* lisp/subr.el (cancel-change-group): Reset cell in case of error

Since the setcdr/setcdr is supposed to be temporary, use unwind-protect
to make sure we properly undo the temporary change even in case of error.

1 files changed, 21 insertions, 20 deletions

diff --git a/lisp/subr.el b/lisp/subr.el
index 937a0506826..2c0be204e0a 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -2535,26 +2535,27 @@ This finishes the change group by reverting all of its changes."
         ;; Widen buffer temporarily so if the buffer was narrowed within
         ;; the body of `atomic-change-group' all changes can be undone.
         (widen)
-        (let ((old-car
-               (if (consp elt) (car elt)))
-              (old-cdr
-               (if (consp elt) (cdr elt))))
-          ;; Temporarily truncate the undo log at ELT.
-          (when (consp elt)
-            (setcar elt nil) (setcdr elt nil))
-          (unless (eq last-command 'undo) (undo-start))
-          ;; Make sure there's no confusion.
-          (when (and (consp elt) (not (eq elt (last pending-undo-list))))
-            (error "Undoing to some unrelated state"))
-          ;; Undo it all.
-          (save-excursion
-            (while (listp pending-undo-list) (undo-more 1)))
-          ;; Reset the modified cons cell ELT to its original content.
-          (when (consp elt)
-            (setcar elt old-car)
-            (setcdr elt old-cdr))
-          ;; Revert the undo info to what it was when we grabbed the state.
-          (setq buffer-undo-list elt))))))
+        (let ((old-car (car-safe elt))
+              (old-cdr (cdr-safe elt)))
+          (unwind-protect
+              (progn
+                ;; Temporarily truncate the undo log at ELT.
+                (when (consp elt)
+                  (setcar elt nil) (setcdr elt nil))
+                (unless (eq last-command 'undo) (undo-start))
+                ;; Make sure there's no confusion.
+                (when (and (consp elt) (not (eq elt (last pending-undo-list))))
+                  (error "Undoing to some unrelated state"))
+                ;; Undo it all.
+                (save-excursion
+                  (while (listp pending-undo-list) (undo-more 1)))
+                ;; Revert the undo info to what it was when we grabbed
+                ;; the state.
+                (setq buffer-undo-list elt))
+            ;; Reset the modified cons cell ELT to its original content.
+            (when (consp elt)
+              (setcar elt old-car)
+              (setcdr elt old-cdr))))))))
 
 ;;;; Display-related functions.