;;; smerge-mode.el --- Minor mode to resolve diff3 conflicts -*- lexical-binding: t -*-

;; Copyright (C) 1999-2021 Free Software Foundation, Inc.

;; Author: Stefan Monnier <monnier@iro.umontreal.ca>
;; Keywords: vc, tools, revision control, merge, diff3, cvs, conflict

;; This file is part of GNU Emacs.

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

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

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

;;; Commentary:

;; Provides a lightweight alternative to emerge/ediff.
;; To use it, simply add to your .emacs the following lines:
;;
;;   (autoload 'smerge-mode "smerge-mode" nil t)
;;
;; you can even have it turned on automatically with the following
;; piece of code in your .emacs:
;;
;;   (defun sm-try-smerge ()
;;     (save-excursion
;;   	 (goto-char (point-min))
;;   	 (when (re-search-forward "^<<<<<<< " nil t)
;;   	   (smerge-mode 1))))
;;   (add-hook 'find-file-hook 'sm-try-smerge t)

;;; Todo:

;; - if requested, ask the user whether he wants to call ediff right away

;;; Code:

(eval-when-compile (require 'cl-lib))
(require 'diff)				;For diff-check-labels.
(require 'diff-mode)                    ;For diff-refine.
(require 'newcomment)

;;; The real definition comes later.
(defvar smerge-mode)

(defgroup smerge ()
  "Minor mode to highlight and resolve diff3 conflicts."
  :group 'tools
  :prefix "smerge-")

(defcustom smerge-diff-buffer-name "*vc-diff*"
  "Buffer name to use for displaying diffs."
  :type '(choice
	  (const "*vc-diff*")
	  (const "*cvs-diff*")
	  (const "*smerge-diff*")
	  string))

(defcustom smerge-diff-switches
  (append '("-d" "-b")
	  (if (listp diff-switches) diff-switches (list diff-switches)))
  "A list of strings specifying switches to be passed to diff.
Used in `smerge-diff-base-upper' and related functions."
  :type '(repeat string))

(defcustom smerge-auto-leave t
  "Non-nil means to leave `smerge-mode' when the last conflict is resolved."
  :type 'boolean)

(defface smerge-upper
  '((((class color) (min-colors 88) (background light))
     :background "#ffdddd" :extend t)
    (((class color) (min-colors 88) (background dark))
     :background "#553333" :extend t)
    (((class color))
     :foreground "red" :extend))
  "Face for the `upper' version of a conflict.")
(define-obsolete-face-alias 'smerge-mine 'smerge-upper "26.1")
(defvar smerge-upper-face 'smerge-upper)

(defface smerge-lower
  '((((class color) (min-colors 88) (background light))
     :background "#ddffdd" :extend t)
    (((class color) (min-colors 88) (background dark))
     :background "#335533" :extend t)
    (((class color))
     :foreground "green" :extend))
  "Face for the `lower' version of a conflict.")
(define-obsolete-face-alias 'smerge-other 'smerge-lower "26.1")
(defvar smerge-lower-face 'smerge-lower)

(defface smerge-base
  '((((class color) (min-colors 88) (background light))
     :background "#ffffaa" :extend t)
    (((class color) (min-colors 88) (background dark))
     :background "#888833" :extend t)
    (((class color))
     :foreground "yellow" :extend t))
  "Face for the base code.")
(defvar smerge-base-face 'smerge-base)

(defface smerge-markers
  '((((background light))
     (:background "grey85" :extend t))
    (((background dark))
     (:background "grey30" :extend t)))
  "Face for the conflict markers.")
(defvar smerge-markers-face 'smerge-markers)

(defface smerge-refined-changed
  '((t nil))
  "Face used for char-based changes shown by `smerge-refine'.")
(define-obsolete-face-alias 'smerge-refined-change 'smerge-refined-changed "24.5")

(defface smerge-refined-removed
  '((default
     :inherit smerge-refined-change)
    (((class color) (min-colors 88) (background light))
     :background "#ffbbbb")
    (((class color) (min-colors 88) (background dark))
     :background "#aa2222")
    (t :inverse-video t))
  "Face used for removed characters shown by `smerge-refine'."
  :version "24.3")

(defface smerge-refined-added
  '((default
     :inherit smerge-refined-change)
    (((class color) (min-colors 88) (background light))
     :background "#aaffaa")
    (((class color) (min-colors 88) (background dark))
     :background "#22aa22")
    (t :inverse-video t))
  "Face used for added characters shown by `smerge-refine'."
  :version "24.3")

(easy-mmode-defmap smerge-basic-map
  `(("n" . smerge-next)
    ("p" . smerge-prev)
    ("r" . smerge-resolve)
    ("a" . smerge-keep-all)
    ("b" . smerge-keep-base)
    ("o" . smerge-keep-lower)           ; for the obsolete keep-other
    ("l" . smerge-keep-lower)
    ("m" . smerge-keep-upper)           ; for the obsolete keep-mine
    ("u" . smerge-keep-upper)
    ("E" . smerge-ediff)
    ("C" . smerge-combine-with-next)
    ("R" . smerge-refine)
    ("\C-m" . smerge-keep-current)
    ("=" . ,(make-sparse-keymap "Diff"))
    ("=<" "base-upper" . smerge-diff-base-upper)
    ("=>" "base-lower" . smerge-diff-base-lower)
    ("==" "upper-lower" . smerge-diff-upper-lower))
  "The base keymap for `smerge-mode'.")

(defcustom smerge-command-prefix "\C-c^"
  "Prefix for `smerge-mode' commands."
  :type '(choice (const :tag "ESC"   "\e")
		 (const :tag "C-c ^" "\C-c^" )
		 (const :tag "none"  "")
		 string))

(easy-mmode-defmap smerge-mode-map
  `((,smerge-command-prefix . ,smerge-basic-map))
  "Keymap for `smerge-mode'.")

(defvar-local smerge-check-cache nil)
(defun smerge-check (n)
  (condition-case nil
      (let ((state (cons (point) (buffer-modified-tick))))
	(unless (equal (cdr smerge-check-cache) state)
	  (smerge-match-conflict)
	  (setq smerge-check-cache (cons (match-data) state)))
	(nth (* 2 n) (car smerge-check-cache)))
    (error nil)))

(easy-menu-define smerge-mode-menu smerge-mode-map
  "Menu for `smerge-mode'."
  '("SMerge"
    ["Next" smerge-next :help "Go to next conflict"]
    ["Previous" smerge-prev :help "Go to previous conflict"]
    "--"
    ["Keep All" smerge-keep-all :help "Keep all three versions"
     :active (smerge-check 1)]
    ["Keep Current" smerge-keep-current :help "Use current (at point) version"
     :active (and (smerge-check 1) (> (smerge-get-current) 0))]
    "--"
    ["Revert to Base" smerge-keep-base :help "Revert to base version"
     :active (smerge-check 2)]
    ["Keep Upper" smerge-keep-upper :help "Keep `upper' version"
     :active (smerge-check 1)]
    ["Keep Lower" smerge-keep-lower :help "Keep `lower' version"
     :active (smerge-check 3)]
    "--"
    ["Diff Base/Upper" smerge-diff-base-upper
     :help "Diff `base' and `upper' for current conflict"
     :active (smerge-check 2)]
    ["Diff Base/Lower" smerge-diff-base-lower
     :help "Diff `base' and `lower' for current conflict"
     :active (smerge-check 2)]
    ["Diff Upper/Lower" smerge-diff-upper-lower
     :help "Diff `upper' and `lower' for current conflict"
     :active (smerge-check 1)]
    "--"
    ["Invoke Ediff" smerge-ediff
     :help "Use Ediff to resolve the conflicts"
     :active (smerge-check 1)]
    ["Auto Resolve" smerge-resolve
     :help "Try auto-resolution heuristics"
     :active (smerge-check 1)]
    ["Combine" smerge-combine-with-next
     :help "Combine current conflict with next"
     :active (smerge-check 1)]
    ))

(easy-menu-define smerge-context-menu nil
  "Context menu for upper area in `smerge-mode'."
  '(nil
    ["Keep Current" smerge-keep-current :help "Use current (at point) version"]
    ["Kill Current" smerge-kill-current :help "Remove current (at point) version"]
    ["Keep All" smerge-keep-all :help "Keep all three versions"]
    "---"
    ["More..." (popup-menu smerge-mode-menu) :help "Show full SMerge mode menu"]
    ))

(defconst smerge-font-lock-keywords
  '((smerge-find-conflict
     (1 smerge-upper-face prepend t)
     (2 smerge-base-face prepend t)
     (3 smerge-lower-face prepend t)
     ;; FIXME: `keep' doesn't work right with syntactic fontification.
     (0 smerge-markers-face keep)
     (4 nil t t)
     (5 nil t t)))
  "Font lock patterns for `smerge-mode'.")

(defconst smerge-begin-re "^<<<<<<< \\(.*\\)\n")
(defconst smerge-end-re "^>>>>>>> \\(.*\\)\n")
(defconst smerge-base-re "^||||||| \\(.*\\)\n")
(defconst smerge-lower-re "^=======\n")

(defvar smerge-conflict-style nil
  "Keep track of which style of conflict is in use.
Can be nil if the style is undecided, or else:
- `diff3-E'
- `diff3-A'")

;; Compiler pacifiers
(defvar font-lock-mode)
(defvar font-lock-keywords)

;;;;
;;;; Actual code
;;;;

;; Define smerge-next and smerge-prev
(easy-mmode-define-navigation smerge smerge-begin-re "conflict" nil nil
  (if diff-refine
      (condition-case nil (smerge-refine) (error nil))))

(defconst smerge-match-names ["conflict" "upper" "base" "lower"])

(defun smerge-ensure-match (n)
  (unless (match-end n)
    (error "No `%s'" (aref smerge-match-names n))))

(defun smerge-auto-leave ()
  (when (and smerge-auto-leave
	     (save-excursion (goto-char (point-min))
			     (not (re-search-forward smerge-begin-re nil t))))
    (when (and (listp buffer-undo-list) smerge-mode)
      (push (list 'apply 'smerge-mode 1) buffer-undo-list))
    (smerge-mode -1)))


(defun smerge-keep-all ()
  "Concatenate all versions."
  (interactive)
  (smerge-match-conflict)
  (let ((mb2 (or (match-beginning 2) (point-max)))
	(me2 (or (match-end 2) (point-min))))
    (delete-region (match-end 3) (match-end 0))
    (delete-region (max me2 (match-end 1)) (match-beginning 3))
    (if (and (match-end 2) (/= (match-end 1) (match-end 3)))
	(delete-region (match-end 1) (match-beginning 2)))
    (delete-region (match-beginning 0) (min (match-beginning 1) mb2))
    (smerge-auto-leave)))

(defun smerge-keep-n (n)
  (smerge-remove-props (match-beginning 0) (match-end 0))
  ;; We used to use replace-match, but that did not preserve markers so well.
  (delete-region (match-end n) (match-end 0))
  (delete-region (match-beginning 0) (match-beginning n)))

(defun smerge-combine-with-next ()
  "Combine the current conflict with the next one."
  ;; `smerge-auto-combine' relies on the finish position (at the beginning
  ;; of the closing marker).
  (interactive)
  (smerge-match-conflict)
  (let ((ends nil))
    (dolist (i '(3 2 1 0))
      (push (if (match-end i) (copy-marker (match-end i) t)) ends))
    (setq ends (apply 'vector ends))
    (goto-char (aref ends 0))
    (if (not (re-search-forward smerge-begin-re nil t))
	(error "No next conflict")
      (smerge-match-conflict)
      (let ((match-data (mapcar (lambda (m) (if m (copy-marker m)))
				(match-data))))
	;; First copy the in-between text in each alternative.
	(dolist (i '(1 2 3))
	  (when (aref ends i)
	    (goto-char (aref ends i))
	    (insert-buffer-substring (current-buffer)
				     (aref ends 0) (car match-data))))
	(delete-region (aref ends 0) (car match-data))
	;; Then move the second conflict's alternatives into the first.
	(dolist (i '(1 2 3))
	  (set-match-data match-data)
	  (when (and (aref ends i) (match-end i))
	    (goto-char (aref ends i))
	    (insert-buffer-substring (current-buffer)
				     (match-beginning i) (match-end i))))
	(delete-region (car match-data) (cadr match-data))
	;; Free the markers.
	(dolist (m match-data) (if m (move-marker m nil)))
	(mapc (lambda (m) (if m (move-marker m nil))) ends)))))

(defvar smerge-auto-combine-max-separation 2
  "Max number of lines between conflicts that should be combined.")

(defun smerge-auto-combine ()
  "Automatically combine conflicts that are near each other."
  (interactive)
  (save-excursion
    (goto-char (point-min))
    (while (smerge-find-conflict)
      ;; 2 is 1 (default) + 1 (the begin markers).
      (while (save-excursion
               (smerge-find-conflict
                (line-beginning-position
                 (+ 2 smerge-auto-combine-max-separation))))
        (forward-line -1)               ;Go back inside the conflict.
        (smerge-combine-with-next)
        (forward-line 1)                ;Move past the end of the conflict.
        ))))

(defvar smerge-resolve-function
  (lambda () (user-error "Don't know how to resolve"))
  "Mode-specific merge function.
The function is called with zero or one argument (non-nil if the resolution
function should only apply safe heuristics) and with the match data set
according to `smerge-match-conflict'.")

(defvar smerge-text-properties
  '(help-echo "merge conflict: mouse-3 shows a menu"
              ;; mouse-face highlight
              keymap (keymap (down-mouse-3 . smerge-popup-context-menu))))

(defun smerge-remove-props (beg end)
  (remove-overlays beg end 'smerge 'refine)
  (remove-overlays beg end 'smerge 'conflict)
  ;; Now that we use overlays rather than text-properties, this function
  ;; does not cause refontification any more.  It can be seen very clearly
  ;; in buffers where jit-lock-contextually is not t, in which case deleting
  ;; the "<<<<<<< foobar" leading line leaves the rest of the conflict
  ;; highlighted as if it were still a valid conflict.  Note that in many
  ;; important cases (such as the previous example) we're actually called
  ;; during font-locking so inhibit-modification-hooks is non-nil, so we
  ;; can't just modify the buffer and expect font-lock to be triggered as in:
  ;; (put-text-property beg end 'smerge-force-highlighting nil)
  (with-silent-modifications
    (remove-text-properties beg end '(fontified nil))))

(defun smerge-popup-context-menu (event)
  "Pop up the Smerge mode context menu under mouse."
  (interactive "e")
  (unless (eq (posn-window (event-end event)) (selected-window))
    (select-window (posn-window (event-end event))))
  (if (and smerge-mode
	   (save-excursion (posn-set-point (event-end event)) (smerge-check 1)))
      (progn
	(posn-set-point (event-end event))
	(smerge-match-conflict)
	(let ((i (smerge-get-current))
	      o)
	  (if (<= i 0)
	      ;; Out of range
	      (popup-menu smerge-mode-menu)
	    ;; Install overlay.
	    (setq o (make-overlay (match-beginning i) (match-end i)))
	    (unwind-protect
		(progn
		  (overlay-put o 'face 'highlight)
		  (sit-for 0)		;Display the new highlighting.
		  (popup-menu smerge-context-menu))
	      ;; Delete overlay.
	      (delete-overlay o)))))
    ;; There's no conflict at point, the text-props are just obsolete.
    (save-excursion
      (let ((beg (re-search-backward smerge-end-re nil t))
	    (end (re-search-forward smerge-begin-re nil t)))
	(smerge-remove-props (or beg (point-min)) (or end (point-max)))
	(push event unread-command-events)))))

(defun smerge-apply-resolution-patch (buf m0b m0e m3b m3e &optional m2b)
  "Replace the conflict with a bunch of subconflicts.
BUF contains a plain diff between match-1 and match-3."
  (let ((line 1)
        (textbuf (current-buffer))
        (name1 (progn (goto-char m0b)
                      (buffer-substring (+ (point) 8) (line-end-position))))
        (name2 (when m2b (goto-char m2b) (forward-line -1)
                     (buffer-substring (+ (point) 8) (line-end-position))))
        (name3 (progn (goto-char m0e) (forward-line -1)
                      (buffer-substring (+ (point) 8) (line-end-position)))))
    (smerge-remove-props m0b m0e)
    (delete-region m3e m0e)
    (delete-region m0b m3b)
    (setq m3b m0b)
    (setq m3e (- m3e (- m3b m0b)))
    (goto-char m3b)
    (with-current-buffer buf
      (goto-char (point-min))
      (while (not (eobp))
        (if (not (looking-at "\\([0-9]+\\)\\(?:,\\([0-9]+\\)\\)?\\([acd]\\)\\([0-9]+\\)\\(?:,\\([0-9]+\\)\\)?$"))
            (error "Unexpected patch hunk header: %s"
                   (buffer-substring (point) (line-end-position)))
          (let* ((op (char-after (match-beginning 3)))
                 (startline (+ (string-to-number (match-string 1))
                               ;; No clue why this is the way it is, but line
                               ;; numbers seem to be off-by-one for `a' ops.
                               (if (eq op ?a) 1 0)))
                 (endline (if (eq op ?a) startline
                            (1+ (if (match-end 2)
                                    (string-to-number (match-string 2))
                                  startline))))
                 (lines (- endline startline))
                 (otherlines (cond
                              ((eq op ?d) nil)
                              ((null (match-end 5)) 1)
                              (t (- (string-to-number (match-string 5))
                                    (string-to-number (match-string 4)) -1))))
                 othertext)
            (forward-line 1)                             ;Skip header.
            (forward-line lines)                         ;Skip deleted text.
            (if (eq op ?c) (forward-line 1))             ;Skip separator.
            (setq othertext
                  (if (null otherlines) ""
                    (let ((pos (point)))
                      (dotimes (_i otherlines) (delete-char 2) (forward-line 1))
                      (buffer-substring pos (point)))))
            (with-current-buffer textbuf
              (forward-line (- startline line))
              (insert "<<<<<<< " name1 "\n" othertext
                      (if name2 (concat "||||||| " name2 "\n") "")
                      "=======\n")
              (forward-line lines)
              (insert ">>>>>>> " name3 "\n")
              (setq line endline))))))))

(defconst smerge-resolve--normalize-re "[\n\t][ \t\n]*\\| [ \t\n]+")

(defun smerge-resolve--extract-comment (beg end)
  "Extract the text within the comments that span BEG..END."
  (save-excursion
    (let ((comments ())
          combeg)
      (goto-char beg)
      (while (and (< (point) end)
                  (setq combeg (comment-search-forward end t)))
        (let ((beg (point)))
          (goto-char combeg)
          (comment-forward 1)
          (save-excursion
            (comment-enter-backward)
            (push " " comments)
            (push (buffer-substring-no-properties beg (point)) comments))))
      (push " " comments)
      (with-temp-buffer
        (apply #'insert (nreverse comments))
        (goto-char (point-min))
        (while (re-search-forward smerge-resolve--normalize-re
                                  nil t)
          (replace-match " "))
        (buffer-string)))))

(defun smerge-resolve--normalize (beg end)
  (replace-regexp-in-string
   smerge-resolve--normalize-re " "
   (concat " " (buffer-substring-no-properties beg end) " ")))

(defun smerge-resolve (&optional safe)
  "Resolve the conflict at point intelligently.
This relies on mode-specific knowledge and thus only works in some
major modes.  Uses `smerge-resolve-function' to do the actual work."
  (interactive)
  (smerge-match-conflict)
  (smerge-remove-props (match-beginning 0) (match-end 0))
  (let ((md (match-data))
	(m0b (match-beginning 0))
	(m1b (match-beginning 1))
	(m2b (match-beginning 2))
	(m3b (match-beginning 3))
	(m0e (match-end 0))
	(m1e (match-end 1))
	(m2e (match-end 2))
	(m3e (match-end 3))
	(buf (generate-new-buffer " *smerge*"))
        m b o
        choice)
    (unwind-protect
	(progn
          (cond
           ;; Trivial diff3 -A non-conflicts.
           ((and (eq (match-end 1) (match-end 3))
                 (eq (match-beginning 1) (match-beginning 3)))
            (smerge-keep-n 3))
           ;; Mode-specific conflict resolution.
           ((condition-case nil
                (atomic-change-group
                  (if safe
                      (funcall smerge-resolve-function safe)
                    (funcall smerge-resolve-function))
                  t)
              (error nil))
            ;; Nothing to do: the resolution function has done it already.
            nil)
           ;; Non-conflict.
	   ((and (eq m1e m3e) (eq m1b m3b))
	    (set-match-data md) (smerge-keep-n 3))
           ;; Refine a 2-way conflict using "diff -b".
           ;; In case of a 3-way conflict with an empty base
           ;; (i.e. 2 conflicting additions), we do the same, presuming
           ;; that the 2 additions should be somehow merged rather
           ;; than concatenated.
	   ((let ((lines (count-lines m3b m3e)))
              (setq m (make-temp-file "smm"))
              (write-region m1b m1e m nil 'silent)
              (setq o (make-temp-file "smo"))
              (write-region m3b m3e o nil 'silent)
              (not (or (eq m1b m1e) (eq m3b m3e)
                       (and (not (zerop (call-process diff-command
                                                      nil buf nil "-b" o m)))
                            ;; TODO: We don't know how to do the refinement
                            ;; if there's a non-empty ancestor and m1 and m3
                            ;; aren't just plain equal.
                            m2b (not (eq m2b m2e)))
                       (with-current-buffer buf
                         (goto-char (point-min))
                         ;; Make sure there's some refinement.
                         (looking-at
                          (concat "1," (number-to-string lines) "c"))))))
            (smerge-apply-resolution-patch buf m0b m0e m3b m3e m2b))
	   ;; "Mere whitespace changes" conflicts.
           ((when m2e
              (setq b (make-temp-file "smb"))
              (write-region m2b m2e b nil 'silent)
              (with-current-buffer buf (erase-buffer))
              ;; Only minor whitespace changes made locally.
              ;; BEWARE: pass "-c" 'cause the output is reused in the next test.
              (zerop (call-process diff-command nil buf nil "-bc" b m)))
            (set-match-data md)
	    (smerge-keep-n 3))
	   ;; Try "diff -b BASE UPPER | patch LOWER".
	   ((when (and (not safe) m2e b
                       ;; If the BASE is empty, this would just concatenate
                       ;; the two, which is rarely right.
                       (not (eq m2b m2e)))
              ;; BEWARE: we're using here the patch of the previous test.
	      (with-current-buffer buf
		(zerop (call-process-region
			(point-min) (point-max) "patch" t nil nil
			"-r" null-device "--no-backup-if-mismatch"
			"-fl" o))))
	    (save-restriction
	      (narrow-to-region m0b m0e)
              (smerge-remove-props m0b m0e)
	      (insert-file-contents o nil nil nil t)))
	   ;; Try "diff -b BASE LOWER | patch UPPER".
	   ((when (and (not safe) m2e b
                       ;; If the BASE is empty, this would just concatenate
                       ;; the two, which is rarely right.
                       (not (eq m2b m2e)))
	      (write-region m3b m3e o nil 'silent)
	      (call-process diff-command nil buf nil "-bc" b o)
	      (with-current-buffer buf
		(zerop (call-process-region
			(point-min) (point-max) "patch" t nil nil
			"-r" null-device "--no-backup-if-mismatch"
			"-fl" m))))
	    (save-restriction
	      (narrow-to-region m0b m0e)
              (smerge-remove-props m0b m0e)
	      (insert-file-contents m nil nil nil t)))
           ;; If the conflict is only made of comments, and one of the two
           ;; changes is only rearranging spaces (e.g. reflowing text) while
           ;; the other is a real change, drop the space-rearrangement.
           ((and m2e
                 (comment-only-p m1b m1e)
                 (comment-only-p m2b m2e)
                 (comment-only-p m3b m3e)
                 (let ((t1 (smerge-resolve--extract-comment m1b m1e))
                       (t2 (smerge-resolve--extract-comment m2b m2e))
                       (t3 (smerge-resolve--extract-comment m3b m3e)))
                   (cond
                    ((and (equal t1 t2) (not (equal t2 t3)))
                     (setq choice 3))
                    ((and (not (equal t1 t2)) (equal t2 t3))
                     (setq choice 1)))))
            (set-match-data md)
	    (smerge-keep-n choice))
           ;; Idem, when the conflict is contained within a single comment.
           ((save-excursion
              (and m2e
                   (nth 4 (syntax-ppss m0b))
                   ;; If there's a conflict earlier in the file,
                   ;; syntax-ppss is not reliable.
                   (not (re-search-backward smerge-begin-re nil t))
                   (progn (goto-char (nth 8 (syntax-ppss m0b)))
                          (forward-comment 1)
                          (> (point) m0e))
                   (let ((t1 (smerge-resolve--normalize m1b m1e))
                         (t2 (smerge-resolve--normalize m2b m2e))
                         (t3 (smerge-resolve--normalize m3b m3e)))
                     (cond
                    ((and (equal t1 t2) (not (equal t2 t3)))
                     (setq choice 3))
                    ((and (not (equal t1 t2)) (equal t2 t3))
                     (setq choice 1))))))
            (set-match-data md)
	    (smerge-keep-n choice))
           (t
            (user-error "Don't know how to resolve"))))
      (if (buffer-name buf) (kill-buffer buf))
      (if m (delete-file m))
      (if b (delete-file b))
      (if o (delete-file o))))
  (smerge-auto-leave))

(defun smerge-resolve-all ()
  "Perform automatic resolution on all conflicts."
  (interactive)
  (save-excursion
    (goto-char (point-min))
    (while (re-search-forward smerge-begin-re nil t)
      (condition-case nil
          (progn
            (smerge-match-conflict)
            (smerge-resolve 'safe))
        (error nil)))))

(defun smerge-batch-resolve ()
  ;; command-line-args-left is what is left of the command line.
  (if (not noninteractive)
      (error "`smerge-batch-resolve' is to be used only with -batch"))
  (while command-line-args-left
    (let ((file (pop command-line-args-left)))
      (if (string-match "\\.rej\\'" file)
          ;; .rej files should never contain diff3 markers, on the other hand,
          ;; in Arch, .rej files are sometimes used to indicate that the
          ;; main file has diff3 markers.  So you can pass **/*.rej and
          ;; it will DTRT.
          (setq file (substring file 0 (match-beginning 0))))
      (message "Resolving conflicts in %s..." file)
      (when (file-readable-p file)
        (with-current-buffer (find-file-noselect file)
          (smerge-resolve-all)
          (save-buffer)
          (kill-buffer (current-buffer)))))))

(defun smerge-keep-base ()
  "Revert to the base version."
  (interactive)
  (smerge-match-conflict)
  (smerge-ensure-match 2)
  (smerge-keep-n 2)
  (smerge-auto-leave))

(defun smerge-keep-lower ()
  "Keep the \"lower\" version of a merge conflict.
In a conflict that looks like:
  <<<<<<<
  UUU
  =======
  LLL
  >>>>>>>
this keeps \"LLL\"."
  (interactive)
  (smerge-match-conflict)
  ;;(smerge-ensure-match 3)
  (smerge-keep-n 3)
  (smerge-auto-leave))

(define-obsolete-function-alias 'smerge-keep-other 'smerge-keep-lower "26.1")

(defun smerge-keep-upper ()
  "Keep the \"upper\" version of a merge conflict.
In a conflict that looks like:
  <<<<<<<
  UUU
  =======
  LLL
  >>>>>>>
this keeps \"UUU\"."
  (interactive)
  (smerge-match-conflict)
  ;;(smerge-ensure-match 1)
  (smerge-keep-n 1)
  (smerge-auto-leave))

(define-obsolete-function-alias 'smerge-keep-mine 'smerge-keep-upper "26.1")

(defun smerge-get-current ()
  (let ((i 3))
    (while (or (not (match-end i))
	       (< (point) (match-beginning i))
	       (> (point) (match-end i)))
      (cl-decf i))
    i))

(defun smerge-keep-current ()
  "Use the current (under the cursor) version."
  (interactive)
  (smerge-match-conflict)
  (let ((i (smerge-get-current)))
    (if (<= i 0) (error "Not inside a version")
      (smerge-keep-n i)
      (smerge-auto-leave))))

(defun smerge-kill-current ()
  "Remove the current (under the cursor) version."
  (interactive)
  (smerge-match-conflict)
  (let ((i (smerge-get-current)))
    (if (<= i 0) (error "Not inside a version")
      (let ((left nil))
	(dolist (n '(3 2 1))
	  (if (and (match-end n) (/= (match-end n) (match-end i)))
	      (push n left)))
	(if (and (cdr left)
		 (/= (match-end (car left)) (match-end (cadr left))))
	    (ding)			;We don't know how to do that.
	  (smerge-keep-n (car left))
	  (smerge-auto-leave))))))

(defun smerge-diff-base-upper ()
  "Diff `base' and `upper' version in current conflict region."
  (interactive)
  (smerge-diff 2 1))

(define-obsolete-function-alias 'smerge-diff-base-mine
  'smerge-diff-base-upper "26.1")

(defun smerge-diff-base-lower ()
  "Diff `base' and `lower' version in current conflict region."
  (interactive)
  (smerge-diff 2 3))

(define-obsolete-function-alias 'smerge-diff-base-other
  'smerge-diff-base-lower "26.1")

(defun smerge-diff-upper-lower ()
  "Diff `upper' and `lower' version in current conflict region."
  (interactive)
  (smerge-diff 1 3))

(define-obsolete-function-alias 'smerge-diff-mine-other
  'smerge-diff-upper-lower "26.1")

(defun smerge-match-conflict ()
  "Get info about the conflict.  Puts the info in the `match-data'.
The submatches contain:
 0:  the whole conflict.
 1:  upper version of the code.
 2:  base version of the code.
 3:  lower version of the code.
An error is raised if not inside a conflict."
  (save-excursion
    (condition-case nil
	(let* ((orig-point (point))

	       (_ (forward-line 1))
	       (_ (re-search-backward smerge-begin-re))

	       (start (match-beginning 0))
	       (upper-start (match-end 0))
	       (filename (or (match-string 1) ""))

	       (_ (re-search-forward smerge-end-re))
	       (_ (when (< (match-end 0) orig-point)
	            ;; Point is not within the conflict we found,
                    ;; so this conflict is not ours.
	            (signal 'search-failed (list smerge-begin-re))))

	       (lower-end (match-beginning 0))
	       (end (match-end 0))

	       (_ (re-search-backward smerge-lower-re start))

	       (upper-end (match-beginning 0))
	       (lower-start (match-end 0))

	       base-start base-end)

	  ;; handle the various conflict styles
	  (cond
	   ((save-excursion
	      (goto-char upper-start)
	      (re-search-forward smerge-begin-re end t))
	    ;; There's a nested conflict and we're after the beginning
	    ;; of the outer one but before the beginning of the inner one.
	    ;; Of course, maybe this is not a nested conflict but in that
	    ;; case it can only be something nastier that we don't know how
	    ;; to handle, so may as well arbitrarily decide to treat it as
	    ;; a nested conflict.  --Stef
	    (error "There is a nested conflict"))

	   ((re-search-backward smerge-base-re start t)
	    ;; a 3-parts conflict
            (setq-local smerge-conflict-style 'diff3-A)
	    (setq base-end upper-end)
	    (setq upper-end (match-beginning 0))
	    (setq base-start (match-end 0)))

	   ((string= filename (file-name-nondirectory
			       (or buffer-file-name "")))
	    ;; a 2-parts conflict
            (setq-local smerge-conflict-style 'diff3-E))

	   ((and (not base-start)
		 (or (eq smerge-conflict-style 'diff3-A)
		     (equal filename "ANCESTOR")
		     (string-match "\\`[.0-9]+\\'" filename)))
	    ;; a same-diff conflict
	    (setq base-start upper-start)
	    (setq base-end   upper-end)
	    (setq upper-start lower-start)
	    (setq upper-end   lower-end)))

	  (store-match-data (list start end
				  upper-start upper-end
				  base-start base-end
				  lower-start lower-end
				  (when base-start (1- base-start)) base-start
				  (1- lower-start) lower-start))
	  t)
      (search-failed (user-error "Point not in conflict region")))))

(defun smerge-conflict-overlay (pos)
  "Return the conflict overlay at POS if any."
  (let ((ols (overlays-at pos))
        conflict)
    (dolist (ol ols)
      (if (and (eq (overlay-get ol 'smerge) 'conflict)
               (> (overlay-end ol) pos))
          (setq conflict ol)))
    conflict))

(defun smerge-find-conflict (&optional limit)
  "Find and match a conflict region.  Intended as a font-lock MATCHER.
The submatches are the same as in `smerge-match-conflict'.
Returns non-nil if a match is found between point and LIMIT.
Point is moved to the end of the conflict."
  (let ((found nil)
        (pos (point))
        conflict)
    ;; First check to see if point is already inside a conflict, using
    ;; the conflict overlays.
    (while (and (not found) (setq conflict (smerge-conflict-overlay pos)))
      ;; Check the overlay's validity and kill it if it's out of date.
      (condition-case nil
          (progn
            (goto-char (overlay-start conflict))
            (smerge-match-conflict)
            (goto-char (match-end 0))
            (if (<= (point) pos)
                (error "Matching backward!")
              (setq found t)))
        (error (smerge-remove-props
                (overlay-start conflict) (overlay-end conflict))
               (goto-char pos))))
    ;; If we're not already inside a conflict, look for the next conflict
    ;; and add/update its overlay.
    (while (and (not found) (re-search-forward smerge-begin-re limit t))
      (condition-case nil
          (progn
            (smerge-match-conflict)
            (goto-char (match-end 0))
            (let ((conflict (smerge-conflict-overlay (1- (point)))))
              (if conflict
                  ;; Update its location, just in case it got messed up.
                  (move-overlay conflict (match-beginning 0) (match-end 0))
                (setq conflict (make-overlay (match-beginning 0) (match-end 0)
                                             nil 'front-advance nil))
                (overlay-put conflict 'evaporate t)
                (overlay-put conflict 'smerge 'conflict)
                (let ((props smerge-text-properties))
                  (while props
                    (overlay-put conflict (pop props) (pop props))))))
            (setq found t))
        (error nil)))
    found))

;;; Refined change highlighting

(defvar smerge-refine-forward-function #'smerge--refine-forward
  "Function used to determine an \"atomic\" element.
You can set it to `forward-char' to get char-level granularity.
Its behavior has mainly two restrictions:
- if this function encounters a newline, it's important that it stops right
  after the newline.
  This only matters if `smerge-refine-ignore-whitespace' is nil.
- it needs to be unaffected by changes performed by the `preproc' argument
  to `smerge-refine-regions'.
  This only matters if `smerge-refine-weight-hack' is nil.")

(defvar smerge-refine-ignore-whitespace t
  "If non-nil, `smerge-refine' should try to ignore change in whitespace.")

(defvar smerge-refine-weight-hack t
  "If non-nil, pass to diff as many lines as there are chars in the region.
I.e. each atomic element (e.g. word) will be copied as many times (on different
lines) as it has chars.  This has two advantages:
- if `diff' tries to minimize the number *lines* (rather than chars)
  added/removed, this adjust the weights so that adding/removing long
  symbols is considered correspondingly more costly.
- `smerge-refine-forward-function' only needs to be called when chopping up
  the regions, and `forward-char' can be used afterwards.
It has the following disadvantages:
- cannot use `diff -w' because the weighting causes added spaces in a line
  to be represented as added copies of some line, so `diff -w' can't do the
  right thing any more.
- Is a bit more costly (may in degenerate cases use temp files that are 10x
  larger than the refined regions).")

(defun smerge--refine-forward (n)
  (let ((case-fold-search nil)
        (re "[[:upper:]]?[[:lower:]]+\\|[[:upper:]]+\\|[[:digit:]]+\\|.\\|\n"))
    (when (and smerge-refine-ignore-whitespace
               ;; smerge-refine-weight-hack causes additional spaces to
               ;; appear as additional lines as well, so even if diff ignores
               ;; whitespace changes, it'll report added/removed lines :-(
               (not smerge-refine-weight-hack))
      (setq re (concat "[ \t]*\\(?:" re "\\)")))
    (dotimes (_i n)
      (unless (looking-at re) (error "Smerge refine internal error"))
      (goto-char (match-end 0)))))

(defvar smerge--refine-long-words)

(defun smerge--refine-chopup-region (beg end file &optional preproc)
  "Chopup the region into small elements, one per line.
Save the result into FILE.
If non-nil, PREPROC is called with no argument in a buffer that contains
a copy of the text, just before chopping it up.  It can be used to replace
chars to try and eliminate some spurious differences."
  ;; We used to chop up char-by-char rather than word-by-word like ediff
  ;; does.  It had the benefit of simplicity and very fine results, but it
  ;; often suffered from problem that diff would find correlations where
  ;; there aren't any, so the resulting "change" didn't make much sense.
  ;; You can still get this behavior by setting
  ;; `smerge-refine-forward-function' to `forward-char'.
  (with-temp-buffer
    (insert-buffer-substring (marker-buffer beg) beg end)
    (when preproc (goto-char (point-min)) (funcall preproc))
    (when smerge-refine-ignore-whitespace
      ;; It doesn't make much of a difference for diff-fine-highlight
      ;; because we still have the _/+/</>/! prefix anyway.  Can still be
      ;; useful in other circumstances.
      (subst-char-in-region (point-min) (point-max) ?\n ?\s))
    (goto-char (point-min))
    (while (not (eobp))
      (cl-assert (bolp))
      (let ((start (point)))
        (funcall smerge-refine-forward-function 1)
        (let ((len (- (point) start)))
          (cl-assert (>= len 1))
          ;; We add \n after each chunk except after \n, so we get
          ;; one line per text chunk, where each line contains
          ;; just one chunk, except for \n chars which are
          ;; represented by the empty line.
          (unless (bolp) (insert ?\n))
          (when (and smerge-refine-weight-hack (> len 1))
            (let ((s (buffer-substring-no-properties start (point))))
              ;; The weight-hack inserts N copies of words of size N,
              ;; so it naturally suffers from an O(N²) blow up.
              ;; To circumvent this, we map each long word
              ;; to a shorter (but still unique) replacement.
              ;; Another option would be to change smerge--refine-forward
              ;; so it chops up long words into smaller ones.
              (when (> len 8)
                (let ((short (gethash s smerge--refine-long-words)))
                  (unless short
                    ;; To avoid accidental conflicts with ≤8 words,
                    ;; we make sure the replacement is >8 chars.  Overall,
                    ;; this should bound the blowup factor to ~10x,
                    ;; tho if those chars end up encoded as multiple bytes
                    ;; each, it could probably still reach ~30x in
                    ;; pathological cases.
                    (setq short
                          (concat (substring s 0 7)
                                  " "
                                  (string
                                   (+ ?0
                                      (hash-table-count
                                       smerge--refine-long-words)))
                                  "\n"))
                    (puthash s short smerge--refine-long-words))
                  (delete-region start (point))
                  (insert short)
                  (setq s short)))
              (dotimes (_i (1- len)) (insert s)))))))
    (unless (bolp) (error "Smerge refine internal error"))
    (let ((coding-system-for-write 'utf-8-emacs-unix))
      (write-region (point-min) (point-max) file nil 'nomessage))))

(defun smerge--refine-highlight-change (beg match-num1 match-num2 props)
  ;; TODO: Add a property pointing to the corresponding text in the
  ;; other region.
  (with-current-buffer (marker-buffer beg)
    (goto-char beg)
    (let* ((startline (- (string-to-number match-num1) 1))
           (beg (progn (funcall (if smerge-refine-weight-hack
                                    #'forward-char
                                  smerge-refine-forward-function)
                                startline)
                       (point)))
           (end (progn (funcall (if smerge-refine-weight-hack
                                    #'forward-char
                                  smerge-refine-forward-function)
                          (if match-num2
                              (- (string-to-number match-num2)
                                 startline)
                            1))
                       (point))))
      (when smerge-refine-ignore-whitespace
        (skip-chars-backward " \t\n" beg) (setq end (point))
        (goto-char beg)
        (skip-chars-forward " \t\n" end)  (setq beg (point)))
      (when (> end beg)
        (let ((ol (make-overlay
                   beg end nil
                   ;; Make them tend to shrink rather than spread when editing.
                   'front-advance nil)))
          (overlay-put ol 'evaporate t)
          (dolist (x props) (overlay-put ol (car x) (cdr x)))
          ol)))))

;;;###autoload
(defun smerge-refine-regions (beg1 end1 beg2 end2 props-c &optional preproc props-r props-a)
  "Show fine differences in the two regions BEG1..END1 and BEG2..END2.
PROPS-C is an alist of properties to put (via overlays) on the changes.
PROPS-R is an alist of properties to put on removed characters.
PROPS-A is an alist of properties to put on added characters.
If PROPS-R and PROPS-A are nil, put PROPS-C on all changes.
If PROPS-C is nil, but PROPS-R and PROPS-A are non-nil,
put PROPS-A on added characters, PROPS-R on removed characters.
If PROPS-C, PROPS-R and PROPS-A are non-nil, put PROPS-C on changed characters,
PROPS-A on added characters, and PROPS-R on removed characters.

If non-nil, PREPROC is called with no argument in a buffer that contains
a copy of a region, just before preparing it to for `diff'.  It can be
used to replace chars to try and eliminate some spurious differences."
  (let* ((pos (point))
         deactivate-mark         ; The code does not modify any visible buffer.
         (file1 (make-temp-file "diff1"))
         (file2 (make-temp-file "diff2"))
         (smerge--refine-long-words
          (if smerge-refine-weight-hack (make-hash-table :test #'equal))))
    (unless (markerp beg1) (setq beg1 (copy-marker beg1)))
    (unless (markerp beg2) (setq beg2 (copy-marker beg2)))
    (let ((write-region-inhibit-fsync t)) ; Don't fsync temp files (Bug#12747).
      ;; Chop up regions into smaller elements and save into files.
      (smerge--refine-chopup-region beg1 end1 file1 preproc)
      (smerge--refine-chopup-region beg2 end2 file2 preproc))

    ;; Call diff on those files.
    (unwind-protect
        (with-temp-buffer
          ;; Allow decoding the EOL format, as on MS-Windows the Diff
          ;; utility might produce CR-LF EOLs.
          (let ((coding-system-for-read 'utf-8-emacs))
            (call-process diff-command nil t nil
                          (if (and smerge-refine-ignore-whitespace
                                   (not smerge-refine-weight-hack))
                              ;; Pass -a so diff treats it as a text file even
                              ;; if it contains \0 and such.
                              ;; Pass -d so as to get the smallest change, but
                              ;; also and more importantly because otherwise it
                              ;; may happen that diff doesn't behave like
                              ;; smerge-refine-weight-hack expects it to.
                              ;; See https://lists.gnu.org/r/emacs-devel/2007-11/msg00401.html
                              "-awd" "-ad")
                          file1 file2))
          ;; Process diff's output.
          (goto-char (point-min))
          (let ((last1 nil)
                (last2 nil))
            (while (not (eobp))
              (if (not (looking-at "\\([0-9]+\\)\\(?:,\\([0-9]+\\)\\)?\\([acd]\\)\\([0-9]+\\)\\(?:,\\([0-9]+\\)\\)?$"))
                  (error "Unexpected patch hunk header: %s"
                         (buffer-substring (point) (line-end-position))))
              (let ((op (char-after (match-beginning 3)))
                    (m1 (match-string 1))
                    (m2 (match-string 2))
                    (m4 (match-string 4))
                    (m5 (match-string 5)))
                (when (memq op '(?d ?c))
                  (setq last1
                        (smerge--refine-highlight-change
			 beg1 m1 m2
			 ;; Try to use props-c only for changed chars,
			 ;; fallback to props-r for changed/removed chars,
			 ;; but if props-r is nil then fallback to props-c.
			 (or (and (eq op '?c) props-c) props-r props-c))))
                (when (memq op '(?a ?c))
                  (setq last2
                        (smerge--refine-highlight-change
			 beg2 m4 m5
			 ;; Same logic as for removed chars above.
			 (or (and (eq op '?c) props-c) props-a props-c)))))
              (forward-line 1)                            ;Skip hunk header.
              (and (re-search-forward "^[0-9]" nil 'move) ;Skip hunk body.
                   (goto-char (match-beginning 0))))
            ;; (cl-assert (or (null last1) (< (overlay-start last1) end1)))
            ;; (cl-assert (or (null last2) (< (overlay-start last2) end2)))
            (if smerge-refine-weight-hack
                (progn
                  ;; (cl-assert (or (null last1) (<= (overlay-end last1) end1)))
                  ;; (cl-assert (or (null last2) (<= (overlay-end last2) end2)))
                  )
              ;; smerge-refine-forward-function when calling in chopup may
              ;; have stopped because it bumped into EOB whereas in
              ;; smerge-refine-weight-hack it may go a bit further.
              (if (and last1 (> (overlay-end last1) end1))
                  (move-overlay last1 (overlay-start last1) end1))
              (if (and last2 (> (overlay-end last2) end2))
                  (move-overlay last2 (overlay-start last2) end2))
              )))
      (goto-char pos)
      (delete-file file1)
      (delete-file file2))))
(define-obsolete-function-alias 'smerge-refine-subst
  #'smerge-refine-regions "26.1")

(defun smerge-refine (&optional part)
  "Highlight the words of the conflict that are different.
For 3-way conflicts, highlights only two of the three parts.
A numeric argument PART can be used to specify which two parts;
repeating the command will highlight other two parts."
  (interactive
   (if (integerp current-prefix-arg) (list current-prefix-arg)
     (smerge-match-conflict)
     (let* ((prop (get-text-property (match-beginning 0) 'smerge-refine-part))
            (part (if (and (consp prop)
                           (eq (buffer-chars-modified-tick) (car prop)))
                      (cdr prop))))
       ;; If already highlighted, cycle.
       (list (if (integerp part) (1+ (mod part 3)))))))

  (if (and (integerp part) (or (< part 1) (> part 3)))
      (error "No conflict part nb %s" part))
  (smerge-match-conflict)
  (remove-overlays (match-beginning 0) (match-end 0) 'smerge 'refine)
  ;; Ignore `part' if not applicable, and default it if not provided.
  (setq part (cond ((null (match-end 2)) 2)
                   ((eq (match-end 1) (match-end 3)) 1)
                   ((integerp part) part)
                   ;; If one of the parts is empty, any refinement using
                   ;; it will be trivial and uninteresting.
                   ((eq (match-end 1) (match-beginning 1)) 1)
                   ((eq (match-end 3) (match-beginning 3)) 3)
                   (t 2)))
  (let ((n1 (if (eq part 1) 2 1))
        (n2 (if (eq part 3) 2 3))
	(smerge-use-changed-face
	 (and (face-differs-from-default-p 'smerge-refined-change)
	      (not (face-equal 'smerge-refined-change 'smerge-refined-added))
	      (not (face-equal 'smerge-refined-change 'smerge-refined-removed)))))
    (smerge-ensure-match n1)
    (smerge-ensure-match n2)
    (with-silent-modifications
      (put-text-property (match-beginning 0) (1+ (match-beginning 0))
                         'smerge-refine-part
                         (cons (buffer-chars-modified-tick) part)))
    (smerge-refine-regions (match-beginning n1) (match-end n1)
                         (match-beginning n2)  (match-end n2)
                         (if smerge-use-changed-face
			     '((smerge . refine) (font-lock-face . smerge-refined-change)))
			 nil
			 (unless smerge-use-changed-face
			   '((smerge . refine) (font-lock-face . smerge-refined-removed)))
			 (unless smerge-use-changed-face
			   '((smerge . refine) (font-lock-face . smerge-refined-added))))))

(defun smerge-swap ()
  "Swap the \"Upper\" and the \"Lower\" chunks.
Can be used before things like `smerge-keep-all' or `smerge-resolve' where the
ordering can have some subtle influence on the result, such as preferring the
spacing of the \"Lower\" chunk."
  (interactive)
  (smerge-match-conflict)
  (goto-char (match-beginning 3))
  (let ((txt3 (delete-and-extract-region (point) (match-end 3))))
    (insert (delete-and-extract-region (match-beginning 1) (match-end 1)))
    (goto-char (match-beginning 1))
    (insert txt3)))

(defun smerge-diff (n1 n2)
  (smerge-match-conflict)
  (smerge-ensure-match n1)
  (smerge-ensure-match n2)
  (let ((name1 (aref smerge-match-names n1))
	(name2 (aref smerge-match-names n2))
	;; Read them before the match-data gets clobbered.
	(beg1 (match-beginning n1))
	(end1 (match-end n1))
	(beg2 (match-beginning n2))
	(end2 (match-end n2))
	(file1 (make-temp-file "smerge1"))
	(file2 (make-temp-file "smerge2"))
	(dir default-directory)
	(file (if buffer-file-name (file-relative-name buffer-file-name)))
        ;; We would want to use `emacs-mule-unix' for read&write, but we
        ;; bump into problems with the coding-system used by diff to write
        ;; the file names and the time stamps in the header.
        ;; `buffer-file-coding-system' is not always correct either, but if
        ;; the OS/user uses only one coding-system, then it works.
	(coding-system-for-read buffer-file-coding-system))
    (write-region beg1 end1 file1 nil 'nomessage)
    (write-region beg2 end2 file2 nil 'nomessage)
    (unwind-protect
	(with-current-buffer (get-buffer-create smerge-diff-buffer-name)
	  (setq default-directory dir)
	  (let ((inhibit-read-only t))
	    (erase-buffer)
	    (let ((status
		   (apply 'call-process diff-command nil t nil
			  (append smerge-diff-switches
				  (and (diff-check-labels)
				       (list "--label"
					     (concat name1 "/" file)
					     "--label"
					     (concat name2 "/" file)))
				  (list file1 file2)))))
	      (if (eq status 0) (insert "No differences found.\n"))))
	  (goto-char (point-min))
	  (diff-mode)
	  (display-buffer (current-buffer) t))
      (delete-file file1)
      (delete-file file2))))

;; compiler pacifiers
(defvar smerge-ediff-windows)
(defvar smerge-ediff-buf)
(defvar ediff-buffer-A)
(defvar ediff-buffer-B)
(defvar ediff-buffer-C)
(defvar ediff-ancestor-buffer)
(defvar ediff-quit-hook)
(declare-function ediff-cleanup-mess "ediff-util" nil)

(defun smerge--get-marker (regexp default)
  (save-excursion
    (goto-char (point-min))
    (if (and (search-forward-regexp regexp nil t)
	     (> (match-end 1) (match-beginning 1)))
	(concat default "=" (match-string-no-properties 1))
      default)))

;;;###autoload
(defun smerge-ediff (&optional name-upper name-lower name-base)
  "Invoke ediff to resolve the conflicts.
NAME-UPPER, NAME-LOWER, and NAME-BASE, if non-nil, are used for the
buffer names."
  (interactive)
  (let* ((buf (current-buffer))
	 (mode major-mode)
	 ;;(ediff-default-variant 'default-B)
	 (config (current-window-configuration))
	 (filename (file-name-nondirectory (or buffer-file-name "-")))
	 (upper (generate-new-buffer
		(or name-upper
                    (concat "*" filename " "
                            (smerge--get-marker smerge-begin-re "UPPER")
                            "*"))))
	 (lower (generate-new-buffer
		 (or name-lower
                     (concat "*" filename " "
                             (smerge--get-marker smerge-end-re "LOWER")
                             "*"))))
	 base)
    (with-current-buffer upper
      (buffer-disable-undo)
      (insert-buffer-substring buf)
      (goto-char (point-min))
      (while (smerge-find-conflict)
	(when (match-beginning 2) (setq base t))
	(smerge-keep-n 1))
      (buffer-enable-undo)
      (set-buffer-modified-p nil)
      (funcall mode))

    (with-current-buffer lower
      (buffer-disable-undo)
      (insert-buffer-substring buf)
      (goto-char (point-min))
      (while (smerge-find-conflict)
	(smerge-keep-n 3))
      (buffer-enable-undo)
      (set-buffer-modified-p nil)
      (funcall mode))

    (when base
      (setq base (generate-new-buffer
		  (or name-base
                      (concat "*" filename " "
                              (smerge--get-marker smerge-base-re "BASE")
                              "*"))))
      (with-current-buffer base
	(buffer-disable-undo)
	(insert-buffer-substring buf)
	(goto-char (point-min))
	(while (smerge-find-conflict)
	  (if (match-end 2)
	      (smerge-keep-n 2)
	    (delete-region (match-beginning 0) (match-end 0))))
	(buffer-enable-undo)
	(set-buffer-modified-p nil)
	(funcall mode)))

    ;; the rest of the code is inspired from vc.el
    ;; Fire up ediff.
    (set-buffer
     (if base
	 (ediff-merge-buffers-with-ancestor upper lower base)
	  ;; nil 'ediff-merge-revisions-with-ancestor buffer-file-name)
       (ediff-merge-buffers upper lower)))
        ;; nil 'ediff-merge-revisions buffer-file-name)))

    ;; Ediff is now set up, and we are in the control buffer.
    ;; Do a few further adjustments and take precautions for exit.
    (setq-local smerge-ediff-windows config)
    (setq-local smerge-ediff-buf buf)
    (add-hook 'ediff-quit-hook
	      (lambda ()
		(let ((buffer-A ediff-buffer-A)
		      (buffer-B ediff-buffer-B)
		      (buffer-C ediff-buffer-C)
		      (buffer-Ancestor ediff-ancestor-buffer)
		      (buf smerge-ediff-buf)
		      (windows smerge-ediff-windows))
		  (ediff-cleanup-mess)
		  (with-current-buffer buf
		    (erase-buffer)
		    (insert-buffer-substring buffer-C)
		    (kill-buffer buffer-A)
		    (kill-buffer buffer-B)
		    (kill-buffer buffer-C)
		    (when (bufferp buffer-Ancestor)
		      (kill-buffer buffer-Ancestor))
		    (set-window-configuration windows)
		    (message "Conflict resolution finished; you may save the buffer"))))
	      nil t)
    (message "Please resolve conflicts now; exit ediff when done")))

(defun smerge-makeup-conflict (pt1 pt2 pt3 &optional pt4)
  "Insert diff3 markers to make a new conflict.
Uses point and mark for two of the relevant positions and previous marks
for the other ones.
By default, makes up a 2-way conflict,
with a \\[universal-argument] prefix, makes up a 3-way conflict."
  (interactive
   (list (point)
         (mark)
         (progn (pop-mark) (mark))
         (when current-prefix-arg (pop-mark) (mark))))
  ;; Start from the end so as to avoid problems with pos-changes.
  (pcase-let ((`(,pt1 ,pt2 ,pt3 ,pt4)
               (sort `(,pt1 ,pt2 ,pt3 ,@(if pt4 (list pt4))) '>=)))
    (goto-char pt1) (beginning-of-line)
    (insert ">>>>>>> LOWER\n")
    (goto-char pt2) (beginning-of-line)
    (insert "=======\n")
    (goto-char pt3) (beginning-of-line)
    (when pt4
      (insert "||||||| BASE\n")
      (goto-char pt4) (beginning-of-line))
    (insert "<<<<<<< UPPER\n"))
  (if smerge-mode nil (smerge-mode 1))
  (smerge-refine))


(defconst smerge-parsep-re
  (concat smerge-begin-re "\\|" smerge-end-re "\\|"
          smerge-base-re "\\|" smerge-lower-re "\\|"))

;;;###autoload
(define-minor-mode smerge-mode
  "Minor mode to simplify editing output from the diff3 program.

\\{smerge-mode-map}"
  :group 'smerge :lighter " SMerge"
  (when font-lock-mode
    (save-excursion
      (if smerge-mode
	  (font-lock-add-keywords nil smerge-font-lock-keywords 'append)
	(font-lock-remove-keywords nil smerge-font-lock-keywords))
      (goto-char (point-min))
      (while (smerge-find-conflict)
	(save-excursion
	  (font-lock-fontify-region (match-beginning 0) (match-end 0) nil)))))
  (if (string-match (regexp-quote smerge-parsep-re) paragraph-separate)
      (unless smerge-mode
        (setq-local paragraph-separate
                    (replace-match "" t t paragraph-separate)))
    (when smerge-mode
        (setq-local paragraph-separate
                    (concat smerge-parsep-re paragraph-separate))))
  (unless smerge-mode
    (smerge-remove-props (point-min) (point-max))))

;;;###autoload
(defun smerge-start-session (&optional interactively)
  "Turn on `smerge-mode' and move point to first conflict marker.
If no conflict maker is found, turn off `smerge-mode'."
  (interactive "p")
  (when (or (null smerge-mode) interactively)
    (smerge-mode 1)
    (condition-case nil
        (unless (looking-at smerge-begin-re)
          (smerge-next))
      (error (smerge-auto-leave)))))

(defcustom smerge-change-buffer-confirm t
  "If non-nil, request confirmation before moving to another buffer."
  :type 'boolean)

(defun smerge-vc-next-conflict ()
  "Go to next conflict, possibly in another file.
First tries to go to the next conflict in the current buffer, and if not
found, uses VC to try and find the next file with conflict."
  (interactive)
  (condition-case nil
      ;; FIXME: Try again from BOB before moving to the next file.
      (smerge-next)
    (error
     (if (and (or smerge-change-buffer-confirm
                  (and (buffer-modified-p) buffer-file-name))
              (not (or (eq last-command this-command)
                       (eq ?\r last-command-event)))) ;Called via M-x!?
         ;; FIXME: Don't emit this message if `vc-find-conflicted-file' won't
         ;; go to another file anyway (because there are no more conflicted
         ;; files).
         (message (if (buffer-modified-p)
                      "No more conflicts here.  Repeat to save and go to next buffer"
                    "No more conflicts here.  Repeat to go to next buffer"))
       (if (and (buffer-modified-p) buffer-file-name)
           (save-buffer))
       (vc-find-conflicted-file)
       ;; At this point, the caret will only be at a conflict marker
       ;; if the file did not correspond to an opened
       ;; buffer. Otherwise we need to jump to a marker explicitly.
       (unless (looking-at "^<<<<<<<")
         (let ((prev-pos (point)))
           (goto-char (point-min))
           (unless (ignore-errors (not (smerge-next)))
             (goto-char prev-pos))))))))

(provide 'smerge-mode)

;;; smerge-mode.el ends here