Fix missing undo-boundary on revert-buffer.

* lisp/simple.el (undo-auto--undoable-change-no-timer): New function.
* src/fileio.c (insert-buffer-contents): Call
  undo-auto--undoably-changed-buffers before changes.

Addresses Bug#23785.

Do not merge to master as c98bc98 also addresses the same bug.

2 files changed, 14 insertions, 1 deletions

diff --git a/lisp/simple.el b/lisp/simple.el
index b66827dfa63..43ad43cf927 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -2940,9 +2940,17 @@ behavior."
                         (cdr buffer-undo-list))))))
         (setq undo-auto--last-boundary-cause 0)))))
 
+;; This function is called also from one place in fileio.c. We call
+;; this function, rather than undoable-change because it reduces the
+;; number of lisp functions we have to use fboundp for to avoid
+;; bootstrap issues.
+(defun undo-auto--undoable-change-no-timer ()
+  "Record `current-buffer' as changed."
+  (add-to-list 'undo-auto--undoably-changed-buffers (current-buffer)))
+
 (defun undo-auto--undoable-change ()
   "Called after every undoable buffer change."
-  (add-to-list 'undo-auto--undoably-changed-buffers (current-buffer))
+  (undo-auto--undoable-change-no-timer)
   (undo-auto--boundary-ensure-timer))
 ;; End auto-boundary section
 
diff --git a/src/fileio.c b/src/fileio.c
index b11f9233ab4..3005ca320e7 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -3436,6 +3436,9 @@ by calling `format-decode', which see.  */)
   if (!NILP (BVAR (current_buffer, read_only)))
     Fbarf_if_buffer_read_only (Qnil);
 
+  if (!NILP (Ffboundp (Qundo_auto__undoable_change_no_timer)))
+    call0 (Qundo_auto__undoable_change_no_timer);
+
   val = Qnil;
   p = Qnil;
   orig_filename = Qnil;
@@ -5797,6 +5800,8 @@ syms_of_fileio (void)
      which gives a list of operations it handles.  */
   DEFSYM (Qoperations, "operations");
 
+  DEFSYM (Qundo_auto__undoable_change_no_timer, "undo-auto--undoable-change-no-timer");
+
   DEFSYM (Qexpand_file_name, "expand-file-name");
   DEFSYM (Qsubstitute_in_file_name, "substitute-in-file-name");
   DEFSYM (Qdirectory_file_name, "directory-file-name");