge-recursively-substitute-key-definition 'write-file
                                                'emerge-query-write-file
                                                emerge-edit-keymap)
  (emerge-recursively-substitute-key-definition 'save-buffer
                                                'emerge-query-save-buffer
                                                emerge-edit-keymap)
  (emerge-shadow-key-definition 'write-file 'emerge-query-write-file
                                (current-global-map) emerge-edit-keymap)
  (emerge-shadow-key-definition 'save-buffer 'emerge-query-save-buffer
                                (current-global-map) emerge-edit-keymap)
  (use-local-map emerge-fast-keymap)
  (setq emerge-edit-mode nil)
  (setq emerge-fast-mode t))

(defun emerge-remember-buffer-characteristics ()
  "Remembers certain properties of the buffers being merged.
Must be called in the merge buffer.  Remembers read-only, modified,
auto-save, and saves them in buffer local variables.  Sets the buffers
read-only and turns off `auto-save-mode'.
These characteristics are restored by emerge-restore-buffer-characteristics."
  ;; force auto-save, because we will turn off auto-saving in buffers for the
  ;; duration
  (do-auto-save)
  ;; remember and alter buffer characteristics
  (setq emerge-A-buffer-values
        (emerge-eval-in-buffer
         emerge-A-buffer
         (prog1
             (emerge-save-variables emerge-saved-variables)
           (emerge-restore-variables emerge-saved-variables
                                     emerge-merging-values))))
  (setq emerge-B-buffer-values
        (emerge-eval-in-buffer
         emerge-B-buffer
         (prog1
             (emerge-save-variables emerge-saved-variables)
           (emerge-restore-variables emerge-saved-variables
                                     emerge-merging-values)))))

(defun emerge-restore-buffer-characteristics ()
  "Restores the characteristics remembered by
emerge-remember-buffer-characteristics."
  (let ((A-values emerge-A-buffer-values)
        (B-values emerge-B-buffer-values))
    (emerge-eval-in-buffer emerge-A-buffer
                           (emerge-restore-variables emerge-saved-variables
                                                     A-values))
    (emerge-eval-in-buffer emerge-B-buffer
                           (emerge-restore-variables emerge-saved-variables
                                                     B-values))))

(defun emerge-convert-diffs-to-markers (A-buffer
                                        B-buffer
                                        merge-buffer
                                        lineno-list)
  (let* (marker-list
         (A-point-min (emerge-eval-in-buffer A-buffer (point-min)))
         (offset (1- A-point-min))
         (A-hidden-lines (emerge-eval-in-buffer
                          A-buffer
                          (save-restriction
                            (widen)
                            (count-lines 1 A-point-min))))
         (B-point-min (emerge-eval-in-buffer B-buffer (point-min)))
         (B-hidden-lines (emerge-eval-in-buffer
                          B-buffer
                          (save-restriction
                            (widen)
                            (count-lines 1 B-point-min)))))
    (while lineno-list
      (let* ((list-element (car lineno-list))
             a-begin-marker
             a-end-marker
             b-begin-marker
             b-end-marker
             (a-begin (aref list-element 0))
             (a-end (aref list-element 1))
             (b-begin (aref list-element 2))
             (b-end (aref list-element 3))
             (state (aref list-element 4)))
        ;; place markers at the appropriate places in the buffers
        (emerge-eval-in-buffer
         A-buffer
         (goto-line (+ a-begin A-hidden-lines))
         (setq a-begin-marker (point-marker))
         (goto-line (+ a-end A-hidden-lines))
         (setq a-end-marker (point-marker)))
        (emerge-eval-in-buffer
         B-buffer
         (goto-line (+ b-begin B-hidden-lines))
         (setq b-begin-marker (point-marker))
         (goto-line (+ b-end B-hidden-lines))
         (setq b-end-marker (point-marker)))
        (setq merge-begin-marker (set-marker
                                  (make-marker)
                                  (- (marker-position a-begin-marker)
                                     offset)
                                  merge-buffer))
        (setq merge-end-marker (set-marker
                                (make-marker)
                                (- (marker-position a-end-marker)
                                   offset)
                                merge-buffer))
        ;; record all the markers for this difference
        (setq marker-list (cons (vector a-begin-marker a-end-marker
                                        b-begin-marker b-end-marker
                                        merge-begin-marker merge-end-marker
                                        state)
                                marker-list)))
      (setq lineno-list (cdr lineno-list)))
    ;; convert the list of difference information into a vector for
    ;; fast access
    (setq emerge-difference-list (apply 'vector (nreverse marker-list)))))

;; If we have an ancestor, select all B variants that we prefer 
(defun emerge-select-prefer-Bs ()
  (let ((n 0))
    (while (< n emerge-number-of-differences)
      (if (eq (aref (aref emerge-difference-list n) 6) 'prefer-B)
          (progn
            (emerge-unselect-and-select-difference n t)
            (emerge-select-B)
            (aset (aref emerge-difference-list n) 6 'prefer-B)))
      (setq n (1+ n))))
  (emerge-unselect-and-select-difference -1))

;;; Common exit routines

(defun emerge-write-and-delete (file-out)
  ;; clear screen format
  (delete-other-windows)
  ;; delete A, B, and ancestor buffers, if they haven't been changed
  (if (not (buffer-modified-p emerge-A-buffer))
      (kill-buffer emerge-A-buffer))
  (if (not (buffer-modified-p emerge-B-buffer))
      (kill-buffer emerge-B-buffer))
  (if (and emerge-ancestor-buffer
           (not (buffer-modified-p emerge-ancestor-buffer)))
      (kill-buffer emerge-ancestor-buffer))
  ;; Write merge buffer to file
  (write-file file-out))

;;; Commands

(defun emerge-recenter (&optional arg)
  "Bring the highlighted region of all three merge buffers into view.
This brings the buffers into view if they are in windows.
If an ARGUMENT is given, the default three-window display is reestablished."
  (interactive "P")
  ;; If there is an argument, rebuild the window structure
  (if arg
      (emerge-setup-windows emerge-A-buffer emerge-B-buffer
                            emerge-merge-buffer))
  ;; Redisplay whatever buffers are showing, if there is a selected difference
  (if (and (>= emerge-current-difference 0)
           (< emerge-current-difference emerge-number-of-differences))
      (let* ((merge-buffer emerge-merge-buffer)
             (buffer-A emerge-A-buffer)
             (buffer-B emerge-B-buffer)
             (window-A (get-buffer-window buffer-A))
             (window-B (get-buffer-window buffer-B))
             (merge-window (get-buffer-window merge-buffer))
             (diff-vector
              (aref emerge-difference-list emerge-current-difference)))
        (if window-A (progn
                       (select-window window-A)
                       (emerge-position-region
                        (- (aref diff-vector 0)
                           (1- emerge-before-flag-length))
                        (+ (aref diff-vector 1)
                           (1- emerge-after-flag-length))
                        (1+ (aref diff-vector 0)))))
        (if window-B (progn
                       (select-window window-B)
                       (emerge-position-region
                        (- (aref diff-vector 2)
                           (1- emerge-before-flag-length))
                        (+ (aref diff-vector 3)
                           (1- emerge-after-flag-length))
                        (1+ (aref diff-vector 2)))))
        (if merge-window (progn
                           (select-window merge-window)
                           (emerge-position-region
                            (- (aref diff-vector 4)
                               (1- emerge-before-flag-length))
                            (+ (aref diff-vector 5)
                               (1- emerge-after-flag-length))
                            (1+ (aref diff-vector 4))))))))

;;; Window scrolling operations
;; These operations are designed to scroll all three windows the same amount,
;; so as to keep the text in them aligned.

;; Perform some operation on all three windows (if they are showing).
;; Catches all errors on the operation in the A and B windows, but not
;; in the merge window.  Usually, errors come from scrolling off the
;; beginning or end of the buffer, and this gives a nice error message:
;; End of buffer is reported in the merge buffer, but if the scroll was
;; possible in the A or B windows, it is performed there before the error
;; is reported.
(defun emerge-operate-on-windows (operation arg)
  (let* ((merge-buffer emerge-merge-buffer)
         (buffer-A emerge-A-buffer)
         (buffer-B emerge-B-buffer)
         (window-A (get-buffer-window buffer-A))
         (window-B (get-buffer-window buffer-B))
         (merge-window (get-buffer-window merge-buffer)))
    (if window-A (progn
                   (select-window window-A)
                   (condition-case nil
                       (funcall operation arg)
                     (error))))
    (if window-B (progn
                   (select-window window-B)
                   (condition-case nil
                       (funcall operation arg)
                     (error))))
    (if merge-window (progn
                       (select-window merge-window)
                       (funcall operation arg)))))

(defun emerge-scroll-up (&optional arg)
  "Scroll up all three merge buffers, if they are in windows.
If an ARGUMENT is given, that is how many lines are scrolled, else nearly
the size of the merge window.  `C-u -' alone as argument scrolls half the
size of the merge window."
  (interactive "P")
  (emerge-operate-on-windows
   'scroll-up 
   ;; calculate argument to scroll-up
   ;; if there is an explicit argument
   (if (and arg (not (equal arg '-)))
       ;; use it
       (prefix-numeric-value arg)
     ;; if not, see if we can determine a default amount (the window height)
     (let ((merge-window (get-buffer-window emerge-merge-buffer)))
       (if (null merge-window)
           ;; no window, use nil
           nil
         (let ((default-amount
                 (- (window-height merge-window) 1 next-screen-context-lines)))
           ;; the window was found
           (if arg
               ;; C-u as argument means half of default amount
               (/ default-amount 2)
             ;; no argument means default amount
             default-amount)))))))

(defun emerge-scroll-down (&optional arg)
  "Scroll down all three merge buffers, if they are in windows.
If an ARGUMENT is given, that is how many lines are scrolled, else nearly
the size of the merge window.  `C-u -' alone as argument scrolls half the
size of the merge window."
  (interactive "P")
  (emerge-operate-on-windows
   'scroll-down
   ;; calculate argument to scroll-down
   ;; if there is an explicit argument
   (if (and arg (not (equal arg '-)))
       ;; use it
       (prefix-numeric-value arg)
     ;; if not, see if we can determine a default amount (the window height)
     (let ((merge-window (get-buffer-window emerge-merge-buffer)))
       (if (null merge-window)
           ;; no window, use nil
           nil
         (let ((default-amount
                 (- (window-height merge-window) 1 next-screen-context-lines)))
           ;; the window was found
           (if arg
               ;; C-u as argument means half of default amount
               (/ default-amount 2)
             ;; no argument means default amount
             default-amount)))))))

(defun emerge-scroll-left (&optional arg)
  "Scroll left all three merge buffers, if they are in windows.
If an ARGUMENT is given, that is how many columns are scrolled, else nearly
the width of the A and B windows.  C-u - alone as argument scrolls half the
width of the A and B windows."
  (interactive "P")
  (emerge-operate-on-windows
   'scroll-left
   ;; calculate argument to scroll-left
   ;; if there is an explicit argument
   (if (and arg (not (equal arg '-)))
       ;; use it
       (prefix-numeric-value arg)
     ;; if not, see if we can determine a default amount
     ;; (half the window width)
     (let ((merge-window (get-buffer-window emerge-merge-buffer)))
       (if (null merge-window)
           ;; no window, use nil
           nil
         (let ((default-amount
                 (- (/ (window-width merge-window) 2) 3)))
           ;; the window was found
           (if arg
               ;; C-u as argument means half of default amount
               (/ default-amount 2)
             ;; no argument means default amount
             default-amount)))))))

(defun emerge-scroll-right (&optional arg)
  "Scroll right all three merge buffers, if they are in windows.
If an ARGUMENT is given, that is how many columns are scrolled, else nearly
the width of the A and B windows.  C-u - alone as argument scrolls half the
width of the A and B windows."
  (interactive "P")
  (emerge-operate-on-windows
   'scroll-right
   ;; calculate argument to scroll-right
   ;; if there is an explicit argument
   (if (and arg (not (equal arg '-)))
       ;; use it
       (prefix-numeric-value arg)
     ;; if not, see if we can determine a default amount
     ;; (half the window width)
     (let ((merge-window (get-buffer-window emerge-merge-buffer)))
       (if (null merge-window)
           ;; no window, use nil
           nil
         (let ((default-amount
                 (- (/ (window-width merge-window) 2) 3)))
           ;; the window was found
           (if arg
               ;; C-u as argument means half of default amount
               (/ default-amount 2)
             ;; no argument means default amount
             default-amount)))))))

(defun emerge-scroll-reset ()
  "Reset horizontal scrolling.
This resets the horizontal scrolling of all three merge buffers
to the left margin, if they are in windows."
  (interactive)
  (emerge-operate-on-windows
   (function (lambda (x) (set-window-hscroll (selected-window) 0)))
   nil))

;; Attempt to show the region nicely.
;; If there are min-lines lines above and below the region, then don't do
;; anything.
;; If not, recenter the region to make it so.
;; If that isn't possible, remove context lines balancedly from top and botton
;; so the entire region shows.
;; If that isn't possible, show the top of the region.
;; BEG must be at the beginning of a line.
(defun emerge-position-region (beg end pos)
  ;; First test whether the entire region is visible with
  ;; emerge-min-visible-lines above and below it
  (if (not (and (<= (progn
                      (move-to-window-line emerge-min-visible-lines)
                      (point))
                    beg)
                (<= end (progn
                          (move-to-window-line
                           (- (1+ emerge-min-visible-lines)))
                          (point)))))
      ;; We failed that test, see if it fits at all
      ;; Meanwhile positioning it correctly in case it doesn't fit
      (progn
        (set-window-start (selected-window) beg)
        (setq fits (pos-visible-in-window-p end))
        (if fits
            ;; Determine the number of lines that the region occupies
            (let ((lines 0))
              (while (> end (progn
                              (move-to-window-line lines)
                              (point)))
                (setq lines (1+ lines)))
              ;; And position the beginning on the right line
              (goto-char beg)
              (recenter (/ (1+ (- (1- (window-height (selected-window)))
                                  lines))
                           2))))))
  (goto-char pos))

(defun emerge-next-difference ()
  "Advance to the next difference."
  (interactive)
  (if (< emerge-current-difference emerge-number-of-differences)
      (let ((n (1+ emerge-current-difference)))
        (while (and emerge-skip-prefers
                    (< n emerge-number-of-differences)
                    (memq (aref (aref emerge-difference-list n) 6)
                          '(prefer-A prefer-B)))
          (setq n (1+ n)))
        (let ((buffer-read-only nil))
          (emerge-unselect-and-select-difference n)))
    (error "At end")))

(defun emerge-previous-difference ()
  "Go to the previous difference."
  (interactive)
  (if (> emerge-current-difference -1)
      (let ((n (1- emerge-current-difference)))
        (while (and emerge-skip-prefers
                    (> n -1)
                    (memq (aref (aref emerge-difference-list n) 6)
                          '(prefer-A prefer-B)))
          (setq n (1- n)))
        (let ((buffer-read-only nil))
          (emerge-unselect-and-select-difference n)))
    (error "At beginning")))

(defun emerge-jump-to-difference (difference-number)
  "Go to the N-th difference."
  (interactive "p")
  (let ((buffer-read-only nil))
    (setq difference-number (1- difference-number))
    (if (and (>= difference-number -1)
             (< difference-number (1+ emerge-number-of-differences)))
        (emerge-unselect-and-select-difference difference-number)
      (error "Bad difference number"))))

(defun emerge-quit (arg)
  "Finish an Emerge session.
Prefix argument means to abort rather than successfully finish.
The difference depends on how the merge was started,
but usually means to not write over one of the original files, or to signal
to some process which invoked Emerge a failure code.

Unselects the selected difference, if any, restores the read-only and modified
flags of the merged file buffers, restores the local keymap of the merge
buffer, and sets off various emerge flags.  Using Emerge commands in this
buffer after this will cause serious problems."
  (interactive "P")
  (if (prog1
          (y-or-n-p
           (if (not arg)
               "Do you really want to successfully finish this merge? "
             "Do you really want to abort this merge? "))
        (message ""))
      (emerge-really-quit arg)))

;; Perform the quit operations.
(defun emerge-really-quit (arg)
  (setq buffer-read-only nil)
  (emerge-unselect-and-select-difference -1)
  (emerge-restore-buffer-characteristics)
  ;; null out the difference markers so they don't slow down future editing
  ;; operations
  (mapcar (function (lambda (d)
                      (set-marker (aref d 0) nil)
                      (set-marker (aref d 1) nil)
                      (set-marker (aref d 2) nil)
                      (set-marker (aref d 3) nil)
                      (set-marker (aref d 4) nil)
                      (set-marker (aref d 5) nil)))
          emerge-difference-list)
  ;; allow them to be garbage collected
  (setq emerge-difference-list nil)
  ;; restore the local map
  (use-local-map emerge-old-keymap)
  ;; turn off all the emerge modes
  (setq emerge-mode nil)
  (setq emerge-fast-mode nil)
  (setq emerge-edit-mode nil)
  (setq emerge-auto-advance nil)
  (setq emerge-skip-prefers nil)
  ;; restore mode line
  (kill-local-variable 'mode-line-buffer-identification)
  (let ((emerge-prefix-argument arg))
    (run-hooks 'emerge-quit-hook)))

(defun emerge-select-A (&optional force)
  "Select the A variant of this difference.  
Refuses to function if this difference has been edited, i.e., if it
is neither the A nor the B variant.
An ARGUMENT forces the variant to be selected even if the difference has
been edited."
  (interactive "P")
  (let ((operate
         (function (lambda ()
                     (emerge-select-A-edit merge-begin merge-end A-begin A-end)
                     (if emerge-auto-advance
                         (emerge-next-difference)))))
        (operate-no-change
         (function (lambda ()
                     (if emerge-auto-advance
                         (emerge-next-difference))))))
    (emerge-select-version force operate-no-change operate operate)))

;; Actually select the A variant
(defun emerge-select-A-edit (merge-begin merge-end A-begin A-end)
  (emerge-eval-in-buffer
   emerge-merge-buffer
   (delete-region merge-begin merge-end)
   (goto-char merge-begin)
   (insert-buffer-substring emerge-A-buffer A-begin A-end)
   (goto-char merge-begin)
   (aset diff-vector 6 'A)
   (emerge-refresh-mode-line)))

(defun emerge-select-B (&optional force)
  "Select the B variant of this difference.
Refuses to function if this difference has been edited, i.e., if it
is neither the A nor the B variant.  An ARGUMENT forces the variant to be selected even if the difference has
been edited."
  (interactive "P")
  (let ((operate
         (function (lambda ()
                     (emerge-select-B-edit merge-begin merge-end B-begin B-end)
                     (if emerge-auto-advance
                         (emerge-next-difference)))))
        (operate-no-change
         (function (lambda ()
                     (if emerge-auto-advance
                         (emerge-next-difference))))))
    (emerge-select-version force operate operate-no-change operate)))

;; Actually select the B variant
(defun emerge-select-B-edit (merge-begin merge-end B-begin B-end)
  (emerge-eval-in-buffer
   emerge-merge-buffer
   (delete-region merge-begin merge-end)
   (goto-char merge-begin)
   (insert-buffer-substring emerge-B-buffer B-begin B-end)
   (goto-char merge-begin)
   (aset diff-vector 6 'B)
   (emerge-refresh-mode-line)))

(defun emerge-default-A ()
  "Selects the A variant.
This selects the A variant for all differences from here down in the buffer
which are still defaulted, i.e., which the user has not selected and for
which there is no preference."
  (interactive)
  (let ((buffer-read-only nil))
    (let ((selected-difference emerge-current-difference)
          (n (max emerge-current-difference 0)))
      (while (< n emerge-number-of-differences)
        (let ((diff-vector (aref emerge-difference-list n)))
          (if (eq (aref diff-vector 6) 'default-B)
              (progn
                (emerge-unselect-and-select-difference n t)
                (emerge-select-A)
                (aset diff-vector 6 'default-A))))
        (setq n (1+ n))
        (if (= (* (/ n 10) 10) n)
            (message "Setting default to A...%d" n)))
      (emerge-unselect-and-select-difference selected-difference)))
  (message "Default A set"))

(defun emerge-default-B ()
  "Selects the B variant.
This selects the B variant for all differences from here down in the buffer
which are still defaulted, i.e., which the user has not selected and for
which there is no preference."
  (interactive)
  (let ((buffer-read-only nil))
    (let ((selected-difference emerge-current-difference)
          (n (max emerge-current-difference 0)))
      (while (< n emerge-number-of-differences)
        (let ((diff-vector (aref emerge-difference-list n)))
          (if (eq (aref diff-vector 6) 'default-A)
              (progn
                (emerge-unselect-and-select-difference n t)
                (emerge-select-B)
                (aset diff-vector 6 'default-B))))
        (setq n (1+ n))
        (if (= (* (/ n 10) 10) n)
            (message "Setting default to B...%d" n)))
      (emerge-unselect-and-select-difference selected-difference)))
  (message "Default B set"))

(defun emerge-fast-mode ()
  "Set fast mode.
In this mode ordinary Emacs commands are disabled, and Emerge commands
are need not be prefixed with \\<emerge-fast-keymap>\\[emerge-basic-keymap]."
  (interactive)
  (setq buffer-read-only t)
  (use-local-map emerge-fast-keymap)
  (setq emerge-mode t)
  (setq emerge-fast-mode t)
  (setq emerge-edit-mode nil)
  (message "Fast mode set")
  ;; force mode line redisplay
  (set-buffer-modified-p (buffer-modified-p)))

(defun emerge-edit-mode ()
  "Set edit mode.
In this mode ordinary Emacs commands are available, and Emerge commands
must be prefixed with \\<emerge-fast-keymap>\\[emerge-basic-keymap]."
  (interactive)
  (setq buffer-read-only nil)
  (use-local-map emerge-edit-keymap)
  (setq emerge-mode t)
  (setq emerge-fast-mode nil)
  (setq emerge-edit-mode t)
  (message "Edit mode set")
  ;; force mode line redisplay
  (set-buffer-modified-p (buffer-modified-p)))

(defun emerge-auto-advance (arg)
  "Toggle auto-advance mode.
This mode causes `emerge-select-A' and `emerge-select-B'  to automatically
advance to the next difference.  (See `emerge-auto-advance'.)  
If a positive ARGUMENT is given, it turns on `auto-advance-mode'.
If a negative ARGUMENT is given, it turns off `auto-advance-mode'."
  (interactive "P")
  (setq emerge-auto-advance (if (null arg)
                                (not emerge-auto-advance)
                              (> (prefix-numeric-value arg) 0)))
  (message (if emerge-skip-prefers
               "Auto-advance set"
             "Auto-advance cleared"))
  ;; force mode line redisplay
  (set-buffer-modified-p (buffer-modified-p)))

(defun emerge-skip-prefers (arg)
  "Toggle skip-prefers mode.
This mode causes `emerge-next-difference' and `emerge-previous-difference'
to automatically skip over differences for which there is a preference.
(See `emerge-skip-prefers'.)  If a positive ARG is given, it turns on
`skip-prefers' mode.
If a negative ARG is given, it turns off `skip-prefers' mode."
  (interactive "P")
  (setq emerge-skip-prefers (if (null arg)
                                (not emerge-skip-prefers)
                              (> (prefix-numeric-value arg) 0)))
  (message (if emerge-skip-prefers
               "Skip-prefers set"
             "Skip-prefers cleared"))
  ;; force mode line redisplay
  (set-buffer-modified-p (buffer-modified-p)))

(defun emerge-copy-as-kill-A ()
  "Put the A variant of this difference in the kill ring."
  (interactive)
  (emerge-validate-difference)
  (let* ((diff-vector
          (aref emerge-difference-list emerge-current-difference))
         (A-begin (1+ (aref diff-vector 0)))
         (A-end (1- (aref diff-vector 1)))
         ;; so further kills don't append
         this-command)
    (save-excursion
      (set-buffer emerge-A-buffer)
      (copy-region-as-kill A-begin A-end))))

(defun emerge-copy-as-kill-B ()
  "Put the B variant of this difference in the kill ring."
  (interactive)
  (emerge-validate-difference)
  (let* ((diff-vector
          (aref emerge-difference-list emerge-current-difference))
         (B-begin (1+ (aref diff-vector 2)))
         (B-end (1- (aref diff-vector 3)))
         ;; so further kills don't append
         this-command)
    (save-excursion
      (set-buffer emerge-B-buffer)
      (copy-region-as-kill B-begin B-end))))

(defun emerge-insert-A (arg)
  "Insert the A variant of this difference at the point.
Leaves point after text, mark before.
With prefix argument, puts point before, mark after."
  (interactive "P")
  (emerge-validate-difference)
  (let* ((diff-vector
          (aref emerge-difference-list emerge-current-difference))
         (A-begin (1+ (aref diff-vector 0)))
         (A-end (1- (aref diff-vector 1)))
         (opoint (point))
         (buffer-read-only nil))
    (insert-buffer-substring emerge-A-buffer A-begin A-end)
    (if (not arg)
        (set-mark opoint)
      (set-mark (point))
      (goto-char opoint))))

(defun emerge-insert-B (arg)
  "Insert the B variant of this difference at the point.
Leaves point after text, mark before.
With prefix argument, puts point before, mark after."
  (interactive "P")
  (emerge-validate-difference)
  (let* ((diff-vector
          (aref emerge-difference-list emerge-current-difference))
         (B-begin (1+ (aref diff-vector 2)))
         (B-end (1- (aref diff-vector 3)))
         (opoint (point))
         (buffer-read-only nil))
    (insert-buffer-substring emerge-B-buffer B-begin B-end)
    (if (not arg)
        (set-mark opoint)
      (set-mark (point))
      (goto-char opoint))))

(defun emerge-mark-difference (arg)
  "Leaves the point before this difference and the mark after it.
With prefix argument, puts mark before, point after."
  (interactive "P")
  (emerge-validate-difference)
  (let* ((diff-vector
          (aref emerge-difference-list emerge-current-difference))
         (merge-begin (1+ (aref diff-vector 4)))
         (merge-end (1- (aref diff-vector 5))))
    (if (not arg)
        (progn
          (goto-char merge-begin)
          (set-mark merge-end))
      (goto-char merge-end)
      (set-mark merge-begin))))

(defun emerge-file-names ()
  "Show the names of the buffers or files being operated on by Emerge.
Use C-u l to reset the windows afterward."
  (interactive)
  (delete-other-windows)
  (let ((temp-buffer-show-function
         (function (lambda (buf)
                     (split-window-vertically)
                     (switch-to-buffer buf)
                     (other-window 1)))))
    (with-output-to-temp-buffer "*Help*"
      (emerge-eval-in-buffer emerge-A-buffer
                             (if buffer-file-name
                                 (progn
                                   (princ "File A is: ")
                                   (princ buffer-file-name))
                               (progn
                                 (princ "Buffer A is: ")
                                 (princ (buffer-name))))
                             (princ "\n"))
      (emerge-eval-in-buffer emerge-B-buffer
                             (if buffer-file-name
                                 (progn
                                   (princ "File B is: ")
                                   (princ buffer-file-name))
                               (progn
                                 (princ "Buffer B is: ")
                                 (princ (buffer-name))))
                             (princ "\n"))
      (if emerge-ancestor-buffer
            (emerge-eval-in-buffer emerge-ancestor-buffer
                                   (if buffer-file-name
                                       (progn
                                         (princ "Ancestor file is: ")
                                         (princ buffer-file-name))
                                     (progn
                                       (princ "Ancestor buffer is: ")
                                       (princ (buffer-name))))
                                   (princ "\n")))
      (princ emerge-output-description))))

(defun emerge-join-differences (arg)
  "Join the selected difference with the following one.
With a prefix argument, join with the preceeding one."
  (interactive "P")
  (let ((n emerge-current-difference))
    ;; adjust n to be first difference to join
    (if arg
        (setq n (1- n)))
    ;; n and n+1 are the differences to join
    ;; check that they are both differences
    (if (or (< n 0) (>= n (1- emerge-number-of-differences)))
        (error "Incorrect differences to join"))
    ;; remove the flags
    (emerge-unselect-difference emerge-current-difference)
    ;; decrement total number of differences
    (setq emerge-number-of-differences (1- emerge-number-of-differences))
    ;; build new differences vector
    (let ((i 0)
          (new-differences (make-vector emerge-number-of-differences nil)))
      (while (< i emerge-number-of-differences)
        (aset new-differences i
              (cond
               ((< i n) (aref emerge-difference-list i))
               ((> i n) (aref emerge-difference-list (1+ i)))
               (t (let ((prev (aref emerge-difference-list i))
                        (next (aref emerge-difference-list (1+ i))))
                    (vector (aref prev 0)
                            (aref next 1)
                            (aref prev 2)
                            (aref next 3)
                            (aref prev 4)
                            (aref next 5)
                            (let ((ps (aref prev 6))
                                  (ns (aref next 6)))
                              (cond
                               ((eq ps ns)
                                ps)
                               ((and (or (eq ps 'B) (eq ps 'prefer-B))
                                     (or (eq ns 'B) (eq ns 'prefer-B)))
                                'B)
                               (t 'A))))))))
        (setq i (1+ i)))
      (setq emerge-difference-list new-differences))
    ;; set the current difference correctly
    (setq emerge-current-difference n)
    ;; fix the mode line
    (emerge-refresh-mode-line)
    ;; reinsert the flags
    (emerge-select-difference emerge-current-difference)
    (emerge-recenter)))

(defun emerge-split-difference ()
  "Split the current difference where the points are in the three windows."
  (interactive)
  (let ((n emerge-current-difference))
    ;; check that this is a valid difference
    (emerge-validate-difference)
    ;; get the point values and old difference
    (let ((A-point (emerge-eval-in-buffer emerge-A-buffer
                                          (point-marker)))
          (B-point (emerge-eval-in-buffer emerge-B-buffer
                                          (point-marker)))
          (merge-point (point-marker))
          (old-diff (aref emerge-difference-list n)))
      ;; check location of the points, give error if they aren't in the
      ;; differences
      (if (or (< A-point (aref old-diff 0))
              (> A-point (aref old-diff 1)))
          (error "Point outside of difference in A buffer"))
      (if (or (< B-point (aref old-diff 2))
              (> B-point (aref old-diff 3)))
          (error "Point outside of difference in B buffer"))
      (if (or (< merge-point (aref old-diff 4))
              (> merge-point (aref old-diff 5)))
          (error "Point outside of difference in merge buffer"))
      ;; remove the flags
      (emerge-unselect-difference emerge-current-difference)
      ;; increment total number of differences
      (setq emerge-number-of-differences (1+ emerge-number-of-differences))
      ;; build new differences vector
      (let ((i 0)
            (new-differences (make-vector emerge-number-of-differences nil)))
        (while (< i emerge-number-of-differences)
          (aset new-differences i
                (cond
                 ((< i n)
                  (aref emerge-difference-list i))
                 ((> i (1+ n))
                  (aref emerge-difference-list (1- i)))
                 ((= i n)
                  (vector (aref old-diff 0)
                          A-point
                          (aref old-diff 2)
                          B-point
                          (aref old-diff 4)
                          merge-point
                          (aref old-diff 6)))
                 (t
                  (vector (copy-marker A-point)
                          (aref old-diff 1)
                          (copy-marker B-point)
                          (aref old-diff 3)
                          (copy-marker merge-point)
                          (aref old-diff 5)
                          (aref old-diff 6)))))
          (setq i (1+ i)))
        (setq emerge-difference-list new-differences))
      ;; set the current difference correctly
      (setq emerge-current-difference n)
      ;; fix the mode line
      (emerge-refresh-mode-line)
      ;; reinsert the flags
      (emerge-select-difference emerge-current-difference)
      (emerge-recenter))))

(defun emerge-trim-difference ()
  "Trim lines off top and bottom of difference that are the same.
If lines are the same in both the A and the B versions, strip them off.
(This can happen when the A and B versions have common lines that the
ancestor version does not share.)"
  (interactive)
  ;; make sure we are in a real difference
  (emerge-validate-difference)
  ;; remove the flags
  (emerge-unselect-difference emerge-current-difference)
  (let* ((diff (aref emerge-difference-list emerge-current-difference))
         (top-a (marker-position (aref diff 0)))
         (bottom-a (marker-position (aref diff 1)))
         (top-b (marker-position (aref diff 2)))
         (bottom-b (marker-position (aref diff 3)))
         (top-m (marker-position (aref diff 4)))
         (bottom-m (marker-position (aref diff 5)))
         size success sa sb sm)
    ;; move down the tops of the difference regions as much as possible
    ;; Try advancing comparing 1000 chars at a time.
    ;; When that fails, go 500 chars at a time, and so on.
    (setq size 1000)
    (while (> size 0)
      (setq success t)
      (while success
        (setq size (min size (- bottom-a top-a) (- bottom-b top-b)
                        (- bottom-m top-m)))
        (setq sa (emerge-eval-in-buffer emerge-A-buffer
                                        (buffer-substring top-a
                                                          (+ size top-a))))
        (setq sb (emerge-eval-in-buffer emerge-B-buffer
                                        (buffer-substring top-b
                                                          (+ size top-b))))
        (setq sm (buffer-substring top-m (+ size top-m)))
        (setq success (and (> size 0) (equal sa sb) (equal sb sm)))
        (if success
            (setq top-a (+ top-a size)
                  top-b (+ top-b size)
                  top-m (+ top-m size))))
      (setq size (/ size 2)))
    ;; move up the bottoms of the difference regions as much as possible
    ;; Try advancing comparing 1000 chars at a time.
    ;; When that fails, go 500 chars at a time, and so on.
    (setq size 1000)
    (while (> size 0)
      (setq success t)
      (while success
        (setq size (min size (- bottom-a top-a) (- bottom-b top-b)
                        (- bottom-m top-m)))
        (setq sa (emerge-eval-in-buffer emerge-A-buffer
                                        (buffer-substring (- bottom-a size)
                                                          bottom-a)))
        (setq sb (emerge-eval-in-buffer emerge-B-buffer
                                        (buffer-substring (- bottom-b size)
                                                          bottom-b)))
        (setq sm (buffer-substring (- bottom-m size) bottom-m))
        (setq success (and (> size 0) (equal sa sb) (equal sb sm)))
        (if success
            (setq bottom-a (- bottom-a size)
                  bottom-b (- bottom-b size)
                  bottom-m (- bottom-m size))))
      (setq size (/ size 2)))
    ;; {top,bottom}-{a,b,m} are now set at the new beginnings and ends
    ;; of the difference regions.  Move them to the beginning of lines, as
    ;; appropriate.
    (emerge-eval-in-buffer emerge-A-buffer
                           (goto-char top-a)
                           (beginning-of-line)
                           (aset diff 0 (point-marker))
                           (goto-char bottom-a)
                           (beginning-of-line 2)
                           (aset diff 1 (point-marker)))
    (emerge-eval-in-buffer emerge-B-buffer
                           (goto-char top-b)
                           (beginning-of-line)
                           (aset diff 2 (point-marker))
                           (goto-char bottom-b)
                           (beginning-of-line 2)
                           (aset diff 3 (point-marker)))
    (goto-char top-m)
    (beginning-of-line)
    (aset diff 4 (point-marker))
    (goto-char bottom-m)
    (beginning-of-line 2)
    (aset diff 5 (point-marker))
    ;; put the flags back in, recenter the display
    (emerge-select-difference emerge-current-difference)
    (emerge-recenter)))

(defun emerge-find-difference (arg)
  "Find the difference containing the current position of the point.
If there is no containing difference and the prefix argument is positive,
it finds the nearest following difference.  A negative prefix argument finds
the nearest previous difference."
  (interactive "P")
  ;; search for the point in the merge buffer, using the markers
  ;; for the beginning and end of the differences in the merge buffer
  (emerge-find-difference1 arg (point) 4 5))

(defun emerge-find-difference-A (arg)
  "Find the difference containing the position of the point in the A buffer.
This command must be executed in the merge buffer.
If there is no containing difference and the prefix argument is positive,
it finds the nearest following difference.  A negative prefix argument finds
the nearest previous difference."
  (interactive "P")
  ;; search for the point in the A buffer, using the markers
  ;; for the beginning and end of the differences in the A buffer
  (emerge-find-difference1 arg
                           (emerge-eval-in-buffer emerge-A-buffer (point))
                           0 1))

(defun emerge-find-difference-B (arg)
  "Find the difference containing the position of the point in the B buffer.
This command must be executed in the merge buffer.
If there is no containing difference and the prefix argument is positive,
it finds the nearest following difference.  A negative prefix argument finds
the nearest previous difference."
  (interactive "P")
  ;; search for the point in the B buffer, using the markers
  ;; for the beginning and end of the differences in the B buffer
  (emerge-find-difference1 arg
                           (emerge-eval-in-buffer emerge-B-buffer (point))
                           2 3))

(defun emerge-find-difference1 (arg location begin end)
  (let* ((index
          ;; find first difference containing or after the current position
          (catch 'search
            (let ((n 0))
              (while (< n emerge-number-of-differences)
                (let ((diff-vector (aref emerge-difference-list n)))
                  (if (<= location (marker-position (aref diff-vector end)))
                      (throw 'search n)))
                (setq n (1+ n))))
            emerge-number-of-differences))
         (contains
          ;; whether the found difference contains the current position
          (and (< index emerge-number-of-differences)
               (<= (marker-position (aref (aref emerge-difference-list index)
                                          begin))
                   location)))
         (arg-value
          ;; numeric value of prefix argument
          (prefix-numeric-value arg)))
    (emerge-unselect-and-select-difference
     (cond
      ;; if the point is in a difference, select it
      (contains index)
      ;; if the arg is nil and the point is not in a difference, error
      ((null arg) (error "No difference contains point"))
      ;; if the arg is positive, select the following difference
      ((> arg-value 0)
       (if (< index emerge-number-of-differences)
           index
         (error "No difference contains or follows point")))
      ;; if the arg is negative, select the preceeding difference
      (t
       (if (> index 0)
           (1- index)
         (error "No difference contains or preceeds point")))))))

(defun emerge-line-numbers ()
  "Display the current line numbers.
This function displays the line numbers of the points in the A, B, and
merge buffers."
  (interactive)
  (let* ((valid-diff
         (and (>= emerge-current-difference 0)
              (< emerge-current-difference emerge-number-of-differences)))
        (diff (and valid-diff
                   (aref emerge-difference-list emerge-current-difference)))
        (merge-line (emerge-line-number-in-buf 4 5))
        (A-line (emerge-eval-in-buffer emerge-A-buffer
                                       (emerge-line-number-in-buf 0 1)))
        (B-line (emerge-eval-in-buffer emerge-B-buffer
                                       (emerge-line-number-in-buf 2 3))))
    (message "At lines: merge = %d, A = %d, B = %d"
             merge-line A-line B-line)))

(defun emerge-line-number-in-buf (begin-marker end-marker)
  (let (temp)
    (setq temp (save-excursion
                 (beginning-of-line)
                 (1+ (count-lines 1 (point)))))
    (if valid-diff
        (progn
          (if (> (point) (aref diff begin-marker))
              (setq temp (- temp emerge-before-flag-lines)))
          (if (> (point) (aref diff end-marker))
              (setq temp (- temp emerge-after-flag-lines)))))
    temp))

(defun emerge-set-combine-versions-template (start end &optional localize)
  "Copy region into `emerge-combine-versions-template'.
This controls how `emerge-combine-versions' will combine the two versions.
With prefix argument, `emerge-combine-versions'  is made local to this
merge buffer.  Localization is permanent for any particular merge buffer."
  (interactive "r\nP")
  (if localize
      (make-local-variable 'emerge-combine-versions-template))
  (setq emerge-combine-versions-template (buffer-substring start end))
  (message
   (if (assq 'emerge-combine-versions-template (buffer-local-variables))
       "emerge-set-combine-versions-template set locally."
     "emerge-set-combine-versions-template set.")))

(defun emerge-combine-versions (&optional force)
  "Combine versions using the template in `emerge-combine-versions-template'.
Refuses to function if this difference has been edited, i.e., if it is
neither the A nor the B variant.
An argument forces the variant to be selected even if the difference has
been edited."
  (interactive "P")
  (emerge-combine-versions-internal emerge-combine-versions-template force))

(defun emerge-combine-versions-register (char &optional force)
  "Combine the two versions using the template in register REG.
See documentation of the variable `emerge-combine-versions-template'
for how the template is interpreted.
Refuses to function if this difference has been edited, i.e., if it is
neither the A nor the B variant.
An argument forces the variant to be selected even if the difference has
been edited."
  (interactive "cRegister containing template: \nP")
  (let ((template (get-register char)))
    (if (not (stringp template))
        (error "Register does not contain text"))
    (emerge-combine-versions-internal template force)))

(defun emerge-combine-versions-internal (template force)
  (let ((operate
         (function (lambda ()
                     (emerge-combine-versions-edit merge-begin merge-end
                                                   A-begin A-end B-begin B-end)
                     (if emerge-auto-advance
                         (emerge-next-difference))))))
    (emerge-select-version force operate operate operate)))

(defun emerge-combine-versions-edit (merge-begin merge-end
                                     A-begin A-end B-begin B-end)
  (emerge-eval-in-buffer
   emerge-merge-buffer
   (delete-region merge-begin merge-end)
   (goto-char merge-begin)
   (let ((i 0))
     (while (< i (length template))
       (let ((c (aref template i)))
         (if (= c ?%)
             (progn
               (setq i (1+ i))
               (setq c 
                     (condition-case nil
                         (aref template i)
                       (error ?%)))
               (cond ((= c ?a)
                      (insert-buffer-substring emerge-A-buffer A-begin A-end))
                     ((= c ?b) 
                      (insert-buffer-substring emerge-B-buffer B-begin B-end))
                     ((= c ?%) 
                      (insert ?%))
                     (t
                      (insert c))))
           (insert c)))
       (setq i (1+ i))))
   (goto-char merge-begin)
   (aset diff-vector 6 'combined)
   (emerge-refresh-mode-line)))

(defun emerge-set-merge-mode (mode)
  "Set the major mode in a merge buffer.
Overrides any change that the mode might make to the mode line or local
keymap.  Leaves merge in fast mode."
  (interactive
   (list (intern (completing-read "New major mode for merge buffer: "
                                  obarray 'commandp t nil))))
  (funcall mode)
  (emerge-refresh-mode-line)
  (if emerge-fast-mode
      (emerge-fast-mode)
    (emerge-edit-mode)))

(defun emerge-one-line-window ()
  (interactive)
  (let ((window-min-height 1))
    (shrink-window (- (window-height) 2))))

;;; Support routines

;; Select a difference by placing the visual flags around the appropriate
;; group of lines in the A, B, and merge buffers
(defun emerge-select-difference (n)
  (let ((diff-vector (aref emerge-difference-list n)))
    (emerge-place-flags-in-buffer emerge-A-buffer
                                  (aref diff-vector 0) (aref diff-vector 1))
    (emerge-place-flags-in-buffer emerge-B-buffer
                                  (aref diff-vector 2) (aref diff-vector 3))
    (emerge-place-flags-in-buffer emerge-merge-buffer
                                  (aref diff-vector 4) (aref diff-vector 5))))

(defun emerge-place-flags-in-buffer (buffer before after)
  (if (eq buffer emerge-merge-buffer)
      (emerge-place-flags-in-buffer1 buffer before after)
    (emerge-eval-in-buffer
     buffer
     (emerge-place-flags-in-buffer1 buffer before after))))

(defun emerge-place-flags-in-buffer1 (buffer before after)
  (let ((buffer-read-only nil))
    ;; insert the flags
    (goto-char before)
    (insert-before-markers emerge-before-flag)
    (goto-char after)
    (insert emerge-after-flag)
    ;; put the markers into the flags, so alterations above or below won't move
    ;; them
    ;; before marker is one char before the end of the before flag
    ;; after marker is one char after the beginning of the after flag
    (set-marker before (1- before))
    (set-marker after (1+ after))))

;; Unselect a difference by removing the visual flags in the buffers.
(defun emerge-unselect-difference (n)
  (let ((diff-vector (aref emerge-difference-list n)))
    (emerge-remove-flags-in-buffer emerge-A-buffer
                                   (aref diff-vector 0) (aref diff-vector 1))
    (emerge-remove-flags-in-buffer emerge-B-buffer
                                   (aref diff-vector 2) (aref diff-vector 3))
    (emerge-remove-flags-in-buffer emerge-merge-buffer
                                   (aref diff-vector 4) (aref diff-vector 5))))

(defun emerge-remove-flags-in-buffer (buffer before after)
  (emerge-eval-in-buffer
   buffer
   (let ((buffer-read-only nil))
     ;; put the markers at the beginning of the flags
     (set-marker before (- before (1- emerge-before-flag-length)))
     (set-marker after (1- after))
     ;; remove the flags
     (goto-char before)
     (if (looking-at emerge-before-flag-match)
         (delete-char emerge-before-flag-length)
       ;; the flag isn't there
       (ding)
       (message "Trouble removing flag."))
     (goto-char after)
     (if (looking-at emerge-after-flag-match)
         (delete-char emerge-after-flag-length)
       ;; the flag isn't there
       (ding)
       (message "Trouble removing flag.")))))

;; Select a difference, removing an flags that exist now.
(defun emerge-unselect-and-select-difference (n &optional suppress-display)
  (if (and (>= emerge-current-difference 0)
           (< emerge-current-difference emerge-number-of-differences))
      (emerge-unselect-difference emerge-current-difference))
  (if (and (>= n 0) (< n emerge-number-of-differences))
      (progn
        (emerge-select-difference n)
        (let* ((diff-vector (aref emerge-difference-list n))
               (selection-type (aref diff-vector 6)))
          (if (eq selection-type 'default-A)
              (aset diff-vector 6 'A)
            (if (eq selection-type 'default-B)
                (aset diff-vector 6 'B))))))
  (setq emerge-current-difference n)
  (if (not suppress-display)
      (progn
        (emerge-recenter)
        (emerge-refresh-mode-line))))

;; Perform tests to see whether user should be allowed to select a version
;; of this difference:
;;   a valid difference has been selected; and
;;   the difference text in the merge buffer is:
;;     the A version (execute a-version), or
;;     the B version (execute b-version), or
;;     empty (execute neither-version), or
;;     argument FORCE is true (execute neither-version)
;; Otherwise, signal an error.
(defun emerge-select-version (force a-version b-version neither-version)
  (emerge-validate-difference)
  (let ((buffer-read-only nil))
    (let* ((diff-vector
            (aref emerge-difference-list emerge-current-difference))
           (A-begin (1+ (aref diff-vector 0)))
           (A-end (1- (aref diff-vector 1)))
           (B-begin (1+ (aref diff-vector 2)))
           (B-end (1- (aref diff-vector 3)))
           (merge-begin (1+ (aref diff-vector 4)))
           (merge-end (1- (aref diff-vector 5))))
      (if (emerge-compare-buffers emerge-A-buffer A-begin A-end
                                  emerge-merge-buffer merge-begin
                                  merge-end)
          (funcall a-version)
        (if (emerge-compare-buffers emerge-B-buffer B-begin B-end
                                    emerge-merge-buffer merge-begin
                                    merge-end)
            (funcall b-version)
          (if (or force (= merge-begin merge-end))
              (funcall neither-version)
            (error "This difference region has been edited.")))))))

;; Revise the mode line to display which difference we have selected

(defun emerge-refresh-mode-line ()
  (setq mode-line-buffer-identification
        (list (format "Emerge: %%b   diff %d of %d%s"
                      (1+ emerge-current-difference)
                      emerge-number-of-differences
                      (if (and (>= emerge-current-difference 0)
                               (< emerge-current-difference
                                  emerge-number-of-differences))
                          (cdr (assq (aref (aref emerge-difference-list
                                                 emerge-current-difference)
                                           6)
                                     '((A . " - A")
                                       (B . " - B")
                                       (prefer-A . " - A*")
                                       (prefer-B . " - B*")
                                       (combined . " - comb"))))
                        ""))))
  ;; Force mode-line redisplay
  (set-buffer-modified-p (buffer-modified-p)))

;; compare two regions in two buffers for containing the same text
(defun emerge-compare-buffers (buffer-x x-begin x-end buffer-y y-begin y-end)
  ;; first check that the two regions are the same length
  (if (not (and (= (- x-end x-begin) (- y-end y-begin))))
      nil
    (catch 'exit
      (while (< x-begin x-end)
        ;; bite off and compare no more than 1000 characters at a time
        (let* ((compare-length (min (- x-end x-begin) 1000))
               (x-string (emerge-eval-in-buffer 
                          buffer-x
                          (buffer-substring x-begin
                                            (+ x-begin compare-length))))
               (y-string (emerge-eval-in-buffer
                          buffer-y
                          (buffer-substring y-begin
                                            (+ y-begin compare-length)))))
          (if (not (string-equal x-string y-string))
              (throw 'exit nil)
            (setq x-begin (+ x-begin compare-length))
            (setq y-begin (+ y-begin compare-length)))))
      t)))

;; Construct a unique buffer name.
;; The first one tried is prefixsuffix, then prefix<2>suffix, 
;; prefix<3>suffix, etc.
(defun emerge-unique-buffer-name (prefix suffix)
  (if (null (get-buffer (concat prefix suffix)))
      (concat prefix suffix)
    (let ((n 2))
      (while (get-buffer (format "%s<%d>%s" prefix n suffix))
        (setq n (1+ n)))
      (format "%s<%d>%s" prefix n suffix))))

;; Verify that we have a difference selected.
(defun emerge-validate-difference ()
  (if (not (and (>= emerge-current-difference 0)
                (< emerge-current-difference emerge-number-of-differences)))
      (error "No difference selected")))

;;; Functions for saving and restoring a batch of variables

;; These functions save (get the values of) and restore (set the values of)
;; a list of variables.  The argument is a list of symbols (the names of
;; the variables).  A list element can also be a list of two functions,
;; the first of which (when called with no arguments) gets the value, and
;; the second (when called with a value as an argment) sets the value.
;; A "function" is anything that funcall can handle as an argument.

(defun emerge-save-variables (vars)
  (mapcar (function (lambda (v) (if (symbolp v)
                                    (symbol-value v)
                                  (funcall (car v)))))
          vars))

(defun emerge-restore-variables (vars values)
  (while vars
    (let ((var (car vars))
          (value (car values)))
      (if (symbolp var)
          (set var value)
        (funcall (car (cdr var)) value)))
    (setq vars (cdr vars))
    (setq values (cdr values))))

;; Make a temporary file that only we have access to.
;; PREFIX is appended to emerge-temp-file-prefix to make the filename prefix.
(defun emerge-make-temp-file (prefix)
  (let ((f (make-temp-name (concat emerge-temp-file-prefix prefix))))
    ;; create the file
    (write-region (point-min) (point-min) f nil 'no-message)
    (set-file-modes f emerge-temp-file-mode)
    f))

;;; Functions that query the user before he can write out the current buffer.

(defun emerge-query-write-file ()
  "Query the user if he really wants to write out the incomplete merge.
If he says yes, call `write-file' to do so.  See `emerge-query-and-call'
for details of the querying process."
  (interactive)
  (emerge-query-and-call 'write-file))

(defun emerge-query-save-buffer ()
  "Query the user if he really wants to write out the incomplete merge.
If he says yes, call `save-buffer' to do so.  See `emerge-query-and-call'
for details of the querying process."
  (interactive)
  (emerge-query-and-call 'save-buffer))

(defun emerge-query-and-call (command)
  "Query the user if he really wants to write out the incomplete merge.
If he says yes, call COMMAND interactively.  During the call, the flags
around the current difference are removed."
  (if (yes-or-no-p "Do you really write to write out this unfinished merge? ")
      ;; He really wants to do it -- unselect the difference for the duration
      (progn
        (if (and (>= emerge-current-difference 0)
                 (< emerge-current-difference emerge-number-of-differences))
            (emerge-unselect-difference emerge-current-difference))
        ;; call-interactively takes the value of current-prefix-arg as the
        ;; prefix argument value to be passed to the command.  Thus, we have
        ;; to do nothing special to make sure the prefix argument is
        ;; transmitted to the command.
        (call-interactively command)
        (if (and (>= emerge-current-difference 0)
                 (< emerge-current-difference emerge-number-of-differences))
            (progn
              (emerge-select-difference emerge-current-difference)
              (emerge-recenter))))
    ;; He's being smart and not doing it
    (message "Not written")))

;; Make sure the current buffer (for a file) has the same contents as the
;; file on disk, and attempt to remedy the situation if not.
;; Signal an error if we can't make them the same, or the user doesn't want
;; to do what is necessary to make them the same.
(defun emerge-verify-file-buffer ()
  ;; First check if the file has been modified since the buffer visited it.
  (if (verify-visited-file-modtime (current-buffer))
      (if (buffer-modified-p)
          ;; If buffer is not obsolete and is modified, offer to save
          (if (yes-or-no-p (format "Save file %s? " buffer-file-name))
              (save-buffer)
            (error "Buffer out of sync for file %s" buffer-file-name))
        ;; If buffer is not obsolete and is not modified, do nothing
        nil)
    (if (buffer-modified-p)
        ;; If buffer is obsolete and is modified, give error
        (error "Buffer out of sync for file %s" buffer-file-name)
      ;; If buffer is obsolete and is not modified, offer to revert
      (if (yes-or-no-p (format "Revert file %s? " buffer-file-name))
              (revert-buffer t t)
        (error "Buffer out of sync for file %s" buffer-file-name)))))
\f
;; Utilities that might have value outside of Emerge.

;; Set up the mode in the current buffer to duplicate the mode in another
;; buffer.
(defun emerge-copy-modes (buffer)
  ;; Set the major mode
  (funcall (emerge-eval-in-buffer buffer major-mode)))

;; Define a key, even if a prefix of it is defined
(defun emerge-force-define-key (keymap key definition)
  "Like `define-key', but isn't stopped if a prefix of KEY is a defined 
command."
  ;; Find out if a prefix of key is defined
  (let ((v (lookup-key keymap key)))
    ;; If so, undefine it
    (if (integerp v)
        (define-key keymap (substring key 0 v) nil)))
  ;; Now define the key
  (define-key keymap key definition))

;;; Improvements to describe-mode, so that it describes minor modes as well
;;; as the major mode
(defun describe-mode (&optional minor)
  "Display documentation of current major mode.
If optional MINOR is non-nil (or prefix argument is given if interactive),
display documentation of acive minor modes as well.
For this to work correctly for a minor mode, the mode's indicator variable
(listed in `minor-mode-alist') must also be a function whose documentation
describes the minor mode."
  (interactive)
  (with-output-to-temp-buffer "*Help*"
    (princ mode-name)
    (princ " Mode:\n")
    (princ (documentation major-mode))
    (let ((minor-modes minor-mode-alist)
          (locals (buffer-local-variables)))
      (while minor-modes
        (let* ((minor-mode (car (car minor-modes)))
               (indicator (car (cdr (car minor-modes))))
               (local-binding (assq minor-mode locals)))
          ;; Document a minor mode if it is listed in minor-mode-alist,
          ;; bound locally in this buffer, non-nil, and has a function
          ;; definition.
          (if (and local-binding
                   (cdr local-binding)
                   (fboundp minor-mode))
              (progn
                (princ (format "\n\n\n%s minor mode (indicator%s):\n"
                               minor-mode indicator))
                (princ (documentation minor-mode)))))
        (setq minor-modes (cdr minor-modes))))
    (print-help-return-message)))

;; Adjust things so that keyboard macro definitions are documented correctly.
(fset 'defining-kbd-macro (symbol-function 'start-kbd-macro))

;; Function to shadow a definition in a keymap with definitions in another.
(defun emerge-shadow-key-definition (olddef newdef keymap shadowmap)
  "Shadow OLDDEF with NEWDEF for any keys in KEYMAP with entries in SHADOWMAP.
In other words, SHADOWMAP will now shadow all definitions of OLDDEF in KEYMAP
with NEWDEF.  Does not affect keys that are already defined in SHADOWMAP,
including those whose definition is OLDDEF."
  ;; loop through all keymaps accessible from keymap
  (let ((maps (accessible-keymaps keymap)))
    (while maps
      (let ((prefix (car (car maps)))
            (map (cdr (car maps))))
        ;; examine a keymap
        (if (arrayp map)
            ;; array keymap
            (let ((len (length map))
                  (i 0))
              (while (< i len)
                (if (eq (aref map i) olddef)
                    ;; set the shadowing definition
                    (let ((key (concat prefix (char-to-string i))))
                      (emerge-define-key-if-possible shadowmap key newdef)))
                (setq i (1+ i))))
          ;; sparse keymap
          (while map
            (if (eq (cdr-safe (car-safe map)) olddef)
                ;; set the shadowing definition
                (let ((key
                       (concat prefix (char-to-string (car (car map))))))
                      (emerge-define-key-if-possible shadowmap key newdef)))
            (setq map (cdr map)))))
      (setq maps (cdr maps)))))

;; Define a key if it (or a prefix) is not already defined in the map.
(defun emerge-define-key-if-possible (keymap key definition)
  ;; look up the present definition of the key
  (let ((present (lookup-key keymap key)))
    (if (integerp present)
        ;; if it is "too long", look up the valid prefix
        (if (not (lookup-key keymap (substring key 0 present)))
            ;; if the prefix isn't defined, define it
            (define-key keymap key definition))
      ;; if there is no present definition, define it
      (if (not present)
          (define-key keymap key definition)))))

(defun emerge-recursively-substitute-key-definition (olddef newdef keymap)
  "Like `substitute-key-definition', but examines and substitutes in all
keymaps accessible from KEYMAP.  Make sure that subordinate keymaps aren't
shared with other keymaps!  (`copy-keymap' will suffice.)"
  ;; Loop through all keymaps accessible from keymap
  (let ((maps (accessible-keymaps keymap)))
    (while maps
      ;; Substitute in this keymap
      (substitute-key-definition olddef newdef (cdr (car maps)))
      (setq maps (cdr maps)))))

;; Show the name of the file in the buffer.
(defun emerge-show-file-name ()
  "Displays the name of the file loaded into the current buffer.
If the name won't fit on one line, the minibuffer is expanded to hold it,
and the command waits for a keystroke from the user.  If the keystroke is
SPC, it is ignored; if it is anything else, it is processed as a command."
  (interactive)
  (let ((name (buffer-file-name)))
    (or name
        (setq name "Buffer has no file name."))
    (save-window-excursion
      (select-window (minibuffer-window))
      (erase-buffer)
      (insert name)
      (if (not (pos-visible-in-window-p))
          (let ((echo-keystrokes 0))
            (while (and (not (pos-visible-in-window-p))
                        (> (1- (frame-height)) (window-height)))
              (enlarge-window 1))
            (let ((c (read-event)))
              (if (not (eq c 32))
                  (setq unread-command-events (list c)))))))))

;; Improved auto-save file names.
;; This function fixes many problems with the standard auto-save file names:
;; Auto-save files for non-file buffers get put in the default directory
;; for the buffer, whether that makes sense or not.
;; Auto-save files for file buffers get put in the directory of the file,
;; regardless of whether we can write into it or not.
;; Auto-save files for non-file buffers don't use the process id, so if a
;; user runs more than on Emacs, they can make auto-save files that overwrite
;; each other.
;; To use this function, do:
;;      (fset 'make-auto-save-file-name
;;            (symbol-function 'emerge-make-auto-save-file-name))
(defun emerge-make-auto-save-file-name ()
  "Return file name to use for auto-saves of current buffer.
Does not consider auto-save-visited-file-name; that is checked
before calling this function.
You can redefine this for customization.
See also auto-save-file-name-p."
  (if buffer-file-name
      ;; if buffer has a file, try the format <file directory>/#<file name>#
      (let ((f (concat (file-name-directory buffer-file-name)
                       "#"
                       (file-name-nondirectory buffer-file-name)
                       "#")))
        (if (file-writable-p f)
            ;; the file is writable, so use it
            f
          ;; the file isn't writable, so use the format
          ;; ~/#&<file name>&<hash of directory>#
          (concat (getenv "HOME")
                  "/#&"
                  (file-name-nondirectory buffer-file-name)
                  "&"
                  (hash-string-into-string
                   (file-name-directory buffer-file-name))
                  "#")))
    ;; if buffer has no file, use the format ~/#%<buffer name>%<process id>#
    (expand-file-name (concat (getenv "HOME")
                              "/#%"
                              ;; quote / into \! and \ into \\
                              (unslashify-name (buffer-name))
                              "%"
                              (make-temp-name "")
                              "#"))))

;; Hash a string into five characters more-or-less suitable for use in a file
;; name.  (Allowed characters are ! through ~, except /.)
(defun hash-string-into-string (s)
  (let ((bins (vector 0 0 0 0 0))
        (i 0))
    (while (< i (length s))
      (aset bins (% i 5) (% (+ (* (aref bins (% i 5)) 35)
                               (aref s i))
                            65536))
      (setq i (1+ i)))
    (mapconcat (function (lambda (b)
                           (setq b (+ (% b 93) ?!))
                           (if (>= b ?/)
                               (setq b (1+ b)))
                           (char-to-string b)))
               bins "")))

;; Quote any /s in a string by replacing them with \!.
;; Also, replace any \s by \\, to make it one-to-one.
(defun unslashify-name (s)
  (let ((limit 0))
    (while (string-match "[/\\]" s limit)
      (setq s (concat (substring s 0 (match-beginning 0))
                      (if (string= (substring s (match-beginning 0)
                                              (match-end 0))
                                   "/")
                          "\\!"
                        "\\\\")
                      (substring s (match-end 0))))
      (setq limit (1+ (match-end 0)))))
  s)

(provide 'emerge)

;;; emerge.el ends here