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;;; git-undo.el Foundation, Inc.
;; Author: John Wiegley <johnw@newartisans.com>
;; Created: 20 Nov 2017
;; Version: 0.1
;; Keywords: git diff history log undo
;; X-URL: https://github.com/jwiegley/git-undo
;; This program 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 2, or (at
;; your option) any later version.
;; This program is distributed in the hope that it will be useful, but
;; WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;; General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING. If not, write to the
;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.
;;; Commentary:
;; Select a region and then use M-x git-undo to revert changes in that region
;; to the most recent Git historical version. Use C-x z to repeatdly walk back
;; through the history. M-x git-undo-browse will let you see the history of
;; changes in a separate buffer.
;;; Code:
(require 'cl)
(defgroup git-undo nil
"Successively undo a buffer region using Git history"
:group 'emacs)
(defvar git-undo--region-start)
(defvar git-undo--region-end)
(defvar git-undo--history)
(defun git-undo--apply-diff (hunk)
(with-temp-buffer
(insert hunk)
(goto-char (point-min))
(while (not (eobp))
(pcase (char-after)
(?\ (delete-char 1) (forward-line))
(?\+ (delete-char 1) (forward-line))
(?\- (delete-region (point) (and (forward-line) (point))))
(t (delete-region (point) (point-max)))))
(buffer-string)))
(defun git-undo--replace-region ()
(goto-char git-undo--region-start)
(delete-region git-undo--region-start git-undo--region-end)
(if (null git-undo--history)
(error "There is no more Git history to undo")
(insert (git-undo--apply-diff (car git-undo--history)))
(setq git-undo--history (cdr git-undo--history)))
(goto-char git-undo--region-end))
(defun git-undo--compute-offsets (start end)
"Taking uncommitted changes into account, find the location in
Git history for a given line."
(let ((file-name (buffer-file-name))
(buffer-lines (line-number-at-pos (point-max))))
(with-temp-buffer
(shell-command
(format "git --no-pager diff -U%d HEAD -- %s"
buffer-lines (file-name-nondirectory file-name))
(current-buffer))
(goto-char (point-min))
(re-search-forward "^@@")
(forward-line)
(let ((adjustment 0)
(line 1)
adjusted-start
adjusted-end)
(while (not (eobp))
(pcase (char-after)
(?\+ (setq adjustment (1- adjustment)))
(?\- (setq adjustment (1+ adjustment)))
(t (setq line (1+ line))))
(when (= (- start adjustment) line)
(setq adjusted-start (+ start adjustment)))
(when (= (- end adjustment) line)
(setq adjusted-end (+ end adjustment))
(goto-char (point-max)))
(forward-line))
(cons (1+ adjusted-start) adjusted-end)))))
(defun git-undo--build-history (start end)
(let ((file-name (buffer-file-name)))
(destructuring-bind (start-line . end-line)
(git-undo--compute-offsets (line-number-at-pos start)
(1- (line-number-at-pos end)))
(with-temp-buffer
(message "Retrieving Git history for lines %d to %d..."
start-line end-line)
(shell-command
(format "git --no-pager log --no-expand-tabs -p -L%d,%d:%s"
start-line end-line
(file-name-nondirectory file-name))
(current-buffer))
(message "")
(goto-char (point-min))
(let ((commit t) history)
(while (and commit
(re-search-forward "^@@" nil t)
(forward-line))
(delete-region (point-min) (point))
(setq commit (and (re-search-forward "^commit " nil t)
(match-beginning 0)))
(setq history (cons (buffer-substring-no-properties
(point-min) (or commit (point-max)))
history)))
(nreverse history))))))
;;;###autoload
(defun git-undo (&optional start end)
"Undo Git-historical changes in the region from START to END."
(interactive "r")
(if (eq last-command 'git-undo)
(git-undo--replace-region)
(set (make-local-variable 'git-undo--region-start)
(copy-marker start nil))
(set (make-local-variable 'git-undo--region-end)
(copy-marker end t))
(set (make-local-variable 'git-undo--history)
(git-undo--build-history start end))
(git-undo--replace-region)))
;;;###autoload
(defun git-undo-browse (&optional start end)
"Undo Git-historical changes in the region from START to END."
(interactive "r")
(let ((history (git-undo--build-history start end)))
(display-buffer
(with-current-buffer
(get-buffer-create "*Git Region History*")
(delete-region (point-min) (point-max))
(dolist (entry history)
(insert (git-undo--apply-diff entry)
#("-----\n" 0 5 (face bold))))
(delete-region (- (point) 6) (point))
(goto-char (point-min))
(current-buffer)))))
;;; git-undo.el ends here
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