Revert "[#15] Attempt to stop wrecking undo history"

This reverts commit 621351bade1b4c5c25e37b3ee51fe604e561e8ae. It made
it impossible to undo reformatting operations.

2 files changed, 111 insertions, 134 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index d8b01f4..230416f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,14 +13,9 @@ The format is based on [Keep a Changelog].
 * Previously, enabling `undo-tree-auto-save-history` caused Apheleia
   to mark the buffer as modified after formatting. This has been
   fixed ([#10]).
-* Under some circumstances Apheleia would cause the buffer's undo
-  history to be lost. An attempt has been made to fix this, although
-  it's not obvious how to reproduce the problem so the fix has not
-  been verified ([#15]).
 
 [#8]: https://github.com/raxod502/apheleia/issues/8
 [#10]: https://github.com/raxod502/apheleia/issues/10
-[#15]: https://github.com/raxod502/apheleia/issues/15
 
 ## 1.1 (released 2020-04-02)
 ### Enhancements
diff --git a/apheleia.el b/apheleia.el
index 2ddbc77..0d1b442 100644
--- a/apheleia.el
+++ b/apheleia.el
@@ -132,134 +132,120 @@ regions will still be applied, but Apheleia won't try to move
 point correctly."
   :type 'integer)
 
-(defmacro apheleia--with-single-undo (&rest body)
-  "Execute BODY as a single undo step."
-  (declare (indent 0))
-  `(unwind-protect
-       (progn
-         (when (car-safe buffer-undo-list)
-           (undo-boundary))
-         (let ((buffer-undo-list t))
-           ,@body))
-     (when (car-safe buffer-undo-list)
-       (undo-boundary))))
-
 (defun apheleia--apply-rcs-patch (content-buffer patch-buffer)
   "Apply RCS patch.
 CONTENT-BUFFER contains the text to be patched, and PATCH-BUFFER
 contains the patch."
-  (apheleia--with-single-undo
-    (let ((commands nil)
-          (point-list nil)
-          (window-line-list nil))
-      (with-current-buffer content-buffer
-        (push (cons nil (point)) point-list)
-        (dolist (w (get-buffer-window-list nil nil t))
-          (push (cons w (window-point w)) point-list)
-          (push (cons w (count-lines (window-start w) (point)))
-                window-line-list)))
-      (with-current-buffer patch-buffer
-        (apheleia--map-rcs-patch
-         (lambda (command)
-           (with-current-buffer content-buffer
-             ;; Could be optimized significantly by moving only as many
-             ;; lines as needed, rather than returning to the beginning
-             ;; of the buffer first.
-             (save-excursion
-               (goto-char (point-min))
-               (forward-line (1- (alist-get 'start command)))
-               ;; Account for the off-by-one error in the RCS patch spec
-               ;; (namely, text is added *after* the line mentioned in
-               ;; the patch).
-               (when (eq (alist-get 'command command) 'addition)
-                 (forward-line))
-               (push `(marker . ,(point-marker)) command)
-               (push command commands)
-               ;; If we delete a region just before inserting new text
-               ;; at the same place, then it is a replacement. In this
-               ;; case, check if the replaced region includes the window
-               ;; point for any window currently displaying the content
-               ;; buffer. If so, figure out where that window point
-               ;; should be moved to, and record the information in an
-               ;; additional command.
-               ;;
-               ;; See <https://www.gnu.org/software/emacs/manual/html_node/elisp/Window-Point.html>.
-               ;;
-               ;; Note that the commands get pushed in reverse order
-               ;; because of how linked lists work.
-               (let ((deletion (nth 1 commands))
-                     (addition (nth 0 commands)))
-                 (when (and (eq (alist-get 'command deletion) 'deletion)
-                            (eq (alist-get 'command addition) 'addition)
-                            ;; Again with the weird off-by-one
-                            ;; computations. For example, if you replace
-                            ;; lines 68 through 71 inclusive, then the
-                            ;; deletion is for line 68 and the addition
-                            ;; is for line 70. Blame RCS.
-                            (= (+ (alist-get 'start deletion)
-                                  (alist-get 'lines deletion)
-                                  -1)
-                               (alist-get 'start addition)))
-                   (let ((text-start (alist-get 'marker deletion)))
-                     (forward-line (alist-get 'lines deletion))
-                     (let ((text-end (point)))
-                       (dolist (entry point-list)
-                         ;; Check if the (window) point is within the
-                         ;; replaced region.
-                         (cl-destructuring-bind (w . p) entry
-                           (when (and (< text-start p)
-                                      (< p text-end))
-                             (let* ((old-text (buffer-substring-no-properties
-                                               text-start text-end))
-                                    (new-text (alist-get 'text addition))
-                                    (old-relative-point (- p text-start))
-                                    (new-relative-point
-                                     (if (> (max (length old-text)
-                                                 (length new-text))
-                                            apheleia-max-alignment-size)
-                                         old-relative-point
-                                       (apheleia--align-point
-                                        old-text new-text
-                                        old-relative-point))))
-                               (goto-char text-start)
-                               (push `((marker . ,(point-marker))
-                                       (command . set-point)
-                                       (window . ,w)
-                                       (relative-point . ,new-relative-point))
-                                     commands))))))))))))))
-      (with-current-buffer content-buffer
-        (let ((move-to nil))
-          (save-excursion
-            (dolist (command (nreverse commands))
-              (goto-char (alist-get 'marker command))
-              (pcase (alist-get 'command command)
-                (`addition
-                 (insert (alist-get 'text command)))
-                (`deletion
-                 (let ((text-start (point)))
-                   (forward-line (alist-get 'lines command))
-                   (delete-region text-start (point))))
-                (`set-point
-                 (let ((new-point
-                        (+ (point) (alist-get 'relative-point command))))
-                   (if-let ((w (alist-get 'window command)))
-                       (set-window-point w new-point)
-                     (setq move-to new-point)))))))
-          (when move-to
-            (goto-char move-to))))
-      ;; Restore the scroll position of each window displaying the
-      ;; buffer.
-      (dolist (entry window-line-list)
-        (cl-destructuring-bind (w . old-window-line) entry
-          (let ((new-window-line
-                 (count-lines (window-start w) (point))))
-            (with-selected-window w
-              ;; Sometimes if the text is less than a buffer long, and
-              ;; we do a deletion, it might not be possible to keep the
-              ;; vertical position of point the same by scrolling.
-              ;; That's okay. We just go as far as we can.
-              (ignore-errors
-                (scroll-down (- old-window-line new-window-line))))))))))
+  (let ((commands nil)
+        (point-list nil)
+        (window-line-list nil))
+    (with-current-buffer content-buffer
+      (push (cons nil (point)) point-list)
+      (dolist (w (get-buffer-window-list nil nil t))
+        (push (cons w (window-point w)) point-list)
+        (push (cons w (count-lines (window-start w) (point)))
+              window-line-list)))
+    (with-current-buffer patch-buffer
+      (apheleia--map-rcs-patch
+       (lambda (command)
+         (with-current-buffer content-buffer
+           ;; Could be optimized significantly by moving only as many
+           ;; lines as needed, rather than returning to the beginning
+           ;; of the buffer first.
+           (save-excursion
+             (goto-char (point-min))
+             (forward-line (1- (alist-get 'start command)))
+             ;; Account for the off-by-one error in the RCS patch spec
+             ;; (namely, text is added *after* the line mentioned in
+             ;; the patch).
+             (when (eq (alist-get 'command command) 'addition)
+               (forward-line))
+             (push `(marker . ,(point-marker)) command)
+             (push command commands)
+             ;; If we delete a region just before inserting new text
+             ;; at the same place, then it is a replacement. In this
+             ;; case, check if the replaced region includes the window
+             ;; point for any window currently displaying the content
+             ;; buffer. If so, figure out where that window point
+             ;; should be moved to, and record the information in an
+             ;; additional command.
+             ;;
+             ;; See <https://www.gnu.org/software/emacs/manual/html_node/elisp/Window-Point.html>.
+             ;;
+             ;; Note that the commands get pushed in reverse order
+             ;; because of how linked lists work.
+             (let ((deletion (nth 1 commands))
+                   (addition (nth 0 commands)))
+               (when (and (eq (alist-get 'command deletion) 'deletion)
+                          (eq (alist-get 'command addition) 'addition)
+                          ;; Again with the weird off-by-one
+                          ;; computations. For example, if you replace
+                          ;; lines 68 through 71 inclusive, then the
+                          ;; deletion is for line 68 and the addition
+                          ;; is for line 70. Blame RCS.
+                          (= (+ (alist-get 'start deletion)
+                                (alist-get 'lines deletion)
+                                -1)
+                             (alist-get 'start addition)))
+                 (let ((text-start (alist-get 'marker deletion)))
+                   (forward-line (alist-get 'lines deletion))
+                   (let ((text-end (point)))
+                     (dolist (entry point-list)
+                       ;; Check if the (window) point is within the
+                       ;; replaced region.
+                       (cl-destructuring-bind (w . p) entry
+                         (when (and (< text-start p)
+                                    (< p text-end))
+                           (let* ((old-text (buffer-substring-no-properties
+                                             text-start text-end))
+                                  (new-text (alist-get 'text addition))
+                                  (old-relative-point (- p text-start))
+                                  (new-relative-point
+                                   (if (> (max (length old-text)
+                                               (length new-text))
+                                          apheleia-max-alignment-size)
+                                       old-relative-point
+                                     (apheleia--align-point
+                                      old-text new-text old-relative-point))))
+                             (goto-char text-start)
+                             (push `((marker . ,(point-marker))
+                                     (command . set-point)
+                                     (window . ,w)
+                                     (relative-point . ,new-relative-point))
+                                   commands))))))))))))))
+    (with-current-buffer content-buffer
+      (let ((move-to nil))
+        (save-excursion
+          (dolist (command (nreverse commands))
+            (goto-char (alist-get 'marker command))
+            (pcase (alist-get 'command command)
+              (`addition
+               (insert (alist-get 'text command)))
+              (`deletion
+               (let ((text-start (point)))
+                 (forward-line (alist-get 'lines command))
+                 (delete-region text-start (point))))
+              (`set-point
+               (let ((new-point
+                      (+ (point) (alist-get 'relative-point command))))
+                 (if-let ((w (alist-get 'window command)))
+                     (set-window-point w new-point)
+                   (setq move-to new-point)))))))
+        (when move-to
+          (goto-char move-to))))
+    ;; Restore the scroll position of each window displaying the
+    ;; buffer.
+    (dolist (entry window-line-list)
+      (cl-destructuring-bind (w . old-window-line) entry
+        (let ((new-window-line
+               (count-lines (window-start w) (point))))
+          (with-selected-window w
+            ;; Sometimes if the text is less than a buffer long, and
+            ;; we do a deletion, it might not be possible to keep the
+            ;; vertical position of point the same by scrolling.
+            ;; That's okay. We just go as far as we can.
+            (ignore-errors
+              (scroll-down (- old-window-line new-window-line)))))))))
 
 (defvar apheleia--current-process nil
   "Current process that Apheleia is running, or nil.
@@ -620,11 +606,7 @@ changes), CALLBACK, if provided, is invoked with no arguments."
        (lambda (formatted-buffer)
          (with-current-buffer cur-buffer
            ;; Short-circuit.
-           (when (and (equal apheleia--buffer-hash (apheleia--buffer-hash))
-                      (not
-                       (equal apheleia--buffer-hash
-                              (with-current-buffer formatted-buffer
-                                (apheleia--buffer-hash)))))
+           (when (equal apheleia--buffer-hash (apheleia--buffer-hash))
              (apheleia--create-rcs-patch
               (current-buffer) formatted-buffer
               (lambda (patch-buffer)