(Fprimitive_undo): Check veracity of delta,start,end.

1 files changed, 22 insertions, 6 deletions

diff --git a/src/undo.c b/src/undo.c
index 5483060eb48..86237e2c59a 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -556,16 +556,32 @@ Return what remains of the list.  */)
                 }
               else if (EQ (car, Qapply))
                 {
-                  /* Element (apply FUNNAME . ARGS) means call FUNNAME to undo.  */
+                  /* Element (apply FUN . ARGS) means call FUN to undo.  */
                   car = Fcar (cdr);
+                  cdr = Fcdr (cdr);
                   if (INTEGERP (car))
                     {
-                      /* Long format: (apply DELTA START END FUNNAME . ARGS).  */
-                      cdr = Fcdr (Fcdr (Fcdr (cdr)));
-                      car = Fcar (cdr);
+                      /* Long format: (apply DELTA START END FUN . ARGS).  */
+                      Lisp_Object delta = car;
+                      Lisp_Object start = Fcar (cdr);
+                      Lisp_Object end   = Fcar (Fcdr (cdr));
+                      Lisp_Object start_mark = Fcopy_marker (start, Qnil);
+                      Lisp_Object end_mark   = Fcopy_marker (end, Qt);
+
+                      cdr = Fcdr (Fcdr (cdr));
+                      apply1 (Fcar (cdr), Fcdr (cdr));
+
+                      /* Check that the function did what the entry said it
+                         would do.  */
+                      if (!EQ (start, Fmarker_position (start_mark))
+                          || (XINT (delta) + XINT (end)
+                              != marker_position (end_mark)))
+                        error ("Changes to be undone by function different than announced");
+                      Fset_marker (start_mark, Qnil, Qnil);
+                      Fset_marker (end_mark, Qnil, Qnil);
                     }
-                  cdr = Fcdr (cdr);
-                  apply1 (car, cdr);
+                  else
+                    apply1 (car, cdr);
                   did_apply = 1;
                 }
               else if (STRINGP (car) && INTEGERP (cdr))