;;; ediff-ptch.el --- Ediff's  patch support  -*- lexical-binding:t -*-

;; Copyright (C) 1996-2024 Free Software Foundation, Inc.

;; Author: Michael Kifer <kifer@cs.stonybrook.edu>
;; Package: ediff

;; 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:

;;; Code:

(require 'diff-mode) ; For `diff-file-junk-re'.

(defgroup ediff-ptch nil
  "Ediff patch support."
  :tag "Patch"
  :prefix "ediff-"
  :group 'ediff)

(require 'ediff-init)
(require 'ediff-util)
(require 'ediff)

(defcustom ediff-patch-program  "patch"
  "Name of the program that applies patches.
It is recommended to use GNU-compatible versions."
  :type 'string)
(defcustom ediff-patch-options "-f"
  "Options to pass to ediff-patch-program.

Note: the `-b' option should be specified in `ediff-backup-specs'.

It is recommended to pass the `-f' option to the patch program, so it won't ask
questions.  However, some implementations don't accept this option, in which
case the default value for this variable should be changed."
  :type 'string)

(defvar ediff-last-dir-patch nil
  "Last directory used by an Ediff command for file to patch.")

;; the default backup extension
(defconst ediff-default-backup-extension
  (if (eq system-type 'ms-dos)
      "_orig" ".orig"))


(defcustom ediff-backup-extension ediff-default-backup-extension
  "Backup extension used by the patch program.
See also `ediff-backup-specs'."
  :type 'string)

(defun ediff-test-patch-utility ()
  (condition-case nil
      (cond ((eq 0 (call-process ediff-patch-program nil nil nil "-z." "-b"))
	     ;; GNU `patch' v. >= 2.2
	     'gnu)
	    ((eq 0 (call-process ediff-patch-program nil nil nil "-b"))
	     'posix)
	    (t 'traditional))
    (file-error nil)))

(defcustom ediff-backup-specs
  (let ((type (ediff-test-patch-utility)))
    (cond ((eq type 'gnu)
	   ;; GNU `patch' v. >= 2.2
	   (format "-z%s -b" ediff-backup-extension))
	  ((eq type 'posix)
	   ;; POSIX `patch' -- ediff-backup-extension must be ".orig"
	   (setq ediff-backup-extension ediff-default-backup-extension)
	   "-b")
	  (t
	   ;; traditional `patch'
	   (format "-b %s" ediff-backup-extension))))
  "Backup directives to pass to the patch program.
Ediff requires that the old version of the file \(before applying the patch)
be saved in a file named `the-patch-file.extension'.  Usually `extension' is
`.orig', but this can be changed by the user and may depend on the system.
Therefore, Ediff needs to know the backup extension used by the patch program.

Some versions of the patch program let you specify `-b backup-extension'.
Other versions only permit `-b', which assumes the extension `.orig'
\(in which case ediff-backup-extension MUST be also `.orig').  The latest
versions of GNU patch require `-b -z backup-extension'.

Note that both `ediff-backup-extension' and `ediff-backup-specs'
must be set properly.  If your patch program takes the option `-b',
but not `-b extension', the variable `ediff-backup-extension' must
still be set so Ediff will know which extension to use.

Ediff tries to guess the appropriate value for this variables.  It is believed
to be working for `traditional' patch, all versions of GNU patch, and for POSIX
patch.  So, don't change these variables, unless the default doesn't work."
  :type 'string)


(defcustom ediff-patch-default-directory nil
  "Default directory to look for patches."
  :type '(choice (const nil) string))

;; This context diff does not recognize spaces inside files, but removing ' '
;; from [^ \t] breaks normal patches for some reason
(defcustom ediff-context-diff-label-regexp
  (let ((stuff "\\([^ \t\n]+\\)"))
    (concat "\\(" 	; context diff 2-liner
            "^\\*\\*\\* +" stuff "[^*]+\n--- +" stuff
            "\\|" 	; unified format diff 2-liner
            "^--- +" stuff ".*\n\\+\\+\\+ +" stuff
            "\\)"))
  "Regexp matching filename 2-liners at the start of each context diff.
You probably don't want to change that, unless you are using an obscure patch
program."
  :type 'regexp)

(ediff-defvar-local ediff-patchbufer nil
  "The buffer of the patch file.  Local to control buffer.")

(ediff-defvar-local ediff-patch-diagnostics nil
  "The buffer where patch displays its diagnostics.")

(ediff-defvar-local ediff-patch-map nil
  "Map of patch buffer.
Has the form:
   ((filename1 marker1 marker2) (filename2 marker1 marker2) ...)
where filenames are files to which patch would have applied the patch;
marker1 delimits the beginning of the corresponding patch and marker2 does
it for the end.")

;; strip prefix from filename
;; returns /dev/null, if can't strip prefix
(defsubst ediff-file-name-sans-prefix (filename prefix)
  (if prefix
      (save-match-data
	(if (string-match (concat "^" (if (stringp prefix)
					  (regexp-quote prefix)
					""))
			  filename)
	    (substring filename (match-end 0))
	  (concat "/null/" filename)))
    filename)
  )



;; no longer used
;; return the number of matches of regexp in buf starting from the beginning
(defun ediff-count-matches (regexp buf)
  (ediff-with-current-buffer buf
    (let ((count 0) opoint)
      (save-excursion
	(goto-char (point-min))
	(while (and (not (eobp))
		    (progn (setq opoint (point))
			   (re-search-forward regexp nil t)))
	  (if (= opoint (point))
	      (forward-char 1)
	    (setq count (1+ count)))))
      count)))

;; Scan BUF (which is supposed to contain a patch) and make a list of the form
;;    ((nil nil filename-spec1 marker1 marker2)
;;          (nil nil filename-spec2 marker1 marker2) ...)
;; where filename-spec[12] are files to which the `patch' program would
;; have applied the patch.
;; nin, nil are placeholders. See ediff-make-new-meta-list-element in
;;    ediff-meta.el for the explanations.
;; In the beginning we don't know exactly which files need to be patched.
;; We usually come up with two candidates and ediff-file-name-sans-prefix
;;    resolves this later.
;;
;; The marker `mark1' delimits the beginning of the corresponding patch and
;;    `mark2' does it for the end.
;; The result of ediff-map-patch-buffer is a list, which is then assigned
;; to ediff-patch-map.
;; The function returns the number of elements in the list ediff-patch-map
(defun ediff-map-patch-buffer (buf)
  (ediff-with-current-buffer buf
    (let ((count 0)
	  (mark1 (point-min-marker))
	  (mark1-end (point-min))
	  (possible-file-names `(,null-device . ,null-device))
	  mark2-end mark2 filenames
	  beg1 beg2 end1 end2
	  patch-map opoint)
      (save-excursion
	(goto-char (point-min))
	(setq opoint (point))
	(while (and (not (eobp))
		    (re-search-forward ediff-context-diff-label-regexp nil t))
	  (if (= opoint (point))
	      (forward-char 1) ; ensure progress towards the end
	    (setq mark2 (move-marker (make-marker) (match-beginning 0))
		  mark2-end (match-end 0)
		  beg1 (or (match-beginning 2) (match-beginning 4))
 		  end1 (or (match-end 2) (match-end 4))
 		  beg2 (or (match-beginning 3) (match-beginning 5))
 		  end2 (or (match-end 3) (match-end 5)))
	    ;; possible-file-names is holding the new file names until we
	    ;; insert the old file name in the patch map
	    ;; It is a pair
	    ;;     (filename-from-1st-header-line . filename-from-2nd-line)
	    (setq possible-file-names
		  (cons (if (and beg1 end1)
			    (buffer-substring beg1 end1)
			  null-device)
			(if (and beg2 end2)
			    (buffer-substring beg2 end2)
			  null-device)))
            ;; Remove file junk (Bug#26084).
            (while (re-search-backward
                    (concat "^\\(?:" diff-file-junk-re "\\)") mark1-end t)
                (move-marker mark2 (match-beginning 0)))
	    (goto-char mark2-end)
	    (if filenames
		(setq patch-map
		      (cons (ediff-make-new-meta-list-element
			     filenames mark1 mark2)
			    patch-map)))
	    (setq mark1 mark2
		  mark1-end mark2-end
		  filenames possible-file-names))
	  (setq opoint (point)
		count (1+ count))))
      (setq mark2 (point-max-marker)
	    patch-map (cons (ediff-make-new-meta-list-element
			     possible-file-names mark1 mark2)
			    patch-map))
      (setq ediff-patch-map (nreverse patch-map))
      count)))

;; Fix up the file names in the list using the argument FILENAME
;; Algorithm: find the files' directories in the patch and, if a directory is
;; absolute, cut it out from the corresponding file name in the patch.
;; Relative directories are not cut out.
;; Prepend the directory of FILENAME to each resulting file (which came
;; originally from the patch).
;; In addition, the first file in the patch document is replaced by FILENAME.
;; Each file is actually a pair of files found in the context diff header
;; In the end, for each pair, we ask the user which file to patch.
;; Note: Ediff doesn't recognize multi-file patches that are separated
;; with the `Index:' line.  It treats them as a single-file patch.
;;
;; Executes inside the patch buffer
(defun ediff-fixup-patch-map (filename)
  (setq filename (expand-file-name filename))
  (let ((actual-dir (if (file-directory-p filename)
			;; directory part of filename
			(file-name-as-directory filename)
		      (file-name-directory filename)))
        (multi-patch-p (cdr ediff-patch-map))
	;; In case 2 files are possible patch targets, the user will be offered
	;; to choose file1 or file2.  In a multifile patch, if the user chooses
	;; 1 or 2, this choice is preserved to decide future alternatives.
	chosen-alternative
	)

    ;; chop off base-dirs
    (mapc (lambda (session-info)
	    (let* ((proposed-file-names
		    ;; Filename-spec is objA; it is represented as
		    ;; (file1 . file2). Get it using ediff-get-session-objA.
		    (ediff-get-session-objA-name session-info))
		   ;; base-dir1 is  the dir part of the 1st file in the patch
		   (base-dir1
		    (or (file-name-directory (car proposed-file-names))
			""))
		   ;; directory part of the 2nd file in the patch
		   (base-dir2
		    (or (file-name-directory (cdr proposed-file-names))
			""))
		   )
	      ;; If both base-dir1 and base-dir2 are relative and exist,
	      ;; assume that
	      ;; these dirs lead to the actual files starting at the present
	      ;; directory. So, we don't strip these relative dirs from the
	      ;; file names. This is a heuristic intended to improve guessing
	      (let ((default-directory (file-name-directory filename)))
		(unless (or (file-name-absolute-p base-dir1)
			    (file-name-absolute-p base-dir2))
		  (if (and (file-exists-p base-dir1)
			   (file-exists-p base-dir2))
		      (setq base-dir1 ""
			    base-dir2 "")
		    ;; Strip possible source/destination prefixes
		    ;; such as a/ and b/ from dir names.
		    (save-match-data
		      (let ((m1 (when (string-match "^[^/]+/" base-dir1)
                                  (cons (substring base-dir1 0 (match-end 0))
                                        (substring base-dir1 (match-end 0)))))
			    (m2 (when (string-match "^[^/]+/" base-dir2)
				  (cons (substring base-dir2 0 (match-end 0))
                                        (substring base-dir2 (match-end 0))))))
			(when (and (file-exists-p (cdr m1))
				   (file-exists-p (cdr m2)))
			  (setq base-dir1 (car m1)
				base-dir2 (car m2))))))))
	      (or (string= (car proposed-file-names) null-device)
		  (setcar proposed-file-names
			  (ediff-file-name-sans-prefix
			   (car proposed-file-names) base-dir1)))
	      (or (string=
		   (cdr proposed-file-names) null-device)
		  (setcdr proposed-file-names
			  (ediff-file-name-sans-prefix
			   (cdr proposed-file-names) base-dir2)))
	      ))
	  ediff-patch-map)

    ;; take the given file name into account
    (or (file-directory-p filename)
	(string= null-device filename)
	(setcar (ediff-get-session-objA (car ediff-patch-map))
		(cons (file-name-nondirectory filename)
		      (file-name-nondirectory filename))))

    ;; prepend actual-dir
    (mapc (lambda (session-info)
	    (let ((proposed-file-names
		   (ediff-get-session-objA-name session-info)))
	      (if (and (string-match-p "^/null/" (car proposed-file-names))
		       (string-match-p "^/null/" (cdr proposed-file-names)))
		  ;; couldn't intuit the file name to patch, so
		  ;; something is amiss
		  (progn
		    (with-output-to-temp-buffer ediff-msg-buffer
		      (ediff-with-current-buffer standard-output
			(fundamental-mode))
		      (princ
		       (format-message "
The patch file contains a context diff for
	%s
	%s
However, Ediff cannot infer the name of the actual file
to be patched on your system.  If you know the correct file name,
please enter it now.

If you don't know and still would like to apply patches to
other files, enter `/dev/null'.
"
			       (substring (car proposed-file-names) 6)
			       (substring (cdr proposed-file-names) 6))))
		    (let ((directory t)
			  user-file)
		      (while directory
			(setq user-file
			      (read-file-name
			       "Please enter file name: "
			       actual-dir actual-dir t))
			(if (not (file-directory-p user-file))
			    (setq directory nil)
			  (setq directory t)
			  (beep)
			  (important-message 2 nil "%s is a directory" user-file)))
		      (setcar (ediff-get-session-objA session-info)
			      (cons user-file user-file))))
		(setcar proposed-file-names
			(expand-file-name
			 (concat actual-dir (car proposed-file-names))))
		(setcdr proposed-file-names
			(expand-file-name
			 (concat actual-dir (cdr proposed-file-names)))))
	      ))
	  ediff-patch-map)
    ;; Check for the existing files in each pair and discard the nonexistent
    ;; ones. If both exist, ask the user.
    (mapcar (lambda (session-info)
	      (let* ((file1 (car (ediff-get-session-objA-name session-info)))
		     (file2 (cdr (ediff-get-session-objA-name session-info)))
		     (session-file-object
		      (ediff-get-session-objA session-info))
		     (f1-exists (file-exists-p file1))
		     (f2-exists (file-exists-p file2)))
		(cond
		 ((and
		   ;; The patch program prefers the shortest file as the patch
		   ;; target. However, this is a questionable heuristic. In an
		   ;; interactive program, like ediff, we can offer the user a
		   ;; choice.
		   ;; (< (length file2) (length file1))
		   (not f1-exists)
		   f2-exists)
		  ;; replace file-pair with the winning file2
		  (setcar session-file-object file2))
		 ((and
		   ;; (< (length file1) (length file2))
		   (not f2-exists)
		   f1-exists)
		  ;; replace file-pair with the winning file1
		  (setcar session-file-object file1))
		 ((and f1-exists f2-exists
		       (string= file1 file2))
		  (setcar session-file-object file1))
		 ((and f1-exists f2-exists (eq chosen-alternative 1))
		  (setcar session-file-object file1))
		 ((and f1-exists f2-exists (eq chosen-alternative 2))
		  (setcar session-file-object file2))
		 ((and f1-exists f2-exists)
		  (with-output-to-temp-buffer ediff-msg-buffer
		    (ediff-with-current-buffer standard-output
		      (fundamental-mode))
                    (with-current-buffer standard-output
                      (insert (format-message
                              (substitute-command-keys "
Ediff has inferred that
	%s
	%s
are two possible targets for applying the patch.
Both files seem to be plausible alternatives.

Please advise:
    Type \\`y' to use %s as the target;
    Type \\`n' to use %s as the target.
")
                                            file1 file2 file1 file2))))
		  (setcar session-file-object
			  (if (y-or-n-p (format "Use %s ? " file1))
			      (progn
				(setq chosen-alternative 1)
				file1)
			    (setq chosen-alternative 2)
			    file2))
		  )
		 (f2-exists (setcar session-file-object file2))
		 (f1-exists (setcar session-file-object file1))
		 (t
                  ;; TODO: Often for multi-patches the file doesn't exist
                  ;; because the directory part is wrong; for instance, if the
                  ;; patch needs to be applied into
                  ;; (expand-file-name "lisp/vc/ediff-ptch.el" source-directory)
                  ;; and default-directory is
                  ;; (expand-file-name "lisp" source-directory)
                  ;; then Ediff assumes the wrong file:
                  ;; (expand-file-name "lisp/ediff-ptch.el" source-directory).
                  ;; We might identify these common failures and suggest
                  ;; in the prompt the possible corrected file. --Tino
		  (with-output-to-temp-buffer ediff-msg-buffer
		    (ediff-with-current-buffer standard-output
		      (fundamental-mode))
		    (princ "\nEdiff has inferred that")
		    (if (string= file1 file2)
			(princ (format "
	%s
is assumed to be %s target for this %spatch.  However, this file does not exist."
                           file1
                           (if multi-patch-p "one" "the")
                           (if multi-patch-p "multi-" "")))
		      (princ (format "
	%s
	%s
are two possible targets for this %spatch.  However, these files do not exist."
				     file1 file2 (if multi-patch-p "multi-" ""))))
		    (princ "
\nPlease enter an alternative patch target ...\n"))
                  (when (and (string= file1 file2)
                             (y-or-n-p (format "Create %s?" file1)))
                    (write-region (point-min) (point-min) file1))
		  (let ((directory t)
			target)
		    (while directory
		      (setq target (read-file-name
				    "Please enter a patch target: "
				    actual-dir actual-dir t))
		      (if (not (file-directory-p target))
			  (setq directory nil)
			(beep)
			(important-message 2 nil "%s is a directory" target)))
		    (setcar session-file-object target))))))
	    ediff-patch-map)
    ))

(defun ediff-show-patch-diagnostics ()
  (interactive)
  (cond ((window-live-p ediff-window-A)
	 (set-window-buffer ediff-window-A ediff-patch-diagnostics))
	((window-live-p ediff-window-B)
	 (set-window-buffer ediff-window-B ediff-patch-diagnostics))
	(t (display-buffer ediff-patch-diagnostics 'not-this-window))))

(defvar ediff-use-last-dir)

;; prompt for file, get the buffer
(defun ediff-prompt-for-patch-file ()
  (let ((dir (cond (ediff-use-last-dir ediff-last-dir-patch)
		   (ediff-patch-default-directory) ; try patch default dir
		   (t default-directory)))
	(coding-system-for-read ediff-coding-system-for-read)
	patch-file-name)
    (setq patch-file-name
	  (read-file-name
           (format-prompt "Patch is in file"
                          (and buffer-file-name
                               (equal (expand-file-name dir)
                                      (file-name-directory buffer-file-name))
                               (file-name-nondirectory buffer-file-name)))
	   dir buffer-file-name 'must-match))
    (if (file-directory-p patch-file-name)
	(error "Patch file cannot be a directory: %s" patch-file-name)
      (find-file-noselect patch-file-name))
    ))


;; Try current buffer, then the other window's buffer. Else, give up.
(defun ediff-prompt-for-patch-buffer ()
  (get-buffer
   (read-buffer
    "Buffer that holds the patch: "
    (cond ((save-excursion
	     (goto-char (point-min))
	     (re-search-forward ediff-context-diff-label-regexp nil t))
	   (current-buffer))
	  ((save-window-excursion
	     (other-window 1)
	     (save-excursion
	       (goto-char (point-min))
	       (and (re-search-forward ediff-context-diff-label-regexp nil t)
		    (current-buffer)))))
	  ((save-window-excursion
	     (other-window -1)
	     (save-excursion
	       (goto-char (point-min))
	       (and (re-search-forward ediff-context-diff-label-regexp nil t)
		    (current-buffer)))))
	  (t (ediff-other-buffer (current-buffer))))
    'must-match)))


(defun ediff-get-patch-buffer (&optional arg patch-buf)
  "Obtain patch buffer.  If patch is already in a buffer---use it.
Else, read patch file into a new buffer. If patch buffer is passed as an
optional argument, then use it."
  (let ((last-nonmenu-event t) ; Emacs: don't use dialog box
	last-command-event)    ; XEmacs: don't use dialog box

    (cond ((ediff-buffer-live-p patch-buf))
	  ;; even prefix arg: patch in buffer
	  ((and (integerp arg) (eq 0 (mod arg 2)))
	   (setq patch-buf (ediff-prompt-for-patch-buffer)))
	  ;; odd prefix arg: get patch from a file
	  ((and (integerp arg) (eq 1 (mod arg 2)))
	   (setq patch-buf (ediff-prompt-for-patch-file)))
	  (t (setq patch-buf
		   (if (y-or-n-p "Is the patch already in a buffer? ")
		       (ediff-prompt-for-patch-buffer)
		     (ediff-prompt-for-patch-file)))))

    (ediff-with-current-buffer patch-buf
      (goto-char (point-min))
      (or (ediff-get-visible-buffer-window patch-buf)
	  (progn
	    (pop-to-buffer patch-buf 'other-window)
	    (select-window (previous-window)))))
    (ediff-map-patch-buffer patch-buf)
    patch-buf))

;; Dispatch the right patch file function: regular or meta-level,
;; depending on how many patches are in the patch file.
;; At present, there is no support for meta-level patches.
;; Should return either the ctl buffer or the meta-buffer
(defun ediff-dispatch-file-patching-job (patch-buf filename
						   &optional startup-hooks)
  (ediff-with-current-buffer patch-buf
    ;; relativize names in the patch with respect to source-file
    (ediff-fixup-patch-map filename)
    (if (< (length ediff-patch-map) 2)
	(ediff-patch-file-internal
	 patch-buf
	 (if (and ediff-patch-map
		  (not (string-match-p
			(concat "^" null-device)
			;; this is the file to patch
			(ediff-get-session-objA-name (car ediff-patch-map))))
		  (> (length
		      (ediff-get-session-objA-name (car ediff-patch-map)))
		     1))
	     (ediff-get-session-objA-name (car ediff-patch-map))
	   filename)
	 startup-hooks)
      (ediff-multi-patch-internal patch-buf startup-hooks))
    ))


;; When patching a buffer, never change the orig file.  Instead, create a new
;; buffer, ***_patched, even if the buff visits a file.
;; Users who want to actually patch the buffer should use
;; ediff-patch-file, not ediff-patch-buffer.
(defun ediff-patch-buffer-internal (patch-buf
				    buf-to-patch-name
				    &optional startup-hooks)
  (let* ((buf-to-patch (get-buffer buf-to-patch-name))
	 (visited-file (if buf-to-patch (buffer-file-name  buf-to-patch)))
	 (buf-mod-status (buffer-modified-p buf-to-patch))
	 (multifile-patch-p (> (length (ediff-with-current-buffer patch-buf
					 ediff-patch-map)) 1))
	 default-dir file-name ctl-buf)
    (if multifile-patch-p
	(error
	 "To apply multi-file patches, please use `ediff-patch-file'"))

    ;; create a temp file to patch
    (ediff-with-current-buffer buf-to-patch
      (setq default-dir default-directory)
      (setq file-name (ediff-make-temp-file buf-to-patch))
      ;; temporarily switch visited file name, if any
      (set-visited-file-name file-name)
      ;; don't create auto-save file, if buff was visiting a file
      (or visited-file
	  (setq buffer-auto-save-file-name nil))
      ;; don't confuse the user with a new bufname
      (rename-buffer buf-to-patch-name)
      (set-buffer-modified-p nil)
      (set-visited-file-modtime) ; sync buffer and temp file
      (setq default-directory default-dir)
      )

    ;; dispatch a patch function
    (setq ctl-buf (ediff-dispatch-file-patching-job
		   patch-buf file-name startup-hooks))

    (ediff-with-current-buffer ctl-buf
      (delete-file (buffer-file-name ediff-buffer-A))
      (delete-file (buffer-file-name ediff-buffer-B))
      (ediff-with-current-buffer ediff-buffer-A
	(if default-dir (setq default-directory default-dir))
	(set-visited-file-name visited-file) ; visited-file might be nil
	(rename-buffer buf-to-patch-name)
	(set-buffer-modified-p buf-mod-status))
      (ediff-with-current-buffer ediff-buffer-B
	(setq buffer-auto-save-file-name nil) ; don't create auto-save file
	(if default-dir (setq default-directory default-dir))
	(set-visited-file-name nil)
	(rename-buffer (ediff-unique-buffer-name
			(concat buf-to-patch-name "_patched") ""))
	(set-buffer-modified-p t)))
    ))


;; Traditional patch has weird return codes.
;; GNU and Posix return 1 if some hanks failed and 2 in case of trouble.
;; 0 is a good code in all cases.
;; We'll do the conservative thing.
(defun ediff-patch-return-code-ok (code)
  (eq code 0))
;;;  (if (eq (ediff-test-patch-utility) 'traditional)
;;;      (eq code 0)
;;;    (not (eq code 2))))

(autoload 'ediff-find-file "ediff")
(declare-function ediff-buffers-internal "ediff"
		  (buf-a buf-b buf-c startup-hooks job-name
			 &optional merge-buffer-file))

(defun ediff-patch-file-internal (patch-buf source-filename
					    &optional startup-hooks)
  (setq source-filename (expand-file-name source-filename))

  (let* ((shell-file-name ediff-shell)
	 (patch-diagnostics (get-buffer-create "*ediff patch diagnostics*"))
	 ;; ediff-find-file may use a temp file to do the patch
	 ;; so, we save source-filename and true-source-filename as a var
	 ;; that initially is source-filename but may be changed to a temp
	 ;; file for the purpose of patching.
	 (true-source-filename source-filename)
	 (target-filename source-filename)
	 ;; this ensures that the patch process gets patch buffer in the
	 ;; encoding that Emacs thinks is right for that type of text
	 (coding-system-for-write
	  (if (boundp 'buffer-file-coding-system) buffer-file-coding-system))
         (ediff--startup-hook startup-hooks)
         target-buf buf-to-patch magic-file-name
	 patch-return-code ctl-buf backup-style aux-wind)

    (if (string-match-p "V" ediff-patch-options)
	(error
	 "Ediff doesn't take the -V option in `ediff-patch-options'--sorry"))

    ;; Make a temp file, if source-filename has a magic file name handler (or if
    ;; it is handled via auto-mode-alist and similar magic).
    ;; Check if there is a buffer visiting source-filename and if they are in
    ;; sync; arrange for the deletion of temp file.
    (setq buf-to-patch (ediff-find-file true-source-filename
		                        'ediff-last-dir-patch))
    (setq startup-hooks ediff--startup-hook)

    ;; Check if source file name has triggered black magic, such as file name
    ;; handlers or auto mode alist, and make a note of it.
    (setq magic-file-name
          (with-current-buffer buf-to-patch ediff--magic-file-name))

    ;; Checkout orig file, if necessary, so that the patched file
    ;; could be checked back in.
    (ediff-maybe-checkout buf-to-patch)

    (ediff-with-current-buffer patch-diagnostics
      (insert-buffer-substring patch-buf)
      (message "Applying patch ... ")
      ;; fix environment for gnu patch, so it won't make numbered extensions
      (setq backup-style (getenv "VERSION_CONTROL"))
      (setenv "VERSION_CONTROL" nil)
      (setq patch-return-code
	    (call-process-region
	     (point-min) (point-max)
	     shell-file-name
	     t   ; delete region (which contains the patch
	     t   ; insert output (patch diagnostics) in current buffer
	     nil ; don't redisplay
	     shell-command-switch   ; usually -c
	     (format "%s %s %s %s"
		     ediff-patch-program
		     ediff-patch-options
		     ediff-backup-specs
		     (ediff--buffer-file-name buf-to-patch))
	     ))

      ;; restore environment for gnu patch
      (setenv "VERSION_CONTROL" backup-style))

    (message "Applying patch ... done")
    (message "")

    (switch-to-buffer patch-diagnostics)
    (sit-for 0) ; synchronize - let the user see diagnostics

    (or (and (ediff-patch-return-code-ok patch-return-code)
	     (file-exists-p
	      (concat (ediff--buffer-file-name buf-to-patch)
                      ediff-backup-extension)))
	(progn
	  (with-output-to-temp-buffer ediff-msg-buffer
	    (ediff-with-current-buffer standard-output
	      (fundamental-mode))
	    (princ (format-message
		    "Patch program has failed due to a bad patch file,
it couldn't apply all hunks, OR
it couldn't create the backup for the file being patched.

The former could be caused by a corrupt patch file or because the %S
program doesn't understand the format of the patch file in use.

The second problem might be due to an incompatibility among these settings:
    ediff-patch-program    = %S             ediff-patch-options    = %S
    ediff-backup-extension = %S             ediff-backup-specs     = %S

See Ediff manual for more details on these variables.
In particular, check the documentation for `ediff-backup-specs'.

In any of the above cases, Ediff doesn't compare files automatically.
However, if the patch was applied partially and the backup file was created,
you can still examine the changes via M-x ediff-files"
		    ediff-patch-program
		    ediff-patch-program
		    ediff-patch-options
		    ediff-backup-extension
		    ediff-backup-specs
		    )))
	  (beep 1)
	  (if (setq aux-wind (get-buffer-window ediff-msg-buffer))
	      (progn
		(select-window aux-wind)
		(goto-char (point-max))))
	  (switch-to-buffer-other-window patch-diagnostics)
	  (user-error "Patch appears to have failed")))

    ;; If black magic is involved, apply patch to a temp copy of the
    ;; file.  Otherwise, apply patch to the orig copy.  If patch is applied
    ;; to temp copy, we name the result old-name_patched for local files
    ;; and temp-copy_patched for remote files.  The orig file name isn't
    ;; changed, and the temp copy of the original is later deleted.
    ;; Without magic, the original file is renamed (usually into
    ;; old-name_orig) and the result of patching will have the same name as
    ;; the original.
    (if (not magic-file-name)
	(ediff-with-current-buffer buf-to-patch
	  (set-visited-file-name
	   (concat source-filename ediff-backup-extension))
	  (set-buffer-modified-p nil))

      ;; Black magic in effect.
      ;; If orig file was remote, put the patched file in the temp directory.
      ;; If orig file is local, put the patched file in the directory of
      ;; the orig file.
      (setq target-filename
	    (concat
             (if (file-remote-p (file-truename source-filename))
		 magic-file-name
	       source-filename)
	     "_patched"))

      (rename-file magic-file-name target-filename t)

      ;; arrange that the temp copy of orig will be deleted
      (rename-file (concat magic-file-name
                           ediff-backup-extension)
		   magic-file-name t))

    ;; make orig buffer read-only
    (push #'ediff-set-read-only-in-buf-A startup-hooks)

    ;; set up a buf for the patched file
    (setq target-buf (find-file-noselect target-filename))

    (setq ctl-buf
	  (ediff-buffers-internal
	   buf-to-patch target-buf nil
	   startup-hooks 'epatch))
    (ediff-with-current-buffer ctl-buf
      (setq ediff-patchbufer patch-buf
	    ediff-patch-diagnostics patch-diagnostics))

    (bury-buffer patch-diagnostics)
    (message (substitute-command-keys
              "Type \\`P', if you need to see patch diagnostics"))
    ctl-buf))

(defun ediff-multi-patch-internal (patch-buf &optional startup-hooks)
  (let (meta-buf)
    ;; this sets various vars in the meta buffer inside
    ;; ediff-prepare-meta-buffer
    (push (lambda ()
	    ;; tell what to do if the user clicks on a session record
	    (setq ediff-session-action-function
		  'ediff-patch-file-form-meta
		  ediff-meta-patchbufer patch-buf) )
	  startup-hooks)
    (setq meta-buf (ediff-prepare-meta-buffer
		    #'ediff-filegroup-action
		    (ediff-with-current-buffer patch-buf
		      (cons (ediff-make-new-meta-list-header
			     nil                     ; regexp
			     (format "%S" patch-buf) ; obj A
			     nil nil                 ; objects B,C
			     nil                     ; merge-auto-store-dir
			     nil                     ; comparison-func
			     )
			    ediff-patch-map))
		    "*Ediff Session Group Panel"
		    #'ediff-redraw-directory-group-buffer
		    'ediff-multifile-patch
		    startup-hooks))
    (ediff-show-meta-buffer meta-buf)
    ))

(provide 'ediff-ptch)
;;; ediff-ptch.el ends here